tests such as shear triplet and diagonal compression have been conducted on the ... (Ref.5). The test results showed that the shear load bearing capacity and the energy absorption capacity .... The unit brick which was used in this study was a plain one (without ... Nine masonry prism specimens were made with the height to.
構造工学論文集 Vol.59 B (2013 年 3 月)
日本建築学会
AN EXPERIMENTAL STUDY ON THE RETROFITTING OF UNREINFORCED MASONRY SPECIMENS WITH ECC AND AFRP SHEET Gholamreza ZAMANI AHARI*, Kentaro YAMAGUCHI**, Hiromi NISHIYAMA* and Masakatsu MIYAJIMA***
It has been proved through past earthquake experiences that unreinforced masonry (URM) structures are not able to resist seismic loads and in order to reduce the serious damages caused by earthquakes, they should be considered for retrofitting. Incapability of lateral load resisting walls is mostly responsible for the collapse of URM structures around the world. In this research work, compressive and monotonic shear tests such as shear triplet and diagonal compression have been conducted on the specimens rehabilitated with engineered cementitious composite (ECC) overlay and aramid fiber reinforced polymer (AFRP) sheet. ECC with multiple fine cracks is a cement-based composite material which exhibits a high tensile strength and strain - hardening behavior. Also FRP products are well known for their retrofitting potential and as the present study, in order to eliminate the debonding behavior of FRP which greatly limits its efficiency, confining bands were utilized. The efficiency of both retrofitting methods were evaluated and discussed based on the test results. As a result, it was found out that the shear strength and deformation capacity of URM improved considerably.
Keywords: Unreinforced masonry, Retrofitting, Engineered cementitious composites, Aramid fiber reinforced polymer, Shear strength, Deformation capacity
1. INTRODUCTION
of crack (Ref.1 and 2). This composite material has shown a high strain
Unreinforced masonry (URM) structures have shown low lateral
capacity and can absorb and dissipate high amounts of energy (Ref.3).
resistance and ductility in earthquake events and should be seismically
Improving the low tensile strength, strain-softening and brittle behavior of
retrofitted. Currently, several methods are being applied for the seismic
URM walls through surface retrofitting with such a ductile strain-hardening
retrofitting of URM structures and some are under study process. The
material was the main motivation of this research work. Improvement in the
philosophies of these techniques are based on the improvement of strength
basic behavioral characteristics of the retrofitted masonry can be evaluated
and deformability or the combination of both.
through series of tests on small-size specimens retrofitted with ECC.
Unreinforced masonry walls are one of the most vulnerable parts of URM
Kyriakides and Billington (Ref.4) studied ECC retrofitting for concrete
structures. Their weak seismic in-plane and out-of-plane response are
frame-infill masonry walls. They conducted a series of experiments in order
known as the most important reason of the major URM damages and
to examine the impact of a thin layer of ECC applied to masonry infill wall
failures around the world. Many researchers around world have conducted
as well as when it is applied on a masonry wall bounded by a non-ductile
static and dynamic experiments to grasp the structural behavior of URM
reinforced concrete frame. The study results showed that ECC can help
wall and examined some retrofitting methods to improve its seismic
keep unreinforced masonry walls in tact to large lateral drifts, adding
performance. The results of these studies have been reported frequently for
significant ductility to the entire structural system under cyclic loading.
some retrofitting techniques such as surface treatment methods, frame
The effect of ECC mixture components on its retrofit functionality for
confinement, center core. In spite of the improvements exhibited by these
masonry walls was studied by Bruedern et al. (Ref.5). The test results
methods, there are some limitations and disadvantages on their application.
showed that the shear load bearing capacity and the energy absorption
Engineered Cementitious Composite (ECC) – also refers to as High
capacity of masonry increased by the application of a thin ECC layer.
