ISET GOLDEN JUBILEE SYMPOSIUM Indian Society of Earthquake Technology

Department of Earthquake Engineering Building IIT Roorkee, Roorkee

October 20-21, 2012 Paper No. D023

REINFORCED CONCRETE STRUCTURAL WALL-FLOOR SLAB CONNECTION–STATE OF THE ART

Surumi R.S.1, Greeshma S.2 and Jaya K.P.3

1Research Scholar, Anna University, Chennai, India, surumirazia@gmail.com 2Assistant Professor, Anna University, Chennai, India, greeshmas@annauniv.edu

3Associate Professor, Anna University, Chennai, India, jayakp@annauniv.edu

ABSTRACT

One of the economic systems of construction of high-rise buildings is shear wall structures which constitute RC structural walls and floor slabs. The floor slabs and shear walls together act as a rigid jointed frame in resisting gravity loads and lateral forces due to wind and earthquake. Connection between structural walls and floor slabs is a key force resisting element which is subjected to severe stress concentration and an essential link in the lateral load resisting mechanism of shear wall structures. This paper reviews the state-of-the-art on the developments in structural wall-floor slab connections. The history of research into the behaviour of the connections is traced starting from the developments in 1969. A review and commentary is presented on the available research to understand and develop structural wall-floor slab connections for high rise buildings. Keywords: Reinforced Concrete, Structural wall, Shear wall, Floor, Slab, Connection, Joint area.

INTRODUCTION Modern tendency is towards the construction of high rise buildings which has become the symbol of pride of nations. Increase in population, shortage of space to build and consequently high cost of land in urban areas has also led to the construction of high rise buildings. One major structural characteristic of tall buildings is that the effect of wind and seismic loads becomes more pronounced with the increase in the height of the building. Search for more types of structural systems and economical methods of construction resulted in the development of a type of tall buildings called shear wall structures. These buildings consist of load bearing walls and slabs. A structure in which the walls carry both gravity as well as the lateral loading is called a shear wall structure. A perspective view of a typical building is shown in Fig.1. It has been observed that shear-walls are more effective in resisting the lateral forces than columnar structures. In this structural form the floor slabs act as diaphragms distributing the horizontal loads to the vertical shear walls. The floor slabs and shear walls act together as a rigid jointed frame in resisting loads. The connection between slab and shear-walls is a key force resisting element subjected to severe stress concentration, in the lateral load resisting mechanism of slab-wall systems. The performance of the connection can influence the pattern and distribution of lateral forces among the vertical elements of the structure.

Fig.1. Perspective view of a shear wall building.

Shear walls not only have the structural function of carrying vertical and horizontal loads but also the non-structural function of dividing and enclosing the space as well; leading to a system called cross-wall construction. The cross-walls are employed as load bearing walls in addition to serving architectural requirements. The longitudinal corridor and facade walls are provided with openings for access to the living areas and balconies, and these longitudinal walls act as flanges for the primary cross-walls. Shear walls are also used to enclose lift shafts and stairwells to form partially open section box structures. Thus, in practice, shear walls of various shapes, planar, flanged or box shaped, may be coupled together in cross-wall structures. The analysis and design of the floor slab-wall junctions of shear wall structures connected by slabs only can be divided into four steps: (1) Analysis of the shear wall to determine the forces due to various loads. (2) If the shear wall is idealized as a two dimensional structure with slab acting as connecting beams, then an effective slab width which has the same shear stiffness as the whole slab is to be determined. (3) Determination of moments, torsion and shear around the connection and (4) Design and detailing of the connection. Thus the factors on which the behaviour of the shear wall-slab connection depends are effective width and stiffness of slab, distribution of moments and shear forces in slab, strength and stiffness of wall-slab connection and the detailing of reinforcement in the wall-slab junction. EFFECTIVE WIDTH AND STIFFNESS OF SLAB The two-dimensional models for the analysis of shear walls assume that the walls are connected by beams. However when the walls are connected solely by slabs the true stiffness of an equivalent beam is less than the total stiffness of the slab considering the entire width. For the sake of convenience it may be-assumed that only a small portion of slab called 'effective width', with stiffness equal to the equivalent connecting beam is effective in resisting the effects of lateral loads. To evaluate the effective width for different sets of circumstances, several investigators have studied the nature of interaction between laterally loaded walls and coupling slabs, both experimentally and analytically.

