Seismic design principles for masonry buildings

Masonry buildings should behave as a strong, tied box so that all walls support each other during shaking.

1. Simple, symmetric and regular plan

• Rectangular, symmetrical plans are best. Avoid L, T and U shapes (or separate them by seismic gaps), because they twist (torsion) and have stress concentrations at re-entrant corners.
• Keep the length-to-breadth ratio not more than about 3, and place walls so that the centre of mass and the centre of rigidity are close.

2. Limited height and storey height

Keep the number of storeys and the storey height low (commonly not more than 3.0–3.4 m per storey). Avoid heavy roofs (stone slabs, thick mud); use light roof materials.

3. Walls

• Provide adequate wall density in both directions, with cross-walls spaced closely to limit the out-of-plane span.
• Keep the thickness related to height (the $h/t$ ratio small) and avoid slender walls.
• Use good-quality units and cement or cement–lime mortar, and fill all joints; use through stones in stone walls.

4. Openings

Keep openings small, symmetrical and away from corners. As a guide (IS 4326): the total width of openings should not exceed about 50 percent of the wall length in a single-storey building (less for higher buildings); pier width should be not less than about 340 mm and openings should be about 600 mm from inside corners. Openings in adjacent storeys should be vertically aligned.

5. Bands and vertical steel

Provide horizontal bands (plinth, lintel, roof, gable) and vertical bars at corners, junctions and door/window jambs to tie the structure.

6. Floors and roofs

Use rigid diaphragms (RC slabs) or well-braced timber floors firmly anchored to the walls to distribute force by box action.

7. Foundation

Use a uniform type of foundation on firm soil, with plinth beams; avoid foundations at different depths.

8. Quality of workmanship

Fill the joints fully, make wall junctions toothed or bonded, cure the masonry well, and avoid cutting chases in walls because they weaken them.