shear strength properties of brick masonry -...
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ISSN 0974-5904, Volume 05, No. 04
August 2012, P.P.
#02050418 Copyright ©2012 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.
Experimental Investigation on the Characterization of Solid Clay
Brick Masonry for Lateral Shear Strength Evaluation
QAISAR ALI1, YASIR IRFAN BADRASHI
1, NAVEED AHMAD
1,2, BASHIR ALAM
3,
SHAHZAD REHMAN3 and FARHAT ALI SHAH BANORI
3
1Earthquake Engineering Center, UET, Peshawar, Pakistan
2ROSE School−IUSS Pavia, Pavia, Italy
3Department of Civil Engineering, UET, Peshawar, Pakistan
Email: [email protected], [email protected]
Abstract: The aim of the paper was to carry out the mechanical characterization of solid fired clay brick masonry
through experimental investigation, essential for structural evaluation under lateral loads due to winds and
earthquakes within the context of design and assessment studies. The basic material properties of masonry including
compressive strength, diagonal tensile strength, shear strength, masonry bond strength, Young’s and shear moduli
are obtained through laboratory testing on masonry prisms (48 samples), triplets (96 samples) and wallets (48
samples). Standard brick unit prevalent in Pakistan is considered, similar to units that can be found also in
neighboring countries like India, Iran and Bangladesh amongst others. Three types of mortar ─ cement-sand,
cement-sand-khaka and cement-khaka are used as bonding material for masonry assemblages. Khaka is obtained as
a byproduct of stone crushing process, employed in mortar preparation to produce relatively workable and
economical mortar. The effect of mix proportions of mortar is also investigated. Empirical relationships are
developed herein whereby basic mechanical properties of masonry are correlated with the mortar strength, mortar
type and mix proportions. An attempt is made to correlate mechanical properties between each other and establish
simplified relationships to help facilitate their use in future applications for design and assessment of unreinforced
masonry wall structures under wind and earthquake induced lateral loading.
Keywords: Shear, Diagonal Tensile Strength, Compression, Elastic Moduli, Mortar, Khaka, Unreinforced Brick
Masonry.
Introduction:
Masonry material is largely practiced for construction of
structures and infrastructures e.g. buildings, bridges,
retaining structures, etc., in most of the underdeveloped
and developing parts of the world. It is due to the
traditional construction practices employed in these
countries, motivated also by the regional climatic
conditions . Brick masonry construction employing
solid clay units and cement-mortar can be found in
many urban exposure of Pakistan and so also in
neighbouring countries like India, Iran, Bangladesh
among others. Most of the structures in these urban
exposures are subjected to frequent lateral loads due to
heavy winds and earthquakes that consequently induce
shear stresses in the structural walls. The behavior of
masonry material under lateral loading is dramatically
different than its counterpart materials - concrete and
steel, due to high non-homogeneity and composite
nature of masonry components. The different
mechanical properties of masonry units and mortar and
their interface makes the masonry system behavior
difficult to predict using simple hypotheses as adopted
for concrete and steel. The masonry mechanical
characterization can be best performed through
experimental investigations, which can help facilitate
development of analytical tools for future applications.
Masonry structures are often composed of several load
bearing walls for carrying both gravity and lateral loads.
In building construction, when the connection at wall
intersections and at floor-to-wall is achieved through
proper means, with controlled out-of-plane deflection of
the floors, the building primarily resist lateral loads by
in-plane response of walls (Magenes, 2006; Tomazevic,
1999). The provision of reinforced concrete slab with
deep spandrels, presence of tie rods, ring beams at floor
levels and efficient floor-to-wall connections favours
the integrity of masonry walls. It enables the structure
respond in a box like action to lateral loading with shear
dominated damage in masonry walls. Flexure rocking,
that may result in toe crushing of walls, is also a
possible mechanism to resist lateral loads (Magenes and
Calvi, 1997; Abrams, 2001, among others).
783 QAISAR ALI, YASIR IRFAN BADRASHI, NAVEED AHMAD, BASHIR ALAM,
SHAHZAD REHMAN and FARHAT ALI SHAH BANORI
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
Figure 1 shows typical damages observed in masonry
wall buildings of the above characteristics during the
2005 Kashmir earthquake. Typical damages that may
occur in masonry infill of concrete structures due to
lateral in-plane forces observed during earthquake are
also shown. Local out-of-plane collapse of wall is also
evidenced in earthquakes for deficient structures
(D’Ayala and Paganini, 2011; Javed et al., 2008).