A theoretical and experimental investigation of the bending stiffness of slabs against the parallel rotation of pairs of in-line walls as in cross wall structures has been carried out by Qadeer and Smith (1969). An idealised structure was chosen with regular spaced pairs of walls as shown in Fig. 2. The slab was analysed as an elastic plate represented by Lagrangian equation and solution was obtained finite difference method. From the analysis slab forces and hence moment/rotation relationship were determined. A nondimensional parameter K used to express the stiffness of the slab was given as in Eq. (1):

…….(1)

where D is the stiffness of the slab per unit width, M is the resultant moment about the wall axis, and θ is the effective slab rotation. The effective slab width Ye to full width of slab, Ye/Y for Poisson’s ratio υ, is given by Eq. (2):

…….(2)

Curves showing the values of stiffness factor K and Ye/Y as a function of L/X for various ratios of C/X were also presented, for various ratios of Y/X. The curves provide values for the stiffness of slab against the rotation of the walls and can be used for determining the horizontal stiffness and stresses in cross-wall structures.

Fig.2. Plan of slab and cross-wall structure (Qadeer and Smith,1969) A finite element study of the interaction between laterally loaded flanged shear walls and floor slabs in cross-wall structures was carried out by Coull and Wong (1985). The influence of local elastic wall deformations on the effective width and coupling stiffness of the slab was studied. The coupling stiffness of the slab was determined by imposing an arbitrary vertical deflection at the slab edge representing the line of contraflexure at the centre of the corridor (axis y-y on Fig. 3), while the remote ends of the wall are fully restrained. The slab stiffness factor K is expressed as in Eq. (3):

…….(3)

where M is the resultant moment about the wall axis, D is the flexural rigidity of the slab, and θ is the effective slab rotation, then the effective slab width ratio Ye/Y is given by Eq. (4):

…….(4)

where Ye and Y are the effective and full slab widths, l is the distance from the line of contra flexure to the centroidal axis of the wall and υ is Poisson's ratio.

C

Y

Y

Y/

C W L W X

Y/2

Fig.3. Plan of wall-slab structure (Coull and Wong,1985)

A measure of the additional flexibility produced by local elastic wall deformation is provided using the stiffness ratio α. If Kr and Yer are the slab stiffness factor and effective slab width respectively determined for the case of a 'rigid' wall, the junction flexibility can be conveniently measured by a stiffness ratio α given by Eq. (5):

…….(5)

Works were carried out on plane wall systems to investigate the relative influence of the different structural parameters on the wall-slab junction flexibility and on the action of the slab in coupling deformable T-shaped shear walls. The results for different storey heights do not differ by more than 0.5%, indicating that the influence of storey height may be neglected in the evaluation of elastic wall deformation effects. The slab/wall thickness ratio (t/h) has a strong influence on junction flexibility. Increasing the slab/wall thickness ratio decreases the values of effective slab width ratio, effective flange width ratio and stiffness ratio. The influence of t/h is relatively more important within the range 0.5-l. The effective flange width ratio is more sensitive than the stiffness ratio to variations in the thickness ratio. The effects of junction flexibility are more significant when the corridor-opening ratio (L/X) is reduced. The effective slab width and the stiffness ratio decrease substantially when corridor-opening ratio is reduced from 0.6 to 0.1, but the effective flange width is not affected significantly by the variation of corridor-opening ratio over this wide range. The local elastic wall deformation produces larger reductions in the effective width of the slab with larger flange width ratios (width of flange/width of slab, Z/Y). The stiffness ratio remains substantially constant over the range of flange width ratios considered. The effective flange width is also not affected significantly by the flange width ratio larger than about 0.25. With smaller flange width ratios, the effective flange width ratio decreases rapidly with a reduction in flange width ratio. Design curves were presented to give a rapid estimate of the effective slab width, stiffness ratio and effective flange width. Curves showing the variation of Ye/Y as a function of L/X for various ratios of t/h were presented, for various ratios of Y/X and Z/Y. Curves showing the variation of α with L/X and t/h for various ratios Y/X and Z/Y were presented. Curves showing the variation of Ze/Z as a function of t/h, for various ratios L/X and Z/Y were also presented. These curves can be used as design curves for evaluating directly the effective slab width, stiffness ratio and effective flange width accounting automatically for the effects of local wall deformation. Another work has been reported by Coull and Wong (1986) about a finite element analysis, in conjunction with Vlasov's theory of warping of thin-walled beams, conducted to study the torsional

