Vol.5, No.8A1, 56-62 (2013) Natural Science
http://dx.doi.org/10.4236/ns.2013.58A1007
Influential aspects on seismic performance of
confined masonry construction
Ajay Chourasia1*, Sriman K. Bhattacharyya1, Pradeep K. Bhargava2, Navratan M. Bhandari2
1CSIR-Central Building Research Institute, Roorkee, India; *Corresponding Author: ajayc@cbri.res.in
2Department of Civil Engineering, Indian Institute of Technology Roorkee, Roorkee, India
Received 16 June 2013; revised 16 July 2013; accepted 23 July 2013
Copyright © 2013 Ajay Chourasia et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Recent earthquakes around the world have re-
sulted in loss of human lives and high economic
losses due to poor performance of unreinforced
masonry constructions as well as poorly-built
reinforced concrete framed buildings. This has
necessitated alternative building technologies
with improved seismic performance. Confined
masonry (CM) construction, has shown excel-
lent behavior during past earthquakes across
the world and requires similar skill at a margin-
ally higher cost than that of unreinforced ma-
sonry. This paper summarizes the main features
of generic construction and gains insight into
the behavior of CM elements under earthquake
excitations, representing a viable alternative for
safe and economical construction in seismic
areas. The paper discusses various influential
aspects like sequence of construction, proper-
ties and type of masonry material, structural
configuration, reinforcement detailing in tie col-
umn/beam and masonry, panel aspect ratio, in-
terface between concrete and masonry, axial
stress, multiple confining column, opening in
wall panels and damage pattern etc. along with
solution to overcome the limitations.
Keywords: Confined Masonry; Reinforcement
Detailing; Panel Aspect Ratio; Masonry Interface;
Multiple Confining Column; Damage Pattern
1. INTRODUCTION
The extensive use of masonry as a construction mate-
rial in buildings is preferred due to its simplicity, du rabil-
ity, aesthetic appeal, material availability and economic
advantages. In spite of associated edges, masonry exhib-
its distinct directional properties due to the strength of
masonry units, mortar, thickness of mortar joints, inter-
facial bond strength between brick and mortar, moisture
in the brick at the time of laying, arrangement of bricks,
state of bricks before casting, curing, workmanship etc.
Consequently, masonry structures display a complex
mechanical behavior and perform badly in past earth-
quakes worldwide. Confined Masonry (CM) Construc-
tion technology, requires similar or locally available con-
struction skills and materials and it may be used as an al-
ternative for low to medium rise unreinforced masonry
or RC fra med stru ct ure s. Th e conf ined mas o nr y wa lls ar e
in use since last seven to eight decade, wherein masonry
is confined with slender tie column and bond beam ele-
ments without much knowledge about its function and
behavior, however, researchers are involved in its inves-
tigation since 1973. Confined masonry comprises of ma-
sonry enclosed with lightly reinforced slender concrete
columns and beams which are cast after the construction
of the 900 - 1000 mm high wall with grooves (~25 - 40
mm) along edges so as to achieve better bonding at in-
terface. Preliminary reports from January 12, 2010, Haiti
earthquake (M 7.0); and February 27, 2010 Maule, Chile
earthquake (M 8.8), documented good performance of
confined masonry construction. In general, CM buildings
may experience some damage in earthquakes, however,
when properly designed and constructed, it sustains
earthquake effects in an efficient manner when compared
with masonry construction, with high degree of life
safety.
On completion, CM construction resembles similar to
RC framed construction with masonry infills. Conversely,
these two construction systems are significantly different.
The basic differences are in sequence of construction
(Figure 1) and the way in which it resists gravity and
lateral forces. In CM construction, confining elements
are not designed or intended to act as a moment-resisting
frame; thus detailing of the reinforcement is less convo-
luted. In general, confining elements are lightly rein-
forced in comparison with corresponding beams and
Copyright © 2013 SciRes. OPEN ACC ESS
A. Chourasia et al. / Natural Science 5 (2013) 56-62 57
(a) (b) (c) (d) (e) (f)
Figure 1. Sequence of construction of confined masonry building. (a) Construction of masonry wall with provision of reinforcement
in tie column; (b) Providing shuttering on two faces of tie column; (c) Casting of tie column followed by subsequent masonry; (d)
Provision of keys in concrete and masonry for better bonding of concrete with masonry; (e) Subsequent shutting of tie column; (f)
Completed confined masonry model.
columns in RC framed structures. Thus, the walls in CM
construction are load-bearing in nature while filler walls
exists in RC frames which are not intend ed to carry load,
this aspect results into economy of CM structural system.
