Paper No. TS-1-1

EXPERIMENTAL STUDY ON DYNAMIC BEHAVIOR OF
UNREINFORCED MASONRY WALLSLuis MOYA1, Cesar FAJARDO2, Taiki SAITO3, Koichi MORITA4

SUMMARY
Dynamic behavior of unreinforced masonry wall was investigated through a shaking table testin which two specimens were prepared. In order to simulate non-engineering houses of one
story, the first specimen consists of a C shaped structure, whose masonry walls are connected
only by their ends. The second specimen was built to idealize an upper story, therefore the C
wall is connected at the top by a rigid diaphragm floor and a weight suspended. The test resultshow different behavior between each specimen. In the first specimen an out-of-plane failuremode governs and in second specimen a shear failure mode governs.
INTRODUCTION
A fundamental issue to be resolved is mitigating the seismic hazard of unreinforced masonry(URM) walls. This concern is relevant to Peru because residential buildings located in areas
with low economic resources are mostly non-engineering houses. Figure 1 illustrates a nonengineering house built with URM walls and without floor diaphragm. And Figure 2 illustrates
typical URM exterior walls of a masonry building, which could injure people around thebuilding when it collapses during earthquakes.
Although the most extensive research on URM buildings was developed by ABK Joint Venture[1,2], it was developed based on structural systems used in USA-California like the use offlexible wood diaphragm. However, it is still the primary source for guidelines developed byFederal Emergency Management Agency [3, 4, 5]. The weakest shape of failure in URM walls
is the out-of-plane failure and in those tests it consists of horizontal cracks located at the bottom,
top and around the middle wall.
An URM building model that includes a floor diaphragm as well as in-plane and out-of-plane
wall components was developed by Simsir et al [6]. In that test the in-plane and out-of-planewalls were connected only by the flexible diaphragm and an axial load was applied to the outof-plane walls. Instead of the mid-height horizontal crack observed in ABK research and others,a horizontal crack located around 70% of the wall height from the base was observed.
1

Master’s Candidate, National University of Engineering, Peru, Email: Lmoyah@uni.pe
Master’s Candidate, National University of Engineering, Peru, Email: cafg07@hotmail.com
3
Chief Research Engineer, Building Research Institute, Japan, Email: tsaito@kenken.go.jp
4
Chief Research Engineer, Building Research Institute, Japan, Email: morita@kenken.go.jp
2This paper summarizes a research that was addressing to better understand the interaction
between in-plane and out-of-plane walls when they are connected by their ends (continuity at
the corners). The research was undertaken into the project “Enhancement of Earthquake andTsunami Disaster Mitigation Technology” which is an international collaboration between
Japan and Peru. The wall test was carried out in the Structural Engineering Laboratory at the
Building Research Institute.

Figure 1 House consists of URM walls

Figure 2 Masonry building with URM external
walls

EXPERIMENTAL TESTOn January 2012 two specimens were constructed on the shaking table of the StructuralEngineering Laboratory at Building Research Institute. Figure 3 and 4 illustrate the idealized
models which represent an URM wall of a single-story building and an upper level of amultistory building respectively. Each specimen consists of three masonry walls: A, B and C.
The ground motion direction was applied perpendicular to the wall B. Therefore, the walls A
and C will behave in-plane and the wall B will behave out-of-plane. In the second specimen, aconstant axial load of 18kN approximately was applied by means of a weight suspended overthe floor diaphragm.
The wall B has height, width and thickness of 1440 mm, 2850 mm and 100 mm, respectively.
The orthogonal walls (A and C) have 1440 mm, 1450 mm and 100 mm of height, width andthickness, respectively. The above dimensions give a slenderness ratio of 14.4. Solid bricks andtype O mortar were used in the specimen. Masonry prisms of four bricks tall were made when
the brick were moist cure for 28 days. The average compressive strength of the masonry prism
was found to be 6.09 MPa. Diagonal tension tests according to the ASTM E519 were carriedout on 430mm x 410 mm specimens. The average shear strength of the masonry after 28 days
was found to be 1.28 MPa.
Grodirund mectio otion nSpecimen

Support

Sh
ak
ing
Ta
ble
Y

X

T
ing
ak
Sh

Z

(a)

le
ab

(b)

