Influence of FRP Composites Strengthening Configurations

on In-plane Failure of Brick Masonry Walls

Sanaa El Malyh

, Azzeddine Bouyahyaoui

and Toufik Cherradi

Mohammadia School of Engineer, Mohammed V University of Rabat, Morocco

Department of Civil Engineering,

Keywords: Carbon fiber reinforced polymer, debonding, masonry, strengthening, composite materials.

Abstract: A high percentage of unreinforced load bearing masonry structures exist in many countries, these structures

shown to be vulnerable to earthquakes, and exhibited important damages. The failure of each element of

structure generates a problem in the load transmission. The seismic evaluation of unreinforced masonry walls

is a complicated task, however, several research investigates the ability of reducing their seismic risk and

ameliorates their mechanical characteristics by using different materials. The carbon fiber-reinforced polymer

(CFRP) composites were used in numerous investigations to reinforce masonry walls, it offers significant

advantages since the fibers can be externally bonded to the surface without affecting the aesthetics of the

structure, and it could improve the strength of the structure. As part of this research, an experimental study

was conducted to investigate the seismic behavior of masonry walls reinforced with unidirectional CFRP

composites and subjected to in-plane loading. This paper evaluates the in-plane behavior of two groups of

masonry walls strengthened with diverse percentage and orientations of CFRP composites.

1 INTRODUCTION

The damage caused by past earthquakes showed the

seismic vulnerability of existing unreinforced

masonry structures. The percentage of masonry

buildings was estimated to be over 70% of the world’s

building inventory (Matthys and Noland, 1989).

Moderate earthquakes could lead to significant human

and material losses caused in the most cases by the

masonry elements.

Several research studies highlighted the need for

developping different effective techniques to enhance

the seismic loading, the strength and the ductility of

unreinforced walls with minimum impact on the

aesthetics of the structure. Actually, repairing

structures doesn’t present just a technical challenge,

but also an economical challenge that depends on the

repairing conditions and the type of damages (cracks,

reinforcement of load-bearing elements, etc.). Within

the available systems is the organic matrix composite

materials. The use of composite materials in recent

years, continually been enhanced because of its

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multiple advantages and specifically for its

weightlessness that does not influence the weight of

the structure, its rigidities, durability and its significant

resistances. Composite materials have low fatigue and

sensitivity, their use improve the performance of the

structures and present a high stiffness-resistance ratio

while keeping the initial appearance of the structures

(Mosallam et al, 2014). Taking into consideration the

mechanical characteristics of the elements

constituting the FRP composites, specifically the type

of fibers and their orientation, the matrix and the

interface between them, influence directly the

behavior of the composite laminate. Several studies

have been carried out to understand the FRP behavior

and to determine the deformations and the failure

modes of different types of structures subjected to

cyclic loading, in order to predict the appropriate

reinforcement system.The analysis of the work and

results related to the behavior of the reinforced infill

panels will be discussed. Different strengthening

technique were studied in the literature (ElGawady et

al, 2004; Chuang and Zhuge, 2005) to repair or to

reinforce masonry walls using several products such

as: reinforced plaster, projected concrete, ferrocement,

injection of epoxy into voids or cracks, the addition of

steel reinforcement injected into the voids drilled

vertically through the mid-thickness of the wall,

exterior reinforcement of the masonry with steel plates

or tubes, confinement of the masonry, reinforced

concrete columns and beams, post-tensioning of the

wall with steel tendons. These techniques are

effective, but they have several disadvantages such as

their expensive prices, and they present a significant

load and influence the aesthetics of the structure.

Textile reinforced cement matrix is widely used

for reinforcing different masonry and concrete

elements. Several studies evaluated the use of TRC

for the reinforcement of reinforced concrete elements

and especially for column confinement to improve

their resistance to compression loads (Ortlepp et al,

2009) and torsion, for reinforcing beams and slabs

subjected to shear and bending (Brückner et al, 2006).

