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 behaviour of a typical precast floor-to-floor system, considering the pull-out failure mode of the deformed bar into grouted keyways of slabs at the joints. To do so, the pull-out behaviour of deformed bars in grouted keyways of the connections was first experimentally studied. Subsequently, by integrating the pull-out 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 pull-out 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 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.

Previous research studies have been conducted to study the seismic response of low-aspect-ratio RC shear walls when designed using normal-strength reinforcement (NSR) versus high-strength reinforcement (HSR). Such studies demonstrated that the use of HSR has the potential to address several constructability issues in nuclear construction practice by reducing the required steel areas and subsequently rebar congestion. However, the response of nuclear RC shear walls (i.e., aspect ratios of less than one) with both HSR and axial loads has not yet been evaluated under ground motion sequences. As such, most nuclear design standards restrict the use of HSR in nuclear RC shear wall systems. Such design standards do not consider the influence of axial loads when the shear strength capacity of such walls is calculated. To address this gap, the current study investigates the influence of axial load on the performance of nuclear RC shear walls with HSR when subjected to ground motion sequences using hybrid simulation testing and modelling assessment techniques. In this respect, two RC shear walls (i.e., W1-HSR and W2-HSR-AL), with an aspect ratio of 0.83, are investigated. Wall W2-HSR-AL had an axial load of 3.5% of its axial compressive strength, while wall W1-HSR had no axial load. The test walls were subjected to a wide range of ground motion records, from operational basis earthquake (OBE) to beyond design basis earthquake (BDBE) levels. The experimental results of the walls are discussed in terms of their damage sequences, cracking patterns, ductility capacities, effective periods, and rebar strains. The test results are then used to develop and validate a numerical OpenSees model that simulates the seismic response of nuclear RC shear walls with different axial load levels. Finally, the experimental and numerical results are compared to the current ASCE 41-23 backbone model for RC shear walls. The experimental results demonstrate that walls W1-HSR and W2-HSR-AL showed similar crack patterns and subsequent shear-flexure failures; however, the former had wider cracks relative to the former during the different ground motion records. In addition, the axial load reduced the displacement ductility of wall W2-HSR-AL by 18% compared to wall W1-HSR. Moreover, the ASCE 41-23 backbone model was not able to adequately capture the seismic response of the two test walls. The current study enlarges the experimental and numerical/analytical database pertaining to the seismic performance of low-aspect-ratio RC shear walls with HSR to facilitate their adoption in nuclear construction practice.

Filling reinforced concrete (RC) frame spans with RC shear walls constitutes a strategic intervention to existing sub-standard buildings. The efficiency of this intervention depends, among other things, on the behavior of interfaces between the shear wall and the frame elements. The failure of critical interfaces that may lead to undesirable shear sliding of the wall at its base can only be prevented if the interfaces are adequately designed. To investigate the cyclic behavior of interfaces within the composite frame-to-wall members, four frames filled with RC walls, as well as two reference specimens (i.e., a bare frame and a monolithic frame/wall specimen), were subjected to cyclic horizontal displacements. The crucial effect of the interface reinforcement ratio, the detailing, the dowel distribution along the interface, and the embedment length on the behavior of the specimens, in terms of maximum capacity, drift, and failure mode, was confirmed.