Journal of Composites for Construction

This paper reports on the design of two highway suspension bridges made of conventional steel and advanced all-composite carbon fiber reinforced polymer (CFRP), and analyzed their life-cycle costs. The writers assumed that the pultrusion molding method would mainly be used for all composite highway bridges, because of its relatively high quality control performance and mass-production capability. First, the writers obtained the steel and composite highway bridge design in the same dimensional specification. Second, they acquired the future cost of the CFRP pultrusion product through hearing research from a fiber reinforced polymer manufacturer. Third, they calculated the initial costs of the steel bridge and CFRP bridge based on the design specification and the future cost of CFRP. Fourth, they compared the life-cycle cost of the steel and CFRP bridges under several conditions of discount rate, repair cost, and cycle. Finally, they found the critical condition where the CFRP bridge becomes more life-cycle cost-effective than the conventional steel bridge, if they could have expected the drastic cost reduction of the CFRP product.

Advantages of diaphragms using glass fiber-reinforced polymer (GFRP) panels in conjunction with plywood panels as sheathing (hybrid diaphragms) are presented in this paper. The strength and behavior of individual connections between GFRP sheathing panels and wood framing are determined through coupon testing. Coupon test results indicate that GFRP sheathing-to-framing connections have significant increases in strength, stiffness, and energy absorption. The strength and behavior of hybrid diaphragms are determined by testing a conventional diaphragm (wood sheathing only) and a hybrid diaphragm. The hybrid diaphragm sustained 34% more load compared to the conventional diaphragm.

The encasement of concrete in fiber-reinforced polymer (FRP) composite jackets can significantly increase the compressive strength and strain ductility of concrete columns and the structural system of which the columns are a part, be it a building or a bridge. Due to the approximate bilinear compressive behavior of FRP-confined concrete, analysis and design of FRP-confined concrete members requires an accurate estimate of the performance enhancement due to the confinement provided by FRP composite jackets. An analytical model is presented for predicting the bilinear compressive behavior of concrete confined with either bonded or nonbonded FRP composite jackets. This article describes the basis of the model, which is a variable plastic strain ductility ratio. The variable plastic strain ductility ratio defines the increase in plastic compressive strain relative to the increase in the plastic compressive strength of the FRP-confined concrete, which is a function of the hoop stiffness of the confining FRP composite jacket, the plastic dilation rate, and the type of bond between the FRP composite and concrete.

The design of fiber-reinforced polymer (FRP)-confined concrete members requires accurate evaluation of the performance enhancement due to the confinement provided by FRP composite jackets. A strain ductility-based model is developed for predicting the compressive behavior of normal strength concrete confined with FRP composite jackets. The model is applicable to both bonded and nonbonded FRP-confined concrete and can be separated into two components: a strain-softening component, which accounts for unrestrained internal crack propagation in the concrete core, and a strain-hardening component, which accounts for strength increase due to confinement provided by the FRP composite jacket. A variable strain ductility ratio described in a companion paper is used to develop the proposed stress-strain model. Equilibrium and strain compatibility are used to obtain the ultimate compressive strength and strain of FRP-confined concrete as a function of the confining stiffness and ultimate strain of the FRP jacket.

Theoretical studies of the influence of shear deformation on the flexural, torsional, and lateral buckling of pultruded fiber reinforced plastic (FRP)-I-profiles are presented. Theoretical developments are based on the governing energy equations and full section member properties. The solution for flexural buckling is consistent with the established solution based on the governing differential equation. The new solutions for torsional and lateral buckling incorporate a reduction factor similar to that for flexural buckling. The solution for lateral buckling also incorporates the influence of prebuckling displacements. Closed form solutions for a series of simply supported, pultruded FRP I-profiles, based on experimentally determined full section flexural and torsional properties, indicate the following conclusions. For members subjected to axial compression, shear deformation can reduce the elastic flexural and torsional buckling loads by up to approximately 15% and 10%, respectively. For members subjected to bending, prebuckling displacements can increase the buckling moments by over 20% while shear deformation decreases the buckling moments by less than 5%.

The use of fiber-reinforced polymers (FRPs) for the strengthening and repair of existing concrete structures is a field with tremendous potential. The materials are very durable and, hence, ideally suited for use as external reinforcement. Although extensive work has been carried out investigating the use of FRPs for flexural strengthening, a fairly recent development is the use of these materials for the shear strength enhancement of concrete. The current system investigates the use of posttensioned, nonlaminated, carbon fiber-reinforced polymer (CFRP) straps as external shear reinforcement for concrete. Experiments were carried out on an unstrengthened control beam and beams strengthened with external CFRP straps. It was found that the ultimate load capacity of the strengthened beams was significantly higher than that of the control specimen. Existing design codes and analysis methods were found to underestimate the ultimate resistance of the control specimen and the strengthened beams. Nevertheless, the modified compression field theory provided insight into possible failure mechanisms and the influence of the strap prestress level on the structural behavior. It is concluded that the use of these novel stressed elements could represent a viable and durable means of strengthening existing concrete infrastructure.

