Journal of Composites for Construction

Numerous studies have been conducted to evaluate bond behavior between fiber-reinforced polymer (FRP) composites and concrete substrate in externally bonded reinforcement (EBR) systems subject to static loads. However, few investigations examined the bond behavior under dynamic loads, and in particular under high loading rates. This study investigates FRP-concrete bond behavior under quasi-static and high loading rates. For this purpose, 12 concrete prisms were strengthened with carbon FRP (CFRP) sheets and subjected to the single-shear test under different loading rates. The particle image velocimetry (PIV) method is used as an image processing technique to obtain the deformation and strain fields. Results indicate that bond capacity rises with increasing loading rate, which is more considerable in the case of low-strength concrete specimens. The increased bond capacity is attributed to the different mechanisms of bond fracturing under quasi-static and high loading rates. This motivates a thorough evaluation of the effects of the relevant mechanisms on bond behavior. Bond analysis by means of the PIV method reveals not only an increasing interfacial shear stress distribution between the CFRP composite and the concrete substrate, but also concentration of strain on the CFRP sheet. Finally, bond-slip graphs are used to show that the high loading rates applied increase the specific fracture energy.

Glass fiber-reinforced polymer (GFRP) bars in construction are increasing in popularity due to their excellent corrosion resistance, high tensile strength to weight ratio, and low maintenance. Geopolymer is a modern cementitious material that is known for its corrosion resistance and low carbon footprint. Combining the two could produce a green yet durable composite material that can be applied to aggressive environments such as Australia’s coastal zones. This paper experimentally investigates the load-moment interaction of GFRP-reinforced air-cured geopolymer concrete columns. The behavior of reinforced geopolymer concrete under combined loading were studied with 11 half-scale specimens. Three different stirrup spacings (75, 150, and 250 mm) were examined. Effective confinement was achieved by reducing the stirrup spacing such that high strains were measured in the concentric columns with closely spaced (75 mm) stirrups. A comparison between the experimental data and international design codes showed that such codes were conservative when ignoring the compressive strengths of the longitudinal GFRP bars. The experimental results were better represented when the compressive strengths of the bars were included; on average, the GFRP-reinforced geopolymer concrete columns exhibited 10.8% increase in strength with respect to unreinforced concrete sections.

RC beams strengthened with transverse prestressed unbonded carbon fiber–reinforced polymer (CFRP) straps have shown substantial increases in shear capacity when subjected to short-term static loading. However, understanding the time-dependent behavior is a further prerequisite in order to better evaluate this strengthening technique and its engineering applications. This paper presents time-dependent experimental results from an unstrengthened RC beam and four RC beams strengthened with CFRP straps. The parameters considered include the concrete strength, applied load level, and prestress level in the CFRP straps. The beams were subjected to sustained loads that were fixed percentages of the short-term failure load. To investigate the development of the external concrete strains, the internal steel shear link strains, the strap strains, and the shear crack patterns, the beams were monitored over a period of about 320 days. The long-term beam deformations were also recorded and decomposed into bending and shear components. Compared with an equivalent unstrengthened beam, the presence of the CFRP straps reduced the proportion of the shear deflection. However, in the strengthened beams the shear proportions of the total midspan deflection were still 24%–28%, which were not negligible. An analysis using a Mohr’s circle of strain confirmed that the long-term tensile behavior in the shear span appears to dominate the development of the shear deformation.

Jacketing using prefabricated fiber reinforced polymer (FRP) composite shells is an attractive repair system for deteriorating structures exposed to the marine environment. However, most available techniques lack an effective joining system capable of providing structural continuity along the hoop direction. This paper addresses the evaluation of the efficiency of a FRP jacket with an innovative joining system and the behavior of damaged concrete columns repaired with jackets considering several parameters, that is, level of steel corrosion, level of concrete cover damage, and the shape effect. The results showed that the jacket restored the load-carrying capacity by 99% and 95% for columns with 25% and 50% corrosion damage, respectively. Moreover, the jacket effectively restored the axial load capacity of columns with 50% and 100% concrete cover damage by 95% and 82%, respectively. The proposed system was more effective in circular columns because the axial load capacity of the repaired columns was 43% higher than the square columns. A theoretical analysis of the axial load capacity of the repaired columns indicated an excellent agreement with the experimental results.