Recycled or artificial aggregate composite

materials of agricultural or industrial origin have been

the subject of numerous studies carried out to

determine the mechanical characteristics of

composites contain renewable materials incorporated

in a cement mortar matrix or concrete. These

materials can be in the form of fibers, particles or

aggregates from agricultural residues of vegetable

origin (jute, palm trees, etc.) that sometimes require

physical or chemical treatment before their use or

both in some cases. Their mechanical characterization

presents the subject of numerous publications (e.g.

Boghossian et al, 2008; Mir et al, 2010; Kriker et al,

2005).

FRP composite laminates are designed to enhance

both strength and ductility of masonry walls. Polymer

composites strengthening can be applied either

externally or using near surface-mounted (NSM)

technique. NSM method has several advantages such

as it doesn’t influence the aesthetic of the structure and

it ensures the fiber protection against fire.

External bonding composites is one of the most

widely used reinforcement methods to repair or to

reinforce different types of structures in order to

improve their mechanical performance. The fabrics

are dry or pre-impregnated with a polymeric matrix,

and for the plate they are glued with the epoxy resin

(Khalifa et al, 1998). By definition the external

bonding is the method by which the FRP laminates

are bonded to the surface of a wall using two-part of

the epoxy adhesive. Prior to FRP application, the wall

surface is cleaned and a fill layer is applied to create

a flat surface to which the FRP will be bonded

(Stratford et al, 2004). External reinforcement with

FRP can be partial by using strips or total by applying

reinforcement to the entire surface of the walls

(Mosallam and Banerjee, 2011).

The efficiency of the reinforcement depends on its

laminate orientation, type of fibers and matrix, as well

as the number of plies. For Valluzzi et al, (2002), the

shear strength of the walls reinforced by diagonal

reinforcement is higher than the orthogonal mesh

reinforcement. On the other hand, results described in

(Santa-Maria et al, 2004) showed that the shear

behavior of masonry walls reinforced by CFRP plates

is influenced by their orientations, the strength results

of walls with diagonal reinforcement has increased

considerably compared to the horizontal

reinforcement.

Konthesingha et al, (2013) tested the repaired

damaged masonry walls reinforced by near surface

mounted (NSM) CFRP plate in three configurations;

namely: horizontal reinforcement of one side,

horizontal reinforcement on both sides, and cross-ply

reinforcements on both sides of the wall. Their results

indicated that wall specimen externally reinforced by

horizontal and vertical system had the highest energy

dissipation, strength and deformation capacities.

2 SPECIMEN PREPARATION

In this study, wall specimens with dimension of

1200X1200X115mm were constructed using clay

brick units of 240X115X63mm. The mortar thickness

used in building wall specimens is 10 mm, 28 days

later and before applying the composites, the

substrate surfaces were cleaned by high air pressure.

Then, the substrates were wet by water then it was

covered by a thin layer of epoxy primer followed

immediately by the application of mortar with

thickness of 12mm, after it hardened, the first layer of

resin was applied to bond the composite, then a

second layer of epoxy polymer is applied to fix and to

protect the composite. During these operations, it is

necessary to ensure that the composite was well

impregnated with resin. The walls were reinforced

using different configurations of the unidirectional

carbon fibers reinforced polymer. The CFRP were

applied on the front and back sides of each wall. After

seven days, the specimens were tested under in-plane

loadings. Then the in-plane performance of the

masonry elements to failure were experimentally

evaluated. In-plane tests were performed in two

groups of the specimens (refer to Table 1 and data

used in (Elmalyh et al, 2020).

3 TEST PROTOCOL

After the specimens were prepared, they were tested

according to (ASTM E519, 2002), first the wall was

fixed between two steel shoes to permit the

transmission of the load machine (see Figure 1). Then

the linear variable differential transducers (LVDTs)

were attached on the both diagonals to measure the

displacements and the deformations in the both

directions. The load was applied at the top corner in

the gravity direction by hydraulic actuator fixed to the

supporting frame.

