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Relevant Literature:
Relevant Literature:
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Buicick k DaDavividsdson on & & GrGrahaham am W W OwOwens ens !!0000"#"#.. SteeSteel l DesiDesignersgners’ ’ ManuaManual l . . $$thth ed. Londoned. London::
Blackwell. Blackwell. %%. "'"( %%. "'"(
Source: )o%* owned +* ,eter -orster Source: )o%* owned +* ,eter -orster S)'1"/
S)'1"/ Design for Construction,Design for Construction, 1"1" %%. 1( 12 $2 $$
%%. 1( 12 $2 $$ Source: 3S Source: 3S 4.W.
4.W. rwin )rwin )R4 R4 Re%ort 10!Re%ort 10! Design of Shear Wall BuildingsDesign of Shear Wall Buildings 1/( 1/( Source: 3S
Source: 3S Struct5
Struct5 Manual for the design of Manual for the design of concrete building structures to Eurocode 2,concrete building structures to Eurocode 2, !00$!00$ %%. 1" $$ "0 10"
%%. 1" $$ "0 10" Source: 3S
Source: 3S 4,4
4,4 Diaphrags and Shear Diaphrags and Shear Walls,Walls, Source: 3S
Source: 3S
6.4. Baird & 5.). O7elton
6.4. Baird & 5.). O7elton !iber Designers’ Manual 2 !iber Designers’ Manual 2 nd nd
ed" ed" 1/(1/( %%. 2$0'2$"
%%. 2$0'2$"
Source: )o%* owned +* Lowr* 8anson Source: )o%* owned +* Lowr* 8anson
Structural Guidance 9otes 3and 4nal*sis o Sim%le Linked and
Structural Guidance 9otes 3and 4nal*sis o Sim%le Linked and )ou%led Shear Wall)ou%led Shear Wall source: Richard 9icholl
source: Richard 9icholl
W.G )urtin G Shaw 6.; Beck & W.4 Bra*
W.G )urtin G Shaw 6.; Beck & W.4 Bra* Design of Bric# Design of Bric# Diaphrag WallsDiaphrag Walls Source: 3S
Source: 3S Struct5
Struct5 Manual for the Design of Manual for the Design of $lain Masonr% in Building Structures to Eurocode &,$lain Masonr% in Building Structures to Eurocode &, !00/!00/ Source: 3S
Source: 3S
)odes o ,ractice:
)odes o ,ractice:
BS 2$!/'1:!002 BS 2$!/'1:!002 BS 2$!/'!:!002 BS 2$!/'!:!002 BS /110'1:1" BS /110'1:1" BS 59 1$'!:!00$ BS 59 1$'!:!00$ BS 59 1$':!00$ BS 59 1$':!00$ BS 59 1/'1:!00( BS 59 1/'1:!00( BS 59 1/':!002 BS 59 1/':!002 9ote: 4l
9ote: 4ll literature and BS can l literature and BS can +e ound in +e ound in the Shear Wall ile under technical literature in the the Shear Wall ile under technical literature in the GG drive.
1.1 Desi<n
Shear walls oer a structurall* eicient means o enclosin< and utilisin< s%ace. =heir stiness is such that swa* movement under wind load can +e minimi7ed. Shear walls are also known as >ertical Dia%hra<ms in 4merica. =here are three main t*%es o Shear Wall:
1. Simple Shear Wall: 4 sim%le shear wall is a vertical cantilever wall to which a lateral load is a%%lied and the wall transmits this load to the oundations.
!. Coupled Shear Wall: =wo walls in line which are ?oined to<ether +* connectin< +eams so that the* ac as one com%osite stienin< element to a <reater or lesser de<ree.
. Linked Shear Wall: =wo or more walls in line which are ?ointed to<ether +* linkin< +eams +ut which act as se%arate elements.
4 connectin< +eam is sim%l* a +eam lintel or stri% o sla+ which eectivel* connects to<ether two walls so that the* act as cone com+ined stienin< element. 4 linkin< +eam is one which ?oins two walls +ut is considered too slender to +e eective o has +een assumed to take no %art in connectin< the elements to<ether.
