STEEL BRIDGE- CONSTRUCTION EQUIPMENTS AND METHODS

CONSTRUTION TECHNIQUES

Through truss bridge Composite bridge Over truss bridge Stayed bridge

THROUGH TRUSS BRIDGE

The easiest construction technique is in situ during the dry season, over causeway and culverts. We advise too much camber, leaving gaps in the top chord, which close when the causeway is removed

THROUGH TRUSS BRIDGE

Truss built in situ on home bank, then craned to half way. The entire bridge is then lifted into position with large cranes on both banks. Good for small, light bridges when large cranes are also available.

THROUGH TRUSS BRIDGE

Roller launch method. The bridge is constructed in situ and then jacked across the span using rollers and cantilever technique. A temporary nose section is used this is removed once the bridge is in place.

COMPOSITE BRIDGE

The easiest construction technique is in situ during the dry season, over causeway and culverts.

COMPOSITE BRIDGE

beams can often be lifted in, single or joined in pairs, by one crane from one side.

COMPOSITE BRIDGE

Once in position it simply remains to bolt in remainder of diaphragms, add flashings, add rebar and then pour concrete finish and cure.

beams can be joined in pairs then roller launched or cantilever launched; then jacked down into place.

OVER TRUSS BRIDGE

The easiest construction technique is in situ during the dry season, over causeway and culverts.

OVER TRUSS BRIDGE2 -3 beams can often be lifted in, singly or joined in pairs, by cranes on each bank.

OVER TRUSS BRIDGE

Roller launch method. The bridge is constructed in situ and then jacked across the span using rollers and cantilever technique.

OVER TRUSS BRIDGE

A temporary nose section is used this is removed once the bridge is in position.

The bridge is then simply lowered into place.

STAYED BRIDGE

1. Build abutments, counter weight and ground struts.2. Erect deck beam, transoms, rail.3. Erect tower.4. Erect home stays.

STAYED BRIDGE

5. Erect rail system.

6. Erect gantry crane.7. Erect new deck beams using gantry, with transoms.8. Erect bridge stays.9. Extend gantry rails.

STAYED BRIDGE

10. Extend deck beams and transoms.

11. Erect further bridge stays

STAYED BRIDGE

12. Continue process

13. Erect simple supported link span to far bank or to far bridge.

STEEL BRIDGE TYPES

Steel Beam Bridge Over truss bridge Steel bowstring girder bridge Steel cable stayed bridge Composite bridges

STEEL BEAM BRIDGE

Beam - Structurally, the simplest type of bridge Relatively short span - 5m to 30m, although become

more expensive after about 15m Can be any width, and are easily widened by simply

adding more beams and deck Frequently used in pedestrian bridges and for highway

overpasses and flyovers Footpaths can be built on both sides Can be built one or two beams at a time, often by direct

craneage or by cantilever launch Longer spans require supporting pillars, making them

unsuitable if lots of space is required beneath

STEEL BEAM BRIDGES

OVER TRUSS BRIDGE

20m - 100m span Very similar to simple beam bridges, but the beams are

replaced with trusses, making them much deeper and lighter

Easily widened with additional trusses More complex to build Depth is typically 12% of the span, so the roadway has

to be higher if the bridge is to have sufficient clearance over water, railways etc.

OVER TRUSS BRIDGES

STEEL BOWSTRING GIRDER BRIDGE Much like a through-truss bridge,

except that the truss can be a higher, deeper segmental curve

Suitable for 50m - 150m spans Attractive Can be constructed on less robust

foundations e.g. atop elevated piers/areas of uneven soil

Can be pre-fabricated offsite and hauled or lifted into place

STEEL CABLE STAYED BRIDGE Although expensive, stayed bridges may be the only viable alternative when:

there is no access to the gap, on which temporary or permanent piers could be built; when there is no staright level run up to the gap which would permit cantilever launching; when the span is too big for regular through truss bridges. And, in particular, one-tower bridges are useful if there is no good access to the far bank, as they can be built from one side only. But please note: you stll need enough space for the large counterweights, which may need to be one fifth of the spann for a two tower bridge.

