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Earthquake Design
28 and
Earthquake Tip
Construction

What is a Confined Masonry Construction?

Basics of Confined Masonry after walls are built. RC confining elements hold the
Confined Masonry (CM) construction typically masonry in place and improve integrity of the house
consists of: traditional strip foundation (in masonry); during seismic shaking (Figure 2). CM houses
reinforced concrete (RC) plinth beam; masonry walls (in performed well even in several severe earthquakes,
bricks or concrete block units) built on top of plinth such as the 2010 Chile earthquake (Magnitude 8.8),
beam; small RC vertical & horizontal confining elements while many unreinforced masonry (URM) and even
built around these masonry walls; and RC floor and roof RC buildings suffered damage during the same events.
slabs built monolithically with the confining elements
(Figure 1a). These vertical and horizontal confining
elements are called tie-columns and tie-beams, 1.2m
respectively. CM construction has a mandatory plinth
beam on top of plinth masonry. CM is a good 1.2m
construction technology for low- and medium-rise
houses in seismic areas (Figure 1b).

Slab Figure 2: Construction Sequence – Plain masonry
walls built first, are held snugly by adjoining RC
elements that are cast in-situ later
Tie-beams
Masonry The concept of masonry wall construction
Walls confined with wood elements has been used for
Tie-columns centuries in many earthquake-prone regions along the
Alpine-Himalayan belt. For example, in the Kashmir
Valley in J&K State (India), Dhajji Dewari constructions
Plinth beam
consists of large masonry walls broken into smaller
panels with wood verticals, horizontals and diagonals.
These houses showed excellent performance in many
Foundation past earthquakes and helped avoid loss of life. These
(a) houses have simple architectural design, good quality
materials and good quality of construction.
CM is different from MRF with URM Infills
CM houses are different substantially from RC
moment resisting frame (MRF) houses with masonry
infills, even though both technologies use the same
constituent structural materials (concrete and
Photos: World housing Encyclopedia, EERI, 1999 masonry) and have very similar appearance when the
buildings are completed. The key differences are:
(a) Different Behaviour:

CM houses are load-bearing structures, because
masonry walls carry both gravity and earthquake-
induced lateral forces. This is similar to unreinforced
masonry (URM) construction, which has been used in
(b) India for many centuries. URM houses perform well
Figure 1: Confined Masonry Construction – (a) under gravity loads, but experience significant
components of CM system, and (b) 4-storey
damage during earthquake shaking, because
house constructed in Chile with CM system. masonry cannot take tension that develops during
earthquake shaking. On the other hand, RC MRF
Construction of CM building with RC confining houses classify under moment-resisting frame system.
elements involves making masonry walls in small RC frames are infilled with unreinforced masonry
panels, each of which is confined on all four sides by walls in some countries, e.g., India (see IITK-BMTPC
vertical and horizontal RC elements. Concrete is Earthquake Tips 17, 21 and 22), and with engineered
poured in vertical and horizontal confining elements infills in others, e.g., New Zealand.