Performance Fiber Reinforced Cement Composite (HPFRCC), Strain-
Maalej et al. (Ref.6) studied the ECC retrofitting for URM walls under
Hardening Cement-based Composite (SHCC) and bendable concrete – with
impact loading. The quasi-static loading test results showed that the ECC-
multiple fine cracks is a cement-based composite material with a strain-
strengthening system improves the out-of-plane resistance of masonry walls
hardening tensile behavior and an excellent capability to control the width
significantly. Moreover with the use of ECC overlay, fragmentations due to
*
Graduate Student, Dept. of Architecture, Graduate School of Human-Environment Studies, Kyushu University
** Assoc. Prof., Dept. of Architecture and Urban Design, Faculty of Human-Environment Studies, Kyushu University. Dr. Eng. *** Prof., Faculty of Environmental Design, Institute of Science and Engineering, Kanazawa University. Dr. Eng.
impact load was also reduced significantly.
for reducing the drying shrinkage, bio-saccharide-type thickening agent for
Also Lin et al. (Ref.7) conducted some in-plane and out-of-plane tests on the ECC retrofitted masonry specimens and examined a two story URM building shotcreted with ECC in New Zealand. As a result of out-of-plane tests, an increase in maximum load of 1.6 times the strength of the bare wall was observed when ECC retrofitting was applied on the compression surface and an increase of 13.2 times when it was applied on the tension side.
flowability and fiber dispersibility and air entraining and high-range water reducing agent for flowability. The fiber type of the used ECC was poly vinyl alcohol (PVA) which its properties are shown in Table 2 (Ref.14). More information about the effect of ECC components on its overall performance could be found on other research works (Ref. 1, 14 and 15). Due to the relatively low workability of ECC mortar, for retrofitting
Although the above mentioned research works provides valuable
purpose the amount of flowability agent in the mixture was increased up to
information about the ECC retrofit method for URM, there is not enough
1.5 times (as shown in Tables 3 as CECP1-3 and BECP1-3 samples).
description of the mechanical characteristics of ECC material, deformation
Information about the tested samples and mechanical properties of ECC
capacity and compressive behavior of the ECC-URM. These points were
mortar are shown in Table 3 and 4, respectively.
studied in present paper.
Compressive stress-strain diagram of ECC mortar (samples CEC7-9 &
The target buildings intended for the application of this method are
CECP1-2) is shown in Fig.1. Also extreme fiber stress-strain diagram of it
general URM structures and rural buildings in particular. Reduction of the
(samples BEC1-3 & BECP1-3) is shown in Fig.2 which is the result of
death toll and injuries was the main objective of this research work.
three point bending test. Tensile strain in Fig.2 is the strain measured at the
Compare to ECC, fiber reinforced polymer (FRP) products are wellknown for their retrofitting potential in the variety of structure types.
bottom side of the specimens' center. The compressive strain range of ECC was close to one of concrete or mortar as shown in Fig.1. Also as it can be
In case of URM structures, research works have shown a considerable improvement in the seismic behavior of FRP-URM as well (Ref.8-11).
seen from Fig.2, strains more than 1% for the most of the test samples were recorded. The average flexural strength of samples BEC1-3 and BECP1-3
However as it has been reported in several research works, debonding of FRP sheet limits its efficiency. In present study, in order to eliminate this undesirable behavior, confining bands which has previously been applied to the retrofitting of RC columns with wall (Ref. 12), was utilized.
is indicated in Table 4. The flexural strain was shown until the detachment of strain gauge from the ECC surface as shown in Fig. 2. It must be mentioned that the mortar mixing process and its workability and treatment method are different of usual cement mortars. So there is a
FRP products are available in various forms such as rods and sheets. Among FRP products, aramid fiber reinforced polymers (AFRP) with light
need to special application system especially in case of shotcrete on the wall surface as it was reported by Lin et al. (Ref.7).
weight and good workability is currently being used for retrofitting of Table 1 ECC mix proportion
concrete structures (Ref.13) and in this study, AFRP sheet has been utilized as a retrofit solution for URM walls. In order to grasp the mechanical impact of ECC and AFRP such as shear
Water by
Sand by binder
Water
Binder ratio
ratio
content
and compressive effect of retrofitting on URM walls, an experimental study was conducted on the efficiency of these techniques on small-size
Fiber volume fraction
3
W/B
S/B
W (kg/m )
Vf (%)
0.32
0.41
382
2.1
specimens. Experiment process and corresponding results are discussed in this paper. Table 2 Properties of PVA fiber
The experiments reported in present paper were conducted on a few number of specimens as a pilot research plan and in the next stages of this study, larger number of specimens will be tested.
