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Journal of Composites for Construction

Journal of Composites for Construction

Archives Papers: 294
The American Society of Civil Engineers
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Experimental and Analytical Study of Bond Stress–Slip Behavior at the CFRP-to-Concrete Interface
Abbas Fathi; Georges El-Saikaly, M.ASCE; and Omar Chaallal, F.ASCE
Abstracts:The application of externally bonded (EB) carbon fiber reinforced polymer (CFRP) systems for strengthening existing structures, such as RC beams, has been widely approved in the construction industry worldwide for its numerous benefits. The CFRP-to-concrete bond has a governing role in the reliability and effectiveness of EB-CFRP systems. Indeed, failure of the CFRP-to-concrete bond can lead to rupture of CFRP-strengthened structures. Hence, ongoing research into assessment of bond behavior at the CFRP-to-concrete interface helps to bring more insightful clarity to the use of EB-CFRP strengthening techniques. The aim of this study is to evaluate the bond behavior between CFRP and concrete by conducting a series of pullout tests. The parameters considered include CFRP type (sheet versus laminate), bonded length, and bonded CFRP width. The results show that using CFRP fabric sheets can contribute to higher bond load-carrying capacity and ductility than CFRP laminates. Furthermore, through the analyses of databases in the literature, a bilinear bond–slip model is proposed that takes into account the CFRP width factor. Through a comparison, it is shown that the proposed model performs well in terms of predicting the maximum local bond stress and CFRP slippage.
Behavior of Reinforced Concrete Beams without Stirrups and Strengthened with Basalt Fiber–Reinforced Polymer Sheets
Wei Zhang, M.ASCE ; Shuaiwen Kang ; Yiqun Huang ; and Xiang Liu
Abstracts:This paper reports on a series of four-point bending experiments to investigate the shear capacity of reinforced concrete (RC) beams strengthened with externally bonded basalt fiber–reinforced polymer (BFRP) sheets. The experimental results show that BFRP sheets can significantly increase RC beams’ shear capacity and ductility. To analyze the fracture and mechanical behaviors of BFRP sheet–strengthened RC beams, a three-dimensional (3D) finite-element model (FEM) based on the application of cohesive elements was developed. Mixed-mode constitutive models of the BFRP–concrete interface, the concrete potential fracture surface, and the reinforcement–concrete interface were proposed. The proposed constitutive models were able to characterize the interface’s normal separation, tangential slip, and friction. A comparison of the simulation and experimental results indicates that the proposed numerical model can appropriately simulate the mechanical response, crack propagation, and crack distribution of BFRP sheet–strengthened RC beams. Finally, based on the proposed 3D FEM, a series of numerical tests were conducted to investigate the influence of key parameters (i.e., sheet elastic modulus, sheet bonding area, and sheet bonding angle) on the shear capacity of BFRP sheet–strengthened RC beams.
Experimental Study on Flexural Cracking and Deformation of Reinforced-Concrete Beams Strengthened with NSM FRP Reinforcement
Cristina Barris, Ph.D. ; Marta Baena, Ph.D. ; Younes Jahani ; Alba Codina ; and Lluís Torres, Ph.D.
Abstracts:A near-surface-mounted (NSM) technique using fiber-reinforced polymer (FRP) reinforcement increases the load-bearing capacity and stiffness of reinforced-concrete (RC) beams and delays the yielding moment. In those cases, the verification of serviceability limit states becomes necessary to guarantee functionality and protection of steel reinforcement. At present, there is a lack of provisions for the crack width prediction, mainly because of the scarceness of experimental data. This work presents the results of an experimental program aiming at studying the effect of different NSM reinforcement arrangements on the midspan deflection, crack spacing, and crack width of NSM FRP RC beams. One RC beam and 11 NSM FRP RC beams were tested under a four-point bending configuration up to failure. Carbon- and glass-FRP rods were used. It was found that NSM FRP reinforcement provides an effective reduction in deflection, crack width, and spacing. Larger crack formation phases were observed in all strengthened specimens. Moreover, crack width decreases with the increase of the NSM FRP reinforcement ratio. Finally, cracks at the bottom of the beam are around 11%–25% wider than at the height of the steel internal reinforcement.