Figure 1: Shear Damages Observed in Load Bearing Walls of Unreinforced Masonry Buildings And Masonry Infill
of Concrete Buildings due to Earthquake Induced Lateral Loads.
783 QAISAR ALI, YASIR IRFAN BADRASHI, NAVEED AHMAD, BASHIR ALAM,
SHAHZAD REHMAN and FARHAT ALI SHAH BANORI
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
A): Diagonal shear cracks in masonry building walls observed during 2005 Kashmir earthquake. A building with
concrete floor slab, deep spandrels and walls with lower vertical aspect ratio (height to thickness). Adopted from
Naseer et al. (2010)
(B): Toe crushing in masonry building walls observed during 2005 Kashmir earthquake. A building with concrete
floor slab, deep spandrels and walls with high vertical aspect ratio. Adopted from Javed et al. (2008)
(C): In-Plane shear cracks observed in masonry infill of concrete structure damaged in 2005 Kashmir earthquake.
A building with reinforced concrete beams and columns provided with concrete floor slab and rigidly connected
masonry infill. Adopted from Javed et al. (2008)
Many available analytical models can be used to
estimate the in-plane strength of masonry walls
(Abrams, 2001; CEN, 1994; FEMA, 2000; Magenes and
Calvi, 1997; Mann and Muller, 1982; Tomazevic, 1999;
Turnsek and Sheppard, 1980, among others). Analytical
models are also available to estimate the strength of
masonry infill panel under lateral loads in concrete
structures (Fardis and Calvi, 1994; Kappos et al., 1998;
Smyrou et al., 2011, among others). All these models
require basic mechanical properties of masonry material
to obtain lateral in-plane strength. This fact makes the
experimental investigation on masonry materials
essential before the assessment of structures can be
performed within the context of existing stock
evaluation and design verification of new construction
schemes (Ahmad et al., 2010, 2011, 2012 among
others).
This paper hence presents an experimental investigation
on solid clay fired-brick masonry material for
mechanical characterization. The experimental work
included laboratory tests under monotonic loading on
masonry prisms: for the estimation of masonry
compressive strength (fmc) and elastic Young modulus
(E), on triplets: for the estimation of bond strength in
shear: cohesion parameter (c) and friction coefficient
(µ) of Mohr-Coulomb model, and on wallets: for the
estimation of diagonal tension strength (ft) and shear
modulus (G), besides tests on constituent materials i.e.
brick units: for unit compression strength, water
absorption and initial rate of absorption and mortar: for
compression strength (fm).
The testing is performed using the standard testing
procedures: ASTM E-519-02 (2002) for wallet tests, EN
1052-3 (2002) for triplet tests, ASTM C-67-06 (2006)
for masonry unit tests, ASTM C109/C109M-08 (2008)
for mortar compression tests and ASTM C-1314-07
(2007) for masonry compression tests. Three types of
mortar are considered; cement-sand mortar (CS),
cement-sand-khaka mortar (CSK), cement-khaka mortar
(CK). The mortars are considered with 12 various mix
proportions (four cases for each mortar type). The
motivation towards investigating masonry in CSK and
CK mortar is that they produce relatively more
workable and economical mortars for masonry
construction (Naeem et al., 1996); It is essential to
understand their impact on the mechanical properties of
masonry. Empirical relationships are developed to relate
the basic mechanical properties of masonry with mortar
strength, mortar constituents and mix ratio. Also, an
attempt is made to correlate the mechanical parameters
with each other. These relationships can provide a
useful means for future applications in the design and
verification studies of masonry construction.
Experimental Investigation of Clay Fired Brick
Masonry:
1.1 Experimental Tests Program:
The experimental program for mechanical
characterization of masonry included tests on masonry
units, mortar, masonry prisms, masonry triplets and
masonry wallets. The tests are performed at the Material
Testing Laboratory of Civil Engineering Department of
UET Peshawar, Pakistan. The following sections briefly
elaborate each of the tests.
