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3.3.3 Masonry PrismsTwo types of masonry prisms were constructed and tested in this study. One type was

three-course high with a height to thickness ratio of 3.3 as shown in Figure 3.20.

Figure 3.20 3-High Prisms testing arrangement

A total of 12 prisms of this type including 3 hollow, and 9 fully grouted were constructed.

The prisms were tested for the compressive strength, the modulus of elasticity, and thestress-strain relationship of the masonry in accordance with ASTM C1314-07 Standard

test methods for compressive strength of masonry prisms.

The second type of masonry prisms, referred to as square prisms, was 4-course high, 2-

course wide with a height to thickness ratio of 4.4. A total of 27 prisms of this type

including 9 hollow, 9 partially grouted, and 9 fully grouted were prepared. The partially

grouted prisms were grouted on the two outer cells of the prisms. They were tested for

compressive strength under three loading conditions. Vertical compression refers to a

loading direction which was perpendicular to the bed joint; horizontal compression

indicates that the loading was applied in parallel to the bed joint; and the diagonal

compression was to load the specimen in diagonal direction. The diagonal, vertical and

horizontal loading conditions are shown in Figure 3.21. These prisms were tested to have


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a better understanding of the effect of loading direction on the compressive strength of

masonry assemblage. All prisms were cured together with the walls and tested at

approximately the same time as the walls. LVDTs were mounted at the front and the back

of all the square prisms to obtain deformation readings. The gauge lengths of the LVDTs

were kept at approximately 200 mm. Horizontal and vertical specimens had a similar

testing procedure to the three-high prisms. For testing in the diagonal direction, two

custom-made supports were used for the loaded corners where each support was a V-

shaped joint inside a rectangular box designed to encase the corners and provide a

straight surface for testing as shown in Figure 3.22.

Diagonal Vertical Horizontal

Figure 3.21 Loading Conditions of Compression Test for Square Prisms.

Figure 3.22 Diagonal prism test loading shoe.


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4.2.2.2MortarType S mortar was used in the construction of wall infills. Three batches of mortar were

used in the building of specimens and mortar cubes were made from each batch. A total

of twenty-six 50mm mortar cubes were tested for their 28-day strength according to CSA

A179-04 (2004) Mortar and grout for unit masonry. For batch 1 mortar, nine cubes were

tested for 7-day strength as well for quality control purposes. Figure 4.3 shows an

example of the failure of mortar cubes under compressive testing where most of the

mortar cubes showed a conical shear or pyramidal shape failure. The compressive

strength for mortar cubes are summarized in Table 4.3 where the mean 28-day

compressive strength of all the mortar cubes tested was 13.6MPa. The average 28-day

compressive strengths were 15.1MPa from batch 1 (BM1) and 9.6MPa for Batch 2

(BM2) mortar cubes. Mortar cubes from batch 3 (BM3) attained compressive strength of

19.6MPa. The COVs of all 3 batches mortar strength were well within the specified limit

of 15%. It should be pointed out that BM2 mortar strength was lower than the minimum

28-day strength (12.5MPa) specified in CSA A179 - 04 (2004) for type S mortar under

laboratory conditions.

Figure 4.3 Failure of mortar cubes under compressive testing


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Figure 4.4 Failure of grout cubes under compressive testing

Figure 4.5 Load-displacement diagram of a grout cube in compressive

0

5

10

15

20

25

0 1 2 3 4 5

Load(kN)

Displacement (mm)


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while the grouted column remained practically intact. These are common failure modes

in prisms as reported by Drysdale and Hamid (2005).

Vertical crack (face-shell) Vertical crack (web) Face-shell spalling

Figure 4.6 Failure of 3-high prisms under compressive loading.

Net areas were used for the calculation of compressive strength of prisms. The net area

for the 3-high ungrouted prisms is the outside shell-area of the prism as shown in Figure

4.7. The net area of the 3-high fully grouted prisms was the gross area less the web area

of the unit block as shown in Figure 4.8.

Figure 4.7 Net area for 3-high ungrouted prisms

Figure 4.8 Net area for 3-high grouted prisms

The compressive stress of the BP1 ungrouted and grouted prisms were 12.7MPa and

8.0MPa, a difference of 37% with the difference in net areas of 49%. The higher


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For the horizontally loaded prisms, net area was calculated to be the same as the

vertically loaded prisms with respect to the different grouting situations. For diagonally

loaded prisms, the net area used for the fully grouted diagonally loaded prisms was the

rectangular area where the prisms were in contact with the loading shoes as shown in

Figure 4.11. The net area of the hollow prisms was taken as the faceshell area contained

within the loading shoe. For partially grouted diagonal loaded prisms, the average areas

between the fully grouted and hollow diagonally loaded prisms were used to calculate the

net areas.

