Experimental Investigation on Behavior of Reinforced Concrete

    Beam Column Joints Retrofitted with FRP Wrap Subjected to Static Load

    Robert Ravi. S, Assistant Professor, Prince Arulraj. G, Director, School of Civil Engineering., Karunya University, Coimbatore.

    Moderate and severe earthquakes have struck different places in the world, causing severe damage to reinforced concrete (RC) structures. Retrofitting of existing structures is one of the major challenges that modern civil engineer have to face. Recent evaluation of civil engineering structures has demonstrated that most of them will need major repairs in the near future. One of the techniques of strengthening the RC structural members is through confinement with a composite enclosure. This external confinement of concrete by high strength fiber reinforced polymer (FRP) composites can significantly enhance the strength and ductility and will result in large energy absorption capacity of structural members. FRP materials, which are available in the form of sheets, are being used to strengthen a variety of RC elements to enhance the flexural, shear, and axial load carrying capacity of elements.

    Beam-column joints, being the lateral and vertical load resisting members in RC structures are particularly vulnerable to failures during earthquakes and hence strengthening of the joints is often the key to successful seismic retrofit strategy. In this paper, an attempt has been made to study the behavior of the reinforced concrete beam-column joints retrofitted with Carbon fiber reinforced polymer wrap and Glass fiber reinforced polymer wrap.

    Nine exterior RC beam-column joint specimens were cast and tested to failure during the present investigation. In six specimens, the reinforcements in both column and beam were provided as per code IS 456:2000 In remaining three specimens, the reinforcements in both column and beam were provided as per code IS 13920:1993. Various percentage of load carrying capacity of column was given as axial load in the column. Static load was applied as cantilever point load on beam till failure. The failed beam-column joint specimens were retrofitted by removing the concrete in the joint portion and recasting with concrete of the same grade and subsequently Carbon fiber reinforced polymer (CFRP) sheet was used to wrap three specimens and Glass fiber reinforced polymer (GFRP) sheet was used to strengthen the other three specimens. The performance of the retrofitted beam-column joints was compared with the control beam-column joint specimens and the results were presented.

    Introduction

    Recent earthquakes have exposed the vulnerability of existing reinforced concrete (RC) beam-column joints to seismic loading. Until early 1990s, concrete jacketing and steel jacketing were the two common methods adopted for strengthening the deficient RC beam-column joints. Concrete jacketing results in substantial increase in the cross sectional area and self-weight of the structure. Steel jackets are poor in resisting weather attacks. Both methods are however labor intensive and sometimes difficult to implement at the site. A new technique has emerged recently which uses fiber reinforced polymer sheets to strengthen the beam-column joints. FRP materials have a number of favorable characteristics such as ease to install, immunity to corrosion, high strength, availability in sheets etc., The simplest way to strengthen such joints is to attach FRP sheets in the joint region in two orthogonal directions.

    The initial developments of the FRP strengthening technique took place in Germany and Switzerland. Strengthening of reinforced concrete members with externally wrapped FRP laminates by Carbon and Glass FRP sheets has been studied in detail by researchers at Swiss Federal Laboratories for Materials Testing and Research, German Institute of Structural Materials and Institute for Building Construction & Fire Protection. The results obtained proved that the FRP strengthening technique is highly efficient and effective.

    Literature Review

    Robert Ravi et al (2009) conducted an experimental investigation on influence of development length in retrofitted reinforced concrete beam-column joints. Nine controlled reinforced concrete beam-column joints specimens were casted, in which six specimens had design and details as per the code IS 456:2000. Remaining three specimens had design and details as per the code IS 13920:1993. Retrofitting was done on failed specimens which had details as per code IS 456:2000.Three specimens were wrapped with GFRP and remaining three with CFRP. Static load test was conducted on control and retrofitted specimens. They conclude that there was an increase in load carrying capacity by 14.5% and an increase in energy absorption capacity by 10% as the development length was increased based on code IS 13920:1993.

