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2004

Effective use of fibrereinforced polymermaterials in construction

S M Halliwell and T Reynolds

BRE Centre for Composites in Construction

BREGarston, Watford, WD25 9XX

constructing the future



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Contents

iii

Acknowledgement iv

Abbreviations iv

Introduction 1

Materials used 2

Material selection 4Selection criteria 4Fire 4Weathering effects 4Chemical resistance 5Sustainability 5Site factors 5

System architecture 6

Fabrication 6Open mould systems 6Closed mould systems 7Automated techniques 8Procurement 9

Performance/cost considerations 9

Mechanical properties 10Stress–strain characteristics 10Typical E-glass laminate properties 11Interlaminar properties 11Fatigue strength 12Creep and stress rupture 12

System design 12Design process 13Anisotropic nature 13Yield 14Young’s modulus 14Shear 14Limit state design issues specific to FRP materials 14

Engineering performance prediction and optimisation 15

Application of FRPs in construction 16

Use of FRP with traditional materials 23

Implementation strategy 23

Future developments 24

Case studies 26

References 65

Further reading 65

Glossary 68



Acknowledgement

This report was produced from the work carried out under FBE project‘Provision of Best Practice Guidance for users and producers of polymer fibrecomposites for construction’.

Abbreviations

ACM advanced composite material

AFRP aramid fibre reinforced polymer

BMC bulk moulding compound

CFRP carbon fibre reinforced polymer

DMC dough moulding compound

GFRP glass fibre reinforced polymer

FRP fibre reinforced polymer

SMC sheet moulding compound

TMC thick moulding compound

iv


Introduction

Fibre reinforced polymers (FRPs) have been used successfully in the construction industry for severaldecades, mainly for architectural applications e.g. cladding. However, FRPs have never becomeestablished as major structural materials in the building industry. In recent years they have started tore-emerge as their inherent benefits are being acknowledged once again. This report looks at thetechnical and cost implications of using FRPs in construction and demonstrates their effective use bymeans of a number of case histories.

The advantages of FRPs over traditional structural materials have long been recognised in the hightechnology engineering sectors such as the aerospace and automotive fields, where the rate ofgrowth in the usage of composites continues to be significant. FRPs have made most rapid progressespecially in weight sensitive applications where the consequential cost of added weight (due togreater propulsion costs) outweighs the incremental cost of the material. As confidence in theperformance of FRPs has grown, their usage, initially mainly confined to secondary structures, isbeing increasingly extended to safety critical primary structures where the consequences of failure interms of cost are far greater.

In the construction field, FRPs are also making inroads, albeit at a slower rate, for a variety ofreasons. Large segments of the construction industry, on both the supply and demand sides, tend tobe more conservative in their support of new technology and innovation. Being less technologyconscious and less technology driven, the industry has been less willing to invest in research anddevelopment and take the commercial risks associated with innovation. Options are traditionallyselected on the basis of initial capital costs and benefits. Only recently has there been a move toselect material options, albeit at the initial planning stage rather than at the tender award stage, on thebasis of whole life costs and benefits, or total annual cost of ownership.

Applications in the construction field differ from those in the aerospace and automotive industries in anumber of significant respects. Infrastructure applications such as bridges are frequently large one-offprojects. These need to have a long service life with high levels of structural reliability throughoutbecause shortcomings in structural performance are very expensive to rectify. Due to their scale andlocation, access is frequently costly. Hence the consequential cost of corrosion and fatigue is oftenconsiderably more significant than the consequential cost of weight and, therefore, the frequency ofmaintenance cycles needs to be minimised. Due to the absence of cost-related running costs,operating costs are primarily due to maintenance and repair associated with corrosion and structuraldegradation (e.g. fatigue), and any consequential disruption and loss of service. In the increasinglybusier networks that characterise modern infrastructure, the cost of disruption caused by the loss ofservice of an element in the network frequently greatly outweighs the direct cost of maintenance andrepair. In these circumstances, the ratio of operating cost to capital cost can be as high if not higherthan in vehicular applications. Final assembly and installation often take place in relatively hostile andunpredictable environments. Hence the speed and reliability of joining and installation processes is asignificant factor in the overall cost effectiveness of a solution.

FRPs offer several important advantages over traditional materials for construction projects:• Time saving – low weight for fast construction in time tight projects• Durability – able to survive, especially in harsh environments• Repair – to allow repair of structures in-situ• Strengthening – strengthening of structures in-situ• Tailor-made properties – where especially high performance is needed in one direction• Appearance – where a particular colour, shape or texture is required• Blast/fire – where blast or fire resistance is required• Radio transparent – for telephone masts and military structures• Low maintenance – in conditions where difficult access makes maintenance hard

The main driver for the adoption of FRPs in construction in the past has tended to be the reduction ofthe direct and indirect costs of corrosion and maintenance. More recently, weight savings and speedof installation have gained in importance. To compete successfully with the conventional structuralmaterials used in construction (such as steel, concrete, aluminium, and their associated maintenanceliabilities) FRP solutions must have optimised benefits and costs and adequate long-term durability.

1


Materials used

ResinsThermosetting resins are most widely used in the construction industry, the most common being theunsaturated polyesters, epoxides and phenolics.

• Polyester resins are relatively inexpensive, easy to process, allow room temperature cure andhave a good balance of mechanical properties and environmental/chemical resistance.

• Epoxy resins are used for the majority of high-performance FRP structures. They have excellentenvironmental and chemical resistance and superior resistance to hot-wet conditions. Comparedto polyesters, they are more expensive and require more careful processing, however, they givebetter mechanical properties and better performance at high temperatures.

• Phenolic resins find specific application in construction due to their flame-retardant properties, lowsmoke generation, dimensional stability at high temperature and excellent resistance toenvironmental degradation.

Table 1: Typical data for common resins1

Resin Tensile strength

(MPa) Young’s modulus(GPa)

Density (103 kg/m2) Cost (£/kg)

Polyester 50-75 3.1-4.6 1.11-1.25 2.5 Epoxy 60-85 2.6-3.8 1.11-1.20 5-10 Phenolic 60-80 3.0-4.0 1.00-1.25 2 For structural applications it is mandatory to achieve some degree of flame retardance. Fireretardants are usually incorporated in the resin itself or as a gel-coat applied to the surface of acomponent. Fillers and pigments are also used in resins for a variety of purposes, the formerprincipally to improve mechanical properties and the latter for appearance and protective action. Fibres A wide range of amorphous and crystalline materials can be used as the fibre. In the constructionindustry the most common fibre used is glass fibre which is divided into four classes: E-glass,AR-glass, A-glass and high strength glass. Carbon fibre, of which there are 3 types (Type I, II, III), canbe used separately or in conjunction with the glass fibre, as a hybrid. It is used to increase thestiffness of a structural member or an area within a structure, so that the stiffness exceeds the valuepossible using only glass fibre. Aramid fibres can also be used to give increased stiffness to thecomposite. Table 2 illustrates typical properties for common fibres2. E-glassE-glass is of lower strength and stiffness than carbon or aramid fibres, but is also considerably lowerin cost. The fibre is denser than the alternatives and resulting structures reinforced with E-glass willtherefore be considerably heavier than those reinforced with higher performance fibres. Typically anE-glass structure may be over twice the weight of a carbon or aramid FRP structure, although this willstill be dramatically lighter than a conventional structure in steel, concrete or even aluminium.The fibre is electrically non-conductive and offers good corrosion resistance. It should be notedhowever, that the fibre can be attacked by strong alkaline solutions and needs to be protected withsuitable resins &/or surface tissues in such situations.

AramidAramid fibres such as Kevlar® offer very high tensile strengths and relatively high elongation to failure.This results in them being very good for absorbing large amounts of energy, for example in structuressubject to impact forces. The fibre has very low density and therefore results in extremely lightweight

2


structures. Most FRP materials exhibit slightly lower strengths in compression than tension, but this isparticularly true for aramid reinforced FRP and any areas subject to significant compressive stress willrequire very careful consideration if reinforced with aramid fibres. Aramid fibres have a negativecoefficient of thermal expansion.

CarbonCarbon fibres are available in a wide range of grades offering different mechanical properties. Allcarbon fibres offer relatively high strengths and stiffness, but are brittle and fail at relatively low strainlevels. They have a negative coefficient of thermal expansion.

Carbon fibres are the only fibres considered here that are electrically conductive. In many applicationsthis may not be relevant but may be critical in others, for example near railway power lines or forproducing radomes. It may also be necessary to consider the possibility of electrolytic corrosion inconjunction with other materials. Carbon exhibits a very high electrolytic potential and behaves as anoble material in the galvanic series. While it will not corrode itself, it may cause galvanic corrosion inother materials particularly aluminium. Table 2: Typical fibre properties2

E-glassAramid

(Kevlar 49)

Highstrengthcarbon

Highmoduluscarbon

Steel(GradeS275)

Tensilestrength (MPa)

2400 36003300-6370

2600-4700

275 Yield430 Ultimate

Tensilemodulus (GPa)

70 130 230-300 345-590 205

Failurestrain (%)

3.5 2.5 1.5-2.2 0.6-1.4 20

Density(kg/m3)

2560 1440 1800 1900 7900

Coefficient ofthermal exp

(10-6/°C)5.0 -2L + 59 T -1L +17T -1L 12

Fibre cost(£/kg)

1.25 15 10-15 ~60 0.4

Fabric cost(£/kg)

2-3 20-25 15-35 ~100 0.4

Specific fabriccost (£/m3 x 10-3)

5-8 29-36 27-63 ~190 3

L = Longitudinal T = Transverse Note: costs are approximate values and are highly dependent on quantities, fabric weights and styles,etc.

Bundles of filaments of the chosen fibre are called strands and these are usually combined to formthicker parallel bundles called rovings. Rovings assembled in this way are used in processes involvingchopping of the fibres during the production of a composite e.g. sheet moulding compound (SMC),spray-up, continuous sheet manufacture. Rovings are also manufactured by a process in which all thefilaments needed in the final roving (up to 4800) are all drawn simultaneously from one bushing.These rovings are called direct rovings and are used in weaving, pultrusion and filament winding.Strands may also be twisted to form several types of yarn; rovings or yarns may be used eitherindividually or in the form of a woven fabric.

3


Material selection

Selection criteriaThe key criteria dictating the selection of the fibre material are cost in relation to:• Elastic modulus• Toughness/resilience• Environmental/chemical resistance

The key physical properties governing the selection of the resin material are cost in relation to:• Mechanical toughness/resilience• Short and long term environmental/chemical resistance to moisture, UV radiation, elevated

temperature, fire, and aggressive chemicals• Processability (ability to wet-out fibres, curing temperature and pressure, etc.)• Compatability with fibres

Rationally, materials can be ranked on the basis of cost/property ratio with respect to some criticalphysical property. This dictates the quantity of material needed in an application to meet the functionalspecification in terms of strength, serviceability, durability, safety etc. For example, for slenderstructures it could be Young’s modulus.

FireIn order to determine the main design criteria with respect to fire, it is necessary to consider whethercomponents must meet specific fire resistance requirements, limit the spread of flame, or avoid thegeneration of smoke or other by-products of fire. These requirements depend largely on theapplication.

Given careful design and the right choice of resins, additives and fillers, FRPs can be used to makestructures with better fire resistance than almost any other material. As an example, phenolics areused within firewalls. FRPs generally are poor thermal conductors, so they do not help the heat of afire to spread in the way that can occur with metals. The smoke from fire can be a concern, and socareful choices need to be made for internal applications.

As with all issues in design there is always a compromise to be struck between the different materialproperties needed for a project. If fire resistance is absolutely critical then FRPs can often be the mostcost-effective solution.

Weathering effectsA specific application and its environment will govern the choice of material. Factors affecting theperformance of a component include water, hot/cold temperature cycling, UV radiation as well as airpollution and salt spray. FRP materials generally perform extremely well in harsh environments, andchoice of material and surface finish can be tailored to optimise performance3.

FRP materials have been used successfully over the past 50 years in a wide range of applications inthe marine and civil engineering sectors. These include diverse applications such as pipes, tanks,slabs, walkways, bridge decks, gratings, column reinforcing wraps and reinforcing bars for concrete.In many of these applications, FRPs are exposed to one or more of the influences noted earlier. AllFRP materials are durable inasmuch as they are water resistant, thermally stable and cannot rust.Applications such as those listed are predicated in more stringent tests of durability. In this respect,particular grades of high durability FRP materials (5-20 year lifetime) are available for particularapplications. For example, FRPs for concrete re-bars incorporate alkali resistant glass fibres in orderto resist fibre attack by pore water, while composites for marine applications incorporate a chemicalbond at the fibre/matrix interface in order to resist water penetration. In almost all applications,imposing a conservative safety factor (2-4) on the design may enhance the durability of an FRP

4


material. In many such cases, additional durability may be achieved by the use of a protective coatingand/or the incorporation of light stabilisers and antioxidants.

Chemical resistanceA surprising number of FRP applications involve occasional or prolonged contact with chemicals.Many FRP articles are routinely placed in contact with detergents, cleaning solvents, acids, alkalis,strong oxidising agents, bleach, cleaning and degreasing agents, fuels, hydraulic and brake fluids,de-icers, paint strippers (methylene chloride based ones are known to be particularly damaging),lubricants, etching chemicals, flue gases, or food and drink.

It must be stressed that the resistance of FRPs to highly reactive chemicals is generally very good.This explains their widespread use in the chemical process equipment industry, where it is oftendifficult to find any other affordable, processable materials capable of withstanding the very harshconditions. It is rare for FRP articles to be attacked as rapidly as some common metals are whenplaced in contact with acids. A few chemicals that are handled in chemical factories, such as powerfuloxidising agents, strong caustic alkalis, bromine and wet chlorine still pose severe problems forgeneral purpose organic matrix resins. Otherwise, the well-informed selection of materials, inconsultation with the suppliers and after reference to the relevant data banks, means that completedisaster is a very rare occurrence.

SustainabilityThe sustainability of a product must be considered at the design stage. The life-cycle of theapplication is crucial in the final solution so as not to over-specify performance requirements and thusincrease costs. However, design for flexibility is becoming increasingly important in sustainabledesign because it allows for the future re-use of the structure or component, thus maximising itsuseful life.

The end-of-use properties of a component are also important in some instances. Again, the issues ofre-use, recycling or disposal should be considered at the design stage in order to ensure ease ofseparation at deconstruction.

Site factorsSite factors may significantly influence the choice of material for certain applications, for examplewhere there is restricted access, when weight is crucial or when disruption or damage has to be keptto a minimum.

5


System architecture

The system architecture should define the structural configuration, the form of components andconnections, the arrangement of dissimilar materials, surface treatments, manufacturing, fabrication,and construction processes, and all other elements needed to meet the functional requirements.

The engineering solution should adopt structural forms that are expected to optimise the performanceof the structure in relation to the quantity of material in terms of stiffness or strength, and in the caseof building enclosures, thermal and acoustic insulation.

