bamt, Le

Received 22 December 2009Received in revised form 20 April 2010Accepted 19 June 2010Available online 24 July 2010

Keywords:

forcing wraps is commonly used to improve the exural behavior of structural members. Flexural

neering applications [1,2]. The steel jackets can be attached tothe R/C member in several forms depending on the shape of themember and the required level of strengthening [3,4]. The struc-tural characteristics of the R/C member: strength, stiffness, andductility, are signicantly upgraded by application of steel jackets[2,5,6].

On the other hand, FRP wraps for strengthening R/C membershas also been used extensively in the last decade in different con-

transfer between the steel members and the R/C member becauseno shear connectors or bonding material are used between the twomaterials, resulting a partial composite behavior between the bareR/C member and the steel members [2]. Accordingly, the level ofconnement reached is less than being fully conned and thus re-ferred to in this paper as Partial Connement (P/C).

An experimental study is presented in this paper carried on aset of one-fourth scale reinforced concrete T-shaped beam speci-mens conned by steel angles and plates. A total of four specimenswere tested. The rst beam was used as a control specimen andhad no external steel jacket for connement. Each of the remaining

* Corresponding author. Tel.: +961 3 333580; fax: +961 1 744462.

Construction and Building Materials 25 (2011) 10371043

Contents lists availab

B

evE-mail addresses: bhamad@aub.edu.lb, bhamad@code-lb.com (B. Hamad).1. Introduction and objectives

It has been well established that structural connement of weakreinforced concrete (R/C) members considerably improves mem-ber exural response in terms of strength, stiffness, and ductility.Several techniques are used for conning structural members inbuilding frames and bridges. The commonly used techniques arethe structural steel jackets and the ber-reinforced polymer(FRP) wraps. Conning by structural steel jackets has proved tobe an effective and low-cost worldwide technique in many engi-

gurations to ensure long service life of the structures [7,8].Although this method is relatively simple in application and doesnot require extensive labor effort in comparison to steel jackets,the aimed structural performance, the anchorage mode of failure[9], cross-sectional shape and re-resistance level of the strength-ened R/C member drive for the use of steel jacketing.

In one popular scheme, longitudinal jacketing steel usuallymade of angles and plate sections is simply wrapped around theR/C member, and tied together by transversal intermittent battenplates; i.e., strapping of the R/C member. Thus, there is no shearReinforced concreteT-beamsStructural steelPartial composite sectionsPartial connementStrengtheningFlexural behavior0950-0618/$ - see front matter 2010 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2010.06.075strengthening of R/C beams by external steel members is among the most effective and convenient tech-niques. A study is presented in this paper investigating the exural behavior of R/C beams having T cross-sections partially conned (P/C) by a combination of various steel members connected together by inter-mittent batten plates. Four R/C specimens, representing dropped beams in solid slabs, were tested. Onecontrol beam had no connement whereas the three other beams had four steel angles simply wrappedand tied around the stem by batten plates, two angles at the bottom corners of the stem and the othertwo angles at the stem-ange junctions. Two plates were placed on the top surface of the ange and con-nected by studs to the two angles at the bottom of the ange. The resulting P/C beams are categorized aspartial composite beams because no shear connectors were used between the R/C beam and the jacketingbottom-tension steel angles as in the case of conventional composite beams. All specimens were tested inpositive bending under two points loading. Test results revealed an enhancement in the exural behavior,particularly in the post-yield range of loading, and ductility due to the proposed strengthening and partialcomposite effect. The number and spacing of the intermittent battens played a signicant role in thebehavior of the strengthened specimens. Analytical values of loads and deformations at yield and ulti-mate loading showed good agreement with the measured values.

