Repair and strengthening of masonry walls with openings using FRP laminates

A Moussa*, Helwan University, Egypt

A M Aly, Helwan University, Egypt

26th Conference on OUR WORLD IN CONCRETE & STRUCTURES: 27 - 28 August 2001, Singapore

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473

26th Conference on Our World in Concrete & Structures: 27 - 28 August 2001, Singapore

Repair and strengthening of masonry walls with openings using FRP laminates

A Moussa*, Helwan University, Egypt A M Aly, Helwan University, Egypt

Abstract

In the presented study, Fiberglass Reinforced Plastic laminates (FRP) have been used for strengthening and repair of masonry shear walls with and without openings. The objective of the presented research is to investigate (he behavior of repaired and strengthened walls under diagonal splitting tension. The experimental program consists of three phases. The First phase presents an investigation of the geometrical, physical and mechanical properties of the used materials. The second phase aims to investigate the behavioral characteristics of small assemblages (plain and strengthened) under axial compression, bed joint shear and diagonal splitting tension. The third phase aims to investigate the behavior of plain, repaired and strengthened walls with and without openings under diagonal splitting tension. The methodology of fabrication and testing of assemblages and walls have been presented. For the small assemblages, tests were performed to determine compressive strength, joint shear strength and diagonal tensile strength. The behavior of masonry walls with and without openings was studied. The main parameters were the effects of repair, strengthening, type of strengthening and size of opening on the behavior of tested masonry walls. The test results clearly demonstrate the efficiency of using FRP laminates as a repair and strengthening technique for unreinforced load-bearing masonry walls to increase the tension and shear capacities and the deformability for resisting lateral loading.

Keywords: Masonry, Shear, Splitting tension, Opening, Repair, Strengthening, FRP

1. Introduction One of the serious problems facing the engineers today is vulnerability of old masonry buildings in

many regions around the world, which become seismically active. Because of their important role as lateral loads resisting elements, masonry shear walls have attracted the attention of many researchers in the past few years. Significant amount of research was carried out to study the behavior of masonry shear walls but unfortunately focus was on solid shear walls despite of the fact that shear walls with openings are the typical walls in real buildings. Although unreinforced masonry is considered one of the oldest types of construction little is known about its unique behavior. Many massive unreinforced masonry structures were built using solid units. Unreinforced masonry is a common type of construction in developing countries. These structures are usually constructed from brick or concrete blocks and in older buildings stone was used. A cement mortar mixture ties the units together. Load-bearing walls are the most vulnerable elements to damage during an earthquake because they are designed primarily to carry vertical loads. However, in case of earthquake event, they must also carry any in-plane and/or out-of­plane horizontal loads according to their relative rigidities. Generally, damage can occur in the form of cracking, spaling or complete collapse. The need of introducing a new system of repair and strengthening for many of unreinforced masonry structures become urgent due to the observation of damage of this type of structures after October 1992 earthquake in Egypt. The presented study program aims to investigate, using Fiberglass Reinforced Plastic laminates (FRP), and the behavior of strengthened and

26th Conference on Our World in Concrete & Structures: 27 - 28 August 2001, Singapore

Repair and strengthening of masonry walls with openings using FRP laminates

A Moussa*, Helwan University, Egypt A M Aly, Helwan University, Egypt

Abstract

In the presented study, Fiberglass Reinforced Plastic laminates (FRP) have been used for strengthening and repair of masonry shear walls with and without openings. The objective of the presented research is to investigate (he behavior of repaired and strengthened walls under diagonal splitting tension. The experimental program consists of three phases. The First phase presents an investigation of the geometrical, physical and mechanical properties of the used materials. The second phase aims to investigate the behavioral characteristics of small assemblages (plain and strengthened) under axial compression, bed joint shear and diagonal splitting tension. The third phase aims to investigate the behavior of plain, repaired and strengthened walls with and without openings under diagonal splitting tension. The methodology of fabrication and testing of assemblages and walls have been presented. For the small assemblages, tests were performed to determine compressive strength, joint shear strength and diagonal tensile strength. The behavior of masonry walls with and without openings was studied. The main parameters were the effects of repair, strengthening, type of strengthening and size of opening on the behavior of tested masonry walls. The test results clearly demonstrate the efficiency of using FRP laminates as a repair and strengthening technique for unreinforced load-bearing masonry walls to increase the tension and shear capacities and the deformability for resisting lateral loading.