LINE OF INFLECTION

Y/2

x

l

C.G.

X

L

h

x

y

y

Z

Y/2

TYPICAL QUADRANT

stiffening of thin-walled open-section cores by the surrounding floor slabs. The standard rectangular Adini-Clough-Melosh plate bending element, with three degrees of freedom at each node (one translational and two rotational), was used. The relative influences of the most important geometrical parameters and slab support conditions were examined, and design curves were presented to allow the equivalent slab width and effective warping stiffness of the slab to be evaluated rapidly. The warping stiffness of the slab was evaluated by summing the products of the reaction and displacement vectors for the core-slab boundary nodes. Assuming that the slab reactions are evaluated as a system of discrete forces Pi and couples Msi and Mni acting respectively in the plane of, and normal to the plane of, the core wall; the bimoment resultants of these forces may be obtained from Vlasov's theory. The warping stiffness of the slab is then given by the sum of the resultants as in Eq. (6):

…….(6)

where N, is the number of nodes at which the slab reactions on the core are evaluated, wi the sectorial coordinate and (dw/ds)i and (dw/dn)i, the rates of change of the sectorial coordinate function in the tangential and normal directions, respectively. The parameters considered to influence the warping stiffness of the slab were the core aspect ratio, the core opening ratio, the slab width ratio, and the support conditions for the interior and exterior edges of the slab. The relative influences of the various parameters were evaluated and effective design curves were produced. It was observed that the effective width increases considerably due to the peripheral slab restraint. The peripheral supports exert a greater influence with a larger core-opening to slab width ratio. The moment connection between slab and core provides a considerable stiffening effect for the slab. By releasing the moment restraint at the core, the warping stiffness of the slab is reduced generally by between 30 and 40%. The investigation on relative influences of the different core-slab geometrical ratios on the effective slab width ratio revealed that, among the three important geometric ratios, the core opening ratio has the greatest influence on the effective width ratio. Influence of support condition was such that, in the case where the slab edges are free, the effective width values for cores without lobby slabs vary from 50-60% of the values for cores with lobby slabs, and in the other cases where the slab edges are simply supported, the corresponding percentage figures were 55-65%. The absolute effective width for the equivalent beam has been shown to be influenced strongly by the support conditions of the slab edges and by the core opening ratio, and less by the core aspect ratio and slab width ratio. Influence of a pseudo crack on the coupling slab behavior was studied by Coull and Wong (1990) by performing a finite element analysis. Theoretical investigations on how a given crack could affect the two important design criteria - effective slab stiffness and principal slab bending moments, were performed so as to gain insight into the effect of a finite crack on slab behavior. Finite element analysis of a coupling slab containing a transverse crack across the most heavily stressed inner end of the wall has shown that the presence of a crack results in a substantial reduction in the effective coupling stiffness, especially when the wall-opening ratio is small. This confirms the results obtained from different experimental investigations. The distribution of longitudinal moments in the slab is not greatly affected by the presence of a crack, apart from the region near the top of the crack, where bending stress concentrations occur. A number of analytical models of slab-coupled T-shaped RC walls were constructed by Smyrou et al. (2008) in order to investigate the effect of parameters on the effective coupling width of slab. By means of studying the rotations and the strain field originated, a simple preliminary expression for the effective slab width Leff is proposed as a function of the total slab width (Ls) as in Eq. (7):

