guidance regarding the seismic safety of masonry buildings * A single storey
building using one brick walls will be relatively safer than three storey
one. The fourth storey, if added, will be unsafe, and make the tower stories
- Use of half-brick
thick (10 to 11.5 cm or 4 to 4.5� thickness) load bearing walls will make the
storey very unsafe during seismic intensity VIII on MSK intensity scale and
if used in 3rd or 4th storey, it may have catastrophic failure.
- Too many window
openings make a wall weaker, and use of smaller size piers less than 18
inches (45cm) in width between them will increase the damageability even
cement-sand mortar of 1:4 mixtures (1part cement by 4 parts of sand) makes
the masonry stronger against earthquake shaking as compared with 1:6 mortars
by factor of 2.5 to 3. Also 1:6 mortars are stronger than lime-cinder or
- Use of clay mud
mortar produces the weakest masonry. Its strength in dry condition reduces to
less than 50% when the walls get wet during rains. Hence, use of good
plastering is essential to protect such masonry during rainy months.
- Longer walls
between consecutive cross walls are found weaker than shorter walls. The
length is controlled by limiting its height to thickness ratio.
- Taller walls
between any two floors are found to be weaker than shorter walls. The storey
height is controlled by limiting its height to thickness ratio.
- All four walls
enclosing a room should be properly connected at each corner. Walls not so
connected will easily separate at corners and overturn under the earthquake
- The most
important seismic safety requirement is provision of seismic bands in all
stories in all external as well as internal walls. These bands maintain the
integrity of the whole building as one unit under earthquake shaking. Besides
the earthquake safety, they also increase the stability of the walls under
the vertical loads.
- The roof
structure of the sloping roofs needs its integrity through bracing and proper
connectivity with the walls. Such integrity is automatically provided by
reinforced concrete slabs wherever used for floors and the roof.