2. ECC RETROFITTING 2.1 Characterization of ECC The components of ECC mortar - based on the mixture plan provided by
Fiber
Fiber
length
diameter
Lf
df
(mm)
(mm)
12
0.039
Fiber
Fiber
elastic
Strength
Specific
modulus
in stan-
gravity
Ef
dard test
(kN/mm2)
(N/mm2)
43
1620
3
Elongation
(g/cm )
(%)
1.3
6
the producing company- is shown in Table 1 (Ref.14). The binder is consisted of cement and fly ash (type II specified in JIS A 6201), with a weight ratio of 7:3.The cement type is ordinary Portland cement (OPC) and design air content is 15%. In addition to above mentioned contents, the ECC mortar mixture contains some additives such as air entraining agent (AE) for adjustment of air content,
calcium
sulfoaluminate(CSA)-type
expansive
additive
for
reduction of drying shrinkage, low alcohol-type shrinkage reducing agent
Table 3 ECC test sample properties Sample CEC1, CEC2, CEC3 CEC4, CEC5, CEC6 CEC7, CEC8, CEC9 CECP1, CECP2, CECP3 BEC1, BEC2, BEC3 BECP1, BECP2, BECP3
Test
Dimension (mm) Age (days) 7 14 Compression 50 X 100 28 28 28 Bending 40 X 40 X 160 28
Table 4 Mechanical properties of ECC mortar
30
Amount
Sample
1.53
CEC1-9 & BEC1-3
1.64 130 134 12.07 15.8
CECP1-3 & BECP1-3 CEC1-9 & BEC1-3 CECP1-3 & BECP1-3 Average of CEC7-9 Average of CECP1-2 Average of CEC7-9 Average of CECP1-2 Average of CEC7-9 Average of CECP1-2 Average of BEC1-3 Average of BECP1-3
3
Specific Weight (g/cm )
2
Compressive stress (N/mm )
Property 25
20
Mortar Flow (mm)
15
Elastic Modulus (kN/mm2)
CEC7 CEC8 CEC9 CECP1 CECP2
10
5
0.210
Poisson's Ratio
0.203 22.1 24.6 7.50 8.33
Compressive Strength (N/mm2 ) Flexural Strength (N/mm2)
Age (days) Fresh Fresh 28 28 28 28
0 0
1000
2000
3000
4000
Table 5 Mechanical properties of bed joint mortar
-6
Normal strain (x10 )
Flow (mm)
Fig.1 Compressive stress-strain diagram of ECC mortar (28 days age)
157 1.96
3
Specific Weight (g/cm ) Elastic Modulus (kN/mm2) Poisson's Ratio
12
2
10
2
Extreme fiber stress (N/mm )
Compressive Strength (N/mm )
12.3 0.158 10.0
triplet and prism. Each series was consisted of both unretrofitted and 8
retrofitted specimens. Also in order to grasp the effect of ECC overlay on the unit masonry brick, retrofitted unit bricks were also tested. Bricks were
6
BEC1 BEC2 BEC3 BECP1 BECP2 BECP3
4 2
tested while they were laid on their largest surface as shown in Fig. 4. Due to the following reasons, thin layers of ECC mortar such as 10 mm and 20 mm were examined in the experiments: (a) Existence of fibers in ECC mixture makes it as a material with high capability in stress redistribution during the cracking process and
0 0
5000
10000 15000 -6 Tensile strain (x10 )
20000
25000
Fig. 2 Extreme fiber stress-strain diagram of ECC mortar (28 days age)
thin layer of it can resist considerable deformations. (b) Considering the added mass in actual application and its seismic disadvantages, thin layer is desirable.
2.2 Properties of masonry brick
(c) Using thicker layers makes it necessary to provide an appropriate shear
The unit brick which was used in this study was a plain one (without
transfer mechanism like shear keys between ECC and URM substrate.
holes) with average size of 210 mm x 110 mm x 60 mm. Three units out of
. Application of shear keys to URM due to weak bed joint mortar and
them were tested under uniaxial compression (namely UBH1-UBH3). Also
possible pre-loading damages, poses to numerous difficulties. These
three unit bricks were tested under three-point bending (namely UBB1-
kind of damages can greatly affect the in-plane and out-of-plane
UBB3). The average modulus of elasticity of the bricks (UBH series) was
behavior of URM wall and should be avoided.
calculated as 17.7 kN/mm2 and the average compressive and flexural
Nine triplet specimens were constructed to obtain the shear effect of ECC
strength of bricks were about 64.5 N/mm2 and 9.0 N/mm2, respectively.
retrofit. Three out of them (namely 10RT1-10RT3) were retrofitted by ECC
The value of the specific weight of bricks was about 2.05 g/cm3.