…….(7) The influence of parameters such as the slab thickness and slab reinforcement on the effective slab width was found to be negligible. The strain field produced showed that the most affected regions of the slab extend along the wall flange faces until the end of the effective slab width. The areas around the flange tips in the compressive side of the coupling part of the slab experienced high strains, highlighting the necessity for special reinforcement. DISTRIBUTION OF MOMENTS AND SHEAR FORCES IN SLAB In designing tall buildings special consideration must be given to provide sufficient stability in all directions against lateral forces due to wind, earthquake or blast. These forces produce critical stresses in the structure, set up vibrations, cause lateral-sway of the building which could cause discomfort to the occupants. The shear walls resist the lateral loads on the structure by cantilever bending action, which results in rotations of the wall cross-sections. The free bending of a pair of shear walls is resisted by the floor slab, which is forced to rotate and bend out of plane where it connects rigidly to the walls. Due to the large depth of the wall, considerable differential shearing action is imposed on the connecting slab, which-develops transverse reactions to resist the wall deformations, and induces axial forces (tensile and compressive) in the walls. As a result of the large lever arm involved, relatively small axial forces can give rise to substantial moments of resistance, thereby reducing the wind moments in the walls and increasing the lateral stiffness of the structure. Similar situation arises if relative vertical deformation of the walls occurs and the effect on the slab is similar to that produced by parallel wall rotation caused by bending. In each case the transfer of moment from wall to slab gives rise to continuously distributed interactive shear forces along the connection. Better understanding of the distribution of moments and shear forces induced due to lateral loads is essential for the design of the wall-slab connection, since the strength of this connection is also affected by the distribution of the forces around the wall-slab junction. In order to give guidance on the design of the slab, Coull and Wong (1983a) carried out a finite element analysis of the bending moments and shear forces in a floor slab coupling a pair of laterally loaded plane shear walls. An elastic analysis of the induced bending moments and shear forces in a slab coupling a pair of plane shear walls was performed. The element used was the simple rectangular Adini-Clough-Melosh element with three degrees of freedom at each node. The finite element mesh adopted for the analysis was chosen to suit the particular geometrical configuration concerned, and used between 88 and 104 elements for the structures considered. The finite element solution furnished the displacements and stress-resultant values at all nodes, and also the slab reactions at the restrained nodes. The reactions at the wall nodes provide the static equivalent wall moment, and the total shear force, transferred from the wall to the slab when the wall undergoes the unit relative displacements assumed. Distribution of bending and twisting moments and shearing forces in a typical quadrant of a slab coupling a pair of plane walls of zero thickness undergoing an arbitrary unit rotation were presented. The moments and shear forces in the slab, calculated for the arbitrary unit wall displacements assumed in the analysis, were expressed in the form of non-dimensional stress-resultant factors to facilitate the calculation of the stress-resultants due to any other wall displacements. These factors define the coupling stress-resultants in a slab of unit corridor width L, unit flexural rigidity D and effective coupling width Ye, induced either by a unit relative wall rotation at the coupled wall end or by a unit relative axial wall displacement δ, in which δ=L . If Mi and Qi represent respectively the calculated bending moment and shear force in the slab, the corresponding stress-resultant factors and may be defined as in Eqs. (8 and 9):

…….(8)

…….(9)

The stress-resultant factors can be expressed in terms of average bending moment Ma and average shear force Qa as given in Eqs. (10,11.12 and 13):

…….(10)

…….(11)

Where …….(12)

…….(13)

The contours of bending moment factors Mx and My for slabs were presented. The contours of stress-resultant factors allow rapid and accurate evaluation of bending moments Mx and My at any point on the slab, induced by any coupled-wall action, and may be used for the design and detailing of the slab reinforcement. Generalized Design Curve for Longitudinal Bending Moments at Critical Transverse Slab Section was also presented. The generalized curve of Mx may also be used to evaluate approximately the effective width Ye of any slab for checking purposes. Since the integration of the bending stress-resultant Mx at the transverse section must equal the value of the external moment, the area under the curve of Mx may be evaluated to obtain the moment rotation relationship leading to the calculation of effective slab width. If the double-area under the truncated curve of Mx for the slab of width Y is Ka, then Eq. (14) gives:

