Masonry details

Masonry detailsKonrad Zilch, Martin Schiitz

Walls are not only enclosing, decorative ele-ments. They also have major structural andbuilding science functions to perform. In termsof structure, we distinguish between load-bearing, stiffening and non-loadbearing walls.Loadbearing walls carry vertical and horizontalloads and transfer these to the subsoil. Stiffen-ing walls in the form of shear walls guaranteethe load-carrying capacity of the building, andin the form of crosswalls or return walls providelateral support to prevent the buckling of load-bearing walls, Therefore, they are always con-sidered as loadbearing walls.Non-loadbearing walls generally only carrytheir own weight and have merely an enclosingfunction. They are not.called upon to assist instabil izing the building or to provide support toother loadbearing walls. However, non-load-bearing walls must be able to transfer horizon-tal loads perpendicular to the face of the wallto loadbearing members.The building science functions of the wall arethermal (insulation and heat storage), soundinsulation, fire protection and protection againstdriving rain. Special requirements that mayneed to be fulfilled by a wall are protectionagainst water (both pressurized and non-pres-surized), e.g. basement walls, and securityfunctions (external walls of certain buildings),e.g. banks, military establishments. The manydemands placed on walls can.lead to conflictsof interest, which can be solved only throughcareful detailing and selection of materials.Basically, the following criteria apply whenchoosing the type of masonry:For facing work the decisive factors are thesurface finish and the strength of the units ortheir frost resistance and resistance tomechanical damage and saturation. Externalwalls, on the other hand, are primarily chosendepending on thermal requirements, while forinternal walls it is sound insulation and load-carrying capacity that influence our choice,When selecting the type of wall and type ofmaterial, other aspects such as weight, oppor-tunities for rationalization on site and the costsof materials and construction have to be con-s idered 132, 71, 91, 41, 1611.

External walls

External walls must be designed and built sothat they withstand driving rain. This require-ment is mandatory for all buildings occupiedmore or less permanently by people. Externalwalls are divided into single- and twin-leafwalls. The single-leaf wall consists of just onewall of masonry, whereas the twin-leaf wallconsists of two parallel walls up to 150 mmapart, joined together with wall ties. As a rule,only the inner leaf is loadbearing. From a ther-mal point of view, external walls are dividedinto single- and double- or multi- layer wall con-structions. The masonry of a single-layer wall islike that of a single-leaf wall, but apart fromcarrying the loads also fulfils the necessarythermal requirements. The double- or multi-layer wall is a loadbearing construction but themasonry fulfils only part of the thermal require-ments. The other layers are made from mate-rials that generally only contribute to the thermalinsulation, e.g. single-leaf external wall withthermal insulation plastering system.

Single-leaf external walls

The design of single-leaf external walls is thesedays determined mainly by thermal require-ments. According to DIN '1053 paft 1, the mini-mum thickness for a single-leaf external wall is1 15 mm. The wall constructions commonly inuse are i l lustrated infig.2.4.1. The regulationson thermal insulation have led to the develop-ment of different solutions to comply with thoseregulations. So the single-leaf monolithic exter-nal wall with ever better thermal insulation val-ues for the masonry and mortar will continue tobe favoured for certain applications, And theuse of insulating plasters will also help tosecure the use of monolithic masonry. Addinga layer of insulation to the loadbearing masonryallows external walls to satisfy practically alldemands. Only in the case of curtain wallfacades do we have to consider the additionalheat losses via the wall ties between wall andfacade.

Pl astered si n g I eJ eaf external wal I sare built without additional layers of thermalinsulation and are provided with a coat of plas-ter on the inside and water-repellent renderingon the outside. The rendering prevents mois-ture from penetrating the masonry and sub-sequently freezing, and permits the use of :non-frost-resistant masonry units. In order tocomply with the strict thermal insulation requir:e-ments and, at the same time, avoid unjustifi-ably thick walls, which although satisfyingbuilding science demands are usually tooexpensive in terms of construction and con-sumption of valuable space. Such walls onlyuse masonry units with very good thermal insu-lation properlies (e.9. aerated lightweight clay,autoclaved aerated concrete, li ghtwei g ht hol-low concrete blocks, the formation of voids,cells and slots, masonry without mortar to theperpends) in conjunction with thermal insula-tion plasters or plastering systems.f al]]e 2.4.2 shows the thermal transmittancevalues that can be achieved for masonry 300.,and 365 mm thick, and how the thermal insula-tion can be improved by using a thermal insu-lation plaster.The use of thin-bed and lightweight modarsinstead of normal mortar together with large-,.format masonry units and laying without mortarto the perpends further reduces the thermal '

bridging effect of the mortar joints.The diagrams in fig. 2.4.3 show the influence oflength of unit and type of perpend as well asthickness of bed joint for normal, LM 36 and -LM 21 mortars. A medium-bed joint of LM 36 ispractically identical with the thin-bed joint. Theuse of lightweight or thin-bed modar represents,a marked imorovement in thermal insulationirrespective of the thermal conductivity of themasonry units.In walls with normal mortar, the thickness of thebed joint and the length of the unit with mortarto the perpends has a noticeable effect on thethermal conductivity of the masonry. Differ- ;ences within lightweight and thin-bed modarsmerely amount to the order of magnitude ofthe range of one thermal conductivity class.However', this can be important if, when deter-

122

i{

External walls

2.4.1 Forms of single-leaf external walls

t >240

Plasteredsingle-leafexternal wall

, > . 1 1 5 4 > 1 1 5.|f-f--

Singleleafexternal Single-leafexternalwall with thermal wall with curtain wallinsulationcomposite facadesyslem

Single-leafexternal Single-leaffacingwall with internal masonry with 20 mminsulation wall joint

> 1 1 5 115 2 > 175.t---.1+

2.4.2 fhermal transmittance values for sinole-leaf masonrvWall thick- Type of Rendering Design value for thermal conductivity of masonry [WmK]ness [mm] plaster 0.1 0 . 1 1 0 . 1 2 0 . 1 3 0 . 1 4 0 . 1 6 0 . 1 8

0.47 0.520.38 0.410.39 0.44o.33 0.36

0.360.310.30.26

300 LP 2WDP 4

366 LP 2WDP 4

0.39 0.410.33 0.340.33 0.350.28 0.3

0.31o.27o.26o.23

0.34o.29o.28o.24

mining characteristic values, the measured orcalculated result for the masonry being evalu-ated l ies on the threshold of a class [A.1, p.1 1 6 1 ,

Single-leaf external walls with thermal insula-tion composite systemsare.constructed from masonry units performingstructural and other functions but exhibiting rel-atively poor thermal insulation properties inconjunction with a thermally insulating coatingapplied to the external wall surface. This wallsystem is employed for new building work, aswell as for subsequently improving the thermalinsulation of existing masonry. The coatingconsists of three layers: bonding coat, thermalinsulation (hard polystyrene foam or mineralfibre batts) and a two-coat plaster finish com-prising reinforcing and final coats.Rail systems or dowels create an additional fix-ing to the substrate. The heat losses caused bythe thermal bridges formed by such mechani-cal f ixings are taken into account by increasingthe thermal transmittance values. However, thiseffect can be ignored when using thermallyootimized dowels.As the thermal insulation composite system isfully responsible for the thermal insulation func-tion, this type of wall is often referred to as a"thermoskin" and is used with masonry withrelatively low thermal insulation but high com-pressive strength (e.9. calcium sil icate mason-ry). This system results in relatively thin walls,which greatly benefits the total amount of inter-nal space available.In principle, this type of wall is an improvementon the thermal insulation plastering systembecause layers of thermal insulation with betterinsulation values are used instead of the olas-ter.As the thermal insulation composite systemdoes not satisfy the requirement for decreasingstrength of the layers from the inside to the out-side, the materials used in the three layersmust be compatible in order to avoid the nega-tive consequences (see "Plasters"). This isguaranteed by using complete systems. Never-theless, it should be noted that this type of wall

0 .10 0 .15 0 .20

Thermal conductivity of masonry [WmK]

0.10 0 .15 0 .20

Thermal conductivity of masonry [WmK]

External: 20 mm lightweight plaster (LP) or 40 mm thermal insulation plaster (WDP)lnternal: 10 mm lime-dvoslJm nlaster

2.43 fhermal conductivity of masonry in relation to thermal conductivity of masonry unit, type of mortar, thickness ofbed joint and length of unit

0.25 0.25

)<F

vc=c

6Eb'=Fol

ccoo

GEosF

YF

=Cl

C

6E

.>bl

!cooEEo

cF

12 mm bed jo int6 mm bed jointt l

NM

NM -a

LM 36:,/

LM 36'/

DIV v, _M t1

a LIV

'// ,/

/):'/

,/t I

t tl

t

Masonry details

2,4.4 Section through 375 mm single-leaf faced wall(sketch showing principle)

Outside

is vulnerable to mechanical damage. Apartfrom that, additional soft skins have anunfavourable effect on the sound insulationproperties of the masonry.Fire orotection reouirements must be observedwhen using flammable or not readily f lammablethermal insulation materials.

Single-leaf external walls with curtain wallfacadelf external walls made from non-frost-resistantmasonry units are not rendered, the externalwall can be protected against the weather anddamage by adding a weatherproof cladding tothe outside. This curtain wall can be attachedeither directly to the external wall or to externalinsulation, which is then protected by the venti-lated cuftain wall facade.The mechanical fixings for the curtain wallresult in additional heat losses which can bequite considerable.

Single-leaf external walls with internal insulationThe thermal insulation effect of a single-leafexternal wall can also be improved by attach-ing insulation made from hard polystyrenefoam or mineral fibre batts to the inside face.This type of wall is particularly suitable for therefurbishment of existing buildings withfacades worthy of preservation, and for thoserooms in new building work which are not per-manently heated (e.9. assembly halls). Owingto the loss of the heat storage effect of theexternal walls, rooms insulated internally arequickly heated and store less thermal energyafter the heating is switched off. Condensationproblems within the wall construction can be aproblem with absorbent masonry, particularlyat junctions between floors and partitions. Like-wise, the sound insulation of adjacent roomscan be impaired through flanking transmis-sions caused by unsuitable internal insulationsystems.

Single-leaf external walls without rendering(si n g le-leaf faced wal l)The decision to omit the rendering from anexternal wall, i.e. the facade masonry remainsexposed (facing brickwork etc.), depends onthe desired apoearance as well as local tradi-tions and experience. The main advantage offacing masonry - in single- or twin-leaf walls -is the low cost of maintenance.A single-leaf faced wall consists of an outerskin of frost-resistant, usually small-format, fac-ing or engineering bricks or calcium sil icatefacing bricks and a backing of, usually, non-frost-resistant masonry units. The use of differ-ent masonry. materials for the backing and thefacing work should be avoided because of thepossible differential deformation and the asso-ciated risk of cracking. Facing and backing arebonded together and together form the load-bearing cross-section, The permissible stresswhich may be used in the design is governed

by the lowest unit strength class used in the wall.Saturation and attack by frost is assumed toonly affect the outer masonry units in single-leaf faced walls. To avoid saturation of the back-ing masonry in regions with severe weather,every course of masonry should include at leasttwo rows of units of equal height separated bya 20 mm wide wall joint (offset in each courseto follow the bond) over the full height of thewall. This must be fi l led without voids usingwaterproof mortar or, better still, run in liquidwaterproof mortar course by course. By in-creasing the thickness of the wall joint from'10 mm to 20 mm, guaranteed by the full mortarfi l l ing, the minimum wall thickness becomes310 mm. This is due to the fact that a 240 mmthick wall would mean that the wall joint couldonly be formed in every second course and acontinuous moisture barrier the full height ofthe wall would not be possible (see fig. 2.4.4.).Thicknesses of 375 and 500 mm are alsofeasible.The joints in the exposed face - if flush point-ing is not carried out - should be raked out to adepth of 15 mm and properly pointed. Sub-sequent pointing has the advantage that pig-ments can be added to the pointing mortar tovary the appearance of the joints (see "Pointing").It is very difficult to fulfil the thermal insulationrequirements with single-leaf facing masonry.Therefore, these days facing masonry is almostexclusively built as pad of a twin-leaf masonrywal l .