1.2 Tests on Masonry Constituents Material:
1.2.1 Masonry Unit Tests Per ASTM C-67-06:
The present study has focused on investigating masonry
of solid clay fired brick masonry units, common in
various parts of Pakistan, which can also be found in
other South Asian countries like India, Iran,
Bangladesh, among others. The tests on brick units
included water absorption test (on nine samples), initial
rate of absorption (IRA) test (on five samples),
compressive strength test (on nine samples). The results
of the experiments showed unit water absorption of
19.3% (COV 4.23%); IRA of 82.20 gm/min/30inch2
(COV 18.21%); compressive strength of 16.91 Mpa
(COV 22.89%).
The water absorption capacity which is less than 20%
indicates a good quality of the unit. The IRA of unit
which is greater than 30gm/min/30inch2
indicates that it
must be wetted well before employing in the
construction of masonry works.
1.2.2 Mortar Tests Per ASTM C109/C109M-08:
Various types of mortars investigated in the present
study included CS, CSK and CK mortars. The addition
of khaka to the ordinary CS mortar produces more
workable and economical mortar for brick masonry
construction (Naeem et al., 1996). Chemical analysis on
khaka shows 95% of CaCo3 content (Naeem et al.,
784 Experimental Investigation on the Characterization of Solid Clay
Brick Masonry for Lateral Shear Strength Evaluation
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
1996). In the present study, the mix proportions of
mortar constituents as found in most of the construction
works are investigated. Four cases for each mortar type
are considered with mix proportions of 1:4, 1:6, 1:8 and
1:10 for CS and CK mortars; and 1:2:2, 1:3:3, 1:4:4 and
1:5:5 for CSK mortar. Gradation tests are performed on
both sand and khaka constituents, see
Figure 2 which revealed a relatively fine graded
aggregate contents of khaka.
Figure 2: Gradation Profile of Sand and Khaka
Constituent Employed For Mortar Preparation
Figure 3: Mean Compressive Strength of Mortar Cubes,
28-days. CS Represents Cement-Sand Mortar, CSK
Represents Cement-Sand-Khaka Mortar and CK
Represents Cement-Khaka Mortar
Mortar cubes of size 50mmx50mm were prepared for
the aforementioned mortar types and tested after 28
days for compression strength. A total of 108 mortar
cubes (nine samples for each mix proportion) were
tested. Figure 3 shows the mean estimated compressive
strength of each mortar cubes (four cases for each
mortar types).
Generally, the strength of mortar decreased with
increasing the mix-ratio. The experiments indicated that
the addition of khaka to ordinary mortar increases the
strength of mortar. On an average the strength is
increased by 72 percent for CK mortar and 50 percent
for CSK mortar.
1.3 Tests on Masonry Assemblages:
1.3.1 Masonry Triplets Tests Per EN-1052-3:
The triplet tests were performed on masonry
assemblages composed of three bricks using the EN-
1052-3 testing setup (Figure 4). The top and bottom
brick units were clamped whereas the central unit was
subjected to horizontal loading. Two cases for pre-
compression (250kg and 500kg) were considered
whereby the prism is loaded at the top.
The testing provides estimates of the shear strength
(bond strength) and friction coefficient of the masonry:
parameters employed in the Mohr-Coulomb shear
strength model.
Figure 4: Triplet Test Specimen and Loading Setup per
EN-1052-3
where τ represents the in-plane shear stress, c represents
the shear strength at zero pre-compression; µ represents
the coefficient of friction; σ represents the pre-
compression stress on the prism. A total of 96 prism
samples (eight samples prepared for each mix
proportion of each mortar type) were tested.
785 QAISAR ALI, YASIR IRFAN BADRASHI, NAVEED AHMAD, BASHIR ALAM,
SHAHZAD REHMAN and FARHAT ALI SHAH BANORI
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
Figure 5: Shows the Mean Shear Strength and the Corresponding Friction Coefficient Observed for each Mortar
Type. On Average, the addition of Khaka to the Ordinary Mortar Increased the Strength by 40 Percent for CK
Mortar type and 22 Percent for CSK Mortar Type whereas the Friction Coefficient is Increased by 20 Percent for
CK Mortar Type and 2 Percent for CSK Mortar Type.