Compressive Behavior of Concrete-Filled Filament-Wound FRP Tubes with Local Tube Damage
Guan Lin, Aff.M.ASCE ; and Yu Xiang
Abstracts:Concrete-filled fiber-reinforced polymer (FRP) tubes (CFFTs) are an emerging and attractive form of column for new constructions. Such a column consists of outer filament-wound FRP tubes that are filled with plain or steel-reinforced concrete. The fibers in the filament-wound FRP tube are predominantly in the hoop direction to confine the inner concrete, which leads to significantly enhanced strength and ductility in the confined concrete. Extensive studies have been conducted on the behavior of CFFTs that were subjected to various loading conditions, which confirmed the excellent performance of such members. As CFFTs become increasingly used in practice, there is a concern about the performance of CFFTs when the FRP tube is subjected to local damage that is caused by accidents, vandalism, or designed holes or cuts to accommodate connections with other structural components. Some studies have been carried out on the performance of CFFTs as flexural members with a locally damaged filament-wound FRP tube; however, the research on such CFFTs as columns remains limited. This paper presented the results of a comprehensive experimental program on the axial compressive behavior of CFFTs with a filament-wound FRP tube that was subjected to local tube damage. Two types of damage (i.e., holes and cuts) with different parameters were investigated. The test results showed that the compressive strength [i.e., peak stress ( f cc )] and the corresponding axial strain (ɛcc) of the damaged CFFTs were significantly reduced due to the local tube damage (e.g., f cc reduced from 12.2% to 64.8% and the corresponding ɛcc reduced from 35.2% to 77.2%). Finally, an existing model for FRP-confined concrete that considered the local FRP damage was evaluated which suggested the need for the recalibration of the model or the development of a new model for CFFTs with a locally damaged filament-wound FRP tube.
Experimental Verification of Load-Bearing Capacity of FRP Bars under Combined Tensile and Shear Forces
Frantisek Girgle ; Ondrej Janus ; Vojtech Kostiha ; and Petr Stepanek
Abstracts:In recent decades, the number of applications of fiber-reinforced polymer (FRP) reinforcement for concrete has significantly expanded. This fact is mainly due to the FRP reinforcement cost competitiveness, the increasing availability of design provisions, and due to the advantageous physical-mechanical and chemical properties of this composite material, which open up new possibilities for the design and implementation of extremely durable elements. Currently, the most commonly used types of reinforcement bars are those containing glass FRP (GFRP) or basalt FRP fibers, which is mainly the result of their favorable price and high resistance to aggressive environments. The use of composites in construction is wide-ranging: it is possible to apply FRP bars not only in the design and strengthening of concrete structures but also in the installation of shear dowels in concrete pavement, as rock bolts or as anchors for overhanging facade components. In the case of the design of load-bearing elements subjected to a combination of tensile and shear force, it is necessary to quantify their shear resistance and concisely describe the effect of the interaction of the tensile and shear force on the load-bearing capacity of the reinforcing element. This is a broadly addressed area as regards composite laminates and fabrics, but when it comes to FRP bars, there are very few available experimental results. For that reason, this research deals with the experimental testing and quantification of the influence of the interaction of normal and shear force. The behavior of GFRP bars from two different manufacturers, with three different diameters, different surface treatments, and mechanical characteristics, was experimentally verified. The findings are presented, a material failure curve is compiled, and the results are compared with those predicted according to the available relationship for composite laminates and von Mises theory.