Figure 3 Specimen 1: (a) Scheme of the test setup (b) Specimen on the shaking tableWeight
suspended

Diaphragm
floor

Gr
ou
dir nd mectio otion nSpecimen
Support

Sh
ak
ing

Y

X

Ta

ble

ing
ak
Sh

Z

Ta

ble

(a)

(b)

Figure 4 Specimen 2: (a) Scheme of the test setup (b) Specimen on the shaking table
Fourteen accelerometers, seven pi-gauges and a data acquisition system were used to record the
dynamic characteristics of the walls in the specimens. The figure 5 (a) shows the position of theaccelerometers. The A00, A05 and A13 accelerometers recorded vibrations in the up-down
direction and all the others recorded vibrations in the direction perpendicular to the wall where
they are located. Assuming that the wall “B” will fail similar to the shape of failure of a slab
(out-of-plane behavior), it was decided to collocate the pi-gauges as illustrated in figure 5 (b).
As you can see, most of the accelerometers were placed on the wall B. That is because previous
researchers showed the out-of-plane as the weakest mode of failure
Three additional accelerometers were placed over the floor diaphragm, for the second specimen.
The accelerometer located at the middle of the diaphragm recorded the acceleration in the same
direction of the shaking table and the other two, which were located at the ends, recorded theacceleration in the up and down direction.
A10

A11

A12

A13

A14

A15 A16

A17

A18

A21

A23
A22

P6

P1

P5

A19

P2

Wall A

Wall B

P7

Wall C

Wall A

P3

P4

Wall B

Wall C(b)(a)

Figure 5 Instrumentation for the wall test: (a) accelerometers and (b) pi-gauges

TEST PROCEDURE AND RESULTSFirst Specimen
A total of twenty unidirectional signals were applied at the base of the first specimen. For eachtest, the type of signal, the amplitude of the table shake, the peak table acceleration, themaximum measured displacement and acceleration at the top and mid-height of the wall B aregiven in Table 1. The displacements showed are relative to the base and the accelerations are
absolute values.
Two types of signals were applied over the tests: frequency sweep test and frequency random
test. Frequency sweep test was useful to monitor the shift of the natural frequency of the wall B.
As a result of the damage produced in the specimen during the tests, the natural frequency of thespecimen had been decreasing continuously. As shown in Figure 6, which is the record of theaccelerometer placed at the middle top of the wall B, the natural frequency decreased from an
initial value of 19.34 Hz to 6.29 Hz by the end of the 19th dynamic test run.

Frequency

25
20
15
10
5
0
0

1

2

3

4

5

6

7

8

9

10 11 12 13 14 15 16 17 18 19 20

Test number

Figure 6 Variation of the natural frequency of the first specimen
Table 1 Shake table runs and recorded peak values for the first specimen
Test
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20

Type Frequency Amplitude
Peak Table
wave
(hz)
(mm)
Acceleration (g)sweep 0.8 - 20
0.5
0.01
sweep 0.8 - 20
0.5
0.43
sweep 0.8 - 20
0.5
0.40
random
5 - 200.5
0.02
random
5 - 2010.0
0.67
random 12 - 20
5.0
0.28
random 12 - 20
5.0
0.24
random 12 - 20
10.0
0.67
random 12 - 20
15.0
1.21
random 10 - 15
5.0
0.17
random 10 - 15
10.0
0.39
random 10 - 15
15.0
0.66
sweep 0.8 - 20
0.5
0.25
random
5 - 1510.0
0.70
random
5 - 1520.0
1.01
random
5 - 1020.0
0.45
random
5 - 1030.0
0.60
random
5 - 1040.0
0.73
random
5 - 1050.0
1.18
random
3-8
70.0
---

DisplacementsTop
Mid-height
0.13
0.09
2.74
1.75
2.31
1.83
0.21
0.15
3.34
2.92
1.21
0.77
1.33
0.76
2.75
1.7
4.93
2.56
1.58
0.62
3.16
1.41
7.46
2.78
3.12
1.03
4.91
2.01
8.39
4.12
7.68
2.93
9.39
3.38
12.94
5.17
11.49
6.18
-----