The shape and size of components is dictated by the capability of the processing method and theconnectivity of the structural system. In many construction applications it has been found that hollowor foam-filled sections are the preferred shape because they offer the following advantages:• Increased local and global buckling strength• Increased number of web mats• Increased continuity of fibre at web-flange junctions• Reduced number of surfaces exposed to the environment• Increased support to the flange, thereby increasing the flange impact strength• Reduced moisture absorption due to an increased effective thickness, hence increased durability• Increased fire resistance due to fire exposure on one face only• Greater ease of making connections between beams.Hollow sections cannot be readily manufactured by contact moulding, unless the cells are very large.Pultrusion is the most suitable manufacturing process for linear elements of constant section. Resintransfer moulding might be chosen to manufacture hollow elements of variable section.

Fabrication

A wide range of different processes have developed for moulding of FRP parts ranging from verysimple manual processes such as hand lay to very sophisticated highly industrialised processes suchas SMC moulding. Each process has its own unique benefits and limitations making it suitable forparticular applications. The choice of process is important in order to achieve the required technicalperformance at an economic cost.

The main technical factors that govern the choice of process are the size and shape of the part, themechanical and environmental performance, and aesthetics. The main economic factor is the numberof identical parts required, known as the run length. This is because FRP parts do not generally comeas standard components but are custom designed for a particular application. Most processes willhave an initial investment or set up cost that must be amortised over the length of the project,although pultrusion and continuous sheeting are exceptions. This is a major factor in the choice ofprocess and is one of the reasons for the proliferation in processing methods.

It is not the intention of this report to detail manufacturing techniques – for further information seehttp://www.ngcc.org.uk/. Brief descriptions of the main techniques employed are given below andTable 3 summarises the types of component produced using common manufacturing processes.

Open mould systemsThese production methods take advantage of an important characteristic of the resin; it does notrequire heat or pressure for complete polymerisation to occur. The resins are known as cold cureresins. There are many variations of the open mould process, only principal ones will be consideredhere.

6


Hand lay-up techniqueIn this technique only one mould is used and this may be either male or female.

The durability of GRP composite in the construction industry is dependent upon the quality of thesurface which is exposed to the atmosphere and it is necessary to protect the fibres on the exposedsurface of the composite with resin-rich coating, known as a gel coat. Gel coat thickness should beabout 0.4-0.5mm and should be uniform throughout.

After the gel coat has become tacky but firm, a liberal coat of resin is brushed over it and the firstlayer of glass reinforcement is placed in position and consolidated with a roller. Subsequent layers ofresin and fibre are then applied until the required thickness of the composite is achieved. Curing ofthe composite takes place at room temperature; this would normally take 28 days at 20°C. Curing isessentially complete after a few hours for practical purposes. However, for maximum performance,essentially weathering and water resistance, at least 2 weeks is recommended.

Spray-up techniqueThe preparatory stages of this technique are similar to those for hand lay-up, but the actual techniqueof applying the resin and fibre to the mould is less labour intensive.

During the spray-up operation, glass fibre roving is fed continuously through a chopping unit and theresulting chopped strands are projected onto the mould in conjunction with a resin jet. The glass fibreresin matrix is then consolidated with rollers.

In the construction industry this technique and the hand lay-up method are used to form load-bearingand infill panels for buildings and face materials for sandwich panels.

Vacuum bag mouldingThis process is similar to hand lay-up, but final laminate consolidation is achieved by covering thecomponent with a plastics film (vacuum bag) and drawing a vacuum over the component. Thepressure differential compresses the uncured composite, forcing our excess resin and drawing outentrapped air. This results in a laminate of higher fibre volume fraction and better consistency whencompared to the hand lay-up process.

Closed mould systemsFor many years fibre/matrix composites have been produced by moulding techniques using matcheddies. These techniques produce mouldings with a good finish on both surfaces of the composite.Compared with the open mould process, this system enables a higher glass content to be used in thecomposite, with improved mechanical properties.

Cold-press (low pressure) moulding techniqueIn the cold press moulding technique, unheated matched tools under pressure are used to impregnatethe resin throughout the fibre reinforcement placed in the mould. A release agent and gel coat areapplied to the surface of the moulds before the fibre and resin are placed in position. This technique issuitable for small batches with good surface finish. It is a simple, low cost and effective technique, butrequires lengthy moulding cycles (usually measured in hours).

Hot-press (high pressure) moulding techniqueIn the hot press moulding technique. The fibre-filled polymer is confined between heated, matched,polished metal dies (at about 150-160°C) brought together under pressure (approximately 15MN/m2).This technique is the highest-volume method for moulding thermoset reinforced polymers, usuallyreaching an economic output at a level of around 10,000 parts/year. To maintain efficiency, preparedcombinations of resin, reinforcement and additives (pre-pregs) are increasingly used. The most widelyused are known as bulk moulding compound (BMC) and sheet moulding compound (SMC).

7


Resin injectionResin injection moulding uses a liquid formulated resin, which is injected into a closed mould intowhich the reinforcement has already been placed. It is most often used for parts with smooth surfacescoated with gelcoat. The reinforcement is placed in position in the bottom mould. The top mould isthen placed in position over the bottom one and secured. Resin is injected at low pressure(400kN/m2). Resin injection can be carried out in cold, warm or hot moulds, at up to 80°C.

Resin injection under flexible tooling (RIFT)For RIFT, dry fabric reinforcement is first laid into a mould. The reinforcement is covered with avacuum bag, the edges sealed and a vacuum drawn. The vacuum bag is used to draw resin into thereinforcement thus forming the composite component. This process results in a laminate of low voidcontent and high volume fraction. The resin infusion process is well suited to largercomponents/structures and where a closed mould process is required to reduce emissions. It is idealfor producing low numbers of components.

Resin transfer moulding (RTM)RTM is similar to RIFT but is suitable where large numbers of components are required. A closedmetal mould is usually used (which tend to be more expensive to make but are more durable that thecheaper tooling for RIFT), and the dry fibre preform is laid up within it. Resin is then injected underpositive pressure (sometimes with vacuum assistance), to form the final component. The mould canalso be heated to accelerate the cure of the resin and so reduce cycle times.

Automated techniquesFilament winding techniqueFilament winding is a technique used to produce high performance hollow symmetrical products suchas pipes, tanks, pressure vessels and load-bearing tubes. A mandrel of the required shape is rotatedon its axis (usually horizontally, but depending on the size and shape of the object to be produced)and wound with a continuous filament of reinforcement. The fibre angle can therefore be controlled toa certain extent, however, geometry of the part usually dictates the angles that can be achieved(fibres naturally follow the high points on the surface profile). When fully wound with resin-wettedreinforcement, the lay-up is cured, on or off the mandrel.

PultrusionA pultrusion machine is designed to produce a continuous length of composite material with a uniformcross-section. Both solid and hollow profiles can be made.

The pultrusion technique is one in which continuous strands of reinforcing material, together with anyadditional required layer of fabric are drawn from creels and are passed through a resin bath fittedwith a constant level device. After picking up an excess of matrix, the saturated fibre is passedthrough a number of wiper rings and into the mouth of a heated die. The formed composite is grippedfirmly between rubber blocks and is pulled through a die at a predetermined speed to enable curing ofthe composite to take place. It is then cut into the desired length by means of a cut-off wheel.

Most forms of geometric sections can be produced by this method. They can be stored and used asstructural units when required.

Thermosetting resins are used almost exclusively, with polyester resin being used for the majority ofthe annual volume of pultruded composite.

8

Table 3: Fabrication

Processing route Typical componentsOpen moulding – hand and spray lamination Cladding panels, radomes, garage doors,

caravan partsVacuum infusion Strengthening of components, mastsPre-pregs Architectural mouldings, infrastructure repairCompression moulding of SMC Electrical cabinets, sectional water storage

panels, modular componentsPultrusion Standard sections, access ladders,

reinforcement bars, roof trusses, spaceframes, window profiles

Filament winding Pipes, wrapping of columnsContinuous sheeting Cladding, roofingCentrifugal casting Pipes, tanks, masts, poles


ProcurementThere are certain FRP parts such as pultrusions, pipes and continuous sheeting that are available instandard sizes so that once manufacturers have been located specification and procurement isrelatively straightforward. However, the vast majority of FRP parts are custom designed and mouldedto meet the needs of a particular application. As described in this report, there is a very wide range ofdifferent manufacturing processes and very often companies will specialise in one or two processes. Itis rare to find a company that possesses every process and material combination and with more than2000 FRP moulders in the UK alone, procurement can be a challenge. A useful source of informationand advice can be the suppliers of the raw material particularly the resin and reinforcementcompanies who will often be willing to advise on the choice of process and sometimes recommendsuitable moulders.

Performance/cost considerations

The primary advantages of FRP materials include low density, high tensile and fatigue strength, highcorrosion resistance, formability, ease of installation, ease of repair, and cold connection methods.Formability allows the manufacture of complex shapes and greater integration of parts or functions,thus opening up the potential for reduced assembly time, labour and cost. Appropriately designedFRPs can offer the added benefits of toughness, resilience, thermal insulation, environmentalinsulation, and electro-magnetic signature. Disadvantages such as lower stiffness, lower surfacehardness, greater combustibility, environmental sensitivity, and greater cost of constituent materialscan usually be minimised by appropriate engineering at the system and material levels.

The material cost is dependent not only on the constituent materials, but also, and sometimescritically, on the manufacturing and fabrication processes. The manufacturing process determines thecost of tooling and labour, the variability of the product in terms of geometric accuracy andmechanical properties, the minimum economic production volume and the speed of production. Thegeometric accuracy of a section or component in terms of overall dimensions, wall thickness, andreinforcement positioning determines not only structural strength, particularly at the critical local levelsof plate buckling strength and the strength of monolithic junctions between plates. It also determinesthe ability of components to fit accurately together and be reliably joined to form larger structures.Thus the manufacturing process indirectly affects the fabrication cost. The manufacturing processalso dictates which types of reinforcement product and reinforcement layout can be used, and thetexture and visual quality of exposed surfaces.

Processes such as contact moulding (hand lay-up) are the most labour intensive and generally yieldmaterial of variable quality which can lead to significant material reject rates and/or more conservative

9


designs. Either way, this results in increased material quantity and cost. When only a small number oflarge components is required, the cost of the mould can be prohibitive. Vacuum assisted resininfusion greatly improves the material properties of contact mouldings but can be relatively costly onaccount of set-up time and consumables.

Closed mould processes such as resin transfer moulding (RTM) and pultrusion deliver improveddimensional accuracy, greater fibre volume fraction and better fibre impregnation. RTM requiresexpensive tooling due to the processing pressures involved and, being a batch process, has a greaterlabour content than pultrusion. Pultrusion is a semi-automated, semi-continuous process forproducing linear elements of constant cross section and good surface finish.

Processes such as autoclave moulding produce the highest quality material and require the mostcostly tooling. Their use tends to be limited to aerospace applications.

Pultrusion, being a fully automated process, produces material of reproducible quality. Componentsmanufactured by pultrusion are being increasingly used in construction.

In structures built in conventional structural materials such as concrete and steel, the current balancebetween unit labour and material costs is such that the most economic solution is frequently thatwhich minimises labour of fabrication and construction rather than material. By contrast, in the case ofFRP structures, the balance is such that the most economic solution is that which minimises the costof the material, which is a function of the quantity of the material and the manufacturing process.

Mechanical properties

The mechanical properties of an FRP laminate are highly dependent on manufacturing techniques,quality, fibre volume fraction, control of fibre direction and straightness etc. The style of reinforcementmay also affect the resulting laminate properties2.

Mechanical properties are highly dependent on the quantity of reinforcing fibre contained within thelaminate, which is generally expressed as either a volume or mass fraction, or a resin:fibre ratio byweight, which are related as follows:

Vf = Mf/Df Vf = Fibre volume fractionMf/Df + Mm/Dm Vm = Matrix volume fraction = 1 – Vf

Mf = Fibre mass fractionMf = Vf.Df Mm= Matrix mass fraction

Vf.Df + Vm.Dm Df = Fibre densityDm = Matrix density

R = (1/Mf) – 1 R= Matrix:Fibre ratio by weight

The possible range of fibre contents within a laminate will be dependent on the manufacturingprocess. Higher fibre contents generally result in higher mechanical properties, but thinner laminates,resulting in a similar load carrying capability for a given quantity of reinforcement.

It should also be noted that hybrid reinforcements can be produced by mixing different types of fibrewithin a laminate.

Stress–strain characteristicsThe majority of FRP composites fail in a brittle manner in tension and may possess significantlydifferent properties in compression than they do in tension. The brittle nature also results in greatersensitivity to stress concentrations, notches, holes etc than may be the case with ductile materialssuch as structural steel. However, FRPs will often give signs of being overstressed beforecatastrophic failure, in the form of crazing, cracking, whitening and delamination.

10


Typical E-glass laminate propertiesE-glass is the most commonly used reinforcement for FRP structures in the construction industry anda wide variety of laminate properties may be produced. Typical properties are shown in Table 4compared to steel and concrete.

Table 4: Typical E-glass/polyester laminate properties2

Choppedstrand mat

(CSM)

Wovenroving/CSM

COMBI

Wovenroving(WR)

UDSteel

(Grade S275)Concrete

Tensilestrength(MPa)

100 180 250 650275 Yield

430 Ultimate2-5

Compressivestrength(MPa)

140 180 210 550275 Yield

430 Ultimate25-60

Tensilemodulus

(GPa)7.5 12 14 30 205 25-36

Tensile failurestrain (%)

2 2 2 2 20 0.01

Density(kg/m3)

1500 1600 1700 1700 7900 2400

Coefficient ofthermal exp

(10-6/°C)30 - 14 10 12 7-12

UD - unidirectional laminate, Vf = 40%, properties in longitudinal direction.Properties are typical values but are highly dependant on laminate quality, fibre volumefraction, etc.

Laminate theory should be used for predicting properties in all directions within a component and foranalysing multidirectional laminates.

The prediction of laminate strength is more complex than the prediction of elastic properties, butseveral failure criteria have been developed and incorporated into laminate analysis programs. As anexample of the increased complexity of analysing FRP composite materials compared to conventionalisotropic materials such as metals, the Tsai-Wu failure criterion may be compared to the well-knownvon-Mises failure criterion commonly used for predicting the failure of metallic structures:

Von-Mises failure criterion

σO2 = σx

2 – σx σy + σy2 + 3 σxy

2

Tsai – Wu failure criterion

σx (1/Xt + 1/Xc) + σy (1/Yt + 1/Yc) + σx2 / (Xt Xc) + σy

2 / (Yt Yc) + Txy2 / S2 + Fxy σx σy = 1

Fortunately, the analysis of FRP laminates is easily automated and several laminate analysis softwareprograms are available4.

Interlaminar propertiesOne of the most significant differences between FRPs and metals is that the through-thickness orinterlaminar properties of FRPs can be significantly lower than their in-plane properties. This can be ofparticular importance around joints or in highly curved areas where significant through-thicknessstresses may be generated.

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Interlaminar properties are highly resin dependent, but interlaminar strengths can often be lower thanthe strengths of the resin alone, due to stress concentrations around the fibres. They are alsodependent on laminate quality, reinforcement type, volume fraction and style.