2010 Elsevier Ltd. All rights reserved.Article history: External connement of reinforced concrete (R/C) members with structural steel sections or ber rein-Behavior of T-shaped reinforced concreteby structural steel

Bilal Hamad a,*, Adnan Masri b, Hisham Basha b, OussaDepartment of Civil & Environmental Engineering, American University of Beirut, BeirubDepartment of Civil Engineering, Beirut Arab University, Beirut, Lebanon

a r t i c l e i n f o a b s t r a c t

Construction and

journal homepage: www.elsll rights reserved.eams partially conned

a Baalbaki b

banon

le at ScienceDirect

uilding Materials

ier .com/locate /conbui ldmat

three specimens was jacketed by four steel angles and two steelplates. Intermittent batten plates and shear studs were used toconnect the steel members. All specimens were tested in positivebending and were subjected to two-point quasi-static loads closeto mid-span in order to examine the enhancement of the exuralstrength, stiffness and ductility, and to better understand the fail-ure mode of the strengthened beams.

The primary objective of this study was to examine experimen-tally the proposed strengthening scheme and the behavior of thistype of members and understand the following inquiries:

1. How does the structural steel improve the moment capacity ofthe R/C beam?

2. How does the spacing of the batten plates affect the response ofthe P/C beam?

3. How does the proposed strengthening scheme contribute toductility characteristics and enhance the failure mode?

4. How does the moment capacity of the P/C beam compare withthe sum of the moment capacities of its two components; i.e.,the R/C beam and the steel jacket?

The experimental program is discussed in Section 2 of the pa-per, a design procedure for the steel jacket is presented in Section3, whereas test results and interpretation of these results are ex-plained in Sections 4 and 5, respectively. Conclusions are madein Section 6.

2. Experimental program

Four reinforced concrete beams having T-shaped cross-sections were con-structed. The length of each beam was 1700 mm. The ange and web dimensionswere 250 50 mm and 200 100 mm, respectively. The average 28-day compres-sive strength of concrete was 31 MPa. Each beam was longitudinally reinforced bytwo 8 mm diameter Grade 40 reinforcing bars on the tension side and two 4 mmbars on the top compression side. The clear concrete cover was 15 mm. Grade 24stirrups, 6 mm diameter, were used in all specimens as transverse reinforcementat 200 mm spacing. Tension tests performed on coupons of the longitudinal bars

Flange thickness (ts)

Flange width (B)

Web depth (h)

Web width (b)

Lower Angle

Upper Plate

Upper Angle

Intermittent Batten Plates (equally spaced)

Shear Stud

Fillet weld

Fig. 1. Strengthening scheme of the T-beam cross-section.

250mm

100mm

L 40x20x3

PL 3x50

Stud s 8mm

b. Cross-section

Fillet weld s=3mm

50mm

2PLs 3x60

2Ls 30x30x3

Studs 8mm @ smm

PLs 3x50@ smm

2Ls 40x20x3

web

flange

L = 1500mm

200mm

a. Longitudinal view

RC Beam

Fig. 2. Views of the partial

4a

N2222

1038 B. Hamad et al. / Construction and Building Materials 25 (2011) 10371043Table 1Details of the four specimens.

Specimen Cross-sectionh bf tw tf (mm)

2 Steel platest b L (mm)

TS1 200 250 100 50 N/ATS2 200 250 100 50 3 60 1500

TS3 200 250 100 50 3 60 1500TS4 200 250 100 50 3 60 1500 22L 30x30x3

ly conned specimen.

Steel angles b t L (mm)

Batten platest b-spacing (mm)

Studs U,spacing (mm)

/A N/A N/ALs 40 20 3 1500 3 50300 8300Ls 30 30 3 1500Ls 40 20 3 1500 3 50250 8250Ls 30 30 3 150050mm

200mm

PL 3x60 Ls 40 20 3 1500 3 50150 8150Ls 30 30 3 1500

indicated average yield and ultimate strength values of 441 MPa and 689 MPa,respectively. The yield and ultimate strength values for the transverse reinforce-ment were 251 MPa and 368 MPa, respectively.

