32walls

32.1.1

Guidelines or design of walls subjected to horizontal and vertical loads are given in 32.3.

32.2.1 Braced Walls

Walls shall be assumed to be braced if they are laterally supported by a structure in which all the following apply:

• a) Walls or vertical braced elements are arranged in two directions so as to provide lateral stability to the structure as a whole.
• b) Lateral forces are resisted by shear in the planes of these walls or by braced elements.
• c) Floor and roof systems are designed to transfer lateral forces.
• d) Connections between the wall and the lateral supports are designed to resist a horizontal force not less than

1. the simple static reactions to the total applied horizontal forces at the level of lateral support; and
2. 2.5 percent of the total vertical load that the wall is designed to carry at the level of lateral support.

32.2.2 Eccentricity of Vertical Load

The design of a wall shall take account of the actual eccentricity of the vertical force subject to a minimum value of 0.05 t.

The vertical load transmitted to a wall by a discontinuous concrete floor or roof shall be assumed to act at one-third the depth of the bearing area measured from the span face of the wall. Where there is an in-situ concrete floor continuous over the wall, the load shall be assumed to act at the centre of the wall.

The resultant eccentricity of the total vertical load on a braced wall at any level between horizontal lateral supports, shall be calculated on the assumption that the resultant eccentricity of all the vertical loads above the upper support is zero.

32.2.3 Maximum Effective Height to Thickness Ratio

The ratio of effective height to thickness, $H_{w e} / t$ shall not exceed 30 .

32.2.4 Effective Height

The effective height of a braced wall shall be taken as follows:

• a) Where restrained against rotation at both ends by

1. floors 0.75 Hw or where
2. intersecting walls or similar members whichever is the lesser. $0.75 L_{1}$

b) Where not restrained against rotation at both

• ends by
• b) floors 1.0 H, or

2. intersecting walls or similar members whichever is the lesser.

32.2.5 Design Axial Strength of Wall

The design axial strength $P_{u w}$ per unit length of a braced wall in compression may be calculated from the following equation:

$\begin{aligned} P_{\mathrm{IIW}} & =0.3\left(t-1.2 e-2 e_{\mathrm{a}}\right) f_{\mathrm{ck}} \\ \text { where }\end{aligned}$

• thickness of the wall,
• e = eccentricity of load measured at right angles to the plane of the wall determined in accordance with 32.2.2, and
• $\begin{aligned} e_{\mathrm{s}} & =\text { additional eccentricity due to slenderness effect taken as } H_{w c} / 2500 t \\ & \end{aligned}$

32.3.1

When horizontal forces are in the plane of the

wall, it may be designed for vertical forces in accordance with 32.2 and for horizontal shear in accordance with 32.3. In plane bending may be neglected in case a horizontal cross-section of the wall is always under compression due to combined effect of horizontal and vertical loads.

32.3.2

Walls subjected to horizontal forces perpendicular to the wall and for which the design axial load does not exceed $0.04 f_{\mathrm{ck}} A_{y}$, shall be designed as slabs in accordance with the appropriate provisions under 24, where $A_{y}$ is gross area of the section.

20

32.4.1 Critical Section for Shear

The critical section for maximum shear shall be taken at a distance from the base of 0.5 $L_{\mathrm{w}}$ or $0.5 H_{\mathrm{w}}$ whichever is less.

32.4.2 Nominal Shear Stress

$\tau_{\mathrm{vw}}=V_{u} / \mathrm{t} . \mathrm{d}$

The nominal shear stress $\tau_{w}$ in walls shall be obtained as follows:

=

$V_{u}=$ shear force due to design loads.

$t \quad=$ wall thickness.

=

$\begin{aligned} d & =0.8 \times L_{w} \text { where } L_{w} \text { is the length of } \\ & \text { the wall }\end{aligned}$

32.4.2.1

Under no circumstances shall the nominal shear stress $\tau_{\mathrm{sw}}$ in walls exceed $0.17 f_{\mathrm{ck}}$ in limit state method and $0.12 f_{\mathrm{ck}}$ in working stress method.

32.4.3 Design Shear Strength of Concrete

The design shear strength of concrete in walls, $\tau_{c w}$, without shear reinforcement shall be taken as below:

• a) For $H_{\mathrm{w}} / L_{\mathrm{w}} \leq 1$ $\tau_{\mathrm{cw}}=\left(3.0-H_{\mathrm{w}} / L_{\mathrm{w}}\right) K_{1} \sqrt{f_{\mathrm{ck}}}$ where $K_{1}$ is 0.2 in limit state method and 0.13 in working stress method.
• b) For $H_{w} / L_{w}>1$ Lesser of the values calculated from (a) above and from

$\tau_{\mathrm{cw}}=K_{2} \text { Vick } \frac{\left(H_{\mathrm{w}} / L_{\mathrm{u}}+1\right)}{\left(H_{\mathrm{w}} / L_{\mathrm{u}}-1\right)}$

where $K_{\mathrm{y}}$ is 0.045 in limit state method and 0.03 in working stress method, but shall be not less than $K_{\mathrm{y}} \sqrt{f_{\mathrm{k}}}$ in any case, where $K_{\mathrm{y}}$ is 0.15 in limit state method and 0.10 in working stress method.

32.4.4 Design of Shear Reinforcement

Shear reinforcement shall be provided to carry a shear equal to $V_{\mathrm{t}}-\tau_{\mathrm{cw}}\left(0.8 L_{\mathrm{w}}\right)$. In case of working stress method $V_{\mathrm{u}}$ is replaced by $V$. The strength of shear reinforcement shall be calculated as per 40.4 or B-5.4 with $A_{\mathrm{av}}$ defined as below:

$A_{w}=P_{w}\left(0.8 L_{w}\right)$

where $P_{w}$ is determined as follows:

• a) For walls where $H_{\mathrm{w}} / L_{\mathrm{w}} \leq 1, P_{\mathrm{w}}$ shall be the lesser of the ratios of either the vertical reinforcement area or the horizontal reinforcement area to the cross-sectional area of wall in the respective direction.
• b) For walls where $H_{\mathrm{w}} / L_{\mathrm{w}}>1, P_{\mathrm{w}}$ shall be the ratio of the horizontal reinforcement area to the cross-sectional area of wall per vertical metre.

32.5.1

For walls having thickness more than 200 mm, the vertical and horizontal reinforcement shall be provided in two grids, one near each face of the wall.

32.5.2

Vertical reinforcement need not be enclosed by transverse reinforcement as given in 26.5.3.2 for column, if the vertical reinforcement is not greater than 0.01 times the gross sectional area or where the vertical reinforcement is not required for compression.