Figure 4.11 Diagonally loaded prisms net area

To study the behavior of the prisms in different loading directions, a stress-strain curve of

each prism specimen was obtained and the Modulus of Elasticity, Em, was also

determined. It is a common practice to express Em in terms of compressive strength, f'm,

obtained with loading applied perpendicular to the prism bed joint. In this study, this

practice was followed and thus Em in the following tables is expressed in terms of f'mV,

compressive strength of the vertically loaded prisms. Figure 4.12 shows the stress-strain

curves of partially grouted prisms loaded in three directions. The full-set of stress-strain

curves can be found in Appendix A. It can be seen that partially grouted prisms loaded in

the horizontal direction displayed the lowest modulus of elasticity. However, diagonally

loaded partially grouted prisms had the highest modulus of elasticity. As expected,

Loading

Shoe

Net Area


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4 Preliminary System Identification

This chapter deals with the results of the component and system tests performed before the start

of the actual shake-table experiments involving the application of earthquake records. The

component tests include standard concrete compression tests and concrete split tension tests on

concrete cylinders fabricated during the construction of the test structure. These component tests

also include masonry compression, shear and bending tests performed on masonry prisms and

masonry panels constructed at the same time as the URM infill wall in the test structure. The

system tests are a series of pull-back (snap-back) tests on the test structure at different stages of

completion of the test structure configuration, namely before and after building the URM infill

wall and after the placement of additional mass on the test structure. The results of these

preliminary tests are used to gather the required data for calibrating and validating analytical

models of the test structure as discussed in Chapter 7 and to document the state of the test

structure at the beginning of the shake-table experiments as a point of reference when discussing

the results of these experiments in Chapter 6.

4.1 COMPONENT TESTS

4.1.1 Concrete Cylinder Compression Tests

A total of 30 test cylinders are prepared after each concrete placement for foundation, columns,

and beams and slab in accordance with ASTM C 837-99. The cylinders are kept in the same

environmental conditions as the test structure. Three uniaxial compression tests are performed

for each patch of concrete at different times to monitor the strength gain with time, the last of

which was performed on the day before the start of the shake-table experiments. Mean values

and the coefficient of variation (COV) of each test group are reported in Tables 4.1 and 4.2,

respectively. It can be observed that the compressive strength of the concrete on the day of the


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test is on average 22% higher than its 28-day compressive strength. No clear conclusion can be

made on the COV for the test results due to the small sample size, namely three for each reported

value. However, based on the results in Table 4.2 and for the purpose of practical reliability

analyses as in Chapter 8, one may consider a mean value of the COV of the concrete

compressive strength of 4.5%. The test setup and the resulting relationship of the mean strength-

gain with time for the used concrete are shown in Figure 4.1. The mean strength values obtained

at the time of the shake-table test are used in the computational modeling of the test structure

(Chapter 7) and for system identification purposes (Chapter 6).

Table 4.1 Mean uniaxial concrete compression test results.

Structural

element

First group

[ksi (MPa)]

Second group

[ksi (MPa)]

Third group (start of

shake-table experiments)[ksi (MPa)]

Foundation 3.27 (22.5)@11 day 4.15 (28.6)@28 day 4.98 (34.3)@567 day

Columns 3.04 (20.9)@5 day 4.36 (30.1)@33 day 5.40 (37.2)@552 day

Beams and slab 3.28 (22.6)@10 day 4.53 (31.2)@32 day 5.56 (38.3)@538 day

Table 4.2 COV of uniaxial concrete compression test results.

Structural

element

First group

(%)

Second group

(%)

Third group (start of

shake-table experiments)

(%)Foundation 7.6@11 day 5.6@28 day 1.1@567 day

Columns 4.0@5 day 4.6@33 day 9.1@552 day

Beams and slab 5.4@10 day 1.6@32 day 1.4@538 day

0 100 200 300 400 500 6000

1

2

3

4

5

6

Concrete

strength[ksi]

Time [days]

Beams and slab

Coulmns

Foundation0

10

20

30

40

[

MPa]

(a) Test setup (b) Concrete compressive strength-gain with time

Fig. 4.1 Concrete compressive strength test.


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4.1.2 Concrete Cylinder Split Tension Tests

Concrete cylinder split tension tests are performed on three concrete cylinders constructed using

the columns concrete batch. The tests are carried out at the start of the shake-table experiments.

The split tension tests conform to ASTM C496 and are used to identify the tensile strength of

concrete cylinders as defined in Equation 4.1.

dl

Pfct

2= (4.1)

where P is the maximum load at failure, l and d are the length and diameter of the cylindrical

specimen, respectively. The failure is sudden, with a vertical splitting crack across the section of

the specimen. The individual results as well as their mean value and COV are summarized in

Table 4.3. The mean value of the tensile splitting strength of concrete (about 8% of the

compressive strength) is used for the computational modeling of the test structure as described in

Chapter 7.

Table 4.3 Concrete split tension tests.

SpecimenMaximum load

[kips (kN)]ctf

[psi (MPa)]

1 48.8 (217) 431 (2.97)

2 50.4 (224) 446 (3.08)

3 46.5 (207) 411 (2.83)

Mean 48.6 (216) 429 (2.96)

COV 3.3% Fig. 4.2 Concrete split tension test setup.

4.1.3 Masonry Compression Tests

Three masonry prisms are constructed at the time of the construction of the URM infill wallaccording to the requirements of the ASTM C 1314. The prisms are capped and secured to two

steel plates on top and bottom using Hydrocal gypsum cement, and tested under uniaxial

compression 28 days after the wall construction. Both the axial load and the axial displacement

(measured between the two steel plates) of the masonry prisms are recorded during these axial

compression tests. Figure 4.3 shows the configuration of the masonry prism tests as well as the

typical failure mode consisting of vertical splitting and crushing. The stress-strain curves for the


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three prisms are shown in Figure 4.4 with the individual results, as well as their mean values and

COV, summarized in Table 4.4. In this table mof , mE , mo , and mu indicate the compressive

strength of the masonry, the modulus of elasticity measured as the secant modulus at 75% of the

compressive strength, and strain corresponding to maximum compressive stress and ultimate

strain of masonry corresponding to the residual stress value of momu ff 15.0= , respectively, as

shown in the insert of Table 4.4.

