Efficiency of Externally Bonded L-Shaped FRP Laminates in Strengthening Reinforced-Concrete Interior Beam-Column Joints Jiangtao Yu, Aff.M.ASCE 1 ; Xingyan Shang 2 ; and Zhoudao Lu 3 Abstract: This study investigated the efficiency of externally bonded L-shaped fiber-reinforced polymer (FRP) laminates in strengthening seismically damaged reinforced concrete (RC) interior joints. Ten ½-scale interior beam-column joints, including two reference specimens, were constructed and then damaged under simulated cyclic lateral loads. In addition to repairing visual cracks with epoxy injections, four of eight specimens were strengthened with externally bonded L-shaped carbon fiber–reinforced polymer (CFRP) laminates and the rest were strengthened with basalt fiber–reinforced polymer (BFRP) laminates. Retesting after retrofitting showed that the average peak strength of the CFRP-strengthened and BFRP-strengthened specimens increased by approximately 20 and 10%, respectively. The two strengthening systems also clearly enhanced the deformability of the specimens. Further analysis indicated strength increase was controlled by the end debonding of FRP laminates near critical sections of the specimens, thus the bending strengthening formulas, which were extensively used in practice, overestimated the strengthening efficiency. To solve this problem, alternative formulas accounting for the end debonding of FRP were pro- posed to predict the peak strength and FRP strain of the specimens. The predictions showed acceptable agreement with the test results, demonstrating the proposed formulas were applicable to predict the efficiency of externally bonded L-shaped FRPs in strengthening damaged interior framed joints. DOI: 10.1061/(ASCE)CC.1943-5614.0000622. © 2015 American Society of Civil Engineers. Author keywords: Fiber-reinforced polymer (FRP); Seismic damage; Beam-column joint; Retrofit; Seismic performance. Introduction Because of inadequate orthogonal reinforcements or weak-column/ strong-beam design philosophy following outdated codes (without seismic modifications), joint failures have been widely observed in numerous existing reinforced concrete (RC) structures subjected to severe earthquake loadings. The Kocaeli earthquake in Turkey in 1999 is an example of this type of failure (Ghobarah and Said 2002). Consequently, joint strengthening has caused concerns in the area of seismic design for RC structures. Common rehabilita- tion techniques, such as the use of RC or steel jackets, have been extensively investigated by researchers including Alcocer and Jirsa (1993), Ghobarah et al. (1997), Tsonos (1999), and Hakuto et al. (2000). In recent years, externally bonded fiber-reinforced polymer (EB-FRP) strengthening has been extensively studied (Bousselham 2010) and widely applied in engineering practice. Compared with traditional rehabilitation techniques, fiber-reinforced polymers (FRPs) have the advantages of being lightweight and high-strength, corrosion resistant, and easy to construct in a relatively short time (Pantelides et al. 2008). FRP materials have the potential to upgrade the seismic perfor- mance of RC structures. Pantelides et al. (2000) strengthened an external beam-column joint with carbon fiber–reinforced polymer (CFRP) laminates. The retrofitted specimen was wrapped with multiple layers of CFRP sheets. The joint strength increased by 25% and the specimen reached 5% drift. Gergely et al. (2000) demonstrated the viability of CFRP composites for their use in im- proving the shear capacity of beam-column T joints as evidenced by experimental results. Granata and Parvin (2001) performed experimental studies for evaluating the moment capacity of the beam-column connections wrapped with Kevlar FRP fabric. Exper- imental results demonstrated that the moment capacity of beam- column connections increases by up to 60% and the column wraps should be at least 35% greater than the overlay thickness. Gergely et al. (1998) performed experiments involving the 1=3-scale testing of exterior beam-column joints with several wrapping configura- tions of advanced composite materials. The authors concluded that CFRP composite effectively improved the strength and ductility of the beam-column joint. Ghobarah and Said (2001) investigated the behavior of beam-column joints wrapped with glass fiber– reinforced polymers (GFRPs). The behavior of the rehabilitated specimen was significantly improved. The failure in the beam- column joint was replaced by the ductile flexural hinging of the beam. In addition, Ghobarah and Said (2001, 2002), El-Amoury and Ghobarah (2002), Ghobarah and El-Amoury (2005), and Li et al. (2002) used FRPs to enhance the strength of exterior joints. Positive effects were reported on both the stiffness and load- carrying capacity. The experimental research program of Pantelides et al. (2008) indicated that CFRP jackets were effective reha- bilitation measures for improving the seismic performance of interior beam-column joints with inadequate seismic protection. Antonopoulos and Triantafillou (2003) investigated the behavior of beam-column joints strengthened with FRPs through the 2=3-scale testing of 18 exterior joints. Test results showed that mechanical anchorages played an important role in limiting prema- ture FRP debonding. Additionally, Karayannis and Sirkelis (2008) 1 Associate Professor, Research Institute of Structural Engineering and Disaster Reduction, Tongji Univ., Shanghai 200092, China (corresponding author). E-mail: [email protected] 2 Ph.D. Candidate, Research Institute of Structural Engineering and Disaster Reduction, Tongji Univ., Shanghai 200092, China. 3 Professor, Research Institute of Structural Engineering and Disaster Reduction, Tongji Univ., Shanghai 200092, China. Note. This manuscript was submitted on November 28, 2014; approved on July 22, 2015; published online on October 9, 2015. Discussion period open until March 9, 2016; separate discussions must be submitted for individual papers. This paper is part of the Journal of Composites for Construction, © ASCE, ISSN 1090-0268. © ASCE 04015064-1 J. Compos. Constr. J. Compos. Constr., 2016, 20(3): -1--1 Downloaded from ascelibrary.org by Tongji University on 12/30/16. Copyright ASCE. For personal use only; all rights reserved.
Efficiency of Externally Bonded L-Shaped FRP Laminates in Strengthening Reinforced-Concrete Interior Beam-Column Joints
Jun 20, 2023
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