Prefabricated High-Strength Headed Steel Reinforcement with High-Strength Concrete for Accelerated Construction of Shear Walls in Nuclear Structures

This dissertation investigates the use of high-strength headed steel reinforcement (HSR), high-strength concrete (HSC), and prefabricated reinforcing bar (rebar) assemblies to accelerate the construction of squat (height-to-length ratio < 2.0) reinforced concrete nuclear shear walls in non-containment, safety-related concrete nuclear structures. The primary goal of using HSR and HSC is to significantly reduce the required reinforcement amounts as compared with state-of-practice walls (using normal-strength materials) with the same dimensions.

From an industry survey and full-scale laboratory evaluation, it was found that prefabricated rebar assemblies can reduce on-site construction times of nuclear walls by 70-80% and that the bars engaged in assembly movement are most susceptible to spacing changes exceeding construction tolerances.

Two experimental programs were conducted to investigate the effects of HSC and HSR on the monotonic and reversed-cyclic lateral load behavior of squat shear walls. These specimens were based on prototype nuclear wall designs from available U.S. Nuclear Regulatory Commission design control documents. These experiments demonstrated that: 1) HSR and HSC perform best when combined, providing improved lateral strength and deformation capacity; 2) using HSR with HSC, a wall with significantly reduced provided reinforcement (less than half) can achieve similar peak lateral strength as a state-of-practice wall; 3) state-of-practice methods are effective for the design of reduced volumes of HSR as trim reinforcement around wall web penetrations; 4) squat rectangular walls with increased normalized base moment-to-shear ratio can be susceptible to flexure failure, contrary to current code commentaries; and 5) intersecting end walls can significantly increase the flexural stiffness and flexural strength of squat walls and should be more accurately incorporated in design.

Closed-form design methods from building codes and literature were evaluated through comparisons with the experimental measurements, resulting in recommendations for accurate and conservative design calculations of lateral stiffness, diagonal-cracking strength, and peak strength of squat walls with HSC and HSR. Additionally, nonlinear finite-element numerical models for the lateral load analysis of squat walls with HSC and HSR were developed. Recommendations were made for models that can accurately: 1) simulate reversed-cyclic wall lateral load behavior; and 2) predict wall peak lateral strength using simpler monotonic pushover analyses.