Design process for masonry wall under lateral loads

A masonry wall under lateral load (wind, earthquake or earth pressure) is designed by the working-stress method as per IS 1905 cl. 5.5.2 and 5.5.3.

Design steps

1. Establish the lateral load: wind pressure from IS 875 (Part 3) (as the design wind pressure $p_z$) or the seismic force; load per metre run $w$.
2. Support conditions: identify the structural system: cantilever (free-standing), simply supported between floor and roof (anchored), propped cantilever (fixed base, tied top), or panel supported on 3 or 4 edges (App. D).
3. Bending moment: cantilever $M=wH^2/2$; simply supported $M=wH^2/8$; fixed both ends $M=wH^2/12$; propped cantilever $M=wH^2/8$ at the fixed end.
4. Vertical load: add the vertical loads and self weight at the critical section.
5. Effective height, slenderness ratio (Tables 4, 5, 7) and eccentricity $e=M/N$ (or the load eccentricity).
6. Stresses: $\sigma = N/A \pm 6M/t^2$ per metre; check for no tension, or tension limited to 0.07 N/mm$^2$ for vertical bending (tension perpendicular to the bed joints) and 0.14 N/mm$^2$ for horizontal bending (tension parallel to the bed joints), with M1 mortar or richer (cl. 5.4.2).
7. Compression check: $\sigma \le f_b k_s k_a k_p$, with a 25 percent increase if $1/24<e/t\le1/6$ (cl. 5.4.1.4).
8. Free-standing wall: stability moment $\ge 1.5\times$ overturning moment, or $H/t$ from Table 11.
9. Shear check for in-plane forces: $f_s=0.1+f_d/6 \le 0.5$ N/mm$^2$ (cl. 5.4.3).
10. Detailing: anchors, damp-proof course, bands, and reinforcement if the masonry cannot take the tension.

 Cantilever      Simply supported     Fixed-propped
   ^ free           anchor                anchor
   | w           ->|w               ->|w
   |              |                    |
   =====          anchor              =====
 M=wH^2/2        M=wH^2/8           M=wH^2/8 (base)