Keywords: Masonry, Shear, Splitting tension, Opening, Repair, Strengthening, FRP

1. Introduction One of the serious problems facing the engineers today is vulnerability of old masonry buildings in

many regions around the world, which become seismically active. Because of their important role as lateral loads resisting elements, masonry shear walls have attracted the attention of many researchers in the past few years. Significant amount of research was carried out to study the behavior of masonry shear walls but unfortunately focus was on solid shear walls despite of the fact that shear walls with openings are the typical walls in real buildings. Although unreinforced masonry is considered one of the oldest types of construction little is known about its unique behavior. Many massive unreinforced masonry structures were built using solid units. Unreinforced masonry is a common type of construction in developing countries. These structures are usually constructed from brick or concrete blocks and in older buildings stone was used. A cement mortar mixture ties the units together. Load-bearing walls are the most vulnerable elements to damage during an earthquake because they are designed primarily to carry vertical loads. However, in case of earthquake event, they must also carry any in-plane and/or out-of­plane horizontal loads according to their relative rigidities. Generally, damage can occur in the form of cracking, spaling or complete collapse. The need of introducing a new system of repair and strengthening for many of unreinforced masonry structures become urgent due to the observation of damage of this type of structures after October 1992 earthquake in Egypt. The presented study program aims to investigate, using Fiberglass Reinforced Plastic laminates (FRP), and the behavior of strengthened and

474

repaired URM shear walls with and without openings under diagonal splitting tension. Fiber composite materials have been used in a variety of industries, such as aerospace, automotive, shipbuilding, chemical processing, etc., for many years. Their application in civil engineering, however, has been very limited. Their high strength-to-weight ratio and excellent resistance to electrochemical corrosion make them attractive materials for structural applications The fibrous composite is obtained when the polymer matrix (epoxy or polymer resin) impregnates the fibers (glass, carbon, graphite or aramied). The properties of the laminates depend on the amount and orientation of fiber. The permanent deformations of fibers under short-term loading are relatively negligible, but they exhibit a brittle tension failure mode. Glass fibers have relatively large creep under long-term stresses. The matrix has generally poor mechanical properties, as the behavior of polymer is dependent on time. The tensile strength of the composite laminate is the most important when used in repair. Previous studies showed the efficiency of FRP laminates in strengthening masonry walls [1,2,3,4]

2. Experimental program Due to the high cost of full-scale testing of masonry structures, potential problems of workmanship

and capacity limitation of loading equipment a more economical method utilising the direct modelling technique is proposed as a replacement to full-scale. This technique has been used to model the masonry walls by 1x1 m specimens. This study program consists of thfee phases. Phase I concerned with the investigation of the geometrical, physical and mechanical properties of the component materials of masonry wall (perforated brick units, mortar, and FRP laminates). Phase II aims to investigate the behavioral characteristics of small assemblages (plain and strengthened) under axial compression, bed joint shear and diagonal splitting tension. These assemblages are investigated experimentally to make a hand calculation prediction of the behavior of the model shear walls. Phase III aims to investigate the behavior of URM walls with and without openings under diagonal splitting tension load as a first part. Three specimens 1 x1 m model shear walls were constructed and tested for this purpose. The second part of phase III aims to investigate the efficiency of using the FRP laminates as a repair technique of damaged URM shear walls .The same three walls were retested after application of the FRP laminates which were glued to both sides of the walls. The third part of phase III aims to investigate the efficiency of using FRP laminates as strengthening technique of URM walls. Six specimens 1 x1 m shear walls were constructed and tested after applying FRP laminates on both sides (three specimens strengthened with diagonal strips of FPR laminates and three specimens strengthened with FPR. laminates on whole surface of the walls).