…….(14)

Shear force distribution at wall support and at various peripheral sections were presented. It was observed that the shear transfer must be effected essentially as a very large reaction over a very short length at the inner edge of the wall, together with much smaller opposite reactions distributed over the rest of the wall. This form of shear transfer is consistent with observed punching shear failures in coupling slabs. Peripheral shear force distributions for slabs of various widths were also presented. The ratio of the critical positive shear force to the applied shear force, which may be considered as a "shear modification factor," has been calculated for various locations of the peripheral section in slabs for walls of zero thickness. The curves showing the variation of the shear modification factor with the peripheral distance are presented and can be used as design curves for evaluating the critical shear at any location of the critical section. An extension of earlier work (Coull and Wong 1983a) about finite element analysis of the stress distribution in a slab coupling a pair of laterally loaded flanged shear walls was carried out by Coull and Wong (1983b) later. The same finite element technique was again used for the analysis of the slab. The finite element solution furnished the displacements and stress-resultant values at all nodes, and also the slab reactions at the restrained nodes produced by the relative wall movement. For a unit relative wall rotation, or relative vertical displacement, distributions of critical bending moments were determined, and a generalized design curve was presented to allow rapid evaluations of the maximum moments in a slab coupling a pair of T-shaped walls. An investigation of the distributions of interactive shear forces between wall and slab, in conjunction with the usual design assumptions regarding shear failure of similar flat plate structures, has enabled a design technique to be proposed

for checking against punching shear failure of the slab. Generalised design curves were also presented for the critical bending moments in slabs coupling planar T-shaped walls, and L-shaped walls. The influence of local wall deformation on critical bending moments which may control the design of the slab section was investigated by Coull and Wong (1985). Illustration curves, showing the distribution of longitudinal bending moment factors along the critical transverse slab section at the inner edge of the flanged wall, for various configurations were presented. The curve for the case of a 'rigid' wall, which should be theoretically similar to the case of t/h (slab/wall thickness) = 0, has been included with each set of curves for 'flexible walls', for the purpose of comparison. It was observed from the various curves that the effects of local wall deformation result in a significant reduction in the large bending moment factors in the slab in front of the wall flanges. Since increasing the slab/wall thickness ratio increases the wall/slab junction flexibility, the reduction in bending moment factor becomes relatively more significant with larger slab/wall thickness ratios. Also, as the flanges are more flexible at the ends than at the centre where they are stiffened by the cross (web) wall, the reduction in bending moment factor is relatively greater at points near the flange tip than at other points nearer the centre. The reduction in bending moment factor near the flange centre is however not affected significantly by the flange width ratio, but is seen to be influenced significantly by the corridor-opening ratio L/X. This can be expected since the bending moment factors in this part of the slab would be influenced primarily by in-plane deformation of the web rather than by flexural deformation of the flange. By comparing the sets of curves for various corridor opening ratios L/X, it is seen that the local wall deformation effects produce a decrease in the bending moment factor at the flange centre position when L/X is small (i.e. 0.1-0.2) and an increase when L/X is large (L/X = 0.4). This seems to be consistent with the fact that as the ends of the flange become flexible, the coupling action is redistributed towards the stiffer central part of the flange. The load redistribution would result in an increase in the slab bending-moment factors in the centre, but with small ratios of L/X, this increase would be offset by the larger reduction in bending-moment factors due to in-plane deformation effects. It was seen from the curves that, the effects of local elastic wall deformation could result in as much as 50% reduction in the bending moment factors over a considerable portion of the slab in front of the wall flanges. The curves presented could be used to evaluate the critical bending moments for the preliminary design of the slab section. STRENGTH AND STIFFNESS OF WALL-SLAB CONNECTION Large shear force will be induced in the connecting slab along the line of contraflexure due to lateral loads. This shear is transferred to the wall at the wall-slab junction. The elastic analysis by Coull and Wong (1983a,1983b) predicts very high concentration of shear force at the nose of the wall. Evidently cracking of the slab will reduce this concentration. Different investigators have put forward recommendations to predict the strength of wall-slab connection against the induced shear. A review of previously reported experimental studies on shear wall-floor slab connections was presented by Pantazopoulou and Imran (1992). Parameters that affect connection stiffness and shear resistance were investigated using the experimental evidence and simple mathematical models. Review of reported experimental studies revealed that vertical loads affect the in plane stiffness and shear resistance of floor slabs, particularly in the vicinity of slab-wall connection. The inplane shear resistance of lightly reinforced slab diaphragms in the vicinity of the connection was found to be well below the estimates obtained using the governing ACI design equations. Plane stress analysis of RC diaphragms was performed and an alternative limit for the nominal shear resistance of the slab-wall connection region of slabs was proposed. The nominal shear resistance υn of a thin reinforced concrete element under a state of plane –stress is shown in Eqs. (15 and 16): For failure mode 1,

