Damaged Rc Beams With Circular Web Opening Repaired Using Different Configurations of Bonding Steel Plate

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International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 6308(Print), ISSN 0976 6316(Online) Volume 3, Issue 2, July- December (2012), IAEME

70

DAMAGED RC BEAMS WITH CIRCULAR WEB OPENING

REPAIRED USING DIFFERENT CONFIGURATIONS OF BONDING

STEEL PLATE

Mohammed J. Abed1, K. Nasharuddin

1, M. A. Alam

1, Zakaria CM

1,and

Moatasem M.

Fayyadh21

Department of Civil Engineering, Universiti Tenaga Nasional, 43000, Selangor, Malaysia.2

Department of Civil Engineering, University of Malaya, 50603, KL, Malaysia.

Abstract

This paper presents the results of an experimental study regarding the repair effectiveness of

steel plates for damaged Reinforced Concrete (RC) beams with a circular web opening atshear zones. It highlights the effect of fixing the steel plates on the damaged beams on the

load capacity, deflection, steel strain, steel plate strain and failure mode. In the experimental

program, three beams were used, with one solid beam used as a control beam and the other

two beams repaired by using two configurations (incline and vertical) of steel plate. Theresults revealed the efficiency of using steel plates for the repairing of damaged beams with

a circular opening, in that it increases the ultimate capacity of the beams significantly and

reduces the deflection under the opening. Furthermore, it was found that using an inclineconfiguration of steel plate for repairing of beams with a web opening is much more

efficient than the use of the vertical configuration. Using an inclined configuration not only

increased the ultimate capacity of the beams, it also changed the mode of failure from shearmode to flexural mode.

Keywords: RC beams, circular opening, repair configuration, steel plate.

1. INTRODUCTION

Reinforcing concrete beams with a web opening are necessary in modern buildingconstruction to accommodate essential services like water supply, sewage, air-conditioning,

electricity, telephone, and computer network because the floor space is limited in most

cases, and it is very important to pass these through a transverse opening in the RC beams.Web openings have various forms such as circular, rectangle, and square. A circular opening

is commonly used in the construction of buildings for water supply, natural gas pipes,

INTERNATIONAL JOURNAL OF CIVIL ENGINEERING

AND TECHNOLOGY (IJCIET)

ISSN 0976 6308 (Print)

ISSN 0976 6316(Online)

Volume 3, Issue 2, July- December (2012), pp. 70-83

IAEME: www.iaeme.com/ijciet.html

Journal Impact Factor (2011):1.2000 (Calculated by GISI)www.jifactor.com

IJCIET

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electricity cables and telephone lines. The presence of a web opening in the reinforced

concrete beams leads to a minus effect on the beams behaviour for things such as beam

stiffness, excrescence cracks, excessive deflection, and the beam strength. Furthermore, thepresence of an opening changes the beams behaviour to become more complex [1]. The

existence of the opening leads to disturbances and discontinuities in the normal flow of

stresses around opening, thus leading to the appearance of cracks within the vicinity of theopening. Therefore, the region around the opening needs special reinforcement in order to

provide sufficient quantity to control the width of cracks and prevent the possible premature

failure of the beam with an opening [2].Previous studies for RC beams with openings started from 1960 [3-9], and most of these

studies are about the behaviour of reinforcing concrete beams with an opening. Some of

these studies focused on beams with a circular opening and others on beams with a

rectangular opening. Some researchers reported the effect of the opening size on thestructural behaviour of the beams [10-13]. Tan and Mansur [14] presented a procedure for a

complete analysis and design of RC beams with a rectangular web opening. Mansur et al.

[15] presented a method for design RC beams with a circular web opening.

Steel plate is one of the most common materials used for strengthening of undamagedstructures and repairing of damaged structures to restore structural performance with respect

to service and ultimate load levels. The major attractions of this technique are availability,cheapness, uniform materials properties, high ductility and high fatigue strength. In recent

years, they are many researchers and studies about repairing and strengthening RC solid

beams by steel plate with different configuration. On the other hand, a very few studies onrepairing and strengthening RC beam with opening by steel plate. The results show whenplates are fixed to the sides (web) of a beam a large increase in the shear capacity can be

realized. It was found that the bolted arrangement provided adequate plate anchorage up to

the ultimate capacity of the beams. Furthermore, the adhesively bonded plates provide avery high degree of surface crack control R.A. Barnes et al. [16]. The epoxy bonded steel

plate provided an average of 72 % increase as compared to the control beams Bimal, B.A.et al. [17]. Using steel plates for strengthening RC beams with web opening not only

restored the beam full shear strength but also changed the mode of failure from shear modeto flexural one Allam et al. [18]. Similar investigation was presented by Alfarabi et al. [19]

was in this study beams were without internal stirrups and steel plates were applied instead