4 RESULTS AND COMPARISON

The performance of the composite materials depends

mainly on the characteristics of the interface between

the fibers and the matrix. The interface ensures the

transfer of the applied load from the matrix to the

reinforcement system. Various studies and analyses

evaluated the influence of the type and thickness of

the interface on the composite properties.

Wall subjected to compressive loads incur a

regular loss of rigidity which is compensated by the

presence of the composite that absorbs energy and

increase deformability and failure load of the wall.

However, the energy dissipation depends also on the

reinforcement configuration. The strengthening ratio

details of the first and the second group are illustrated

in the table 1. Experimental data presented in

the table 2 is compared to evaluate the performance

of the strengthening configuration in improving the

behavior of URM wall under in-plane compressive

loading. It should be highlighted that all the CFRP

composite reinforcement configurations evaluated in

this study were effective in improving the integrity

and the load bearing capacity of the masonry walls.

Comparing failure of unreinforced wall with the

reinforced specimens, the URM specimen exhibited

rapid crack propagation, indeed in all cases the

response of the reinforced walls had high strength and

the crack propagation was obstructed by the CFRP

caused by the shear tensile transmitted via the

masonry-CFRP interface.

Regarding the experimental results illustrated in

the figure 1, 2 and 3, all the strengthened walls

showed similar failure modes (shear failure at the

ends of the vertical diagonal, delamination of the

CFRP and compression failure of masonry).

Nevertheless, for wall specimen reinforced with one

diagonal composite strip at each side (W-1D-CFRP),

the failure mode was similar to unreinforced wall.

The tensile resistance of the compressive loads was

higher than the URM wall by 59.56%, even if the

diagonal reinforcement presented 41% of each side.

From the results obtained from this study, it is

clearly seen that the walls W-CFRP-W1,

W-3D-CFRP, W-2DX-2V-CFRP had the highest

shear strength, which correspond to the following

load bearing capacities 32.3 kN and 37.8 kN. Despite

the amount of composites applied to specimen

W-3D-CFRP which is 47% lesser than the specimen

W-CFRP-W1 that was fully reinforced on its both

sides. It seems that applying just 53% of composites

per side provided a higher flexible response and the

most important lateral deformations. Nevertheless,

the lateral deformations for the specimen

W-CFRP-W1 had significantly increased too.

Table 1: Retrofit details applied on each side

Desi

nation Ratio (%) Confi

uration CFRP

(

)

Grou

e N°1

W-CFRP-W1 100 Full face

1200X1200

W-CFRP-W2 50 3 Vertical

200X1200

W-CFRP-W3 75

3Verticals &

3 horizontals

6X200X1200

Groupe N°2

W-1D-CFRP

41 One diagonal 350

W-3D-CFRP 53

Three parallel

diagonals

300

& 2X200

W-2DX-CFRP 74 Diagonal X

2X350

W-2DX-2V-

CFRP

Two verticals

& dia

onal X

2X350

& 2X200

* URM-W-CFRP-W-X-: URM: unreinforced masonry, W: wall,

CFRP-W: carbon fiber reinforced polymer, W: wrap, X: number

of walls.

Comparing the specimen W-CFRP-W3

(reinforced by three verticals and three horizontals

CFRP (cross play composites) that covered 75% of

each substrate) with W-2DX-CFRP (reinforced by

two perpendicular diagonal CFRP applied on 74% of

each substrate), their response and their load bearing

capacities, which correspond to 26.2 kN, 27.4 kN

were almost similar.

Experimental results indicated that wall specimen

W-2DX-2V-CFRP, with CFRP composites covering

90% of each wall side, has the highest load bearing

capacity of 39 kN. The behavior of this wall specimen

is similar to W- CFRP-W 1 specimen.

The strengthening ratio used in those two cases

enhanced the tensile strength of the retrofitted walls,

which developed a larger strain that leads to high

lateral deformations.