The component materials can be classified into three categories: the brick units, the mortar and the strengthening material (FRP mat and type of resin). The structural behavior of masonry is function of the properties of the component materials. Perforated silty sand brick unites were used. The unit dimensions were 12x25x6 cm. Each unit has 10 0 3 cm holes. The average compressive streng~h of unit brick was 122 kg/cm 2, while the average splitting tensile strength was 24.1 kg/cm 2. The average compressive strength of used mortar was 234 kg/cm 2 , while the average splitting tensile strength was 24.21 kg/cm2

3. Tests on assemblages The characteristics of the unreinforced masonry are determined by the interaction of different

components from which the masonry is made. The basic tests of small masonry assemblages are important in studying the effect of variation in properties of component materials on the assemblage strength and in providing practical methods for quality control.

3.1. Axial compression prisms Tests are carried out on six compression prisms as shown in Fig.1. Three of them were plain

masonry prisms and the other three were strengthened by FRP laminates. The average compressive strength for plain prisms was 61.3 kg/cm2, while that for strengthened prisms was 69.5 kg/cm2. The failure mode was brittle due to vertical splitting cracks for both cases. The test results indicate that the strengthened prisms achieved an increase in the strength compared with the plain (unstrengthened) prism strength by about 13 %. The little effect of the FRP on the compressive strength can be attributed to the debonding failure of the prisms before the full benefit of the FRP strength can be mobilised

3.2 Joint shear tests Different shapes of specimens associated with different test techniques have been used by various

researchers [5 & 6] to investigate the joint shear capacity of masonry assemblages. A detailed and comprehensive study' of advantage and disadvantages of the various shapes of shear specimens and testing techniques can be found in Reference [5].

In this work, the main objective of the shear test was to study the shear strength of brick masonry along the bed jOints for the plain and the strengthened specimens. Figure 2 shows the employed test

475

11.- Plailepeeinen

$I", I FAP LlI.minlllt'" I

b- strengthenedspecmen

Fig.1: Joint shear test specimens

T

103cm

SWPH

I

I g ""'"l II 'iI "

I

I

103cm

SWP2-1

T

E

~ ,

SWP3-1

._""HlIO=""'",,· _I ,I

11.- PlaIn specimen

FRP Lamnatlles

) '---="---} /

b- strengthened apecinen b- strengthened specimen

Fig. 2: Prisms for axial compression lesl Fig.S: Splitting diagonal tenlion specimens

FRP laminates /

FRP lanmates &H' I ~

-tit fffFFF I FfP

I

..It K

t::tIt if:>. "tt-W

SWst-2 SWst-3

/ /

I

s

= ""'"l

"

SWS2-2 SWS2-3

/

I

I ~ , i--J ~

P r::: IIIEIlElE!El

SWS3-2 SWS3-3

Fig. 4: Details of tested walls

476

model. Mode of failure for the plain specimens was generally a sudden shear slip along the bed joint. The failure initiated by debonding at brick and mortar interface as shown in Fig. 5. The mode of failure of strengthened specimens was started by debonding of the FRP laminates around the gap joint followed by buckling of the FRP at the area of the gap joint which resulted in the joint bond failure.

Test results clearly show that strengthening of joint shear specimens by FRP laminates is very effective. The average failure load for plain prisms was 1.04 tons, while that of strengthened prisms was 3.2. It is also found that the strain at maximum stress for the strengthened specimens are 3 times more than that of the plain specimens. These results clearly demonstrate that the use of FRP laminates does not only increase the jOint shear strength but also increases the deformation capacity and ductility of masonry assemblages. Because this is one of the most critical modes of failure of solid masonry walls, it is clear that the use of FRP laminates can be very effective in increasing the shear strength of plain (unreinforced ) shear walls.

3.3 In-plane splitting tests One of the important parameters, which affect the behavior of masonry structures, especially for

unreinforced masonry, is the tensile strength. Shear walls are subjected normally to in-plane horizontal forces from wind or seismic forces which produce tensile stresses. When the tensile stresses exceed the ultimate tensile strength of masonry, a diagonal tension crack starts and propagates.

The main objective of this phase of the test program is to determine the diagonal tensile capacity for plain as well as for strengthened specimens. A total number of 6 model plain and strengthened specimens were constructed with a hexagonal shape in a running bond. All the specimens were tested under a diagonal load (450 with respect to the bed joint). The details of th~ test specimen are shown in Fig 3. Procedures and construction techniques were similar to that used for the compression and joint shear test specimens. All model specimens were air cured in the laboratory under controlled temperature and humidity.

