Journal of Composites for Construction

Since bridge deck slabs directly sustain repeated moving wheel loads, they are one of the most bridge elements susceptible to fatigue failure. Recently, glass fiber-reinforced polymer (FRP) composites have been widely used as internal reinforcement for concrete bridge deck slabs as they are less expensive compared to the other kinds of FRPs (carbon and aramid). However, there is still a lack of information on the performance of FRP–reinforced concrete elements subjected to cyclic fatigue loading. This research is designed to investigate the fatigue behavior and fatigue life of concrete bridge deck slabs reinforced with glass FRP bars. A total of five full-scale deck slabs were constructed and tested under concentrated cyclic loading until failure. Different reinforcement types (steel and glass FRP), ratios, and configurations were used. Different schemes of cyclic loading (accelerated variable amplitude fatigue loading) were applied. Results are presented in terms of deflections, strains in concrete and FRP bars, and crack widths at different levels of cyclic loading. The results showed the superior fatigue performance and longer fatigue life of concrete bridge deck slabs reinforced with glass FRP composite bars.

An experimental and analytical investigation of bond durability of E-glass fiber-reinforced polymer reinforcement bars in concrete beams is presented. Beams were conditioned with sustained flexural loads in indoor, outdoor, $60°\mathrm{C}$ alkaline solution, or freeze/thaw environments for up to $3\text{years}$ , after which they were subjected to eccentric three-point flexure tests to evaluate bond. Experimental bar force and slip were used to draw direct conclusions on bond durability, and also to calibrate a proposed local bond–slip model that incorporates concrete cover splitting. Experimental bar force at the onset of free-end slip varied little after any of the conditionings, although the characteristic of bond failure was noted to be less ductile in the moister environments. The interfacial fracture energy associated with bond–slip did not change with conditioning time in any of the environments except freeze/thaw, where a monotonic reduction versus time was seen. The effective bond length of the bar under various conditionings varied roughly in proportion to the local slip at complete local bond failure.

The effectiveness of external wrapping with fiber-reinforced polymer for enhancing the curvature ductility of lightly reinforced concrete members is investigated. Referring to members with circular transverse cross sections, the performances in terms of both strength and ductility capacities are analyzed, and the predictive reliability of two different recent constitutive models, available in the literature and able to take into account the softening behavior of confined concrete, is checked. A parameter characterizing the effectiveness of the confining wrapping is proposed, and characteristic values are suggested. Moreover, referring to ductility increases due to confinement effects, a comparison is made between the predictions obtained using the constitutive models and simple expressions given in recent codes. Parametric analyses carried out highlight the importance of a definition of the limits of validity of expressions given in the literature for estimation of ductility increases in order to avoid nonconservative assessment.

This paper reports the test results of 11 reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) sheets and subjected to an aggressive environment. In this study, eight beams were cracked and repaired with CFRP sheets, while the remaining three beams were kept uncracked as a control. The beams were $150\mathrm{mm}$ wide by $250\mathrm{mm}$ deep by $\mathrm{2,400}\mathrm{mm}$ long and lightly reinforced with a reinforcement ratio of 0.6%. Two types of carbon FRP products were considered: Sheets and strips. In terms of environmental exposure, three beams were kept at room temperature and eight beams were subjected up to 300 wetting and drying cycles with deicing chemicals (3% NaCl). Following the exposure, the beams were tested to failure in four-point bending. In addition, nondestructive tests were performed to determine the corrosion rate, as well as destructive tests to determine chloride diffusion and reinforcing bar mass loss. Based on the findings of the study, the long-term effectiveness of the CFRP strengthened reinforced concrete in aggressive corrosive environments was established.

Reinforced concrete (RC) beams subject to service loads of 40 or 60% of steel yielding were strengthened using hybrid continuous carbon fiber sheets. The hybrid systems were made of high-strength and high-modulus carbon sheets, and compared with systems using only high-strength carbon. It was found that the use of high-modulus carbon sheets in hybrid systems could increase the yielding load, the flexural stiffness, the postyielding ductility, and reduce the crack opening in concrete. The slope changes on load-deflection curves at steel yielding are not noticeable in hybrid systems. The tensile strains developed in hybrid sheets after the fracture of high-modulus carbon are higher in magnitude and distributed in a larger area, leading to an ultimate carbon fracture with concrete crushing. These unique features are attributed to the high stiffness and low ultimate tensile strain of the high-modulus carbon fibers which stiffen the structures, avoid or delay the fiber-reinforced polymer debonding, and facilitate the deformability during their subsequent breakdown.

