Journal of Composites for Construction

Glass-fiber reinforced polymer (GFRP) reinforcement is being used in bridge decks as a replacement for steel reinforcement. It is thought that since the GFRP reinforcement does not corrode, it could be a more sustainable material for reinforced concrete structures. However, it is widely reported that GFRP bars do deteriorate when embedded in concrete or when immersed in concrete pore solutions. The American Concrete Institute (ACI) and AASHTO use environmental exposure factors to reduce the design strength due to this loss of capacity. However, these exposure factors have not been calibrated. In addition, limited research has been performed to quantify the time-variant flexural moment capacity of GFRP-reinforced flexural members. Recently, a Bayesian approach was used to develop a time-variant probabilistic capacity model based on capacity data of GFRP reinforcement embedded in concrete for a period of up to seven years. This model is used herein to assess the time-variant flexural moment capacity and the time-variant structural reliability of a bridge deck considering different types and sizes of GFRP bars. Even though GFRP-reinforced bridge decks are designed to be overreinforced and the designs are governed by the serviceability limit, the analysis results indicate that the probability of failure of the decks containing both 13M (#4) and 19M (#6) GFRP bars at a reference temperature $T_{23}$ of 23°C (73°F) is higher than the failure probability generally accepted in the AASHTO load and resistance factor rating (LRFR) specifications. A lower exposure temperature reduces the probability of failure over the 75 year period. The probability of failure is less than values accepted by AASHTO.

A research program was initiated to develop a nonferrous reinforcement system for concrete bridge decks using continuous fiber-reinforced polymer (FRP) bars and discrete, randomly distributed polypropylene fibers. This hybrid system may eliminate problems related to corrosion of steel reinforcement while providing requisite strength, stiffness, and desired ductility, which are shortcomings of the FRP reinforcing system in plain concrete. This paper presents the results of a part of this research program [i.e., the long-term bond behaviors of this FRP/fiber-reinforced concrete (FRC) hybrid system]. Bond durability for the FRP/plain concrete system that served as a reference is also reported. Test results indicated that ultimate and design bond strength experienced noticeable degradation when exposed to combined environmental conditioning, including freeze-thaw cycles, high temperature (60°C), and deicing salt solution. Test results showed that bond durability significantly improved owing to the restriction of the concrete crack by the addition of polypropylene fibers. The larger specimens with thicker concrete cover and relatively smaller direct exposed area to the solution of sodium chloride (NaCl) showed better bond durability. Comparing glass FRP specimens with carbon FRP specimens, it was found that bond degradation was tightly correlated to the degradation of FRP bars.

More sustainable precast concrete structural elements are emerging from the research community utilizing high-strength, self-consolidating fiber-reinforced concrete (HPSCC) reinforced with noncorroding prestressed carbon-fiber-reinforced polymer (CFRP). An example of this is a new type of precast CFRP pretensioned HPSCC panel intended as load-bearing beams or columns for use in building envelopes. Such elements have recently been applied to architectural façade elements in Europe. A key issue in the implementation of these elements as load-carrying members in buildings is demonstrating satisfactory performance in fire. It is well known that the bond between FRP reinforcing bars and concrete deteriorates at elevated temperatures. It is also known that high-strength concrete is susceptible to explosive spalling when subjected to fire. Reductions in FRP reinforcement tensile and bond strength during fire, effects on the load-bearing capacity of prestressed concrete structures, and the explosive spalling response of HPSCC during fire all remain largely unknown. This paper provides insights into the fire behavior of CFRP prestressed HPSCC slabs through an experimental study on thin slabs exposed to a standard fire while subjected to sustained service loads. It is shown that the fire resistance of these elements is governed by fire-induced spalling or, if spalling is prevented by the use of high dosages of polypropylene microfibers in the concrete, by thermal splitting-crack-induced bond failure of the CFRP tendons in their prestress transfer zone. Neither reductions in tensile strength of the tendons nor reductions in bond strength due to resin softening at high temperature appeared to play critical roles for the tests described in this paper. Key areas for future research are highlighted.

Intuitively, the fire endurance of concrete members reinforced with fiber reinforced polymer (FRP) bars is related to the decrease in the mechanical properties of the materials concerned, especially resin. Large-scale fire tests recently performed on nine concrete slabs reinforced with glass FRP bars demonstrated the importance of bond between FRP and concrete for performance under fire situations. The experimental results showed that (1) the length of the FRP bars in the zone of slabs not directly exposed to fire (namely, anchoring length in fire situations) can be much more relevant to fire endurance than the concrete cover in the zone directly exposed to fire; and (2) the shape of the bar, for instance bent at the end, allows a reduction in anchoring length. From a design point of view, evaluating the necessary anchoring length through a bond model seems to be a key aspect. Full-scale test results, extensively presented elsewhere, are used in this paper to investigate the bond behavior of FRP bars embedded in concrete at high temperature and to assess a procedure to predict bond stress, slip, and load transfer at elevated temperature, based on both the results of numerical thermal analysis and the predictions of a bond theoretical model adjusted for fire situations. The design procedure outlined for calculating the minimal required anchoring length proves a valuable approach for the practicing engineer and stands together with the experimental and numerical results presented earlier. Finally, design nomograms are shown as examples of application of the procedure.

The focus of the work described in this paper is on the development of a practical Drucker-Prager (DP) type constitutive model for the nonlinear finite-element analysis (NLFEA) of fiber-reinforced polymers (FRP)–confined masonry columns under concentric compression. This paper introduces analytical relations for the cohesion and internal friction angle for masonry constituents, i.e., solid clay bricks and mortar. The proposed relations account for the slight change of the linear part of the compressive meridian into a curve at higher hydrostatic pressure values and predict the compressive and tension meridians of concrete even for high hydrostatic pressure. Evaluating possible failure criteria in FRP-confined masonry columns, 14 test specimens from three major experimental studies are successively modeled through the proposed approach. The results of NLFEA show both satisfactory predictions of the stress-strain response of the columns and theoretical understanding for the strain distributions in the FRP sheets.