Twin-leaf external walls

Twin-leaf masonry is increasingly being usedfor external walls to achieve the necessarythermal insulation. The various functions of awall are separated in this type of constructionand allocated to the individual leaves. Theinner leaf (backing masonry) provides a solidenclosure to the interior and carries the vedicaland horizontal loads. The outer leaf (facingmasonry or rendered outer leaf) determines ihevisual appearance and serves as protectionagainst the weather and mechanical damage.Any thermal insulation required is fixed againstthe whole of the outside face of the inner leaf.The outer skin uses non-efflorescent, frost-resistant solid masonry units. Perforated unitsare less suitable because they can becomeseverely saturated, which can be aggravatedby possible lack of care during pointing.We distinguish between cavity, partial-fill cav-ity, full{ill cavity and plaster-filled collar-jointed(see fig. 2.4.5).Only the thickness of the inner leaf (min.1 15 mm) may be considered in the structuralanalysis. When analysing the inner leaf accord-ing to the simplified method of analysis, thethickness of ' l{5 mm is only suitable for build-ings of no more of than two full storeys plus anattic; in addition, crosswalls must be providedfor stabilitv. The minimum thickness of the

Wall joint filledwithout voids

./tnsiae

20-ff

1 3 7 5 1-

2.4.5 Forms of twin-leaf external walls

Outside

Outer leal

MG ll (lla)

>90l_

't24

lns ide

Wall tieembedded> 5 0 m mWall tie withdr ip d isc

Cavity

lnner leaf

Internal plaster

> 9 0 1 6 0 < d < 1 5 O m m...].-....'.'.-..]T

PaftialJill cavity wall

LoadbearingleafAir space> 4 0 m m

Internal plaster

Wall tie withdr ip d isc

> 9 0 < 1 5 0 m m----T---->40

....]T

Full{ill cavity wall

Facingmasonry

MG ll (la)

> 1 5 0 1 I r < 1 5 0-

Plaster-f illed collar-jointed wall

Minimalair space

Plaster

lnner leaf

Wall tie

Cavity wall

E{ernal walls

outer leaf should be 90 mm for reasons of sta-bil i ty during construction.

SupporTing the outer leafThe weight of the outer leaf must be supportedon the loadbearing leaf. The complete outerleaf should be supported over its full length(e.9. on nibs projecting from the floors, on steelsections bolted on or cast in). lf the support isnon-continuous (e.9. separate brackets), everymasonry unit must be supported at both endsat the suppoft level.Using a metal angle as a support creates acontinuous thermal bridge which, in thearrangement shown in 'f i7.2.4.6, means anadditional heat flow to the outside of 0.1 5WmK [A.2] along the length of the angle.For support over two storeys this means anincrease in heat losses of AU = 0.025 WmrKcompared to a wall without such supports. Theinfluence of the support can be neglected foran outer leaf 12 m high. Support details whichcan no longer be inspected after being built inmust be permanently protected against corro-sion.Outer leaves 1 15 mm thick have oroved to beworthwhile in practice, Owing to their goodstability, these need to be supported onlyevery 12 m in'height. When supported at everysecond floor, a 1 15 mm outer leaf can projectbeyond its support by up to one third of itsthickness. Outer leaves less than 1 15 mm thickmust be supported every 6 m in height andmay not be built more than 20 m above groundlevel owing to their limited resistance to windloads, Buildings comprising no more than twofull storeys may include a triangular gable upto 4 m high without any additional support. lf a115 mm leaf is not provided with flush pointing,weakening due to subsequent raking out of thejoints must be taken into account.

Anchoring the outer leafThe outer leaf is to be anchored to the load-bearing inner leaf by means of wall ties to pre-vent it from overturning, buckling and bulgingas a result of unequal temperature changes. Inaddition, this anchoring serves to transfer thewind loads. As the wind generates both pres-sure and suction forces, the anchors must beable to resist tension and compression. Wallties must be of stainless steel to DIN 17440.Their shape and dimensions must be as giveninI tg.2.4.7.When the bonding of the loadbearing leaf andthe outer leaf coincide, then Z-shape ties maybe used. Otherwise the L-shaoe is more suit-able because this can be bent to suit. lf thebed joints of the two leaves are not in the sameplane or if the outer leaf is built at a later date,ties for subsequent fixing into the inner leaf ofmasonry are necessary.The use of such anchors is also recommendedwhen attaching an additional layer of thermalinsulation in order to ensure that the insulation

is pressed tightly against the outside face ofthe inner leaf.Wall ties shouid be soaced at max. 500 m ver-tically, max. 750 mm horizontally. In addition tothe requirements outl ined in table 2.4.8,Ihreeties per metre of edge length are requiredaround openings and at the corners of thebuilding as well as along movement joints andat the tops of outer leaves.The type, number and arrangement of ties incurved masonry or masonry with projectionsshould be specified, taking into account thedeformation due to, for example, wind and/ortemperature changes.'Table 2.4.10 shows the influence of wall t ies onheat transmission for a number of typical typesof wall. In cavity walls the ties are practicallyineffective as thermal bridges.The use of additional layers of insulation in thecavity increases the heat transmission by up to5% for optimum 150 mm thick cavity insulationand 5 mm thick wall t ies; these influences canbe ignored. Therefore, to comply with DIN4108 part 2, no analysis of the thermal bridgeeffect has to be carried out for minimum thermal insulation when using conventional formsof fixing, e.g. wire ties. When using l ightweightmortar, LM 36 is always required when wall tiesare to be built in. Other types of tie are permis-sible when they can accommodate min. 1.0 kNtension and compression at 1.0 mm slip pertie. The number of t ies must be increased if thisvalue cannot be guaranteed, Other types ofties (e.9. f lat steel) and dowelled fixings in themasonry are permissible when their service-ability is verified by a building authority certifi-cate.Wall t ies should be built in so that they cannotconvey moisture from the outer to the innerleaf. This is achieved by positioning the tieshorizontally and by fitting a plastic disc (dripdisc). The drip disc ensures that water pene-trating the outer leaf does not reach the ther-mal insulation or the loadbearing leaf, but isintercepted.

Ad d itional requirementsA damp proof course (dpc) should be includedat the bottom of the cavity between the leavesin order to protect the inner leaf and the tloorfrom moisture which penetrates the outer leafand collects at the base of the cavity. Thedamp proof course must be laid with a fall tothe outside within the cavity and horizontalunder the outer jeaf. The outer leaf must besupported in such a way that it cannot slip.To do this, place the first row of ties as low aspossible and ensure that the waterproofingcomplies with DIN 18195 part 4. The dampproof course should extend as far as the frontedge of the outer leaf and should continuemin. 150 mm up the inner leaf on a firring pieceand be fixed to this leaf (see 2.4.9).Openings for doors, windows etc. in the outerleaf are formed as transfer structures

2,4.6 Outer leaf support details

Facingmasonry

This jointsealed with

permanenlryelastic

Strips fordistributing

load

Continuousstainless

steel anglesupport

Movementjoint

Joinlseareo

Masonry details

Plastic disc

2.4.7 Wall ties for twin-leaf external masonry

130 >cn

2.4.8 Minimum number and diameter of wall ties Der m2of wall area

Wall ties:min. No. diameter

neither of thefollowing twolines applyWali sections> 12 m aboveground level, or

(e.9. individual brackets or steel sections), asreinforced masonry or as lintels. The latter maybe constructed using specials or in the form ofcambered or semicircular arches.Refer to "Joint design" for details of thearrangement of movement joints.

Cavity wallsIn contrast to the curtain wall facade, in thistype of wall, the cavity between the masonryleaves may be included in calculations todetermine the thermal insulation because theopen vedical joints in the outer leaf are not pro-vided for ventilation. Rainwater or condensa-tion in the cavity can drain away or evaporatewithout causing problems and without the innerleaf becoming saturated. In addition, the cavityhelps the outer leaf to dry out faster. The ther-mal insulation is mainly determined by theinner leaf, although this is usually only econom-lcal in conjunction with inner leaves with veryhigh insulation values.The cavity should be at least 60 mm wide. Thisminimum distance is based on the fact thatadequate circulation of the air cannot beexpected if the gap is too small. However, thewidth of the cavity may be reduced to 40 mm ifthe mortar is struck off flush on at least oneside of the cavlty, thus preventing mortarbridges from interrupting the cavity. The maxi-mum distance between the two leaves is deter-mined by the load-carrying capacity of the wallt ies under compression and should be no morethan 150 mm. Ventilation openings (e.9. openperpends) should be included at the top andbottom of the cavity and at any intermediatesupports to guarantee circulation of the air.Openings at the bottom also serve to drain thecavity (weep holes). This also applies to span-drel panels. A total of 7500 mm2 of ventilationopenings should be provided for every 20 m2of wall area (including doors and windows).This figure means that for a single-storey build-ing and an outer leaf of thin-format unitsapproximately every second perpend at thebase and below the roof or the underside ofsupports in the outer leaf must be left open.The damp proof course must be positionedexactly in order to prevent the masonry belowthe open perpends becoming saturated atthebase of the wall. As water may collect in cer-tain areas at the base, the inner leaf is to beprotected against rising damp by extendingthe damp proof course up the face of the innerleaf. Openings must be at least 100 mm aboveground level.

Parlial-fi ll cavity wal lsIn this type of wall the functions of the individ-ual layers are clearly demarcated under opti-mum building science conditions. A layer ofthermal insulation is attached to the outsideface of the inner, loadbearing leaf but a venti-lated gap remains between this and the outerleaf. This cavitv means that condensation and

driving rain penetrating to the inside face of theouter leaf can drain without saturating the ther-mal insulation. Consequently, the outer leafprotects the layer of thermal insulation againstthe direct effects of the weather and impact orother damage. lf a vapour-permeable materialis used for the thermal insulation, then the cir-culating air not only dries out the outer leaf butalso keeps the insulation dry, causing any con-densation to evaporate.The maximum distance between inner andouter leaves is 150 mm (see "Cavity walls").This does not need to be fully exploited if theinner leaf has good insulation properties. But itis important when the inner leaf makes use ofmasonry types that exhibit high compressivestrength but low thermal insulation, In that case,the thermal properties of the wall are providedsolely by the layer of insulation. This can partlycompensate for the disadvantage of the totalthickness of the wall construction necessary toaccommodate thermal insulation plus cavity. Afurther disadvantage is the high cost of con-structing such walls.The minimum width of the air space is 40 mm.lf we use the maximum width of 150 mm betweenthe two leaves, we are left with 1 10 mm whichmay be filled with insulation. However, owing tothe unevenness of the surfaces of the twoleaves, it is advisable to include a reasonabletolerance in our planning. Insulating batts arerecommended; these are butt jointed togetherand fixed by suitable means (e.9. clampingdiscs on wall t ies or wall anchors etc.). Blan-kets, on the other hand, tend to swell orexpand and hence reduce the width of the airspace. Therefore, they should not be used forthis type of wall.The details at the top and bottom of the wallregarding openings and waterproofing corre- '

spond to those for cavity walls.

Full-fill cavity wallsThese are external walls in which the cavitybetween the leaves is filled completely withinsulation material in order to increase thethermal insulation value, or the cavity is omittedin order to reduce the overall thickness of thewall. The outer leaf should consist of frost-resistant masonry units at least 1 15 mm thickto increase the resistance to driving rain. Theclear distance to the face of the loadbearinginner leaf should not exceed 150 mm. Glazedunits or units with surface coatings must exhibitenhanced frost resistance. The thermal insula-tion is installed between the leaves without anyair space. The insulation materials used maybe in the form of batts, blankets, granulatesand loose materials which are permanentlywater-repellent (hydrophobic) as well as inject-ed cellular foams (e.9. hard polystyrene orpolyurethane), mineral wool, loose expandedperlite or polyurethane or urea formaldehyderesin injected cellular foams. Up to now, theserviceabilitv of these materials has had to be

7

distance betweenmasonry reaves70-120 mm

7o r 5

45

A wall tie diameter of 3 mm is adeouate for a Dlasterf illed collar-iointed wall.