Three of the R/C specimens were partially conned with structural steel mem-bers. Angles and plates proles were chosen for connement. The proposedstrengthening scheme is shown in Fig. 1. Two angles (30 30 3 mm) were placedat the bottom corners of the R/C beam, and two angles (40 20 3 mm) wereplaced at the bottom face of the ange at the stem-to-ange junction. The four an-gles were tied together around the stem of the R/C beam by three intermittenttransverse batten plates (3 50 mm) at a variable spacing. Fillet welding was usedto connect the steel angles and the batten plates. Additionally, two plates(3 60 mm) were placed at the top face of the ange. Threaded studs were usedto connect the plates and the two angles through the ange at the same spacingas the batten plates. Longitudinal and cross-sectional views of the conned speci-men are shown in Fig. 2. The details of the four specimens are identied in Table 1.

Mild structural steel was used for the plates, angles and batten plates. Tensiontests indicated average yield and ultimate strength values of 246 MPa and 357 MPa,respectively. Shear studs with average yield and ultimate strength values of251 MPa and 363 MPa, respectively, were used.

3. Design of the structural steel members

The behavior of a P/C beam with external structural steel is as-sumed to be partially-composite behavior rather than a fully-com-posite behavior. Although there is a full shear transfer between theange of the R/C beam and the steel plates laid at the top face(compression side, in positive bending) of the beam due to theuse of shear studs, there is no such shear transfer between the steelangles placed at the bottom face of the web (tension side, in posi-tive bending) and the R/C beam mainly due to the absence of shearstuds.

Neglecting the effect of any binding action between the R/C

where (Mn)P/C is the moment capacity of the partially connedbeam, (Mn)R/C the moment capacity of the reinforced concretebeam, and (Mn)ST is the moment capacity of the steel jacket.

The moment capacity of the R/C beam (Mn)R/C is accuratelydetermined using basic concepts for design of T-sections as stipu-lated in the ACI Building Code ACI 318-08 [10], (refer to Fig. 3).

The steel sections selected for jacketing of the R/C beam com-prises the steel plates and angles at the top and bottom faces ofthe beam, respectively, and batten plates with shear studs whichare used to connect between the steel plates and angles. Analysisof the steel jacket is based on two possible failure mechanisms.The rst failure mechanism is based on yielding in the bottom steelangles and top steel plates due to tensile and compressive stressescaused by exural bending. The second mechanism assumes yield-ing or fracture in the intermittent batten plates or in the shearstuds due to horizontal shear forces developed between the com-ponents of the steel jacket. Accordingly, the moment capacity ofthe steel jacket (Mn)ST dened in Eq. (1) is taken as the minimumof the two values computed from the two failure mechanisms asillustrated later.

The axial compressive and tensile forces that would develop inthe upper plates and the lower angles greatly depend on the spac-ing and strength of both the batten plates and the studs. The role ofthe battens is considered to be complementary to that of the studs.The latter allow for shear transfer between the upper steel platesand the two angles at the bottom face of the ange [11], whereasthe allow for shear transfer between the two angles at the under-side of the ange and the other two angles at the bottom of theweb, as shown in Fig. 1. If the battens and studs are spaced closely

h

inat

B. Hamad et al. / Construction and Building Materials 25 (2011) 10371043 1039beam and the structural steel jacket, it is rational in the design ofthis type of beams to consider that the nominal moment capacitywould be equal to the sum of the moment capacities of the R/Cbeam and the steel jacket.

MnP=C MnR=C MnST 1

hf

B

d

b

Ar

PNA

Fig. 3. Determ

A2

A1

ts

h

A3

Y3

Y1

PNA

Support Fig. 4. Determination of (Mn)ST based onwith sufcient shear resistance, the plates and angles would becapable to reach their axial capacity in both tension and compres-sion without buckling in any steel element. In the rst failuremechanism, the moment capacity of the steel jacket is fully devel-oped (refer to Fig. 4). Selecting approximately equal cross-sectional

c

0.85fc

Fy

stresses

C =0.851cBfc

T=ArFy

forces

ion of (Mn)R/C.

PNA

s ss

T= A3 Fy

C= A1 Fy

Mid-Span

A1 2 studs2 battensA3

yield mechanism of the steel jacket.