At the age of two weeks, the loading surfaces were capped using hydrostone gypsum cement. For the strengthened specimens, the FRP laminates were prepared and applied by the hand-lay-up. After at least 24 hours from applying the laminates the specimens were tested under splitting line loads using a universal machine. The centroid of the specimen-bearing surface was carefuJly aligned vertically with the center of thrust of the spherical seat of the testing machine. The load was applied through roller bearing at the top and the bottom of the model panel. A computerised system was used to measure the deformation from which the splitting tension stress-strain curves are obtained. The specimens were incrementally loaded at a slow rate to permit recording of deformations.

The modes of failure for most of the test specimens were splitting a long the loaded plane caused by the transverse tensile stresses. The shape of failure plane was different according to the type of test specimens (plain or strengthened). For plain specimens the general failure plane was a fracture crack extending through the bricks and mortar joints starting at the pOints of load application and then followed the mortar-brick interfaces in a zigzag plane of failure as shown in Fig. 6. The mode of failure in this case Garl be described as a mixed shear (slip at the brick-mortar interface) and tension (splitting of brick). The mode of failure of the plain specimens was stepped wise plane through the mortar/unites interface. The mode of failure of strengthened specimens was a plane crossing the bricks and the mortar and in some cases diverged from the plane connecting the two applied loads. This inqicates the significant influence of FRP laminates on modifying the behavior and strength of solid unreinforced masonry.

The spitting tensile strength and the shear deformation of the specimens increased significantly by the FRP strengthening. The average failure load for plain prisms was 3.73 tons, while that of strengthened prisms was 6.97. This means that the strength of plain specimens increased by 83 %. Stress-strain curves shown in Fig. 8 indicate that the strengthened specimens exhibited a much more ductile behavior than that of plain specimens.

4. Tests on masonry walls In this phase nine URM walls were constructed and tested under inplane monotonically increasing

load. The scope of the proposed research is focused on unreinforced brick masonry walls with and without openings and the effect of repair and strengthening on its behavior. All walls have the same overall dimensions (103x96.5x12 cm) as shown in Fig. 4. Failure modes, crack patterns, load-deflection relationships, ductility and ultimate capacity of masonry walls are investigated. The main parameters studied in this investigation are:

1- Effect of presence and size of openings. 2- Effectiveness of repair and strengthening using FRP laminates. 3- Effectiveness of alternative types of strengthening (FRP strips or whole surface).

477

4.1 Tested walls The tested walls are classified into three groups:

Group (1): without opening. Group (2): with a small opening which has side length/ wall length of 0.25. Group (3): with a large opening which has side length / wall length of 0.39. Each group contains one plain wall and two strengthened walls. Strengthening is either by strips of FRP laminates or with covering the whole surface as mat of FRP. The tested plain walls were repaired and retested.

Table 1 Tested walls

Group Wall Type Opening Opening Strengthening Repaired

dimension side ratio type _._-,--- _._ ... _--

SWP1-1 Plain ----- 0.0 ----- SWR1-1 1 SWS1-2 Strengthened ----- 0.0 Strips -----

SWS1-3 Strengthened ----- 0.0 Mat -----SWP2-1 Plain 27x23.5 cm 0.25 --~-- SWR2-1

2 SWS2-2 Strengthened 27x23.5 cm 0.25 StrjQs -----SWS2-3 Strengthened 27x23.5 cm 0.25 Mat -----SWP3-1 Plain 39.5x38.5cm 0.39 ----- SWR3-1 --

3 SWS3-2 Strengthened 39.5x38.5cm 0.39 Strips -----SWS3-3 Strengthened 39.5x38.5cm ·0.39 Mat -----

4.2 Fabrication of walls All walls were constructed in running bond with a half brick overlap. The mortar used with a joint

thickness 10 mm. All the joints in the masonry walls were tooled on both sides to be fl,Jrther compacted. The excess mortar was carefully cleaned using a brush before setting of the mortar. Walls were cured by spraying with water (two times per day) for 15 days. Mortar control specimens were made during the construction of the walls and cured in the laboratory under the same conditions as the corresponding walls.