Figure 5: Observations made from the Triplet Tests. From Left to Right: Masonry Bond Strength (Shear Strength
at Zero Pre-Compression) and Friction Coefficient. CS Represents Cement-Sand Mortar, CSK Represents Cement-
Sand-Khaka Mortar and CK Represents Cement-Khaka Mortar.
It is worth to mention that for the estimation of lateral in-plane shear strength of wall a correction factor is employed
to the Mohr-Coulomb parameters i.e. c & µ. It is due to the fact that these parameters are obtained from tests at local
level. Their correction for strength evaluation of walls is essential (Magenes and Calvi, 1997).
786 Experimental Investigation on the Characterization of Solid Clay
Brick Masonry for Lateral Shear Strength Evaluation
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
where k represents the correction factor; ∆x represents the length of the brick unit, 230mm in the present study; ∆y
represents the height of the brick unit, 70mm in the present study; µ represents the friction coefficient. The new
parameters can be calculated then as follow: cnew = c×k & µnew = µ×k.
1.3.2 Masonry Wallets Tests Per ASTM E-519-2:
Tests on masonry panels (wallets) of size 690mmx690mm with 230mm thickness were prepared in English masonry
bond pattern. Tests were performed on panels for the estimation of diagonal tension strength of masonry. The testing
setup was designed as per the ASTM E-519-2 recommendations (see
Figure 6). Linear variable displacement transducers (LVDTs) were installed, both on each horizontal and vertical
directions to measure the mean horizontal and mean vertical deformation of the specimen during loading.
Figure 6: Diagonal Tension Test Setup per ASTM E-519-2
This test setup is generally interpreted for diagonal tensile strength evaluation based on the consideration that the
specimen is subjected to pure shear, the specimen is cracked when the principal stress at the center of the panel
becomes equal to the tensile strength of masonry (ASTM E519-02; RILEM, 1994). However, it is urged based on
numerical and analytical studies that the specimen in reality is not subjected to uniform and homogenous state of
stresses. Because of this the specimen is not under pure shear (Brignola et al., 2009; Frocht, 1931; Magenes et al.,
2010).
The analytical formula recently proposed and employed by Magenes et al. (2010) is used in the present study to
estimate the diagonal tensile strength of tested wallets.
where ft represents the diagonal tensile strength; P represents the peak vertical loading; t represents the thickness of
the specimen; l1 and l2 represent the length of sides of the specimen. A total of 48 wallet samples (four samples
prepared for each mix proportion of each mortar type) were tested.
787 QAISAR ALI, YASIR IRFAN BADRASHI, NAVEED AHMAD, BASHIR ALAM,
SHAHZAD REHMAN and FARHAT ALI SHAH BANORI
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
The diagonal tension strength is also interpreted to estimate the shear rigidity i.e. shear modulus, of masonry
material using the ASTM procedure, which is employed and recommended for shear modulus estimation (Magenes
et al., 2010).
where G represents the shear modulus; τ represents the shear stress; γ represents the corresponding shear strain; Pmax
represents the peak vertical load at failure; ∆V & ∆H represent the vertical and horizontal deformation in the vertical
and horizontal LVDT’s, respectively; g represents the gauge length of either of the LVDTs.
The above equation (4) is meant to obtain the shear modulus as the slope of the shear stress-strain curve between the
two specified points when the loading reaches 5 percent of the peak load and 33 percent of peak load i.e. the slope of
stress-strain curve between 5 percent and 33 percent of peak load. Other parameters are defined earlier.
Figure 8 reports the mean shear modulus of the
masonry wallets obtained for each mortar types.
Figure 7 reports the mean diagonal tensile strength of tested masonry wallets for each mortar type. It can be
observed from the typical damage pattern that the crack developed upon failure follows bed and head joints of
masonry. It is an indication that the strength is largely contributed by the masonry mortar and mortar-brick interface
bond strength. Thus, the use of various mortar types will affect the tensile strength of masonry wallets.
On average the addition of khaka to the ordinary mortar increases the diagonal tension strength by 110 percent for
CK mortar type and 93 percent for CSK mortar type.