Shear crack formation along the diagonal and the delamination of CFRP (Group N°1)

Wall shear cracking (Group N°2) CFRP delamination and the wall shear cracking (Group N°2)

Figure 1: Failure mode of the tested walls

Figure 2: Shear Stress-Strain curves of the tested walls (Group N°1)

ure 3: Shear Stress-Strain curves of the tested walls

(

Grou

N°2

)

5 CONCLUSION

The in-plane behaviour URM walls strengthened with

external CFRP composites was tested to evaluate the

effectiveness of using different configuration. The

following conclusions can be drawn:

The retrofitted walls load bearing capacities has

known an increase from 26.2 kN to 32.3 kN compared

to the reference wall. Specimens reinforced with three

parallel and vertical CFRP strips (50% reinforcement

ratio) indicated a significant enhancement in ductility

and deformability, despite the small amount of CFRP

used for reinforcement.

This study showed that the vertical and/or

horizontal reinforcement system increased the safety

of structures during an earthquake by improving

strength, energy dissipation and the ductility of the

URM walls. For example, the strength of the first

group was experimentally observed to be 181.72% to

247.31% higher than the URM wall. By using three

Table 2: Results of diagonal compression tests

Configuration

type

Side N° Load (kN) ΔV

(mm) ΔH

(mm)

Shear stress

(N/mm²)

Shear strain

(mm/mm)

Modulus of

Rigidity (MPa)

W- CFRP-W 1

32.3

1.2 0.18

0.17

0.0028

60.71

4.83 0.37 0.01

17.00

W- CFRP-W 2

29.4

1.03 0.15

0.15

0.0023 65.22

2 1.90 1 0.0058

25.86

W- CFRP-W 3

26.2

1.02 0.7

0.13

0.0034

38.24

1.46 3.02 0.009

14.44

W- 1D-CFRP

0.273 0.51

0.12

0.0016 75.25

2 0.467 0.887 0.0027 43.51

W- 3D-CFRP

37.8

1.592 7.188

0.194

0.0176 11.03

2 1.219 5.751 0.0139 13.89

W-2DX-CFRP

27.4

1.141 0.571

0.1404

0.0034 41

2 0.884 3.359 0.0085 16.54

W-2DX-2V-CFR

2.05 0.493

0.1998

0.0051 39.30

2 2.263 0.989 0.0065 30.72

vertical CFRP strips, the strength of the externally

reinforced wall significantly improved with a gain of

216.13% as compared to the reference unreinforced

wall specimen.

The ultimate strength of all wall specimens with

diagonal reinforcement configurations significantly

increased by 2.5 to 4.2 times the capacity of the

corresponding unreinforced wall specimens. In

addition, the shear strength of the wall specimens

increased considerably by 319%. The ultimate

strength of the walls strengthened with the second

reinforcement scheme group is 147.31 to 319.35%

higher than that of the unreinforced specimens.

CFRP reinforcement configuration with two

perpendicular diagonal strips and parallel vertical

strips applied on each side reached the highest in-

plane shear strength. Results also indicated that the

configuration with three parallel diagonal CFRP

strips is the optimum reinforcement ratio that

improves the in-plane response of the wall with

minimum cost. For example, the strength gain

obtained from this specimen with 53% CFRP

reinforcement ratio is 306% as compared to the

unreinforced wall specimen.

The model reinforced by a single diagonal CFRP

composite applied on each side showed a less

strength. The wall strength degrades quickly and the

reinforcement did not show a remarkable decrease in

rigidity. On the other hand, the wall rigidity

deteriorates rapidly, and it was accompanied by large

deformations, which provide the wall failure at a low

load of 23 kN. The strength of the wall reinforced

with diagonal stripes is the lowest compared to the

other configurations.

Experimental comparisons of the performance of

CFRP strengthening systems demonstrate that the

strength of the reinforced wall depends on the

percentage, the orientation and the position of the

CFRP reinforcement.