Repair and strengthening of walls were done simply as follows. Two pieces of FRP mat were cut with a horizontal dimension equal to the length of the wall and a vertical dimension smaller than the height of the wall to prevent direct touching between load and FRP which can cause early debonding of FRP laminates. The two pieces were attached to the wall one from each side and clamped at the top. The polyester resin was then placed in plastic bowl and mixed with cobalt and peroxide as a catalyst using a ratio of 100:2: 1. The three components were mixed very well. The first coat of resin was applied on the wall surface at top part over the level of the two clamps by using a small hand brush to insure uniform distribution of the resin over the whole surface of the wall followed by the attachment of the FRP mat. The second coat of the resin was then applied on the top of the mat within half an hour before the first coat started to set. A small brush was used to insure complete wetting of the mat and to intermix the resin from both coatings. The process was repeated for the lower part. Great care was paid to prevent trapping air gaps under the mat which can affect on the interface botld conditio.! between ihe laminate and the wall. The resulting thickness of the FRP laminate was approximately 1.75mm. This gives a ratio of FRP laminate cross-sectional area to the area of the wall section approximately equal to 0.03.

Because the walls were unreinforced they were very sensitive to any movement or any impact load during handing. Great care and certain steps were followed for transportation of wall from the location where it was built to testing frame.

4.3. Test setup and instrumentation The wall panels were tested as a specimen subjected to in-plane vertical line load inclined 45° with

the bed jOint. The vertical load was applied through a roller made with 1.0 in. diameter steel rod and bearing steel plate at the middle of the wall. The vertical load was applied through a hydraulic jack of maximum capacity 25 tons supported at the top by the testing frame. This connection has limited rotation ability. The hydraulic jack was attached to 'a calibrated load cell (37 ton capacity and 1 kg accuracy) to monitor the load during the test. The load cell was placed in vertical position between the hydraulic jack and the top of the wall panel. The wall was guided and prevented from out-of-plane displacement by a system of non frictional supports (four vertical steel angle and pieces of rubber. Mechanical dial gages had been used to monitor the wall response with loading. Two rows of demic point gages were arranged vertically and horizontally with a spacing of ten cm to monitor the shear deformation of the wall during the test. . . .

478

a. Plain specimen b. Strengthened specimen

Fig. 5: Mode of failure for joint shear test

a. Plain specimen o. Strengthened specimen

Fig. 6: Mode of failure for inp!ane splitting test

Wall SWP1-1

Wall SWR3-1 Wall SWS2-3

Flg, 7: Failure modes for some ofthe tested walls

479

80 N

70 E

i 60

"' "' 50

~ 40 1ii

30

20

10

0 0 0.001 0.002 0.003 0.004

strain

Fig. 8: Effect of strengthening on (j-g curve for axial compression prisms

12

8

4

o o 0.001 0.002 0.003 0.004 0.005

strain

Fig. 9: Effect of strengthening on (j-g curve for joint shear prisms

7

6 N 5 E 0 -- 4 C> ~ -If) 3 If) Q)

2 ..... -en

0

0 0.001 0.002 0.003 0.004 0.005

Strain

Fig. 10: Effect of strengthening on (j-g curve for splitting tension prisms

25

20 ""2 g

15 "C

~ ~ ~

10 'iii u..

5

0

0 0.1 0.2 0.3 0.4 0.5

Opening size

Fig. 11: Effect of opening size on load capacity of walls

480

0.2 c 0

~ 0.15 E

Small opening Large opening

.E 0:1 Q) "0

N 0.05 I

E 0 5 c -0.05 0 Without opening ~

-0.1 E .E Q) -0.15 "0

:> arge opening Small opening

-0.2 Load (ton)

Fig. 12: Effect of opening on wall deformations

0.4

c 0.3 0

~ E 0.2 .2 Q) "0

0.1 N :r:

E 0

.s 6 8

c -0.1 0

~ -0.2 Plain E .E Q) -0.3 Strip strength. "0

:> -0.4

Load (ton)

Fig. 13: Effect of repair and strengthening on p-8 Curve foe walls with small openings

0.1 c 0 0.08 ~ E 0.06 .E Q) 0.04 Plain

"C

Whole strength.