2.4.9 Detail at base of twin-leaf facing masonry

1 1 5 > 6 0I T f

Loadbearingleaf

MG ll (l la)

Fresh air inlet, e.g.vra open perpends

in '1st and 2ndcourses

126t

External walls

2.4.10 lnfluence of wall ties on thermal transmittance values of twin-leaf

lnner leaf

Thermal insulation

Cavity/Air spaceOuter leaf

Wall tie

175 mm

100 mml, = 0.04040 mm1 1 5 m m), = 0.81

S m m A

175 mml. = 0.56120 mml, = 0.040

1 1 5 m mI = 0.815 per m24 m m A

175 mml. = 0.36

60 mm1 1 5 m ml. = 0.81

3mmt l )

verified by a general building authority certifi-cate. In future the requirements these insula-tion materials have to meet lvill be covered bycorresponding standards.In practical terms, it is virtually impossible tobuild the outer leaf without a gap for the brick-layer's fingers when using batts and blankets(not loose materials or injected cellular foams),However, this has the advantage that anywater which does penetrate can drain awayunhindered.When used as full-fill cavity insulation, water-proof or water-repellent materials do not needto be treated any differently to their use else-where with resoect to their thermal conductiv-ity. However, full-fill cavity insulation can func-tion effectively only when the amount of waterpenetrating the insulation is not excessive and,above all, does not accumulate at certain posi-tions. This is guaranteed by ensuring that theouter leaf is built to a high standard of work-manship - which means erecting the masonrywith fully filled joints capable of transmittingstresses. Lime-cement mortars of group ll orlla with a good sticky consistency are pre-ferred. In addition, proper bricklaying tech-niques appropriate to the material of the outerleaf are essential (e.9. prewetting high ab-sorbency units, reducing the plasticity of themortar for low absorbency units). Furthermore,openings in the outer leaf totalling at least5000 mm2 per 20 m2 of wall area (includingdoors and windows) must be included at thebase of the wall so that any moisture that doesbecome trapped in the cavity insulation -despite careful construction - can drain to thebase of the wall and escape to the outside.Mineral fibre insulation materials in the form ofbatts and blankets, or sheets of foamed plasticand foamed glass are to be fixed to the innerleaf by, for example, plastic discs fitted to thewall ties, in such a way that the thickness of theinsulatlon remains constant. Blankets of insulat-ing materials are butt jointed together but thestiffer batts require joints to be formed (e.9.rebate, tongue and groove) or fixed with layersoffset so that water cannot penetrate the joints.Missing sections of hard foam materials (e.9.where wall ties penetrate) must be made goodwith a suitable sealing compound.When using loose thermal insulating materials(e.9. mineral fibre granulate, polystyrene foambeads, expanded perlite), it must be ensuredthat the insulating material completely fills thecavity between the leaves with a consistentpacking density and also that the drainageopenings at the base of wall remain unob-structed by using, for example, a stainlesssteel mesh, An inconsistent, incomplete fi l l ingto the cavity impairs the thermal insulationvalue. This is particularly so at the top of thewall if the material settles shortly after filling orover the course of time, However, voids andirregularit ies in fi l l ings of loose insulatingmaterials and injected foams are particularly

1.O23au. 0.003 0.009 0.006uc 1.026 0.312 0.282

where e = ratio of longer to shorter side of infill panelMax. permissible sizes for side ratios 1.0 < e < 2.0 may be interpolated linearly.1) The sizes may be doubled for masonry units of strength classes > 20 and ratios M > 2.0 (where h = height of infill

panel, | = length of infill panel).2) Permissible for masonrv unit comDressive strenoth classes > 12

2.4.11 Max. permissible sizes of infill panels in non-loadbearing external walls without mathematical

uVall thicknebs Permissible max. size of infill panel for a height above ground level of:

mm

0 t o B me = 1 . 0 e > 2 . 0 1 )mz

8 t o 2 0 me = 1 . 0 e > 2 . 0 1 )m2 m2

20 to 100 me = 1 . 0 l e > 2 . 0 1 )

' l m '

1 1 5115 r )175240> 300

12 .016 .020.o36.050.0

8.010 .614.O25.O33.0

8.010 .613.O23.035.0

5.06.79.0

16:023.O

6.08.09.0

16.025.O

4.05.36.0

12.O17.0

Masonry details

2.4.1 2 Sliding and elastic joints at sides of infillpanels

Joint masked by channel Wall recessed into grooveor angle section

Anchor in s lot , e.g.of stainless steel

Sliding joint at steel column

2.4.13 Detail at base of infill oanel

2,4.14 Junction between infill oanel and timber oosl

Mortar group ll or self-adhesive sealing strips

Stainless steel flatanchor bent to form angle

Galvanized clout nails

critical as these allow moisture to penetrateunchecked right up to the inner leaf. The onlyway to avoid thls is to use proven equipmentand techniques in the hands of experiencedpersonner.

Pl aster-f i I I e d co I I ar-joi nted extern al wa I I sThis type of twin-leaf construction makes use ofa continuous layer of plaster applied to the out-side face of the inner leaf. Like the cavity wall,the inner leaf in this case consists of masonryunits with good thermal insulation properties.This type of construction prevents water fromreaching the inner leaf and provides protectionagainst driving rain. The outer leaf (facingmasonry) is erected as close as possible to theplaster (gap for bricklayer's fingers) with jointsfully filled with mortar, In terms of constructionand function, this wall is an improvement onthe single-leaf faced wall with its continuous20 mm wall joint. In contrast to the single-leafexternal wall, which often suffers from damageattributable to lack of care when casting thewall joint, plastering the outside face of theinner leaf and hence the standard of workman-ship and function of the continuous coat ofplaster can be easily inspected before theouter leaf is built. However, the disadvantageof the twin-leaf wall compared to the single-leaffaced wall is that the vertical loads must becarried solely by the inner leaf. Compared tothe cavity wall, this type of wall is thinner over-a l l .

lf a rendered outer leaf is preferred to facingmasonry, then the plaster coat on the outsideface of the loadbearing, inner leaf may be omit-ted. Frost-resistant facing bricks are not neces-sary with such a rendered outer leaf.Drainage openings (e.9. weep holes) arerequired only at the base of the wallto allowwater which has penetrated the outer leaf anddrained down to escape. Openings at the topof wall are not necessary because ventilation inthe narrow gap between inner and outer leavescannot be expected. Wall t ies just 3 mm thickare adequate to connect the two leaves.

Flat or round barin bed joint approx.every 400 mm

Internal plaster

128

lnternal walls

Non-loadbearing external walls

Non-loadbearing external masonry walls areslab-like components which, apart from theirown weight, have to carry loads acting perpen-dicular to their face (e.9, wind loads) andtransfer these to adjoining, loadbearing com-ponents, e.g. shear walls, f loor plates. ln thestructural analysis they may not be taken intoaccount when assessing the stability of thebuilding or as lateral restraint to loadbearingwalls. These walls are popular for the infi l l pan-els of frame or cellular structures of reinforcedconcrete, steel or timber. Such panels can bebuilt in single- or multi- leaf form, with or withoutplaster, with additional thermal insulationand/or curtain wall facade. Single-leaf, ren-dered walls must be min. 1 15 mm thick, single-leaf facing masonry min. 310 mm. In a twin-leafwall the outer leaf must be at least 90 mm andthe inner leaf at least 1 15 mm thick.

Basis for designAccording to DIN 1053 part 1 , the infi l l panelsof frame or cellular structures need not beassessed structurally when the panels are sup-ported on four sides (e,9. by bonding, tongueand groove joints or anchors), normal mortar ofat least mortar group lla or lightweight mortarLM 36 or thin-bed mortar is used and the con-ditions of DIN 1053 part 1 table 9 (see table2.4.11) are maintained. The dimensions of theinfi l l panel are to be taken as the clear dimen-sions between the supporting construction,The heights above ground level refer to the topedge of the respective infill panel. To classifytwin-leaf masonry, it is recommended to usethe thickness of the inner leaf plus half thethickness of the outer leaf as the design wallthickness. In contrastto loadbearing masonry,the conditions of table 2.4.11 take into accountthe low tensile strength perpendicular to thebed joints. This is possible because failure of apanel does not lead to collapse of the entirestructure. lf the above conditions are not met oropenings are provided in non-loadbearingexternal walls (e.9. windows, doors) whichimpair the load-carrying abil ity, a structuralanalysis is required.

Connections to loadbearing componentsInfi l l panels achieve their stabil ity by beingfixed to adjoining components. The connec-tions must be able to transfer loads acting onthe infill panels to the loadbearing constructionand also accommodate deformations in theadjoining construction. They may be rigid orsliding and elastic. However, a rigid connec-tion, e.g. steel inserts, anchors, mortar joints,bonding, should only be used when excessiverestraint and deformation is not exoected fromthe masonry and the surrounding loadbearingconstruction. The use of sliding connectionsmeans there is no opportunity to span the infillwalls between the adjoining components. Theinfi l l panel is generally built into a groove, or

between overlapping fittings or attached byway of stainless steel anchors in slots (see fig.2.4.12) in order to achieve the sliding and elas-tic connection. Strips of resilient, elastic, rot-proof material (e.9. mineral f ibre or bitumenfelt) are placed between infi l l panel and adjoin-ing component, outer and inner joints sealedwith elastoplastic material or prefabricated jointfi l lers. The sides of panels are easily connect-ed to steel columns when the overall dimen-sions of the sections are selected to suit thethickness of the infi l l panel (see fig.2.4.12).Strips of foil are placed between steel flangeand mortar to achieve a slidlng joint. Mineralfibre pads between the mortar and the web ofthe steel section help to improve sound insula-tion and fire protection. The transfer of forcesbetween masonry and column is ensured bycompletely filling the void between steel sec-tion and panel with mortar. At the top of thepanel a 20 mm tolerance is generally sufficient.The gap is filled with a soft, rotproof material.This prevents the loadbearing adjoining com-ponent unintentionally transferring loads to thenon-loadbearing panel by way of deformationand subsequent deflection. At the base of thewall the horizontal forces from, for example,,wind loads, are transferred from the non-load-bearing external wall to the loadbearing com-ponent by friction. A layer of roofing felt can beincluded between the wall and the loadbearingcomponent (f ig. 2.4.1 3).Infi l l panels to a timber frame should always becompleted with a mortar joint 10-20 mm widebetween timber and masonry. This compen-sates for tolerances and deformations in thetimber construction. A secure connection to thetimber is provided by way of triangular fillets toall sides fixed with stainless steel nails. Thispresupposes reliable adhesion between mortarand masonry units (e.9. provided by suitablepretreatment, the use of low-shrinkage mortaretc.). Alternatively, stainless steel flat anchorsbent to form an angle can be specified as amechanical f ixing, particularly with largepanels.

Gable walls

Gable walls without vertical loadMasonry gable walls are necessary on build-ings with pitched roofs. With steep roof slopes,such walls can constitute considerable areasof masonry. Couple and collar roofs do nottransfer any load to the gable wall, whichtherefore only carries its own weight and windloads. These should be considered as non-loadbearing external walls. They may beanalysed structurally or by comparison withthe permissible values for infi l l panels accord-ing to DIN 1053 part 1 table 9, provided thegable wall is supported at the edges or bycrosswalls or integral piers. At the base thewall is held in position by the relnforced con-crete floor either by means of tension anchorsor via adhesion and friction, at the top by a ringbeam or the roof construction. To do this, theroof construction must be braced (e.9. timberor metal diagonal bracing). The better solutionin structural terms is the formation of a ringbeam, whose ends at least must be connectedto the roof construction by way of steel anchors.The simpler solution is to support the gablewall at roof level via a connection rigid in thehorizontal direction. This is usually achievedby way of masonry anchors.

Gable walls with vertical loadlf purlins span onto the gable wall, then a load-bearing masonry pier can be assumedbeneath the bearing for the purlin as a result ofthe vertical load. Apart from carrying the roofload, this also stiffens the gable wall.Therefore, the gable wall is divided into load-bearing and non-loadbearlng areas. The load-bearing sections (masonry piers) beneath thepurlins have to be examined according to themore accurate method of analysis. In doing so,the clear height of the pier should be used asthe buckling length. The distribution of loadbelow the purlins may be assumed to be 60'.The roof construction must accommodate thehorizontal support reactions, e.g. by way ofdiagonal bracing in the plane of the roof, aris-ing from the provision of support to the pier.The non-loadbearing sections adjacent to themasonry piers should be analysed as gablewalls without vertical load.

lnternal walls

Loadbearing internal walls

ln the latest edition of DIN 1053 pad 1 , the mini-mum thickness for a loadbearing internal wallhas been reduced trom 240 mm to 1 15 mm.This reduction in thickness has resulted in auseful gain in floor space, particularly forsingle- and two-storey buildings in which theloads are only minimal. This is particularly evi-dent when it can be guaranteed that the cross-sections of such thin walls are not reduced bychases and recesses. Reducing the minimum

129

Masonry details

2.4.15 Structural loading scheme according toDIN 4103 part 1 for non-loadbearing internalpartitions

Horizontal \load

--,7

Location 1: P, = 9.5 P57tLocation 2: P, = 1.6 L17t

wail thickness to 1 15 mm has also allowedinternal walls, previously classed as non-load-bearing on account of their thickness, to nowbe included as loadbearing elements. As aresult, stiffening to the building is improved,floor spans are shortened, connection prob-lems for non-loadbearing walls are minimizedetc. ln some circumstances, design and con-struction of the building is, on the whole, madeeasier.