…….(15) For Failure mode 2,

…….(16)

Where failure mode 1 denote yielding of reinforcement in both directions and failure mode 2 denote yielding of reinforcement in t direction, followed by crushing of concrete struts. The yield strength of steel reinforcement is fy, ρt and ρl are the reinforcement ratios, υ is the average panel shear stress and fc’ is uniaxial compressive strength of concrete and Eq. (17) gives:

…….(17)

An analytical study of strength and stiffness of shear wall floor slab connections was conducted by Bari (1996) using a specially written 3-D nonlinerar finite element program. The program used 20 noded isoparametric brick element with embedded steel. The accuracy of theoritical predictions were tested against results of experimental works done on RC models. Main considerations were reasonable representation of the stress state in the actual structure. Specimens were monitored for ultimate load, mode of failure, crack development and tensile stress in the reinforcement. From the results of finite element program, the distribution of vertical shear stress over the depth of slab at different loading stages was presented. Approximate parabolic distribution of shear stress was observed as expected. Contours of horizontal shear stresses at different loading stages were presented to illustrate progressive redistribution of shear stresses around connection. The area around the wall nose was found to be highly stressed, which is the critical area for punching failure. Theoretical ultimate load, deflections and strains were compared with the experimental values. Good agreement was observed between the two values. Theoretical analysis showed that the adopted modeling was satisfactory in terms of predicting ultimate load with acceptable accuracy. Not only was the flexural type of failure successfully predicted, but also the punching type. The analysis was able to predict correct values of the loads and strains irrespective of the mode of failure. A suitable way for strength estimation of frameless structures under lateral out plane loading on the base of wall-slab connection test data was proposed by Kudzys et al. (1995). Slab deflections, wall and slab shear forces, loads, bending deformations and reinforcement strains were measured during the experiments conducted on six interior and two exterior full scale cast in situ RC wall-slab connection specimens. Experimental results showed that construction method with single layer reinforcement for intensive horizontal forces was absolutely unsuitable because of low bearing capacity of the structure. Influence of axial loading to joint core shear strength was evaluated. From the experimental data, equation for evaluating the joint core shear strength τju for wall- slab connections was proposed as in Eq. (18):

…….(18) Where, Qwu is the ultimate shear force, bw and bs are the wall and slab width, bj is the effective width of connection, bj=(bw+bs)/2, jw and js are the wall and slab arms of inner couples (j=7/8d, where d is effective depth), h and ls are the wall and slab loading arms, α=2 for double layer and α=1 for single layer reinforcement and Eq. (19) gives:

…….(19)

Experimental investigations on the performance of interior full scale slab-wall connection specimens loaded by gravity and low-cycle lateral forces were conducted by Kudzys (2000). Equations were proposed to estimate joint strut strength and an analysis model for joint structural safety estimation was suggested.