An experimental investigation is conducted on the improvement of the torsional resistance of reinforced concrete beams using fiber-reinforced polymer (FRP) fabric. A total of 11 beams were tested. Three beams were designated as control specimens and eight beams were strengthened by FRP wrapping of different configuration and then tested. Both glass and carbon fibers were used in the torsional resistance upgrade. Different wrapping designs were evaluated. The reinforced concrete beams were subjected to pure torsional moments. The load, twist angle of the beam, and strains were recorded. Improving the torsional resistance of reinforced concrete beams using FRP was demonstrated to be viable. The effectiveness of various wrapping configurations indicated that the fully wrapped beams performed better than using strips. The 45° orientation of the fibers ensures that the material is efficiently utilized.

In this work, the results of an experimental study conducted in a 1964-vintage building are presented. Twelve reinforced concrete (RC) T-joists strengthened with fiber-reinforced plastic (FRP) composites were loaded until failure in a short shear span configuration. Different strengthening schemes, including different FRP materials and a new FRP anchorage system, were adopted in order to compare the performance of the different installations. Carbon FRP and aramid FRP sheets in an epoxy matrix were bonded to the RC joists using the wet layup technique. All of the joists were loaded close to one end support and showed similar cracking patterns at failure. The design calculations were based on experimental results. All of the unanchored FRP strengthened beams showed failure due to peeling, while the anchored FRP strengthened members showed failure due to anchor pullout at higher load values. It was found that an increase in the amount of FRP did not result in a proportional increase in the shear capacity, as expected by design equations, but all of the beams showed a considerable increase in stiffness. The experimental results are compared with the results expected by analytical models in order to discuss the structural behavior of FRP strengthened beams tested in a real building with a short shear span. It was found that theoretical calculations resulted in nonconservative results for the tested specimens.

An experimental and analytical investigation was made into the flexural creep behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFT). While creep effects reduce the flexural stiffness of CFFT specimens, ultimate strength is not significantly altered. The slow rate of loading and short-term creep at 70% of static capacity may cause premature rupture of the tube. Fiber analysis of CFFT beam-columns by discretizing the section into filled and hollow FRP tubes can adequately simulate the flexural creep behavior. Isochronous sustained stress-creep strain curves are used as a constitutive nonlinear relationship for creep analysis in flexure. Creep deflection of CFFT beam-columns is much less than that of CFFT beams, mainly because axial compressive loads tend to retard the cracking of concrete and tensile creep of FRP. The stiffness ratio of FRP tubes with respect to the concrete core has a pronounced effect on the creep deflection of CFFT beam-columns. As the stiffness ratio increases, creep deflection decreases. However, there exists a threshold beyond which stiffer tubes do not provide additional benefit. CFFT beam-columns under high levels of sustained axial loads have a lower creep rupture life expectancy, mainly because failure moments under large axial forces are lower. The creep rupture life expectancy of CFFT beam-columns with diameter-to-thickness ratios of 40 or less is at least 50 years at transverse loads as high as 60% of the static capacity.

The durability of fiberglass composite sheet piles in water was studied through the specimens cut from flanges and webs of pultruded sheet pile sections. The experiments were performed to evaluate the water absorption at ambient temperature in complete immersion, and its effect on the tensile properties and the freeze-thaw resistance of the saturated composites. The high temperature at $70°C$ was used to accelerate the tests, and $100°C$ (boiling water) to verify the state of saturation. The non-Fickian absorption behavior of the pultruded composites was modeled based on the Berens and Hopfenberg two-phase absorption theory to predict the long-term performance and the change in mechanical properties of saturated composites. The results indicated that the water absorption process of the pultruded sheet pile composites followed a combination of Fickian diffusion and polymeric relaxation. The percent absorption at saturation was about 1.72% for the flange and 3.11% for the web. The water absorption model predicted that saturation would be reached after 5.8 years for the flange and after 14.5 years for the web immersed in tap water at ambient temperature. The tensile strength was found to decrease initially with the increase in the percent water absorption, and finally stabilize at the state of saturation. On the other hand, there was no noticeable change in the tensile modulus of elasticity during the entire water-aging period. The saturated composites showed excellent resistance to freeze-thaw cycling from $4.4$ to $-17.8°C\text{.}$