Interlaminar shear strengths are easily tested with a short beam shear test and values are oftenquoted by resin suppliers for typical laminates. Interlaminar shear strengths may typically vary from10 MPa for polyester laminates to 80 MPa for high quality epoxy laminates.

Interlaminar tension strengths can also vary considerably, with typical values around 10 MPa forpolyester laminates.

Fatigue strengthFatigue strength is highly dependent on resin properties and laminate quality. Fatigue failure oftenoccurs progressively, starting with fibre debonding and resin cracking. It should be noted that FRPlaminates can be prone to fatigue failure in compression as well as in tension, in contrast to metalswhich will generally only develop fatigue cracks in tension.

Creep and stress ruptureFRP structures subject to long-term loading can suffer from creep and stress rupture and allowancefor this must be made during design. The creep properties are highly dependent on resin properties,fibre types and environmental conditions such as temperature and humidity.

System design

The objectives of system design are to find materials best suited to the end use of the system, andstructural forms best suited to materials. To afford maximum freedom in usage, systems should becomponent-based and have built-in modularity and flexibility. The system design should giveintegrated consideration to the material microstructure, structural configurations, connections, andproduction processes. Performance should be modelled at the system, component, and materiallevels. The system should be designed to afford the end-user benefits in installation, operation,maintenance, and total life-cycle cost.

There is significant interaction between manufacturing aspects and design. The production processdictates what structural forms are feasible, minimum economic production volumes, and materialvariability. Constituent materials and their variability dictate the factors of safety to be used in designand hence the required thickness of the material. The component geometry and fibre configurationdetermines what methods of joining are feasible and thus the fabrication costs and the reliability of thefinal structure.

Historically, the design of FRP applications has been a time-consuming and costly process. Due tolack of confidence in design based on calculation, there has been a tendency to design by proto-typetesting. Even when the specialist FRP designer has full confidence in his analytical designmethodologies, there may be doubts on the part of specifiers, certification bodies, and end-usersabout whether the design methodology yields a level of reliability equivalent to established designcodes for conventional structural materials.

In the case of components intended to be produced in large numbers, a performance-based standardpredicated from proto-type testing might be acceptable. On the other hand, components intended tobe produced in small numbers need to be reliably designed by predictive methods which takemanufacturing process into account.

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Design processUnlike metals, FRPs are only created at the component manufacturing stage. Thus there is an addeddimension to the design process. The materials, the geometry to be produced and the manufacturingprocess to be used are entirely interrelated.The design process consists of several iterative stages5. The first stage is to determine the brief. Thisconsists of for example:• What general shape• What size• Quantity• Performance• Timescale etc

The creative stage considers the interaction of the materials, the processes and the geometry options.This uses ingenuity, intuition, experience, guesswork and even prejudices. This stage is highlyiterative in itself. A particular material may not work with one process but will work with another. Thisis a melting pot of ideas and options from which potential solutions appear.

The potential solutions are then analysed and compared to determine if any are adequate to meet thedesign requirements. The design process with FRPs has the advantage that there are a large numberof options available to the designer. The reinforcement type and its form produce an infinite variety.

Although in principle the design process remains the same, in practice different activities dominatedepending whether the design process is primarily ‘selective’ or whether the intention is to produce anoptimum such that the lowest possible cost or weight has been achieved. There are techniquesavailable which allow this to be carried out efficiently.

Selective design requires the same activities but once a solution has been found very little or noattempt is made to optimise it. This is the case when designing with FRP structural elements whichare available as standard pultrusion in the form of box beams, angles, channels etc. The propertiesand performance are known thus allowing structural analysis to be carried out. Hence designs may bemade on a selective basis from these ‘off-the-shelf’ parts.

On the other hand, FRPs in general and pultrusions in particular may be ‘tailor made’ for a particulardesign brief and allowing an optimised design to be achieved.

Classical analysis using isotropic equations can be used under appropriate circumstances but forcomplex constructions using multi-layers of differing materials laminate analysis is likely to berequired. This is a powerful tool for the analysis of FRPs. It allows materials to be modelled consistingof multi-layers of differing fibre reinforcements at any angle. The elastic properties may be predictedand with the application of a failure criterion, the failure can be predicted.

Anisotropic natureIt is relatively straightforward to design with materials that are isotropic (with same physical propertiesin all directions) such as steel and aluminium. However complications arise when the material to bedesigned is anisotropic such as FRP. For example an FRP may consist of unidirectional fibres butwith the fibre pointing off axis. If a tensile load is applied to the strip it will stretch as would beexpected but it will also deform in shear.

Similarly in the case of a laminate strip reinforced with two layers of unidirectional fibre each offsetfrom the axis by small but opposite angles. When a tensile load is applied to the axis the strip extendsbut will also twist. The resulting stresses and strains must be determined and this requires the use oflaminate analysis methods.

These problems are significantly simplified if the laminate is balanced both in plane and about theneutral axis. Bi-directional reinforcements such as woven fabric can fall into this classification and aredefined as orthotropic.

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Laminates with random reinforcement such as chopped strand mat can be considered to be isotropic(in plane but not through the thickness).

YieldFRPs do not exhibit a yield zone in their stress/strain response. In practice this means that twocomponents one say in aluminium and one in FRP each designed to do the same job will behavedifferently when subjected to a severe stress.

In the design of steel and aluminium elements 'local yielding' is often relied upon to solve certaindesign problems. For instance steelwork elements that are misalignment generate stressconcentrations, this dissipates as the steel is allowed to yield. If the elements were FRP, the materialwould not yield and the stress would remain in place and may result in premature failure. Similarlybolted connections in FRPs, due to the lack of a yield zone, often require the use of large washers toallow local stresses to be spread more evenly.

Young’s modulusThe design procedure for a steel or aluminium beam would generally consider the strengthrequirements first. Subsequently the deflection criterion would be checked and usually found to beappropriate. However some FRPs, notably glass fibre have a significantly lower Young’s modulusthan steel or aluminium. Consequently the design procedure is concerned initially to ensure that thedeflection limits are not exceeded. Once an appropriate design is achieved for deflectionrequirements the strength requirements are dealt with. This is usually found to be suitable.

The relatively low modulus of glass fibre FRPs also requires that buckling characteristics be assesseda little more critically than would be the case with a steel component, which have an abundance ofstiffness relative to their strength.

ShearThe shear stiffness of FRPs is relatively low. This can give rise to deflections due to shear in beamsthat are appreciable, and can be of similar magnitude to those due to bending. It is therefore essentialto determine the values of these deflections to ensure they are insignificant or that they are taken intoaccount. This is particularly important with deep sections, short spans and hollow sections.

Limit state design issues specific to FRP materialsAt the most general level the safety criteria are a definition of the target probability of failure for thevarious limit states identified. The probability of failure refers to a specific design life. A shorter designlife may permit a higher probability of failure. The design of FRPs is best based on a Limit Stateframework:

S(xLi γFLi)γ F3 < R(xGi,xMi/γMi)

where S is a destabilising load effect such as a stress, xLi are the load variables, γFLi are theassociated partial safety factors, R is the structure resistance, xGi the geometric variables, xMi thematerial variables, and γMi the material partial safety factors.

Ultimate Limits States include fibre rupture, global delamination, and global buckling leading to loss ofequilibrium of the structure and collapse. Serviceability limit states include deflection limits, vibrationlimits, strain limits to avoid initial damage, local buckling, and localised impact damage. Durability limitstates include fatigue failure and creep rupture. Accidental load conditions include fire and impact.

The manufacturing process has a greater impact on factors of safety in FRPs than in conventionalstructural materials due to the greater variability of laminate thickness, ply thickness, defect levels,and fibre impregnation levels. For example, in the pultrusion of hollow sections, inadequate stiffnessof the mandrels or their fixing can cause significant variability in wall thickness due to mandrel

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movement. These significant geometric variabilities must be adequately taken into account in thepartial material factors of safety.

FRPs are subject to shrinkage during curing which is associated with cooling from the peakexothermic temperature and the polymerisation reaction. Asymmetrical sections will warp as well asshrink. The built-in stresses due to shrinkage may need to be specifically taken into account in thestructural design.

Each independent FRP material property may have a different degree of variability (in terms ofcoefficient of variation) and hence require a different partial safety factor. In general, propertiesdominated by matrix failure require higher factors of safety than properties dominated by fibre failure.Furthermore the environmental and age reduction factors also vary according to the materialdirection.

Because serviceability limits states often control the design it is important to consider the limit statesfrom the point of view of the cumulative effect over the service life of the structure rather than fromthat of a single violation.

Engineering performance prediction and optimisation

The understanding of the behaviour of FRPs is sufficiently advanced to permit the design of moststructures for construction to be carried out with relatively little test data beyond that required tocharacterise the constituent materials or the constituent lamina types. Due to the low modulus of theFRP materials, serviceability rather than ultimate load conditions govern the design of manystructures for construction. Serviceability requirements include limiting deflections or vibrations andinterlaminar or intralaminar cracking under normal service load conditions. Under serviceabilityconditions FRP materials behave in a linear elastic manner. Therefore, the composite structure maybe analysed in the linear elastic range. The composite thermoelastic properties of laminas andlaminates can be readily and sufficiently accurately predicted by micromechanics and laminateanalysis. Subsequently, the elastic response of an FRP structure can be accurately determined bytheoretical or numerical solutions for anisotropic materials. Many programs for finite element analysisallow laminates to be modelled as layered shells.

Ultimate strength cannot be predicted with as great a level of certainty as thermoelastic properties.However, the limit state methodology allows this uncertainty to be adequately taken into account inthe material factors of safety6. The properties most difficult to predict analytically are those which arehighly sensitive to defects within the matrix or which involve a succession of several failuremechanisms along the path to ultimate failure. The analysis of these failure modes can sometimes besimplified by adopting an energy-based fracture mechanics approach. For example, delamination andbonded joints may be analysed and designed on the basis of energy release rate rather than the veryhigh stress concentrations that occur in the vicinity of geometric discontinuities or cracks.

Impact resistance is one of the more difficult properties to predict by an analytical route. However,crack initiation and propagation models are now available in some finite element packages that doallow a reasonable numerical estimate to be obtained. For practical design, it is better to use a simpleexperimental correlation developed for specific patterns of impact.

Useful theoretical models are available for estimating thermal and moisture diffusion fields within thecomposite material after long periods of exposure in a particular design environment. Using this datathe long-term properties of the material can be estimated, and hence the long term structuralperformance and reliability.

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Application of FRPs in construction

Applications of FRPs in buildings include, in order of increasing structural demand, window and doorframes, architectural mouldings, secondary structures such as wall, roof and floor panels, gratings,parapets, etc., and primary structures for monocoque modular buildings1,6.

Applications in infrastructure include bridge enclosure, footbridges, vehicular bridges, aerodynamicfairings, reinforced concrete forms, lighting columns, pressure vessels, odour containment roofs andenclosures, etc.

ArchitecturalThese applications were initially embraced in the U.S., where they now form a massive market forFRPs. UK markets are now following suit, with the introduction of the first domestic FRP doors around15 years ago. The various compositions of FRP enables products to be tailored to meet the diverserequirements of different market sectors such as new build, refurbishment, private and public sectors.A major advantage is the ability to meet the most stringent of fire, security and sound insulationstandards. This is achieved most effectively when FRPs are combined with other materials (mainly ascore materials) such as steel, thermoplastics or recycled plastics to provide the required propertiescost effectively. Social and economic benefits include improved thermal efficiency of the home, andenhanced durability, increasing replacement intervals.

Development of production processes means that FRPs can be manufactured to imitate othermaterials in appearance, thus increasing their social acceptance.

See case studies:• Windows• FRP doors• Canopies

BridgesFRP materials offer bridge designers the advantages of high stiffness-to-weight and high strength-to-weight ratios when compared to conventional construction materials such as steel and reinforcedconcrete. FRP can be preformed into complete structural units, thus reducing construction time. Inaddition, FRPs have excellent corrosion resistance particularly against de-icing salts.

Bridges are one of the highest forms of civil engineering - few other structures command the samecombination of functionality and visual impact. Major projects both in the UK and abroad have beenquite regular events over the past decades (e.g. Humber Bridge, Second Severn Crossing). In recentyears there has been something of a renaissance in the art of medium-span bridge design,particularly of footbridges. One catalyst for this has been the 27 bridges funded by the MillenniumCommission with notable examples being The River Lune, Shanks, Lowry and Gateshead MillenniumBridges. A feature common to all of these is the slenderness of the design and use of steel (eitherstainless or non-corroding Cor-Ten). To a certain extent the cost of materials and complexity ofdesign have taken a back seat to aesthetics and innovation. The most extreme example of this is theArup/Lord Foster "Blade of Light" across the Thames.

For vehicle carrying bridges in the UK, particularly across motorways, reinforced concrete or steel isthe norm. FRP materials may have particular applications in deck replacement (see Decks), wherecorrosion resistance and speed of installation are important, and in bridge enclosure systems wherethey provide environmental protection (see Bridge enclosure systems). One highly specialistapplication for FRP has been air-transportable military bridges. In countries such as Canada, NorthAmerica, Norway, Sweden and Denmark there have been major programmes developing the use oftimber as a renewable resource for footbridges and medium span vehicle bridges. Particulardevelopments have been the stress laminated timber deck and composite concrete/timber deck (alsofeaturing the use of non-ferrous FRP reinforcement), and carbon fibre strengthening of glulam and

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other engineered wood (see Strengthening). Timber has an obvious aesthetic and environmentalappeal over FRP which is hard to ignore, and perhaps will be the major competitor for footbridgesparticularly in parkland or the countryside. Interestingly, both timber and FRP suffer from the sameprejudices of poor fire resistance, durability and vandal resistance. FRP offers bridge designers analternative material with excellent properties of high strength, stiffness and good durability in completestructural units. The challenge will be to use FRPs in aesthetically pleasing designs, and incombination with traditional materials such as timber (for example, as parapets or decking).

See case studies:• Aberfeldy Footbridge• Fiberline Bridge

Bridge decksFRP bridge decks comprise sandwich profiles, spanning transversely or longitudinally betweensupporting elements (such as steel beams) or suspended from tension cables. Several variants havebeen developed. Most comprise pultruded multi-cell sections which have been glued or boltedtogether to form a compound structure. For example:• ACCS system (Advanced Composites Construction System) uses pultruded multi-cell box section

with connecting toggles and gluing• Superdeck system uses bridge truss sections with hexagonal shear keys• ASSET system (Advanced Structural System for Tomorrow’s infrastructure) uses a two-cell

prismatic profile.

Bridge decks are usually constructed from pultruded glass fibre reinforced polyester or vinylestersections, although some types are hand-laminated. Decks are prefabricated and craned ontobearings as a single unit leading to considerable savings in installation time. Principal advantages ofthis construction method are improved durability and lightness. The biggest deck spans are up to10m. Designs capable of carrying 40 tonne loads are possible. The wear surface or top surface isusually polymer concrete (often applied before installation) and asphalt.