Non-loadbearing internal walls

When built from masonry, non-loadbearinginternal walls - or non-loadbearing internal par-titions - are usually built as lightweight parti-t ions in the sense of DIN 1055 part 3. Non-loadbearing internal paditions are only subject-ed to considerable wind loads in exceotionalcases, e.g. in shed-type buildings with largedoor openings where the pressure can buildup inside the building. ln such cases they areto be treated as non-loadbearing externalwalls. Otherwise, non-loadbearing internal par-titions not subjected to wind loads are coveredby the provisions of DIN 4103. The require-ments and analyses of DIN 4103 part 1 are notrelated to material. Construction guidelines formasonry partitions are stipulated in DIN 4103paft 3. At present this standard only exists inthe form of an unpublished draft. Details givenhere are based on the current state of know-ledge with respect to non-loadbearing masonrypartitions based on the information sheet pub-lished by Deutsche Gesellschaft fur Mauer-werksbau (German Masonry Association) [97,1721.Non-loadbearing internal partitions are wallsbetween interior spaces that do not fulfil anystructural function for the overall structure, i.e.they are not called upon to stabil ize the build-ing not to carry vertical loads. Consequently,they may be removed without adversely affect-ing the stabil ity of the building.

RequirementsApaft from self-weight plus plaster and/orcladding, these walls must be able to carrylight loads from brackets and horizontalimpacts from people or hard objects and trans-fer these loads to adjoining, loadbearing com-ponents. They gain their stability from beingconnected to adjoinin g components.DIN 4103 part 1 distinguishes between the fol-lowing locations for partitions with their associ-ated loads:

Location 1:Locations with low numbers of people, e.g.housing, hotels, offices, hospital patientaccommodation and interiors with similar func-tions (including corridors):horizontal line loadPr = 0.5 kN/m at a height of 9OO mm above thebase of wall.

Location 2:Locations with large numbers of people, e.g.larger assembly buildings and schools, lecturetheatres, exhibition halls, retail premises andsimilar facil i t ies:horizontal line loadPz = 1.0 kN/m at a height of 900 mm above thebase of wall.lrrespective of location, a bracket load of0.4 kN/m wall length (see 2.4.15) and animpact load with a force of Euu"i" = 100 kNmacting at an unfavourable position must also beallowed for. The impact load can be caused bya person (soft impact) or a hard object (hardimpact).According to DIN 1055 paft 3, the structuralanalysis of a loadbearing floor suppoding suchpartitions may assume - instead of a moreaccurate calculation - a uniformly distributedadditional imoosed load of 0.75 kN/m'zfor wallweights (including plaster) < 1.0 kN/m'zwallarea and 1.25 kN/m2 for wall weights (includingplaster) 1.0-1 .5 kN/m2 wall area.For wall weights > 1.5 kN/m2 wall area - or> 1.0 kN/m2 wall area for floors without ade-quate transverse distribution of the loads - theposition and magnitude of the wall load is to betaken into account accurately when analysingthe floor.

Materials for non-loadbearing internal masonrypartitionsOnly materials covered by DIN standards orbuilding authority certificates may be used forbuilding partitions. Partitions of masonry unitsor wall elements may use only mortar of mortargroups l l, l la or l l l to DIN 1053 part 1. The mor-tar should not be unnecessarily firm in order topreserve sufficient elasticity in the masonry toaccommodate deformation. Thin-bed mortarcovered by building authority certificate maybe used for wall elements and gauged units.

Structural analysisAn assessment of the ability to carry horizontalloads according to DIN 4103 part 1 (see'ti1.2.4.15) may be carried out mathematicallyor by means of tests. However, a mathematicalanalysis is difficult because tensile stressesperpendicular to the bed joint may not betaken into account even though they are pre-sent to a limited extent.Maximum dimensions that satisfy the require-ments of DIN 4103 part t have been deter-mined experimentally[97].These maximum dimensions (taken from [97])are given in table 2.4.16tor various types ofmasonry and supporl conditions according tolocation, thickness and height. Designersadhering to these dimensions do not need tocarry <iut a (less favourable) mathematicalanalysis. lf these maximum dimensions areexceeded, additional support in the form ofsteel, reinforced concrete or reinforced mason-ry columns must be provided.

--"j .:.

d

130

lnternal walls

2,4.16 Max, dimensions for non-loadbearing internal paftitions of man-made masonry units

Suppoded on4 s ides

Supported on 3 sideswith 1 unsupported\ , 6 d i ^ . 1 o d d 6

Supported on3 sides with un-supported topedge

Max. dimensions for walls suoported on 4 sidesl) without vertical load'z)

d [mm] Max. wall length [m] for wall height [m] for location 1 (upper value) and location 2 (lower value)

h Im l 2.5 3.0 3.5 4.O A A

50 3.0t . c

3.52.O

4.O2 .5

60 4.02.5

/ q

3.05.03.5

5.5

70 5.0 5.5 6.0 6.5 7.O

9o3.5 4.O 4.s 5.0 5.5

5.0 5.510.0

6.5 7.06.01 0.0 10.0 1 0.0 1 0.0

6.0 6.5 7.O 7.5 8.0

6.0 6.5 7.O 7.5 8.0175 no restriction on length

12 .0 12 .O 12.0 12.0 12.O1)Themax.wal l lengthsaretobehalvedforwal lssuppor ledonSsides(1 unsupportedvert ical edge).2) The values given here apply to calcium silicate and autoclaved aerated concrete units when using MG lll or thin-bed

mortar, Forwall thicknesses < 175 mm and MG llor lla, the values areto be halved when using thesetypesofmasonry units.

Max. dimensions for walls suoported on 4 sidesl) with vertical load2;

d lmml Max. wall length [m] for wall

h tml 2.5 3.0 3.5 4.0 4.5

The type of junction between a partition andthe floor above determines whether any load istransferred from the floor to that partition.Therefore, we distinguish between partitionswith and without vertical loading. Reinforcedconcrete floors with high slenderness ratiosrequire us to assume partitions with verticalloading. The minimum thickness of 50 mm inthe tables is based on practical considerations.The maximum wall length is restricted to 12 min order to limit cracking. Load transfer onthree sides may be assumed up to aheighVlength ratio of h/l < 0.66. Smaller ratiosmean that the partition is supported only topand bottom. In this case there must be a mor-tar joint between top of wall and underside offloor slab.

Design and construction rulesFollowing the recommendations below wil l helpensure good quality non-loadbearing internalpartitions:

. Max. final floor slab deflection l,/500(lt = eQuivalent span depending on structuralsystem).

. Reduce the floor slab deflection due to creepand shrinkage by adhering to striking timesand subsequently treating the concrete.

' Build non-loadbearing internal partitions aftercompletion of the primary structure wheneverpossible so that the majority of deformationsresulting from shrinkage and creep of theloadbearing construction are already com-pleted. At the very least, the topmost courseof masonry units and the plastering should becarried out as late as possible in order to min-imize the risk of cracks.

. Erect non-loadbearing partitions in such away that floor slab deformation due to theweight of such partitions does not introduceany additional loads into non-loadbearingpartitions in the storey below (if possible, startin the topmost storey and work down).

Up to an equivalent f loor span of l, = 7.66 t, unon-loadbearing partition can carry a load byway of arching action without damage, provid-ing the recommendations are followed and it isguaranteed that the horizontal thrust can becarried by the supports at the ends of the wall.Larger spans require additional measures tobe taken, e.g. separating the base of wall fromthe floor slab by means of sanded buildingpaper or reinforcing the areas of wall at risk ofcracking.

50 5.52.5

6.0 6.53.57.0

6.5

60 6.04.0 4.5 5.0 - -

70 8.0 8.5 9.0 9.5b.c o .u 7.0 7.5

90 12.O7.O

12 .O7 .5

12 .O8.0

12 .O8.5

12.09.0

100 12.O8.0

12.08.5

12 .O9.0

12 .O9.5

12.O10 .0

t t c no restriction on length1 2 . O 12 .0 12.0 12.O

120 no restriction on length12.O 12.0

175 no restriction on lenqth1) The max. wall lengths are to be halved for walls supported on 3 sides (1 unsupported vertical edge).2) The values given here apply to calcium silicate and autoclaved aerated concrete units when using MG lll or thin-bed

mortar, and also for MG ll or lla with wall thicknesses > 100 mm. For wall thicknesses < 100 rpm and MG ll or lla, the

values are to be halved when using these types of masonry units.

A A

Max. dimensions for walls supported on 3 sides without vertical loadl) (top edge unsupported)dtmn' [ lv lax wal l length[m] forwal l height [m] for locat ionl (uppervalue) andlocat ion2( lowervalue)

2.5 3.0 3.5 4.Oh Iml 2.0 2.2550 3.0

t . c

3.52.O

42.5

5 6

6.03.0

60 5.02.5

5.52.5

7.O3.5

8.04.O

9.0

70 7 .O3.5

7.53.5

8.04.O

9.0 10.05.0

10.06.0

10.07.O

8.04.0

90 8.54.O

9.05.0

10 .06.0

10.07.O

12.O8.0

12.O9.0

100 10 .0 10 .0 10.0 12 .0 12 .O 12 .O 12.O5.0 5.0 6.0 7.0 8.0 9.0 10.0

1 1 5 1 1 .5 8.0 9.0 1 0.0 10.0 12.0 12 06.0 6.0 7.0 8.0 9.0 1o.o 19.q

1zo a.0 9.0 10.0 12.O 12.O 12.O 12.07,O 8.0 9.0 10.0 10.06.0 6.0

175 no restriction on length8 . 0 9 . 0 1 0 . 0 1 2 . 0 1 2 . 0 . 1 2 . 0 1 2 0 . .

@tomasonryuni tSofc|ayor l ightWeightconcreteWithnorma|mortaraSWe||aSautoclaved aerated concrete blocks or calcium silicate units with thin-bed modar or mortars of mortar group lll. When

using units of autoclaved aerated concrete and calcium silicate with normal mortar, reduce the max. wall lengths asfollows: a) for walls 56 and 70 mm thick reduce to 40%; b) for walls 90 and 100 mm thick reduce to 50%; c) for walls

115 and 120 mm thick in location 2 reduceto 50% (no reduction for location 1). The units should be prewetted when

using mortar group lll.

131

Masonry details

2.4.17 Sl id ing jo int detai ls

Sliding joints between walls

Junctions with adjoining, loadbearingcomponentsConnections must take account of the possibleinfluence that deformations in adjoining com-ponents may have on the internal partition.According to DIN 4103 part '1

, the service-abil ity of junctions must be guaranteed.The junction details shown in figs. 2.4.'17 and2.4.18 do not normally require further assess-ment.Rigid junctions are those which are fully bond-ed, f i l led with mortar or employ similar meas-ures (anchors, dowels or steel inserts). Suchdetails are used for walls where no or very lowrestraint forces from the adjoining membersare expected to act on the wall.Rigid lateral connections are usually limited tohousebuilding (wall length | < 5.0 m). A rigidjunction between top of wall and underside offloor slab can be achieved by fi l l ing the jointwith mortar, Introducing a strip of hard foamreduces the influence of the deformation of theadjoining loadbearing construction, but guar-antees the transfer of horizontal forces due tothe hard foam strip being compressed as thefloor slab deflects.Sliding junctions are particularly suitable forapplications where it is necessary to reducethe risk of cracking due to unintentional forcesbeing introduced into the non-loadbearinginternal partition as a result of the deformationof adjoining components.Sliding connections are achieved by using pro-files, grooves and stainless steel anchors inslots, maybe with the addition of foil to create as l id ing bear ingThe joint should be fi l led with mineral wool inorder to improve fire protection and soundinsulation (see "Non-loadbearing externalwal ls") .