The diagonal tension strength is also interpreted to estimate the shear rigidity i.e. shear modulus, of masonry
material using the ASTM procedure, which is employed and recommended for shear modulus estimation (Magenes
et al., 2010).
786 Experimental Investigation on the Characterization of Solid Clay
Brick Masonry for Lateral Shear Strength Evaluation
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
where G represents the shear modulus; τ represents the shear stress; γ represents the corresponding shear strain; Pmax
represents the peak vertical load at failure; ∆V & ∆H represent the vertical and horizontal deformation in the vertical
and horizontal LVDT’s, respectively; g represents the gauge length of either of the LVDTs.
The above equation (4) is meant to obtain the shear modulus as the slope of the shear stress-strain curve between the
two specified points when the loading reaches 5 percent of the peak load and 33 percent of peak load i.e. the slope of
stress-strain curve between 5 percent and 33 percent of peak load. Other parameters are defined earlier.
Figure 8 reports the mean shear modulus of the
masonry wallets obtained for each mortar types.
Figure 7: Diagonal Tension Strength of Masonry Wallets. From Left to Right: Typical Damage Mechanism of one
of the Representative Samples and Mean Estimates of Masonry Diagonal Tensile Strength for Each Mortar Type. CS
Represents Cement-Sand Mortar, CSK Represents Cement-Sand-Khaka Mortar and CK Represents Cement-Khaka
Mortar.
Figure 8: Shear Modulus of the Wallets obtained
through Diagonal Tension Test on Masonry Wallets. CS
Represents Cement-Sand Mortar, CSK Represents
Cement-Sand-Khaka Mortar and CK Represents
Cement-Khaka Mortar.
786 Experimental Investigation on the Characterization of Solid Clay
Brick Masonry for Lateral Shear Strength Evaluation
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
Figure 9: Masonry Bond Strength (Shear Strength) to
Mortar Compression Strength.
On average, the addition of khaka to the ordinary mortar
increases the shear stiffness (shear modulus) by 91
percent for CK mortar type and 90 percent for CSK
mortar type.
2 Simplified Empirical Relationships for Masonry
Mechanical Properties:
The basic mechanical properties (masonry bond strength
and diagonal tensile strength) obtained experimentally
for each mortar types are correlated with the mortar
compressive strength to establish simplified
relationships for future applications. Furthermore,
correlation is performed between the mechanical
properties (bond strength and coefficient of friction) and
mortar types and mix proportion.
Additionally, correlation is performed between various
mechanical properties (bond strength to tension
strength, compressive strength to tensile strength,
Young modulus to shear modulus) to provide easy
means for estimation and conversion of masonry
mechanical properties. These relationships can be used
for future applications given either of the information on
the mortar strength or type and constituents.
2.1 Mortar Strength to Masonry Mechanical
Properties:
2.1.1 Mortar Strength to Masonry Bond
Strength:
For each mortar type, the mean bond strength obtained
is correlated with the mean compressive strength of
mortar. Nonlinear regression analysis is performed and
empirical relationship is established between mortar
strength and masonry bond strength through best fitting.
The following relationship is developed.
where fm (MPa) represents the compressive strength of
mortar, Additionally, constrained regression analysis is
performed whereby the power of fm is kept 0.60 and 1.0,
in order to possibly further simplify the above equation.
Either of the above equation may be employed, for most
of the practical cases, to obtain the masonry bond
strength given the mortar compressive strength.
shows the experimentally obtained data employed for
correlating the bond strength to mortar strength and
possible best fitting through regression (unconstrained
and constrained) analysis.
2.1.2 Mortar Strength to Masonry Diagonal
Tension Strength:
For each mortar type, the mean masonry diagonal
tension strength is correlated with the mean
compressive strength of mortar. Nonlinear regression
analysis is performed and empirical relationship is
established between the mortar compressive strength
and diagonal tensile strength through best fitting. The
following relationship is developed.
The above Equation 8 is found to provide higher
estimate of diagonal tension strength for CS mortar type
(see
Figure 10). Thus additionally constraint regression
analysis is performed for CS mortar type only whereby
the power of mortar compression strength fm is kept
0.80, in order to establish relationship between CS
mortar strength and masonry diagonal tension strength.
