Validation of Nonlinear Finite Element Analysis on Reinforced Concrete Slab under Concentrated Out-of-plane Load Combined with Uniaxial In-plane Load Based on Case Study

Abstract

Finite element analysis is becoming a popular tool for engineers recently. Nonlinear finite element analysis is more advanced due to that it can deal with the nonlinearity of structures, which leads to more accurate approximation of structural behaviour. In Model Code 2010, nonlinear finite element analysis, which belongs to the higher level of approximation, can predict the structural behaviour with refined physical parameters but by devoting more time to the analysis. This leads to better accuracy. Thus, it is important to study how to apply nonlinear finite element analysis to approximate the structural strength.
When it comes to the existing design codes, the shear design methods of reinforced concrete slabs loaded in uniaxial in-plane force are developed from the tests of beams rather than slabs, which may lead to the underestimation of the design resistance. Through experiments of seven slabs, a related study of the validity of existing shear design methods has been performed by Bui et al. (2017). However, there is no existing literature about the application of nonlinear finite element analysis towards the reinforcement concrete slabs mentioned above so far. In this thesis, one single nonlinear finite element analysis is applied to seven slabs of experiment to study the validation of nonlinear finite element analysis on the RC slabs without shear reinforcement loaded in concentrated out-of-plane load and uniaxial in-plane loads. The validation is studied by comparing results from finite element analysis, experiment and finite element analysis from Nana et al. (2017), which mainly includes shear load – displacement curve, development of crack pattern, failure modes and the influence of uniaxial load on the structural behaviour. In addition, the shear capacity under uniaxial in-plane load is studied by comparing results from analytical assessment based on existing codes, experiment and nonlinear finite element analysis.
When compared with experiment, nonlinear finite element analysis shows a close shear capacity of all seven slabs but stiffer structural behaviour. The development of cracks is similar to the observation of experiment. The failure modes indicated by nonlinear finite element analysis is more likely punching shear rather than one-way shear that is demonstrated in the experiment. The influence of increasing uniaxial compression on shear capacity is larger than what is observed in experiment while increasing tension has smaller influence. By comparing the prediction of shear capacity from experiment, existing codes and nonlinear finite element analysis, it can be concluded that NLFEA is unconservative in prediction of shear capacity of the RC slabs without shear reinforcement loaded in concentrated out-of-plane loads and uniaxial in-plane loads. Some suggestions are given for further study. Improvement of modelling is suggested. For instance, finer mesh could lead to more accurate results, and insights of bond-slip reinforcement could generate more precise results. Furthermore, the study of safety formats is suggested in further study to consider the uncertainty due to random variation of material properties. In addition, more experiments and nonlinear finite element analysis are suggested to get insights of the influence of uniaxial loads on structural behaviour of RC slabs without shear reinforcement.