Experimental and Numerical Study on Seismic Performance of PEN FRP-Jacketed Circular RC Columns
Yu-Lei Bai; Yu-Feng Zhang; Peng-Xuan Sun; Jian-Guo Dai; and Togay Ozbakkaloglu, M.ASCE
Abstracts:This paper presents an experimental study on the seismic behavior of polyethylene naphthalate (PEN) fiber–reinforced polymer (FRP)-jacketed circular reinforced-concrete (RC) columns. A total of seven specimens were tested under constant axial load and cyclic lateral load. The key parameters studied were the thickness (one, two, and three layers) and type (PEN FRP and CFRP) of FRP jacket. Test results indicated that the control column failed by buckling of the longitudinal reinforcement and shortage of ductility, while concrete spalling and bar buckling were effectively inhibited by the application of external FRP jacket. It is also observed that PEN FRP-jacketed specimens had more additional strain capacity compared with CFRP-jacketed specimens at the final condition. The additional strain capacity can serve as a safety reserve for structures and make PEN FRP more suitable for strengthening large or noncircular columns. Furthermore, it is found that 1-ply PEN FRP and 1-ply CFRP had a similar strengthening effect and thus the design of PEN FRP-strengthened column can simply refer to the design method of CFRP-strengthened columns in current codes. Different FRP thickness and types had marginal impact on the hysteretic curves of the specimens, which was attributed to the low axial load ratio (0.15) and high slenderness ratio (5.25) adopted in this paper. Finally, based on a cyclic stress–strain model for longitudinal reinforcement, including buckling effect, developed by the authors in a previous study, the test columns were simulated by the Open System for Earthquake Engineering Simulation (OpenSee)s to achieve an in-depth understanding of the experimental findings and associated strengthening mechanisms. Further parametric analyses showed that considering bar buckling played a significant role in accurately predicting the hysteretic response of FRP-jacketed columns.
Fatigue Repair of Cracked Steel Plates Using Small-Patch Ultrahigh-Modulus CFRP Governed by Bond Failure
Liam Knoll; Amir Fam, F.ASCE; Joshua E. Woods, Aff.M.ASCE; and Brahim Benmokrane
Abstracts:This study evaluates the effectiveness of externally bonded small-patch ultrahigh-modulus (UHM) carbon fiber–reinforced polymer (CFRP) plates of 460 GPa modulus in extending fatigue life and slowing crack propagation in steel plates with simulated fatigue cracks. The study investigates a range of very short bond lengths for applications where bonding space may be limited or accessibility restricted, together with the effect of single- versus double-sided application, on fatigue performance. It also compares short UHM CFRP plates with similar length normal modulus (NM) (165 GPa) CFRP plates with regard to extending fatigue life and reducing stress concentration at the crack tip. Distributed fiber-optic sensors (DFOS) and digital-image correlation (DIC) are used to capture the full strain field and track crack growth. Results showed that fatigue life was increased by up to 2.0 and 2.34 times for single- and double-sided UHM CFRP repairs. As bond length increased from 25 to 100 mm, fatigue life increased from 1.36 to 2.0. UHM CFRP more effectively reduced stress concentration at the crack tip, by 60% compared with 37% for NM CFRP, indicating that it has the potential for superior fatigue life gains, relative to NM CFRP if the necessary bond length to prevent or delay debonding is provided. As debonding failure governed in this study, NM CFRP plates achieved comparable fatigue life extension. DIC tracking of crack growth matched the traditional “beach marking” technique with less than 6% difference.
Dilation Characteristics of FRP-Confined Square Engineered Cementitious Composite Columns
Pengda Li, A.M.ASCE ; Deqing Huang ; Yingwu Zhou ; and Songbin Zheng
Abstracts:As emerging high-performance concrete, the engineered cementitious composite (ECC) has demonstrated excellent application potential in civil engineering. With the wide application of ECC, it not only excels in the tension state and the structural elements but also in the more complex stress state of nonuniform confinement. For a reliable and economic ECC element design, understanding the dilation behavior of ECC is crucial under complicated stress conditions. This paper presents an experimental investigation and a detailed discussion of the ECC dilation characteristics under different confinement rigidities. The authors evaluate the effects of column parameters, such as different types of fiber-reinforced polymer (FRP) composites, confinement levels, and cross-sectional shapes. Test results indicate that the ECC dilation amplitude (secant dilation) under FRP confinement is less than that of concrete due to fiber bridge effects within ECC. However, the maximum dilation rate (tangent dilation ratio) shows an opposite trend. Based on the data analysis in this study, a new lateral strain-to-axial strain model was proposed, which can predict the dilation behavior of FRP-confined ECC with nonuniform confining pressure. The proposed model not only accurately captures the dilation process of FRP-confined ECC but also precisely predicts its ultimate strain. In addition, the existing peak strength and ultimate strength models were also evaluated by the ECC test results. The comparison indicates that the strength models for concrete also apply to FRP-confined ECC when the ultimate hoop-confining stress is accurately determined.