Golumns and free-standing masonry walls

Columns

Columns are elements with a cross-sectionalarea < 0.01 m2. To act as a loadbearing ele-ment, a column must have a minimum cross-section of 0.004 m2, Hence, the minimumdimensions of a loadbearing column are 1 15 x365 mm or 175 x 240 mm. Columns have a lowmoment of area and therefore a low stiffnessEl. Their help in distributing horizontal loads isnegligible, and so they are not called upon tocarry horizontal loads in the structural analysis.So columns carry only vertical axial loads. Theymay be analysed for concentric or eccentriccompression using either the simplif ied ormore accurate method of analysis. The simpli-fied method makes use of the reduction factorkr = 1.0, and the more accurate method usesthe safety factor y* = 2.0. In this case thecolumn should consist of one or more wholemasonry units or divided units with < 35% per-forations and should not weakened bv chases

or recesses. In all other cases, the safety factoris increased to 1, = 2.5.The reduction factor is consequently definedas ki = 2.0/2.5 = 0.8. The use of dividedmasonry units or divided units with > 35% per-forations makes the columns more vulnerableto irregularities and flaws in the construetion.Unlike walls, these cannot be compensated forby neighbouring parts of the cross-section andso this high risk of structural failure has to betaken into account by way of an increasedsafety factor.

Free-standing masonry walls

The problem of the free-standing masonry wallis that it is suppoded only at its base, and sothe system must span vertically. The exceptionto this rule is when suitable measures, e.g.reinforced concrete columns, masonry piers orcrosswalls at close spacing, are introduced toensure that the wall spans horizontally by wayof arching action or by employing reinforcedmasonry. Without such measures, the permis-sible height of the wall is very limited owing tothe fact that the cross-section may only crackas far as the centre of the wall.Masonry units for free-standing walls must befrost resistant if they are not rendered. Free-standing masonry walls are always built with aproper bond and with all joints fi l led.The foundation should be taken down to a levelwhere it is not affected by frost. A horizontaldamp proof course of water-repellent moftar orwaterproof paint should be included aboveground level in order to protect the wall againstrising damp and splashing water. Verticalfaces of masonry in contact with the groundshould also be protected against ingress ofmoisture from the soil. The length of an individ-ual segment of masonry should not exceed6-8 m; longer lengths should include move-ment joints. They are a number of ways inwhich long walls may be segmented attrac-tively (see fig.2.4.19). The top of the wall mustbe covered in such a way that water cannotpenetrate, indeed that it drains away clear ofthe face of the wall. l f used as a coping, abrick-on-edge course must consist of wholebricks and be carefully jointed. The joint belowa brick-on-edge coping must be waterproof.Owing to the many joints, this type of coping islimited in its applications. Other types of cop-ing include clay roof tiles, corrugated roofingunits of fibre-reinforced cement or speciallydesigned coping units. Also suitable are pre-cast concrete units with permanently plasticjoints laid in water-repellent mortar or on adamp proof course, or metal cappings ofgalvanized steel, copper or aluminium eithernailed or screwed on.

JTr*ro"n beadoredse] chamfered with trowel

Cast-in dovetail slot

Mineral wool or similar

Anchor positioncan be adjustedveftically

Elastoplastic seal

Sliding joint at underside of floor

Mineral woolor s imi lar*

Aluminium orsteel section as

- Incombustible material if required to comply with fireprotection regulations

Sliding joint at intermediate column

d

lMortar Mineral fibre

132

Sliding layer, Flat or round bar in bed ioinle.g. foil strip approx. every 400 mm

External basement walls

Pafiwalls

For reasons of sound insulation, party wallsbetween adjoining residential buildings (ter-raced houses, semi-detached houses) shouldbe built as twin-leaf walls with a continuousseparati.ng joint (cavity) from foundation to roof.lf twin-leaf external walls are used, the separat-ing joint must be taken through the outer leafas well in order to avoid an acoustic bridge.According to DIN 1053 part 1 , the minimumthickness of each leaf should be 1 15 mm. lf theweight of the party wall exceeds 100 kg/m2 wallarea (including plaster), the width of the jointmust be at least 50 mm: if over150 kg/m'z, then 30 mm is permissible but 50 mmis sti l l recommended. To comply with thesound insulation requirements of DIN 4109, thecavity must be completely filled with mineralfibre batts to DIN 181 65 part 2. Closed-cellhard foam sheets or wood-fibre boards areunsuitable for sound insulation. The insulationmust always extend above the leaf built last inorder to prevent mortar and debris falling intothe cavity and possibly forming acousticbridges between the leaves. Install ing the insu-lation in two layers with their joints offset is re-commended for improving the sound insula-tion. As the separating joint also passes throughthe floors, the insulation should extend abovethe thickness of the floor during casting, beprotected by suitable means and supportedagainst the pressure of concrete on one side.lf the weight of a single leaf exceeds 2OO kglm2wall area, the separating joint may remainopen. Special care must be taken here toensure that mortar or debris does not drop intothe cavity and form acoustic bridges. This isless of a problem when using thin-bed mortar ifthe mortar is applied by way of mortar sledges.Otherwise, mortar - or concrete when castingthe floors - can be prevented from falling intothe cavity by using suspended battens raisedas the work proceeds or joint forms, whichhave to be removed subsequently.

External basement walls

Basements are no longer restricted to subordi-nate roles such as the storage of food or fuel,but provide space for diverse activit ies, e.g.washing, hobbies, workshop, playroom, guestroom, study etc, They represent a relativelyinexpensive way of extending the useful floorspace available. At the same time, they corre-spond to the concept of dense, space-savingconstruction IB].Basement rooms normally heated require addi-tional thermal insulation if that of the masonryalone is not sufficient. External thermal insula-tion is recommended. This should consist ofmaterials covered by a standard but with extrafunctions regarding resistance to water, irostand earth pressure covered by a general build-

ing authority ceftificate or by the provisions ofDIN 4108 part 4. Products suitable for externalinsulation include extruded polystyrene sheets,foamed glass sheets and polystyrene beadfoam sheets with a minimum bulk density of 30kg/m3.

External basement walls are subjected to ver-tical loads in the plane of the wall and horizon-tal loads resulting from, for example, earthpressure, perpendicular to the plane of thewall. Earth oressure loads are assumed to bemainly active earth pressures, provided thewalls are not substantially thicker than thestructural analysis requires, and the backfillmaterial is only compacted to medium density,lf the backfi l l material is highly compacted, anincreased earth pressure, e.g. earth pressureat rest, must be assumed. The earth pressuregenerates bending moments in the wall whichare usually the deciding factor in the design ofthe wall,

Stability of external masonry basement walls

Vertical uniaxial loadbearing actionlf the basement wall is supported top and bot-tom, we can assume that the wall acts as a ver-tical loadbearing member spanning in onedirection between two supports with a crackedsection of no more than half the wall thickness.The tensile stresses perpendicular to the bedjoints may not be taken into account (see"Analysis of tension and bending tension").They are "neutralized" by vertical loads.DIN 1053 part 1 includes two methods whichmay be applied in order to avoid the need toanalyse the wall for earth pressure. The follow-ing conditions have to be satisfied for bothmethods (see fig. 2.4.20)

' Clear height of basement wall h" < 2.60 m,thickness of wall d >240 mm.

. The roof to the basement must act as a plateand be able to accommodate the forces gen-erated by the earth pressure,

'The imposed load on the ground over thearea in which the earth pressure influencesthe basement wall may not exceed 5 kN/m2.At the same time, the sudace of the groundshould not slope upwards from the wall andthe depth of fill h" must be less than the clearheight of the basement wall h".

ln the first method the decisive criterion is thepermanent load No at the top of the basementwall below the basement roof, which must liewithin the following l imits:

max No > No > min No

Compliance with the permissible edgepressure is checked using the equation

max No = 0,45 d oo

2.4,19 Segmentation of free-standing masonrywalls (plan views)

6 t o 8 m_+ -+-

d = 1 7 . s t o 9 6 . 5 c m _

-

2.4.18 Rigid jo int detai ls

Rigid joints between walls

Bonded joint

a

Rigid joint at base of wall

Wall built onbonded screed

Joint with anchors

Section b-b

Joint plastered over(only location 1)

Wall built onloadbearing floor

Et

7777777r'.Mortar joint

133

Masonry details

2,4,20 Loading assumptions for basement walls withoutmathematical analysis

2.4.21 Min. N^ for basements walls without mathe-maticai analysis

Wall min No in kN/mthickness d for depth of bacKill he ofmm 1 .0 m 1 .5 m 2 .0 m 2 .5 m

20 45 75

where d = wall thickness and oo = basic valueof permissible compressive stress.

The minimum loads min. N^ are listed in DIN 1053part 1 table B (see table i.+.211. These ensurecompliance with the permissible eccentricity ofthe basement wall as a result of axial force andbending moment due to earth pressure.The second method is based on the findings ofMann/Bernhardt [9] and enables the wail to beanalysed with slightly less vertical load. Theaxial force N, resulting from permanent loadingat half the depth of fill must lie within the follow-ing l imits:

d x B r / ( 3 y ) > N r > m i n N

wneremin N = (p" x h""x h"r) / (20 d)Fo characteristic compressive strength

vpe

of masonrysafety factorbulk density of fill [kN/m3]

lf the vedical loads No and N, do not l ie withinthe given l imits, the basement wall must bedesigned according to the more accuratemethod of analysis taking the earth pressureinto account. This involves analysing the com-oressive stresses as well as the slab shearresulting from the shear force generated by theearth pressure. Alternatively, the permissibleupper and lower limits may be adjusted byincreasing the thickness of the wall, reducingthe height of the wall by forming the base inreinforced concrete, or choosing a uniVmortarcombination with a higher compressivestrength. This is also necessary if the designaccording to the more accurate method ofanalysis taking earth pressure into account isnot possible. Finally, the load-carrying capacityof the basement wall can be increased byusing reinforced masonry or by considering itto span in two directions or horizontally [154].

Biaxial loadbearing actionStability can be checked by assuming that theexternal basement wall subjected to earthpressure spans in two directions when cross-walls or structural components, e.g. piers orstiffening columns of reinforced, concrete-filledchannel blocks, support the wall at a clearspacing b < 2 hs. The necessary vertical loadsmay then be reduced as follows according toDIN 1053 part 1 (intermediate values may beobtained through linear interpolation):

. f o r b < h " :No > 0.5 ffiiI No rn,"r,u,Nj > 0.5 ffiifl Nuniaxiar

. f o r b > 2 h . :No > min No rnia",",N., > min Nuniaxial

H ori zonta I loa d beari n g actionlf supports are closely spaced, then it is pos-sible to carry the horizontal load of earth pres-sure to the supports by way of tensile bendingstresses parallel to the bed joints. Owing to ihelow tensile bending strength of masonry paral-lel to the bed joints, this form of horizontal load-bearing action is, however, very limited, partic-ularly with walls which need to be thin in orderto maximize the usable interior space. lf thevertical loads are very low owing to, for exam-ple, large window openings or f loor slabsspanning parallel to the basement wall, or if.there are segments of wall with unsupportedtop edges, e.g. spandrel panels beneath largebasement windows, the structural system can,be taken to be a horizontal arch. However, theexternal basement wall must be supported bythe transverse elements and at a close spacingto guarantee that the arch is formed and the :horizontal thrust accommodated. At an inter-mediate support between two arches withroughly equal spans and loads, the archthrusts in the plane of the wall cancel eachother out and only the component perpendic-ular to wall has to be resisted by the support.But at an end supporl, resistance to horizontalshear has to be proved. The type of construc-tion which usually fulfils the requirements ofsuch an analysis is reinforced masonry usingreinforced, concrete-filled specials. The base-ment wall must be as thick as possible in orderto achieve an adequate "rise" to ensure arch-ing action. In addition, a cracked section up tohalf the thickness of the wall may be assumedat the centre of the arch in the calculations.The perpends must be fully filled with mortar inorder to transfer the compression. The charac-teristic value that may be used for the strengthof the masonry in the basement wall perpen-dicular to the perpends is - based on DIN1053 part 3 - the characteristic value Bo forsolid units and half the characteristic value pofor compressive strength perpendicular to thebed joint for perforated solid units and otherperforated units.

