Behavior of Nuclear RC Shear Walls Designed for Similar Lateral Strengths Using Normal-Strength versus High-Strength Materials

Abstract

This paper describes an experimental investigation on the use of high-strength steel and high-strength concrete to reduce the required reinforcement areas in nuclear shear walls. Two squat rectangular walls with uniformly distributed reinforcement (i.e., without boundary regions) and rectangular penetrations commonly found in nuclear power plant construction were tested under reversed-cyclic lateral loading. Specimen W1 used normal-strength materials and a high reinforcement ratio typical of the state of practice. Specimen W2 had identical dimensions (since nuclear wall lengths and thicknesses are often governed by nonstructural requirements), but used high-strength concrete and significantly reduced areas (by about 50%) of high-strength reinforcement to result in a lateral strength similar to that of Specimen W1. Specimen W2 was able to achieve nearly the same lateral strength (about 90%) as that of Specimen W1 and had slightly greater initial stiffness and diagonal-cracking strength (important design considerations for nuclear walls). As potential limitations, the postcracking stiffness of Specimen W2 was reduced and the wall had wider cracks than Specimen W1 prior to peak load. However, by the attainment of peak load, the crack patterns (i.e., orientation and spacing between diagonal cracks) of the two walls were similar, demonstrating that the reduced reinforcement areas with the same spacing in Specimen W2 did not negatively affect the ultimate load-resisting mechanism. Both walls had shear-dominant failure, but Specimen W2 had a more gradual loss in strength after peak load. Estimations of initial lateral stiffness, diagonal-cracking strength, and peak strength from numerical finite-element analyses were reasonably close; however, the diagonal-cracking strength and peak strength estimates were unconservative (i.e., higher than measured) and need improvement. Needed improvements to existing code design methods and equations for the initial stiffness, diagonal-cracking strength, and peak strength of squat RC walls are also discussed.