Experimental analysis of shear deficient reinforced concrete beams strengthened by glass fiber strip composites and mechanical stitches

Ceyhun Aksoylu 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.40 No.2

This study was conducted to present a new technique to increase the capacity of reinforced concrete beams with insufficient shear reinforcement. Four beam specimens at ½ scale were produced. One of these beams was used for reference, while the other three were strengthened using different methods. The strengthening methods were performed using Mechanical stitches (MS), Glass fiber reinforced polymer (GFRP), and a hybrid of the two (GFRP and MS). In the experiments, the reference beam (E0), the MS-strengthened beam (E1), the GFRP-strengthened beam (E2), and the GFRP+MS-strengthened (E3) beam were tested under vertical load. Following the experiment, vertical load-bearing capacity, ductility value, initial stiffness value, and energy dissipation capacity were calculated for each beam. Afterward, extensive micro and macro damage analyses were performed. In the experiment, the E0 specimen resulted in a failure mode with direct shear damage. The strengthened E1 and E2 beams showed a typical bending behavior. The vertical load-bearing capacity of the E1 and E2 beams increased by 16.8% and 18.1%, respectively, compared to E0. The load-bearing capacity of the newly proposed technique, the hybrid E3 beam, was increased by 19.2%, although it failed with shear damage. Thus, this study has clearly demonstrated that beams with insufficient shear reinforcement can be strengthened using single-layer GFRP (E2). Considering its cost-efficiency compared to other composite materials, it has been suggested that GFRP should be used more widely in the market. In addition, it is reccommended that future studies can use the proposed E1 strengthening for beams weak against shear. The experiments revealed the most appropriate strengthening method for shear beams to be E1>E2>E3 in terms of performance/cost. Finally, the results suggest that the proposed hybrid strengthening (E3) can be turned to a ductile behavior through further experiments with different configurations.

FRP로 보강된 RC보의 전단보강효과 비교연구

심종성,김규선 한국콘크리트학회 1998 콘크리트학회지 Vol.10 No.4

본 논문의 목적은 전단내력이 부족한 R/C보에 CFS(Carbon Fiber Sheets), CFRP(Carbon Fiber Reinforced Plastic), GFRP(Glass Fiber Reinforced Plastics)를 이용해 전단보강을 할 경우에 보의 역학적 거동특성을 규명하기 위한 것이다. 본 논문의 목적을 달성하기 위하여 총 19개의 시험체가 제작되었으며, 실험변수로는 전단스팬비, 보강재료, 보강방법, 보강간격 및 방향을 산정하였다. 본 논문의 실험결과, FRP를 이용해 전단내력이 부족한 R/C보에 보강을 하였을 경우 약 50~70%정도의 보강효과를 나타내었다. 또한 소성이론에 근거한 철근콘크리트보의 전단강도 예측모델을 개발하였고 실험치와의 비교를 통해 개발된 모델의 적합성을 검증하였다. This study presents test results of RC beams strengthened by carbon fiber sheet(CFS), carbon fiber reinforced plastics(CFRP) or glass fiber reinforced plastics(GFRP) for increasing shear resistance. Nineteen specimens were tested, and the test was performed with different parameters including the type of strengthening materials(CFS, GFRP, CFRP), shear-strengthening methods(wing type, jacket type, strip type), strip-spacing, strengthening direction of FRP. The test results show that shear-damaged RC beams strengthened by FRP(CFS, GFRP, CFRP) have more improved the shear capacity. The mathematical model based on plastic theory was also developed to predict shear strength of shear-damaged RC beams strengthened by FRP. The predictions using the mathematical model. are agreed with the observations from the observed shear strengths for 19 test beams.

Shear-Strengthening of Reinforced & Prestressed Concrete Beams Using FRP

Moustapha Ibrahim Ary,Thomas H.-K. Kang 한국콘크리트학회 2012 International Journal of Concrete Structures and M Vol.6 No.1

Fiber-Reinforced Polymers (FRP) are used to enhance the behavior of structural components in either shear or flexure. The research conducted in this paper was mainly focused on the shear-strengthening of reinforced and prestressed concrete beams using FRP. The main objective of the research was to identify the parameters affecting the shear capacity provided by FRP and evaluate the accuracy of analytical models. A review of prior experimental data showed that the available analytical models used to estimate the added shear capacity of FRP struggle to provide a unified design equation that can predict accurately the shear contribution of externally applied FRP. In this study, the ACI 440.2R-08¹ model and the model developed by Triantafillou and Antonopoulos² were compared with the prior experimental data. Both analytical models failed to provide a satisfactory prediction of the FRP shear capacity. This study provides insights into potential reasons for the unsatisfactory prediction.