One-way reinforced concrete joist floors with wide shallow beams (WSBs) are used widely in building construction throughout the Middle East. The short- and long-term behavior of WSBs externally strengthened with carbon fiber-reinforced polymer (CFRP) reinforcement was studied on isolated beams and as part of full-scale building. This paper presents the results of the experimental investigation on the flexural performance of isolated WSBs externally strengthened with CFRP reinforcement. A total of six full-scale beams were constructed and tested to failure. The test variables were the amount, type, configuration, and the elastic modulus of CFRP reinforcement. The test results were presented in terms of deflections, ultimate capacities and modes of failure, crack width development, and strains in reinforcement and concrete. The test results showed significant improvement in the flexural performance of the strengthened beams with respect to flexural capacity, flexural stiffness, and crack width. All but one of the strengthened beams failed because of the debonding of CFRP reinforcement; however, the load carrying capacity of WSBs were more than that predicted by relevant design guidelines.

Circumferential wrapping of fiber-reinforced polymer (FRP) sheets is one of the most common applications for repair and rehabilitation of large-scale columns. Common types of fibers used for wrapping are carbon FRP (CFRP), glass FRP (GFRP), and aramid FRP (AFRP). Recently, steel FRP (SFRP) has been introduced as a new class of composites for strengthening applications. Up to now, there has been no experimental data available on the behavior of large-scale columns wrapped with SFRP sheets. Thus, in this paper, the behavior of nonreinforced and reinforced large-scale columns ($300\times 1,200\mathrm{mm}$) wrapped with CFRP and SFRP sheets is examined and compared with that of unwrapped columns. The experimental results include stress-strain behavior, ultimate stress, ultimate strain, dilation, and ductility of large-scale columns. This study presents the first ever insight into the strain variation of large-scale circular columns wrapped with CFRP and SFRP sheets using the digital image correlation technique (DICT). This technique is a photogrammetric technique that allows capturing strains from the surface of FRP-confined concrete. Results from DICT were used to analyze the strain efficiency of the SFRP sheets. Results indicate that the overall performance of the SFRP-wrapped concrete columns is superior to that of the CFRP-wrapped concrete columns.

This paper presents the durability performance of axially loaded concrete cylinders with or without carbon fiber-reinforced polymer (CFRP) confinement subjected to a typical cold region environment associated with various instantaneous load intensities. These factors have been identified from previous research that examines critical attributes affecting the deterioration of constructed bridges in cold climate: aging and live load. A total of 31 cylinders are tested to study the effect of such critical factors. A three-dimensional finite-element model is developed to predict test results. Load-carrying capacity of the unconfined concrete decreases due to the environmental exposure and the decrease rate is accelerated with the presence of live load effects, including substantial crack propagation. For the confined cylinders, the effect of environment and instantaneous intensities is not significant in terms of strength and energy dissipation. The ACI440.2R-08 provisions are found to be adequate to estimate the capacity of CFRP-confined concrete subjected to a combined cold region environment and live load effect.

An important application of fiber-reinforced polymer (FRP) composites is as a confining material for concrete, both in the seismic retrofit of existing reinforced concrete columns and in the construction of concrete-filled FRP tubes as earthquake-resistant columns in new construction. The reliable design of these structural members against earthquake-induced forces necessitates a clear understanding of the stress-strain behavior of FRP-confined concrete under load cycles. This paper presents the results of an experimental study on the behavior of FRP-confined normal- and high-strength concrete under axial compression. A total of 24 aramid and carbon FRP-confined concrete cylinders with different concrete strengths and FRP jacket thicknesses were tested under monotonic and cyclic loading. Examination of the test results has led to a number of significant conclusions in regards to both the trend and ultimate condition of the axial stress-strain behavior of FRP-confined concrete. These results are presented, and a discussion is provided on the influence of the main test parameters in the observed behaviors. The results are also compared with two existing cyclic axial stress-strain models for FRP-confined concrete.

This paper presents a study on the influence of material properties on the energy absorption capabilities of composite sandwich panels. This is of interest as increased energy absorption capability is an effective approach to providing blast resistance. The primary scope of work includes finite element parametric studies, carried out using LS-Dyna, of single-fiber-reinforced polymer (FRP) composite face sheets and FRP composite sandwich panels to determine the most influential material property parameters and suggest optimum values for these parameters in conceptual terms. The analyses also consider simultaneously varying the material properties throughout the panel and the influence of independently varying these properties among the different structural components of the panel. The results of this work can serve to design new or specify existing composite materials that have material properties optimized for increasing the blast resistance of composite sandwich panels in future work. Validation of the modeling techniques utilized and the development of quantified energy absorption metrics specific to blast applications are also discussed.

A model for predicting the buckling and wrinkling behavior of glass-fiber-reinforced polymer (GFRP) plates and sandwich panels subjected to in-plane biaxial compression–tension loading is presented in this paper. In-plane biaxial compression–tension loading occurs in the webs of plate girders or cell-core sandwiches. The model is able to simulate two counteracting effects of increasing transverse tension load on buckling and wrinkling loads as observed in experiments. A stabilizing effect tends to push the plate back to the median plane and thereby delays the onset of buckling/wrinkling instability. In contrast, lateral contraction accelerates the bending of the plate, which leads to a significant decrease in buckling/wrinkling loads. In composite plates, the first effect predominates and increases the buckling loads, while in sandwich panels the second effect is dominant and decreases the wrinkling loads. The theoretical predictions are in good agreement with the corresponding experimental results.