Journal of Composites for Construction

Interaction between static fatigue and zero stress aging of E-glass fiber composites is investigated. A comprehensive gathering of available experimental data for E-glass fibers and unidirectional composites is presented. A methodology is proposed that allows us to utilize seemingly ill-assorted data developed under noncomparable environmental exposure conditions. This is made possible by using the concept of inert aged strength, which allows us to homogenize all aging data regardless of the conditions of exposure by shifting it to the inert condition. Such inert aged data is then used to generalize the static fatigue model. Models for the two phenomena, static fatigue and zero-stress aging, acting separately and jointly are presented. Conditions are established for proper determination of the static fatigue susceptibility. Available experimental data of fibers and unidirectional composites is used to support the arguments made for an interacting model. The conditions for which aging becomes significant are outlined.

This paper discusses the experimental results on properties and transfer length of the common types of fiber-reinforced polymer (FRP) tendons. Based on the experimental results, an equation is proposed for predicting the creep coefficient of aramid-based FRP (AFRP) tendons. The results show that the creep of carbon-based FRP (CFRP) is less than 0.2%. The test results show that the transfer length of CFRP is in the range of 300–800 mm and the concrete strength at transfer is one of the major factors affecting the transfer length of CFRP. A new factor accounting for the concrete strength is proposed for estimating the transfer length of CFRP tendons, and the verification is made for this equation. The transfer length was found to vary from 170 to 270 mm, which was 20–30 times the tendon diameter for these AFRP tendons. Despite the creep and shrinkage of concrete and the relaxation of the tendon itself, the range for transfer length did not vary with time.

The research work reported here investigates the out-of-plane flexural behavior of masonry walls reinforced externally with glass fiber reinforced polymer (GFRP) sheets and subjected to cyclic loading. A full-scale test program consisting of eight wall specimens was conducted. Nine tests were performed, in which three parameters were studied. These included the level of compressive axial load, amount of internal steel reinforcement, and amount of externally bonded GFRP sheet reinforcement. Of the three parameters studied, varying the amount of GFRP sheets was the only parameter that significantly affected the behavior of the walls. The GFRP sheet reinforcement governed the linear response of the bending moment versus centerline deflection hysteresis. Increasing or decreasing the amount of GFRP sheet reinforcement either increased or decreased both the wall stiffness and the ultimate strength, respectively. Except for visible cracks, the walls maintained their structural integrity throughout the out-of-plane cyclic loading. The unloading/reloading paths for successive loading cycles were similar, indicating little degradation. Thus, the general behavior of the walls was very predictable. The system, therefore, could be used to advantageously rehabilitate older masonry structures that are inadequately reinforced to withstand seismic events. A simple model of the behavior is also presented to allow for the evaluation of the strength and deformation characteristics of these elements.

Concrete columns encased in fiber-reinforced polymer (FRP) tubes offer an attractive solution to enhance behavior of concrete in terms of strength as well as ductility. Analytical models for development of stress-strain curves for concrete confined with FRP are proposed in this paper. The predicted stress-strain curves for confined concrete using the proposed models are compared with those of tests for concrete specimens confined with FRP. It is demonstrated that the proposed models predict the stress-strain behavior of confined concrete very well. Based on the confidence gained in the proposed models, the effects of using different fibers, the presence of voids, and the number of layers are established.

The results of a comprehensive experimental program, aimed at providing a fundamental understanding of the behavior of shear-critical exterior reinforced concrete (RC) joints strengthened with fiber reinforced polymers (FRP) under simulated seismic load, are presented in this study. The role of various parameters on the effectiveness of FRP is examined through 2/3-scale testing of 18 exterior RC joints. Conclusions are drawn on the basis of certain load versus imposed displacement response characteristics, comprising the strength (maximum lateral load), the stiffness, and the cumulative energy dissipation capacity. The results demonstrate the important role of mechanical anchorages in limiting premature debonding, and they provide important information on the role of various parameters, including: area fraction of FRP; distribution of FRP between the beam and the column; column axial load; internal joint (steel) reinforcement; initial damage; carbon versus glass fibers; sheets versus strips; and effect of transverse beams.

A new graphite/epoxy/concrete (G/E/C) cross section was developed and tested under fatigue loading with constant amplitude for one million cycles. The cross section consisted of a G/E box element, a G/E channel element, a concrete slab, and a concrete box formed by the walls of the G/E elements. Epoxy resin and vertical steel stirrups provided shear connection between G/E elements and the concrete slab. The results showed that the epoxy interface slipped after 150,000 cycles of fatigue loading. Softening of the girder continued for another 350,000 cycles of loading, after which the stiffness and strains stabilized. The failure testing of the girder after fatigue loading showed that the load and displacement capacities were only moderately reduced by fatigue loading.

Carbon fiber reinforced polymers (CFRP) are being increasingly used in many structural applications due to their excellent mechanical and corrosion resistance characteristics. CFRP sheets and strips are being used to strengthen waterfront concrete structures, such as piers and wharves. The CFRP reinforcements are bonded to beams, piles, and decks using structural adhesives. Adhesive strength can be affected by both short-term and long-term environmental exposure. In the current study, short-term effects of temperature, moisture, and chloride content on the CFRP adhesion are evaluated using pull-off tests. Three structural adhesives were chosen to assess the effects of three different temperatures and four different relative humidities on the CFRP adhesion to concrete cubes. In the case of concrete piles exposed to marine conditions, the effect of superficial chloride content on the short-term bond strength was also investigated. It was shown that high relative humidity may reduce bond strength below acceptable levels.

This paper presents the results of an experimental and analytical comparison of a study on the flexural behavior of concrete beams reinforced with sandblasted carbon fiber-based composite rods. Twelve beams, including three control beams reinforced with steel, were tested for strength, deformation, and failure characteristics. Analytical comparisons included the generation of the theoretical strength and moment curvature relations. Experimental data from pullout tests indicated that bonding of sandblasted rods is not a major concern. However, excessive deformation in achieving the predicted moment capacity could be a limiting factor in the design of these beams.

Steel plate connections are frequently used in tilt-up and precast concrete building construction to tie adjacent wall panels together for shear and overturning effects, and to provide continuous diaphragm chord connections for wind and seismic loading. These welded connectors perform poorly in regions of high seismicity and are vulnerable to corrosion. Until now, retrofit and repair strategies for in-plane shear transfer strengthening were limited to attaching steel sections across panel edges. In the present paper, an experimental program is described that utilizes carbon fiber reinforced plastic (CFRP) composites to develop a viable retrofit scheme for precast concrete shear walls and diaphragms. Nine full-scale precast wall panel assemblies with CFRP composite connectors have been tested. The results show that the CFRP composite connection is an effective solution for the seismic retrofit and repair of precast concrete wall assemblies and other precast concrete elements, such as horizontal diaphragms, that require in-plane shear transfer strengthening.