Seismic resistant retrofitting for buildings
Practical Action
Notes
1.
2.
3.
4.
N = Number of made
longitudinal wires in the belt at
spacing of 25 mm.
H = Height of belt on wall in
micro-concrete, mm.
The transverse wires in the
mesh could be spaced up to
150 mm.
The mesh should be galvanized
to save from corrosion.
Gauge Diameter
g10 3.25 mm
g11 2.95 mm
g12 2.64 mm
g13 2.34 mm
g14 2.03 mm
Categorisation of Buildings
Seismic
Zone*
V
IV
Ordinary
Building
s
E
D
Import
ant
Buildin
gs
E
E
III C D
*Where seismic zone is refers
to the Modified Mercalli
Intensity scale.
Roof stiffening
Having a stiff roof that is capable of diaphragm action is important, as this allows loads to be
distributed more evenly to the walls to which they are connected. A roof that acts as a
diaphragm is able to transfer lateral loads to walls that are able to take in-plane shear. Many flat
roofs that are made with parallel timber joists and covered by either earth or planks cannot act as
a rigid diaphragm. The roof (or floor) needs to be diagonally braced. Arya (2003) suggests that
planks similar to that already used, or galvanised metal strips (1.5mm x 50mm) should be used
to create an X-brace. The timber joists should also be nailed at both ends to joists below.
Brick or stone wall
Wood planks
Wood joist
Planks underneath
joists
Diagonal tie (X - brace)
Figure 5: How to stiffen a flat roof/floor based National Disaster Management Division,
Govt. of India (2006).
In the case of sloping roofs that are carrying clay tiles of galvanised iron, the roof tends to push
out during an earthquake (Arya, 2003). Rafters should be tied to the seismic belt and rafters
opposite each other should be tied with cross ties at half the height of the roof, or with collar
beam ties at 2/3 of the roof height (UNDP India, 2007).
See page 81-85 of Manual for Restoration and Retrofitting of Rural Structures in Kashmir.
Timber construction
Provided good connections are made and good materials are used, timber buildings usually
perform well during earthquakes. Members are lighter, attracting fewer seismic forces, and nailed
5