    K.R.Bindu et al (2008) conducted a detailed investigation on the performance of exterior beam-column joints with inclined bars at joints under cyclic loading. They investigated the effect of inclined bars at the joint region. Four exterior beam column joints were cast and tested under cyclic loading. The performance of specimens which had joint reinforcement with inclined bars was compared with the specimen without inclined bars. They concluded that specimens with inclined bars show more ductility and energy absorption capacity than the specimen without inclined bars.

    Alexander G. Tsonos et al (2008) conducted a detailed investigation on effectiveness of CFRP jacket and RC jacket in post earthquake and pre earthquake beam-column sub assemblages. The feasibility and technical effectiveness of high strength fibre jacket system and reinforced jacket system were discussed. Four exterior beam-column joint sub assemblages were tested under cyclic loading. They concluded that in case of post earthquake, specimens retrofitted with RC jacket shows more effective but in case of pre earthquake both retrofitting technique shows equal effectiveness.

    G.A. Lakshmi et al (2008) conducted a detailed investigation by numerical and experimental study on strengthening of beam-column joints under cyclic excitation using FRP composites. In that study three typical modes of failure namely flexural failure of beam, shear failure of beam and shear failure of column were discussed. Comparison was made in the terms of load carrying capacity. Three exterior beam-column joint sub assemblages were caste and tested under cyclic loading. All the three specimens were retrofitted using FRP materials and result were compared with control specimens. Finite element analysis has been carried out using ANSYS to numerically simulate each of these cases. They concluded that the shear failure was very brittle and hence retrofitting should be done in such a manner that the eventual failure occurs in the beam in flexure.

    G. Appa roa et al (2008) conducted detailed investigation on performance of RC beam-column joints strengthened by various schemes subjected to seismic loads. In this study different strengthening methods such as steel jacketing, fibre wrapping and providing haunch elements were discussed. The important design parameters such as joint shear strength and energy dissipation capacity for various schemes were discussed. They concluded that to enhance the strength, stiffness and energy dissipation, it lacks proper placements and arrangements of FRP sheets and strips. Hence it could not improve the joint shear strength. The numerical studies revealed that the haunch element had significant reduction of shear force and bending moment in the frame members leading to significant reduction of joint shear force.

    Based on the review of literature it is found that only few experimental investigations have been carried out on beam-column joints. Hence an attempt has been made to carry out an investigation on beam-column joint specimens retrofitted with glass and carbon FRP wrap.

    Experimental Investigations

    The experimental program consisted the testing of nine reinforced concrete beam-column joint specimens. The column had a cross section of 200mm x 200mm with an overall length of 1500mm and the beam had a cross section of 200mm x 200mm with a cantilevered portion of length 600 mm based on the availability of mould. Six specimens had 4nos. of 12mm diameter bars as longitudinal reinforcement in column as per IS 456:2000, cl 26.5.3.1. The lateral ties in the column were provided at a spacing of 180 mm c/c as per IS 456:2000, cl 26.5.3.2(c). Beam had 2 nos.16 mm diameter bar as tension reinforcement and 2nos.12 diameter as compression reinforcement as per code IS 456: 2000, cl. 26.5.1.1 (a) & cl. 26.5.1.2. Beam had vertical stirrups of 6 mm diameter at 120mm c/c as per code IS 456:2000, cl.26.5.1.6. The development length of the tension and compression rods in beam were also provided as per clause 26.2.1 of IS 456:2000.

    For the remaining three specimens, 4nos.12mm diameter bars were provided as longitudinal reinforcement. The lateral ties in the column were provided as 8mm diameter bar at 75 mm c/c for the central distance of 1100mm as per IS 13920:1993,cl 7.4.6 and 6mm diameter bars at 100mm c/c for the remaining length of the column. Beam had 2 nos. each 16mm diameter bar as tension and compression reinforcement. Beam had vertical stirrups of 6mm diameter bar at 40mm c/c. up to 340mm from the face of the column as per code IS 13920:1993,cl 6.3.5 and 6 mm diameter bar at 80mm c/c for remaining length of the beam. The development length of the beam rods were also provided as per code IS 13920:1993,cl 6.2.5. The concrete mix was designed for a target strength of 25 MPa at the age of 28 days. The load carrying capacity of the column was found to be 525 kN. The details of the typical test specimens are given in Fig.1(a) & Fig.1(b).