(a) Test setup (b) Typical failure mode

Fig. 4.3 Masonry prism tests.

0 0.005 0.01 0.0150

0.5

1

1.5

2

2.5

3

Strain

Stress[ksi]

0

5

10

15

20

[MPa]

Specimen 3

Specimen 2

Specimen 1

Fig. 4.4 28-day compression stress-strain curves for masonry prisms.


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Table 4.4 28-day uniaxial compression test results for masonry prisms.

Specimen mof

[ksi (MPa)]

mE

[ksi (GPa)]mo mu

1 2.31 (16.0) 948 (6.54) 0.0038 0.0120

2 2.31 (16.0) 812 (5.60) 0.0035 0.00863 2.76 (19.0) 935 (6.45) 0.0040 0.0120

Mean 2.46 (17.0) 898 (6.19) 0.0038 0.0109

COV 10% 8.3% 6.1% 18% Tension Compressionmo

mu

mof

muf

mE

mo0.75 f

Tension Compressionmo

mu

mof

muf

mE

mo0.75 f


mu

mof

muf

mE


mu

mof

muf

mE

mo mu

mof

muf

mo

mo mumu

mofmof

mufmuf

mEmE

mo0.75 fmo0.75 f

4.1.4 Masonry Diagonal Tension (Shear) Tests

In order to determine the shear strength of masonry, diagonal tension (shear) tests in accordance

with ASTM E519 are performed on three specimens. The used specimens are 2 -5"2-5" (75

cm75 cm) instead of the usual 44 (122 cm122 cm) as specified in ASTM E519 in order to

facilitate the construction and handling of the specimens. This reduction in size is suggested and

allowed by ASTM E519. The specimens are loaded in compression along the diagonal, and the

applied load and its corresponding vertical and horizontal deformations (along the diagonals) are

recorded. The loading causes almost diagonal cracking (vertical splitting in the testing position)

along an axis parallel to the direction of loading corresponding to a rapid drop in the load-

carrying capacity of the specimen. The force-deformation plots corresponding to the vertical and

horizontal diagonal deformations of the three tested specimens are shown in Figures 4.5 (a) and

(b), respectively. From these plots, note that the horizontal deformation (corresponding to the

crack opening of the vertical splitting cracks) is one order of magnitude higher than the vertical

deformation.


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0 0.01 0.02 0.03 0.04 0.05 0.06 0.070

5

10

15

20

25

30

35

40

45

Vertical deformation [in]

Verticalforce[kip

s]

Specimen 1

Specimen 2

Specimen 3

0 0.5 1 1.5

0

50

100

150

200

[kN]

[mm]

0 0.1 0.2 0.3 0.4 0.5 0.6 0.70

5

10

15

20

25

30

35

40

45

Horizontal deformation [in]

Verticalforce[kip

s]

Specimen 1

Specimen 2

Specimen 3

0 5 10 15

0

50

100

150

200

[mm]

[kN]

(a) Deformation along vertical diagonal

axis of specimen

(b) Deformation along horizontal diagonal

axis of specimen

Fig. 4.5 Diagonal force-deformation plots for masonry shear tests.

The shear strength of the masonry vf is obtained using Equation 4.2.

eff

vA

Pf = (4.2)

where P is the applied peak compressive diagonal force on the specimen and effA is the gross

sectional area of the specimen along its diagonal direction calculated as th2 where h and t

are the side length and thickness of the square specimen, respectively. The applied peak

compressive force and its corresponding shear strength for the three specimens as well as the

mean value (about 11% of the masonry compressive strength) and COV are presented in Table

4.5. The test setup and a typical failure mode are shown in Figure 4.6.

Table 4.5 Masonry shear test results.

SpecimenPeak compressive

load [kips (kN)]

Shear strength

[psi (MPa)]

1 44.2 (197) 283 (1.95)2 41.1 (183) 263 (1.81)

3 38.0 (169) 243 (1.68)

Mean 41.1 (183) 263 (1.81)

COV 7.6%


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Fig. 4.6 Masonry diagonal tension (shear) test.

4.1.5 Masonry Bending Test

To determine the tensile strength of the masonry assembly, a bending test on 2 -5"2-5" (75

cm75 cm) specimen is performed. The test setup is such that the middle third of the span of the

specimen is subjected to pure bending moment (i.e., no shear) as shown in Figure 4.7(a).

Assuming an elastic-brittle behavior for masonry in tension, the tensile strength of the masonry

assembly can be calculated from Equation 4.3:

6/

6/2tb

LP

S

Mft == (4.3)

where is the applied bending moment, S is the section modulus, P is the total applied peak

vertical load, L is the span, and b and t are the width and thickness of the specimen,

respectively. The total applied peak vertical load recorded during the test is 978=P lbs (4.35

kN) which corresponds to 5.69=tf psi (479 kPa) representing only 3% of the masonry

compressive strength and 26% of its shear strength. This relatively low value, compared to those

in more homogeneous materials, such as concrete, is attributed to the mode of failure of themasonry composite (two-phase) material (Loureno 1996), in Figure 4.7(b), which is dominated

by a single vertical crack along the weak plane of the mortar-brick interface.