2. EXPERIMENTAL WORK

The experimental program of this study includes two RC beams with a circular web openingas well as a beam without any opening which was considered as a control beam. Table 1

shows the beams description according to the pre-repair damage level, repair material and

configuration. The opening zone was repaired using steel plates with two configurations asshown in Figure 1. Each beam has a clear span of 2.2 m and the beam cross section is 150

mm width and 400 mm depth. The RC beams with a circular opening in the shear zone were

designed according to Mansur [15], where the beams are reinforced with two 16 mm

diameter deformed steel bars, whereas the solid beam is designed according to ACI 318(2008) code requirements. Figure 2 presents the details of the dimensions and reinforcement

of the solid beam. The details of the dimensions and reinforcement of beams with a web

opening are shown in Figure 3. Figure 4 shows the static load setup. Table 2 presents thephysical properties of the RC beams. The RC beams were tested under two point loads. The


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load was applied gradually with a loading rate of 4 Kn/min. The repaired beams were

initially damaged under the ultimate load. The repairing procedure included preparing the

surface of beams where roughness equipment has been used to get a suitable face to have asmuch friction as possible with the repair materials. Figure 5 shows the roughness procedures

and the fixing of the plate. The surface was cleaned by using air pressure to avoid any dust

on the surface. When the concrete surface was prepared, the plate was fixed by using anadhesive material and then left for one week for hardening. The steel plate used in this

research has a width of 100 mm and 3 mm thickness. The surface of the steel plate was sand

blasted to eliminate rust and to make the surface rougher as shown in Figure 6 and steelplates are shown in Table 3.

Table 1: Description of RC beams

Table 2: Properties RC beams

Table 3: Steel plates material properties

Materials Width

(mm)

Thickness

(mm)

Tensile strength

(MPa)

Modulus of

Elasticity (MPa)

Steel 100 3 400 200,000

Figure 1: Vertical configuration (left) and incline configuration (right)

BeamsSteel bar

diameter (mm)

Steel tensile

stress (MPa)

Rupture steel

stress (MPa)

Concrete compressive

strength (MPa)

CB 16 521 603 30.35

B1 16 521 603 30.35

B2 16 521 603 30.35

Beams Pre-repair damage levelRepair material

Configuration

CB N/A N/A N/A

B1Ultimate Load Steel Plate

Inclined

B2 Vertical


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Figure 2: Details of dimensions and reinforcement of the solid beam


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Figure 3: Details of dimensions and reinforcement of beams with opening

Figure 4: Static load test setup

Figure 5: Surface preparation and steel plate fixing


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Figure 6: Sand blasted steel plate

3. EFFECT REPAIR OF STEEL PLATE

This section presents the results of testing damaged RC beams with a circular web opening

which were repaired using steel plates with different configurations. Two beams, B1 andB2, were tested and repaired with the two configurations incline and vertical as shown in

Figure 1. The results cover the load, deflection, strain, crack patterns and mode of failure for

the beams in two stages, the pre and post repair stages.

3.1 Effect on load deflection relationship

The load against deflection at both the mid-span and under the opening are presented inFigures 14 and 15 respectively. The results of Figure 7 show that the maximum mid-span

deflection of the control beam (CB) is 18.74mm at the failure load of 230 kN, while the

maximum deflection of beam B3 at the pre-repair stage is 4.14mm at the failure load of 140

kN. The maximum deflection of beam B4 at the pre-repair stage was 4.34 mm at the failureload of 140 kN. The failure of the control beam (CB) was a flexural failure at mid-span,

while for beams B1 and B2 the failure was a shear failure in the opening at the pre-repair

stage. The maximum mid-span deflection for beam B3 at the post-repair stage was 11.57mmat the failure load of 225 kN, and the failure was a flexural failure at mid-span, whereas the

maximum mid-span deflection for beam B4 at the post-repair stage was 9.85 mm at the

failure load of 215 kN and the failure was steel plate de-bonding at the opening. The results of Figure 8 show the maximum deflection at the shear zone for the control beam

