Question

A reinforced concrete bearing wall supports 12” wide beams bearing on the full width of the wall spaced 10’ o.c. The bottom of the wall is a fixed connection. The top of the wall is a pinned connection. The wall is 20’ tall. The load from each beam, Pu, is 30 kips. Determine whether a 10” wide wall will work for this condition. Select vertical and horizontal reinforcing steel.

Answer 1

Following are the steps and procedure on how to solve the above problem for 12" and 10" wide wall:-

Reinforced concrete wall is designed as a compression member. The reinforced concrete wall is used in a case where the beam is not provided and load from the slab is heavy or when the masonry wall thickness is restricted.

Guidelines for Design of Reinforced Concrete Wall

1. The limiting slenderness () if any for the unbraced wall is 30 and for the braced wall is 45.

2. For short braced RC wall (< 12),

Pu = 0.4 x fck x Ac+ 0.67 x fy x Ast

3. For short unbraced RC wall, along with the above axial load Pu, the moment due to minimum eccentricity is checked for emin= t/20 or 20mm, where, M = P x e.

For the above axial load and moment, the RC wall is designed similar to RC column subjected to axial load and uniaxial moment.

4. Slender braced wall (< 45):

The additional moment due to additional eccentricity as per Table 1 of SP16 is considered. Where the additional eccentricity,

The additional moment due to eccentricity is added with the moment on the column and moment on the wall. The wall is designed for axial load with uniaxial moment.

5. For slender unbraced wall [limited to 30]: Similar procedure as in case 4 is adopted.

The support conditions for an effective length of wall:

1. Both ends fixed (Restrained against rotation and displacement)
2. Both ends hinged
3. One end fixed and other ends
4. One end fixed and other end hinged

The reinforced concrete wall is classified as:

• Plain concrete wall, when reinforcement < 0.4%
• Reinforced concrete wall, when reinforcement > 0.4%

The load from the slab is transferred as an axial load to the wall. When depth is large, it is called RC wall. Design is similar to a RC column, breadth equal to the thickness of wall and depth equal to 1m. RCC Wall is designed as:

• Axially loaded wall
• Axially loaded with uniaxial bending

Slenderness ratio is equal to least of (l/t or h/t), where, l is the effective length of the wall, h is the effective height of the wall, t is the thickness of wall If < 12, the wall is short and if > 12, the wall is slender.