The results of this study confirmed the ability of

CFRP reinforcement in improving the mechanical

behavior of URM walls. The diagonal composite

reinforcement scheme presents a high potential

strengthening alternative as compared to full-surface

reinforcement scheme.

REFERENCES

Matthys, H., and Noland, L., 1989, proceedings of an

international seminar on Evaluation, strengtheningand

retrofitting masonry buildings, TMS, Colorado, USA.

Mosallam, A.S., Bayraktar, A., Elmikawi, M., Pul, S., and

Adanur, S., Polymer Composites in Construction: An

Overview, SOJ Materials Science & Engineering, 2(1),

25, 2014.

ElGawady, M., Lestuzzi, P., Badoux, M., A review of

conventional seismic retrofitting techniques for URM,

In: proceedings of 13th international brick and block

masonry conference. Amsterdam, July 4-7, 2004.

Chuang, S. W., and Zhuge, Y., Seismic Retrofitting of

Unreinforced Masonry Buildings - A Literature

Review, Australian Journal of Structural Engineering,

6 (1), 25-36, 2005.

Ortlepp, R., Lorenz, A., Curbach, M., Column

Strengthening with TRC: Influences of the Column

Geometry onto the Confinement Effect, Advances in

Materials Science and Engineering, 2009.

Brückner, A., Ortlepp, R., Curbach, M., Textile reinforced

concrete for strengthening in bending and Shear,

Materials and Structures, 39 (8), 741-748, 2006.

Boghossian, E., Leon, D., Wegner, R., Use of flax fibres to

reduce plastic shrinkage cracking in concrete, Cement

and Concrete Composites, 30, 929-937, 2008.

Mir, A., Zitouni, R., Colombet, F., Bezzazi, B., Study of

Mechanical and thermomechanical properties of

jute/epoxy Composite Laminate, Journal of reinforced

plastics and composites, 29 (11), 1669-.1680,2010.

Kriker, A., Debicki, G., Bali, A., Khenfer, M.M.,

Chabannet, M. , Mechanical properties of date palm

fibres and concrete reinforced with date palm fibres in

hot-dry climate, Cement & Concrete Composites, 27,

554-564, 2005.

Khalifa, A., Gold, W., Nanni, A., Abdel Aziz, M. I.,

Contribution of externally bonded FRP to shear

capacity of flexural members, 2(4), pp.195-203, 1998.

Stratford, T., Pascale, G., Manfroni, O., Bonfiglioli, B.,

Shear strengthening masonry panels with sheet glass-

fiber reinforced polymer, Journal of Composites for

Construction, 8(5), 434-443, 2004.

Mosallam, A., Banerjee, S., Enhancement in in-plane shear

capacity of unreinforced masonry (URM) walls

strengthened with fiber reinforced polymer composites

Composites, 42 (6), 1657-1670, 2011.

Valluzzi, M.R., Tinazzi, D., Modena, C., Shear behavior of

masonry panels strengthened by FRP laminates,

Construction and Building Materials,16 (7),409-416,

2002.

Santa-Maria, H., Duarte, G., Duarte, A., Garib, A.,

Experimental Investigation of masonry panels

externally strengthened with CFRP laminates and

fabric subjected to in-plane shear load, 13th World

Conference on Earthquake Engineering Vancouver,

B.C., Canada, No. 1627, August 1-6, 2004.

Konthesingha, K.M.C., Masia, M.J., Petersen, R.B.,

Mojsilovic, N., Simundic, G., Page, A.W., Static cyclic

in-plane shear response of damaged masonry walls

retrofitted with NSM FRP strips – An experimental

evaluation, Engineering Structures, 50, 126– 136, 2013.

ElMalyh, S., Bouyahyaouo, A., Cherradi, T., Rotaru, A.,

Mihai, P., Shear Strength of Unreinforced Masonry

Walls Retrofitted with CFRP, Advances in Science,

Technology and Engineering Systems Journal, 5 (2),

351-359, 2020.