International Concrete Abstracts Portal

This study investigates the ultimate flexural strength (UFS) of reinforced concrete beams strengthened with 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 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.

This paper presents an experimental study on the residual bond of glass fiber-reinforced polymer (GFRP) rebars embedded in ultra-high-performance concrete (UHPC) subjected to elevated temperatures, including a comparison with ordinary concrete. Based on the range of thermal loading from 25°C (77°F) to 300o°C (572o°F), material and push-out tests are conducted to examine the temperature-dependent properties of the constituents and the behavior of the interface. Also performed are chemical and radiometric analyses. The average specific heat and thermal conductivity of UHPC are 12.1% and 6.1% higher than those of ordinary concrete, respectively. The temperature-induced reduction of density in these mixtures ranges between 5.4% and 6.2% at 300o°C (572o°F). Thermal damage to GFRP, in the context of microcracking, is observed after exposure to 150°C (302°F). Fourier transform infrared spectroscopy reveals prominent wavenumbers at 668 cm^-1 (263 in.^-1) and 2,360 cm^-1 (929 in.^-1), related to the bond between the fibers and resin in the rebars, while spectroradiometry characterizes the thermal degradation of GFRP through diminished reflectivity in conjunction with the peak wavelength positions of 584 nm (2,299×10^-8 in.) and 1,871 nm (7,366×10^-8 in.). The linearly ascending bond-slip response of the interface alters after reaching the maximum shear stresses, leading to gradual and abrupt declines for the ordinary concrete and UHPC, respectively. The failure mode of the ordinary concrete interface is temperature-sensitive; however, spalling in the bonded region is consistently noticed in the UHPC interface. The fracture energy of the interface with UHPC exceeds that of the interface with the ordinary concrete beyond 150o°C (302o°F). Design recommendations are provided for estimating reductions in the residual bond of the GFRP system exposed to elevated temperatures.

The deformability of reinforced concrete walls with staggered lap splices was studied through tests of six cantilevered walls under constant axial load and cyclic reversals of lateral displacement. The height-to-length aspect ratios of the walls were approximately 3.2. Four walls had staggered laps, one wall had non-staggered laps, and one wall had mechanical couplers. Laps were detailed to yield the spliced reinforcement. Test walls with staggered laps lost lateral-load resistance at smaller drift ratios (1.0% to 2.1%) than both the test wall with non-staggered laps (2.3%) and the test wall with mechanical couplers (3.5%). Staggered lap splices resulted in larger strain concentrations than non-staggered lap splices. It was concluded that both staggered and non-staggered lap splices a) can have reduced strain capacity relative to continuous bars (leading to bond failure before or after yield) and b) alter inelastic strain distributions, causing large reductions in effective plastic hinge length.

In performance-based seismic design, buckling and fracture of longitudinal steel in reinforced concrete columns are damage limit states that may be considered for damage control and near collapse, respectively. This study evaluates the progression of buckling instability, which eventually leads to bar fracture, based on bending strains measured in buckled bars of cyclic quasi-static column tests. Buckling-induced bending strains are calculated with bare bar fiber models and experimental buckled shapes of longitudinal reinforcement in the column data set. This study proposes an empirical equation that calculates the buckling-induced bending strain based on column displacement ductility, low-cycle fatigue, and column design parameters for grade 60 steel. This study also identifies the buckling-induced bending strains that trigger transverse steel yielding, visual bar buckling, and brittle bar fracture.

Industrial facilities (such as offshore platforms, power plants, and treatment plants) are typically labyrinthine structures because they possess intricate layouts (resembling mazes or labyrinths), and most of their structural walls are interconnected. These reinforced concrete (RC) structural walls need to be designed for eight simultaneous demands. The existing US codes provide limited procedural guidance for the design of these walls. A novel Panel-based ACI (PACI) design approach for RC walls, rooted in the design concepts and formulations of ACI 349 and ACI 318.2, is proposed. The PACI approach is validated using two validation and verification (V&V) approaches. For the first V&V approach, existing experimental data is used to estimate PACI approach-based reinforcement areas, which are then compared against the reinforcements provided in the experiments (and against the reinforcement areas suggested by the EC2 sandwich model approach). Benchmarked numerical models are developed to compare the capacities of specimens using PACI-based reinforcements with experimentally observed capacities and with EC2-based reinforcement. For the second V&V approach, analytical data of publicly available design demands for real-world structures are used to estimate PACI-based reinforcements for a critical region of a nuclear power plant. Numerical models are developed to compare the capacities of the panels with PACI-based reinforcements against the design demands. The results from V&V1 approach showed that the PACI approach: (i) suggests similar reinforcement areas than those used in the experiments, with an average ratio of PACI suggested reinforcement areas over experimental provided areas of 0.97 for all 21 tests; and (ii) suggests similar reinforcement areas that those suggested by the EC2 approach, with an average ratio of EC2 based reinforcement areas, over PACI based reinforcement of 1.01 for all 21 tests as well. For the V&V2 approach, the numerical capacities of the models with PACI suggested reinforcements are greater than or equal to the design demands. The V&V studies illustrate that, despite its methodological simplicity, the PACI approach results in reinforcement recommendations that closely approximate the outcomes derived from the more rigorous procedures inherent to the EC2 approach. The design implementation of the PACI approach is also illustrated using a sample calculation.