(CB) is 10.08 mm at the failure load of 230 kN, while the maximum deflection at the

opening for beam B3 at the pre-repair stage is 6 mm at the failure load of 140 kN. The

maximum deflection at the opening for beam B1 at the post-repair stage is 5.91 mm at thefailure load of 225 kN. Furthermore, the maximum deflection at the opening for beam B2 at

the pre-repair stage is 5.94 mm at the failure load of 140 kN, and the maximum deflection at

the opening for beam B2 at the post-repair stage is 7.23 mm at the failure load of 220 kN.The results show that repairing beam B1 with the incline configuration of steel plate reduces

the deflection at the opening. It could be seen that the deflection at the pre-repair stage for

beam B1 at a load of 140 kN is 6 mm, while the deflection at the post-repair stage at thesame load of 140 kN is 3.4 mm. The contribution of the incline configuration for steel plates

reduces the deflection at the opening by 76%. It can be seen that the deflection at the pre-


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repair stage for beam B2 at a load of 140 kN is 5.94mm, while the deflection at the post-

repair stage at same load of 140 kN is 4.64 mm. The presence of the vertical configuration

of steel plates reduces the deflection at the opening by 28%.

Figure 7: Load vs. deflection at mid-span curves for beam CB and beams B1 and B2 at pre

and post repair stages

Figure 8: Load vs. deflection at shear (under opening) for CB and beam B1 in pre and post

repair stage

0

50

100

150

200

250

0 5 10 15 20

Load

kN

Deflection mm

CB

B1 - Pre-repair

B1 - Post - repair

B2 - Pre- repair

B2 - Post - repair

0

50

100

150

200

250

0 2 4 6 8 10 12

Load

(kN)

Deflection (mm)

CB

B1-Pre-repair

B1-Post-repair

B2-Pre-repair

B2-Post-repair


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3.2 Effect on steel bars strain and stirrupsThe load against the main steel bar strain at mid-span for the control beam (CB) and beams B1 andB2 at the pre and post repair stage are shown in Figure 9. It can be seen that the steel reached the

yield limit at a load of 195 kN for beam CB, while for beam B1 the steel bar reached the yield limit

at a load of 200 kN at the post-repair stage, and for beam B2 at the load of 190 kN at the post-repair

stage. For beams B1 and B2 at the pre-repair stage, the curve showed that the steel did not reach itsyield limit, where the failure happened at the opening (shear failure) before the steel reaches its yieldlimit. It can be seen that there is an immediate increase in the strain values when the first crack

occurs at a load of 45 kN for beam B1 and at a load of 35 kN for beam B2 at the pre-repair stage.

The results show that the higher strain is 4714 st at a load of 200 kN for beam CB, while the higher

strain is 3371 st at a load of 220 kN for beam B1 at the post-repair stage, and the higher strain for

beam B2 is 3645 st at a load of 215 kN at the post-repair stage. Therefore the presence of the steel

plate reduces the strain in the steel bar. The steel reaches the rupture strain when the failure occurs in

both beams CB and B1 at the post-repair stage. For beam B2, the steel reaches a strain of 4456 st

which is less than the rupture limit.

The load against the shear stirrups strain at the opening for the control beam (CB) and

beams B1 and B2 at the pre and post repair stages are shown in Figure 10. It can be seen that

the steel reached the yield limit at a load of 120 kN for beam B1 at the pre-repair stage,whereas the steel reached the yield limit at a load of 130 kN for beam B2 at the pre-repair

stage. It can also be seen that the peak value of strain at the opening for the shear stirrups

was 1500 st and 1487 st at a load of 140 kN for beams B1 and B2 respectively. Theresults show very low values of strain after repairing the damaged beams, and that's because

of the contribution of the steel plate which reduces the strain in the steel bar. It is clear in

Figure 17 that an immediate increase in the strain values is presented when the first crackoccurs.