Long span (50m - 200m) Very strong, but also flexible Economical as allow a slender and lighter structure which is still able to span

large distances Light weight is an advantage in earthquake-prone areas Modern and simple design makes attractive and distinct landmarks Easy to build in segments where in-situ construction or cantilever launch on

rollers is not possible. This requires substantial piers and large counterweights

Less suitable for very windy places due to its lightness

STEEL CABLE STAYED BRIDGE

STEEL PEDESTRIAN FOOT BRIDGE

Designed for pedestrians and cyclists rather than vehicular traffic Useful for crossing water/railways where there are no road bridges Allow safe crossing of busy roads Can also be used for walkways between buildings or in car parks Must be at least 1.2m wide (unless designed for maintenance work

only), but can be as wide as needed Can be the simplest beam type with hand rails, or a through-truss

with hand rails fixed to the two trusses Through-trusses useful if the bridge is to have overhead cover and

sides with cladding or mesh (essential for road or rail crossings) Usually require stairways and ramps

STEEL PEDESTRIAN FOOT BRIDGE

COMPOSITE BRIDGE 'Composite' means that the steel structure of a bridge is

fixed to the concrete structure of the deck so that the steel and concrete act together, so reducing deflections and increasing strength. This is done using 'shear connectors' fixed to the steel beams and then embedded in the concrete. Shear connectors can be welded on, perhaps using a 'stud welder', or better still on export work, by fixing nuts and bolts.

Shear connectors, correctly spaced to resist the loads, make the concrete work 'compositely' with the steel.

Usually the steel carries its own weight and that of the wet concrete. But when the concrete is 'cured' and has acquired its full strength, then all future loads (traffic, surfacing, wind, water, pressure, seismic loads) are shared by the steel/concrete composite.

The concrete is good in compression, while the steel is good in tension and compression. This composite bridge design can be used in the following ways:

COMPOSITE BRIDGE

COMPOSITE BRIDGE

Simple Beam Bridges - On short spans (8m, 10m, 15m and then more expensively up to 24m), bridges can be made from a number of beams under the roadway straight across the gap. The bridges benefit the most from composite action.

Over Truss Bridges - These are similar to simple beam bridges but for longer spans, from say 18m up to approx 100m. The deck is still on top of the steel structure, so goes into compression when deflected.

Transoms on any type of bridge - Transoms go from side to side across a bridge and carry the deck loads to strong steel frames on either side. This is usually on 'open top' through truss bridges or 'closed-top' through truss bridges.

COMPOSITE BRIDGE

COMPOSITE BRIDGE

Decking - In a normal steel building the concrete can act together with steel decking, the steel decking taking the place of the regular steel reinforcing bars within the concrete. However in a bridge, the underside of the decking is liable to corrode over time, so is not counted as part of the reinforcement. It is just used as 'lost formwork'.

EQUIPMENTS USED

launching equipment straddle carriers and low bed carriers gantry cranes over head cranes form travelers movable scaffolding systems special equipment for post tensioning

GANTRY CRANES

GANTRY CRANES: Gantry cranes,bridge cranes, and overhead cranes,

are all types of cranes which lift objects by a hoist which is fitted in a hoist trolley and can move horizontally on a rail or pair of rails fitted under a beam. An overhead travelling crane, also known as an overhead crane or as a suspended crane, has the ends of the supporting beam resting on wheels running on rails at high level, usually on the parallel side walls of a factory or similar large industrial building, so that the whole crane can move the length of the building, while the hoist can be moved to and from across the width of the building. A gantry crane or portal crane has a similar mechanism supported by uprights, usually with wheels at the foot of the uprights allowing the whole crane to traverse. Overhead crane and gantry crane are particularly suited to lifting very heavy objects

STRADDLE CARRIER

A straddle carrier is a non road going vehicle for use in port terminals and intermodal yards used for stacking and moving ISO standard containers. Straddles pick and carry containers while straddling their load and connecting to the top lifting points via a container spreader. These machines have the ability to stack containers up to 4 high. These are capable of relatively low speeds (up to 30 km/h) with a laden container. The workers that use this machinery sit at the very top seated facing the middle as they can see behind them and in front of them. Straddle carriers can lift up to 60 tons which equals up to 2 full containers.