300 3 15 30 50365 0 10 25 404 9 0 0 5 1 5 3 0

polation

2.4.22 Waterproofing of basement walls for the "non-hydrostatic pressure" loading case

Thick bitumencoating

Protective layer(e,9. drainage board)

Horizontal water-proofing

at base of wall

Horizontal water-proofing

at base of wall

Separatingmembrane

2,4,23 Walerproofing of basement walls for the "tem-porary build-up of seepage water" loading case

Thick bitumenvuaur r9

Bl inding

Masonry with normalmortar in bed jointswith/without mortar toperpends in accordancewith DIN 1053 pt 1

Cement screed laidon separating membrane

Polyethylene foil> 0.2 mm

134

Protective screed

J

Natural stone masonry

Reinforced masonryReinforced external basement walls are usefulwhen the vertical loads are so low that acracked section larger than half the thicknessoccurs under vertical or biaxial loadbearingaction, or when carrying the loads horizontallyvia tensile bending stresses parallel to the bedjoints or via horizontal arching action leads touneconomically thick walls. Generally, the rein-forcement is placed horizontally in the bedjoints. However, vertical reinforcement is pos-sible in conjunction with specials. Please refer '

to "Reinforced masonry" for details of the de-sign and construction of reinforced externalbasement walls,

Waterproofing

As they are constantly in contact with the soil,external basement walls are permanently sub-jected io especially arduous conditions. lf thebasement is an extension to the l iving or ancil-lary space of a building, then the external wallsmust be permanently protected against theingress of moisture.Together with the customary waterproofingsystems, masonry basements, without elabo-rate treatment, satisfy the requirements fordesign and construction to meet the loadingcases "ground damp" to DIN 18195 part 4,"non-hydrostatic pressure" to DIN 18195 part 5and "hydrostatic pressure" to DIN 18195 part 6with "low load" (temporary build-up of seepagewater). Most basement walls designed for theloading case "hydrostatic pressure" with "highload" (groundwater) will continue to be con-structed in concrete to ensure adeouate water-proofing (external tanking). The most popularwaterproofing systems for external basementwalls are bitumen and polymer bitumen sheet-ing; cold-application self-adhesive bitumensheeting; and modified synthetic bitumen thickcoatings. The latter are used for the majority ofwaterproofing tasks in housebuilding and re-present the most economic solution [93].

Hor i zontal wate rp roofi n gHorizontal waterproofing in the form of a com-plete sealing membrane is applied to theground slab for the loading cases "grounddamp" and "non-hydrostatic pressure". lt isextended to the outside at the base of theelternal walls beneath the first course ofmasonry units to overlap with the verticalwaterproofing. The ground slab must projectsufficiently beyond the external wall to ensurean adequate connection between horizontaland vertical waterproofing. Placing the water-proofing beneath the first course of masonryunits means that the entire floor construction,e.g. f loating screed, is carried out in the dry.No further horizontal waterproofing is required.Sheets of waterproofing material are usuallyused because these are more robust thancoatings with regard to mechanical damage

during the subsequent construction of the floor(see fig. 2.4.22).The loading case "temporary build-up ofseepage water" requires a layer of blinding tobe laid first which is then covered with a min.0.2 mm thick polyethylene foil as a separatingmembrane and then a screed to protect thisagainst mechanical damage. The ground slabis then cast on this (internal tanking) (see fig.2.4.23).

Ve rti c a I w ate r p roof i n gWaterproof sheeting bonded to the wall orsealing compounds worked cold (modifiedsynthetic bitumen thick coatings) spread orsprayed on are suitable for the vertical water-proofing. The number of layers of waterproofsheeting depend on the type of sheetingselected. Thick coatings may be one- or two-component sealing systems and are alwaysapplied in two operationsSpecial care must be exercised at the junctionwith the horizontal waterproofing. The founda-tion/wall transition should be rounded off with aconcave fi l let (min. radius 40 mm). The overlapshould be at least 100 mm and be formed asan overlapped water check joint.

Protective layerThis protects the vertical waterproofing to thebasement walls against mechanical damageduring bacKill ing and subsequent compactionof the excavation. Suitable materials are, forexample, textured plastic sheeting, thermalinsulation batts or drainage boards of no-finesbitumen-bound polystyrene. This protectivelayer guarantees that the vertical waterproofingsystem remains fully functional.

Separating membraneThe inclusion of a non-woven fabric as a sepa-rating or sliding membrane between water-proofing and protective layer prevents loadsdue to settlement of the backfill from beingtransferred to the waterproofing, causing this tobecome detached.

Service penetrationsBuilding services (e.9. waste water, freshwater, electricity etc.) must be routed in such away that the waterproofing is not impaired. Inaddition, service penetrations must be able toaccommodate settlement of the structure with-out damage.

Construction jointsThe waterproofing must safely bridge overconstruction joints. Any waterstops that are in-cluded must be permanently connected to thewaterproofing.

Transition to superstructure, plinthIt is undesirable - both from a visual and atechnical point of view - to continue the verticalwaterproofing above ground level at the base

of the superstructure. A plinth must be water-proofed and protected against splashing waterto a height of about 200 mm above groundlevel. Therefore, waterproof paint or suitablerendering is applied to exposed surfaces andthis must overlap the vertical waterproofing byat least 100 mm. In twinleaf masonry the water-proofing is placed on the outside face of theinner leaf.

Natural stone masonry

Natural stone masonry can be classed as drywall ing, rubble masonry, various forms ofcoursed masonry, ashlar masonry or facedmasonry depending on the degree to whichthe natural stones are worked and their result-ing geometry.

Drywallingis made from rubble stone without mortar. Thestones should be laid with minimal dressing ina proper bond so that joints and voids are assmall as possible. Smaller stones are to bewedged into the voids to create tensionbetween the main stones. This helps the wall tokeep its shape and remain stable. Dry wallingis used for gravity retaining walls. In assessingstability, the density used should be taken ashalf the bulk density of the natural stone. Whenbuilding gravity retaining walls, the naturalstones are allowed to pile up against the soilto be retained in order to improve the stabilityof the wall. The largest and most regular (rect-angular) stones are used to frame the wall atthe corners and ends, and for the base (seet i7.2.4.24) .

Uncoursed random rubble masonryis made from unworked stones as they occur innature. The round form of the stones results ina highly irregular appearance.The finished wall is highly susceptible to slidingand does not exhibit any noteworthy compres-sive strength despite the hard rock used.To secure the masonry bond, the joints mustbe carefully filled with mortar and small piecesof stone. In addition, the corners are built usingstones with a more regular shape and thecourses held together with headers (through-stones) trued up horizontally every approx.1 .0 m of wall height (see fi1.2.4.25).

Coursed random rubble masonryThe bed faces ofthese stones (150-300 mmhigh) obtained from quarries undergo only mini-mal working. Natural stones of various sizesare laid in moftar in approximate courses.Coursed random rubble masonry is trued uphorizontally across its complete thickness(> 500 mm) every max. 1.5 m of wall height.The same applies to the inclusion of a dampproof course, which should be built in approx.150 mm above ground level. Large stones

135

Masonry details

2,4.24 Dry walling

2.4.26 Coursed random rubble masonrv

2.4.28 lrregular coursed masonry

2.4.30 Ashlar masonry

2.4.25 Uncoursed random rubble masonry

2.4.27 Hammer-dressedmasonrv

2.4.29 Regular coursed masonry

[--']E[][--lt_l[--'1t----l

[-lL]2.4.31 Stone facing with backing of man-made

masonrv units or concrete

should be used at the base and at corners inorder to secure the masonry bond. Normalmortar of group ll or l la is used depending onthe type of rock.These days, coursed random rubble masonryis only used for less important basement walls,free-standing boundary walls and for retainingwalls in vineyards (see fig. 2.4.26).

Hammer-dressed masonryThe bed joints and perpends of the stones inexposed faces are worked to a depth of atleast 120 mm. However, the natural stonesbeyond this depth of wall are either not workedat all or only very little. Vertical and horizontal '

joints are.approximately at right-angles; -The height of a course may change within acourse and between courses; however, the..masonry is to be trued up horizontally acrossits complete thickness every max. 1.5 m of wallheight, For information on mortars and horizon-tal damp proof courses, refer to "Coursed ian-dom rubble masonry" above (see ttg.2.4.27),

I rreg u lar coursed masonryThe bed joints and perpends of the stones inexposed faces are worked to a depth of atleast 150 mm. Vertical and horizontal joints areapproximately perpendicular to each other andto the surface.Perpends and bed joints may not be thickerthan 30 mm. The height of a course maychange within a course and between courses,but not excessively; however, the masonry is tobe trued up horizontally across its completethickness every max. 1.50 m of wall height {seefig.2.4.28).

E[ ][]n[--l-_l

EE

E[---]r -]E[l ]E[ ]l

> h/3 > 100l f +. > )40

> 100g

> 24n.l

+

136

Openings in walls

Regular coursed masonryThe stones should be worked as for irregularcoursed masonry. However, the height ofstones may not change within a course. Inaddition, the height of every course is to betrued up (see fig. 2.4.29).When used for vaulting, domes and similarconstructions, the bed joints must passthrough the complete thickness of the curvedelement. Therefore, the bed joints should beworked over the full depth, while perpendsneed only be worked to a depih of 150 mm.

Ashlar masonry .The stones for ashlar masonry should be workedaccurately to the specified dimensions and allperpends and bed joints worked to the fulldepth. The principles for bonding ashlar ma-sonry are basically the same as for masonryusing man-made units; all the different typesof bonds using stretchers and headers can beproduced. The joint thickness can be 4-30 mm;mortar is difficult to apply to joints thinner than4 mm. Dry ashlar masonry requires the bedfaces to be ground and is hardly used thesedays (see'fig. 2.4.30).

Stone-faced masonryconsists of a skin of regular coursed or ashlarmasonry on a backing of man-made units orconcrete (see fig. 2.4.31).The stone facing may be considered as part ofthe loadbearing cross-section when

' the stone facing is built at the same time asthe backing and is bonded to it,

' the stone facing is bonded to the backing byat least 30% headers,

. the headers ofthe stone facing are at least240 mm deeo and are bonded at least100 mm into the backing,

. the thickness of the stone facing is > '1l3 itsheight or min. 1 '15 mm,

' with backings of man-made units, at leastevery third course of natural stone consisisentirely of headers.

The thickness of the total wall constructionshould be as determined by the structuralanalysis, but this is seldom less than 500 mmfor oractical reasons. The conditions describedabove apply similarly when the backing ismade from concrete. Here, the concrete ispoured and compacted after every course offacing stonework to prevent voids beingformed beneath the header stones. The oer-missible stress for the comolete wall construc-tion is governed by the material with the lowestpermissible stress. Stone facings that do notcomply with the conditions outlined above maynot be included as part of the loadbearingcross-section. Coursed stones may be laidagainst their stratification only when they ex-hibit a minimum compressive strength of20 MN/m2 parallel to their stratification. A non-loadbearing stone facing should be anchoredand supported as for a non-loadbearing outerleaf of a twin-leaf wall. Cladding panels maynot be included as part of the loadbearingcross-section of a column.

Openings in walls

Openings in walls for windows, doors andlarger items, e.g. ventilation ducts and lightwells, are bridged over by way of lintels orarches (masonry "l intels").

Arching action over openings

When designing a l intel or arch, we canassume an arching action in the masonryabove the opening in the wall, provided thereare no openings adjacent to and above thelintel or arch and the associated load triangle,and thatthe arch thrust (horizontal supportreactions) can be resisted at the sides of theopening. Therefore, the lintel or arch carriesthe load only below the assumed arch (see fig.2.4.32).This is taken into account by the (equilateral)load triangle of masonry above the lintel or arch.