The present paper investigates the suitability and effectiveness of fiber-reinforced polymers (FRP) in strengthening and/or repairing unreinforced masonry infill walls in reinforced concrete frames which are subjected to in-plane seismic/cyclic loading. For this purpose, a detailed experimental program was conducted. Specimen geometry, test setup, instrumentation, and a loading procedure that simulates earthquake loading are presented in a detailed fashion. Results of experimental observations are discussed in the form of load-displacement hysteretic loops and envelopes; column profiles; strain diagrams, and wall shear distortion. The test results, in general, indicate that the use of glass FRP (GFRP) sheets as strengthening materials provides a degree of enhancement to the infill wall, upgrades its deformation capacity, and makes the wall work as one unit. These results thus show great potential for externally bonded GFRP sheets in upgrading and strengthening the infill walls under in-plane seismic loads.

Seismic retrofitting of monument structures requires compliance with restrictive constraints related to the preservation of original artistic and structural features. Any conceived intervention must achieve structural performance yet still respect the appearance and structural mechanism of the original and be as minimally invasive as possible. Therefore, traditional retrofit strategies may not be suitable for such purposes, and structural engineers need to develop specific techniques. Innovative materials (e.g., composites) may be helpful, as demonstrated by the case study presented in this paper. Fiber-reinforced plastics (FRPs) were used for the design, analysis, and installation of the retrofit for the medieval bell tower in Serra San Quirico (Ancona, Italy). A FRP tie system is applied to the inner walls and anchored at the base by a reinforced concrete slab, independent of the tower’s foundation. The intervention enhances the seismic capacity of the structure and is fully provisional as it may be removed by heating the FRP with a hot air jet. The design process consisted of preliminary finite-element simulation and on-site structural assessment. Effectiveness is evaluated by a comparison of nonlinear static analyses (pushover) of the retrofitted and original structures. Finally, seismic risk reduction is computed by considering probabilistic seismic hazard at the site. Installation issues and the current appearance of the structure are also discussed.

The original design of existing aluminum overhead sign structures (OSS) did not consider fatigue as a limit state. Cracks propagate in the welds of the connection between the main chord and branches of OSS due to fatigue stresses caused by wind-induced vibration, which occasionally lead to complete fracture of the welds. A rehabilitation method for cracked aluminum welded connections using glass fiber-reinforced Polymer (GFRP) composites is investigated for its effectiveness under fatigue stresses. The results of constant amplitude fatigue tests for three types of aluminum connections from actual OSS are presented: (1) connections with no known cracks; (2) cracked connections rehabilitated with GFRP composites; and (3) connections with 90% of the weld removed and subsequently repaired with GFRP composites. The fatigue limits of the three connection types are established for four stress ranges including the constant amplitude fatigue limit threshold. The rehabilitated connections from OSS exceeded the fatigue limit of the aluminum welded connections with no known cracks. The repaired connections with 90% of the weld removed satisfied the constant amplitude fatigue limit threshold. A cumulative damage index is established which leads to a fatigue reduction factor for the rehabilitation design of cracked aluminum connections using the GFRP composites.

Fiber-reinforced polymer (FRP) composite beams are increasingly finding use in construction. Due to their lower stiffness relative to steel sections, the design of FRP structures is usually deflection controlled. Furthermore, shear deformation can be significant in FRP beams, thus, requiring the use of the Timoshenko beam theory to estimate deflections. However, the Timoshenko shear stiffness can be difficult to measure. Part of the measurement error has been attributed to shear warping effects. It has been hypothesized that warping restraints at loading points and supports increase the apparent shear stiffness to a degree that is significant at relatively short spans, e.g., $L∕h<10$ to 15. In this study, the influence of warping on short to moderate length FRP beams under various types of loading and boundary conditions is considered using finite-element analysis. In particular, a commercially available thin-walled FRP beam was investigated. The results suggest that warping has a negligible effect for thin-walled beams at reasonable spans, i.e., $L∕h>5$ . On the contrary, the effective shear stiffness is found to decrease at shorter span lengths. This is the first of two papers in a series.

This is the second of two papers devoted to the issue of measuring the Timoshenko shear stiffness of thin-walled composite beams. In the first paper, the effect of warping on the effective Timoshenko shear stiffness, as measured through bending tests, was studied. The bending test was simulated using finite-element analysis, and the results indicated that the warping effect was minimal. On the other hand, the evidence suggests that transverse flexibility may have a significant influence on the effective Timoshenko shear stiffness, decreasing the effective shear stiffness at shorter test spans. The purpose of the present study is to further investigate this effect and to explore the use of a sandwich theory to predict the measurement error. A higher-order sandwich theory, which captures the transverse strain at concentrated loads and supports, is applied to a commercially available thin-walled composite beam. The results indicate that the sandwich model does capture the decrease in the effective shear stiffness at short spans, and the dependence of the shear stiffness on span-to-depth ratio is similar to that calculated in the first paper, using the finite-element method.