Page 24 - EQTips_Eng

Learning

12 Earthquake Design
Earthquake Tip and

Construction

How do Brick Masonry Houses behave during Earthquakes?

Behaviour of Brick Masonry Walls by horizontal forces due to earthquake. A wall topples
Masonry buildings are brittle structures and one of down easily if pushed horizontally at the top in a
the most vulnerable of the entire building stock under direction perpendicular to its plane (termed weak
strong earthquake shaking. The large number of direction), but offers much greater resistance if pushed
human fatalities in such constructions during the past along its length (termed strong direction) (Figure 1b).
earthquakes in India corroborates this. Thus, it is very The ground shakes simultaneously in the vertical
important to improve the seismic behaviour of and two horizontal directions during earthquakes
masonry buildings. A number of earthquake-resistant (IITK-BMTPC Earthquake Tip 5). However, the
features can be introduced to achieve this objective. horizontal vibrations are the most damaging to normal
Ground vibrations during earthquakes cause masonry buildings. Horizontal inertia force developed
inertia forces at locations of mass in the building. at the roof transfers to the walls acting either in the
These forces travel through the roof and walls to the weak or in the strong direction. If all the walls are not
foundation. The main emphasis is on ensuring that tied together like a box, the walls loaded in their weak
these forces reach the ground without causing major direction tend to topple (Figure 2a).
damage or collapse. Of the three components of a To ensure good seismic performance, all walls
masonry building (roof, wall and foundation) (Figure must be joined properly to the adjacent walls. In this
1a), the walls are most vulnerable to damage caused way, walls loaded in their weak direction can take
advantage of the good lateral resistance offered by
walls loaded in their strong direction (Figure 2b).
Further, walls also need to be tied to the roof and
Walls foundation to preserve their overall integrity.
Roof

Toppling
A

B

Foundation B
(a) Basic components of a masonry building
Pushed in the plane of the wall
A
Direction of
earthquake
shaking

A Weak (a) For the direction of earthquake shaking shown,

Direction wall B tends to fail
Toothed joints
in masonry
courses
B A or L-shaped
Direction of B dowel bars
earthquake shaking
Strong Toppling
Direction B
A

Pushed perpendicular
to the plane of the wall
Direction of
earthquake
shaking Direction of
earthquake
shaking

(b) Direction of force on a wall critically determines (b) Wall B properly connected to Wall A (Note: roof
its earthquake performance

is not shown): Walls A (loaded in strong direction)

Figure 1: Basic components of a masonry support Walls B (loaded in weak direction)

building – walls are sensitive to direction of Figure 2: Advantage sharing between walls –
earthquake forces. only possible if walls are well connected.
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