    Experimental Investigation

    Static tests were conducted on the control and retrofitted reinforced concrete beam-column joint specimens. Generally, when the axial load on the column exceeds 50 to 60% of its capacity, the effect of axial load will be more predominant on the joint. But in the case of the seismic forces, the effect of lateral load will be more predominant. Hence in order to truly reflect the performance of the joint under seismic load conditions, it was decided to restrict the axial loads of column to a maximum of 240 kN which is less than 50 % of load carrying capacity of the column. The experimental investigation consisted of applying three axial loads of 80 kN, 160 kN and 240 kN on the column and applying a point load at the free end of the cantilever beam portion till the failure of the specimen. The loading was continued till the joint failed by crushing of concrete in the case of control specimens and rupture of wrap in the case of retrofitted specimens. The details of the experiments are given in Table 1

    Experimental Investigation

    Glass fiber reinforced polymer sheets (GFRP) wrap was used to strengthen the three failed beam-column joint specimens C1,C2 & C3 and they are redesignated as retrofitted specimens R1, R2 & R3.
    Experimental Investigation
    Carbon fiber reinforced polymer wrap (CFRP) was used to strengthen the other three failed beam-column joint specimens C4,C5 & C6 and they are redesignated as retrofitted specimens R4, R5 & R6. They were again tested to failure. The performance of the retrofitted beam-column joint specimens was compared with that of the control beam-column joint specimens. The physical properties of GFRP and CFRP were given in Table 2 and Table 3

    Preparation of Test Specimens

    The RC beam-column joint specimens were cast using fabricated steel moulds. Reinforcement was prepared and placed inside the mould. The grade of concrete used was M25.ACI method of mix proportioning namely, ACI 211.4R-99 was adopted to arrive the initial mix proportions. However, the following proportions were arrived at after several trial mixes.

    Experimental Investigation

    Concrete was mixed in a tilting type mixer machine. Care was taken to see that concrete was properly placed and compacted. The sides of the mould were removed 24 hours after casting and the test specimens were cured in water for 28 days. Fig .2 a) & Fig. 2 b) shows the typical test specimen before and after concreting.

    Experimental Investigation

    Preparation of the Retrofitted Specimens

    The failed specimens C1, C2, C3 & C4, C5 ,C6 were retrofitted and redesignated as specimens R1, R2, R3 & R4, R5, R6 . The concrete near the area of failure was removed completely. After applying cement paste in this area, the portion was filled and compacted with the same grade of concrete. Fig 3.a) & 3.b) shows the reconcreting process.

    Experimental Investigation

    The specimens were cured for 28 days. Before wrapping GFRP, CFRP sheets, the faces of the specimens were ground mechanically to remove any laitance. All the voids were filled with putty. Then a two component primer system was applied on the concrete surface and allowed to cure for 24 hours. A two component epoxy coating was then applied on the primer coated surface and GFRP or CFRP sheet was immediately wrapped over the entire surface of the reinforced concrete beam-column joint.

    A hand roller was then applied gently over the wrap so that good adhesion was achieved between the concrete surface and the GFRP or CFRP wrap, as suggested by the manufacturers and allowed to cure for seven days. Another coat of the two component epoxy was applied over the fiber sheet. Then the second wrap was applied by following the same procedure and allowed to cure for a further period of seven days. Both the wrapped layers were orthogonal to each other. Fig 4.a) & 4.b) shows the wrapped specimens by GFRP and CFRP.

    Experimental Investigation

    Description of the Test Programme

    Experimental Investigation
    The specimen C1, C4 & C7 were tested in a loading frame in the horizontal plane. Both the ends of the column were hinged using roller plates. The axial load of 80 kN was applied at one end the column using a hydraulic jack of 500kN capacity and the load was measured using an electrical load cell. The other end of the column was supported by the steel bulkhead attached to the loading frame. A transverse load was applied at the free end of the beam through a hydraulic jack of capacity 250 kN to develop a bending moment at the joint. The load on the beam was also measured using an electrical load cell. The deflection at the free end of the beam was recorded at regular load intervals up to a control deflection of 75mm. The specimens C2,C5,C8 and C3,C6,C9 were tested in the same way and the axial loads applied on these specimens were 160 kN and 240 kN respectively. The retrofitted specimens R1&R4, R2&R5 and R3&R6 were also tested for the axial loads of 80kN, 160kN and 240kN.Fig 5. shows the typical experimental set up.

