International Concrete Abstracts Portal

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.

Punching shear failure of RC flat slab connections cause loss of slab’s supports. The detached slab is falling and impacting the slab below. That problem requires thorough investigation and appropriate design guidelines. This paper presents research results on various aspects of this impact scenario. The analysis is based on an advanced numerical model that has been formulated, and the impact analyses follow the damage evolution in the concrete and reinforcement until complete connections failure of the impacted slab is developed, and a progressive collapse scenario starts. The effects of slab geometry and material properties were examined, and the contribution of special shear reinforcement and integrity rebars were investigated. The potential contribution of added drop panels to enhance slab resistance were examined. The slabs impact effect on the supporting columns has been investigated as well. The suitability of current static loading design-criteria to provide safe design against dynamic/impact punching shear is assessed. It shows that the current static-loading based design standards cannot ensure resilience of flat slab connections to impact loading and therefore cannot prevent a progressive collapse scenario. Analyses results are compared with inspected failure details of a collapsed RC flat slabs parking garage building, and excellent agreement is obtained.

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.

As glass fiber-reinforced polymer (GFRP) reinforcing bars become more widely used, there is a need to better understand the behavior of GFRP reinforced members. GFRP reinforced deep beams are one example of concrete members that are not currently well understood. Besides the linear elastic behavior of GFRP material, another significant difference between GFRP and steel reinforcement is the difference in surface treatment. While deformation requirements are prescribed for steel reinforcing bars, FRP bars may have different surface treatments depending on the manufacturer. The different surface treatments lead to different bond characteristics and, ultimately, a difference in performance. This research explores the effect of bond through both an analytical study using VecTor2 and a series of large-scale deep beam tests reinforced with GFRP bars. Analytically, VecTor2 was able to capture the behavior of published experiments from the literature, reinforced with sand-coated GFRP bars. An alternative surface preparation consisting of machined indentations was introduced as a parameter in this study, resulting in significant changes in the performance and behavior of the deep beams. VecTor2 was also able to capture the behavior of these beams when adjustments were made to the bond model to match the observations of the experiments.

Developed 40 years ago by Frank Vecchio and Michael Collins, the Modified Compression Field Theory (MCFT) and its successor, the Disturbed Stress Field Model (DSFM), have proven to be robust methodologies in modeling the response of concrete structures. Originally developed for newly designed concrete structures, they have been refined over the years to expand their applicability to various engineering problems, including modeling deteriorated and repaired structures. This paper reviews the evolution and application of MCFT in modeling and assessment of deteriorated and repaired concrete structures. The first part focuses on the application of MCFT to advanced field structural assessment, including stochastic analysis procedures that incorporate field data. The second part discusses the evolvement of MCFT to account for two of the most common deterioration mechanisms, reinforcement corrosion and alkali-silica reaction. The last part explores the application of the model to structures repaired with fiber-reinforced polymer composites. It is concluded that the extension of the MCFT formulation has enabled it to reliably predict the behavior of both deteriorated and repaired concrete structures.