mortar in both sides with thickness of 10 mm and other three ones (namely
2.3 Properties of bed joint mortar
20RT1-20RT3) were retrofitted in a similar way but with thickness of 20
In order to reach more realistic results from the study, bed joint mortar
mm. Three specimens (namely UT1-UT3) were left unretrofitted as control
was prepared with a 28 day compressive strength as low as the one being
ones. Nine masonry prism specimens were made with the height to
used in common masonry construction in earthquake-prone regions. This mortar was prepared by mixing of cement, sand, light weight silica powder blended with proportion of 1:6.5:1, respectively. Also w/c ratio was chosen
H H
equal to 130%. Specific weight and compressive strength of bed joint mortar was calculated as 1.96 g/cm3 and 10.0 N/mm2, respectively. Mechanical properties of bed joint mortar are shown in Table 5.
D
W D
2.4 Masonry test specimens The masonry specimen types and test results are shown in Fig.3 and Table
(a) Masonry triplet
W (b) Masonry prism
6. Two series of masonry specimens were cons tructed such as Fig. 3 Masonry specimen forms (ECC Retrofitting)
Table 6 Masonry specimen types (ECC Retrofitting) Type
Brick
Triplet
Prism
Name UBH1 UBH2 UBH3 RBH1 RBH2 RBH3 UBB1 UBB2 UBB3 RBB1 RBB2 RBB3 UT1 UT2 UT3 10RT1 10RT2 10RT3 20RT1 20RT2 20RT3 UP1 UP2 UP3 10RP1 10RP2 10RP3 20RP1 20RP2 20RP3
Dimensions (mm) Width (W) Depth (D) Height (H) 209.90 99.06 59.83 209.00 98.42 59.14 210.50 99.69 59.86 209.80 112.80 59.21 210.60 120.20 59.17 210.10 114.70 58.60 209.35 98.76 59.45 209.65 99.18 59.57 209.1 99.14 59.23 210.31 120.02 60.17 209.97 120.07 59.55 210.9 120.64 61.01 191.00 99.12 209.70 191.30 98.49 210.60 189.00 99.72 212.40 192.00 120.30 212.50 194.00 117.70 211.20 191.60 119.60 212.20 191.80 136.00 213.20 195.00 138.80 212.90 195.00 137.50 212.90 210.00 98.65 337.70 209.50 99.32 344.00 210.30 100.20 340.50 210.40 121.70 338.20 209.80 119.30 336.00 210.60 119.90 337.30 210.90 138.40 341.00 210.80 138.30 341.70 210.50 137.60 340.30
ECC Thickness (mm)
Age (day) Pmax(kN)
0 0 0 10 10 10 0 0 0 10 10 10 0 0 0 10 10 10 20 20 20 0 0 0 10 10 10 20 20 20
− − − 49 49 49 − − − 30 30 30 378 42 378 378 378 42 42 378 378 378 378 42 42 378 378 42 378 378
1262 1452 1386 2434 2234 1954 15.15 12 17.66 17.26 16 16.4 39.6 19.45 19 72.5 72.9 72.4 95.6 109.6 119.8 820.5 703 634.5 688 730 760 664 795 738
(a) Specimen type UBH1
(b) Specimen type RBH3 Fig. 4 Failure mode of masonry unit bricks
length ratio about 1.6 to find out the compressive effect of ECC treatment.
strength of the retrofitted bricks was observed. Test configuration and
Three of these specimens (namely 10RP1-10RP3) were retrofitted by ECC
failure mode of both retrofitted and bare unit bricks were shown in Fig.4.
mortar in both sides with thickness of 10 mm and other three ones (namely
In case of UBB and RBB specimen series, flexural strength of retrofitted
20RP1-20RP3) were retrofitted with 20 mm thick mortar. Three specimens
ones was not changed as shown in Table 6.
(namely UP1-UP3) were left bare.