난연성 FREP에 의한 철근콘크리트 보의 전단보강 성능평가

강기연,최기선,한상환,유영찬 대한건축학회 2003 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.23 No.2(구조계)

The purpose of this study is to evaluate the shear strengthening effects of the iFREP(incombustible Fiber Reinforced Epoxy Panel) to the reinforced concrete members and to provide the basic design recommendation for shear strengthening. The main variable were the thickness of iFREP, the amount of stirrup and the type of strengthening. Thirteen specimens were tested under static monotonic loading. From the test results, it was shown that the failure mode of RC beams which are strengthened by iFREP was governed by the delamination of iFREP. The shear capacity of beams strengthened by iFREP can be determined as the summation of the shear strengths provided by concrete, stirrup, and iFREP The shear strength by iFREP should be calculated based on the effective strain of iFREP. Also, the shear strengthening effects of specimen with two-side bonded iFREP is similar to those of specimen with three-side bonded iFREP (U-TYPE).

Shear-strengthening of RC continuous T-beams with spliced CFRP U-strips around bars against flange top

Chaoyang Zhou,Da Ren,Xiaonian Cheng 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.64 No.1

To upgrade shear performance of reinforced concrete (RC) beams, and particularly of the segments under negative moment within continuous T-section beams, a series of original schemes has been proposed using carbon fibre-reinforced polymer (CFRP) U-shaped strips for shear-strengthening. The current work focuses on one of them, in which CFRP U-strips are wound around steel bars against the top of the flange of a T-beam and then spliced on its bottom face in addition to being bonded onto its sides. The test results showed that the proposed scheme successfully provided reliable anchorage for U-strips and prevented premature onset of shear failure due to FRP debonding. The governing shear mode of failure changed from peeling of CFRP to its fracture or crushing of concrete. The strengthened specimens displayed an average increase of about 60% in shear capacity over the unstrengthened control one. The specimen with a relatively high ratio and uniform distribution of CFRP reinforcement had a maximum increase of nearly 75% in strength as well as significantly improved ductility. The formulas by various codes or guidelines exhibited different accuracy in estimating FRP contribution to shear resistance of the segments that are subjected to negative moment and strengthened with well-anchored FRP U-strips within continuous T-beams. Further investigation is necessary to find a suitable approach to predicting load-carrying capacity of continuous beams shear strengthened in this way.

Direct Shear Test of Retrofit Anchors Using Deformed Reinforcement and Adhesive

Choi, Dong-Uk,Kim, Yong-Gon Korea Concrete Institute 2000 KCI concrete journal Vol.12 No.1

A new type of retrof=t anchor bolt that uses deformed reinforcing bars and a commercial adhesive was developed and then an experimental study was carried out to determine the behavior of the anchors in direct shear. The steel-to-concl몫ete interface was tested. Plain concrete slabs with about 20-MPa compressive strength were used for 23 direct shear tests performed Test variables were anchor diameters (D16, D22. and D29) and edge effect. Three different shear tests were completed: simple shear, edge shear where anchors were pulled against the concrete core, and edge shear where anchors were pushed against the concrete cover In the simple and the edge shear tests where the anchors were pulled against the core, the theoretical dowel strength determined by (equation omitted) was achieved but with relatively large displacements. The shear resistances increased with the increasing displacements. In the edge shear test where the anchors were pushrd against the cover, the peak shear strengths signif=cantly lower than the theoretical dowel strength were determined due to cracks developed in concrete when the edge distance was 80 mm. The peak strengths were about 50% of the dowel strength for Dl6 bar. and about 25% or less of the dowel strength for D22 and D29 bars. Test results revealed that the edge shear where the anchor was pushed against the cover controled.

Experimental and Numerical Investigation of Shear Behavior of RC Beams Strengthened by Ultra-High Performance Concrete

Ashraf Awadh Bahraq,Mohammed Ali Al-Osta,Shamsad Ahmad,Mesfer Mohammad Al-Zahrani,Salah Othman Al-Dulaijan,Muhammad Kalimur Rahman 한국콘크리트학회 2019 International Journal of Concrete Structures and M Vol.13 No.1

This paper presents a study on the shear behavior of reinforced concrete (RC) beams strengthened by jacketing the surfaces of the beams using ultra-high performance fiber reinforced concrete (UHPC). The surfaces of the RC beams were prepared by sandblasting and UHPC was cast in situ over the surfaces of RC beams. The beams were strengthened using two different strengthening configurations; (i) two longitudinal sides strengthening (ii) three sides strengthening. The bond between normal concrete and UHPC was examined by conducting splitting tensile strength and slant shear strength tests on composite cylindrical specimens cast using normal concrete and UHPC. The control and strengthened beam specimens were tested using four-point loading arrangement maintaining different shear span-to-depth ratios. The results of tested beams showed the beneficial effects of strengthening the RC beams using UHPC, as evident from enhancement of the shear capacity and shifting of the failure mode from brittle to ductile with more stiff behavior. In addition, a non-linear finite element model (FEM) was developed to examine the sufficiency of the experimental results used to study the shear behavior of control and strengthened beams. The failure loads and the crack patterns determined experimentally matched well with those predicted using the proposed model with a reasonably good degree of accuracy.