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Fig. 4.7 Masonry bending test.

4.2 SNAP-BACK TESTS

Pull-back (snap-back) tests are performed on the test structure before and after the URM infill

wall construction to determine the stiffness, natural frequency, and damping ratio of the

structural system before starting the shake-table experiments. These tests are separately

conducted for both the longitudinal (north-south) and transverse (east-west) directions of the test

structure. It is to be noted that the torsional response of this symmetric test structure is not of

interest; therefore, asymmetric snap-back tests of the longitudinal and transverse directions are

not considered in this study. For each test, the structure is pulled in one direction by applying 3

8 kips (1336 kN) lateral force, depending on the stiffness of the test structure, using lever hoist

(come-along), and then released suddenly to allow free vibration. The floor acceleration and

displacements are measured during both the loading (pulling) phase and the free vibration phase

of the test. The force-displacement results of the pull test are used to obtain an estimate of the

stiffness of the test structure. The floor acceleration responses during the free vibration after

releasing the pulling force, both in the time and frequency domains, are analyzed and used to

estimate the natural period of vibration of the test structure and the corresponding damping ratio.A typical configuration and sample test results of the snap-back test is shown in Figure 4.8. The

results in this figure refer to the second snap-back test in the north-south and east-west directions

after building the URM infill wall, post-tensioning of the columns, and installation of additional

mass on the RC slab. The complete results of the snap-back tests are presented in Appendix B.


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70 4. Experimental tests on FRP strengthened masonry wall panels

also includes a comparison of the reinforcement schemes, and comparisons of the

results with other tests from the literature.

4.2 Experimental programThe Diagonal Tension/Shear Test involves subjecting a square section of ma-

sonry, with height and length both equal to 1.2 m, to a compressive load applied

along the diagonal. A schematic of the test is shown in Figure 4.1a. A photograph

of the test is shown in Figure 4.1b.

(a) Test schematic (b) Setup URM-1

Figure 4.1: The Diagonal Tension/Shear Test

The panels were constructed from solid clay masonry units with nominal di-

mensions 230 mm long, 110 mm wide and 76 mm high. Five batches of mortar

were used in the construction of the panels, all having a mix ratio of 1:1:6 (ce-

ment:lime:sand by volume). The mortar joints were 10 mm thick. These are the

same material specifications as used for the pull tests presented in Chapter 3.

The mortar batches used to construct each panel are presented in Table 4.1.

The flexural tensile bond strength of each mortar batch was determined using the

bond wrench test, AS3700-2001, Standards Australia (2001c). The bond wrench

test is described in further detail in Section 5.3.1. The average flexural tensile bondstrength (coefficient of variation in brackets) of each mortar batch is also presen-


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122 5. Finite element modelling

Table 5.1: Summary of all bond wrench results

Test Mortar batch Bond Strength (MPa) COV (%)Compression test 1:1:6 mortar 1.22 31

(Section 5.3.2) Han (2008) specimens

(1:1:6 + air entrainer) 0.176 -

Torsion test Series 1 (1:1:6 + air entrainer) 0.14 26

(Section 5.3.3) Series 2 (1:1:6) 1.74 11

Pull tests 1 1.84 23

(Section 3.2.1) 2 1.73 22

3 1.22 31

Wall Panel tests 1 1.25 51

(Section 4.2) 1+W 0.65 34

2 0.49 37

2+W 0.29 46

3 0.47 47

3+W 0.31 57

4 0.57 48

5 1.26 32

5+W 0.41 59

5.3.2 Compression tests on masonry prismsCompression tests on 7-brick high masonry prisms were used to determine the

elastic properties of the brick unit and mortar joint, as well as the compressive

strength of the masonry. Five prisms were constructed using the same clay brick

and mortar specification used to construct the pull test specimens and the wall

panels tested in diagonal tension/shear. The flexural bond strength of these speci-

mens was 1.22 MPa (COV 31%), determined using AS 3700 bond wrench test (Stan-

dards Australia, 2001c). This value was approximately equal to the bond strengths

of the strongest panels tested (URM-1, URM-2 and H4A - see Table 4.1 in Chap-

ter 4).

The compression specimens were constructed and tested in accordance with

AS3700 Appendix C (Standards Australia, 2001b). Specimens were constructed 7

bricks high to achieve a height-to-thickness ratio greater than 5 to minimise theinfluence of platen restraint. A photograph of the test is shown in Fig. 5.7.

Potentiometers were placed on both sides of the specimen to measure the dis-

placement across a mortar joint and across 3 bricks to calculate the strain in the

mortar joint and masonry respectively (as recommended by Drysdale et al. (1994)).

Potentiometers were not used to measure the displacement within a single brick

unit because they were not sensitive enough to measure the small brick displa-

cement. Potentiometers were mounted onto brackets that were screwed onto the

specimen at fine target points to allow the gauge lengths for displacement measu-

rement to be determined accurately.

To improve the determination of the elastic modulus from the compressiontest each specimen was loaded and then unloaded three times before being loa-


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5.3 Compression tests on masonry prisms 123

Figure 5.7: Compression test setup

ded to failure. Specimens were loaded to approximately 40 % of their predicted

peak load, before unloading, to capture the elastic loading range and minimise

non-recoverable damage. Specimen 1 was loaded to 200 kN before unloading (ba-

sed on an estimate ofPc = 500 kN); specimens 2-4 were loaded to 260 kN before

unloading (40% ofPc specimen 1); and specimen 5 was loaded to 300 kN before

unloading (approximately 40% of average ofPc for first four specimens). The dis-

placements recorded from the second, third and final load cycles were averaged

and used in the calculations to determine the elastic modulus values of the ma-

sonry and the mortar (displacements recorded from the first load cycle were igno-

red). All of the compression tests were stopped once the ultimate load was reachedto avoid damaging the potentiometers.