2.5.2 Shear triplet tests
Also six retrofitted unit brick specimens were provided. Three specimens
The failure modes of triplet specimens are shown in Fig.5. Bare triplet
(namely RBH1-RBH3) and the other three ones (namely RBB1-RBB3)
specimen was failed through the departing of brick and bed joint mortar in
were retrofitted for compressive and three-point flexural tests.
their interface at a very low displacement as such as shown in Fig.5(a). It
In all masonry specimens, the thickness of bed joint mortar was kept about 10 mm. All specimens were cured after construction for at least 28 days. Then they were retrofitted in both sides and cured again. In order to provide an adequate cohesion between ECC overlay and URM, polymer dispersion primer liquid (ethylene vinyl acetate copolymer emulsion) was applied to masonry surface. This primer prevents the mortar water to be absorbed by the masonry substrate as well. Also in the all retrofitted specimens, load was applied on both masonry
can be explained as a result of weak bed joint mortar and low bond strength – calculated as about 0.46 N/mm2- between brick and mortar interface. Symmetrically developing cracks were observed in the failure mode of retrofitted triplet specimens as shown in Fig.5(b). Also it decreased local weakness by preventing unsymmetrical failure mode. Shear stress-strain diagram of both bare and retrofitted specimens are shown in Fig.6. Shear strength was considered as the maximum shear stress which specimens were subjected to during the test. Also shear stress was
and ECC layer during the tests.
calculated simply using maximum vertical load recorded during the
2.5 Test results and discussion
experiment and corresponding sectional area which is subjected to shear
Test results are discussed in three parts such as masonry unit brick, shear
stress. For ECC retrofit overlay of thickness 10 mm, increase in shear
triplet and prism tests. Failure mode and ultimate load, behavioral data such
strength was about 203% for specimens aged 42 days and 106% for 378
as stress-strain diagram and other mechanical characteristics are used as a
days.
basis to evaluate the effectiveness of the retrofitting method. 2.5.1 Masonry unit brick tests Both bare and retrofitted unit brick specimens were failed in a vertical
In case of ECC thickness of 20 mm, the corresponding increase was about 251% for specimens aged 42 days and 179% for 378 days as shown in Fig. 7 and 8.
splitting mode of brick along with the departing of ECC overlay in the
Also deformation capacity of the retrofitted specimens was increased
retrofitted ones. However as it was observed, buckling of ECC overlay was
significantly as shown in Fig.6. The average deformation capacity – in this
occurred prior to brick failure. An increase about 38% in compressive
study refers to the deformation at 80% of maximum strength – of ECC
overlay of thickness 10 and 20 mm at age of 378 days was about 33 and 28
retrofitted specimens can improves the energy dissipation capability of the
times the one of deformation capacity at maximum strength of reference
URM specimens.
(bare) specimen, respectively.
In some retrofitted specimens with ECC thickness of 20mm, detachment
The lower bound of this deformation capacity for the retrofitted specimens
of ECC overlay from brick surface was observed. However in some of
with 10 and 20 mm thick ECC overlay was obtained as about 20 and 27
them,vertical tension cracks were observed in side bricks prior to the
times of the unretrofitted ones. The position of the above mentioned 80%
detachment and resulted in their splitting.
strength was shown as point marks in all diagrams of Fig.6. As it can be seen in Fig.6, higher shear strength and deformability of the
2.5
Shear Strength (N/mm 2)
2
1.5
1
0.5
0
UT2
10RT3 Triplet Specimens
20RT1
Fig.7 Shear strength of masonry triplet specimens
(a) Specimen type UT2
aged 42 days 2.5
2
Shear Strength (N/mm )
2
1.5
1
0.5
(b) Specimen type 10RT3 0
Fig. 5 Failure mode of masonry triplet specimens
2.5
UT1
UT3
10RT1 10RT2 20RT2 20RT3 Triplet Specimens
Fig.8 Shear strength of masonry triplet specimens
80% of Maximum strength of RT series
aged 378 days
Maximum strength of UT series
Shear stress (N/mm2)
2
2.5.3 Shear stress and strain in triplet specimens Shear strain induced by vertical compressive test load is shown by
1.5
schematic drawings in Figure 9, where shear strain, average relative displacement of the two adjacent brick center points, d is the distance
1
between the brick centers and P is the compressive load. H and D are height UT1 10RT1 20RT2
0.5
and depth of specimen, respectively as indicated in Table 6.
UT3 10RT2 20RT3
Shear strain is calculated using following relation,
γ tan γ 0
(1)
d 0
3000
6000
9000
Shear
strain (x10-6)
12000
15000
Fig. 6 Shear stress-strain diagram of masonry triplet specimens aged 378 days
Shear stress is simply calculated as follows,
P 2A
(2)
d
L
Displacement meter δ
γ
Fig. 11 Configuration of prism test
Fig.9 Shear strain in masonry triplet specimens 35
2
Compressive stress (N/mm )
in which, the cross sectional area A is,
A H D
(3)
2.5.4 Prism tests Failure mode in bare prism specimen was represented by vertical tensile cracks parallel to the loading direction. They appeared mostly on the longer sides of prism such as shown in Fig.10(a). In case of the retrofitted
30 25 20 15
UP1 10
10RP1
5
20RP1
specimens, due to the confining effect of ECC overlay, failure condition was similar to buckling behavior as shown in Fig.10(b).
