International Concrete Abstracts Portal

Experimental testing of a reinforced concrete shear wall subjected to combined axial load and reverse cyclic lateral displacements was conducted to investigate rocking and sliding observed in a companion wall tested without axial loading, and to assess the effect of axial load on residual drifts. The application of 10% axial load resulted in greater lateral load capacity and stiffness, as well as increased ductility. The presence of axial load contributed to satisfying lower residual drift limits at higher transient drifts. Further analysis was conducted to disaggregate the total lateral displacement into sliding, rocking, shear, and flexure mechanisms. Comparison to the companion wall demonstrated that the present wall had significantly greater contribution from flexural effects with the axial load delaying the influence of rocking until crushing of the concrete. A complementary numerical study of the wall with axial load was conducted, and a modelling methodology was presented to better capture the fracture phenomena of steel reinforcement. This methodology accounted for local fracture of reinforcement and a reduction of reinforcement area due to the presence of strain gauges. The simulation of failure and the predicted lateral displacement capacity were significantly improved compared to a model that did not consider these phenomena.

Retrofit of reinforced concrete bridge columns with steel jackets is a commonly implemented strategy to increase column ductility in earthquakes. If the steel jacket retrofit is designed using available guidelines, fatigue fracture of longitudinal reinforcement is a likely cause of strength degradation. Fatigue fracture in reinforcement is dependent upon strain history in reinforcement. A model was developed to determine the strain history in longitudinal reinforcement at the plastic hinge in steel jacket retrofitted reinforced concrete columns. The model was validated with existing test data, and single degree of freedom nonlinear time history analyses were conducted using the model. Earthquake duration was shown to have a significant impact on the number of plastic excursions and the total plastic strain in the reinforcement, based on the results of analyses using an existing suite of long-duration earthquake ground motions that were each paired with a short-duration ground motion with similar response spectra. Results from analyses of 600 Magnitude-9.0 Cascadia Subduction Zone simulated site-specific ground motions for western Washington State were used in the formulation of a new testing protocol for steel jacket retrofitted reinforced concrete bridge columns that better accounts for expected demands in this region.

This study evaluates the bond performance of concrete epoxy bonds using an image segmentation-based image processing technique. The Concrete Epoxy Interface (CEI) plays a crucial role in the structural performance of FRP-repaired concrete as it transfers stresses from the concrete to the epoxy. By employing the image segmentation technique, the performance of the CEI is assessed through the ratio of Interfacial Failure (IF) to other failure types, namely cohesive failure in Epoxy (CE) and Cohesive cracks in Concrete (CC). The effects of sustained loading duration on CEI bond performance are quantitatively analyzed using 21 single-lap shear (SLS) specimens and 28 notched 3-Point Bending (3PB) specimens. The findings highlight vital conclusions: CE is the least failure mode in SLS and 3PB specimens. In contrast, CC is the predominant failure mode, indicating the susceptibility of the concrete substrate in FRP-repaired concrete. Moreover, IF generally increases with longer sustained loading durations in 3PB specimens but decreases with increased loading duration in SLS specimens. The study also demonstrates the effectiveness of the image segmentation approach in evaluating CEI performance in 3PB specimens, where color distinguishes epoxy, FRP, and concrete substrate.

Small-scale plain concrete precracked beams strengthened with glass fiber reinforced polymer (GFRP) sheets underwent testing in 3-point flexure to assess variations in the FRP-concrete Mode II interfacial fracture energy after 6 and 13 years of sustained loading in indoor and outdoor environments. The Mode II fracture energy of the interfacial region, GF, was determined by analyzing strain profiles along the length of the FRP sheet, which were obtained using digital image correlation and photoelastic techniques. In the experiments conducted after conditioning, higher GF values were observed as the debonded zone progressed from the region of sustained shear stress transfer to the unstressed section of the interfacial region, particularly in beams subjected to outdoor conditioning. In the interfacial region near the notch, GFRP beams showed reductions in GF in both indoor and outdoor environments. For outdoor beams with GFRP sheets, there was no additional degradation in GF when the FRP was exposed to direct sunlight, in comparison to beams with the FRP exposed to indirect sunlight.

Embedded Through-Section (ETS) method is a shear rehabilitation technique for concrete structures involving pre-drilling vertical holes into a reinforced concrete member and installing FRP bars to be bonded using epoxy adhesive. Due to the lack of reliable models for predicting the ETS FRP bond behaviour, developing an accurate model to predict the maximum pull-out force of the ETS technique was deemed a knowledge gap. In this study, the main parameters used in an analytical bond-slip model proposed by the authors were obtained empirically and evaluated against the existing experimental results in the literature. To be able to calculate the maximum pull-out force for ETS FRP bars with different materials, a fracture mechanics-based bond model was defined in terms of the joints' geometrical and material properties, to allow the model to predict the performance of any FRP type with any concrete compressive strength. By using data in the available literature on FRP ETS pull-out tests, statistical analysis was utilized to fit the parameters against experimental data. The proposed model was able to produce superior analytical predictions of the experimental test data when compared to the existing bond models for ETS FRP bars.