All of the specimens failed by crushing in the mortar joint and vertical cracking

through the front and back faces of the brick units. The ultimate load (Pc) and cor-

responding maximum compressive stress (fc), masonry strain at fc, and the elastic

modulus of the mortar (Emor) and masonry (Emas) are shown in Table 5.2. The

elastic modulii of the mortar (Emor) and masonry (Emas) were determined as the

gradients of the compressive stress-strain curves (for mortar and masonry respec-

tively) between 5 and 33% of the maximum compressive strength (Drysdale et al.,

1994).

The average elastic modulus of a single brick unit Eunit was determined indi-rectly using the average values ofEmor and Emas and by considering compatibility


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of displacements between masonry, brick unit and mortar joint. This calculation

was required because brick unit displacement (used to calculate strain) was not re-corded. The total masonry displacement is equal to the sum of the displacement

of the units and mortar. The masonry displacement across 3 bricks and 3 mortar

joint is equal to:

mas= 3unit+3mor (5.6)

The displacements are calculated using:

mas=PLmas

EmasA(5.7)

unit=PLunitEunitA

(5.8)

mas=PLmor

EmorA(5.9)

Where P=compression load, A=bedded area of prism, Lmas=258 mm, Lunit=76

mm, Lmor=10 mm. By substituting Equations 5.7, 5.8, and 5.9 into Equation 5.6,

Eunit was determined as 27592 MPa.

Table 5.2: Compression test results (bond strength = 1.22 MPa)

Specimen Pc (kN) fc (MPa) Masonry strain at fc Emor (MPa) Emas (MPa)1 664.88 26.28 0.0013 4801 17698

2 651.73 25.76 0.0030 8047 18895

3 970.51 38.36 0.0027 5067 17909

4 894.86 35.37 0.0025 2650 18157

5 873.10 34.51 0.0023 4854 18415

Average 811.12 32.06 0.0025 5084 18215

The average shear modulus values of the brick unit (Gunit) and mortar (Gmor)

were calculated as 11497 MPa and 2118 MPa respectively, using Equation 5.10 and

Equation 5.11. A Poissons ratio (

) equal to 0.2 was adopted for both the brick unitand the mortar (Loureno, 1996a).

Gunit=Eunit

2(1+)(5.10)

Gmor=Emor

2(1+)(5.11)

The experimentally determined elastic properties of the brick unit and mortar

joint were valid for the actual dimensions of the unit and the joint. As expanded

units and zero-thickness mortar joints were used in the FE model, adjustments

to the elastic properties were required to achieve an equivalent overall elastic res-ponse. A method that alters the elastic properties of the interface elements and


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5.3 Compression tests on masonry prisms 125

leaves the enlarged unit properties untouched is described in Rots (1997) and Lou-

reno (1996a). The normal elastic stiffness (kn) and the shear elastic stiffness (ks)of the mortar joint interface element were altered using Equation 5.12 and Equa-

tion 5.13, respectively, where hmor = thickness of mortar joint = 10 mm. The nor-

mal elastic stiffness (kn) was calculated as 623 N/mm3 and the shear elastic stiff-

ness (ks) was calculated as 260 N/mm3.

kn=EunitEmor

hmor(EunitEmor)(5.12)

ks=GunitGmor

hmor(GunitGmor)(5.13)

In addition to the maximum compressive stress (fc), the equivalent plastic re-

lative displacement (p) and the compressive fracture energy (Gc) were also re-

quired to model compression failure. The equivalent plastic relative displacement

(p) was calculated using Equation 5.14 as 0.024 mm in order to obtain a total ma-

sonry strain of 0.25% at fc (Table 5.2) (Loureno, 1996a). In Equation 5.14 hunit is

the height of the brick unit = 76 mm.

p=

0.0025fc

1

Eunit+

1

kn(hunit+hmor)

fc (5.14)

As each compression test was stopped just after the ultimate load was reached the

compressive fracture energy was not recorded. The compressive fracture energy

was estimated as 25 N/mm using Equation 5.15 (Loureno, 1996a).

Gc= 15+0.43fc0.0036f2c (5.15)

To estimate the elastic and compression properties for masonry panels with a

weaker bond strength (the average bond strength for some of the panels tested was

as low as 0.29 MPa) the results of Han (2008) were used. Han tested five masonry

prisms constructed using a similar clay brick (as the current investigation), but a

weaker mortar was used. This mortar consisted of cement:lime:sand in propor-

tions of 1:1:6 by volume with eight times the recommended dose of air entrainingagent added to deliberately create low bond strength. The bond strength of these

specimens was 0.176 MPa. The average values of the ultimate load (Pc), maximum

compressive stress (fc), and the elastic modulus of the mortar (Emor), masonry

(Emas) and brick unit(Eunit) are shown in Table 5.3. The masonry strain at fc was

not reported.