0 0
1000
2000
Moreover, it was observed that in case of ECC overlay of 20 mm
3000
4000
5000
6000
-6
Normal strain (x10 )
thickness, detachment of ECC overlay from brick surface was started before the above mentioned buckling behavior. The test configuration and compressive stress-strain diagram of both bare
Fig.12 Compressive stress-strain diagram of masonry prism specimens aged 42 days
and retrofitted prism specimens at age of 42 days are shown in Fig.11 and 12, respectively. The comparison between compressive strength and
35
Fig.13 -16. The test results were shown in Fig.12 until the detachement of the displacement meters from the specimen but since the compressive force was still rising, the compressive strength shown in Fig.13 and the corresponding value in Fig.12 are different (for example in case of specimen type 10RP1). An improvement in initial stiffness of the retrofitted prism specimens was observed and it seems that the compressive strength of the retrofitted
Compressive Strength (N/mm2)
maximum compressive load of bare and unretrofitted prisms are shown in
30 25 20 15 10
specimens was decreased compare to bare ones as shown in Fig.13 and 14.
5 0
UP3
Based on the observation during the failure of the retrofitted prisms, part of compressive load is resisted by ECC overlay which buckled before the
10RP1
20RP1
Masonry Prism Specimens
Fig. 13 Compressive strength of masonry prism specimens aged 42 days
Compressive Strength (N/mm 2)
40 35 30 25 20 15 10 5 0
(a) Specimen type UP3
(b) Specimen type 10RP1
Fig.10 Failure mode of masonry prism specimens
UP1
UP2 10RP2 10RP3 20RP2 20RP3 Masonry Prism Specimens
Fig. 14 Compressive strength of masonry prism specimens aged 378 days
3.2 Material and specimen specifications
Maximum Compressive Load (KN)
800 700
Inclination degree (θ) of specimens was about 48° as shown in Fig.17.The
600
specimen types which tests were conducted on are shown in Fig.18. The
500
specifications of specimens, aramid sheet - which was suggested by
400
producing company (Ref.13) – and test results are shown in Tables 7-9.
300
The brick used for the construction of specimens was the same as the one
200
used in ECC retrofitting with approximate dimensions of 210 mm x 110
100
mm x 60 mm with an average compressive strength of 65.0 N/mm2. The compressive strength of the bed joint mortar - with same mixture as ECC
0
UP3 10RP1 20RP1 Masonry Prism Specimens
retrofitting phase - used in the construction of specimens series A and B were measured as 14.6 N/mm2 (63 days age) and 17.3 N/mm2 (119 days
Fig.15Maximum compressive load carried by masonry prism specimens aged 42 days
age), respectively. In order to avoid pre-mature debonding of AFRP sheet, aramid bands
Maximum Compressive Load (KN)
were applied to the top and bottom of the specimens. This method has 800
Table 7 Specimen specifications (AFRP Retrofitting) 600
Specimen
400
200
0
UP1
UP2 10RP2 10RP3 20RP2 20RP3 Masonry Prism Specimens
Fig.16 Maximum compressive load carried by masonry prism specimens aged 378 days
Dimension (mm) Width (W) Depth (D) Height (H)
on the compressive load bearing capacity of the specimens and mechanical behavior of prism specimens under compression before and after retrofitting was almost the same. Normal strain (ε) was calculated based on the average vertical displacements (δ) recorded by two side displacement meters as shown in
209.65
100.09
189.03
Unretrofitted
150.2
A21
209.01
102.08
192.59
Sheet A
139.1
A22
209.51
102.12
190.80
Sheet A
137
A31
209.64
102.58
191.34
Sheet A + Band A
A32 B11
210.74 331
102.52 99.4
194.45 271.5
Sheet A + Band A Unretrofitted
196.4 174.6
B12
324
100.4
272.6
Unretrofitted
36.2
B21
328
103.3
298.4
Sheet B1 + Band B
127.6
B22
329
101.9
299.6
Sheet B1 + Band B
114.8
B31 B32
329 328
103.9 104.5
274.1 278.2
Sheet B2 + Band B Sheet B2 + Band B
120.8
60.0
Dimension (mm) Sheet type Material A AK-10/10 190 x 180 B1 AK-10/10 310 x 250 B2 AK-20/20 310 x 250 Band A AK-90 20 x (640 + 250 overlap) Band B AK-90 20 x (900 + 250 overlap)
Thickness 1 layer 1 layer 1 layer 3 layers 3 layers
Table 9 Aramid sheet material specifications (Ref.13) (4)
Material
L in which L is the distance between centers of the second and fourth bricks.