Figure 9: Load vs. strain of steel bar at mid-span for beams CB, B1 and B2 at pre and post

repair stage

0

50

100

150

200

250

0 2000 4000 6000 8000 10000 12000 14000

Load

(kN)

Strain (ust)

C.B

Pre-repair1B

Post-repair1B

Pre-repair2B

Post-repair2B


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Figure 10: Load vs. strain of steel strips at shear for beams CB, B1 and B2 at pre and post

repair stage

3.3 Effect on steel plate strainThe steel plate strain gauges were fixed at two positions around the opening. The first strain

gauge (SGS 1) is the closest to the point of the applied load at the top and the second straingauge (SGS 2) is the closest to the supports at the bottom as shown in Figures 11 and 13

respectively. The load against the steel plate strain for the two strain gauges for both beamsB1 and B2 is presented in Figures 12 and 14 respectively. The results show that higher strain

is recorded at the first strain gauge (SGS1) which is located between the point of the appliedload and the opening. The maximum value recorded for beam B1 is 447 st in SGS1, which

is considered a small value compared to the ultimate strain of the steel plate, while the

maximum value recorded is 349 st in the SGS2 at the bottom. Both strain gauges SGS1and SGF2 indicate that the steel plate is able to support the load without any release in strain

up to failure. On the other hand, the results show that SGS1 indicates a release in the steel

plate strain beyond a load of 100 kN where new cracks start to appear in the adhesive layerbetween the steel plate and the concrete surface in beam B2. The decrease in the value of

strain continues until the de-bonding failure occurs. The strain gauge SGF2 also shows a

release in the value when the cracks start to appear between the steel plate and the concretesurface. From Figure 14, it can be seen that the curves for both strain gauges SGS1 andSGS2 showed changes in the trend after the cracks appeared between the steel plate and the

concrete surfaces.

0

50

100

150

200

250

0 500 1000 1500 2000

Load

(kN)

Strain (ust)

Pre-repair1B

Post-repair1B

Pre-repair2B

Post-repair2B


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Figure 11: Position of CFRP strain gauge around opening for beam B1

Figure 12: Position of steel plate strain gage around opening for beam B2

Figure 13: Load vs. strain of CFRP laminates at shear for beam B1

0

50

100

150

200

250

0 100 200 300 400 500

Load

(kN)

Strain (st)

SGS1

SGS2


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Figure 14: Load vs. strain of steel plate at shear for beam B2

3.4 Crack pattern and failure mode

The first crack was observed at a load of 45 kN for beam B1 and at a load of 35 kN forbeam B2 at the pre-repair stage. The cracks at the pre-repair stage started appearing around

the opening and mid-span. The trend of the cracks around opening was from the opening

toward the point of the applied load at the top and from the opening toward the support pointat the bottom. As the load increased, the cracks started to become wider and propagated

toward the point of the applied load. In the post-repair stage for beam B1, cracks started

propagating at mid-span and became wider when the load increased until the failure,

whereas, the repair area around the opening didnt show any new cracks. This indicated thecontribution of steel plate increased the stiffness of the beam at the opening and prevented

the appearance of new cracks, whereas in the post-repair stage for beam B2 cracks started

propagating from the opening toward the point of the applied load, and the amount of cracksalso increased at mid-span. The space between the top corner of the opening and the point of

applied load witnessed the emergence of many cracks that have been implemented between

the steel plate and the concrete surface, and this then led to the de-bonding failure.

The results show that repairing beam B1 with an externally bonded steel plate transferredthe behaviour of the beam from brittle behaviour (shear failure) at the pre-repair stage to

ductile behaviour (flexural failure) at the post-repair stage. This is the optimal status that a

repaired RC beam with a web opening can achieve. On the other hand, the results show thatrepairing beam B2 with an externally bonded steel plate as a vertical orientation shifted the

failure from a shear failure in the opening at the pre-repair stage to a steel plate de-bonding

failure at the post-repair stage. The mode of failure for beams as shown in Figure 15.

0

50

100

150

200

250

0 50 100 150 200 250 300 350

Load(kN)

Strain (st)

SGS1

SGS2


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a- Mode failure of control beam

b- Mode failure of beam B1

c- Mode failure of beam B2

Figure 15: The mode failre of beams CB, B1 and B2 at post repair stage


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3.5 Configurations comparison of steel plate

From the aforementioned results, it can be observed that beam B1 achieved a higher

ultimate capacity than beam B2. The increase in the ultimate load for beam B1 was 60%,whereas for beam B2 it was 53%. The results show that the maximum deflection for beam

B1 at the post-repair stage was 11.57 mm at a load of 225 kN, whereas the maximum

deflection for beam B2 at the post-repair stage was 9.85 mm at a load of 215 Kn. Thedeflection at mid-span for beam B1 is more than for beam B2 because the failure for beam

B1 occurs in mid-span as a flexural failure while the beam B2 failure occurs at the shear

level as steel plate de-bonding.It can be seen that the maximum deflection for beam B1 is 5.91 mm at a load of 225 kN at

the opening, whereas the maximum deflection for beam B2 is 7.33 mm at a load of 215 kN.

