International Concrete Abstracts Portal

The bond property between deformed bars and concrete plays a significant role in the safety of construction. Numerous database-dependent empirical models are proposed to evaluate the bond behavior without considering the effect of additional confinement, whose application range is quite limited as a result of unstable accuracy. In this paper, a new model was established based on the thick-walled cylinder model and fictitious crack theory, which can predict bond strength and bond-slip response with fiber-reinforced polymer (FRP)-steel confinement. The effects of various factors on the bond behavior such as concrete strength, concrete cover, reinforcing bar diameter, bar surface geometry, and FRP/steel confinement were comprehensively discussed. According to radial crack radius, the radial stress and displacement induced on bond interface can be calculated, and thus analytical formulae of bond strength and slip were respectively developed in conjunction with deformed bar surface geometry. Finally, a new analytical model was proposed, which can simulate the bond-slip curves of the specimens with different confinement levels, covering unstrengthened, FRP-strengthened, stirrup-strengthened, and FRP-stirrup dually strengthened specimens. Compared with existing models, the proposed model can provide better agreement with existing test results.

During past earthquakes, failures of beam-column joints have commonly been observed on the exteriors of buildings. However, only one side of these joints can be retrofitted because of the presence of beams on the other three sides. Therefore, this study aims to test four exterior beam-column joints with transverse beams, leaving the rear side as the only viable location for placing fiber-reinforced polymer (FRP) laminate. All four test specimens were designed with insufficient joint shear strength, as determined by ACI 318-19 equations, while satisfying the criteria for a strong-column/weak-beam mechanism and sufficient development length for bar anchorage. A total of two un-retrofitted specimens, with and without joint hoops, were constructed as controls. Subsequently, two similar specimens were retrofitted by applying FRP laminate on the rear side. The results show that sufficient FRP laminate can enhance the seismic performance of joints in terms of deformability, energy dissipation, and failure delay.

This paper presents the implications of variable bond for the behavior of concrete beams with glass fiber-reinforced polymer (GFRP) bars alongside shear-span-dependent load-bearing mechanisms. Experimental programs are undertaken to examine element- and structural-level responses incorporating fully and partially bonded reinforcing bars, which are intended to represent sequential bond damage. Conforming to published literature, three shear span-depth ratios (av/d) are taken into account: arch action (av/d < 2.0), beam action (3.5 ≤ av/d), and a transition from arch to beam actions (2.0 ≤ av/d < 3.5). When sufficient bond is provided for the element-level testing (over 75% of 5db, where db is the reinforcing bar diameter), the interfacial failure of GFRP is brittle against a concrete substrate. An increase in the av/d from 1.5 to 3.7, aligning with a change from arch action to beam action, decreases the load-carrying capacity of the beams by up to 40.2%, and the slippage of the partially bonded reinforcing bars dominates their flexural stiffness. Compared with the case of the beams under beam action, the mutual dependency of the bond length and shear span is apparent for those under arch action. As far as failure characteristics are concerned, the absence of bond in the arch-action beam prompts crack localization; by contrast, partially bonded ones demonstrate diagonal tension cracking adjacent to the compression strut that transmits applied load to the nearby support. The developmental process of reinforcing bar stress is dependent upon the av/d and, in terms of using the strength of GFRP, beam action is favorable relative to arch action. Analytical modeling suggests design recommendations, including degradation factors for the calculation of reinforcing bar stresses with bond damage when subjected to arch and beam actions.

Corrosion—one of the major threats to the integrity of concrete structures—can consequently affect structure serviceability and ultimate limit state, possibly resulting in failure. Glass fiber-reinforced polymer (GFRP) can be used as an innovative alternative for conventional steel reinforcement in concrete structures, effectively addressing corrosion issues. In addition to its corrosion resistance and high strength-to-weight ratio, GFRP is commonly selected for nonprestressed bars and stirrups due to its cost advantage over other fiber-reinforced polymer (FRP) materials. The study endeavored to provide a comprehensive overview of the shear resistance in GFRP-reinforced concrete (RC) beams with short shear spans. The manuscript aims to synthesize and analyze shear test data based on published studies on GFRP-RC beams with a short shear span (a/d = 1.5 to 2.5). A comprehensive literature review was conducted to compile a database comprising 64 short GFRP-RC beams to evaluate the efficiency of using the strut-and-tie model (STM) for predicting the shear resistance of GFRP-RC beams. The findings reveal that ACI 318-19 STM yielded the most accurate predictions of the shear resistance of GFRP-RC beams with a/d of 1.5 to 2.5, because the current ACI CODE-440.11-22 and ACI 440.1R-15 design codes and guidelines do not include shear equations using the STM for predicting the shear resistance of GFRP-RC beams. Based on the findings of this study, the results could contribute to establishing shear equations in the upcoming revision of the ACI CODE-440.11-22 and ACI 440.1R-15 design codes and guidelines, specifically tailored for designing short GFRP-RC beams using the STM. The study also provides sufficient data to apply the STM in the design of GFRP-RC beams.

This study investigates the ultimate flexural strength (UFS) of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP) (RCB-SCFRP), focusing on the identification and quantification of flexural overstrength concerning the nominal flexural strength (NFS) as defined by ACI 440.2R. A total of 106 full-scale specimens tested were carefully selected from previous research, varying in concrete strength, reinforcement configurations, and CFRP materials from multiple manufacturers. Results show that ACI 440.2R provisions accurately and conservatively estimate the flexural capacity of CFRP-strengthened beams. Including CFRP transverse reinforcement (TR) resulted in a slight increase in UFS. The type of strengthening, whether preloaded and repaired or strengthened, had little effect on the UFS/NFS ratio. Steel reinforcement ratio (SRR) significantly influenced overstrength, with higher UFS/NFS ratios observed between 0.70% and 1.00% SRR. CFRP axial rigidity (Kf ρf) notably affected overstrength, with optimal performance between 0.10 and 0.50 GPa·mm. Deflection ductility was mainly affected by the rigidity of CFRP, with a 13% increase noted due to CFRP TR. A log-normal model was developed to estimate UFS for RCB-SCFRP beams based on experimental data and ACI 440.2R guidelines.