International Concrete Abstracts Portal

Due to the low lateral stiffness of slabs supported on columns alone reinforced concrete flat plates are typically combined with other structural elements, such as shearwalls. In these structures, the slab-column connections are designed to carry gravity loads only, and the shearwalls, which also carry gravity loads, are required to resist the lateral forces. Therefore, the slab-wall connections (SWCs) are essential for the adequate performance of both the gravity and lateral force resisting systems. However, the majority of punching shear research and design provisions have been focused on slab-column connections, even though punching failures around slab-wall connections have been observed experimentally. Empirical testing of slab-wall connections is difficult due to the required specimen size. This paper investigates the punching shear behaviour of interior slab-wall connections subjected to concentric vertical loading, and combined concentric vertical loading and uniaxial unbalanced moment using a plasticity-based nonlinear finite element model (FEM) in Abaqus. The FEM, developed to study the impact of column aspect ratio on punching shear, was calibrated considering seven isolated slab-column specimens. The analysis of isolated slab-wall connections demonstrates that punching failures can occur before one-way shear failures, although the connection capacity is much higher than the expected loads in most structures. Punching shear design methods for interior slab-wall connections subjected to gravity load only, developed from finite element analysis results, are developed and presented in the paper.

The limited availability of research studies related to the behavior of Steel Fiber Reinforced Concrete (SFRC) members subjected to torsion has hindered the development of clear and reliable design guidelines. Recent efforts by various researchers have been devoted to the development of analytical models for predicting the torsional response of SFRC members, supported by experimental results which have highlighted the efficiency of steel fibers in improving the torsional resistance and stiffness. For beams subjected to moderate or low levels of torsion, steel fibers, even at moderate dosages, have demonstrated the potential to replace minimum conventional torsion reinforcement, thus providing significant advantages for practical applications. This paper presents a discussion of the recent developments in research related to testing SFRC members under pure torsion. A comprehensive database of experimental test data is collated to provide a state-of-the-art in this respect. Additionally, the manuscript delves into analytical prediction models for the torsional capacity by some European code-oriented models, recently introduced by the Eurocode 2 as well as by the Authors of this paper. The results of model predictions are compared with available experimental data to assess the effectiveness and reliability of the models.

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.

Should concrete core samples extracted from a structure be submerged in water until testing? This month’s Q&A provides answer to that question along with a discussion on proper and improper moisture conditioning of cores to be tested per ASTM C42/C42M.

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.