On structural finite element modeling strategies and their influence on the optimization of final constructability of reinforced concrete structures

Abstract

The design of nuclear civil structures based on rules in European standards makes extensive use of the Finite Element Method (FEM). The size and complexity of the models are continuously increasing. Lately, the post-processing of the FEM results has centered the engineers’ contribution on analyzing the reinforcement density produced using automated methods dealing with shell or plate models, which often leads to excessive plate use even in D-regions (discontinuity or disturbance region). This practice is particularly problematic for nuclear structures, which exhibit a large set of massive parts due to radiation protection requirements in many areas such as the reactor pit, the raft, or the containment gusset. Furthermore, these substructures are generally not well aligned with thin structural elements (such as slabs and walls) due to heavy equipment, piping, and HVAC (heating, ventilation, and air conditioning) constraints. This is contrary to what should be done to achieve the best engineering design.To address these issues, an overall modeling and post-processing approach is proposed herein. The objective is to enhance the implementation of the finite element model and the post-processing phase to improve the quality of the modeling and reinforcement of B (non-disturbed region) and D regions without significantly impacting the time needed for the design.A second objective of the proposed methods is to improve the constructability of reinforced concrete nuclear structures. Indeed, the current modeling approach, which often misuses shell elements, often leads to a significant overestimation of the required reinforcement density and consequently complicates the fabrication of the reinforced concrete structures.To illustrate the approach used here, an example based on a building typical of a nuclear structure is presented. The distinct benefits of both the overall modeling and the reinforcement post-processing are highlighted. This approach exhibits a saving of nearly 25% on the bending reinforcement sections of the outer walls compared to a practice that doesn’t account for the improvements presented in the paper. Moreover, it reduces the maximum values of reinforcement due to bending of a plate by almost 40% without changing the reinforcement calculation process. It also provides a smoothing method of the reinforcement ratio fringes based on energy conservation. The method is automated and replaces the common, time-consuming practice of averaging the reinforcement ratios for arbitrary defined sets of finite elements.