Multi-hazard investigation and testing of steel-plate composite (SC) wall piers: Seismic and thermal loads

Abstract

Design of structural walls in safety-related nuclear facilities needs to consider the combination of seismic and accident thermal loads. However, current codes provide limited procedural guidance for the analysis and design of walls for this load combination. Experimental studies were conducted to evaluate the cyclic in-plane response of steel-plate composite (SC) wall pier test units at ambient and typical accident temperatures (up to 232 °C). The test unit was subjected to two durations (1-hour and 3-hour) and magnitudes (149 °C and 232 °C) of surface temperatures in combination with cyclic in-plane loading. Accident temperatures result in the evolution of non-linear thermal gradients through the thickness of the test unit. The thermal gradients result in extensive concrete cracking, thus reducing the stiffness of the specimens. For surface temperature of 149 °C, the secant stiffness of the test unit reduced by 20% in comparison to the ambient secant stiffness. The reduction in secant stiffness was 40% for surface temperature of 232 °C. The lateral strength of flexure-controlled SC wall pier test unit subjected to typical accident temperatures was 25% higher than the strength corresponding to the initiation of compression yielding in the faceplates (at ambient temperatures). Evaluation of the experimental results suggests that the ambient strength equations for flexure-controlled SC wall piers can also be used to calculate the strength at typical accident temperatures (up to 232 °C). The stiffness for accident thermal loading combinations can be considered to linearly reduce from cracked stiffness at ambient temperature to fully cracked, i.e., steel only stiffness as the surface temperature increases up to typical accident values.