1. `
Seismic Enhancement of Partially Grouted Reinforced Masonry: Shear Friction Analysis
Kerianne Westphal, NEES REU, Manhattan College, kwestphal.student@manhattan.edu
Benson Shing, PhD., Andreas Koutras, University of California, San Diego
The specimen met only the minimum code requirements (Shing, et al. 2014). Plan and elevation
views of the specimen (Figure 2, Figure 3) display where the steel reinforcement was located in the
structure and, therefore, where the structure contained grout.
Figure 2 – Plan view of specimen one. Figure 3 – Elevation view of specimen one.
The specimen failed rigidly. Figure 4 displays the types of damages that occurred within the
structure during the shake table tests. One of the failure mechanisms was the sliding that occurred
between the base of the structure and the concrete foundation, which was resisted by shear friction.
Figure 4 – Typical damages to the masonry structure during shake table tests.
FORMULA DERIVATION RESULTS
CONCLUSIONS
ACKNOWLEDGMENTS
INTRODUCTION
Reinforced masonry
buildings are used to
construct:
• Schools
• Industrial buildings
• Public facilities
(libraries)
• Hospitals
Two types
West Coast: Areas ofFull Grouting:
• All masonry blocks
are filled with grout
• Seismically resilient
Partial Grouting:
• Only masonry blocks
containing steel
reinforcement are filled with
grout
• Economically competitive
• Not as seismically resilient
Middle America/East
Coast: Areas of
• Low seismic risk
• Moderate seismic
risk
• High seismic risk
• Moderate seismic
risk
• High seismic risk1)
2)
Current Formula: where V = nominal shear-friction strength
µ = friction coefficient (1.0 for
intentionally roughened
surfaces, 0.70 for all other
Ast = area of steel rebar
fy = yield strength
Pu = normal force
Only valid for walls with shear-span ratio (height to length ratio)
less than 0.5 (Figure 5), so that the wall is short and long.
These walls are not controlled by bending and, therefore, can
be governed by the formula currently used in ACI 318.
Figure 5 – Short, long masonry wall for which the current shear friction formula is acceptable
Looking at a wall whose shear span ratio is
greater than 0.5 and is controlled by bending
(Figure 6), only the side of the wall in
compression will be able to produce a shear-
friction against the foundation. This region has a
distance:
a = c*0.80 where a is the
approximate distance of an
equivalent rectangular force.
Therefore, the equivalent shear friction formula
for this case and it’s subsequent simplifications
are as follows:
Force, P
Compression
Tension
a = c*0.80
Figure 6 – Tall, small in height
masonry wall for which the new shear
friction formula applies.
where µ = .65
a = 0.80*c
t = wall thickness
f’m = masonry strength
Anc = net area in compression
0 20 40 60 80 100
1
2
3
4
V (kips)
TESTWALL
Theoretical and Experimental
Shear Strength
Theoretical
Experimental
Figure 7 – Graph of the difference between
experimentally and theoretically determined
shear friction strength in four wall samples
Wall
Name
Theoretical
(kips)
Experimental
(kips)
Error
%
1) UT-03 51 47 8.67
2) UT-04 87 82 6.01
3) Shing 8 48 49 2.84
4) Shing 6 49 50 7.76
Table 1 – Wall names corresponding to graph,
theoretical and experimental shear friction
strength values, and the percent error between
them.
• Shear friction is a governing failure mode in
certain cases of reinforced masonry walls
and the MSJC code should require it to be
calculated for new buildings.
• The new shear friction formula is relatively
accurate in predicting the shear friction
strength of a wall.
• However, more testing and refinements
must be done to make it more accurate.
• NEES program Award No. CMMI-1208208
• NEES REU grant number EEC- 1263155
• NEES Operations award number CMMI-0927178
• Dr. B. Shing; mentor, provider of research for UCSD shake table tests and
2 theoretically tested wall samples
• Andreas Koutras; mentor, provider of research for UCSD shake table tests
• University of Texas; provider of 2 theoretically tested wall samples
REFERENCES
Masonry Standards Joint Committee. “Building
Code Requirements and Specification for
Masonry Structures.” 2013.
Shing, Benson, et al. Improving Seismic
Performance of Partially-Grouted
Reinforced Masonry Buildings. 2014.
OBJECTIVE
The Masonry Standard Joint Committee (MSJC) does not currently require a calculation of a shear
friction strength estimate. Therefore, new recommendations for accurate estimation of shear
friction strength in a reinforced masonry wall are being formulated and evaluated with the aim
of improving the MSJC code.