Accelerations (g)TopMid-height
0.05
0.03
2.15
1.56
2.02
1.37
0.11
0.08
3.10
2.18
0.88
0.45
1.06
0.47
2.31
0.88
5.01
1.41
1.18
0.23
1.96
0.55
3.33
0.97
1.47
0.33
2.69
1.17
5.00
1.50
2.45
0.91
3.24
1.22
4.89
1.69
5.73
2.59
-----

Although most the cracks were observed over the out-of-plane wall component, the crack
patterns before the failure was different than previous investigations. As shown in Figure 7, thefirst cracks were observed after the 5th test and it was located at the middle top of the wall B andalso at the top of the corners. After the 9th test the initial cracks become wider and a diagonal
crack appear over the wall B. This diagonal crack has not been seen in previous research.
Another diagonal crack appears in the same wall after the 19th test. Besides, the cracks located at
the upper corners became larger and they reached the half-height of the wall. Finally, when theconnection between in-plane and out-of-plane walls were partially lost, a horizontal crack
formed at the middle of the wall, which corresponds to the collapse of the specimen (see Figure8).

Wall A

Wall C

Wall B

Wall A

Wall B

Wall A

After test 13

Wall A

Wall C

After test 09

Wall C

Wall B

Wall B

Wall A

After Test 05

Wall C

After test 19

Wall B

Wall C

After test 20

Figure 7 Crack patterns developed in the first specimen

Figure 8 Shape of failure of the second specimen

Second Specimen
A total of 23 unidirectional signals were applied at the base. The Table 2 shows the type ofsignal, the amplitude of the table shake, the peak table acceleration, the maximum measured
displacement and acceleration at the top and mid-height for the second specimen. However,while the values of displacement and acceleration at the top are from the rigid diaphragm, thevalues at the mid-height are from the wall B.
There are no information of the maximum values of displacement and acceleration for the tests
21 and 22 because the accelerometers were removed before. Three types of signals were applied
over the tests: frequency sweep test, frequency random test and Kobe earthquake. As mentioned
above, frequency sweep test was used to find out the shift of the natural frequency of thespecimen.

Table 2 Shake table runs and recorded peak values for the second specimen
Test
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22

Type
Frequency Amplitude
Peak Table
Displacements (mm)
wave
(hz)
(mm)
Acceleration (g)TopMid-heightsweep
0.8 - 20
0.5
0.15
0.91
0.48
sweep
0.8 - 20
0.5
0.15
1.37
0.21
random
5 - 20
0.5
0.02
0.14
0.10
random10 - 15
0.5
0.01
0.11
0.13
random10 - 15
2.0
0.04
0.27
0.10
random10 - 15
10.0
0.23
1.31
0.42
random10 - 15
15.0
0.52
1.92
1.17
random10 - 15
15.0
0.90
2.06
1.45
random12 - 15
20.0
0.78
3.38
1.36
Kobe earthquake--0.2*
0.19
13.87
0.13
random12 - 15
20.0
1.13
2.66
1.44
sweep
0.8 - 20
0.5
0.17
0.97
0.29
random
5 - 15
30.0
1.35
5.27
2.38
random
5 - 15
30.0
1.44
4.25
2.99
random
5 - 15
30.0
1.82
4.20
5.45
sweep
0.8 - 20
0.5
0.20
1.18
0.86
random
5 - 15
30.0
1.52
4.70
6.25
random
5 - 15
40.0
1.97
5.32
9.04
random
5 - 15
40.0
2.11
4.87
6.34
random
5 - 15
40.0
2.05
5.24
8.18
random
5 - 1050.0------Kobe earthquake--0.5*-------

Accelerations (g)TopMid-height
0.33
0.23
0.33
0.24
0.04
0.03
0.02
0.02
0.10
0.07
0.59
0.49
0.94
1.13
0.98
2.89
0.90
2.25
0.20
0.20
1.16
2.72
0.33
0.49
1.14
4.19
1.09
4.32
0.96
3.65
0.22
0.43
1.08
3.96
1.17
4.75
0.89
4.73
1.10
4.96
---------*These values represent the fraction of the Kobe earthquake that is applied in the test
This time most of the cracks were developed over the in-plane walls. It seems that the axial load
produced by the weight suspended at the top had improved the flexural strength of the wall B.
Furthermore, a kind of confinement is provided by the floor diaphragm and the roof. As shownin Figure 9, at the beginning the cracks patterns developed over the in-plane walls components
were totally different between them. After the 15th test, a bed-joint sliding on a horizontal planelocated at the top was developed in the wall A; on the other hand, a sliding on a stair-stepped
diagonal crack was developed in the wall C. Due to the difference of behavior between the inplane wall components, torsional movements was developed in the specimen. After the 18th
test, diagonal cracks, which began in the in-plane walls and end up on the wall B, weredeveloped because the torsional behavior. Finally, the shape of failure is illustrated in Figure 10.
20