강섬유콘크리트의 전단보강 효과에 대한 고찰

장극관 ( Chang Keug-kwan ),이현호 ( Lee Hyun-ho ),양승호 ( Yang Seung-ho ) 한국구조물진단유지관리공학회 2000 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.4 No.1

Since the steel fiber (SF) used in concrete to improve shear and ductility capacity, a number of laboratory tests have studied to define shear-strengthening effects according to span-to-depth ratio (a/d) and SF contents (V_f) in concrete. This study investigates shear-strengthening effects of SF from the literature studies, and investigation parameters are with or without shear reinforcement, a/d and f. From the test results review, following conclusions can be made; the maximum shear-strengthening effect can be achieved at about 1.5 % of V_f and 1.5 to 2.5 of a/d

Experimental Study of the Shear Behavior of RC Beams Strengthened with High-Performance Fiber-Reinforced Concrete

Najib Gerges,Camille A. Issa,Elias Sleiman,Melissa Najjar,Ali Kattouf 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.3

In this study, the efficacy of strengthening of reinforced concrete (RC) beams in shear by utilizing high-performance fiber-reinforced concrete (HPFRC) was explored. The shear strengthening was achieved by epoxy bonding of prefabricated HPFRC strips or plates onto the beams. The beams were strengthened utilizing two different strengthening schemes: (i) plates side strengthening (ii) vertical strips applied at shear critical sections. The behavior of the two configurations was compared to the behavior of non-shear reinforced and shear-reinforced RC beams. The high-performance concrete (HPC) utilized contains 1.5% of steel fibers per volume of HPC mortar and is known as HPFRC. Parameters determined were the flexural strength and compressive strength of HPFRC mortar. The obtained results revealed that HPFRC realized a 28-day flexural strength of 20 MPa and a compressive strength of 108 MPa. Moreover, HPFRC strengthened RC beams experienced an increased in strength capacity of about 50% for plates and 36% for vertical strips compared to the RC beams with no stirrups. The results for HPFRC strengthened beams with plates were superior compared to those of the stirrup-reinforced beams, whereas the results of HPFRC strips strengthened beams were almost identical to the stirrup-reinforced beams. Also observed, was an improvement in the ductility of the beams with the best results achieved when employing HPFRC plates and strips.

Shear strengthening of reinforced concrete beams using NSM/EBR techniques

Abdel-kareem, Ahmed H.,Debaiky, Ahmed S.,Makhlouf, Mohamed H.,Abdel-baset, M. Techno-Press 2021 Advances in concrete construction Vol.12 No.1

This paper presents the experimental results of research into the behavior of shear-enhanced reinforced concrete R.C beams using steel stirrups, Fiber Reinforced Polymers FRP rods, and Fiber Reinforced Polymers FRP strips. This enhancement was accomplished by the Near Surface Mounted technique NSM. The NSM technique contains a groove on the outside surface of the concrete member to adjust the depth to be less than the cover of the member. After cleaning, the epoxy paste was used to fill half of the groove's depth. In the groove, the particular FRP element is then installed. Finally, the groove is filled with epoxy and the outside surface of the concrete is levelled with so much epoxy. This method enables the fiber reinforcement polymer FRP materials is covered completely by epoxy. The objective of this research is to study the effect of NSM technique on shear resistance for stressed beam. 13 experimental studies of half-scale R.C beams were involved in this paper. The experimental program included two specimens strengthened with steel stirrups, eight specimens strengthened with stirrups of Glass Fiber Reinforced Polymer GFRP rods with the shape of deferent end anchorage and angle, two specimens strengthened with externally bonded GFRP strips. The remaining un-strengthened specimen was allocated for comparison as a control one. The test results included ultimate load of capacity, deflection, cracking, and failure mode. All beams enhanced with GFRP rods showed a capacity improvement ranging from 14% to 85% compared to the reference beam, and compared to the reference beam, beams enhanced with GFRP strips showed a capacity improvement ranging from 7% to 22%.