The literature provides extensive information in isola-
tion about the experimental and analytical evaluation of
confined masonry walls dealing with different parame-
ters to clarify failure patterns of walls, different unit
types, effects of reinforcements in columns and walls on
ultimate capacities, ductile behavior, energy dissipation
capacity etc. [1-7]. Mostly these studies are on wall pan-
els submitted to lateral displacement control loading
combined in plane normal and shear. Meli [8] carried out
tests on confined masonry panels to assess the shear
strength, ductility and energy absorption capacity; Ber-
nardini [9] reported the results of tests to clarify issues
on stiffness degradation, crack evolution and energy dis-
sipation; Luders and Hidalgo [10] performed cyclic tests
in partly and fully grouted CM walls to study the effect
of reinforced horizontal mortar joints; Tomazevic and
Lutman [11] presented study on seismic resistance of
reinforced masonry walls; Sanchez and Astroza [12]
studied the behavior under cyclic loading and quantified
the confining improvement; Kumazwa [13], Yoshimura
[14] studied non-linear characteristics of CM wall with
lateral reinforcement in mortar joint at corner part of wall;
Yoshimuara [15] again evaluated effect of wall rein-
forcement subjected to lateral forces at different heights
and axial load; Yanez [16] showed the comparison of
CM wall panels made of hollow concrete and clay brick
masonry unit with four cases of openings; Zabala [17]
presented a complete study on CM walls with different
column reinforcement; Marinilli [18] presented the re-
sults of four full-scale wall panels with 2, 3, and 4 tie
columns under reversed cyclic lateral and constant verti-
cal load; Gouveia and Lourenco [6] reported test results
on CM walls showing influence of confinement, hori-
zontal reinforcement and different kinds of units; Wijaya
[19] presented a complete study on CM walls with
grooves at interface of masonry and tie column, short
anchor between column-wall and continuous anchorage
embedded in mortar joint and RC column and carried out
comparative study with reinforced concrete frame with
masonry infill. Meanwhile, the knowledge of various
parameters of CM walls under cyclic loading is very
scanty. The objective of this paper is to contribute to a
comprehensive understanding of seismic behavior of CM
construction and to overcome seismic deficiencies.
This paper attempts to summarize the main features of
generic construction and gains insight into the seismic
behavior of CM elements, representing a viable alterna-
tive for safe and economical construction in seismic ar-
eas. The paper outlines in various influential asp ects like
sequence of constru ction, properties and type of masonry
material, structural configuration, reinforcement detail-
ing in tie column/beam and masonry, panel aspect ratio,
interface between concrete and masonry, axial stress,
multiple confining column, opening in wall panels and
damage pattern etc. along-with the solution to overcome
the limitations.
2. SEISMIC BEHAVIOUR
Due to lack of standards and design procedures for
confined masonry construction, besides technological
motivations, such typology are not widely used as a
structural system in spite of its adequate economy in
construction and exhibit excellent seismic performance
in past earthquakes. The various key constituents and
procedure of construction of confined masonry contri-
buting for seismic behavior are discussed in subsequent
sections.
2.1. Characteristics of Masonry Unit and
Mortar
Masonry is a heterogeneous material which consists of
units and joints. Units are such as clay bricks, blocks,
ashlars, while mortar can be clay, bitumen, chalk,
lime/cement based mortar. The huge number of possible
combinations emerged out by the geometry, nature and
arrangement of units, characteristic of mortar makes
masonry a complex mechanism. The compressive
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A. Chourasia et al. / Natural Science 5 (2013) 56-62
58
strength of units and mortar is a good indicator of the
general quality of material and thereby masonry strength.
In addition, most popularly solid burnt clay bricks are
used as units due to its numerous advantages viz. cost,
availability, traditional knowledge etc., which possess
better seismic features as compared to their hollow, con-
crete blocks and calcium silicate units [20]. The use of
hollow units is not favored in high seismic zones due to
inherent brittle behavior that could be ascribed to their
high rigidi t y.
