International Concrete Abstracts Portal

Although the issue of progressive collapse has been significantly studied within the broader field of structural engineering, the literature on the analysis and design of connections in precast concrete cross-wall buildings is rather limited. This study aims to investigate the progressive collapse behavior of a typical precast floor-to-floor system, considering the pullout failure mode of the deformed bar into grouted keyways of slabs at the joints. To do so, the pullout behavior of deformed bars in grouted keyways of the connections was first experimentally studied. Subsequently, by integrating the pullout force-displacement data with findings from full-scale floor-to-floor experiments, an approximate analytical approach was formulated and validated to estimate the resistance to progressive collapse. The findings reveal that the floor-to-floor system, when subjected to the pullout failure mode following the removal of a wall support, demonstrates a secondary peak strength and considerable ductility in contrast to the bar fracture failure mode.

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 from 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.

The influence of alkaline aging on basalt fiber-reinforced polymer (BFRP) bar-reinforced concrete beams has not been thoroughly investigated, and the deterioration level can be further increased in seawater sea-sand concrete (SSC) due to increased alkalinity. This study aims to unveil the coupled influence mechanism of accelerated seawater aging and impact loading on the impact resilience of BFRP-SSC beams. The influence of concrete strength, reinforcement ratio, falling weight height, and accelerated aging in seawater on the impact resistance of BFRP-SSC beams is examined. The results indicate that enhancing concrete strength can increase the peak impact force more significantly than increasing the reinforcement ratio, due to the higher strain-rate sensitivity. The increased drop-weight energy can increase the peak impact force while reducing the residual bearing capacity. The accelerated aging in seawater can reduce the peak impact force and increase the maximum midspan displacement. Furthermore, the impact failure mode of the BFRP-SSC beam can be changed from concrete crushing to BFRP bar fracture due to the bar degradation. The peak impact forces of beam specimens soaked in seawater at room temperature and 55°C conditions were reduced by 13.8% and 15.5%, while the maximum midspan displacements were increased by 32.2% and 47.1%, respectively. This study can serve as a solid base for the impact design of FRP bar-reinforced seawater sea-sand concrete beams.

This paper presents an experimental study on the residual bond of glass fiber-reinforced polymer (GFRP) reinforcing bars 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 to 300°C (77 to 572°F), material and pushout tests were conducted to examine the temperature-dependent properties of the constituents and behavior of the interface. Also performed were 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 300°C (572°F). Thermal damage to GFRP, in the context of microcracking, was observed after exposure to 150°C (302°F). Fourier transform infrared spectroscopy (FTIR) reveals prominent wavenumbers at 668 and 2360 cm–1 (263 and 929 in.–1), related to the bond between the fibers and resin in the reinforcing bars, while spectroradiometry characterizes the thermal degradation of GFRP through diminished reflectivity in conjunction with the peak wavelength positions of 584 nm (2299 × 10–8 in.) and 1871 nm (7366 × 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 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 150°C (302°F). Design recommendations are provided for estimating reductions in the residual bond of the GFRP system exposed to elevated temperatures.

Concentrated shear deformation near the base of a squat wall, referred to herein as sliding shear, is one of the major mechanisms that can limit the strength and deformation capacity of reinforced concrete (RC) low-rise or squat walls. This paper reports tests of five large-scale RC squat wall specimens without axial load to investigate the effects of (1) longitudinal reinforcement layout, (2) shear stress demand, (3) high-strength materials, and (4) aspect ratio on the sliding shear behavior of squat walls. All specimens were tested under lateral displacement reversals. Test results indicate that the maximum strength of all test specimens with an aspect ratio of 0.5 was primarily associated with, or limited by, sliding shear at the wall base. For specimens with an aspect ratio of 0.5 and negligible axial load, the presence of special boundary elements did not have an apparent influence on wall behavior. Increasing the amount of longitudinal reinforcement, which also increased wall strength, resulted in less sliding deformation before 1.0% drift ratio. Beyond 1.0% drift ratio, all specimens with an aspect ratio of 0.5 exhibited a substantial pinching of the hysteretic response, where sliding along the wall base accounted for 80% of the overall deformation. Specimens with high-strength materials exhibited less deformation capacity than other specimens due to bar fracture at the wall base. As the aspect ratio increased to 1.0, the relative contribution of sliding deformation to overall drift decreased substantially to less than 20% of overall deformation. Based on the response characteristics of the test specimens, a sliding shear strength model for walls with negligible axial load is proposed. A database consisting of test results from fifty-five specimens (including five from this study) was developed to verify the proposed strength model.