2. M

T T2V1V1

ral s

1

on s

uildis ss

MaxSupport 2 plates 2 studs2 battens

Fig. 5. Vierendeel structu

HbHb

ts

h

s

A

Support

Fig. 6. Determination of (Mn)ST based

1040 B. Hamad et al. / Construction and Bareas for the top plates (A1) and the lower angles (A3), and neglect-ing the effect of the angles at the bottom of the ange (A2) due toits relatively small contribution in exure being close to the neu-tral axis position, the rst value of the moment capacity of the steeljacket (Mn)ST is determined based on the yield resistance of the topor bottom steel sections, and is calculated using Eq. (2).

MnST RAiYi Fy AFy h ts 2

where Ai is the cross-sectional areas of the top plates (A1) or the bot-tom angles (A3), Yi the distances between the plastic neutral axisand the centroids of the top plates (A1) or the bottom angles (A3),Fy the yield strength of the steel sections, A the minimum of (A1)and (A3), and (h + ts) is the total depth of the beam approximatelyconsidered equal to the moment arm between the top and bottomsteel sections comprising the steel jacket.

In the second failure mechanism, the vierendeel structural sys-tem shown in Fig. 5 is used to determine the second value of themoment capacity of the steel jacket (Mn)ST. Under simple bending,the battens and studs act as vertical links between the top and bot-tom horizontal steel plates and angles, respectively. The top andbottom steel members will be subjected to axial and shear forcesbesides bending moments at the connections with the verticallinks. The batten plates will be mainly subjected to shear forcesin addition to bending moments at the connections with the hori-zontal steel members. If the spacing and strength of the battenplates and studs are not adequate, the moment capacity of the steeljacket (Mn)ST would be determined based on the shear strength ofeither the batten plates or stud, as shown in Fig. 6.

The value of (Mn)ST is determined using Eq. (3).

MnST nH h ts 3

where n is the total number of battens/studs between zero andmaximum moment sections, H the minimum of (Hb) and (Hs), Hb angles s/2 s/2

1

ystem of the steel jacket.

Hb HbHbHbHb Hb

T= n Hb

A3

2 studs2 battens

ss

C= n Hb

Max. Moment

hear mechanism of the batten plates.oment

T2 T1

C1 C2V1 V1

C2 C1

ng Materials 25 (2011) 10371043the shear capacity of the batten plate determined from Eq. (4),and Hs is the shear capacity of the stud determined from Eq. (5).

Hb Ab Fvy 4Hs As Fvf 5

where Ab is the cross-sectional area of the batten plate, As the cross-sectional area of the stud, Fvy the shear yield stress of the battenplate, and Fvf is the shear fracture stress of the stud.

It is worth mentioning that the shear resistance of the stud, asgiven by Eq. (5), excludes the concrete contribution around thestud as commonly used in the design of the shear studs in compos-ite design [11]. This assumption is conservative and it accounts forthe method used in putting these studs in the specimen by simplydrilling holes in the ange, then inserting the studs to connect thesteel plates and angles without any epoxy ller material.

The batten plates are sufciently welded at the connections tothe steel angles to prevent any failure due to bending moments.This weld is designed to resist a shear force Hb given in Eq. (5),and the in-plane moment Mb given in Eq. (6).

Mb Hb 0:50h 6

4. Test results

All specimens are tested as simple beams under two point loads250 mm apart, and a clear span of 1500 mm. Experimental resultsfor all specimens are presented in this section.

4.1. Control R/C specimen

The behavior of the control R/C specimen TS1 remained elasticup to a load of 26 kN and a deection of 4.3 mm. After that, the

stiffness degradation was very sharp as expected, and themaximum measured load and the corresponding deection were31 kN and 48 mm, respectively. The loaddeection relationshipof the specimen is shown in Fig. 7. The failure mode of this beamis exural as shown in Fig. 8, where a plastic hinge is clearly ob-served at the mid-span section of the beam. A crack was rst initi-ated at the bottom surface of the maximum bending momentsection, at mid-span, and then propagated quickly into upper sur-faces. Analytically, the yield load and corresponding deection ofthe R/C beam were calculated and found to be equal to 27 kNand 4.5 mm, respectively. The applied loads, required to attainthe section exural capacity and the shear capacity, were calcu-lated and found to be equal to 30 and 71 kN, respectively.