2.4.32 Atch action over opening in wall

2.4.33 Effective loads over opening in wall with archactron

Vertical load

137

Masonry details

Reinforced concrete lintel asupstand beam with channelblocks as permanent formworkto outside face

7)(////)

w-nAL)T)q7/)ICalcium si l i -cate channelblocks

2,4.36 Supporting a soldier course "fake" lintel

| ) " " 'n# ] orca

Reinforced concrete lintelmasked by channel blocksfor facing masonry

2,4,35 Shallow lintel details

2.4.34 Reinforced concrete lintel details

Reinforced concrete lintelwith cast-in thermal insulation(only suitable for certainapplications)

Uniformly distributed floor loads above the loadtriangle are not taken into account whendesigning the construction over the opening inthe wall. For floor loads that act within the loadtriangle as a uniformly distributed load on themasonry (e.9. floor slabs and joist floors withjoist spacing < 1,25 m), only the section whichlies within the triangle is assumed to transferload onto the lintel. Point loads, e.g. frombeams, which l ie within or near the load trian-gle are assumed to distribute their loadsat 60". If point loads occur outside the loadtriangle, they need be taken into account only ifthey lie within the span of the lintel or arch andbelow a horizontal line 250 mm above the apexof the load triangle. In this case the self-weightof the wall below the point load also has to betaken into account (see fig. 2.4.33).lf arching action cannot be established in themasonry above the load triangle over the open-ing in the wall, the l intel or arch must beassumed to carry the entire load above theopening.

Beam-type lintels

Beams of, for example, timber, steel or rein-forced concrete transfer the loads acting onthem to their supports at each end by way ofbending. Therefore, the beams must be de-signed to resist bending and shear forces.Owing to their excellent material properties,steel sections can be generally quite small, butfor reasons offire protection have to be encasedin concrete and to comply with building sciencerequirements must be provided with thermalinsulation.Reinforced concrete lintels are usually chosenwhen the l intel can be combined with a rein-forced concrete floor or in certain loading situ-ations. They may be precast units or cast insitu with the reinforced concrete floor. A rein-forced concrete lintel must always be providedwith insulation to meet thermal insulationrequirements. The problem with this is that theeffective cross-section of the lintel must bereduced in order to accommodate the insula-tion and this creates a substrate for plasteringwhich is different to the surrounding wall.Despite the provision of a plaster backingspanning across the thermal insulation, thistype of detail often leads to cracks in the ren-dering and staining of the finish.One solution to this problem is to provide chan-nel blocks in the respective type of masonry aspermanent formwork instead of the reinforcedconcrete. The reinforced concrete lintel (pre-cast or in situ) is then integrated into this. Thiscan also be used in conjunction with a rein-forced concrete lintel cast together with thefloor slab. In this detail a prefabricated l intelunit made from channel blocks (with integralinsulation) forms one side of the formwork forthe reinforced concrete lintel. As the structural-ly effective width of this lintel is only very small,

it may need to be formed as an upstand beam.There are channel blocks available to matchthe respective formats and course heights offacing masonry and these may be used to formprefabricated lintels and employed as form-work to the side of a reinforced concrete lintelcast in situ (see fig. 2.4.34).

Shallow lintels with masonry above

Shallow lintels consist of a prefabricated, rein-forced tension flange and only achieve their fullload-carrying capacity in conjunction with acompression zone of masonry or concrete orboth (e.9. masonry and floor or capping beam)above. The tension flange may be prefabri-cated from concrete or from channel blocks ofclay, l ightweight concrete, calcium sil icate etc.;filled with concrete in which the reinforcement(prestressed if required) is placed. In contrastto beam-type lintels, shallow lintels carry theloads acting on them in conjunction with thewall above like a tied frame (a closed system).The shallow lintel (tie) resists the tensile forcesfrom the arch (frame) in compression andtherefore replaces the end supports whichwould otherwise be necessary to accommo- .date the horizontal thrustThe advantage of shallow lintels is that theycan easily be made from the same material asthe surrounding wall. This avoids cracks in anddamage to the plaster. By matching the dimen-sions of the sl'lallow lintel to the modular sizesof the surrounding wall, this type of construc'tion can be integrated into the masonry withouthaving to adapt or cut the masonry units ad-jacent the opening in the wall. This leads tomore economic and more rational site opera-tions. For further information, see "Reinforcedmasonry" and [35] (see fig. 2.4.35).

Masonry lintels and arches

Prefabricated or in-situ lintels of horizontallyreinforced masonry may be used for facingwork. The loadbearing behaviour correspondsto the tied frame model of the shallow lintel withwall above. The horizontal reinforcement isplaced either in trough-shaped specials orhorizontal channel blocks or perforated unitswith a continuous hole to suit the bond of thefacing masonry. Design and constructionshould be in accordance with DIN 1053 oart 3.Please also refer to "Reinforced masonry".In twin-leaf facing masonry the outer leaf abovethe opening in the wall can be carried by nibson the side of the floor slab or by supportsbolted to or cast into the floor slab (e.9. steelangles or brackets). To satisfy architecturalrequirements we can also provide a horizontall intel in the form of a soldier course in conjunc-tion with brackets and bars passing throughthe masonry units. The shear- and tension-resistant connection to a reinforced concretebeam behind means that this is onlv a "fake"

Claychannelblocks

compresstonzone

shallow lintel astension flange

Nt t rv^z '''- L H ) 4

ER T-

1 7 5 1 1 5

t l | z D Fanw, J6rH J=IT +

1 7 5

--__lrtl

4 5 f l [

1 Bolt2 Angle bracket3 6 mm dia. V4A steel anchor4 Continuous bar carrying soldiers (10 dia. V4A steel)5 Continuous hole

138

Vaulting and arch floors

2.4.37 Semicircular and pointed arches according to [162] 2.4.38 Cambered and gauged arches according to [162]

The span (S) feasible depends on type of arch, compression in arch and vertical loads. The width (M,f of the abutment depends on the span; the values given here apply to abut-ment widths essentially without vertical load. All values are guidelines which may be exceeded in an accurate analysis. Cambered arches in non-loadbearing facing work can bebuilt for spans up to approx, 1.75 m without the need for a structural analysis.

l intel with no loadbearing function (see fig.2.4.36).Masonry lintels in the form of arches are pri-marily used in the refurbishment of older build-ings, but are also being rediscovered as amodern design option in conjunction with fac-ing masonry. Owing to the high labour input,these arches are often produced as prefabri-cated elements, which are then lifted into placeon prepared abutments. With a favourablerise/span ratio and predominantly permanentloads, i.e. dead loads considerably higher thanimposed loads, the arch may be designedaccording to the line of thrust method. Thismeans that the construction is subjected onlyto axial compression and no shear or bendingmoments when the axis of the arch coincideswith the line of thrust. However, this ideal caseis hardly possible in practice because chang-ing loads, and hence different loading cases,mean that various lines of thrust have to beconsidered when designing the arch.'Never-theless, to ensure that exclusively compressivestresses without a cracked section occur in thecross-section of the arch, the geometry of thearch should be such that, if possible, the l inesof thrust for all possible loading cases l ie in themiddle third of the cross-section. Lines ofthrust can thus be used independently oftheloads in oider to design a suitable, economicarch for masonry which, in theory, cannotaccommodate any tension. In doing so, weassume thatthe structural system is based ondetermining the lines of thrust for a three-pinarch in which the pins are positioned at thespringing points and at the crown of the arch.Arches with longer spans and more pronouncedchanges of loading have to be designedaccording to elastic theory. Providing resis-

tance to the arch thrust at the supports alsohas to be taken into account when designingan arch. Shallow arches with a low rise gener-ate a greater horizontal thrust than arches witha smaller radius and larger rise. The horizontalthrust must be resisted without displacement atthe supports irrespective of the curvature of thearch because the arch itself undergoes asevere increase in stresses due to the reduc-tion in the riSe even with onlv minimal disolace-ment of the supoorts.

Semicircular and pointed archesThe radius of a semicircular arch is eoual tohalf the width of the opening, and for a pointedarch equal to the full width of the opening, withthe centres of the radii being the respectiveopposite springing points. The abutments forsernicircular and pointed arches are generallypositioned horizontally at the level of thespringing points. The arches are normally con-structed with tapering bed joints. The thicknessof the joints at the underside of the arch (intra-dos) should not be less than 5 mm, at the outerring of the arch (extrados) not greater than20 mm. Special tapering units (voussoirs) maybe necessary for small radii. When using small-format units, the size of the bed joints at theextrados of the arch increase as the archbecomes thicker. Therefore, thick arches arealso built in individual rings, one above theother. Arches are always constructed using anodd number of units so that there is never ajoint at the crown but rather always a keystone.The bed joints must be arranged perpendicularto the line of thrust and fllust run the full deothof the arch. The bond for masonry arches is tobe produced according to the bonding rulesfor masonry piers [32, 141,1611(tig.2.4.37).

Cambered and gauged archeshave inclined (skewback) abutments alignedwith the centre of the arch. The bed joints alsopoint to the centre of the arch. The rise of acambered arch is max. 1/50 of the width of theopening, that of a gauged arch max. 1/12. Acambered arch without any rise may also actas an arch in comoression if the soldier coursedeviates slightly from the vertical and iswedged into abutments built at a very slightangle.The arch l intel is produced from an odd num-ber of courses, which can make it necessaryto inset the abutments by half the width of acourse on the masonry at the sides. The extra-dos should always end in a bed joint of themasonry above in order to avoid large com-pensating courses above the arch or un-attractive gussets above the abutments. Therequirements regarding joint thicknesses andbonding correspond to those for semicircularand pointed arches (see fig. 2.4.38).

Vaulting and arch floors

Vaults

These are roof-like, one-way-spanning, or alsobidirectional arch-like or spherical curved roofconstructions of masonry. The various types ofvaulting are based on the two fundamentaltypes: barrel vaults with cylindrical curvature,and domes with spherical curvature. Besidesthe barrel vault, other cylindrical forms includethe Prussian cap vault; the cloistered vault; thetrough vault; the cov; and the groined vault.The dome is a spherical form of vaulting whosesurfaces generally form part of the surface of asphere (see fig. 2.4.39).

o

Eo'oI

139

Masonry details

2.4.39 Types of masonry vaulting Vaults with smaller spans, a favourable span/rise ratio (f/l > 1/10) and essentially permanentloading can be designed according to the l ineof thrust method. They are built from taperedmasonry units that support each other and aresupported on immovable abutments in such away that they are only subjected to compres-sion. The arch thrust can also be resisted byties (in tension) instead of abutments.Vaults with large spans and pronouncedchanges of loading are designed according toelastic theory.

Masonry arch floors between beams

These are the upper part of an arch builtbetween steel beams as vertical suppotls (seetig.2,4.40). The structural system employed fordetermining the vertical and horizontal suppotlreactions for arch floors is a three-pin arch withthe centre pin at the crown. With an essentiallystationary imposed load according to DIN 1055part 3, arch floors with a thickness based onempirical rules and with beams spaced at max.approx. 2.50 m do not need to be analysedstructurally. In this case, the minimum thick-ness must be 1 15 mm, they must be built using"Kuff" bond or herringbone bond, and the ratioof rise to span must be at least 1/10. Centeringfor parallel arches should, l ike the bricklayingitself, be carried out simultaneously in order tolimit the horizontal thrust caused by the archesat the end bays of multi-bay floors. Ties can beintegrated to transfer the horizontal thrust fromthe end bays of multi-bay floors to the sidewalls. These must be included in the end baysparallel to the direction of span of the floor atthe ends of the beams and at a spacing equalto the span of the end bay but at least at third-points. In order to consider the end plateformed by ties as an adequate abutment (rigidhorizontal olate) able to transfer the horizontalthrust to the sides, the width of the end platemust be equal to one third of its length. Theties used must be longer than the minimumwidth of the plate. ln the case of narrow endbays it is sometimes necessary to extend theties over several bays (see fig.2.4.41).The end bays must be provided with supportsat the sides which are in the position to acceptthe horizontal thrust of the middle bays evenwhen the end bays are not loaded. The sup-ports may be secured by means of masonry,permanent vertical load, anchors or other suit-able measures. In the basements of buildingswith an essentially stationary imposed load ofmax. 2.0 kN/m2 we can assume, without astructural analysis, that the horizontal thrustfrom arch floors up to 1.3 m span can beaccommodated by means of 2 m long, 240 mmthick crosswalls at a spacing of max. 6.0 m.The crosswalls must be built simultaneouslywith and fully bonded to the end bay supportwalls or - in the case of toothing - via a non-mechanical connection (see fig. 2.4.42).

