International Concrete Abstracts Portal

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.

During past earthquakes, failures of beam-column joints have commonly been observed on the exteriors of buildings. However, only one side of these joints can be retrofitted because of the presence of beams on the other three sides. Therefore, this study aims to test four exterior beam-column joints with transverse beams, leaving the rear side as the only viable location for placing fiber-reinforced polymer (FRP) laminate. All four test specimens were designed with insufficient joint shear strength, as determined by ACI 318-19 equations, while satisfying the criteria for a strong-column/weak-beam mechanism and sufficient development length for bar anchorage. A total of two un-retrofitted specimens, with and without joint hoops, were constructed as controls. Subsequently, two similar specimens were retrofitted by applying FRP laminate on the rear side. The results show that sufficient FRP laminate can enhance the seismic performance of joints in terms of deformability, energy dissipation, and failure delay.

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.

In high-rise buildings, lower-story columns must withstand significant seismic shear forces while maintaining sufficient deformation capacity. This capacity is provided through effective confinement using transverse reinforcement. The ACI 318-25 building code specifies that confining reinforcement should be proportional to the applied axial load when the axial load exceeds 0.3A_gf'c and requires all longitudinal bars to be laterally supported with seismic hooks. However, the implementation of seismic hooks at both ends of crossties brings challenges for on-site reinforcement assembly.

This study experimentally investigates full-scale RC column specimens subjected to quasi-static cyclic loading while under a constant high axial load. The objectives are to validate the ACI 318-25 confinement requirements and to evaluate the feasibility of relaxing seismic hook requirements. The results confirm that columns designed in accordance with the ACI 318-25 building code satisfy the required 3% deformation capacity. Furthermore, satisfactory seismic performance can be achieved with crossties incorporating alternating 135-degree and 90-degree hooks, although at the expense of increased confining reinforcement.

A machine learning (ML) model is developed using a gradient-boosted decision-tree algorithm to estimate the drift capacity of reinforced concrete (RC) columns. A reliable estimate of the drift capacity of a structure is critical to both its design and assessment. The drift capacity of a structure is also broadly interpreted as a measure of its seismic vulnerability. The estimated drift capacity from the ML model is compared against that of existing methods using test results from a dataset of 341 RC columns subjected to cyclic loading. The mean of the ratio of measured to estimated drift capacity for the developed ML model was 1.0 with a coefficient of variation (CV) of 0.31. In comparison, the regression equation currently adopted in New Zealand and the US to estimate the drift capacity of RC columns has a mean of 3.13 and a CV of 1.07. Other empirical methods assessed in this study also led to large scatter and no discernible correlation between estimated and measured drift capacity. The developed ML model provides more accurate results than existing methods and can estimate the drift capacity for a broad range of RC columns. The developed model is published under an open-source license and is freely available to practitioners and researchers.