    Analysis of the Results

    In the case of the specimen C1, first crack was formed in the beam portion approximately at a distance of 45 mm from face of the column at a load of 19.5 kN. At a load of 20.5 kN, another crack was formed in the beam-column joint of the test specimen. The cracks in the beam started to widen at a load of 21 kN. Spalling of concrete occurred in the tension zone of the beam at a load of 22 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 23 kN.

    In the case of the specimen C2, the first crack was formed in the beam portion approximately at a distance of 47 mm from face of the column at a load of 19.5 kN. At a load of 20.5 kN, cracks propagated to the compression zone of the beam. Spalling of concrete occurred in the beam at a load of 21 kN. Cracks propagated to the beam-column joint portion at a load of 21.5 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75mm. The load corresponding to this deflection was 22 kN.

    In the case of the specimen C3, first crack was formed in the beam portion approximately at a distance of 50 mm from face of the column at a load of 20 kN. At a load of 21 kN, cracks propagated to the compression zone of the beam. Spalling of concrete occurred in the beam at a load of 21.5 kN. Cracks propagated to the beam-column joint portion at a load of 22.5 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 23.5 kN

    In the case of the specimen C4, first crack was formed in the beam portion approximately at a distance of 50 mm from face of the column at a load of 20.5 kN. At a load of 21 kN, cracks propagated to the compression zone of the beam. Spalling of concrete occurred in the beam at a load of 21.5 kN. Cracks propagated to the beam-column joint portion at a load of 22 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 22.5 kN.

    In the case of the specimen C5 the first crack was formed in the beam portion approximately at a distance of 55 mm from face of the column at a load of 19 kN. At a load of 19.5 kN, another crack was formed in the beam-column joint of the test specimen. The cracks in the beam started to widen at a load of 20 kN. Spalling of concrete occurred in the tension zone of the beam at a load of 20.5 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 21 kN.

    In the case of the specimen C6, the first crack was formed in the beam portion approximately at a distance of 50mm from face of the column at a load of 19.5 kN. At a load of 20 kN, cracks propagated to the compression zone of the beam. Spalling of concrete occurred in the beam at a load of 20.5 kN. Cracks propagated to the beam-column joint portion at a load of 21 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 21.5 kN. Fig.6 a) & 6.b) shows the beam-column joint specimen before and after testing.

    Experimental Investigation

    In the case of the specimen C7 the first crack was formed in the beam portion approximately at a distance of 60 mm from face of the column at a load of 21 kN. At a load of 22.5 kN, cracks propagated to the compression zone of the beam. Spalling of concrete occurred in the beam at a load of 23.5 kN. Cracks propagated to the beam-column joint portion at a load of 25.5kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 26 kN.

    In the case of the specimen C8 the first crack was formed in the beam portion approximately at a distance of 55mm from face of the column at a load of 22 kN. At a load of 23 kN, cracks propagated to the compression zone of the beam. Spalling of concrete occurred in the beam at a load of 24 kN. Cracks propagated to the beam-column joint portion at a load of 25 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 26.5 kN.

    In the case of the specimen C9 the first crack was formed in the beam portion approximately at a distance of 58 mm from face of the column at a load of 21.5 kN. At a load of 22.5 kN, cracks propagated to the compression zone of the beam. Spalling of concrete occurred in the beam at a load of 24.5 kN. Cracks propagated to the beam-column joint portion at a load of 25 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 26 kN. The best load deflection curve among the specimens was shown in Fig.7.a) & 7.b).

    Experimental Investigation

    The load carrying capacity of six control specimens were given in Table 4.

