Validation of reinforced concrete pile caps using non-linear finite element analysis and finite element limit analysis

Analysis methods based on the rigid-plastic material models, such as the strut-and-tie method (STM), are often used to validate the designs of solid reinforced concrete structures in the ultimate limit state. However, the validation can be quite cumbersome since it involves much manual labor. Another analysis method based on the rigid-plastic material model is Finite Element Limit Analysis (FELA). The workflow when using FELA is easily automatized since the method is fully numerical. The capacity, stress fields, and collapse mode of the structure are the results that can be obtained from a FELA analysis. Another fully numerical method for validating solid reinforced concrete structures is the Non-Linear Finite Element Method (NLFEM). Using advanced material models, NLFEM programs such as DIANA FEA can accurately describe the structural behavior of reinforced concrete structures, even post the peak load. However, this modeling precision comes at the cost of increased complexity, and many material parameters are required for the models. This trade-off between precision and complexity in NLFEM is in contrast to FELA, which requires very few material parameters but only provides information about the structure at peak load. In this paper, the two methods are briefly introduced, whereafter they are compared by analyzing two four-pile cap experiments. Results obtained from the two models are presented and compared both to each other and to the experimental results. At the end, conclusions about the strengths and weaknesses of the two types of analysis are drawn.