Masonry exhibits distinct directional properties due to
the strength of masonry units, mortar, thickness of mortar
joints, interfacial bond strength between brick and mortar,
moisture in the brick at the time of laying, arrangement
of bricks, state of bricks before casting, curing, work-
manship etc. It is also observed that there is wide varia-
tion in elastic modulus and compressive strength of units
and cement mortar (1:6) adopted for the construction
across the world and in general the brick masonry
strength increases with increase in brick/mortar strength.
Thus, the compatibility of elastic modulus of units and
mortar is important parameter responsible for cracks
propagation through constituent materials of masonry. In
addition, low shear strength of bricks in comparison to
mortar leads to inclined cracks mainly passing through
units causing possibility of masonry crushing at high
seismic loads.
2.2. Masonry Walls
While dealing the design of CM construction, wall
density i.e. ratio of total wall area in each princip al d irec-
tion to floor area, is one of the criterion for adequate load
resistance. Further, the effect of earthquake forces de-
pends on number of stories, seismicity, soil conditions,
construction material, adequate design provisions, de-
tailing of structural elements and the code used as the
basis of design. Based on analytical studies, minimum
wall density of 1.15% for moderate wall damage and
0.85% for light wall damage is essentially required to be
provided in each principal direction [4] .
Further, wall density per unit weight i.e. wall density
in the first storey divided by total weigh t of the structure,
is another criteria as suggested by Moroni [21], as a bet-
ter measure of seismic resistance than that of wall density.
It earmarks minimum density per unit weight to confine
low damage in walls as 0.018 m2/ton wh ile for moderate
damage the corresponding value shall be 0.012 m2/ton. It
is clear that to present extensive damage to CM con-
struction under severe shaking, adequate wall densities
are desirable in both principal directions. It is to be noted
that high wall density is better in load-carrying capacity
under gravity, however limits deformation demands un-
der seismic loads. Thus, incorporating more wall area in
is not necessarily the proposition for improving seismic
performance.
2.3. Confining Members
The improvement in seismic performance of CM walls
in comparison to URM walls is primarily achieved by the
provision of tie column and tie beams confining masonry
panel, which mainly preventing premature wall disinte-
gration after formation of crack in masonry [14,22]. Also
it reduces rate of stiffness degradation to large extent
thereby enhancement in deformation and energy dissipa-
tion characteristics. The other governing factors influ-
encing the effectiveness of confining elements are loca-
tion, type, size, shape, reinforcement detailing, grade of
concrete and the number of tie columns and bond beams.
Mainly minimum longitudinal reinforcement in tie
column is provided to avoid predominance of flexural
deformation as a result of rebar yielding at end regions
[17]. Eurocode-8 [23] suggests the minimum longitudi-
nal reinforcement in tie column and beams as 1% of
cross-sectional area. It is obvious that increase in amount
of tie column reinforcement substantially increases load
carrying capacity of CM constructions, hence corner tie
columns at first storey level are to b e provided with large
reinforcement ratio especially when it is founded on firm
soil. However, excessively large reinforcement in tie
column is not always a right choice as it may trigger brit-
tle shear failure mode. On the other hand, closely spaced
lateral ties in tie column with adequate (70 mm long)
hook length provides confinement to the core concrete
resulting into increase of deformability and energy dissi-
pation of the system. In general, the detailing of rein-
forcement in tie column is illustrated at Figure 2 [4].
2.4. Interface between Masonry and
Concrete
The seismic performance of CM construction im-
proves with the effective bonding at interface between tie
columns and confined masonry panels. Figure 3 illus-
trates that when concrete-masonry adherence merely
provides the required bond under the influence of lateral
Figure 2. Tie-column reinforcement detailing-reduced tie spac-
ing at end region [4].
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A. Chourasia et al. / Natural Science 5 (2013) 56-62 59
Figure 3. Separation of masonry-concrete element at interface
[14].
loads and occurrence of vertical separation and partial
disintegration of the panel and confining elements at
large deformations, which adversely affect the seismic
performance of CM walls [14].
To overcome above problem, casting concrete against
toothed (~25 - 40 mm or 1.5 times the average size of
course aggregate in concrete) at masonry and concrete
interface can be provided which act as shear keys. Alter-
natively, providing the CM wall with connection rebar
(U-shape or L-shape rebar that are anchored adequately
into walls) helps to improve the bond and load trans-
fer/deformation capacity [24]. Experimental tests per-
formed on CM model by the authors demonstrates the
formation of 0.5 mm wide crack at toothed interface be-
tween tie column and masonry at a very later stage of
formation of cracks in masonry panel (Figure 4). The
interface effectiveness can also be enhanced by provision
of 6 mm dia (450 mm long) reinforcement as dowel ade-
quately embedded in tie column concrete and masonry
mortar at every 5th course .
