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Seismic Enhancement of Partially Grouted Reinforced Masonry: Shear Friction AnalysisKerianne 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*0.80Figure 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)

TE

ST

WA

LL

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

REFERENCESMasonry 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.