    Experimental Investigation

    Effect of Lateral Ties

    It was seen from Table.4, there was not much difference in the load deformation characteristics of the beam-column joint specimens with an increase in the axial load. It was seen that there was only 12% increase in the ultimate load capacity and 13% increase in energy absorption capacity of the RC beam-column joint specimen, as the stirrup spacing is decreased as per code IS 13920:1993. In the case of control specimens, cracks emanated from the beam portion and with an increase in the load, the cracks propagated into the joint portion of the specimens and spalling of concrete was noticed.

    Retrofitted Specimens

    In the case of the retrofitted specimen R1, first crack was formed in the beam portion very close to the column at a load of 22 kN. At a load of 24 kN, a crack propagated to the compression zone of the beam. The cracks in the beam started to widen at a load of 26 kN and bond failure of the wrap was noticed on the tension side of the beam at a distance of 50 mm from the face of the column. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 29 kN.

    In the case of the specimen R2, first crack was formed in the beam portion at a distance of 30 mm from the face of the column at a load of 24 kN. At a load of 26 kN, the crack propagated to the compression zone of the beam. The cracks propagated into the column portion at a load of 27 kN. Bond failure of the wrap was noticed on the tension side of the beam at a load of 28 kN and the compression side of the beam at a load of 29 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 30 kN.

    In the case of the specimen R3, the first crack formed in the beam portion at a load of 23 kN. Bond failure of the wrap was noticed on the tension side of the beam at a load of 25 kN and on the tension side of the compression side of the beam at a load of 27 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 29 kN.

    In the case of the retrofitted specimen R4, first crack was formed in the beam portion very close to the column at a load of 23 kN. At a load of 25 kN, a crack propagated to the compression zone of the beam. The cracks in the beam started to widen at a load of 27 kN and bond failure of the wrap was noticed on the tension side of the beam at a distance of 55 mm from the face of the column. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 31 kN.

    In the case of the specimen R5, the first crack was formed in the beam portion at a distance of 40 mm from the face of the column at a load of 25 kN. At a load of 27 kN, the crack propagated to the compression zone of the beam. The cracks propagated into the column portion at a load of 28kN. Bond failure of the wrap was noticed on the tension side of the beam at a load of 29 kN and the compression side of the beam at a load of 30 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 32 kN.

    In the case of the specimen R6, the first crack formed in the beam portion at a load of 24 kN. Bond failure of the wrap was noticed on the tension side of the beam at a load of 26kN and on the tension side of the compression side of the beam at a load of 28 kN. The application of the load was stopped when the deflection at the free end of the beam reached 75 mm. The load corresponding to this deflection was 30 kN. Fig 8.a) & 8.b) shows the failed retrofitted specimens.

    Experimental Investigation

    Effect of Retrofitting

    Experimental Investigation
    The load deflection curves of control, GFRP and CFRP wrapped RC beam-column joint specimens were shown in Fig.9. The load carrying capacity of the various reinforced concrete beam-column joint specimens (both control and retrofitted) are given in Table.5. It was seen from the table that the increase in the load carrying capacity was 13% to 36% for the retrofitted specimens. It was also seen that the area of the load deflection curve up to a deflection of 75 mm for specimens retrofitted with a double layer of GFRP was 14 % and CFRP was 26 % more compared to the control specimens. The load deformation characteristics also improved to a larger extent in the case of wrapped specimens over the control specimens. This resulted in a substantial increase in the energy absorption characteristics of the specimens that were wrapped with both GFRP and CFRP.

    Experimental Investigation

    Conclusion

    Based on the experimental investigations carried out on the control and retrofitted beam-column joint specimens using GFRP & CFRP wrapping, the following conclusions were drawn:
    • There was 12% increase in load capacity and 13% increase in energy absorption capacity of the RC beam-column joint specimen, as the stirrup spacing is decreased as per code IS 13920:1993
      There was 13% increase in the load capacity and 14% increase in energy absorption capacity of the RC beam-column joint specimen, retrofitted using GFRP wrapping.
    • There was 36% increase in the load capacity and 26% increase in energy absorption capacity of the RC beam-column joint specimen, retrofitted using CFRP wrapping
    • The load deformation characteristics also improved to a larger extent in the case of the retrofitted specimens over the control specimens. This resulted in a substantial increase in the energy absorption characteristics of the specimens that were retrofitted using both GFRP and CFRP.
    • The enhancement in the energy absorption capacity of the wrapped specimens was in the range 14%-26% over the control beam-column joint specimens.
    • The failure was in the column portion of the joint for the control specimen which is to be avoided. In the case of the wrapped specimens, the failure was noticed in the beam portion only and the column was intact and this is the most preferred type of failure under seismic loads which will prevent progressive collapse of the structure.