Reasons for choosing FRP materials:• Lower installation costs as a result of prefabrication and lightness of elements• Lower through life cost, higher durability and reduced maintenance requirements.• In refurbishment projects, the ability to use existing support structures and foundations.• Efficient section, reduction in use of materials, alternative to steel and reinforced concrete.• Non-toxic, non-polluting in service• Reduced installation time results in lower traffic disruption• Ability to replace decking in heritage bridges, increasing capacity through dead-load reduction,

whilst conserving the outward appearance.• Lightweight (replacement decks, heritage bridges, lift bridges, cable stayed and suspension

bridges, swing bridges, increasing capacity, decrease in foundation loads)• Lightweight - ease and speed of handling, cranage and transport leading to lower disruption and

reduced need to curtail traffic etc. and allows use lower capacity lifting gear.• Speed of installation (eg concrete curing) leading to reduced disruption, through road closures

etc.• Durability - waterproof and corrosion resistant (eg from de-icing salts)• Freeze-thaw resistant• Ability to accommodate service conduits.

See case studies:• Bonds Mill Lift Bridge• Parson’s Bridge

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Bridge enclosuresBridge enclosures are hybrid bridge systems and are an example of an application where compositeson their own would not provide the most effective solution. A system has been developed for highperformance bridges which feature the combination of several materials utilised in an optimumcomplementary manner. The hybrid system features a lightweight tubular steel space frame, steelcast nodes, an aerodynamically profiled FRP enclosure shell, and reinforced concrete roadway slab.The structure may be widened by additional space framing and post-tensioning cables. The spaceframe is enclosed by an aesthetic, aerodynamically profiled shell which provides permanentprotection for the steelwork and safe access for inspection and maintenance of the superstructure andbearings.

Quality and overall efficiency are achieved by assembly of factory-built modular units on site, and thespace frame affords savings in steel and fabrication content. For long span viaducts, whole spanspace frames up to 150m long may be erected in a single lift, and for cable-stayed bridges havingmain spans of up to 750m, SPACES decks can be economically constructed from large segments.For suspension bridges, the aerodynamic shape and good torsional stiffness of a SPACES deckmake it an attractive system. On a smaller scale, the SPACES system is ideal for motorway wideningover bridges. Slender decks can cross 60m carriageways in a single span. The enclosed space framecan be installed rapidly and the concrete deck slab added with minimum disruption to traffic. SPACESdecks may also be used to construct high-speed and urban railway bridges which are quiet.

See case studies:• Bromley South Bridge• Bridge enclosures on the Second Severn crossing approach roads

CladdingFRP mouldings offer a highly cost effective means of adding aesthetic value to buildings, both in new-build applications and refurbishment or replacement. Architectural features such as facades,sculptures, clock towers, domes and cupolas can be easily and effectively made in FRP, providingconsiderable advantages over traditional materials such as low weight, rapid installation, durabilityand low maintenance requirements.

Reasons for choosing FRP materials:• Highly cost effective material for production of replica cupolas, chimneys, domes, clock towers,

pinnacles, statues, pediments etc. as an alternative material to stone, brick and wood, alsoroofing materials such as slates, tiles and lead.

• Principal savings arise through reduction in use of skilled craftsmen and on site labour.• Lower initial cost.• Low whole life costs from reduced maintenance, cleaning and repairs.• Lower transport and lifting costs.• Reduced need for quarried materials such as Purbeck limestone, Portland stone, granite etc,

(land use, blasting, dust pollution).• Reduced heavy transport requirements.• Adds aesthetic value to buildings.• Ability to easily replicate product.• Lightweight - easy to crane and manhandle on site, particular at height.• Lightweight - low loads to supporting structures such as trussed rafter roofs and brickwork

cladding.• Durable - reduced maintenance needs, easy to clean.• Choice of colour and surface texture• UV stable.

See case studies:• Burj Al Arab Hotel, Saudi Arabia• Lancaster University louvres

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FencingAirport fences are situated in areas where good mechanical performance is required, radartransparency is imperative and safety is critical. The main reasons for the uptake in use of FRPs forairport fencing is their inherent radar transparency (which infers they do not interfere with aircraftInstrument landing Systems) and frangibility. That means they are stiff and strong during operationbut fragile when hit by an aircraft in the case of an emergency. This feature significantly improvesaircraft passenger safety and protection of the surrounding area.

Couple these two major benefits with sound mechanical integrity, ease of installation, maintenancefree service life and in-depth colouring and it can easily be seen why composites are now chosen forairport fencing applications.

There are also apparent through life cost benefits. The fences do not corrode, even in severe weatherconditions and do not require finishing or painting. The pre-assembled panels are light to carry andhave simple and efficient fixing systems meaning no plant machinery is required for installation.

In the future recycled plastics may also be incorporate into the core material, which would furtherincrease effectiveness whilst benefiting the environment. Approach masts and other aerospaceground constructions are now under development in composite materials because of these significantadvantages.It is anticipated that FRP fence systems will penetrate the UK and US markets on the back of Aviationauthority regulations. The Civil Aviation Authority (CAA) in the UK has recently made law for all utilitystructures around airports to be frangible, and it is anticipated that fencing will be included in this. TheEuropean Passive Safety standard for roadside structures will also support the introduction of FRPairport fences.

The FRP fencing market will also develop on a domestic scale. Although ILS transparency is notrequired for domestic applications, it is anticipated that end users will opt for the low maintenance andlightweight of these alternatives compared to wood or concrete.

See case study:• Fencing – London

Modular structuresModular construction systems consist of high quality interlocking pultruded FRP panels which arebonded together to form a membrane structure in which walls, floors and roof provide completestructural integrity without additional framework. The Advanced Composite Construction Systemprovides rapid, cost effective, high quality construction, even in locations where access is difficult. Thekey advantages from using FRPs in this application are:• Monocoque structure, no additional framework required• Lightweight modular components• Designed for easy erection• Thermally insulated and fire resistant

Transportation, installation and safety benefits prevail with the use of FRP modular components. Pre-fabrication is possible, minimising site assembly and installation time, lighter components are cheaperto transport and safer to operate with on site.

See case studies:• Car wash• Stores building, Wollaston• Severn Bridges Visitors Centre• Odour control covers

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Masts and towersFRP pole sections have been around for many years. However, developments in manufacturingprocesses and UV stabilised resins have now made them a cost-effective solution for electricitydistribution, utilities and domestic use. FRP utility poles offer substantial engineering advantages overtheir conventional timber and steel counterparts. Poles can be designed to exhibit high strength,stiffness and fatigue resistance in critical areas with preferential fibre orientation.

The dielectric properties of FRPs provide significant benefits to electricity supply companies aselectric lines can be closer without the risk of electrical arcing, more circuits can be placed on existingcorridors, bringing financial and environmental benefits. FRP poles aid conformance to environmentalregulations and bring about a reduction in the use of toxic pesticides and wood preservatives utilisedwith equivalent timber products.

Financial benefits arise from reduced through life costs (they have a design life up to 80 yearscompared to 10 - 20 for wood and steel) low maintenance requirements and lower transportation andinstallation costs. Small helicopters can be used to locate the poles, there is no need to constructroads especially for transporting the poles to site as is the case with steel and timber because of theirweight.

See case studies:• GRP telecom masts and antenna• GRP light stations• Lightning tree• Telegraph pole• Church spire

PilesFRP piles can be used for marine applications such as quays, dolphins, jetties etc., as an alternativeto driven timber, steel and reinforced concrete.

FRP can be used to overcome common problems with corrosion of steel and marine borer attack intimber piles. There are also environmental concerns over the use of creosote and Copper ChromeArsenic treated timber in water. FRP piles have been used successfully in a number of largewaterfront developments in North America.

Tropical hardwoods from sustainable certified sources are still favoured for marine works in the UK,mainly due to their resistance to abrasion and when replacing like-with-like on a structure withhistorical significance. Timber is very infrequently used for on-shore works today as a piling material,although prior to 1900 many buildings were placed on timber piles (e.g. Old London Bridge). In softerground on-shore, pre-cast concrete sectional piles and continuous flight auger piling is mainly used.Large marine structures in the UK tend to be founded on pre-cast concrete piles with well-protectedsteel or non-ferrous reinforcement. Steel can be coated with polymer to provide corrosion resistance.The uptake of an FRP/composite pile for lighter marine works such as marinas and on sensitivefreshwater sites is likely to be significant.

Reasons for choosing FRP materials:• lower through-life costs through improved durability• Low inspection costs in service• Non-toxic in use, no leeching of timber preservatives (such as creosote or CCA/copper chrome

arsenic into seawater)• Alternative to tropical hardwood from rainforests• FRP sheet piling offers alternative to steel (high energy costs associated with steel manufacture)• Lightweight - easy to handle over water• Flexible - avoids damage to ships• Durable - imperious to marine borers and corrosion resistant• Abrasion resistant• Easy to drill and fix on site.• Drivability of FRP piling may limit applications, although for hollow section piles driving using an

internal drop hammer onto a robust shoe or concrete plug would be possible.

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PipesApplications of FRP piping are increasing. They are particularly advantageous in corrosive, hostile oraqueous environments where their inherent properties offer substantial engineering and financialbenefits. Lower through-life costs are realised from extended design lives and reduced maintenancerequirements. In America, about $20 billion is spent annually in combating corrosion damage toconventional piping. The cost of manufacturing and erecting offshore oilrigs could be cut significantlyif heavy metal pipelines were replaced with FRP pipelines.

FRP pipes are lighter than conventional steel products, meaning transportation and installation iseasier, cheaper and safer. They can operate at higher working pressures due to their superiorstrength to weight ratios and good fatigue performance means that they can also withstand severethermal cycling, both at high and low temperatures. They do not leach toxic preservatives into theearth or marine surroundings, which minimises environmental and wildlife effects.

Successful hybrid solutions have also been exhibited with this type of application. An example is theinclusion of a steel strip core encapsulated between two impervious composite jackets. The maximumoperating pressure is increased and remote electrical monitoring permitted.

RefurbishmentThe use of FRP materials in strengthening structures such as beams, floors, bridges, columns, silos,cooling towers and chimneys has rapidly gained acceptance worldwide since the development of thetechnique in the 1980's. For beams and bridges, the technique involves bonding either unstressed orpre-stressed carbon fibre reinforced polymer (CFRP) plates to the underside (soffit) or bottom flangeof the beam. This has the effect of increasing the capacity of the lower part of the beam which isunder tension. For materials such as reinforced concrete and cast iron, which are strong incompression but weak in tension, this is usually the most critical area. Pre-stressing the CFRP plateshas the effect of further reducing the tensile stress on the bottom flange, hence the load capacity isincreased. CFRP plates can also be bonded to the sides of beams near to the supports to increasethe shear capacity. For structures such as columns, silos and cooling towers, the reinforcement isapplied cross-wrapped or in bands, with the tensile capacity of the carbon fibres acting asconfinement.

The most obvious advantage of the use of CFRP plates over the more traditional use of bonded steelplates is the reduction in dead load on the structure. Carbon fibres have a much higher tensilestrength than steel but with much less weight. They are also non-corroding. Glass fibre reinforcementis a lower cost alternative to carbon fibres. The bonding between the CFRP plates and the structure isof great importance for the technique to be successful. To prevent failures, non-destructive testmethods for the detection of voids indicating bond failure such as the use of ultrasonic and transientpulse thermal imaging have been developed.

Reasons for choosing FRP materials for refurbishment:• Highly cost effective method of maintaining or upgrading existing structures.• Quick application results in lower disruption and shorter contract periods.• The technique may allow continued usage of structure or facility during strengthening works.• Increases the capacity with minimal addition of dead load to the structure.• Materials are easy to transport and handle - no lifting gear required. Easy to use at height.• Ability to work in confined areas and in situations with difficult access (e.g. tunnels, basements)• Minimal plate preparation required - by use of peel ply plates• Plates may be any length with no lap joints needed.• For wall strengthening overlaps are simple.• Plates may be thinner than alternative steel - less reduction in headroom.• Durable, corrosion resistant.• Good fire performance.

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See case studies:• A638 Wakefield Road• Chatham Dock wall reinforcement• Sycamore Lane footbridge, Warrington• Hythe Bridge, Oxford• Office block refurbishment• Pioneer Centre, London• Shadwell vent shaft, London

StructuralThe flexibility of FRP materials has allowed them to be utilised for innovative structural developments.The ability to combine them with conventional building materials has major benefits; shapes andforms that cannot be formed with individual materials are possible.

The main structural use of FRPs is in synergy with other more conventional materials to provideinnovative solutions whilst maintaining structural integrity and cost effectiveness. The superiordurability and corrosion resistant properties implies that structure owners will not be inconveniencedwith maintenance requirements as frequently as with other materials, thus minimising disruption andassociated costs.

Transportation, installation and safety benefits prevail with the use of FRP composite structuralelements. Pre-fabrication is possible, minimising site assembly and installation time, lightercomponents are cheaper to transport and safer to operate with on site.

Architects are presented with greater freedom with the availability of composite materials, and newstructures can gain social acceptance more easily - they are not of dull appearance.

See case studies:• GRP cupola• Harare International Airport• Pultruded FRP pultrusion factory• Spherical FRP radomes• Simulator dome• Large GRP structural frame

Wind turbinesThe use of FRP materials in wind turbines is an important technical element. Components mustexhibit excellent fatigue strength, resist random loading and corrosion, require minimal maintenanceand serve for 30+ years. Uncertainties over the performance of initial experiments with steel andaluminium have been overcome with the use of composite members, on which production is nowalmost entirely based. The blades are the main components, and the performance of the turbine isultimately dictated by their efficiency. The use of lighter weight FRP materials means that the turbinescan produce more power per unit volume, minimising impact on the landscape.

There is mixed public opinion over the introduction of large wind 'farms', the main concerns being overvisual intrusion. However, it is envisaged that the potential economic savings, along with substantialenvironmental benefits will dispel these concerns. There are numerous examples of wind farms world-wide that are now in public favour.

Offshore wind farms are a recent, high impact development. FRP materials will be instrumental in thesuccess of offshore programmes due to their proven performance in corrosive and hostileenvironments, which will maintain efficiency of the structures under increased locational costs.

As materials and manufacturing processes develop rapidly, making turbines cheaper and moreefficient, the cost of electricity they produce will be continually reduced.

See case study:• Wind turbines

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Use of FRP with traditional materials

Although FRP materials can and have been used entirely on their own, for example, in all-compositebridges, there are many examples where FRPs have been used in conjunction or synergistically withconventional or traditional building materials, particularly for strengthening. There is an inherentsynergy within the fibre and matrix combination of FRP materials themselves. The pace ofdevelopment of construction products is such that there is no real definition of a traditional buildingmaterial - punched metal plate trussed rafters and extruded PVC window frames being examples ofonce quite innovative technologies but are now commonplace. However, there are equally as manyinstances where FRPs because of their superior properties are used as direct replacements forconventional materials.