2.5. Aspect Ratio
Aspect ratio of masonry panel (height to length) is one
of the governing factors from damage pattern and failure
mode consideration of CM walls. Squat CM walls with
aspect ratios around one are commonly used in practice
and its seismic behavior is mostly governed by shear
deformations [25]. Nevertheless, as the aspect ratio in-
creases, the flexural deformations become more domi-
nant, leading to early crack formation and higher stiff-
ness degradation, thereby affecting strength characteris-
tics of the panel. For slender CM walls, flexural defor-
mations greatly outdo those of shear, and, therefore,
these walls are likely to fail in flexural mode. As a con-
sequence, squat CM walls possess lower deformability as
compared to its counterpart. While this aspect is of
paramount importance, it has been overlooked in many
codes and regulations that address seismic behavior of
CM walls [26].
2.6. Openings Size
A typical masonry wall when subjected to earthquake
Figure 4. Effectiveness of toothed interface
between tie column and masonry.
load, usually initiate shear cracks at the corners of open-
ings and extends towards the middle of piers. Further,
crushing of masonry units at corners is also a common
phenomenon at higher loads. Thus, size, shape, location
and confinement detailing of openings have a great im-
pact on the seismic performance. The stiffness of walls
with an opening ratio around 11% of total wall area is
close to that of the specimen without openings [16].
2.7. Horizontal Reinforcement in Masonry
The provision of horizontal reinforcement in masonry
panel influences the uniform distribution of cracks and
improves shear resistance, deformation capacity, and
energy dissipation characteristics of CM walls (Figure 5).
Moreover, the rate at which stiffness and strength de-
grade will substantially decline, and therefore, more sta-
ble response curves are achieved, even at large deforma-
tion levels.
The ratio between horizontal reinforcement in ma-
sonry panel to longitudinal reinforcement of tie column
should be dealt judiciously so as to avoid the high possi-
bility of flexural failure mode in case of over-reinforced
walls [17]. As a result of provision of horizontal rein-
forcement in masonry, delayed emergence of inclined
cracks and spreading of shear cracks at the toe of wall
were also noticed during various tests. When there is
insufficient reinforcement at first-storey panels, fracture
of rebar occurs near inclined cracks and in the mid part
of the wall resulting into sliding of upper walls over the
cracks [3].
The test results advocate horizontal reinforcement ra-
tio in wall between 0.005 - 0.017, with an optimum value
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60
(a) (b)
Figure 5. Comparison of crack pattern for masonry panel
without and with horizontal rebar [3]. (a) 0%; (b) 0.71% panel
reinforcement.
of about 0.01 [1]. The tests also indicate that with small
horizontal reinforcement in the masonry panel, the crack
widths are quite large for small inter-story drift. In order
to keep the crack widths under 1.5 mm, the inter-story
drift ratio should be limited to 1%, while for crack
widths under 3.0 mm the inter-storey drift should be no
larger than 2% [27].
2.8. Axial Loads
Axial loading are also one of the influential parameter
responsible for increase in shear and energy dissipation
capacity of CM construction. The effect is more distinct
for the unreinforced (in both vertical and horizontal di-
rection) masonry panels [28]. On the contrary, in case of
excessively high axial loads i.e. more than masonry
compressive strength, the ultimate deformation capacity
is adversely affected. Therefore, the performance of CM
construction can be enhance by proper planning of
square and regular grids of structure in plan and vertical
direction, use of two-way slab, uniform distribution of
gravity loads [29].
2.9. Multiple Confining Columns
The presence of more than two confining-columns in
CM wall is very common due to limitation in length of
masonry panel. From the experimental results [18], it is
evident that the presence of more confining columns in
walls of the same global dimensions increases the initial
stiffness. However, it is important to note that after stiff-
ness degradation process, the similar residual stiffness is
observed in all cases. Further, inclusion of multiple con-
fining columns in walls, tends to increases the initial
stiffness, system ductility, strength, and allows better
damage distribution in masonry panels. However, inclu-
sion of confining columns does not improve energy dis-
sipation capacity or equivalent damping ratio, mainly
due to its dependence on friction between horizontal
mortar joint. The o ccurrence of crack in multiple conf in-
ing case of CM construction is similar to single CM
wall panel i.e. cracks are primarily along the horizontal
and vertical mortar joints in zig-zag fashion, following a
45˚ inclination path.