Fig.4. Action effects and inner forces in the joint (Kudzyz,2000)

Experimental study of the failure of interior slab –wall joints subjected to gravity as well as lateral loading was carried out. The strength and safety analysis of slab – wall rigid joints of multi-storey buildings has been carried out using strut model. The diagonal compression force and concrete strut strength were estimated. The joint action effects are presented in Fig.4. The resultant tensile force which provoke shear cracks in joint core concrete and the compressive force which reduced it in failure, F is obtained as in Eq. (20):

…….(20)

Where T1=C1=M1/z1; C2=T2=M2/z2; C3=M3/z3+0.5N3; T3=M3/z3-0.5N3; T4=M4/z4-0.5N4; C4=M4/z4+0.5N4 are the inner forces in tension reinforcement and compression concrete at joint core faces. The predicted compression strength of the concrete strut is given by Eq. (21) as:

…….(21) Where the strut thickness is given by Eq. (22):

…….(22)

F

V1 V2

N4

M3

M1

M2

M4

N3 V3

V4 V4

V2

V3

V1

C4 T4

C1

T1 C2

T2

C3 T3

z4

z3

z2 z1

F F

F

t t

χ is the factor of the ratio hh/hv between heights of horizontal and vertical joint members. The value χ= 0.4 and 0.45 can be used if the ratio hh/hv is 1.25 and 1 respectively; zh and zv are the arms of inner couples of these members on the joint core faces; bj is the effective joint width; γc is the parameter which defines the concrete strength, the value varying from 0.85-1. DETAILING OF WALL-SLAB CONNECTION The existing codal provisions as per American (ACI 318 M-02) and British Standards (BS EN 1998-1:2004 (E)) regarding the detailing of shear wall – slab joint are as follows: Detailing of Shear Wall – Slab joint as per ACI 318M-02: According to Section 12.11.2, ACI 318 M-02, when a flexural member is part of a primary lateral load resisting system, positive moment reinforcement required to be extended into the support by Section 12.11.1 shall be anchored to develop the specified yield strength fy in tension at the face of support. (Section 12.11.1: At least one-third the positive moment reinforcement in simple members and one-fourth the positive moment reinforcement in continuous members shall extend along the same face of member into the support) At simple supports and at points of inflection, positive moment tension reinforcement shall be limited to a diameter such that Ld satisfies Eq. (23); except, Eq. (23) need not be satisfied for reinforcement terminating beyond centerline of simple supports by a standard hook, or a mechanical anchorage at least equivalent to a standard hook.

…….(23)

Where Mn is nominal moment strength assuming all reinforcement at the section to be stressed to the specified yield strength fy, Vu is factored shear force at the section, La at a support shall be the embedment length beyond center of support. Detailing of Shear Wall – Slab joint as per as per British Standards BS EN 1998-1:2004 (E): According to BS EN 1998-1 :2004 (E), when a flexural member is part of a primary lateral load resisting system, both positive and negative moment reinforcement shall be limited to the diameter of the reinforcement. A standard U hook is provided at the joint for a lap length of Ld from the interior face of shear wall. Research works have been reported with proposed non-conventional type of detailing with additional bars, cross bars, hook bars, and shear reinforcements in slabs. A three-dimensional non-linear finite element analysis of shear wall-slab connection under seismic loading has been reported by Greeshma and Jaya (2008). Analyses were performed using the reinforced concrete model of the general purpose finite element code ANSYS. The main objective of the study was to identify the optimum connection detailing of slab to shear wall. Three patterns of detailing were proposed for the shear wall to slab connection viz. bars bent at 90o at connection, bars bent at 45o at connection and hook bars at connection. Dynamic analysis was carried out for the three configurations of shear wall- diaphragm connection subjected to El Centro, Northridge and Loma Prieta earthquakes. It was noticed that the difference in maximum displacements for the three configurations of the shear wall- slab connection for El Centro earthquake loading were within 6%. For Northridge and Loma Prieta earthquake the variation was within 2 %. It was found that, within the allowable deflection (H/425), the shear wall diaphragm connection with hook deflects more when compared to the other two configurations. Hence, it was stated that the shear wall- diaphragm connection with hook was more efficient under dynamic lateral loadings. Experimental and analytical investigations were conducted by Greeshma and Jaya (2011) to study the performance of the shear wall – slab connection with two types of detailing. Two different reinforcement detailing adopted were (i) Conventional joint with the provision of U hooks connecting

