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Learning

13 Earthquake Design
Earthquake Tip and

Construction

Why should Masonry Buildings have simple Structural Configuration?

Box Action in Masonry Buildings consider a four-wall system of a single storey masonry
Brick masonry buildings have large mass and building (Figure 2). During earthquake shaking, inertia
hence attract large horizontal forces during earthquake forces act in the strong direction of some walls and in
shaking. They develop numerous cracks under both the weak direction of others (See IITK-BMTPC
compressive and tensile forces caused by earthquake Earthquake Tip 12). Walls shaken in the weak direction
shaking. The focus of earthquake resistant masonry seek support from the other walls, i.e., walls B1 and B2
building construction is to ensure that these effects are seek support from walls A1 and A2 for shaking in the
sustained without major damage or collapse. direction shown in Figure 2. To be more specific, wall
Appropriate choice of structural configuration can B1 pulls walls A1 and A2, while wall B2 pushes
help achieve this. against them. At the next instance, the direction of
The structural configuration of masonry buildings shaking could change to the horizontal direction
includes aspects like (a) overall shape and size of the perpendicular to that shown in Figure 2. Then, walls A
building, and (b) distribution of mass and (horizontal) and B change their roles; Walls B1 and B2 become the
lateral load resisting elements across the building. strong ones and A1 and A2 weak.
Large, tall, long and unsymmetric buildings perform Thus, walls transfer loads to each other at their
poorly during earthquakes (IITK-BMTPC Earthquake junctions (and through the lintel bands and roof).
Tip 6). A strategy used in making them earthquake- Hence, the masonry courses from the walls meeting at
resistant is developing good box action between all the corners must have good interlocking. For this reason,
elements of the building, i.e., between roof, walls and openings near the wall corners are detrimental to good
foundation (Figure 1). Loosely connected roof or seismic performance. Openings too close to wall
unduly slender walls are threats to good seismic corners hamper the flow of forces from one wall to
behaviour. For example, a horizontal band introduced another (Figure 3). Further, large openings weaken
at the lintel level ties the walls together and helps to walls from carrying the inertia forces in their own
make them behave as a single unit. plane. Thus, it is best to keep all openings as small as
possible and as far away from the corners as possible.
Roof that stays together as a single
Good integral unit during earthquakes Inertia force
connection from roof
between roof
and walls Walls with Inertia force

small from roof
openings A1

Lintel B2

Band B1

A2

Stiff Foundation Good
connection
between
walls and
Good connection foundation Regions
at wall corners Direction of where load
Figure 1: Essential requirements to ensure box transfer
earthquake takes place
action in a masonry building. shaking from one
wall to
Influence of Openings another

Openings are functional necessities in buildings. Figure 2: Regions of force transfer from weak
However, location and size of openings in walls walls to strong walls in a masonry building –
assume significance in deciding the performance of wall B1 pulls walls A1 and A2, while wall B2
masonry buildings in earthquakes. To understand this, pushes walls A1 and A2.
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