N Repaired I 0.02 Strip stren tho

E 0

5 ·0.02 6 8 c 0 ·004 ~ E -0.06

tho .E OJ

0.08 "C

:> -0.1

Whole strength~-----------

Load (ton)

Fig. 14: Effect of repair and strengthel lillg 011 p-6 Curve for solid walls

0.8

c 0.6

~ E

0.4 ~ 0

0.2 N I

E .s ·0.2 c .Q 1;; -0.4 E J2 " -O.S "0

:> ·0.8

Load (ton)

Fig. 15: Effect of repair and strengthening on p-o Curve for walls with large openings

481

Table 2: Test results of masonry wall specimens

Group Type of Model prisms

Plain SWP1-1

Strengthened SWS1-2 1

Strengthened SWS1-3

Repaired SWR1-1

Plain SWP2-1

Strengthened SWS2-2 2

Strengthened SWS2-3

Repaired SWR2-1

Plain SWP3-1

Strengthened SWS3-2 3

Strengthened SWS3-3

Repaired SWR3-1

5. Analysis of test results 5.1 Effect of openings

Opening side Ratio

0.0

0.0

0.0

0.0

0.27

0.27

0.27

0.27

0.41

0.41

0.41

0.41

Maximum Vertical Horizontal load Pmax Deformation at Deformation at

(ton) 0.5 Pmax (mm) 0.5 Pmax (mm)

9.1 - 0.030 0.030

18 - 0.025 0.034

not reached - -8.6 - 0.023 0.034

8.3 - 0.143 0.123

13.2 - 0.066 0.154

16.1 - 0.270 0.263

7.8 - 0.0"74 0.110

1.9 - 0.870 0.730

5.8 - 0.278 0.49 . 7.2 - 0.304 0.49

5.4 - 0.314 0.375

The effect of openings can be determined from comparing the results of walls SWP1-1, SWP2-1 and SWP 3-1. The load capacity of wall decreases as the opening size increases as shown in Table 2 and Fig. 11. The load capacity of wall with small opening was 10% lower than that of plain wall without opening. Large opening wall had a load capacity 80% lower than plain wall without opening. The load deformation curves demonstrate that the stiffness of wall with openings is less than that of wall without opening. Mode of failure depends on the presence and size of opening. Wails without openings showed shear sliding failure mode, while walls with openings had splitting along the vertical axis and the right part, and sliding in the left part (along the mortar joint) as shown in Fig. 7. It should be noted that the unsymmetrical failure mode is dependent on the orientation of brick units. Figure 12 shows that horizontal and vertical deformation (relative to' plain solid wall) increase when opening size increases and rate of this increase was high in the walls with large openings.

5.2. Effect of repair For walls without openings, the load capacity of repaired wall was about 95 % of that plain wall. At

low load levels, stiffness of the repaired walls were less than those of piain walls due to previous damage. At higher loads, repaired walls keep its stiffness, especially in tension zones; This leads that the stiffness of repaired walls exceeds that of plain walls and the deformation decrea$ed. Failure started by successive debonding of FRP laminates. For repaired walls with small and large openings, the exhibited strengths were 0.94 and 2.8 of that of plain wall respectiv~ly. This means that repah- is more effective in case of large openings. Also, ductility and the energy absorption are improved by repair with FRP laminates.

5.3 Effect of strengthening The load carrying capacity of walls has been greatly increased by strengthening using FRP

laminates. This increase was 150% for solid walls, 94% for walls with smaii opening and 280% for walls with large opening. The average load capacity of wall strengthened by FRP strips was 20% less than that of walls strengthened on the whole surface. This means that strengthening with strips gives good results and may be adequate for most cases. In general in all groups, there was not great difference in the initial stiffness between the strengthened and plain walls as shown in Figs 12 to 15. This can be attributed to at early stages, the load is mainly transferred by compression and the uncracked bricks still can sustain tension. Since FRP is not a stiff material, it increases the deformation and tension capacities without increasing the rigidity of the wall. In addition, stiffness degradation of the strengthened wall had not been observed until failure. The strengthened wall exhibited higher stiffness compared to the plain and the repaired walls.

