Abstracts: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.

Abstracts: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.

Abstracts: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.

Abstracts: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.

Abstracts: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.