Shear walls should be designed as vertical cantilevers, and the reinforcement arrangement should be checked as for a beam. Where the shear walls have returns at the compression end, they should be treated as flanged beams. This guide assumes that shear walls are sufficiently stiff that global second order effects do not need to be considered. The walls should be sized such that:
2 , ! . " # $"% . & L I E n n F cm c s s Ed V
∑
+ ≤Where: F ', (dis the total vertical load #on the whole structure stabilised by the wall ns is the number of storey)s
L is the total height of building above level of moment restraint E cm is the mean modulus of elasticity
I c is the second moment of area #uncracked concrete section of the wall#s. This assumes that:
• Torsional instability is not governing, i.e. structure is reasonably symmetrical
• *lobal shear deformations are negligible #as in a bracing system mainly consisting of shear walls
without large openings
• +ase rotations are negligible
• The stiffness of the wall is reasonably constant throughout the height
• The total vertical load increases by approimately the same amount per storey.
-n the above euation for F ', (d it should be noted that the value &.$"% should be halved if the wall is likely to be cracked.
/ore detailed design calculations should be carried out using computer analysis. The advantages of shear walls are:
• The beam0to0column connections throughout the frame are simple, easily fabricated and rapidly erected. • Shear walls tend to be thinner than other bracing systems and hence save space in congested areas such
as service and lift cores.
• They are very rigid and highly effective. • They act as fire compartment walls
The disadvantages of shear walls are:
• The construction of walls, particularly in low0 and medium0rise buildings, is slow and less
accurate than steelwork.
• The walls are difficult to modify if alterations to the building are reuired in the future. • They are a separate form of construction, which is likely to delay the contract programme. • -t is difficult to provide connections between steel and concrete to transfer the large forces
generated.
Concrete Shear Walls:
/onolithic shear walls can be classified as either short, suat or cantilever according to their height depth ratio #1igure ", their walls may be planar, flanged or core in shape.
1igure ": eight34epth 5atios of /onolithic Shear Walls, 6-5-7 5eport "&2, "89
-n many cases, when a shear wall is used the walls are pierced by openings such that the behaviour of the individual wall sections is coupled to a variable degree, depending on the proportion of the walls and connecting beams.
The plan distribution of walls should be such that the building is torsionally, as well as fleurally, stiff #figure 2. -n rectangular plan buildings, shear walls are often placed at the etremities of the building in order to resist load on the wider face of the building. -n the orthogonal direction, frame action may be utilised. Wind resisting cores #rather than pierced shear walls are usually preferred internally within buildings.
and aial forces. ;ateral restraints are reuired at each floor level and adeuate tie reinforcement should be provided. The wall should be braced against relative translation of its ends. The compressive resistance of a wall element is a function of it slenderness < effective height3thickness # eh3t . The
effective height may be taken as &.%$ Storey height if the wall is fully restrained at is ends. Where the wall is connected to a fleible floor element, the use of the full storey height is more appropriate. -n design of slabs with slenderness ratio higher than "2, out0of0plane moment transfer from the slabs and destabilising moment from eccentricity of aial loads should be taken account of.
The minimum amount of reinforcement varies with the design reinforcement varies with the design reuirement. 7 minimum percentage of &.2$= high yield steel or &.>= mild steel both horizontally and vertically is usually reuired for shrinkage and temperature reasons.
1igure 2: ?lan distribution of shear walls, 6-5-7 report "&2, "89
1igure : Typical 1loor ;ayout to /aimise ?re0 stressed effects. -Struct( 4esign /anual to (urocode
1igure $: ;ayout of shear walls to reduce loss of prestress and cracking effects. -Struct( 4esign /anual to (urocode
Masonry Shear Walls:
4esign 6riteria:
". /asonry buildings shall be composed of floors and walls, which are connected in two orthogonal horizontal directions and in the vertical direction.
2. The connection between the floors and walls shall be provided by steel ties or reinforced concrete ring beams.
>. 7ny type of floors may be used, provided that the general reuirements of continuity and effective diaphragm action are satisfied.
. ? Shear walls shall be provided in at least two orthogonal directions. $. Shear walls should conform to certain geometric reuirements, namely:
• the effective thickness of shear walls, t ef , may not be less than a minimum value, t ef, min@ • the ratio hef 3t ef of the effective wall height #see (A "88!0"0":2&& to its effective
thickness may not eceed a maimum value, #hef3t ef ma@ and
• The ratio of the length of the wall, l , to the greater clear height, h, of the openings
adBacent to the wall, may not be less than a minimum value, (l/h) min.