Cyclic Behavior of Beam–Column Pocket Connections in GFRP-Reinforced Precast Concrete Assemblages
Tohid Ghanbari-Ghazijahani ; Reza Hassanli ; Allan Manalo ; Scott T. Smith ; Tom Vincent ; Rebecca Gravina ; and Yan Zhuge
Abstracts:This paper presents details of an experimental program evaluating the behavior of six half-scale glass fiber–reinforced polymer (GFRP) reinforced concrete beam–column precast members connected together through pocket connections, which are subjected to cyclic loading. The novel beam–column connection was constructed by incorporating either epoxy resin or tensioned or untensioned GFRP rock bolts in conjunction with different-sized pocket connections. The effects of an additional connection bar between the column and beam components in the connection, as well as the confinement of the concrete around the pocket region, were also investigated. An innovative test setup was designed so that the beam–column joint could rotate without restraint provided by the supports. All specimens were tested under an incrementally increasing cyclic load. The load-carrying capacity, deformational behavior, failure modes, energy dissipation, and hysteretic damping were all recorded and evaluated. All specimens failed as a result of column failure within the pocket connection region. This was attributed to the relative rotational flexibility of the column with respect to the beam, owing to the low elasticity of the epoxy resin used in the pocket region, and hence the stress concentration at the column ends within the pocket area. According to the results, a pocket connection containing GFRP reinforcement providing confinement around the embedded area yielded the highest capacity, ductility, and energy dissipation under cyclic loading. The connection containing a GFRP bolt, regardless of whether or not the bolt was prestressed, did not significantly improve the performance of the connection. The findings presented here can be used for the design of precast elements reinforced with GFRP bars. Of particular relevance is application to jetties and other offshore concrete infrastructure where steel reinforcement (because of corrosion issues) needs to be replaced with GFRP reinforcement.
Experimental Study on the Bond Performance of Steel–Basalt Fiber Composite Bars in Concrete
Shengjiang Sun ; Lili Xing ; Peng Gui ; Bo Li ; Hangyu Li ; Lei Zhao ; and Kuihua Mei
Abstracts:Steel–basalt fiber composite bars (SBFCBs) exhibit excellent strength, elastic modulus, toughness, corrosion resistance, and low cost. Understanding the bond performance between SBFCBs and concrete is important for evaluating the mechanical behavior of SBFCB-reinforced concrete structures. In this study, the bond–slip performance of SBFCB in concrete was experimentally assessed via pullout and beam bond tests. The influence of various factors on the bond performance was discussed, and the bond mechanism between SBFCB and concrete was analyzed. The results indicate that reducing the thread pitch ratio in the SBFCB can reduce slippage at the postpeak bonding stress–slip curve. The bond strength of the SBFCB was significantly improved by sandblasting. Longer bond lengths correspond to smaller average bond strengths in SBFCB. The load corresponding to the maximum bond strength of a specimen with a bond length of 10d was determined as the ultimate load value for the SBFCB. An increase in the SBFCB diameter had a negative impact on the bond strength. Moreover, an increase in the concrete cover thickness was conducive to improving the bond strength; if the thickness of the concrete cover was sufficiently increased, failure occurred owing to SBFCB tension rather than bonding. Based on the test results and the existing bond–slip model, a simple bond–slip constitutive model of the SBFCB embedded in concrete was proposed to simulate the pullout process of the SBFCB. Subsequently, the established bond–slip model can be used to analyze the mechanical performance of SBFCB-reinforced concrete structures.
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