Beam B1 has a lower deflection at the opening from beam B2 because the beam B4 failure

occurs at the opening as steel plate de-bonding, while the beam B1 failure occurs at mid-span as a flexural failure. The lower deflections at the opening indicate the contribution of

the inclined configuration of steel plate.

It can be seen that the steel bar strain at midspan for both beams at the pre-repair stage

didnt reach the yield limit because the failure at this stage for both beams occurs in theopening zone. After repair, beam B1 reached the yield limit at a load of 200 kN, whereas

beam B2 reached the yield limit at a load of 190 kN. However, the strain of the steel bar inmid-span for beam B1 reached the rupture strain when the failure occurs as a flexural

failure, while the steel bar in mid-span for B2 didnt reach the rupture limit because the

failure occurs at the shear zone as a steel plate de-bonding failure. The results also show thestrain of the strips at the shear zone with the opening for beam B1 reached the yield limitwhen the load was 120 kN at the pre-repair stage, whereas beam B3 reached the yield limit

when the load was 130 kN. After repair, the strain of the stirrups for beam B1 shows very

low values because of the contribution of the inclined steel plate, while the strain of thestirrups for beam B2 shows high values because of the de-bonding of the vertical steel plate.

The results show that for beam B1, both strain gauges SGF1 and SGF2 indicate that the steelplate with the incline configuration is able to support the load without any release in strain

up to failure. On the other hand, the strain of the vertical steel plate configuration for beamB2 for both strain gauges SGF1 and SGF2 showed changes in the trend after the cracks

appeared between the steel plate and the concrete surfaces.

The crack trends for both beams are almost the same around the opening when the failureoccurs at the pre-repair stage. In the post-repair stage the crack patterns are different for

each beam depending on the form of failure, for beam B1 many cracks appeared at the mid-

span, whereas for beam B2 the cracks started increasing and widening between the verticalsteel plate and the concrete surfaces until the de-bonding failure occurs. The contribution of

the inclined steel plate shifted the mode of failure in beam B1 from a brittle failure at the

opening to a ductile failure at mid-span, while the vertical configuration didnt change thebrittle behaviour of the repaired beam.

From the results of both beams B1 and B2, it was found that using an incline configuration

for repairing beams with a circular web opening is more efficient than using a vertical

configuration.

4. CONCLUSIONThe present study aimed to investigate the repair effectiveness of damaged RC beams with a

circular web opening using externally bonded steel plates with different configurations. Thestudy was based on the comparison of the load, deflection, strain and crack pattern and


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failure mode. The study also investigates the effect of the configuration of repairing

materials on the repair effectiveness. Based on the experimental results of the tested beams,

the following are the main conclusions.

Repairing an RC beam with a circular web opening using steel plate increases the loadcapacity and decreases the deflection and steel strain.

External repairing of the beam opening using an incline configuration of steel plate ismore effective than using a vertical configuration.

Using an incline configuration changed the behaviour of the beams failure from brittle toductile.

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[2] Bower, J.E. (1966a). Elastic stresses around holes in wide- flange beams, Journal of the structural

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[10] Nasser , K.W., Acavalas, A., and Daniel, H.R. (1979). Behavior and design of large openings inreinforced concrete beams, ACI Journal, vol. 64,No.1, pp. 25-33.

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[13] Mansur , M.A., Lee, Y.F., Tan, K.H., and Lee, S.L. (1991). Test on RC continuous beams withopenings, Journal of Structural Engineering, ASCE, vol. 117, No.6, pp. 1593-1606.

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[15] Tan, K.H., Mansur, M.A. and Hung, L.M. (2001). Design of reinforced concrete beams with

circular openings, ACI Structural Journal, vol. 98, No.3, pp. 407-415.

[16] R.A. Barnes, P.S. Baglin, G.C. Mays, and N.K. Subedi. (2001). External steel plate systems forthe shear strengthening of reinforced concrete beams, Engineering Structures, vol. 23, pp. 1162-1176.

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[18] Allam, S.M.( 2005). Strengthening of RC beams with large openings in the shear zone,

Alexandria Engineering Journal, vol. 44, No.1, pp. 59-78.[19] Alfarabi, S., M. Hussain, I.A. Basunbul, M.H. Baluch and G.J. Al-Sulaimani. (1995). Steel Plate

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Damaged Rc Beams With Circular Web Opening Repaired Using Different Configurations of Bonding Steel Plate

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