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Nine squat shear walls were tested under cyclic loading to investigate the effect of flanges on the seismic resistance of the walls. Test parameters were failure mode, flange thickness, reinforcement ratio, aspect ratio, and grade of the reinforcing bars. The test results showed that, for squat walls, vertical reinforcing bars in the flanges or boundary elements significantly increased the shear strength of the wall, while the shear contribution of the flange concrete was marginal. On the other hand, due to the strut-and-tie mechanism of squat walls, horizontal reinforcing bars in the web did not effectively contribute to the shear strength of the walls and remained elastic at peak strength. The shear-friction strength was also significantly increased by virtue of the vertical reinforcing bars in flanges. The test results provided evidence that the vertical reinforcement in flanges effectively contributed to shear and shear-friction strength and should be considered in the strength prediction.
Keywords: cyclic loading tests; flanged walls; shear-friction strength; shear strength; squat walls.
INTRODUCTION
Recent earthquakes such as Tohoku earthquake (Japan) and North Anna earthquake (United States) have resulted in the emergence of safety issues in nuclear power plants (NPPs) owing to increasing seismic demands (that is, beyond design basis earthquakes [DBEs]). Therefore, seismic probabilistic risk assessment (SPRA) is performed to reevaluate the seismic safety of operational NPPs based on the increased site-specific seismic demands. Because the seismic demand is greater than the level of the DBE, the primary objective of SPRA is to accurately evaluate the actual seismic capacities of the structures and equipment, which are expected to be greater than the design strength. Generally, the containment structure in NPPs is known to be relatively safe because of its high strength. Therefore, safety of an auxiliary building, which consists of low-rise shear walls, is the primary concern in the evaluation of NPP structures.
The strength of low-rise walls is usually determined by shear or shear-friction failure modes. Walls parallel to the loading direction are known to resist shear and shear-friction strengths. Thus, the majority of the existing experimental studies for evaluating shear and shear-friction strengths have focused on rectangular walls without flanges. The shear strength of rectangular shear walls was studied by Cardenas et al.,1 Wood,2 Gulec et al.,3 Gulec and Whittaker,4 Tran...