Weight Tensile capacity Thickness (kN/m) (mm) (g/m2)
AK- 10/10
180
98/98
0.048
AK- 20/20 AK-90
325 623
196/196 882
0.096 0.430
(N/mm2)
Young's Modulus (kN/mm2)
2060
118
Tensile Strength
Also compressive stress is simply calculated by dividing the vertical force by the application area.
+
+
3. AFRP RETROFITTING
In order to evaluate the improvement in shear behavior of retrofitted URM
θ
-
3.1 Experiment outline
+
+
-
-
+
+
wall with aramid fiber reinforced (AFRP) sheet, diagonal compression test -
was conducted on the bare and retrofitted specimens. The results of such an -
experimental study can be used for evaluating the behavior of the retrofitted masonry wall.
127.9
Table 8 Aramid sheet specifications
Fig.11 by the following relation,
Pmax (kN)
A12
failure of the whole specimen and resulted in lower compressive strength of the specimen. Therefore ECC retrofitting did not have considerable effect
Retrofitting scheme
+ +
Fig.17 Configuration of diagonal compression test
H
W A1 type
A2 type
D
A3 type
H
W
D
B3 type
B2 type
B1 type
Fig.19 Application of AFRP band
Fig.18 Specimen types (AFRP Retrofitting) previously been applied to the retrofitting of RC columns (Ref. 12).
to URM wall
without being in touch with bed joint mortar. Also the application of the
Two bands at top and bottom of specimens were considered as the
band to actual URM wall was considered in which creating holes in wall for
minimum requirements to ensure proper confining efficiency. They were
wide bands is almost impossible. As a result, considering the average height
wrapped around the specimens and were fixed using adhesive. In
of a unit brick (about 60 mm), 20 mm was decided as the width of the
application of the band to actual building, a sewing like method can be used
aramid band. Also in order to eliminate debonding of aramid sheet and
in which the aramid band passes through the holes created in URM wall
ensure the maximum possible efficiency of it, three layers of band were
and confines the sheet in both side of URM wall. This method is shown as a
applied. The application of aramid sheet consisted of the following five
schematic illustration in Fig.19.
steps:
Width of the aramid band was decided in the way that it covers sheet
1) Cleaning of specimen surface and application of primer 2) Surface treatment using putty to make a flat surface 3) Application of adhesive 4) Wrapping sheet and removing air with roller
γ
γ1
5) Coating with adhesive
γ2
Three types of material for primer, putty and adhesive were used which all mainly were based on epoxy resin adhesive and each of them were consisted of two parts as main and hardening components. 3.3 Shear stress and strain in diagonal specimens
1
δH
Shear strain induced by vertical compressive test load is shown by
2
schematic drawings in Fig.20, where γ shear strain, δ displacement of the specimen edge, δH relative diagonal deformation of specimen in horizontal W
γ
direction, δV relative diagonal deformation of specimen in vertical direction, L diagonal length, θ inclination degree and P is the compressive
δV
load. W, H and D are width, height and depth of specimen, respectively.
δ L
Shear strain is calculated based on the following relation,
γ tan γ
θ
(5)
H H
in which,
Fig. 20 Shear strain in diagonal specimen
H
cos sin V
In the case of θ =45º, relation (5) can be written as:
(6)
V H
(7)
Shear stress is simply calculated by the following relation,
L
which is recommended by ASTM (Ref.16).