Table 5.3: Compression test average results from Han (2008) (bond strength = 0.176

MPa)

Pc (kN) fc (MPa) Emor (MPa) Emas (MPa) Eunit (MPa)

516 20.0 2772 18135 35360


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From these tests the values of fc = 20 MPa and Emor = 2772 MPa were adop-

ted to represent masonry with a bond strength of 0.176 MPa. For consistency, theelastic modulus of the brick unit (Eunit) from the previously described test series

(equal to 27592 MPa) was kept. The input properties required for the mortar joint

interface elements were calculated the same way as described previously, and are

shown in Table 5.4. For the calculation ofp, the masonry strain at fc was assu-

med as 0.2% (Loureno, 1996a). The input properties required for the mortar joint

interface elements determined for masonry with a bond strength of 1.22 MPa, are

also shown in Table 5.4.

Table 5.4: FE model input properties determined from compression tests

Property Bond strength = 0.176 MPa Bond strength = 1.22 MPakn (N/mm

3) 308 623

ks (N/mm3) 128 260

fc (MPa) 20 32

Gc (N/mm) 22 25

p (mm) 0.010 0.024

5.3.3 Torsion testTo characterise the shear behaviour of the mortar joint the torsion test (shown

in Figure 5.8), developed by Masia et al. (2006, 2007), was used. In this test anannular masonry specimen, which contains a single bed joint (Figure 5.8a), is sub-

jected to combined compressive stress (normal to the bed joint) and torsion. The

torsion test produces close to uniform distributions of normal and shear stress,

thus allowing the shear behaviour at a point to be characterised.

As part of the current investigation a set of torsion tests were performed on

specimens constructed using the same brick and mortar as the wall panel tests.

The specimens were prepared by coring a complete annular specimen through the

height of a pre-cast masonry couplet. These specimens were prepared differently

from previous torsion tests, reported in Masia et al. (2007). In Masia et al.s tests the

specimens were prepared by coring annular sections from two separate solid units

first, and then bonding them together with mortar. After testing, and then analy-

sing the results of the current investigation (joints cast before coring) it was found

that the joint shear strengths were lower than expected when compared to joints

that were cast after coring (as in Masia et al. (2007)). The reduced joint strength

was thought to be caused by damage to the joint during the coring procedure. The

results from the current investigation were unreliable and therefore were not used

for the characterisation of the shear behaviour. The results of tests conducted by

Masia et al. (2007) were used instead.

Torsion tests by Masia et al. (2007)

This section outlines the specimens tested by Masia et al., the testing proce-dure they used, and their results. Torsion tests were performed on specimens


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37

Figure 3.4 Triplet Test setup

Figure 3.5 Shear stress vs. Lateral compressive stress graph (Average shear

stresses)


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CHAPTER 6

PANEL TESTS

6.1 GENERALBefore the frame tests, two series of panel tests were conducted to obtain

information about the behavior of the strengthened masonry walls. The information

gathered in panel tests were used to model the frame tests in analytical evaluation.

In these tests, square masonry walls having dimensions of 700 700 mm and width

of 69 mm were loaded in diagonal direction.

Test set-up was prepared between two heavy concrete support blocks. Test

specimen was placed on thin metal plates parallel to floor. Steel plate was oiled and

sat on ball roller supports to ensure friction free movement of panel specimens.

Steel heads were placed to corners of the wall specimen in the diagonal direction

and were attached with gypsum. Dial gages were placed in six directions to measure

displacements on the wall. Test set-up is illustrated in Figures 6.1 and 6.2.

Figure 6.1 Test Set-up of Panel Tests


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Figure 6.2 General View of Panel Tests

6.2 PANEL TESTS6.2.1 First Series Panel Tests

In the scope of the first series, 12 tests were conducted. First, 6 reference wall

specimens, composed of 3 non-plastered and 3 plastered, were tested. Then, 6

plastered wall specimens strengthened in different ways were tested. Plastered wall

specimens were produced of 10 mm plaster thickness on both sides. 10 mm

thickness of mortar with 2% volumetric ratio of steel fibers was applied on one side

of 3 specimens. To the remaining 3 specimens, 20 mm thickness of mortar with 2%

volumetric ratio of steel fibers was applied again on one side. Specimen properties

are given in Table 6.1.

Mix proportions of the mortar used for the first series brick laying are presented in

Table 6.2 and mix proportions of the mortar used for plastering are given in Table

6.3.Mix proportions for 1 m3 of the mortar with steel fibers applied on the plaster of

the first series panel specimens are shown in Table 6.4.


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Figure 6.31 Views of SF2P-1



Figure 6.34 View of 2SNPP-1 Figure 6.35 View of 2SNPP-2


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Figure 6.44 View of 2SSF1P-3 Figure 6.45 View of 2SSF2P-1

Figure 6.46 Views of 2SSF2P-2

Figure 6.47 View of 2SSF1PD-1 Figure 6.48 View of 2SSF1PD-2

Figure 6.49 View of 2SSF1PD-3 Figure 6.50 View of 2SSF2PD-1


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Figure5:Bondwrenchtestapparatusandjointfailure

2.5.Masonrytensilebondstrength(Splittingtest)Becausethefailureofthewallettesalsoinvolvedsomeverticalsplitting,forlatermodellingpurposes,

itwas

also

useful

to

determine

the

transverse

strength

of

the

masonry

composite.