20

After 12th test
20

Wall A

20

Wall C

Wall B

Wall A
20

20

Wall B

Wall C

20

After 15th test
20

Wall A

Wall C

Wall B

Wall A
20

20

After 16th test

20

20

Wall B

After 18th test

Figure 9 Crack patterns developed in the second specimen

Wall C

20

20

20

Wall B

Wall A

20

Wall C

After 20th test

20

Wall A

20

Wall B

After 21st test

Wall C

Figure 9 Crack patterns developed in the second specimen (continuation)

Figure 10 Shape of failure of the second specimen
The change of the natural frequency can be used as a trace of the damage produced in thespecimen. The figure 11 illustrates how the natural frequency of the accelerations recorded overthe diaphragm had been reducing. However, the natural frequency recorded at the middle-height
middleof the wall B had not been reducing significantly.
25

Frequency

20
15
Diaphragm
Wall B

10
5
0
0

1

2

3

4

5

6

7

8 9 10 11 12 13 14 15 16 17 18 19 20
Test number

Figure 11 Variation of the natural frequency of the second specimen

CONCLUSIONS
The interaction between in-plane and out-of-plane components of an URM wall when they areconnected by their ends (corners) has been studied. For this reason, two specimens were tested
through a shaking table. The shape of failure of the first specimen, which simulates a singlestory building, was out-of-plane. However, at the beginning the crack patterns were different
than previous research due to the influence of the in-plane walls.
It was expected that the shape of failure in both specimens was out-of-plane. Nevertheless, mostof the damage in the second specimen was observed on the in-plane walls. The floor diaphragmand the axial load produced by the weight suspended at the top had enhanced the stability of theout-of-plane wall component.
As happened in the second specimen, the possibility of different modes of behavior in the inplane walls components of a building could produce torsional movements. Besides, the URM
walls have several shear behavior modes like wall-pier rocking, bed-joint sliding, spandrel-joint
sliding, rocking/toe crushing, etc.
Almost all the cracks observed were located in the mortar. It means, the brick units had not beenbroken. Therefore, analytical models based on simulations of rigid body dynamics could give us
a good estimate of the dynamic behavior of URM buildings.
ACKNOWLEDGEMENT
This study was supported by the research project on earthquake and tsunami disaster mitigationin Peru under the framework of "Science and Technology Research Partnership for Sustainable
Development (SATREPS)," by Japan Science and Technology Agency (JST) and Japan
International Cooperation Agency (JICA).
REFERENCES
1. ABK. “Methodology for Seismic Hazard in Existing Unreinforced Masonry Buildings:
Wall Testing, Out-of-Plane, Topical Report 04”. ABK Joint Venture, California, December
1981.
2. ABK. “Methodology for Seismic Hazard in Existing Unreinforced Masonry Buildings: The
Methodology, Topical Report 08”. ABK Joint Venture, California, January 1984.
3. FEMA 306. “Evaluation of Earthquake Damaged Concrete and Masonry Wall Buildings,
Basic Procedures Manual”. Federal Emergency Management Agency, Washington, D.C.,
1999.
4. FEMA 307. “Evaluation of Earthquake Damaged Concrete and Masonry Wall Buildings,
Technical Resources”. Federal Emergency Management Agency, Washington, D.C., 1999.
5. FEMA 356. “Prestandard and Commentary for the Seismic Rehabilitation of Building”.
Federal Emergency Management Agency, Washington, D.C., 2000.
6. Simsir CC, Aschheim MA, Abrams DP. “Out-of-Plane Dynamic Response of Unreinforced
Masonry Bearing Walls Attached to Flexible Diaphragms”. 13th World Conference on
Earthquake Engineering, Vancouver, B.C., 2004.