STRADDLE CARRIER

FORM TRAVELER

FORM TRAVELER

FORM TRAVELER

The form traveler is a large piece of equipment that, once assembled and attached to the edge of the bridge deck, will allow the bridge deck to be built over the inlet. The process can be complex, but it is as simple as the traveler locking onto the completed deck area, a new deck area is poured in front of it, and the traveler moves to that edge to begin the process again. This continues until both sides meet in the middle.

The form traveler that is going to be used on the bridge was designed and built specifically for this project. When the bridge is complete, the form traveler will be disassembled and recycled. It could not be used for another project.

MOVING SCAFFOLDING SYSTEMS

MOVING SCAFFOLDING SYSTEMS Both the overhead and the underslung MSS consist of a self

supporting structure combined with a project specific exterior formwork. The MSS is easily adaptable to cross sections ranging from double T to single box and span lengths from 20m to 70m.

Special design solutions from some of our most challenging projects:

Separation of the Main structure into three sections ( Front Nose – Main Girder – Rear Nose ) and design of a unique hinged connection between the parts has made it possible to build superstructures  with a horizontal radius as small as 250m.

A rebar trolley and portal crane can be integrated onto the MSS system for prefabricated reinforcement cages.

Bracket moving system. Placement of concrete PVMPS and cranes onto the MSS system. This system is most suitable for bridges over waterways,

bridges with high piers as well as for site conditions where access for external cranes is difficult or impossible.

STEEL BRIDGE CONSTRUCTION

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STEEL BRIDGE CONSTRUCTION.mp4

ADVANTAGES OF STEEL BRIDGE

Steel offers many advantages to the bridge builder, not only from the material itself, but also from its broad architectural possibilities. The following are some of the advantages that steel can offer.

High quality material Speed of construction Versatility Modification and repair Recycling Durability Aesthetics

HIGH STRENGTH TO WEIGHT RATIO The high strength to weight ratio of steel minimises

substructures costs, which is particularly beneficial in poor ground conditions. Minimum self-weight is also an important factor in trasnporting and handling components. In addition, it facilitates very shallow construction depths, which overcome problems with headroom and flood clearances, and minimises the length of approach ramps.

The Newark Dyke rail bridge, shown on the left, comprises a 77m span bowstring truss with 820 tonnes of S355 steel. The selection of steel was made because of its high strength to weight ratio, which permitted a shallow construction depth and minimised the total weight to be slid into position. The low self-weight also minimised foundation works adjacent to the existing rail line.

This bridge was the first UK steel bridge to be designed for the next generation of 225 Km/hr trains

HIGH QUALITY MATERIAL

Steel is a high quality material, which is readily available worldwide in various certified grades, shapes and sizes. The testing regime carried out at the steel mills should give confidence to all clients and engineers who specify steel for their project.

Prefabrication in controlled shop conditions leads to high quality work at minimum cost. The quality control extends from the material itself and follows on through the processes of cutting, drilling, welding, fit-up and painting.

SPEED OF CONSTRUCTION

The prefabrication of components means that construction time on site in hostile environments is minimised. The speed of steel bridge construction reduces the durations of rail possessions and road closures, which minimises disruption to the public using those networks. The light-weight nature of steel permits the erection of large components, and in special circumstances complete bridges may be installed overnight.

For example, the Hallen Bridge, is a 500T truss bridge that carries a single-track railway over the M5 near Bristol. Sections were shop-fabricated and transported to site where the bridge was fully assembled off line. The whole structure was then transported into position using multi-wheeled ‘Econofreight’ vehicles during an overnight closure of the M5.