This

was

achieved

using thesplitting testreportedbyAli (7),seeFigure6,performedonspecimenswhichwerebuilt

accordingtoreference(7)andwerecuredinairinthelaboratory.Usingthisprocedure,thetransverse

strengthisgivenby:

T

CF

Dt

where/ 4

hlD

andhandlarethespecimenheightandwidth,respectively.Inaddition,tdenotes

the

specimen

thickness;F

is

the

applied

load

andC

a

constant

of

0.648.

This

constant

depends

on

brick/jointstiffnessandthechosenvaluewasbasedonmoduliofelasticityratioofbrickandmortar,

Eb/Em,ofapproximately2,seealso(7).

Using this approach, the mean transverse tensile strength of the five specimens was found tobe

0.62MPawithacoefficientofvariationof22.4%.DetailedresultsaregiveninTableA4.

Figure6:Tensilebondtestapparatusandsplittingfailure


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TableA7 inAppendixA shows the specimendimensions, failure loadsaswellas the compressive

strengthandmodulusofelasticity(asasecantmodulusattheloadof30%oftheultimate)forallfour

specimens.ThemeanvalueforthemodulusofelasticityEmobtainedfromtestsonspecimens1and4

was6.81GPa.Themeanvalueforthemasonrycompressivestrengthobtainedfromthetestswasonly

ahalfof thatobtained from theprism tests inaccordancewith theAustraliancode (seeTableA6).

Apartfromanysizeeffects,itisalsopossiblethatthespecimensmayhavebeendamagedduringthe

cuttingoutprocess.The failuremodesof these specimens (Figure9)alsodiffered from thatof the

masonrytripletsindicatingthatthetypeofspecimenmayhavealsoplayedarole.

Figure9:Compressiontestoncutoutspecimenanditsfailure


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The objectives of these small-scale tests were (1) to understand the impact of a thin layer

of ECC on unreinforced masonry, (2) to examine the performance of different ECC

retrofit schemes, and (3) to help develop a retrofit scheme for unreinforced masonry

infills in non-ductile reinforced concrete frames.

The small-scale tests were compression tests, flexural tests and triplet (shear) tests

(Figure 3.2). Compression tests of masonry prisms were conducted representing the

compression strut of a masonry infill under in-plane lateral loading. Flexural tests of

brick beams using a quarter point bending configuration with the constant moment region

intended to approximately represent direct tension (in particular in the ECC), were

performed to investigate the approximate response of tension struts in the masonry infill.

Triplet specimens with ECC in the joints between the bricks were tested in shear to

evaluate the ECC-brick bond in shear. With the small-scale tests different reinforcement

ratios, as well as ECC-masonry bonding techniques were examined.

(a) (b) (c)

Figure 3.2. Schematic of the small-scale test set-ups (a) compression test, (b) flexural

test, and (c) triplet test.

3.2. Compression Experiments

Masonry prisms with and without retrofit were fabricated and tested in compression. The

procedure followed for the fabrication of the specimens, the design of the different

______________________________________________________________________________________Chapter 3 Small-Scale Tests

40


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research had triple-wythe masonry infills and the intention was to use a 39 mm (1.5 in.)

ECC layer for its retrofit. A thickness of 39 mm (1.5 in.) is the maximum thickness that

the sprayable ECC was reported to reach when sprayed on a vertical surface (Kim et al.,

2003) at the time these experiments were designed.

(a) (b) (c) (d) (e) (f) (g)Figure 3.3. Schematic of the different variables tested, a) Tall plain specimen, b) Short

plain specimen, c) ECC retrofit, d) ECC retrofit with stitch dowels, e) lightly reinforced

ECC, f) lightly reinforced ECC with stitch dowels, and g) heavily reinforced ECC with

stitch dowels. All dimensions are in mm.

3.2.2. Fabrication of Masonry Prisms

All specimens tested in compression had four mortar joints no thicker than 13 mm (0.5

in.) each. As indicated in Figure 3.3, the specimens of group (a) were taller than those of

groups (b) through (g). The tall plain prisms had a height of approximately 343 mm (13.5

in.). The specimens of groups (b) through (g) had a height of approximately 267 mm

(10.5 in.) with the top and bottom bricks being cut down to 20 mm (0.8 in.) in thickness.

The height of the short specimens was controlled by the maximum specimen height that

the Forney compression tester at Stanford could accommodate when modified to give the

full compressive stress-strain response of the specimen. However, due to limitations in

the free rotation of the loading plates of the compression tester when modified, all

specimens were tested in the Powell laboratory, at The University of California, San


42


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Diego.

A professional mason from a local masonry company (Walton & Sons Masonry Inc.),

was hired to build the brick specimens in order to ensure real practice conditions (Figure

3.4). All fabrication was performed in one day in the laboratory of the John A. Blume

Earthquake Engineering Center at Stanford University.

200 mm200 mm

Figure 3.4. Fabrication of masonry specimens for compression tests.

The materials used were:

Yellow clay bricks 94 mm x 58 mm x 196 mm (3.7 in. x 2.3 in. x 7.7 in.), grade

MW, type FBS, and manufactured to meet ASTM C216-10.

Mortar consisting of 1 part cement (Type I/II), 1 part lime (Type S) and 5 parts

sand (Oly 1) by volume. The above types of cement, lime and sand were

recommended by the masonry company. This type of mortar is similar to Type

N which uses a 1:1:6 mix and results in a mortar with low compressive strength

(ASTM C270-10).

