International Concrete Abstracts Portal

Progressive collapse behavior of reinforced concrete frame buildings has been studied extensively, but most of the research has concentrated on frames containing seismic details. This paper presents results from analyses of the progressive collapse behavior of reinforced concrete frame buildings containing details used in regions of low seismicity following ACI CODE-318-19. The analytical simulations presented in this paper include the effect of moment redistribution that occurs after plastic moments are reached at sections of maximum moment. Ten-story 3-D frame models were designed in accordance with ACI CODE-318-19 and analyzed under progressive collapse scenarios involving the non-simultaneous removal of an interior and a corner perimeter column following ASCE 76-23. Nonlinear material behavior in these analytical models was captured using a lumped plasticity approach using hinge properties calibrated using results from laboratory experiments of full-scale sub-assemblages representing a portion of the perimeter frame containing details corresponding to non-seismic zones. The effect of catenary action in beams after column removal was included in the analyses, and the potential for premature shear failure of beams was assessed. Furthermore, models were also constructed to investigate the beneficial effects of increased rotational capacity of perimeter beams that result from using closer stirrup spacing at beam ends. This study demonstrates the importance of incorporating properly detailed continuous longitudinal bars enclosed within closely spaced closed stirrups at ends of beams of reinforced concrete frames in non-seismic zones to provide progressive collapse resistance. The study also highlights the importance of considering three-dimensional effects in models of frames to account for out-of-plane moment redistribution after loss of supporting elements.

Traditional analytical models have commonly been employed to assess the progressive collapse performance of building structures subjected to seismic loads. However, few studies addressed the effect of initial damage to adjacent components following the failure of a key component under explosion loads. In this paper, a damage assessment method for reinforced concrete structures was proposed based on the component analytical model, taking into account damage to adjacent members caused by close-in explosive scenarios. The reliability of the proposed analytical model was validated through comparison with experimental results in the existing literature. Besides, comparing the damage levels of a five-story reinforced concrete frame with those predicted by the proposed component models, the proposed assessment method based on components for predicting the damage degree of a reinforced concrete frame was validated to be reliable under a close-in explosion. The results indicated that the proposed analytical model can offer the advantage of not requiring a complex modelling process or the consideration of safety concerns associated with field explosion testing by comparing to numerical models of equivalent accuracy and experimental results.

As modern industrial and residential buildings become larger and longer, the use of precast concrete (PC) has been essential in current practice. PC lateral force-resisting system has inevitable discrete joints between precast components, which are considered one of its major concerns in structural integrity and emulative seismic performances comparable to monolithic connections. It can be overcome through code-compliant joint details and tight connection quality under a capacity design philosophy, for which suitable emulative design methods also need to be adopted. This study aims to investigate various design options based on the so-called degree-of-coupling (DOC) in vertical wall-to-wall connections in the lateral seismic design of an intermediate precast coupled shear wall system. To this end, a flexible and cost-effective lateral design method is proposed by addressing a simple but reasonable factor (G). To verify the proposed approach, an experimental campaign and robust analytical studies were conducted. Especially in the experimental program, several precast coupled shear walls with semi-emulative and fully emulative connection details in wall-to-wall vertical connections were tested under cyclic loading. On this basis, it appeared that the existing design process of precast coupled shear wall systems can be simplified, providing reasonable accuracy and design flexibility for engineers toward cost-effective intermediate precast shear wall systems.

This study investigated the flexural behavior and seismic connection performance of precast lightweight aggregate concrete shear walls (PLCWs) using the relative emulation evaluation procedure specified by the Architectural Institute of Japan (AIJ). Six PLCW specimens connected through a bolting technique were prepared and tested under constant axial and cyclic lateral loads. In addition, three companion shear walls connected through the most-used spliced sleeve technique for precast concrete members were prepared to confirm the effectiveness of the bolting technique for the seismic connection performance. The main parameters were the concrete type (all-lightweight aggregate [ALWAC], sand- lightweight aggregate [SLWAC], and normalweight concrete [NWC]); the compressive strength of the concrete; and the connection technique. The test results showed that none of the specimens connected through the conventional spliced sleeve technique reached the allowable design drift ratio specified by the AIJ, indicating that the spliced sleeve is an unfavorable technique for obtaining a seismic connection performance of PLCWs equivalent to that of cast-in-place reinforced concrete shear walls. However, the specimens made of ALWAC or NWC and connected through the bolting technique not only reached the allowable design drift ratio specified by the AIJ but also satisfied the requirements of the seismic connection performance (lateral loads and allowable error at yield displacement) within the allowable design drift ratio. Consequently, the displacement ductility ratio of the specimens connected through the bolting technique was 1.52 times higher than those for the specimens connected through the conventional spliced sleeve technique, respectively. This difference was more prominent in the specimens made of ALWAC than in those made of SLWAC or NWC. Thus, the use of the bolting technique as a wall-to-base connection in shear walls can effectively achieve a seismic connection performance equivalent to that of cast-in-place shear walls while maintaining the medium-ductility grades.

Previous research studies have been conducted to study the seismic response of low-aspect-ratio reinforced concrete (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 reinforcing bar congestion. However, the response of nuclear RC shear walls (that is, aspect ratios of less than 1) with both HSR and axial loads has not been yet 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 also 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 modeling assessment techniques. In this respect, two RC shear walls (that is, 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, whereas 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 reinforcing bar strains. The test results were 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 were compared to the current ASCE 41 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 latter 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 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.