In the role of strengthening, FRPs show distinct synergy with traditional and conventional buildingmaterials such as timber, brick, reinforced concrete, steel and iron. FRPs are also used incombination with these more familiar materials in a number of applications. However, most buildingmaterials are used in combination with other types and it is often the case that there is no particular orspecial compatibility of polymer composites when compared with combinations these more familiarmaterials. Polymer composites exhibit useful properties such as corrosion resistance, high strengthand stiffness, and can be tailor-made in a cost-effective manner - thus frequently FRPs are simplybetter replacement materials. FRPs because of their greater durability are used as protectiveelements, the main examples being pile encapsulation and bridge enclosures. In a number ofspecialist applications such as radomes and non-conductive structures FRPs offer the only practicalalternative.

Implementation strategy

Designers must identify existing and new construction applications where the advantages of FRPscarry significant economic benefit. The benefit of low density and high specific strength is greatest instructures in seismic regions, in high rise buildings, decks and aerodynamic fairings for long spanbridges, rapid deployment buildings, etc. The benefits of corrosion resistance afford greatest value inprocess plants, structures in marine or industrially polluted atmospheres, and steel bridge enclosures.The benefits of rapid installation and cold joining are greatest where there is an interaction betweenthe construction of the structure and the installation of plant, equipment, and architectural finishes,such as buildings, process plants, off-shore installations, and ship building. The ability to formcomplex three-dimensional shapes can be exploited in architectural and mechanical engineeringapplications.

The prerequisites for the greater use of FRPs in construction must be aimed at improving reliabilityand reducing relative cost. These include:• The design of better and more cost effective FRP structural systems• The achievement of improved performance and reliability based on improved design methodology• The achievement of more cost effective manufacturing processes that are appropriate for the

structural systems and their potential production volumes• Greater availability of off-the-shelf components and systems that can be used to meet a wide

range of structural needs• The development of structural systems which better exploit the advantages of FRPs, used either

on their own or in combination with other materials in hybrid systems• The promotion of better market awareness of the advantages of FRPs through demonstration

projects etc.

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Future developments

Design for recyclingRecycling of technical components is a desirable objective and will become another criterion for thedesigner of the original product. There are many advantages in taking recycling into account at theoriginal design stage.

The fundamental decision confronting the original designer will, of course, be the choice of thematerial itself. (The Green Guide Specification: Environmental profiling System for Building Materials2nd Edition by N Howard, Pub CRC). There are some signs that recycling requirements are beginningto move preferences away from some materials and towards others, which are thought to be moreenvironmentally friendly. The case for and against specific materials is not simple, and it would be amistake in the reinforced plastics field to take ease of recycling as the overall priority. Work onthermosetting materials has demonstrated that every material is capable of being recycled. (BREInformation Paper 12/97 Plastics Recycling in the Construction Industry, S M Halliwell, and HalliwellSM and Hobbs G, Recycling of Plastics and Polymer Composites, Proc. Composites and Plastics inConstruction, BRE/RAPRA, BRE, Watford, November 1999, Paper 24.) The real question is howrelevant is it to the overall service value of the material, particularly its contribution to saving energyand making best use of resources. There are no clear design rules as yet, but here is a suggestedchecklist:• Can the product, or any part of it, have a secondary use, without significant change?• How/where will the product arrive for disposal?• What happens to the product during use? (wear, degradation, contamination etc)• What is the value of each material used/largest parts?• How can the most useful parts be removed more easily for reprocessing?• How could it better be dismantled in the future?• Are there any financial or legal obligations to recycle?• Is there any value in establishing a system for collection/disposal?

It is a good design principle to use only the minimum of material. The call for recycling reinforces thisrule:• Minimise the amount of material entering the waste stream. Design the product to be re-used in

the same form.• Minimise the use of material, look to using compatible materials• Minimise the volume of material – use computer aided design to optimise.Materials suppliers and/or manufacturers should be consulted for detailed advice on how to use thesetechniques.

The presence of other materials in the compound, particularly fillers and reinforcements, may limit theoptions in re-formulating any recycled material. It would be prohibitively expensive to removeadditives, and the new compound must therefore contain them. Glass fibre presents no difficulty. Inthermosets, it may be ground with the resin material, while in thermoplastics it simply goes to makeup a new glass-reinforced compound. In all cases of direct material recycling, however, there is likelyto be some loss on mechanical properties (up to about 20%), which can be offset in the newcompound by adding new material and/or corrective additives.

Wood plastics compositesA wood plastics composite (WPC) is a term which refers to a composite material containing wood inany form, combined with either thermoplastic or thermoset resin.

Most WPCs currently on the market are made from thermoplastics, in particular high densitypolyethylene (HDPE). The nature of the wood content is either wood flour or sawdust. At firstinspection, the combination of wood fibre and a thermoplastic does not seem promising. Wood fibres(eg in the form of sawdust) are short, tend to absorb moisture and are not strong when compared witheither the glass or carbon fibres used in FRPs. Thermoplastics are much weaker than thermosetting

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resins, soften with increasing temperature and creep under load. However, WPCs combineinexpensive or waste raw materials, and the production process for low technology sections such asdecking planks, fencing and handrails is relatively simple. Particularly in the USA, WPCs have beenhugely successful because they offer advantages of durability and lower maintenance over naturalwood. Solid recycled plastics lumber (RPL), is usually made from waste plastics without any wood orfibre element (and is therefore is not a composite), also competes in this non-structural role. PolyvinylChloride (PVC-U) is another type of plastics which has familiar application for window frames, doorsand fascia panels.

Although very much more low-tech compared with the more advanced FRPs, WPCs are beginning tobe used for structural applications. Developments such as fibre orientation and better couplingadditives have already taken place. Although WPCs are generally weaker than timber, particularly inflexural stiffness, in many cases their structural performance will be adequate. The main advantage ofWPCs is the resistance to decay, insect attack, warp and splintering.

Future development of WPCs for structural use may take the following form:• Co-extrusion with reinforcing rods (either steel or FRP)• Co-extrusion/pultrusion with longitudinal glass fibres (bundles, tapes or mats)• Modification of the thermoplastic/wood fibre mix into stiffer, more resin-like materials• Better bonding between matrix and fibre by advances in additive and cross-linking technologies

WPCs require fine ground, dry, clean sources of wood fibre. This is most likely going to be obtainedfrom the wood working industry rather than from sawmills or from virgin timber such as forestthinnings. Increased recycling of waste plastics and wood waste, and developments in productionprocesses, will decrease the price of WPCs and encourage usage. Two WPC manufacturers haverecently started production in the UK.

WPCs will displace use of solid timber in both outdoor and indoor markets. Advanced FRPs also offeran alternative to timber for some engineering applications such as bridges, and are also beginning tobe used for doors, window frames and cladding.

Eco-compositesEco-composites is a term which is used to describe composite materials with environmental andecological advantages over normal composite materials such as FRPs. The drive towards sustainableconstruction and environmental legislation such as the End of Life Vehicle Directive and Landfill Taxhas resulted in considerable interest in the use of reclaimed waste such as plastics packaging forconstruction materials, as well as the use of natural plant fibres, wood, and bio-derived resins andadhesives. An eco-composite may contain natural fibres such as hemp, sisal, jute or flax, or consist ofa natural polymer matrix derived from cashew nut shell liquid (CNSL). Plastics materials can also beproduced from corn, and even chicken feathers. Eco-composites can be produced from combinationsof reclaimed waste such as wood, newspaper, and plastics. Natural composites based on starch canbe produced which have the important advantage of biodegradability. Softwood timber can bechemically modified using waste cellulose from agriculture to produce a composite material with theproperties of a tropical hardwood. A composite which is easier to recycle such as an all polypropylenematerial may also be termed an eco-composite.

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Case studies

There are many hundreds of examples of application of FRP materials in construction projects. Thestructures chosen for inclusion in this report represent key applications of polymer composites inconstruction. They are given in the order they are referred to in the applications section.

Windows

Description GRP window frameApplication type ArchitecturalWherecompositesused and why

GRP used as the frame for several reasons:• High dimensional stability• Low thermal conductivity – therefore better insulation that other

materials• Load bearing – therefore no need for metal inserts, and option to

produce larger windows• High durability – expected life 50 years• Compatible with other materials to achieve maximum benefits

Nature ofserviceenvironmentand designloads

Exterior subject to weatheringCan be used for larger windows than PVC-U due to high strength

Developmentand provingtrials

Frames tested to appropriate performance standards as for timber, PVCand aluminium windows

Geometry ofcomposite

Pultruded hollow sections

Type ofcomposite used

Glass reinforced polyesterPultruded

Specialrequirements ofcomposite

High durability, strength, load bearing, high dimensional stability, costscomparable to existing window options

Performance inservice

Guaranteed for 20 years, expected service life of 50 years

Joiningtechnique used

Pultruded sections can be bonded together or mechanically fixed

Furtherinformation

Crown Fenestration or Lindman Fenestration

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FRP Doors

Description FRP external doorApplication type ArchitecturalWherecompositesused and why

GRP used for skins of doors – usually filled with foam core. GRP offersdurability, choice of colour and texture, minimal maintenance, costcomparable with other options. Can be repaired and re-stained.


External surface exposed to weathering. Possible vandal abuse.Designed for security standards.


Developed and tested to product performance standards for durability, fireand security.


GRP skin


Moulded glass fibre reinforced polyester sandwich panel with foam core –foam depends on insulation and fire requirements


High durability, low cost, fire performance, security performance, choice ofexternal and internal finish, low maintenance.


Guaranteed for 25 years.


Most doors have wooden stiles that can carry any locking system.

Furtherinformation

Lindman Doors

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Canopies

Description Canopy over entrance to buildingApplication type ArchitecturalWherecompositesused and why

As non-structural feature attached to building. GRP used for highdurability, light weight, lower cost, high quality, aesthetic appearance, widerange of colour and texture choice, prefabrication off-site, low maintenanceand ease of installation.


Exposed to weathering. Usually non-load bearing.Often required to mimic traditional material in appearance.


Tested to usual performance standards for durability and fire.


Depends on component. Usually moulded GRP component/sheet.


Hand lay-up, open moulded glass reinforced polyester material.


Durability, fire performance, low cost, prefabrication, range of colour andtexture, low maintenance.


Guaranteed for 25 years – expected to exceed this in service.


Usually moulded modular component, joined to structure by mechanicalfixings. If necessary, FRP components will be joined together by bondingor mechanical fixings.

Furtherinformation

BRE

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Aberfeldy Footbridge

Description All composite footbridge over a golf courseApplication type BridgeWhere FRPsused and why

This is the world’s first major FRP footbridge. Maunsell worked closely withDundee University whose final-year bridge engineering students providedthe bridge erection team. A unique method of erection of towers, cablesand deck was used which needed no site cranage. This was madepossible by the lightweight components. The bridge was completed by theaddition of GRP handrailing and a wear-resistant deck finish, providing alife to first maintenance of over 20 years. The minimal foundations andrapid site assembly meant that the solution was very cost effective for theclient. Key benefits from using FRPs are:• Fully bonded FRP structure• Light and durable• Erected without cranage


The bridge is a cable-stayed structure with a main span of 63m and twoback spans. It is stayed from two 18m-high ‘A’ shaped GRP pylons usingParafil cables – Kevlar aramid fibres sheathed in a protective low densitypolyethylene coat. The 120m-long fully bonded lightweight deck wasassembled on site in only ten weeks.


Load tests on parapets to verify strengthStrength tests on cable/deck connectionsStudies demonstrated that dynamic response can be controlled bycalibrating the magnitude and distribution of the mass of the deck andtailoring the damping of the parapets, cables and surfacing.

Geometry ofFRP

Deck – 600mm wide longitudinal ACCS panels stiffened by edge beamsand cross beams.Parapets – non-ACCS sections

Type of FRPused

Parapets – pultruded GRP sectionsCables – Kevlar-49 fibres sheathed in low density polyethyleneDeck – pultruded GRP sectionsGRP – E-glass fibre and isophthalic polyester resin

Specialrequirements ofFRP

Light weight, durability, minimal disruption to golf course


Good. For full report see BRE Report 461.


Bond and toggle type mechanical connectors.

Furtherinformation

Maunsell Structural PlasticsMaunsell House, 160 Croydon Road, Beckenham, Kent, BR3 4DETel: 0181 663 6565 Fax: 0181 663 6723 http://www.fabermaunsell.com/

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Fiberline Bridge

Description All-FRP footbridge crossing railway track in Denmark.Application type BridgeWhere FRPused and why

FRP used for whole structure.GRP offers electrical non-conductance. Weight is low, so transportationand installation are easy. The GRP profile constructions are corrosionresistant and maintenance costs are minimal.


Design load capacity: 500 kg/m2

Design total vehicle load: 5 metric tonsWeight: 12 metric tonsTower height: 18.5mLength: 40m, width: 1.3m

Geometry ofFRP

Standard pultruded profile

Type of FRPused

Isophthalic polyester resin and E-glass


Electrical non-conductance


Excellent


Mechanical bolts.

Furtherinformation

http://www.fiberline.com/

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Bonds Mill Lift Bridge

Description Advanced FRP road bridgeApplication type BridgeWhere FRPsused and why

Complete FRP bridge – worlds first advanced FRP road bridge.FRPs used for cost savings, provide low maintenance and good durability.


The bridge is 8.2m long and 4.3m wide carrying a single lane of traffic.


Bridge monitored by University of Surrey.

Geometry ofFRP

The 8.2m span bridge deck is manufactured from ACCS. There are aseries of pultruded GRP sections running longitudinally which are bondedtogether using an epoxy resin to form a cellular box girder with six maincells which are filled with epoxy foam. The deck is a ‘double ply’ of ACCSskins with cells running in two orthogonal directions. The total weight of theACCS deck and surfacing is 4.5 tonnes for 35m2 of deck area giving a liveto dead load ratio of 13.5.

Type of FRPused

GRP pultruded sections


Cost effective, durable in marine environment


Good performance


Epoxy bonding of GRP sections

Furtherinformation


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Halgavor Bridge

Description Cycle bridge crossing A30 close to Bodmin, Cornwall, UKApplication type BridgeWherecompositesused and why

Bridge deck is of sandwich construction with girder sections handlaminated along with the internal structure. The GRP deck is covered witha rubber layer made from recycled car tyres. The span is suspended fromsteel masts and suspension cables attached to steel parapet posts boltedto the deck structure. Composites were chosen for light-weight, excellentdurability and low maintenance. A single piece construction allowed for aquick installation, reducing the time when the A30 had to be closed to24 hours.


Cyclists, walkers and horse riders will use the bridge. It is constructed inthree parts, 8.5m x 2m and with the main span 32m long. The bridge is 4mwide.


Bridge deck tested to footbridge and equestrian-bridge performancestandards.


Bridge deck is of sandwich construction with girder sections handlaminated along with the internal structure.


Vinylester resin and E-glass.One grade vinylester used for vacuum infusion process and another for thehand lamination assembly work.


Durability, low maintenance


Opened 2001


Adhesive bonding and mechanical fixing.

