STABILITY OF REINFORCED MASONRY SHEAR WALLS UNDER SEISMIC LOADING
Research Collaborators: Professors Ken Elwood and Don Anderson, UBC Civil Engineering, and Dr.
Svetlana Brzev, BCIT Civil Engineering
Project Summary - August 2012
Reinforced masonry (RM) shear walls subjected to combined gravity axial stresses and overturning
moments due to lateral seismic loads can experience lateral instability when longitudinal reinforcement
in the wall end zones is subjected to compression loads subsequent to cycles of high tensile strain.
Lateral instability is characterized by out-of-plane buckling of the wall end zone along the plastic hinge
height (see Figure 1).
A significant damage due to lateral instability was observed in a few reinforced concrete wall buildings
affected by the February 2010 Maule, Chile earthquake (M 8.8) and the February 2011 Christchurch,
New Zealand earthquake (M 6.3), as shown in Figure 2. However, there is a lack of evidence of similar
damage to RM shear walls in past earthquakes. Current Canadian masonry design standard CSA
S304.1-04 has restricted height-to-thickness (h/t) ratio for ductile masonry walls (from 14 to 20) to
prevent lateral instability in these walls, however these restrictions prevent the use of masonry in some
of the common applications (such as fire halls or warehouse buildings).
Insufficient experimental evidence prompted a need for a research program which would characterize
out-of-plane instability in RM shear walls and develop rational criteria for lateral instability in these
walls. This project seeks to identify the parameters influencing lateral instability of RM walls during
seismic loading and recommend improved code provisions to prevent against this failure mode while
maintaining the economy of masonry construction. The four-year program started in November 2010,
with financial support provided by the Canadian Concrete Masonry Producers Association and the
Masonry Institute of BC and NSERC through a Collaborative Research Development grant.
The research has been performed in two phases. Phase 1 was completed in April 2012 and it involved
testing of five reinforced masonry uniaxial specimens under reversed cyclic tension and compression.
The specimens represented the end zone of a RM shear wall and were 3.8 m high, corresponding to
(h/t) ratio of 27 (based on 140 mm block thickness). The purpose of the testing was to gain insight into
the factors influencing out-of-plane instability. The design parameters considered were longitudinal
reinforcement ratio and height-to-thickness (h/t) ratio. Specimen matrix is presented in Figure 3. A
model capturing the instability behavior shown in Figure 2 has been developed and calibrated with the
test data.
Phase 2 (currently in progress) involves experimental and analytical study of full-scale RM shear wall
specimens subjected to reversed-cyclic lateral loading. The test setup and specimen are shown in
Figure 4. The objective of this phase is to develop a rational analysis procedure and criteria for
assessing lateral instability in RM shear walls, which could be followed by design practitioners in
Canada and incorporated in CSA S304 standard.
This research program is a collaborative effort of Civil Engineering faculty and students from UBC and
BCIT. Two UBC Masters students (N. Azimikor and B. Robazza) and five BCIT undergraduate students
(D. Das, P.K. Lim, W. Yang, P. Lam, and J. Levasseur) have been engaged in the project to date.
Seven project-related papers and reports have been prepared to date and are listed below.
C
T
P
T
M
C
T
C
Figure 1. End zone of a shear wall subjected to axial tension and compression in end zones due to seismic
loading (Azimikor, 2012).
Lateral instability of a reinforced concrete shear
wall in the 2010 Chile earthquake (Elwood, K.)
Lateral instability of a Phase 1 specimen in
the UBC Structures Lab (Azimikor, 2012)
Figure 2. Wall instability in the 2010 Chile earthquake and a test specimen which experienced instability.
Specimen
Cross section
Reinforcement
3‐15M
C1
C2
C3
C4
C5
=0.71%
3‐20M
=1.07%
3‐15M
=0.71%
2‐15M
=0.48%
2‐10M
=0.24%
a)
b)
Figure 3. Phase 1 specimens: a) specimen matrix showing vertical reinforcement, and b) specimens before
the testing (Azimikor, 2012).
Figure 4. Phase 2 wall specimens: test setup and a specimen after construction (Robazza, B.).
PROJECT-RELATED PUBLICATIONS
1. Azimikor, N., Brzev, S., Elwood, K., and Anderson, D. 2011. Out-of-Plane Stability of Reinforced Masonry
Shear Walls, Proceedings of the 11th North American Masonry Conference, Minneapolis, MN, USA.
2. Azimikor, N. 2012. Out-of-Plane Stability of Reinforced Masonry Shear Walls under Seismic Loading:
Cyclic Uniaxial Tests, a Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of
Master of Applied Science, the Faculty of Graduate Studies (Civil Engineering), the University of British
Columbia, Vancouver, BC (completed in April 2012).
3. Azimikor, N., Robazza, B., Brzev, S., Elwood, K., and Anderson, D. 2012. An Experimental Study on the
Out-of-Plane Stability of Reinforced Masonry Walls Under Cyclic Axial Loads, Proceedings of the 15th
World Conference on Earthquake Engineering, Lisbon, Portugal (accepted for publication).
4. Lim, P.K. 2011. Stability of Reinforced Concrete Block Masonry Columns Under the Uniaxial ReversedCyclic Loading, Civil Engineering Research Project, Report No. CERP-2011/02, Department of Civil
Engineering, British Columbia Institute of Technology, Burnaby, BC.
5. Das, D. 2011. Testing of Masonry and Steel Mechanical Properties for Reinforced Masonry Columns,
Report for the CIVL 4090 Civil Engineering Industry Project course, Department of Civil Engineering, British
Columbia Institute of Technology, Burnaby, BC.
6. Lam, P. 2012. An Experimental Study on the Stability of Reinforced Masonry Columns, Report for the CIVL
4090 Civil Engineering Industry Project course, Department of Civil Engineering, British Columbia Institute
of Technology, Burnaby, BC.
7. Yang, W. 2012. Experimental Study on Seismic Resistance of Masonry Shear Walls, Report for the CIVL
4090 Civil Engineering Industry Project course, Department of Civil Engineering, British Columbia Institute
of Technology, Burnaby, BC.