shear wall and slab (ii) Extending the slab reinforcement into the shear wall as 90° bent at the core region with the provision of shear reinforcement in the slab. Performance of exterior shear wall – diaphragm joints with non-conventional reinforcement detailing was examined experimentally and analytically. The experimental results were compared with analytical results carried out using the Finite Element software ANSYS and it was found that the experimental results are in good agreement with the analytical result. With respect to load and moment carrying capacities from experimental and analytical studies, the specimens detailed with 90° bent slab bars with slab shear reinforcement (Type 2 specimens) exhibited higher ultimate strength compared to Type1 specimens. Finite element analysis was conducted by Greeshma and Jaya (2012) to investigate the effect of extending the slab reinforcement as cross inclined bars at the joint on the behaviour of exterior shear wall – floor slab joint. The analysis included modeling of exterior shear wall- slab joint with conventional and non-conventional reinforcement detailing. With respect to ultimate load and moment carrying capacity, specimens with cross inclined bars at the joint exhibited higher ultimate strength. Type specimens with cross inclined bars at the joint exhibited an increase in average ductility of 58% and 39% during positive and negative loading than that of specimens with conventional detailing. The energy dissipated for specimens with cross inclined bars at the joint was 49% higher than energy dissipation capacity of conventionally detailed specimens. It was found that the exterior shear wall – slab joint with 45° cross slab bars can be effective in moderate to high seismic risk region. Seismic performance of exterior shear wall – slab joint with non-conventional reinforcement detailing has been reported by Greeshma et al. (2012). Four joint sub assemblages were tested under reverse cyclic loading applied at the end of the slab. The specimens were sorted into two types based on the joint reinforcement detailing. Type 1 model comprises of two joint assemblages having joint detailing as per the conventional detailing of slab bars at the joint. The second set of models (Type 2) comprises of two specimens having additional cross bracing reinforcements for the joints detailed as per the provisions given for beam – column joint in IS 13920:1993. Analytical investigations were employed to compare the experimental results. The experimental results and analytical studies indicate that additional cross bracing reinforcements improves the seismic performance. CONCLUSIONS This state-of-the-art used the various experimental and analytical works on the shear wall-floor slab connections reported by various researchers. The review has shown that in the previous decade much progress has been made in developing and understanding practical structural wall-slab connections for structures. An appraisal of these recommendations indicates that further work is needed to develop agreed definitions for the connection properties used in design calculations, develop standard test methods to determine these connection properties under various loading conditions and consider new connection detailing, which will guarantee a connection with structural properties adequate for the design to be considered safe and reliable. ACKNOWLEDGEMENT The authors acknowledge the financial assistance provided by Anna University, Chennai through the Anna Cenetary Research Fellowship research grant. REFERENCE 1. Coull Alexander, Wong Yang Chee (1983a). ‘Design of floor slabs coupling shear walls’, Journal

of Structural Engineering, ASCE 109(1), 109-125. 2. Coull Alexander, Wong Yang Chee (1983b). ‘Effect of Local Elastic Wall Deformations on the

Interaction Between Floor Slabs and Flanged Shear Walls’, Journal of Structural Engineering, ASCE 110(1), 105-119.

3. Coull A., Wong Y. C. (1985). ‘Effect of Local Elastic Wall Deformations on the Interaction between Floor Slabs and Flanged Shear Walls’, Building and Environment 20(3), 169-179.

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5. Coull Alex, Wong Yang Chee (1990). ‘Cracked Coupling Slabs in Shear wall buildings’, Journal of Structural Engineering, ASCE 116(6), 1744-1748.

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