VERSATILITY

Steel suits a range of construction methods and sequences. Installation may be by cranes, launching, slide-in techniques or transporters. Steel gives the Contractor flexibility in terms of erection sequence and programme. Components can be sized to suit access restrictions at the site, and once erected the steel girders provide a platform for subsequent operations.

MODIFICATION & REPAIR      Steel bridges are adaptable and can readily be altered for a

change in use. They can be widened to accommodate extra lanes of traffic, and strengthened to carry heavier traffic loads.

For example, the Tamar suspension bridge in Plymouth needed widening and strengthening due to increased traffic loads and volumes. The solution was to replace the concrete deck with a new lightweight steel one, and add steel cantilever sections. The result was that the widened 5-lane bridge was only 25 Tonnes heavier than the old 3-lane structure, and was able to accommodate 44 Tonne trucks.

MODIFICATION & REPAIR

Steel bridges can readily be repaired after accidental damage. The photograph (opposite) shows a steel composite bridge over the M5 near Weston that was struck by an over-height lorry. The outer girder was deformed by 400mm over a length of 2.5m, and initially considered  “Beyond repair”. A costly beam replacement scheme would have taken many months and caused severe disruption to the motorway. 

However, a heat treatment technique, based on the theory of restrained expansion, was proposed by a UK fabricator as a more economic and less disruptive solution. Heat was applied locally in a carefully controlled manner, and over a period of only two days the girder was straightened to within 18mm of its original line. No external forces were applied to bring the girder back on line, and the contract was completed for considerably less than the beam replacement option.

RECYCLING

Steel is a ‘sustainable’ material. When a steel bridge reaches the end of its useful life, the girders can be cut into manageable sizes to facilitate demolition, and returned to steelworks for recycling.

DURABILITY

Steel bridges now have a proven life span extending to well over 100 years. The potential durability of steel may be summarised in the following quote by a Mr J.A.Waddell in 1921:

DURABILITY (CONTD)

“The life of a metal bridge that is scientifically designed, honestly and carefully built, and not seriously overloaded, if properly maintained, is indefinitely long.”

Steel has a predictable life, as the structural elements are visible and accessible. Any signs of deterioration are readily apparent, without the need for extensive investigations. Corrosion is a surface effect, which rarely compromises the structural integrity of a bridge, and any problems may be swiftly addressed by repainting the affected areas. In addition, the latest coatings are anticipated to last well beyond 30 years before requiring major maintenance.   

An alternative form of corrosion protection is the use of weathering steel, as on the Westgate bridges in Gloucester, as shown above left.

AESTHETICS Steel has broad architectural possibilities.  Steel bridges can

be made to look light or heavy, and can be sculptured to any shape or form. The high surface quality of steel creates clean sharp lines and allows attention to detail. Modern fabrication methods have removed restrictions on curvature in both plan and elevation. The painting of steelwork introduces colour and contrast, and repainting can change or refresh the appearance of the bridge to appear as new.

Bridges are an essential feature of a countries infrastructure and landscape. Few man made structures combine the technical with the aesthetics in such an evocative way.

This arch-truss bridge connects Incheon international airport to Seoul in Korea (opposite), and has a main span of 540m. Steel was considered the only option for such a high profile site

ADVANTAGES OF STEEL CONSTRUCTION

VALUE OF MONEY

FLEXIBILITY SPEED SAFETY

Steel is an-economic construction material

In design Pre-engineered structural steel solutions

During design and fabrication

Continuous development in steel frame technology

During Construction

Short construction period

During construction

Built in a short construction period

In use

Savings throughout the project

ADVANTAGES OF STEEL CONSTRUCITON

QUALITY AND RELIABILITY

PROFESSIONAL APPROACH

SUSTAINABILITY

PRESTIGE

During the design process

Competent and responsible steel contractors

At the construction stage

Aesthetically pleasing

During construction

Advice and support

After completion A structure that reflects the clients

Relating to cost Integrated electronic transfer of information

Environmentally friendly

After occupation