Furtherinformation

http://www.flintneill.co.uk/

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Parson’s Bridge, Dyfed

Description Footbridge over ravineApplication type BridgeWhere FRPsused and why

Parson’s Bridge footbridge crosses the Afon Rheidol not far from Devil’sBridge. An all FRP bridge deck was used. The lightweight glass reinforcedplastics construction made it possible to use a local helicopter to lift thebridge into place, avoiding the cost of bringing in a heavy freight helicopterfrom the North Sea. At the same time, because of the material’s durability,maintenance costs will be minimal. Key benefits in using FRPs for thisapplication are:• Light and durable• Cost effective installation and maintenance.


Since the site is totally inaccessible by road, the bridge had to be lifted intoplace by helicopter.

Geometry ofFRP

The all FRP structure consists of a single span, 17.5m long. 0.76m wideand weighs just one tonne

Type of FRPused

GRP pultruded sections. The structure is a typical example of ACCSgenerating considerable savings in the total project cost when compared toalternatives using traditional materials.

Furtherinformation


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Bromley South Bridge, Kent

Description GFRP enclosure on railway bridgeApplication type Bridge enclosure, claddingWhere FRPsused and why

Bromley South Bridge is the major element of a road built to remove trafficfrom the town centre. It passes between residential and business areas,and includes a crossing over the main line railway. The plate girders of themain spans of the bridge are enclosed in a GRP membrane enclosure, inorder to provide access for inspection and maintenance and to enhancethe appearance of this section of the bridge. The ‘caretaker’ system wasused with ACCS components. Great importance has been given to theappearance of the scheme. The bridge parapets, pier and abutments areclad in intricately patterned brickwork, with panels manufactured from GRPto simulate brickwork.


The length of the bridge is 210m, made up of ten spans, with a main spanof 42m. The three principal spans, over the railway, have seven variabledepth plate girders with a composite concrete deck. The seven approachspans are a uniform depth concrete slab, supported on slender columns.

Geometry ofFRP

GRP membrane enclosure

Type of FRPused

GRP


Low maintenance, aesthetic appeal


Adhesive bonding

Furtherinformation


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Green Bridge, London

Description GRP cladding to the Green Bridge, LondonApplication type Bridge enclosure, claddingWhere FRPsused and why

Curved panels were attached to the underside of this new bridge in orderto improve the corrosion resistance of the steel bridge beams and toprovide a working platform for future bridge inspections and maintenance,enabling these tasks to be completed without any traffic disruption


Heavy traffic pollution.Loading – wind and imposed loads


Fire testing carried out

Geometry ofFRP

Curved moulded GRP panels

Type of FRPused

Fire retardant polyester resin with glass reinforcements and end grainbalsa cores


Durability, colour , Fire resistance


No problems reported to date.


Bolted joints

Furtherinformation

CETEC Consultancy LtdCoopers House, The Horsefair, Romsey, Hants SO51 8JZTel: 01794 256500 Fax: 01794 526501

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Bridge Enclosures on Second Severn Crossing ApproachRoads

Description Three motorway approaches to the new bridge across the Severn estuaryApplication type Bridge enclosureWhere FRPsused and why

GRP skin acts as enclosure to steel framework, protects and allows easieraccess for inspection and maintenance.


In Avon two approach roads of dual two-lane motorway link the M4motorway at Awkley and the M5 Motorway at Lawrence Weston to a newinterchange at the main estuary crossing embankment at Pilning. The totallength of the new motorways is 15km. Some 24 new structures areprovided, seven of which incorporate advanced composite enclosuresystems for improved maintenance life. The scheme also involves therealignment of 12 side roads.


Traffic studies, geotechnical investigations, planning and environmentalconsiderations were carried out. Preferred routes were selected afterpublic consultation and the submission of a Parliamentary Bill for whichclient support was provided at Select Committee stage.

Furtherinformation


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Burj Al Arab Hotel (Arabian Tower Hotel)

Description GRP cladding on interior and exterior of 7-star hotel in DubaiApplication type CladdingWhere FRPsused and why

33,000m2 of GRP sandwich panels act as dividers between the rooms andthe 200m high atrium.GRP used for freedom of design, high strength, low maintenance costs,high fire retardancy and good sound insulation. Due to low weight,transportation and installation are easier and more cost effective.


Coastal environment, high UV levels.

Geometry ofFRP

GRP sandwich panels

Type of FRPused

Fire retardant polyester resin and Gelcoat with E-glass.


>2 hours fire resistance

Furtherinformation

Client: HH General Sheikh Mohammed Bin Rashid Al Maktoum, CrownPrice of DuabiConsultants: WS Atkins Overseas (WSAO)Contractor: Al Habtoor Murray Roberts Joint Venture (AHMRJV)

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GRP Louvres at Lancaster University

Description The 57 GRP louvres, 6.2m high, are used to shield a glazed wall on theaward winning library extension at Lancaster University. This is a veryexposed site with design wind speeds of 100mph resulting in a load of2 tonnes on each louvre.

Application type Louvres/claddingWhere FRPsused and why

CETEC were responsible for design, stress analysis and manufacturingdrawings, together with the selection of a suitable manufacturer for thelouvres. The architect’s original scheme was for an internal steel framewith GRP cladding, but this was revised by CETEC into an all-GRP self-supporting structure. This resulted in a 50% weight saving givingsignificant savings in the installation costs, removing concerns regardingthe corrosion of internal steelwork and produced a much more economicstructure. The louvres were moulded in two halves and bonded togetherusing Crestomer adhesive.


ExposedHigh wind loads

Geometry ofFRP

Aerofoil section

Type of FRPused

Biaxial glass fibres, polyester reins


Lightweight, durability


Bonded joints

Furtherinformation

CETEC Consultancy Ltd

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Cladding of Liverpool Roman Catholic Cathedral

Description Re-cladding of RC Cathedral in Liverpool where mosaic tiles on thestanchion had debonded from the mortar/concrete, resulting in large lumpsof material falling from the building.

Application type CladdingWherecompositesused and why

GRP was chosen over stainless steel for the following reasons:• Proven success in marine and other structures• Low maintenance (stainless steel would need regular cleaning)• Good corrosive resistance• No need to remove existing cladding – over-clad with GRP• Good fire resistance


Marine environment, therefore exposure to attack by chloride ions.Non-load-bearing panels.Fire resistance rating – Class 0/1.


Proven success of same fibre/resin combination in marine industry


Flat sheets with fire resistant resin.


Hand lay-up glass reinforced polyester panels.Granite effect finish to all panels.


Fire resistance, durability, corrosion resistance, low maintenance.


No reported problems.


Panels mechanically fixed to existing structure.

Furtherinformation

BRE

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Fencing – London

Description Secure fencing around a new electromagnetic shielding facility.Application type FencingWherecompositesused and why

Composites were used as reinforcement for fencing. GRP was chosen asit offered significant cost savings by designing optimised thin concretesections specifically for the new reinforcement. A further benefit is theelimination of attack by high chloride environments, such as marine androadside.


The components were hand cast on a vibrating table with a standardconcrete mix designed to give about 40 MPa strength.


Trial units were mechanically tested and found to crack at 1kN and fail at aload of 10kN meaning that they would easily carry their design load withoutcracking. A thermal cycling regime, from room temperature to 350°C, wasconducted over a six month period - no cracks were found


Posts were 3.9m long by 200mm with slots in to accommodate the panels.Each had 6, 13.5 mm diameter, glass fibre reinforced polymer bars runninglongitudinally, with shear straps bonded at 200mm intervals. The tongueand groove panels, which were 1.9m long, 300mm high and only 50mmthick, were reinforced with 3, 8mm square rods connected at 300mmcentres. The metal moulds were existing profiles and the reinforcementcages positioned using nylon spacing clips.


GRP pultruded bars


Add strength, durable, no interference with equipment, low cost

Furtherinformation

Eurocrete LimitedChurch House, Pointon Fen, Sleaford, Lincs NG34 0LF, UKTel & Fax: +44(0)1529 241123e-mail: [email protected]://www.ngcc.org.uk/

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Advanced Composite Car Wash

Description Car wash structureApplication type Building, structureWhere FRPsused and why

The building houses car wash equipment on a garage forecourt. It is abonded structure manufactured with components from ACCS. This form ofstructure was chosen for three reasons:• The inherent durability of the material in a corrosive environment• Its high quality finish without the need for secondary cladding• Its ease and speed of assembly from a small number of factory

manufactured panels.The car wash housing is designed to meet U.K. building standards. Inparticular, the panels have a Class 0 fire rating for spread of flame. Theyare self-coloured with a white fire rated resin, and were painted grey to theclient’s specification.


Harsh, corrosive environment.

Geometry ofFRP

The structure is a membrane structure with no support framing and is 11mlong, 5m wide and 4m high. The components are assembled into panels,typically 2.5m in width by 4m or 5m long.

Type of FRPused

GRP with Class 0 fire rating


Class 0 fire rating, good durability in corrosive environment, ease ofassembly.


Good


Adhesive bonded

Furtherinformation


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Stores Building, Scott Bader, Wollaston

Description General stores building for containers of raw materialApplication type Modular structureWhere FRPsused and why

A modular GFRP stores building was constructed at the Scott Bader site atWollaston to demonstrate the suitability of this material for constructionpurposes. The structure has a steel and timber frame with GFRP boltedonto the timber beams. It is a self-supporting structure – no addedsupports are needed for the roof (this is the unique part of its design)


Constant use. Forklift trucks in and out daily.


Demonstration project


The walls are of a folded plate design

Type of FRPused

Filled FP resin and a green (chrome oxide) pigmented gelcoat; the roofutilises a translucent FR resin and a translucent gelcoat.


Structural as well as aesthetic properties, durability, low maintenance


The stores building was inspected in February 2002. No majormaintenance had been carried out to date. The building has notexperienced any change in use and is in constant use .The structure was mechanically sound and light transmission inside thebuilding was still sufficient to avoid the need for artificial lighting during theday.

Furtherinformation

Scott Bader Company Ltd

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Severn Bridges Visitors Centre

Description Multi-storey advanced composite buildingApplication type Modular structureWhere FRPsused and why

The system consists of high quality interlocking pultruded glass reinforcedpanels which are bonded together to form a membrane structure in whichwalls, floors and roof provide complete structural integrity withoutadditional framework. The Advanced Composite Construction System(ACCS) provides rapid, cost effective, high quality construction, even inlocations where access is difficult. The key advantages from usingcomposites in this application are:• Monocoque structure, no additional framework required• Lightweight modular components• Designed for easy erection• Thermally insulated and fire resistant.


Harsh marine environment. Exposed site.


The world’s first advanced composite multi-storey building constructedusing ACCS was commissioned be the client as an alternative toconventional accommodation for the Government’s Agent team on theSecond Severn Crossing project. This has since been converted into theSevern Bridges Visitors centre.

Geometry ofFRP

Pultruded panels with jointing strips to provide interlocking structure(ACCS).

Type of FRPused

Glass fibre reinforced polyester.


Good thermal insulation and fire-resistance are key features of the buildingdesign. Panels are insulated to a high standard and double-glazedwindows have been fitted. In critical areas, panels meet Class 0 fireregulation specifications with a fire resistance of at least 30 minutes whentested in accordance with BS 476: Part 21.


After 8 years service the GRP was in excellent condition and hadundergone minimal maintenance being jet-washed just once. Some dirtaccumulation was evident.


Interlocking system and adhesive bonding.

Furtherinformation

Maunsell Structural PlasticsMaunsell House, 160 Croydon Road, Beckenham, Kent, BR3 4DETel; 0181 663 6565 Fax: 0181 663 6723 http://www.fabermaunsell.com/

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GRP Telecom Masts and Antenna

Description Telecommunications mastApplication type Mast, antennaWhere FRPsused and why

GRP masts were developed with several key advantages overconventional steel masts. Advantages include lightweight, corrosionresistance, electrically non-conductive and transparency to radar etc




Microwave testing

Geometry ofFRP

Masts – LatticeAntenna – parabolic

Type of FRPused

Masts – Glass fibreAntenna – Carbon fibre/epoxy


LightweightAntenna – electrical conductivity of carbon fibre used for microwavereflectivity


Good

Furtherinformation

CETEC Consultancy LimitedCoopers House The Horsefair Romsey Hampshire SO51 8JZTel +44 (0) 1794 526500 Fax +44 (0) 1794 526501 e-mail [email protected]

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GRP Light-Stations

Description These 10m high self-supporting GRP towers provide solar powerednavigation lights to remote islands and rocks in the Philippines.

Application type TowersWherecompositesused and why

The structures were designed for wind speeds of 162mph and havealready survived several tornadoes that are prevalent in this part of theworld. The panels are moulded using a resin injection process and so farover 300 towers have been constructed. This design has also beenextended to towers up to 15m high for locations in other parts of the world.


ExposedVery high wind loads


Curved panels


Glass fibre/polyester


Durability


Very good


Bolted joints

Furtherinformation


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‘Lightning Tree’

Description ‘False’ dead tree to camouflage mobile telephone siteApplication type Architectural; Special Structures; TowersWhere FRPs usedand why selected

FRPs were used due to their ease of construction and assembly, andlightweight nature, in preference to conventional building materials. Theability to form the material into the required shape was also animportant consideration. A key to the selection of FRP materials wasthe necessity to provide RF transparency to enable successfuloperation of the mobile telephone antennas concealed within thestructure.

Nature of serviceenvironment anddesign loads

Rural location

Development andproving trials

RF performance testing

Geometry of FRP Complex 3D shapeType of FRP used Hand-lay manufacturing technique, using a combination of CSM and

foam sandwich materials.Specialrequirements ofFRP

Cost; durability; fire retardant; RF translucent


Recent installation – no problems to date

Joining techniqueused

Combination of bolting and bonding

Further information Many other camouflaged solutions available.

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‘Telegraph Pole’

Description ‘False’ telegraph pole to camouflage mobile telephone siteApplication type Architectural; special structures; towersWhere FRPs usedand why selected

The ability to form the material into the required shape was also animportant consideration. A key to the selection of FRP materials wasthe necessity to provide RF transparency to enable successfuloperation of the mobile telephone antennas concealed within thestructure.


Rural/urban location



Geometry of FRP CylindricalType of FRP used Hand-lay manufacturing technique, using a combination of CSM and




Recent installation – no problems to date



Further information Many other camouflaged solutions available

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Church Spire

Description ‘False’ church spire to camouflage mobile telephone siteApplication type Architectural; special structures; towersWhere FRPs usedand why selected

FRPs were used due to their ease of construction and assembly, andlightweight nature, in preference to conventional building materials. Akey to the selection of FRP materials was the necessity to provide RFtransparency to enable successful operation of the mobile telephoneantennas concealed within the structure.


Urban location



Geometry of FRP Complex 3D shapeType of FRP used Hand-lay manufacturing technique, using a combination of CSM and




No problems reported



Further information Many other camouflaged solutions available

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A638 Wakefield Road

Description Scheme to protect the safety of pedestrians and motorists from thepossibility of rock fall.