    References

    Robert Ravi.S, Prince Arulraj.G., “Experimental Investigation on Influence of Development Length in Retrofitting Reinforced Concrete Beam-Column Joints”NBMCW 2009, Vol 4, Pg 148-158.

    K.R.Bindu and K.P.Jaya, “Performance of Exterior Beam Column Joints with Cross Inclined Bars Under Seismic Type Loading,” Journal of engineering and applied science, 2008 ,Vol 7, Pg 591-597.

    Alexander G. Tsonos, “Effectiveness of CFRP Jackets and RC Jackets In Post–earthquake and Pre– earthquake Retrofitting of Beam Column Sub Assemblages,” Journal of engineering structures 2008, Vol 30, Pg 777-793.

    G.A. Lakshmi, Anjan Dutta,and S.K.Deb, “Numerical Study of Strengthening of Beam Column Joints Under Cyclic Excitation Using FRP Composites,” Journal of structural engineering 2008,Vol 35, Pg 59-65.

    G. Appa roa, M.Mahajan and M.Gangaram, “Performance of Nonseismically Designed RC Beam Column Joints Strengthen by Various Schemes Subjected to Seismic Loads,” Journal of structural engineering 2008,Vol 35, Pg 52-58.

    Yousef A. Al-Salloum and Tarek H.Almusallam,”Seismic Response of Interior RC Beam Column Joints Upgrade with FRP Sheets. I: Experimental Study” Journal of composite for construction 2007, Vol 11, Pg 575-589.

    Yousef A. Al-Salloum and Tarek H.Almusallam, “Seismic Response of Interior RC Beam Column Joints Upgrade With FRP Sheets. II: Analysis And Parametric Study “Journal of composite for construction 2007, Vol 11, Pg 590-599.

    Devados Menon, Pradip Sarkar and Rajesh Agrawal, “Design of RC Beam Column Joints Under Seismic Loading–A Review.” Journal of structural engineering 2007, Vol 33, Pg 449-457.

    M.Jamal Shannag, and Nabeela Abu-Dyya, “Lateral Load Response of High Performance Fibre Reinforced Concrete Beam Column Joints” Journal of construction and building materials 2005 Vol 19, Pg 500-508.

    A.M.Said and M.L Nehdi, “Use Of FRP For RC Frame In Seismic Zones, Evaluation of FRP Beam Column Joints Rehabilitation Techniques” Journal of applied composite materials, 2004, Vol 11, Pg 205-226.63

    Abhijit Mukherjee and Mangesh Joshi, “FRPC Reinforced Concrete Beam Column Joints Under Cyclic Excitation” Journal of composite structures 2004, Vol 70, Pg 185-199.

    Costas P.Antonopoulos and Thanasis C. Triantafillou, “Experimental Investigation of FRP-Strengthened RC Beams Column Joints” Journal of composite for construction 2003, Vol 7, Pg 39-49.

    Costas P.Antonopoulos and Thanasis C. Triantafillou, “Analysis of FRP-Strengthened RC Beam Column Joints” Journal of composite for construction 2002, Vol 6, Pg 41-51. Ahmed Ghobaraah and A.Said, “Shear Strength of Beam Column Joints.” Journal of engineering structures 2002, Vol 24, Pg 881-888.

    T.El-Amoury and A.Ghobarah, “Seismic Rehabilitation of Beam Column Joints Using GFRP Sheets” Journal of engineering structures 2002, Vol 24, Pg 1397-1407.

    Ze-Jun Geng, Micheal J Chajes and Tsu-Wei Chou, “Retrofitting of Reinforced Concrete Column-To-Beam Connections” Journel of composite science and technology, Vol 58, Pg 1297-1305.

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