Design of Modular Composite Walls Subjected to Thermal and Mechanical Loading

Modular composite (MC) walls consist of steel plates on the exterior to serve as stay-in-place formwork and equivalent rebar. This type of construction is attractive for reducing the schedule and field labor associated with massive concrete construction projects (e.g., nuclear facilities). This paper presents analysis and design approach for MC walls subjected to simultaneous thermal loading and transverse applied loads. The applied loads can be due to accident pressure or a seismic event. Thermal loading can be due to severe temperature gradient across the wall thickness. Such gradient can be determined by performing heat transfer analysis. ACI 349 provides a simple treatment for determining the effects of temperature gradient on a conventionally reinforced concrete wall. For MC walls, similar techniques are not available that account for actual behavior under thermal and mechanical loads. Based on experimental and analytical research, the authors have developed an approach for determining the thermally induced moment on MC walls. Unlike the ACI method, the proposed method does not require determination of an equivalent (approximate) linear thermal gradient; rather, the actual thermal gradient, which has a sharp nonlinear profile within the first few to several inches of the wall thickness, can be directly used for determination of the thermally induced moment. For structural analysis of walls/compartments subjected to combined thermal and mechanical loading, the authors have developed an approach that takes into account the self-limiting nature of the thermally induced moment. The subsequent design of the walls is thus not unduly conservative.