787 QAISAR ALI, YASIR IRFAN BADRASHI, NAVEED AHMAD, BASHIR ALAM,
SHAHZAD REHMAN and FARHAT ALI SHAH BANORI
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
Figure 10: Masonry Diagonal Tension Strength to
Mortar Compression Strength. CS Represents Cement-
Sand Mortar, CSK Represents Cement-Sand-Khaka
Mortar and CK Represents Cement-Khaka Mortar.
The above equation (8) may be employed for CK and
CSK mortar type to obtain the masonry diagonal tensile
strength given the mortar compressive strength.
Equation (9) can be employed for masonry in case when
CS mortar is used in the construction work.
Figure 10 reports the experimentally obtained data
employed for correlating the masonry diagonal tension
strength to mortar compressive strength and possible
best fitting through regression (unconstrained and
constraint) analysis.
2.2 Mortar Type and Mix Proportion to Masonry
Mechanical Properties
2.2.1 Mortar Type and Mix Proportion to Masonry
Bond Strength and Friction Coefficient:
For each mortar type, the mean masonry bond strength
and friction coefficient, parameters c & µ employed in
Equation (1), are correlated with the mortar constituents
proportion (mainly sand, khaka, and sand-khaka).
Linear regression analysis is performed and empirical
relationships are established between the mortar
constituents proportion and shear strength parameters of
masonry. Each mortar type is considered separately.
The following relationships are developed for c & µ of
the Mohr-Coulomb strength law for considered mortar
types.
Bond Strength:
Friction Coefficient:
In the above equations, S represents the proportion of
sand for unit cement proportion in CS mortar; K
represents the proportion of khaka for unit cement
proportion in CK mortar; SK represents the combined
proportion of sand-khaka for unit cement proportion in
CSK mortar considering that sand and khaka are
employed in equal proportion.
788 Experimental Investigation on the Characterization of Solid Clay
Brick Masonry for Lateral Shear Strength Evaluation
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
Figure 11 reports the experimentally obtained data
employed for correlating the masonry shear strength
parameters to mortar constituent for considered mortar
types and possible best fitting through linear regression
analysis. The horizontal axis of the Figure 11 represents
the proportion of sand to cement for CS mortar; khaka
to cement for CK mortar and combined khaka-sand
(added being equally) proportion to cement for CSK
mortar.
Figure 11: Masonry Shear Strength Parameters to Mortar Types and Mix Proportion.
From Left to Right: Masonry Bond Strength and Friction Coefficient Employed in Mohr-Coulomb Strength Model.
CS Represents Cement-Sand Mortar, CSK Represents Cement-Sand-Khaka Mortar and CK Represents Cement-
Khaka Mortar.
The above equations may be employed to estimate the
masonry shear strength given the type of mortar (i.e.
mortar constituents), and mix proportion. It is worth to
mention that these parameters are obtained at local level
and will require to be modified by the Mann and Muller
(1982) correction factor k i.e. Equation (2) before
employing them in shear strength evaluation of masonry
wall (Magenes and Calvi, 1997).
2.3 Correlating Masonry Mechanical Properties:
2.3.1 Masonry Compressive Strength to Masonry
Diagonal Tension Strength:
The mean masonry compressive strength is correlated
with the mean masonry diagonal tensile strength as
elsewhere (Ali, 2006). Nonlinear regression analysis is
performed and an empirical relationship is established
between the masonry compressive strength and diagonal
tensile strength through best fitting. The following
relationship is developed.
where fmc represents the masonry compressive strength.
The model can be employed to estimate the masonry
compressive strength given the masonry diagonal tensile
strength and vise versa.
reports the experimentally obtained data employed for
correlating the masonry diagonal tensile strength to
masonry compressive strength and possible best fitting
through nonlinear unconstrained regression analysis.
2.3.2 Masonry Young Modulus to Shear Modulus:
For each mortar type used herein, the mean masonry
Young modulus is correlated with the mean shear
modulus of masonry, in order to provide an easy means
of converting elastic moduli of masonry. Linear
regression analysis is performed and an empirical
relationship is established between the masonry Young
789 QAISAR ALI, YASIR IRFAN BADRASHI, NAVEED AHMAD, BASHIR ALAM,
SHAHZAD REHMAN and FARHAT ALI SHAH BANORI
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
modulus and masonry shear modulus through best
fitting. The following relationship is developed.