4.2. Partially conned specimens

The elastic behavior of the partially conned specimens TS2,TS3, and TS4 was almost identical. The yield load ranged between44.2 and 52.7 kN, and the corresponding deection ranged be-tween 7.2 mm and 8.1 mm. The elastic stiffness of the three spec-imens was almost equal to that of the control specimen TS1. In theinelastic phase, the maximummeasured loads and the correspond-ing maximum deections were: 78 kN and 70 mm for specimenTS2; 81 kN and 80 mm for specimen TS3; and 100 kN and105 mm for specimen TS4. It has been noticed that the strengthdegradation in specimens TS2 and TS3 was faster than that of spec-imen TS4 due to fracture of several studs, resulting in weaker com-posite action. The loaddeection curves of the three specimensare plotted along with that of the control specimen in one graph,shown in Fig. 7. The failure mode of specimens TS2 and TS3 wasfracture in several studs close to the support, whereas the failuremode of specimen TS4 was exural as yielding was observed inthe lower steel angles.

Table 2 provides a numerical comparison between the fourspecimens regarding the conguration of the intermittent battenplates, measured yield loads and deections, and maximum at-tained loads and corresponding deections. The failure modes ofthe four specimens are shown in Fig. 8.

5. Interpretation of test results

The test results for all specimens reveal a dramatic enhance-ment in the exural behavior of the control R/C specimen due toFig. 7. Loaddeection curves of all tested specimens.

Specimen (TS1)

s of

)

B. Hamad et al. / Construction and Building Materials 25 (2011) 10371043 1041Specimen (TS3)Fig. 8. Failure mode

Table 2Loads and deformations in the tested specimens.

Specimen # of Battensper face

% of Battens PLsto beam length

Experimental values

Py (kN) Dy (mm

TS1 26.0 4.3TS2 6 20 44.2 7.2

TS3 7 25 45.0 7.3TS4 11 40 52.7 8.1Specimen (TS2)

Specimen (TS4)the four specimens.

Pu (kN) Du (mm) Pu Py Du Dy % Strength increase

31 48 1.2 11.2 78 70 1.8 9.7 2.5

81 80 1.8 10.9 2.6

100 105 1.9 13.0 3.2

jacketing. The crack patterns of the tested specimens, shown inFig. 8, indicate that the mode of failure of this type of semi-com-posite beams varied between shear-exural failure mode inspecimens TS2 and TS3 and exural failure mode in specimenTS4. Flexural cracks were initiated at mid-span and propagatedgradually towards the supports. On the other hand, cracking ofthe control R/C specimen was unfavorably localized at mid-spanof the beam resulting in premature and localized failure. Conse-quently, the exural behavior and failure modes of the P/C beamsare much favorable in terms of ductility and failure mode.

In the elastic range of loading, the R/C beam provided themajority of the overall stiffness with minimal contribution fromthe steel angles. Thus, the control as well as the P/C beams showedalmost equal elastic stiffness. The yield load of the strengthenedbeams was greater than that of the R/C beam although of equalstiffness. A logical interpretation for this result is that the curvatureof the R/C beam forced the lower steel angles, which were not di-rectly connected to the concrete, to bend and enhance the strengthof the R/C beam. The steel jacket had in turn postponed cracking ofconcrete and yielding of the reinforcing steel in the R/C beam. Thereinforcing steel in the control R/C beam had yielded at a load of26 kN, while the attained yield load in the P/C specimens was equalto 52.7 kN.