P sin (8)
A in which, the cross sectional area A is:
AW D
(9)
3.4 Experiment results and discussion Failure of unretrofitted specimens (A1and B1 types) was represented by departing of brick and bed joint mortar in a very low displacement. In case of specimens A2 type departing of aramid sheet from brick surface was followed by brick sliding and rupture of sheet along the adjacent bed joint. In case of A3, B2 and B3 specimen types, failure was started by departing of sheet and its rupture at a place close to the confining band located in top and bottom of specimens and followed by diagonal cracks passing both brick and bed joint mortar (Fig.21).
a) Specimen B12
Shear stress-strain diagram of specimens A and B are shown in Fig.22 and Fig.23, respectively. As it is shown in Fig.24 shear strength of specimens
3 B11 B12 B22 B32
Shear Stress (N/mm 2)
2.5
2
1.5
1
b) Specimen B22 Fig. 21 Failure mode of bare and retrofitted specimens type B
6
0.5
0 0
2
3
4
4
8 7
3
2
2
1
6 5 4 3 2 1
0 0
1
2 3 Shear Strain (%)
4
5
Fig. 23 Shear stress-strain diagram of specimens type B
Shear Strength (N/mm )
Shear Stress (N/mm 2)
5
1
Shear Strain (%)
A12 A21 A22
5
Fig.22 Shear stress-strain diagram of specimens type A
0
A12
A21
A22 A31 Specimen
A32
Fig.24 Shear strength of specimens series A
about 33 and 28 times the one of reference (bare) specimens,
3
respectively. (3) ECC retrofitting changed the brittle failure mode of the URM to a
2
Shear Strength (N/mm )
2.5
ductile and developing failure which means a better energy dissipation
2
behavior. 1.5
(4) Symmetric developing cracks in the failure mode of shear triplet test showed a considerable improvement in brittle behavior of URM.
1
(5) ECC retrofitting does not have considerable effect on the compressive 0.5 0
load bearing capacity. - AFRP retrofitting B11
B12
B21 B22 Specimen
B31
B32
(1) Shear strength of specimens A31 and A32 compare to bare specimen A12 were increased about 28% and 13%, respectively.
Fig.25 Shear strength of specimens series B
(2) Compare to bare specimen B-1, shear strength of specimens B2 and B3 A31 and A32 compare to specimen A12 were increased about 28% and
were increased about 146% and 149%, respectively.
13%, respectively. In case of series B, compare to specimen B1 type, shear
(3) A2 type showed ductility about 4.5 times of bare A1type specimen.
strength of specimen types B2 and B3 were increased about 146% and
(4) B2 and B3 types showed ductility about 4 and 5.5 times of bare B1type.
149%, respectively as shown in Fig.25.
(5) Beneficial effect of confining band on strength and ductility was
High shear strength obtained from the retrofitted specimens with aramid
observed.
sheet and band compare to ones retrofitted with sheet only shows the
However ECC retrofitting has some disadvantages compare to AFRP
confining effect of it on specimen strength and ductility as observed during
method like relatively difficult application, high disturbance and added
the failure of specimens.
mass to structure. Taking into account both advantages and disadvantages
Through the same method used for evaluation of deformability in ECC test results, A2 type showed ductility about 4.5 times bare A1 type. Also B2 and B3 types showed ductility about 4 and 5.5 times bare B1 type. There is a difference between the results of A and B series for both bare and retrofitted specimens. This can be attributed to the size effect of the specimens. Bond characteristics between brick and aramid sheet (FRP sheet in
of ECC and AFRP techniques, they can be considered as suitable retrofitting alternatives for URM walls. As the next phase of this research, cyclic in-plane test will be conducted on the URM walls retrofitted with ECC and AFRP to grasp the in-plane hysteresis behavior of the retrofitted URM wall. Also in order to predict shear capacity of the retrofitted URM wall an appropriate rational model will be investigated.
general) plays the key role in the debonding behavior of the sheet and consequently governs the performance of AFRP-URM retrofit technique. This bond behavior was not studied at present stage of study. However
ACKNOWLEDGEMENT This study was supported in part by the Grant-in-Aid for Scientific
recently this fact have been investiagated in some research works (Ref.17).
Research from the Ministry of Education, Culture, Sports, Science and
Also some retrofitting codes (Ref.18) introduced slip-shear strength models
Technology, Japan (No.21254001).The authors are thankful to Kajima
which are mainly based on the bond studies of concrete- FRP and furthur
Corporation and Futase Yogyo Corporation for their contribution to ECC
investigations are needed for rational model of FRP-URM bond behavior.
experiments. Also the contribution of Fibex Co., Ltd. to AFRP tests is gratefully acknowledged.
4. SUMMARY AND CONCLUSION REMARKS By comparing the test results and the failure modes of unretrofitted and retrofitted URM specimens, the findings are summarized for both
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