This paper presents an experimental investigation of a novel precast segmental bridge column (PSBC) that is longitudinally reinforced with both fiber-reinforced polymer (FRP) bars and conventional steel bars. The major objectives of this study were (1) to compare the seismic performance of FRP-steel–reinforced PSBCs (FSR-PSBCs) with the conventional steel-reinforced PSBC (SR-PSBC) members; and (2) to investigate the effects of the proportion of FRP to steel reinforcement and the gravity load level on the cyclic behavior of the FSR-PSBC. To this end, quasi-static tests were conducted on four large-scale PSBC specimens with heights of 4.2 m and cross sections of $0.6\times \mathrm{0}\mathrm{.4}\mathrm{m}$. Basalt FRP (BFRP) bars were employed in the FSR-PSBC specimens. Test results showed that as compared with the SR-PSBC, FSR-PSBC specimens exhibited appreciably improved self-centering capacities, postyield stiffness ratios, displacement ductility, and comparable hysteretic energy dissipation abilities. Furthermore, after the FSR-PSBC specimens were cyclically loaded up to a drift ratio of 5.5%, the damages were insignificant and could be repaired rapidly, indicating promising post-earthquake serviceability of these bridge columns.

This study focuses on the fire performance of glass fiber–reinforced polymer (GFRP) stay-in-place structural formwork used for the rapid construction of reinforced concrete (RC) bridge decks and serves to direct future studies on the matter. Seven beam sections of a concrete deck reinforced using a GFRP stay-in-place form are tested. The beams in this study are subjected to both fire and simulated-fire damage and tested in four-point bending to assess the mechanical contribution of the GFRP stay-in-place formwork. Fire damage was applied to one beam via a 14.5-min heptane pool fire. Experimental results show that the simulated damage was an overly conservative representation of the fire damage sustained. The fire damage was insufficient to reduce the ultimate load or change the failure mode of the specimen when compared to an undamaged control. The embedded T-rib of the GFRP form was protected from fire damage and provided redundancy to the system. Despite a char thickness of about 15% of the base thickness, the GFRP base plate was able to protect the adjacent concrete from temperatures exceeding 100°C. An increased flexural capacity was observed in the fire-damaged specimen hypothesized to be a result of concrete precompression arising from the heating and cooling of the GFRP formwork. A series of direct bond shear tests between GFRP–concrete samples at elevated temperatures found a decrease in bond shear stress and bond stiffness as bond temperatures increased.

Numerous studies have been conducted on strengthening techniques using prestressed fiber-reinforced polymer (FRP) laminates, bars, and tendons. However, to date, no technique has been developed for prestressed FRP grids, which are an attractive solution for strengthening slabs, walls, and tunnels. In this paper, a novel waveform anchor is proposed and verified by tensile tests to be capable of feasibly and effectively anchoring the basalt FRP (BFRP) grid. Five hollow-core slabs, including one control slab and four strengthened slabs, were tested to failure to investigate the flexural behavior of slabs strengthened with prestressed BFRP grids. The effect of the anchorage system and prestressing force on the flexural performance of the slabs was studied. The test results showed that the failure mode of the prestressed BFRP grid–strengthened slabs was rupture of the BFRP grids, and no end peeling was observed. At increasing prestressing force in the BFRP grid, the failure mode changed from sequential rupture to essentially simultaneous rupture of the longitudinal bars. Thus, the flexural capacity of the strengthened slabs increased with the prestressing level of the BFRP grids. Improved cracking behavior of the slab could be obtained by prestressing the BFRP grid, and the crack width remarkably decreased as the prestressing force in the BFRP grid increased. However, the ductility of the strengthened slabs decreased with increased prestressing force in the BFRP grid.