2.10. Damage Pattern of CM Walls
The CM walls can be approximated as elastic shear
beam whose stiffness is provided jointly by masonry
panel and confining elements regardless of stiffness de-
cay due to initiation of flexural cracks in tie columns and
micro-cracks in masonry [2,7,30]. Masonry being a brit-
tle material, the stiffness of masonry decreases drasti-
cally after formation of crack and further its extension
towards the middle of solid panels. Mostly, these cracks
pass through mortar joints in a zig-zag pattern [7,18], and
at few locations through the bricks as well where com-
pressive strength of bricks is relatively low.
The response of post-cracking behavior of CM walls
mainly governed by shear deformations, which is di-
rectly influenced by friction at mortar joint (bed and head
joints), brick interlock, and shear resistance of tie column
at end region [31]. Figure 6 shows the cracking limit
state in CM panel by formation of tension in tie column
and compression strut in masonry. Also it is seen that due
to lightly reinforced tie column and high aspect ratio of
masonry there is a high possibility of flexural deforma-
tion in masonry leading to sliding shear and its exten sion
into tie column end (Figure 6(b)), at peak point of the
response i.e. maximum load state. Thus, cracked wall
pushes tie columns sideways, and produces permanent
tension [22,32], while the masonry panel, is subjected to
more compressive stresses, provided that an adequate
bond allows sufficient load transfer between wall and
confining elements.
At large deformation, generally partial separation of
masonry and confining elements [17] followed by crush-
ing of masonry at mid panel at high strain location oc-
curs. Subsequently, penetration of cracks into masonry
units [22,32] also occurs due to increase in bending
stress of units. At the same time, tie column also suffers
with extensive concrete cracking/crushing, and rup-
ture/buckling of longitudinal bars at end region [2]. As a
result, there is considerable degradation of stiffness, to
the tune of 20% of its initial stiffness [2]. In case of
multi-storyed CM constructions, concentration of dam-
age is relatively more at first story due to the softening
action, which may be attributed to the higher shear span
ratio. Thus, the damage at first-story can be minimized
by increasing energy absorption capacity through proper
confinement and prov ision of horizontal reinfo rcement at
joint [2,7,22,32].
To prevent these cracks from opening up considerably,
drift capacity of CM walls are to be controlled [33] to
reasonable extent. This can be overcome by providing
horizontal reinforcement in mortar joint and continuing
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A. Chourasia et al. / Natural Science 5 (2013) 56-62
Copyright © 2013 SciRes.
61
(a) (b) (c)
Figure 6. Failure mode of CM panel (a) at cracking limit state (b) flexure failure (c) [17].
4. ACKNOWLEDGEMENTS
through tie columns and placing closely spaced lateral
ties in tie column with 135˚ hooks of adequate length. Authors gratefully acknowledge Council of Scientific & Industrial
Research (CSIR), New Delhi for promoting R&D in earthquake engi-
neering at CSIR-Central Building Research Institute (CBRI), Roorkee,
India.
3. CONCLUSIONS
Confined masonry is a most su itable build ing typolog y
for low to medium rise construction. The paper attem-
pted to discuss various aspects of influencing perform-
ance of confined masonry typology, under seismic events
and solutions that could be incorporated to overcome.
The past earthquakes, including major ones and labora-
tory tests on CM walls demonstrate the effectiveness in
terms of strength and ductility of confined masonry sys-
tem over unreinforced masonry. Furthermore, it is indi-
cated that the performance of confined masonry not only
depends on system of construction but also on the prop-
erties and masonry type, material and structural configu-
ration, reinforcement detailing in tie column, beam and
masonry, panel aspect ratio, interface of concrete and
masonry, axial loads, and multiple con f ining elements etc.
Therefore, the influential aspects are investigated based
on damage pattern and limitations. These limitations are
overcome by adopting suitable approaches like provision
of horizontal reinforcement in masonry, dowels at inter-
faces, ductile detailing of reinforcement in tie-column
etc.
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