Application type Reinforcement (soil nails primary reinforcement)Wherecompositesused and why

Nails installed in rows along a 10 metre high cutting to secure thegalvanised steel wire plastics coated rocknetting. Composite nails selectedfor ease of installation, durability and ability to cause less damage to theplastics coated mesh during installation


To secure plastics coated mesh to the rock cutting.Design loads of 25kN.


Gripforce 25mm diameter bar, 2m and 1.5m long, standard nutassembly.


Pultruded highbred vinylester and modified E-glass


Installed into a pre-drilled hole 32mm diameter.


Random pull out tests to 40kN were made to test the bond strengthbetween the resin rock interface.


Slow set polyester resin capsules used to bond the nails into the strata.

Furtherinformation

http://www.weldgrip.com/

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Chatham Dock Wall Reinforcement

Description Reinforcement of existing dock walls along side the River MedwayApplication type Reinforcement (soil nails secondary reinforcement)Wherecompositesused and why

Nails installed vertically through the wall.Composites selected for their durability, lightweight and ease ofinstallation. Alternative stainless steel nails – these would have increasedthe material and installation cost.


To reinforce and stabilise an existing stone block wall. At high tide 5m ofthe installed nail below water line.Design loads of 40kN.


Gripforce 31/15mm (OD/ID), 6 metres long injection tubes with high loadnut assembly.


Pultruded highbred vinylester and modified E-glass


Installed into a pre-drilled hole 45mm diameter. To improve the asceticsafter nail installation the high load nut assemblies were counter sunk intothe coping stones at the top of the wall.


OPC cementitious grout pumped through ID of the tube to fully bond thenails

Furtherinformation

Wall height 6m.For further information see http://www.weldgrip.com/

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Sycamore Lane Footbridge, Warrington

Description After an abnormally high load, carried by a truck, crashed into the deck ofa footbridge over a heavily trafficked road in the north of England, it wasnot only the displacement of the deck that caused concern. A subsequentanalysis by the owner exposed the inadequacy of a slender pier support towithstand current UK design loads for impact.

Application type StrengtheningWherecompositesused and why

The solution was found by providing external FRP reinforcement under adesign and install contract. Following careful preparation of the concrete bythe specialist applicator, eleven layers of vertically aligned and two layersof horizontally wound carbon fibre sheets, were installed by hand lay-uparound the rectangular tapered cross-section of the support. Each layerwas impregnated by resin saturant and finally protected from ultra-violetlight by a protective coating.


Exposed to salt spray, rain and direct sunlight.

Vehicle impact loads to Highways Agency Standard BD 21/97.


Transport Research Laboratory load testing and application trials on theA30 Bible Christian Bridge, Cornwall.


Rectangular jacket


Carbon fibre and epoxy resin laminated insitu


Minimal thickness to avoid reduction in sightlines for vehicle drivers.


Installed in 2000. No defects reported.


Contact moulding

Furtherinformation

Tony Gee and PartnersTGP House, 45-47 High Street, Cobham, Surrey KT11 3DP

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Hythe Bridge, Oxford

Description Hythe Bridge is a busy 125 year old cast iron beamed bridge with brickjack arches in-between which carries the western approach road intoOxford over a River Thames backwater with two 7.8m spans. Assessmentof the bridge revealed that it required to be strengthened.

Application type Strengthening, plate bondingWherecompositesused and why

Four CFRP (carbon) strips were bonded to the underside of the bridge withepoxy resin to strengthen the 7.5 tonne capacity cast iron beams to full40 tonne capacity. All other techniques were discounted because of themassive disruption it would cause to traffic entering and leaving Oxford.


Surface preparation involved grit blasting and grinding of beam soffits, thenbonding anchorages to the ends of the beams. Epoxy resin was thenapplied and four CFRP plates, each stressed to 18 tonne each wereclamped tightly up to the soffit so that they would bond over their fulllength. All 16 beams were strengthened.


Well proven technique for bridge strengthening.


CFRP plate/strip


Carbon fibre reinforced polymer


Surface preparation crucial to enable efficient adhesion between beam andCFRP plate.


No problems reported.


Epoxy resin

Furtherinformation

Mouchel ConsultingBalvac

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Office Block Refurbishment

Description Office block refurbishment – existing structure demolished to 2nd floor, thenrebuilding done in lightweight steel frame, composites used to strengthen2nd floor

Application type Strengthening, plate bondingWherecompositesused and why

CFRP plate bonding used to increase loading of existing structure.Technique meant minimum disruption to surrounding buildings.


CFRP plates used to strengthen 2nd floor to cater for increased loading andchanged column locations


Well proven technology


CFRP strips/plates


Carbon fibre reinforced polymer


Surface of beams had to be prepared to enable efficient adhesion of CFRPplates


No problems reported


Epoxy resin

Furtherinformation

Mouchel Consulting

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Pioneer Centre, London

Description Modification of an early Grade II Listed reinforced concrete structure inNunhead, south London. As part of the conversion process, the architect’sdesign introduced a substantial number of staircases to connect the split-levels of each unit and this necessitated alternative load paths beingintroduced.

Application Plate bonding, strengtheningWherecompositesused and why

The cement laitance on the surface of the concrete substrate was carefullyremoved before the contractor bonded more than 500 metres of 1.2mmthick CFRP laminates onto the top and bottom faces of the floor and roofslabs


Domestic apartments.

Loading to BS 6399 Part 1


Despite their slender design, tests indicated the floor slabs (152mm thick)were composed of concrete with an adequate insitu compressive strengthof 35 N/mm2. In these circumstances, specialist designer Tony Gee andPartners identified that strengthening the slabs in flexure with FRPcomposites provided an ideal solution.


Rectangular strips up to 100mm wide and 1.2mm thick


Pultruded CFRP strip


To fit within the depth of existing soffit insulation


No maintenance inspections documented


Bonding to concrete with two part thixotropic epoxy adhesive

Furtherinformation

Tony Gee and PartnersTGP House, 45-47 High Street, Cobham, Surrey KT11 3DP

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Shadwell Vent Shaft

Description Strengthening of 19th century cast iron struts with carbon fibre at Shadwellvent shaft on London underground. The struts were loaded to near theircapacity, similar struts at Rotherhithe had failed.

Application type Strengthening, refurbishmentWherecompositesused and why

Additional steel struts were installed and jacked out to reduce stress levelswithin the cast iron. Carbon fibre was then used to strengthen the cast ironso that additional loads could be carried. This was the most cost effectiveoption. 160 surfaces, totalling a length of 1km were strengthened over aperiod of 10 weeks.Following strengthening, the beams were painted white to minimiseheating from exposure to sunlight.


The underground line could not be closed.Surface of cast iron had to be cleaned by wet abrasive blasting to removeany paint. This was followed by grinding and chipping to remove looseelements and then final dry abrasive blasting to prepare the surface toSA21/2 .The technique preserves the load path in the vent shaft and the beamshape whilst increasing the capacity.


Laboratory scale tests extending to full-scale on struts removed fromRotherhithe station to validate the technology.


Carbon fibres laid on cast iron struts and then resin introduced undervacuum.


Ultra-high modulus carbon fibre – the composite manufactured in situ hasa modulus of 310Gpa c.f. cast iron of 100GPa, therefore any additionalload is carried by the stiffer composite.Composite manufactured in-situ using RIFT (resin infusion underflexible tooling)


High stiffness, low cost, no disruption to underground train line.


Accepted design life is 40 years – up to 150 years is predicted.


None

Furtherinformation

DML Devonport, London Underground Ltd

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GRP Cupola

Description The cupola shown above is installed at Lerwick, in the Shetland Islandsand is an all GRP structure, including the fake slate roof.

Application type Structure, architecturalWhere FRPsused and why

CETEC have design numerous architectural features using GRP materials,often as in the case above, utilising the GRP mouldings as the primarystructure, avoiding the need for secondary steelwork. This philosophyresults in a lighter, more efficient and maintenance free structure



Type of FRPused

Glass fibre/polyester resin


Durability

Furtherinformation

CETEC Consultancy LimitedCoopers House The Horsefair Romsey Hampshire SO51 8JZ Tel +44 (0) 1794 526500 Fax+44 (0) 1794 526501 e-mail [email protected]

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Harare International Airport

Description This GFRP lattice structure is installed on the top of the new air trafficcontrol tower at Harare International Airport in Zimbabwe.

Application type StructuralWhere FRPsused and why

The shape of the structure was defined by the architects and has importantreligious significance. Several alternative materials were considered,including steel, aluminium and GFRP. GFRP was selected as this offeredthe most economic solution, both in terms of initial and through-life costsand is also non-conductive, therefore allowing aerials and antennae to befitted inside the structure.

The structure was manufactured in the UK in sections and assembled onthe ground in two pieces. As the structure was reasonably light it waseasily lifted into position using a mobile crane.


The structure was designed to withstand high wind loads and seismicloading, where the lightweight solution was advantageous in minimisingthe inertia loads applied to the supporting cabin structure.

Geometry ofFRP

Complex frame

Type of FRPused

Glass fibre/polyester


Durability


Bonded and bolted

Furtherinformation


57


Pultruded FRP Pultrusion Factory

Description The FRP building will form the factory for a new pultrusion company,Protec Materiali Compositi, based in Sicily.

Application type Building structureWhere FRPsused and why

The building was originally designed as a conventional steel framedstructure, but Protec decided to use their own factory building as ademonstration of their ability to provide complete structural solutions inreinforced plastics. This will be a very significant structure, measuring42m x 29m x 10m high, without any internal columns, to give the maximumworking area and flexibility to the factory. The structure will be verylightweight enabling many parts to be assembled into modular units off-sitefor easy and rapid assembly.


The structure has been designed to withstand snow, wind and seismicloads in accordance with the latest Eurocodes and is adaptable to enablesimilar buildings to be produced in other locations. Everything fromindividual sections to the global structure has been optimised using finiteelement analysis to design the most efficient structure.

Type of FRPused

Pultrusions


Durability


Bolted

Furtherinformation

CETEC Consultancy LimitedCoopers House The Horsefair Romsey Hampshire SO51 8JZ

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Spherical FRP Radomes

Description Self-supporting FRP structures using glass and/or Kevlar reinforcedsandwich panels.

Application type RadomeWhere FRPsused and why

The structures are designed as monocoque shells without any internalframework and are transparent to radar. The radomes have been designedfor use in remote locations, such as high altitude locations in the NorthCape of Norway with design wind speeds up to 120m/s (270 mph) at–50°C!


ExposedVery high wind and snow loadsSeismic loads

Geometry ofFRP

Spherical

Type of FRPused

Glass and Kevlar fibres, foam cores


Transparent to radardurability


Very good


Bolted joints

Furtherinformation


59


Simulator Dome

Description Dome for use for flight training theatresApplication type Dome; special structuresWhere FRPs usedand why selected

FRPs were used due to their ease of construction and assembly, andlightweight nature, in preference to conventional building materials.


Internal location

Geometry of FRP Spherical shapeType of FRP used Hand-lay manufacturing technique, using CSM FRP materials.Specialrequirements ofFRP

Cost; durability; fire retardant


Bolted

Further information Many other sizes of dome available.

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Large GRP Structural Frame

Description This is one of the largest structures produced from pultruded GRP sectionsin the world. It was built in the UK for a client in the Middle East andsupports extensive electrical equipment.

Application type StructureWhere FRPsused and why

For electrical reasons the whole structure needed to be non-conductiveeven including the fasteners. The structure is produced from GRPpultruded beams, plates and angles, with bonded and bolted joints usingGRP studs and moulded nuts. Extensive finite element analysis wascarried out on the bonded joints to predict stresses in the adhesive andpultrusions.


Imposed dead loads

Geometry ofFRP

Frame

Type of FRPused

Glass fibre pultrusions


Electrically non-conductive


Very good


Bonded joints, glass fibre bolts

Furtherinformation


61


‘Tyne’ GRP Tank Cover

Description This highly efficient tank cover was developed as an in-house project byCETEC and manufactured under license.

Application type Tank coverWhere FRPsused and why

The self-supporting all GRP structure was designed for tanks up to 50mdiameter and optimised using computer modelling and finite elementanalysis.Several covers have been produced to this design, using polyester andvinyl ester resins and biaxial glass reinforcements. They have beendesigned to withstand full snow and wind loading in addition to internalpressures and vacuums.CETEC have recently undertaken the design for a new range of FRPcovers to cover tanks up to 64m diameter, for a client in the Middle East


ChemicalWind, snow, internal pressures and vacuum

Type of FRPused

Glass fibre


Chemical resistanceDurability, economy


Very good


Bolted joints

Furtherinformation

CETEC Consultancy LimitedCoopers House The Horsefair Romsey Hampshire SO51 8JZ

62


GRP Tank Covers at Worthing

Description Tank covers to contain odours and gasses emitted from the tanks.Application type Tank coversWhere FRPsused and why

GRP tank covers at Worthing water treatment works, to contain odoursand gasses emitted from the tanks. Main covers have a free span of 15mand have a highly optimised GRP structure, designed using finite elementanalysis.


ChemicalWind, imposed and snow loads

Geometry ofFRP

Monocoque

Type of FRPused

Glass fibre


Chemical resistance


Bolted

Furtherinformation


63


Wind Turbines

Description Wind turbine blades for on-shore or off-shore application. Sea basedturbines are large – the cost of building one large turbine is less thanbuilding 2 half the size.

Application type Wind turbine bladeWherecompositesused and why

FRP used for the 3 blades – usually glass fibre for smaller blades andcarbon fibre for larger blades. C-fibre is often used to strengthen thethickened blade root of GRP blades. C-fibre can be used to make CFRPblades up to 80m in length – offers high strength to weight ratio.


Blades can be used for on-shore or off-shore applications.Have to be able to withstand hurricanes and lightening strikes.FEA software used to calculate blade strength.


Continuous R&D being carried out to produce longer, stronger, lighter andmore cost effective blades.


Sandwich-based parts in longer blades in 3 layers – core usually balsa orsynthetic foam – an inner shell and an outer shell.


Glass fibre and/or carbon fibre woven or stitched fabric pre-preg.Vacuum infusion process.


High stiffness, light weight, durable.


Blades have to withstand 20 years in service.


Mechanical fixing at root.

Furtherinformation

BRE

64


References

1. Cripps A, CIRIA report C564 ‘Fibre-reinforced polymer composites in construction’, London 2002.2. Kendall DK, ‘Engineering properties of FRP materials’, NGCC course, Institution of Structural

Engineers, December 2002, also http://www.ngcc.org.uk/3. Halliwell SM, BRE report BR405 ‘Polymer composites in construction’ CRC, 2000.4. http://www.npl.co.uk/cog/5. Quinn J, ‘Design with FRP’, NGCC course, Institution of Structural Engineers, December 2002,

also http://www.ngcc.org.uk/6. Halliwell SM, BRE report ‘ Long-term performance in service of FRPs in construction’, CRC 2003.

Further reading

Properties and designQuinn J, Composites Design Manual, 2nd edition, James Quinn Associates Ltd, Liverpool, 1998.Hollaway L, BPF Handbook of Polymer Composites for Engineers, London, 1994.