Extensive research has been conducted on FRP (fiber-reinforced polymers)-confined concrete columns under concentric compression, leading to many stress-strain models for such concrete. These concentric-loading (CL) stress-strain models have generally been used in the analysis of both concentrically and eccentrically loaded columns. Existing tests, however, have shown that eccentrically loaded FRP-confined concrete columns exhibit some behavioral aspects that cannot be closely predicted using a CL stress-strain model. This paper presents an in-depth investigation into this problem using an advanced three-dimensional (3D) finite element (FE) approach. The stress-strain response of concrete is shown to vary significantly over the section, and the direct use of a single CL stress-strain model for the entire section in the analysis of eccentrically loaded columns may lead to significant errors in the prediction of ultimate displacement/curvature. A stress-strain model for the confined concrete at the extreme compression fiber of the section is also shown to provide a relatively simple and much more accurate option for predicting the ultimate displacement/curvature of eccentrically loaded columns. Based on this conclusion, a so-called eccentricity-dependent (EccD) stress-strain model is proposed based on a comprehensive parametric study using the FE approach. The proposed model can be directly used in a section analysis or a theoretical column model and is proven to provide much more accurate predictions of the ultimate displacement/curvature of test columns than existing CL stress-strain models.

Compared to cast-in-situ RC buildings, precast concrete (PC) buildings may have lower redundancy and integrity depending on their construction methods and the types of beam-to-column connection. In this study, a series of multipanel PC beam-column-slab substructures were tested to evaluate the performance of a typical existing PC building with bolted connection, which is a typical dry connection in industrial buildings, subjected to the loss of a single penultimate column scenario. It was found that an existing PC substructure with bolted connections exhibited very low ductility and load-resisting capacity. The deficient connection between the PC slab and beams led to the specimen failing in a brittle manner and gaining fewer benefits from tensile membrane action. To overcome the poor performance of existing PC buildings with bolted connections, improvement in detailing and strengthening schemes relied on glass fiber–reinforced polymer (GFRP) strips were proposed. Based on the test results, the improvement could enhance the redundancy of PC substructures effectively. Moreover, the proposed strengthening scheme further enhances the flexural capacity, initial stiffness, and the postpeak behavior in large deformation stage significantly.

This paper presents an experimental study on the seismic performance of underwater bridge columns retrofitted with the combination of prestressed precast concrete panels (PPCP) and embedded fiber-reinforced polymer (FRP) reinforcements (PPCP-FRP). A newly developed retrofitting method with PPCP-FRP and the corresponding retrofitting processes were conceived based on the specific demands for underwater bridge columns. Traditional steel strands were placed outside the PPCP to connect the panels in a ring configuration and offset premature failure of the panels during an earthquake. Due to the potentially corrosive environment, the steel strands were designed to be easily replaced underwater, and the FRP reinforcement was set inside the PPCP to ensure a long-term service. A total of six 1/4-scale circular bridge column specimens were fabricated. Five specimens were strengthened either with different strengthened lengths of PPCP-FRP or with different types and reinforcement ratios of longitudinal FRP bars, and the remaining specimen was used as the control specimen. The retrofitting procedure of the PPCP-FRP method was verified as viable and efficient through experimentation. All column specimens were tested under reversed cyclic lateral loading along with a constant axial load. The load capacity, stiffness, ductility, and energy-dissipation capacity of the columns were significantly improved through strengthening. In addition, a more uniformly distributed column curvature and a reduced residual displacement were obtained for the strengthened columns, indicating enhanced repairability. A sufficient strengthening length and FRP reinforcements with a lower elastic modulus and higher ultimate strain are recommended during the retrofitting design with PPCP-FRP.