The above equation may be employed for most practical
cases to obtain the masonry shear modulus given the
masonry Young modulus. The condition, E>1000 (MPa)
given alongside the equation is again essential to avoid
any unrealistic estimate of shear modulus.
Figure 12: Masonry Diagonal Tension Strength to
Masonry Compression Strength.
Figure 13 report the experimentally obtained data
employed for correlating the masonry shear modulus to
masonry Young modulus and possible best fitting
through linear unconstraint regression analysis. The
figure also shows the code specified relationships e.g.
the EC6 specified like most of the building codes, for
masonry which in the present case seems to provide a
very higher estimate of the shear modulus for a
specified value of masonry Young modulus.
Figure 13: Masonry Young Modulus to Shear Modulus.
3 Conclusions:
The paper presented the mechanical characterization of
solid fired clay brick masonry through experimental
investigation. Laboratory tests were performed on 108
mortar cubes, 96 masonry prisms for triplet tests, 48
masonry prisms for compression tests and 48 masonry
wallets for diagonal tension tests. The effect of various
mortar types (cement-sand CS, cement-khaka CK and
cement-sand-khaka CSK) and mix proportion on the
mechanical properties are investigated.
Simplified relationships are developed to relate the
mortar strength, mortar types and mix proportion with
the masonry basic mechanical properties. The study
provided tools essential within the context of
assessment and design verification of masonry walls
subjected to lateral loads. The relationships: mortar type
and mix proportion to masonry bond strength and
friction coefficient are first of its kind and of a great
importance for practical applications. Masonry
constructions common in Pakistan and which can also
be found in neighboring countries (like India, Iran,
Bangladesh among others) are considered in the present
study. The following conclusions are drawn based on
the experimental study.
Given the mortar compression strength, the basic
mechanical properties of masonry can be found as
follow:
Bond Strength = 0.0326×Mortar Strength0.6633
Diagonal Tension Strength = 0.11×Mortar Strength0.8281
,
for CK and CSK mortar
Diagonal Tension Strength = 0.07×Mortar Strength0.80
,
for CS mortar
Masonry Compression Strength = 4.57×Diagonal
Tension Strength0.30
Masonry Young Modulus = 1790×Diagonal Tension
Strength0.30
Masonry Shear Modulus = 175.06× Diagonal Tension
Strength0.70
790 Experimental Investigation on the Characterization of Solid Clay
Brick Masonry for Lateral Shear Strength Evaluation
International Journal of Earth Sciences and Engineering
ISSN 0974-5904, Vol. 05, No. 04, August 2012, pp. 782-791
Given the mortar composition and mix ratio, the
basic mechanical properties of masonry for Mohr-
Coulomb relationship can be found as follow:
Bond Strength:
Friction Coefficient:
where S represents the proportion of sand, K represents
the proportion of khaka and SK represents the combined
proportion of sand-khaka per unit cement.
Masonry bond strength, compression strength,
diagonal tension strength and elastic moduli decreases
with increasing the relatively proportion of sand and
khaka constituent in mortar.
Masonry friction coefficient increases with
increasing the relatively proportion of sand and khaka
constituent in mortar for CS and CSK mortar type
whereas it decreases with increasing the relatively
proportion of khaka constituent in mortar for CK mortar
type.
The relationship between shear modulus and Young
modulus as specified by the Code appears to provide an
over-conservative estimate for shear modulus for the
considered masonry type.
The research study revealed that mortars with
khaka either alone as the fine aggregate or in
combination with sand, provide relatively high shear
strength and stiffness as compared to mortars with only
sand as fine aggregate. The positive aspects of use of
khaka as a masonry constituent are the good mechanical
characteristics besides being economical and more
workable in construction work.
Acknowledgements
The authors acknowledge the reviewers for kindly
providing constructive remarks which improved the
presentation of the research work significantly. The first
author gratefully acknowledges the support and
financial assistance provided by the University of
Engineering & Technology in the form of three years of
study leave. He also wishes to place on record his
gratitude to the Higher Education Commission (HEC)
of Pakistan for providing the funds for this research
under its Merit Scholarship scheme for PhD studies in
Science and Technology.
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