Primary and secondary nuclear containments serve the critical function of providing an external protection and a leak proof boundary for containing radiation in nuclear power plants. Reinforced concrete containment in a nuclear power plant typically has a cylindrical wall and a spherical dome. Within the cylindrical shell, it is common to use different hoop reinforcing ratios at different elevations, in order to optimize the design. Reinforced concrete containments are designed for thermal effects, generally following methods provided in the committee reports of ACI 307 for chimneys or ACI 349 commentary for nuclear concrete structures. The behavior of concrete structures under thermal effects has been studied for decades. It is well know that stresses resulting from thermal effects are self-relieving and that magnitudes of thermal forces and moments are directly related to the reinforcement within the concrete member. In particular, for a given thermal and mechanical load combination, more reinforcing steel the concrete section contains, larger thermal forces/moments will be observed with correspondingly less deformations. The conventional approach provided in aforementioned building codes is to solve the equilibrium of a given reinforced concrete section with a predetermined reinforcement configuration. However, no research has been conducted to study thermal forces and moments in transition zones interfacing two regions with different reinforcement configurations. The compatibility at the interface between two regions with different reinforcement introduces further redistribution of thermal forces and moments within the transition zone, which should be considered in the design.
In this paper, a comprehensive study has been carried out using the closed form mechanical solution, in order to evaluate the redistribution of thermal forces and moments at a conceptual interface within a reinforced concrete cylindrical containment, between two regions with different reinforcement configurations. Based on this, consideration for thermal design at such an interface is provided. A practical example is presented at the end of the paper to illustrate the use of the proposed design method, followed by the conclusion.