Shear walls not conforming to the minimum geometric reuirements of condition $ may be considered as secondary seismic elements. They should conform to conditions " and 2.
4epending on the product ag.S at the site and the type of construction, the allowable number of storeys
above ground, n, should be limited and walls in two orthogonal directions with a minimum total cross0 sectional area Amin, in each direction, should be provided. The minimum cross0sectional area is
The shear walls of the building should fulfill all of the following conditions:
a The building should be stiffened by shear walls, arranged almost symmetrically in plan in two orthogonal directions@
b 7 minimum of two parallel walls should be placed in two orthogonal directions, the length of each wall being greater than >&= of the length of the building in the direction of the wall under consideration@
c 7t least for the walls in one direction, the distance between these walls should be greater than %$= of the length of the building in the other direction@
d 7t least %$= of the vertical loads should be supported by the shear walls@ e Shear walls should be continuous from the top to the bottom of the building.
-n cases of low seismicity the wall length reuired may be provided by the cumulative length of the shear walls in one ais, separated by openings. -n this case, at least one shear wall in each direction should have a length, l, not less than that corresponding to twice the minimum value of l/h.
-n both orthogonal horizontal directions the difference in mass and in the horizontal shear wall cross0 sectional area between adBacent storey)s should be limited to a maimum value of Cm,maand C7,ma.
1or un0reinforced masonry buildings, walls in one direction should be connected with walls in the orthogonal direction at a maimum spacing of % m.
Shear Walls in Steel Frames:
When reinforced concrete or masonry elements are present in a steel frame building, the designer can profit by using these stiff elements to resist lateral loads. 7 typical eample is a building with a reinforced concrete lift shaft, to which the steelwork can be attached. Similarly, masonry walls forming in0fill panels between steel columns can replace bracing members by providing in0plane stiffness.
The ideal position for a shear wall is on the line of the lateral loads, to avoid eccentric loading. (amples of structurally efficient and less efficient locations are shown in 1igure >. 6learly, there will be many other constraints on the position of a wall or lift shaft which may make eccentric loading unavoidable. -n such cases the steel frame will reuire some additional bracing members to prevent torsional displacement of the building. The position of this additional bracing for the particular eamples is shown in the figure. The mechanism by which the bracing resists torsion is also indicated for one of the eamples.
1igure >: Steel 6onstruction -nstitute, esi!n "#r $#nstructi#n Timber Shear Walls:
See Timber 4esign *uide, or Tim%er esi!ners& /anual #;owry /anson.
Force Actions
-n limit0state design, forces are multiplied by their appropriate load factors to euate to the structural strength. ;oad factors are related to the levels of probability of loading and the possible combinations of load.
Loadings/ Movements:
Dead load: Structural and dead weight are important as they contribute to the overturning resistance of the foundations. 6ertain shear wall elements receive relatively little vertical load in comparison to lateral load, which they are reuired to resist. Serious under0estimates of dead load can lead to increased dynamic response.
Imposed load: -ntensities of prescribed floor loading depend on the use of the building. 7ll floors may be considered to be uniformly loaded in assessing overall structural action
Wind load: ;ateral loading often dictates the proportions of a shear wall building. Wind loading is characterised by a design wind speed at a certain recurrence period. -n the design of buildings, a "0in0 $& year recurrence win is used to assess the ultimate strength of the structure.
+oth the steady and the gust components of the wind contribute to the structural response. The increase in load over that of the building considered uasi0statically #i.e. as a rigid structure is termed the Ddynamic magnification of load).
Seismic loading: *round accelerations from seismic activity can be the principal design condition. This is usually epressed in terms of euivalent lateral loading.
Creep/ Shrinkage of Concrete: These effects take place over a number of years, and they may be estimated using information found in the design guide for pre0stressed concrete.
Temperature: 4ifferential temperature movement between the roof and internal floors and the basement, or between eposed and shaded sides of the building or eposed and insulted members can be significant.
Out-of-plumb Walls: +ecause of sway displacements, construction tolerances, and differential settlement, the enhanced moment resulting from aial loading should be taken into account during design.
Note: /ore detail and relevant factors can be found in the specific design guides for the individual loadings.