In the inelastic range, after cracking of concrete and yielding ofthe reinforcing steel in the R/C beam, the stiffness of the P/C spec-imens was better than that of the R/C specimen, where thestrength degradation was slower indicating the onset of compositeaction between the R/C beam and the steel jacket. Stiffness reduc-tion gradually occurred in the three jacketed beams. The stiffnesswas mainly supplied by the steel jacket which provided partialconnement to the R/C beam. A signicant observation is thatthe number and spacing of the batten plates and shear studsplayed a major role in attaining the improved behavior. The yieldcapacity of the steel angles and plates has not been reached inspecimens TS2 and TS3, mainly due to the relatively large spacingof the battens and studs causing premature failure in the studs dueto low shear resistance. However, the angles and plates in speci-men TS4 had yielded because sufcient battens and studs were

(h + ts)

strains in steel jacket0.4y

0.4y

d

kd

y strains in RC beam

c < 0.002

Fig. 9. Strain distribution for computation of (My).

Table 3Computed versus experimental ultimate loads.

Specimen Ultimate loads Eqs. (2) and (3) Analytical Experimental

Pu (kN) Yield inangles

Pu (kN) Yieldin battens

Pu (kN)(governing)

Pu (kN)

TS2 94 75 75 78TS3 94 81 81 81TS4 94 116 94 100

1042 B. Hamad et al. / Construction and Building Materials 25 (2011) 10371043Fig. 10. Development of the aused at closer spacing, thus providing adequate shear resistance.Comparing the two P/C specimens TS2 and TS4, it is noticed that

increasing the ratio of intermittent batten plates to beam lengthfrom 20% to 40%, lead to a 39% increase in ultimate strength. Alsoto be mentioned is that the measured ultimate strength in speci-mens TS2 and TS3 were almost equal because failure in both spec-imens was due to fracture of several shear studs. The attained loadnalytical bi-linear model.

(mm

5

uildi5.1. Analytical prediction for estimating loads and deformation

Analytical values of the yielding moment and the correspondingyield load of the P/C beam were calculated by assuming the straindistribution shown in Fig. 9. The strain in the lower steel angles(tension side) was assumed to be 40% of its yield value mainlydue to the lack of any binding effect between the R/C beam andsteel angles. On the other hand, the deection in the jacketedbeams corresponding to the yielding loads is determined fromelastic analysis of the simple beam using the cracked exural stiff-ness of the R/C beam (EcIcr). The cracked moment of inertia (Icr) wascomputed assuming yielding of the reinforcing steel and perform-ing balanced section equilibrium by iteration.

As was mentioned earlier in the paper, the ultimate load value(Pu) is taken the least of two values which are based on the twopossible failure mechanisms in the steel jacket. Thus, one can pre-dict the ultimate load value (Pu) from Eqs. (2) and (3). The ultimatevalues (Pu) of the tested specimens were computed and shown inTable 3. In order to estimate the deformation corresponding tothe load at ultimate, a bi-linear analytical load-deformation curvewas developed based on results obtained from this study. The pro-posed bi-linear model captures the elastic as well as the inelasticpoints of interest such as values of Py, Dy, as well as Pu and Du.The model comprises of two segments: the elastic segment, up toa load of 1.25 Py, and the inelastic segment, up to the ultimate loadPu. The model adopts a post-yield slope (k2) equal to 15% the elasticslope (k1), as shown in Fig. 10. Thus, the ultimate deection thatcorresponds to the nominal load can be calculated from:

Du Dy 0:25Pyk1 Pu 1:25Py

0:15k17

A comparison between the experimental values, of loads anddeection, and the analytical nominal values predicted in thestudy, showed a good agreement in the elastic (at yield) as wellas in the inelastic range (post-yield range) with tolerance of lessthan 10%, as shown in Table 4.

6. Conclusionsin the P/C specimens ranged between 2.5 and 3.2 times that of thecontrol specimen TS1.

Table 4Comparison between experimental and predicted analytical values.