,'/ar-'ll

Groined vault

,,iY--',,4''\ /

/,' \/Cloistered vault

,2r-ilD-" 7

6)Barrel vault

/ _ - - - - - - l(_ ,_-_,__)Hemispher ical

Trough vaull

2.4.40 Design requirements for masonry arch floors

"Kuff" bond

2,4.41 Assumptions for arch thrust for multi-bay arch floor

lE Direction of span

-': Steel -'/oeams

Steelbeams

Hetringbone bond

Lateral support

17-7-7=7-71.--i -

, ' I

-Lateralsupport

..-..:

II

I

c

cooo

!o

Eo

l

Ec

4I

T

i;fo -

Length of anchor

>1/3 |

Details of end bay

Side support

>1 /31

Structural system fortransferring horizontalthrust from end bay

Cove

Star vaulting Sail vaull

Arch floor in masonry bond

R i s e f > 1 / 1 0 x 1

140

Connections

Point loads

Masonry can be subjected to point (concen-trated) loads from beams (e.9. window lintels);joists (e.9. joist f loors); or columns (e.9. win-dow mullions, roof posts). These generate ver-tical concentrations of stress on the bearingsurfaces and horizontal spitting tensile forcesin the load dispersion zone. The spitting tensileforces can be accommodated by the tensilestrength of the masonry bond, by reinforce-ment or by reinforced concrete elements.A padstone or similar is always integrated intothe masonry to distribute the load from heavypoint loads. This is usually of reinforced con-crete but may be of steel. The reinforced con-crete ring beam or the suppor/floor strip isoften used. lt may also comprise masonry unitsof higher strength incorporated in the masonrybond below the point load. In both cases thedesigner must take account of possible crack-ing in the masonry as a result of restraintscaused by the change in material (see fig.2.4.43). A load distribution of 60" may beassumed within a section of wall strengthenedwith units of higher strength. The strengthrequired for this masonry is determined by thebearing stresses beneath the point load. Theheight over which the wall must be strength-ened is determined by the fact that the normalmasonry of the wall (of lower strength) must beable to carry the load beneath the 60" load dis-persion.The permissible stresses for masonry belowpoint loads are greater than for the rest of thewall because the inclined "struts" created bythe 60'load dispersion generate a biaxial com-pression condition at the point of action of thepoint load which increases the load-carryingcapacity of the masonry locally. However, theinclined struts mean that there are also horizon-tal "ties" in the lower courses of the wall, the ten-sion in which has to be resisted by horizontalreinforcement or by the floor slab acting as a tie.Point loads that act at the end of a wall createan inclined strut, which is balanced by a hori-zontal tension at the top of the wall. This ten-sion leads to vertical cracks, to tearing of themasonry bearing, if it cannot be accommodat-ed by the masonry bond, the reinforced con-crete floor slab or ring beam acting as a tie orby horizontal reinforcement in the masonry.When analysing the point load and thedispersion of the load according to DIN 1053part 1, the position of the point load is takeninto account through the dimensions of thepoint of action of the load (see fig.2.4.43).Point loads perpendicular to the plane of thewall, e.g. from horizontal impacts, should notexceed 0.5p* according to the more accuratemethod of analysis in DIN 1053 part 1 and0,5 x2.67 oo = 1.33 oo according to the simpli-f ied method of analysis. In addition, the shearstresses in the bed joints of the individualmasonry units under load must be analysed for

horizontal point loads perpendicular to theplane of the wall where F > 3 kN. Perforatedand cellular units require a plate or similar tobe incorporated underneath so that the hori-zontal load is transferred to at least two websin order to avoid overloadinq the webs of indi-vidual masonry units.

Connections

Walls must be connected to floors and roofframes in order to guarantee transfer of forcesand provision of horizontal support for load-bearing and stiffening walls. This can beachieved either by anchors or through ad-hesion and friction.In order to also achieve three-dimensionalstabil ity for the building, ring beams must beplaced in all external and crosswalls which actas vertical plates for carrying horizontal loads(e.9. wind). This presupposes that the floorsact as horizontal plates. Floors that do not actas plates (e,9. timber joist floors), or thosewhich are supported on the walls via slidingbearings in order that deformations are notrestrained (e.9. roof slabs) require that thewalls, and hence the building, gain horizontalrestraint by way of capping beams or othereouivalent structural measures.

Connecting walls to floors and roof frames

In principle, all walls - including internal wallsor pafty walls separating buildings - must beconnected to floors such that forces can betransferred, provided the floors are intendedto provide lateral support to the walls.

Connection using anchorsAnchors (with vertical straps in the case of tim-ber joist floors) must always be included inloadbearing areas of walls and never in non-loadbearing spandrel panels. Only by provid-ing vertical load is the wall in a position toaccommodate the anchor forces and guaran-tee the transfer of forces to the floor. A lack ofvertical load might dictate the use of a dngbeam. Generally, the spacing between anchorsshould not exceed 2.0 m in order to limit the -forces placed on them. However, the spacingmay be increased to max. 4.0 m in exceptionalcircumstances if the particular constructiondoes not permit any other solution.Walls parallel to the direction of span of thefloor require straps which extend at least 1.0 minto the floor and are fixed to at least two floorribs or Mo beams (three joists in the case oftimber floors). This distribution of load overseveral ribs or beams/joists is necessary be-cause otherwise the restraint forces subject thefloor members to lateral bending (see fig.2.4.46). Beams spliced over internal walls andtied to the perimeter walls must have a tension-resistant splice connection. This is necessary

2.4.42 Accommodating the arch thrust withoutstructural analysis for a multi-bay arch floorover basement

2.4.43 Load dispersion below point load

Masonry of lower strength

or : to be carried by masonry of higher strengthoz : to be carried by masonry of lower strength

_f:I l " '

? r ' t 'T.--f

a l

#applies for

A t = 2 d 2

and

e < d / 6

o . . S 1 1 + o 1 A ) < r . s b' - ' y ' - l ' 1

Permissible bearing stress to DIN 1053 pt 1

Masonry of higher strength

01 from point load(beam, column, joist)

141

Masonry details

Unbraced gable wallAnchor at apex

2.4.44 Support options for gable walls

Suooort via braced roof frame

Support via integral column

2.4,45 Load distribution of a ring beam for buildingstiffened bv floor olates

in order to link opposing external walls togetherand ensure an effective connection betweenexternal walls and floors.Gable walls can be connected via anchors toa braced roof frame. Alternatively, they gaintheir stability by way of crosswalls or othermeasures (e.9. reinforced concrete columnsrestrained by the floor slab, masonry piers)(see fig. 2.4.44).

Connection using adhesion and frictionSecure support for walls by way of adhesionand friction is provided by concrete floorswhen the depth of bearing of the slab on thewall is at least '100 mm; anchors are thenunnecessary. An adhesion/friction connectionassumes that a connection caoable of transfer-ring forces is generated by the adhesion alone,and is only reinforced by the friction arisingfrom vertical loads if necessary; however, thepresence of friction is not absolutely essential.We can also assume this situation at the junc-tion between a wall and a capping beam.

Ring beams and capping beams

These are horizontal straight members in theplane of the wall. Ring beams accommodatetension within the wall plate, which ensues as aresult of external loads or differential deforma-tion, and hence increases the stability of thewalls and that of the whole structure.Capping beams also serve as ring beamswhen they form a complete ring around thewhole building. Furthermore, their reinforce-ment arrangement allows them to accommo-date loads perpendicular to the plane of thewall by way of bending.

Ring beamsact as ties to hold the structure together. Theyare required in buildings with more than two fullstoreys, or those longer than 1B m at wall ele-ments provided for stabilizing the structure(external walls, twin-leaf party walls, crosswallsetc.) at or immediately below every floor level.Ring beams may be interrupted only when theireffectiveness is guaranteed by other compo-nents, e.g. window lintels or landings in the caseof continuous windows to a staircase.It is also necessary to hold the structure togetherby way of ring beams in the case of walls withmany or particularly large openings; this isespecially the case when the sum of the widthsof the openings exceed 60% of the length ofthe wall or 40%;o in the case of windows greaterthan A3 of the storey height.Other functions of ring beams are to act as a tiefor the compression arch in a horizontal floorplate; to act as a tie for the vedical masonryplate; and to accommodate tensile stresses inthe masonry as a result of differential deforma-tion caused by temperature fluctuations,shrinkage or differential settlement of the sub-soil [54] (see fig. 2.4.45).

Ring beams may be made from timber, steel,reinforced masonry or reinforced concrete.They are to be designed for a tensile force of30 kN under service loads. This figure corre-sponds to the forces to be expected in build-ings of normal dimensions. The beams shouldbe designed for greater tensile forces when astructural analysis of the wall plate, floor plateor differential deformation results in larger fig-ures. Ring beams of reinforced masonry mustcomply with the corrosion protection, reinforce-ment arrangement and mortar or concretecover requirements of DIN 1053 paft 3. Ringbeams of reinforced concrete must have atleast two continuous 10 mm reinforcing bars toDIN 1045. The reinforcement laps should be inaccordance with DIN 1045, and staggered ifoossible.The reinforcement required for ring beams ofreinforced masonry or reinforced concrete mayinclude the full cross-section of continuousreinforcement not fully utilized in floor slabs orwindow lintels no more than 500 mm from thecentreline of the wall or floor parallel to thebeam (see tig.2.4.47). The use of differentmaterials for the masonry and the ring beamcan lead to damage to masonry. Above all,severe temperature deformations in ringbeams generally as well as the shrinkage ofreinforced concrete ring beams in padicularcan lead to cracks in the masonry. Tempera-ture deformations can be minimized by includ-ing adequate thermal insulation, shrinkagereduced by late striking of the formwork and bysubsequently treating the concrete. To mini-mize cracking in rendering, a reinforced con-crete ring beam should make use of fabricreinforcement or, alternatively, should be fabri-cated from channel blocks to match the sur-rounding wall and hence provide a consistentsubstrate for the rendering. This or the use ofreinforced masonry as a ring beam means thatthe disadvantages of changing the materialare, on the whole, avoided.

Capping beamsare subjected not only to tensile forces but alsoto bending moments from horizontal loads.Capping beams are necessary when floors donot act as plates, e.g. timber joist floors, or areprovided with sliding bearings where ihey aresupporled on the walls and so do not providelateral restraint at floor level. The ring beambecomes a capping beam and takes on a sta-bilizing task. As a rigid horizontal beam it trans-fers the horizontal loads from wind, reversal offorces, earthquakes etc. to the shear walls (see' f i7 .2.4.48) .

The capping beam and its connections to theshear walls should be designed for a horizontalload equal to 1/100 of the vertical load of thewalls and for a proportion of the wind loads. Inaddition, capping beams beneath sliding bear-ings must take account of tensile forces fromthe residual friction forces of the floors.

142

Connections

Shear walls must be analysed to ensure theycan accommodate the support reactions ofcapping beams, and that they adequatelytransfer the forces to the foundations.lf a capping beam does not fulf i l r ing beamfunctions at the same time, it needs only toextend as far as necessary to iransfer its sup-port reactions to another element. Cappingbeams may be made of t imber, steel or rein-forced concrete. They must be rigid enough toprevent any cracks in the masonry due todeformations. This reouirement means that thefeasible span of such a beam is sometimeslimited. Reinforced concrete capping beamsmust have shear l inks and at least one longitu-dinal reinforcing bar in each corner of the l ink.Capping beams should be treated l ike ringbeams with regard to the problem of the risk ofcracks in masonry caused by a change ofmaterial between wall and beam, This alsoapplies to the use of channel blocks to achievea consistent plaster substrate. r

2.4.46 Fixing lension anchors in masonry

> 240T T

ln-situ concrete floor withring beam reinforcement

> 2 4 0t--|

Reinforcementbetween planks

t l ot ) , , , ' , ' ,r a /[:T

Precast plank

O

N

O

6

"f:

1Strap > 15 x 50 mmGable anchor must befixed to 3 joists

.%%

Strutting

Fixing to masonry at right-angles to span of floor

Precast floor with reinforced Reinforced masonry asconcrete ring beam ring beam

Fixing to masonry in direction of span of floor

2.4.47 Delails of ring beams taking into account parallel reinforcement

Timber joist floor with rein-forced concrete ring beam

EO

ooVI

S 5 0 c m

Max. spacing of parallel reinforcement which may be consideredRing beam made fromprefabricated channel blocks

2.4.48 Capping beam action

143

l