482

6. Conclusions

1 In general, the test results show that modes of failure for unreinforced masonry shear walls are significantly affected by the type of strengthening and the size of the opening. For both repaired walls and strengthened walls, it has been found that FRP laminates increase the load and deformation capacities.

2 Results of tests on plain walls show that the behavior and the load carrying capacity of the masonry walls are highly sensitive to presence of opening. Large size of opening dramatically decrease the strength and stiffness of the wall. This decrease is nonlinearly proportioned to the increase in size of opening. Failure of wall without opening started by splitting and local crushing at loading zones followed by sliding over the whole length of the wall. For walls with opening failure started by splitting along the vertical axis from the opening corner towards the loading pOints. Splitting in right part and sliding on the left part (// bricks) followed.

3 It has been found that FRP laminates is an efficient repair technique for damaged unreinforced masonry walls. For cases of small opening and solid walls, the load carrying capacity of the repaired walls achieved about 95% of that of original plain walls. In case of large opening, the load carrying capacity was much higher than that of original plain walls (185%). This means that FRP repair technique is more efficient in case of large openings. FRP laminates is very effective in eliminating debonding of the mortar joint-brick interface. Walls repaired with FRP laminates showed higher deformability than original walls.

4 Strengthening of brick walls with FRP laminates increases the load carrying capacity without significant increase in the wall stiffness. This leads to great improvement of deformability, ductility and seismic behavior of the strengthened walls. The strengthened walls reserved its stiffness without significant degradation up to failure especially for walls with openings. The load carrying capacities of strengthened walls are about four times higher than that of plain walls for cases of large opening, and nearly twice for small opening and solid walls.

5 Walls strengthened with FRP strips achieved about 80-90% of the failure load of the walls strengthened on whole surface. This means that laminate strips are also effective and can be used in retrOfitting of walls especially in case of openings.

6 Results of tests on small masonry assemblages showed reasonable concurrence with that of walls. Strengthened specimens showed a much more ductile behavior than plain specimens. Strengthening with FRP laminates is very efficient in increasing the assemblage strength especially the joint shear strength. The joint shear strength for the strengthened specimens were 3 times that of the plain specimens. The compressive strength of strengthened prisms increased by 15% than that of the plain prisms. Strengthening of diagonal tension specimens results in 80% increase in the splitting tensile strength compared with plain specimens.

References

[1] Ghanem, G.M., Abo Zied, M., and Salama, A.E., "Repair and Strengthening of Masonry Assemblages Using Fiber Glass", Proc. of 10 th IB2 Mac, University Calgary, Calgary, Alberta, Canada July, 1994.

[2] Ehsani-MR, Saadatmanesh-H, AI.-Saidy-A, "Shear Behavior of URM Retrofitted with FRP Overlays ", Journal of CompOSites for Construction Feb. 1997.

[3] Saadatmanesh,"Fiber Composites for New and Existing Structures" ACI Structural Journal May-June 1994.

[4] HamidA-, Mahmoud,A.S., Abou El Magd, S., "Strengthening and Repair of Unreinforced Masonry Structures: State-of-the Art", Proc. of 10th HB2 Mac, University of Calgary, Alberta, Canada, July, 1994.

[5] Ghanem, G.M., "Behavioral Characteristics of Partially Reinforced Load-bearing Masonry Wall Structures, PhD. Thesis Helwan University, 1992.

[6] Hamid, A.A. and Abdoud, B.E., "Direct Modelling of Concrete Block Masonry under Shear and in-plane Tension ", Journal of Testing Evaluation, JTEVA, Vol. 14. No.2 March 1986.

[7) Mahmoud, A.S., " Strengthening of Load-bearing Unreinforced Masonry Structures" , Ph.D. TheSiS, Helwan University, Cairo Egypt, 1995.

[8] American Society for Testing and Material ASTM C-150, "Standard Specification for Portland Cements" Annual Book of Standard, Vol. 4.02, Philadelphia, PA, 1985.