Specimen Experimental values

Py (kN) Dy (mm) Pu (kN) Du

TS1 26.0 4.3 31 48TS2 44.2 7.2 78 70TS3 45.0 7.3 81 80TS4 52.7 8.1 100 10

B. Hamad et al. / Construction and BThe main conclusions that could be deduced from this experi-mental study are:

1. The overall behavior of the T-shaped R/C beams was signi-cantly improved by being partially conned with structuralsteel. Connement resulted in better distribution of exuralcracks and higher ductility. The failure mode of the P/C beamwas much favorable to that of the control R/C beam.

2. The jacketing steel increased the load capacity of the three con-ned specimens between 2.5 and 3.2 times that of the controlR/C specimen, leading to higher moment and shear resistancein the conned specimens.3. The elastic stiffness of the R/C and the P/C beams were almostequal. The yield load of the P/C beam was almost twice thatof the R/C beam.

4. The inelastic behavior of the P/C beams was better than that ofthe R/C beam; characterized by higher strength, better stiffnessand improved ductility.

5. The spacing of the batten plates and studs signicantly affectsthe behavior and failure mode of the P/C beam. According tothe results, a partial connement with a 40% ratio is recom-mended in order to reach full yielding in the steel jacket.

6. Analytical model and a developed relationship proposed in thisstudy will assist in predicting yield and ultimate values of loadand deection of P/C beams. The proposed design approach andanalytical model are rational for such type of semi-compositebeams. The analytical and experimental results were in goodagreement with an offset of approximately 10%.

The study shows the importance of the proposed strengtheningscheme for strengthening design of R/C beams by practicing engi-neers seeking out more strength and better ductility. The retrot-ting scheme can be practically implemented for upgrading ofgirders in both buildings and bridge structures.

Acknowledgement

This study was supported by a research grant from ConseilNational De La Recherche Scientique CNRS-Liban for twoconsecutive years. The authors would like to express their grati-tude to the administration staff at CNRS for their assistance andencouragement.

References

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[3] Elnashai AS. Seismic capacity rehabilitation of reinforced concretestructures. London, UK: Civil Engineering Department, Imperial College; 1999.

[4] Bai JW. Seismic retrot for reinforced concrete building structures.Consequence-based engineering (CBE) institute nal report, Texas A&MUniversity; August 2003.

[5] Oh BH, Cho JY, Park DG. Failure behavior and separation criterion forstrengthened concrete members with steel plates. ASCE J Struct Eng2003;129(9):11918.

Analytical values

) Py (kN) Dy (mm) Pu (kN) Du (mm)

27 4.5 48 7.4 75 5648 7.4 81 7448 7.4 94 114

ng Materials 25 (2011) 10371043 1043[6] Su RKL, Zhu Y. Experimental and numerical studies of external steel platestrengthened reinforced concrete coupling beams. Eng Struct2005;27(10):153750.

[7] Garden HN, Hollaway LC. An experimental study of the inuence of plate endanchorage of carbon ber composite plates used to strengthen reinforcedconcrete beams. Compos Struct 1998;42(2):17588.

[8] Saadatmanesh H, Malek AM. Design guidelines for exural strengthening of RCbeams with FRP plates. ASCE J Compos Constr 1998;2(4):15864.

[9] El-Mihilmy MT, Tedesco JW. Prediction of anchorage failure for reinforcedconcrete beams strengthened with ber-reinforced polymer plate. ACI Struct J2001;98(3):30113.

[10] ACI Committee 318. Building code requirements for reinforced concrete andcommentary (ACI-318-08/ACI-318R-08), American Concrete Institute,Farmington Hills, Michigan; 2008.

[11] American Institute of Steel Construction. Load and resistance factor designspecications for structural steel buildings, AISC, Chicago; 2005.

Behavior of T-shaped reinforced concrete beams partially confined by structural steelIntroduction and objectivesExperimental programDesign of the structural steel membersTest resultsControl R/C specimenPartially confined specimens

Interpretation of test resultsAnalytical prediction for estimating loads and deformation

ConclusionsAcknowledgementReferences