The type of bricks and mortar used were recommended by the Professional Advisory

Panel (PAP) of the project to represent the mechanical properties of the materials used for

the construction of masonry infills of a building that served as the project's prototype


43


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Table 3.13. ECC-brick interface shear strength of TEB specimens.

Joints are named based on Figure 3.79.

TEB specimen Joint 1 Joint 2 f's ECC-brick

1 1' 2 2' MPa (psi )1 R R* S S* 2.08 (302)

2 R R* S S* 2.38 (346)

3 S* S R* R 1.72 (250)

4 R R* S S* 2.00 (289)

5 R R* S S* 2.08 (302)

Average f 's ECC-brick = 2.05 (298)

S.D. f's ECC-brick = 0.21 (31)

* toweled surface

94 mm

58 mm

94 mm

58 mm

Figure 3.80. TE triplet specimen: Brick-ECC interface failure

94 mm

58 mm

94 mm

58 mm

3.81. TEB triplet specimen: Brick shear failure


128


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42

Figure 2.32: equipment set up for vertical compression tests: the steel

profiles fitted onto the Metrocom 3000 kN press (left), a wall ready to be

crashed inside the press (right)

Figure 2.33: diagonal compression tests set up, steel supports for

diagonal compression tests (left), wall ready to be crashed inside the

press (right)

Figure 2.34: suspension system of the upper steel profile


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47

Figure 2.45: equipment for compression test parallel to holes on hollowbrick walls (front and back view of the panel)

Figure 2.46: equipment for compression test orthogonal to holes on

hollow brick walls (front and back view of the panel)

Figure 2.47: equipment for diagonal on hollow brick walls (front and

back view of the panel)


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48

Figure 2.48: equipment for compression test parallel to holes on half-full

brick walls (front and back view of the panel)

Figure 2.49: equipment for compression test orthogonal to holes on half-

full brick walls (front and back view of the panel)

Figure 2.50: equipment for diagonal compression test half-full brick

walls (front and back view of the panel)


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Plugging this raw data into the formula, along with the measurements and parameters as defined

by the equation, the tensile strengths are found, shown in Table 2.

Table 2: Bond Wrench Flexural Strength Results

Gross Area flexural Tensile Strength (psi)

PRISM

6(H + H)

I$

( + )

I

Tensile Strength

1 142.4 7.2 135.2 psi

12 109.2 5.8 103.4 psi

15 72.2 4.1 84.8 psi

17 162.6 8.1 154.5 psi

26 93.06 5.1 88.0 psi

28 113.5 6.0 107.5 psi

average 112.2 psi

Taking the average of these values, neglecting the values of Prisms 8 and 15, yield an average of

112.2 psi for the tensile strength of the mortar joints. However, there is a wide range of values,

anywhere from 84 psi to 154 psi, which indicates that the accuracy of these values is not certain.

3. SHEAR TEST

a. MethodsThe second major material testing conducted is the shear test in which a triplet of bricks aremade with the center brick protruding on the top, as shown in Fig. 5.

Prior to being tested, the triplets are capped using hydrostone and following ASTM 1552-07standards (Standard Practice for Capping Concrete Masonry Units). This is done so that the two

bottom prisms are flat against the floor

and the top of the prism is perfectly flat.

To ensure the top is flat, a level is used inall directions to find the best possible fit of

the capping with the triplets.

However, it was found that the friction

forces between the hydrostone capping

and the bottom plate impacted the resultsof the testing. As a result, a steel plate was

placed under the hydrostone, along with a

small roller. The roller was used to eliminate the friction forces at the bottom of the triplets, andthe steel plate, which is hot glued directly onto the hydrostone, prevented the roller from digging

in and crushing the hydrostone capping. This set up is shown in a close up view on Fig. 7.

Figure 5: Shear Test Setup


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The triplets are then tested in the MTS 500k machine where the

central brick is subjected to a downward force while the entire

prism has a horizontal load at various stresses. An in-housedesign for the test arrangement was used, as there are no

ASTM Standards regarding this shear test. Following some

tweaking to the apparatus and the construction, the shear test asused in the experimented is shown in Fig. 6.

Stresses exerted on the mortar joints are 50 psi, 100 psi, 150psi, and 200 psi. Using the formula:

= (2)

the forces to be exerted in compression on the prisms are

determined as shown in Table 3. This axial compressive stressis generated by tightening screws on plates surrounding the

triplets, using an external load cell (shown in blue in Fig. 6)to measure the amount of force placed axially. Levels areused to ensure that the plates and the prisms are both as close

to perpendicular with the base plate as possible. Wooden

blocks, shown in Fig. 6, are placed on the sides as safetyprecautions, preventing the metal plates or the prisms from

hitting the MTS machine upon the sudden failure of the

mortar joint. In almost all the triplet tests, only one side of themortar joint failed while the other remained intact.

Table 3: Shear Test Axial Forces

Stress (psi) Force (kips)50 1.172

100 2.344

150 3.416

200 4.688

The results from this test are recorded through a data acquisition system which records both axialand shear forces. The shear displacements are recorded using a pair of pots located on the center

brick, as shown in Fig. 7 in addition to the recording of the distance being pushed downward

onto the prism. This is then post-processed and plotted to form coherent and readable graphs.

b. ResultsThe results of the shear data is in forces and displacements; this is then converted to shear vs.

displacement, as shown in Fig. 8.

Figure 6: Shear Testing

Figure 7: Shear Test, a close up

view of the plates and the rollers

Dolgu Duvar Deney Resimleri

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