BridgesCadei J and Stratford T, The design, construction and in-service performance of the all-compositeAberfeldy footbridge. In "Advanced polymer composites for structural applications" Thomas Telford,London, 2002.

Daniel R.A. A bridge of pultruded sections for pedestrians and theEnvironment Proceedings of the 6th World Pultrusion Conference "A StrongerProfile for the Future", EPTA, Prague, 3-5 April 2002.

A Look at the World's Composite Bridges: Charting the Evolution of Bridge Engineering Using FRPComposites Market Development Alliance, SPI Composites Institute, New York, 1998.

Aref AJ and Alampalli S, Vibration characteristics of a fiber-reinforced polymer bridge superstructureComposite Structures: 2001, Vol. 52, Iss. 3-4, pp. 467-474

Rizkalla, S, Advanced Composite Materials for Bridges Fifth International Conference on Short andMedium Span Bridges, July 13-16, 1998, Calgary, Alberta.

Advanced Composite Materials in Bridges and Structures, Proceedings of the First InternationalConference, Quebec, Canada 1992. Edited by K.W. Neale and P. Labossiere. The Canadian Societyfor Civil Engineering

Bridge decksHodgson J, Luke S, Canning L, Development Of An Advanced Composite Decking System For New-Build, Structural Faults and Repairs 2001.

Canning L, Hodgson J, Jarman A , Karuna K, Luke S, The Analysis, Design and Optimisation of anAdvanced Composite Bridge Deck, ACIC 2002, 15-17 April 2002, Southampton, UK.

Davalos JF, Qiao P, Frank Xu X, Robinson J, Barth KE, Modelling and characterisation of fiber-reinforced plastic honeycomb sandwich panels for highway bridge applications, CompositeStructures: 2001, Vol. 52, Iss. 3-4, pp. 441-452

Hassan, T., Abdelrahman, A., Tadros, G., and Rizkalla, S., Design Guidelines for Bridge Deck SlabsReinforced by CFRP and GFRP. Bridge Engineering Conference 2000, Sharm El-Sheikh, Egypt,March 26 to 30, Vol. 1, pp. 259-270.

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Williams, B., Shehata, E., Church, K., Stewart, D., and Rizkalla, S., GFRP Modular Bridge Decks,World Wise '99, Winnipeg, MB, Canada, December 6 to 8.

Bridge enclosuresRichard Irving, Strongwell, Bridge Enclosure Reporthttp://www.polymercomposites.co.uk/bridgeenclosures

Airport fencingInternational Standards and Recommended Practices – Aerodromes – Annex 14, Vol. 1, 2nd Edition,July 1995.

Civil Aviation Authority (CAA) (UK): http://www.caa.co.uk/PilesIskander, M. G., Hassan, M., State of the practice review in FRP Composite Piling, (1998) Journal ofComposites in Construction , ASCE, 2(3) 116-120

Mayer, M.H., et al., Composite fender and sheet piles in marine front systems(1996) Proc. Fibre Composites in Infrastructure, Dept Civil Eng Mech, University of Arizona, Tucson665-675.

Ashford SA, La Jolla and Jakrapiyanun W, , Driveability of Glass FRP Composite Piling, Journal ofComposites for Construction, Vol 5, No.1, February 2001, pp. 58-60

Han, J. and Frost J.D., Load-Deflection response of transversely isotropic piles under lateral loads(2000) Int. J. Numer. Anal.Meth.Geomech. 24:509-529

Hassan M, and Iskander M G, Accelerated degradation of recycled plastic piling in aggressive soils,Journal of Composites in Construction vol 5 issue 3 pp 179-187, 2001.

Heinz, R. (1993), Plastic Piling, Civil Engineering , Apr. 63-65 (review of composite plastic/steel pilesfor marine structures with examples)

Refurbishment/strengtheningHollaway, L.C. and Leeming, M.B, Strengthening of reinforced concrete structures (The ROBUSTbook), 1999, Woodhead Publishing, Cambridge, England

Luke, S., Strengthening of structures with carbon fibre plates - case histories for Hythe Bridge, Oxfordand Qafco Prill Tower, Qatar, Network Group for Composites in Construction First AnnualConference, BRE, Watford, England, 30-31 October 2001

Ballinger, C. A., Strengthening of Engineering Structures with Carbon Fiber Reinforced Plastics - AnOverview of History and Current Worldwide Usage International SAMPE Symposium and Exhibition1997 p927-932

Saadatmanesh, H., Ehsani M.R. and Limin J, Seismic Strengthening of Circular Bridge Pier Modelswith Fiber Composites, ACI Structural Journal nov/dec 1996 p639-647

Gentile C, Svecova W, Salzberg W, Rizkalla S H., FRP for Flexural Strengthening of Timber BridgeBeams, International Conference on Advanced Engineered Wood Composites, Bar Harbour, Maine,5-8 July 1999. p 29-30

Dier A F, Strengthening of Cast Iron Struts, Carbon Fibre Composites for Structural Upgrade and LifeExtension, ICE Seminar 11th May 2000

Moy SSJ (Ed), FRP Composites - life extension and strengthening of metallic structures, ThomasTelford, ISBN 0 7277 3009 6, 2001.

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Advanced Polymer Composites for Structural Applications, Proceedings of ACIC 2002(http://www.cosacnet.soton.ac.uk/), Thomas Telford, London, 2002

Hill P S, Smith S and Barnes F J, Use of high-modulus carbon fibres for reinforcement of cast-ironcompression struts within London Underground: project details. Conference on Composites andPlastics in Construction, Nov 1999, BRE, Watford, UK RAPRA Technology, Shawbury, Shrewsbury,UK, paper 16 1-6

Delpak, R, Shih, J. K. C., Andreou, E., Hu, C. W. and Tann, D. B. Thermographic blister detection inFRP strengthened RC elements and degradation effects on section performance. In "FRPComposites in Civil Engineering", Elsevier, pp1135-1142, 2001.

Strengthening metallic structures using externally bonded fibre reinforced polymersCIRIA report RP645, 2003.

Design guidance for strengthening concrete structures using fibre composite materials, TechnicalReport 55, The Concrete Society, UK, 2000.

FRP composites - Life extension and strengthening of metallic structuresICE design and practice guides (2001) Thomas Telford, UK

International Technology Research Institutehttp://wtec.org/loyola/compce/toc.htm

ConFibreCretehttp://www.shef.ac.uk/~tmrnet/

FRPRCS-5 Conference (5th International Conference on Fibre Reinforced Plastics for ReinforcedConcrete Structures )Cambridge, July 16th-18th, 2001http://www-civ.eng.cam.ac.uk/frprcs5/proceedings.htm

Wind turbinesRenewable Energy World Online: http://www.jxj.com/magsandj/rewOffshore Wind Energy in Europe: http://www.offshorewindenergy.org/The British Wind Energy Association (BWEA): http://www.britishwindenergy.co.uk/Institute for Wind Technology, University of Delft: http://www.windenergy.citg.tudelft.nl/

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Glossary

These terms are frequently used in the reinforced plastics and allied industries

Ablative: material that absorbs heat through decomposition process called pyrolysis at or near theexposed surface

Accelerator: accelerates cure of a resin

Additives: the term used for a large number of specialist chemicals which are added toresins/compounds to impart specific properties, for example, flame retardancy, and UV resistance

Adhesive: substance applied o mating surfaces to bond them together by surface attachment. Anadhesive can be in liquid, film or paste form

Aramid: high-strength, high-stiffness aromatic polyamide fibres

Aspect ratio: the length/diameter ratio of a fibre

Blister, blistering: undesirable raised areas in a moulded part caused by local internal pressure, dueusually to rapped air, volatile reaction by-products or water entering by osmosis

Bulk moulding compound (BMC): polyester resin/glass fibre premix, for injection or transfermoulding, also known as dough moulding compound (DMC)

Carbon fibre: reinforcing fibre known for its light weight, high strength and high stiffness.

Catalyst (also called hardener): a chemical compound (usually an organic peroxide) which initiatespolymerisation of a resin

Chlorinated paraffins: flame-retardant additives for polyester resins

Chopped strands: short strands cut from continuous filament strands of reinforcing fibre, not heldtogether by any means

Coefficient of thermal expansion: a material’s fractional change in length corresponding to for agiven unit change in temperature

Composite: a material made up of resin and reinforcement (usually fibre)

Compression strength: the crushing load at failure of a material, divided by cross-sectional area ofthe specimen

Contact moulding: moulding of fibre-reinforced resins without application of external pressure

Core: in sandwich construction, the central component to which inner and outer skins are attached.Foam, honeycomb and wood are all commonly used core materials

Corrosion resistance: the ability of a material to withstand contact with ambient natural factorswithout degradation or change in properties. For composites, corrosion can cause crazing

Coupling agent: a substance, which promotes or establishes a stronger bond at the resinmatrix/reinforcement interface

Cracking: actual separation of moulded material, visible on opposite surfaces of a part ad extendingthrough the thickness (fracture)

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Crazing: fine cracks, which may extend in a network on or under the surface of a moulded part

Cure: the process of hardening of a thermosetting resin (by cross-linking of the molecular structure),under the influence of heat

Curing agents: chemical compounds used to cure thermosetting resins

Curing time: the time taken for a resin to cure to its full extent

Delamination: splitting, physical separation or loss of bond along the plane of layers of a laminatedmaterial

Direct roving: roving produced by winding a large and determined number of filaments direct from abushing

Dough moulding compound (DMC): polyester/resin fibre premix, for injection or transfer moulding,also known as bulk moulding compound (BMC)

Fibre: a unit of matter of relatively short length, characterised by a high ratio of length to thickness ordiameter

Filament: a single textile element of small diameter and very long length considered as continuous

Filler: material (usually low cost) added to a resin to extend it, or give special properties

Finishing: application of coupling agent to textile reinforcements to improve the fibre/resin bond

Flexural strength: the strength of a material in bending expressed as the stress if a bent test sampleat the instant of failure.

Flow: the movement of a resinous material, thermosetting or thermoplastic, under pressure, to fill allparts of a closed mould

Fracture: cracks, crazing or delamination resulting from physical damage.

Gate: the opening through which a moulding compound is injected into a closed mould; the size,geometry and positioning of the gate can strongly influence properties of the finished moulding

Gel: the state of a resin, which has set to a jelly-like consistency

Gelcoat: a thin layer of unreinforced resin on the outer surface of a reinforced resin moulding; it hidesthe fibre pattern of the reinforcement, protects the resin/reinforcement bond, gives smooth externalfinish and can also provide special properties; it is usually pigmented

Glass fibre: reinforcing fibre made by drawing molten glass through bushings. The predominantreinforcement for polymer composites, it is known for its good strength, processability and low cost.

Hardener: see catalyst

HET acid anhydride: saturated dicarboxylic acid anhydride, containing chlorine

Honeycomb: light weight cellular structure made from either metallic sheet materials or non-metallicmaterials and formed into hexagonal nested cells, similar in appearance to the cross-section of abeehive

Hybrid: a resin or reinforcement made from two or more different polymers or reinforcement materials

69


Impact strength: a material’s ability to withstand shock loading as measured by fracturing aspecimen

Impregnation: saturation of reinforcement with liquid resin

In-mould coating (IMC): a process used with SMC (and recently developed also for thermoplastics)in which a liquid/melt coating layer is applied to the exterior of a moulding while still in the mould, aspart of the moulding cycle

Interface: the contact area between reinforcement and resin

Laminate: the structure resulting from bonding multiple plies of reinforcing fibre or fabric

Lay-up: a resin-impregnated reinforcement in the mould, prior to polymerisation

Mat: a widely used sheet-type reinforcement made up of filaments, staple fibres or strands, cut oruncut, oriented or random, lightly bonded together

Monomer: a compound containing a reactive double bond, capable of polymerising

Polyester: usual term for an unsaturated polyester resin

Polymer: a long-chain molecule, consisting of many repeat units

Porosity: numerous air pockets or voids in a moulded product

Post-cure: application of external heat to bring a resin to a stable state of cure in the shortestpossible time

Preform: reinforcement pre-shaped to the general geometry of the intended moulded part; it is usedon more complex and deep-draw mouldings, to optimise distribution and orientation of fibres

Premix: a moulding compound prepared prior to, and apart from, the moulding operation, containingall components necessary for moulding

Pre-preg: a factory-made combination of reactive resins and reinforcing fibres, plus other necessaryadditive chemicals, ready to be moulded

Reactive resins: liquid resins which can be cured by catalysts and hardeners to form solid materials

Release agent: a substance which prevents a moulding from sticking to the mould surface; it may bea chemical compound or a solid material such as a cellulose or plastics film

Reinforcement: key element added to resin (matrix) to provide the required properties; ranges fromshort fibres and continuous fibres through complex textile forms

Resin: polymer with indefinite and often high molecular weight and a softening or melting range thatexhibits a tendency to flow when subjected to stress. As composite matrices, resins bind togetherreinforcement fibres

Resin transfer moulding (RTM): a moulding process in which catalysed resin is injected into aclosed mould already containing the pre-formed reinforcement

Roving: endless glass fibre bundles; a collection of parallel strands (assembled roving) or parallelfilaments (direct roving) assembled without intentional twist

Sandwich structure: composite composed of lightweight core material to which two relatively thin,dense, high strength, functional or decorative skins are adhered

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Sheet moulding compound (SMC): a flat pre-preg material, comprising thickened resin, glass fibreand fillers, covered on both sides with polyethylene or nylon film, ready for press-moulding

Size: a coating applied to glass fibres or filaments during manufacture, to improve handling andprotect from abrasion

Strand: an assembly of parallel filaments simultaneously produced and lightly bonded

Thermoplastic: a plastic, which softens each time it is heated

Thermoset: a plastic which flows and then sets permanently on first heating, as s result of setting upa three-dimensional cross-linked molecular structure, and subsequently will not soften or dissolve

Thick moulding compound (TMC): a compound similar to BMC, but continuously produced in sheetform with a thickness of 25mm or more

Void: a pocket of gas or air trapped in a laminate or moulding

Wet-out: complete wetting/saturation of a fibrous surface with a liquid resin

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Effective use of fibre reinforced polymermaterials in construction

BRE Bookshop

151 Rosebery Avenue, London,

FB8

ISBN 1 86081 683 5

Foundation for tThe Foundation foEngland and WaleFor further informaT + 44 (0) 1923 6


The aim of this state-of-the-art report is to present information to enable theeffective specification and application of fibre reinforced polymers (FRPs) inconstruction. It will be of particular interest to those with little previousknowledge of fibre reinforced materials, or their application in construction.The report gives a brief review of design and specification considerations whichmay lead to the choice of FRPs, outlines the key benefits of using FRPs forcertain applications, and details case studies illustrating best practice in the useof FRP components. A comprehensive reference and further reading list is alsogiven.

EC1R 4GB

he Built Environmentr the Built Environment is a Company Limited by Guarantee incorporated in s (no 3282856) and registered as a charity (no 1092193)tion contact the FBE secretary John Burdett, at BRE, Garston, Watford WD25 9XX64598, F + 44 (0) 1923 664089, E [email protected], http://www.fbe.org.uk