Nonlinear finite element analysis of reinforced concrete slabs: Comparison of safety formats

According to the new fib Model Code 2010 the design shear resistance of a reinforced concrete (RC) structure can be evaluated through analytical and numerical calculation methods that fall into four different levels of approximations; the complexity and the accuracy of the calculated shear resistance increases with increasing the level of approximation. Nonlinear finite element (NLFE) analyses belong to the highest level of approximation (Level IV) thanks to their advantage to take into account real material properties and “hidden” capacities of the structure. Nevertheless, even if NLFE analyses are more and more becoming an usual instrument in the daily design process, building codes do not provide specific guidance on how to perform these analyses and if appropriate checks are not done on the model used, a big scatter in the results obtained can be detected. For this reason the Dutch Ministry of Transport, Public Works and Water Management is running a project to re-evaluate the carrying capacity of existing bridges and viaducts (e.g. reinforced and prestressed concrete beams and slabs) through NLFE analyses and published in a document containing guidelines for nonlinear finite element analyses to be followed by users in order to reduce model and users factors. In the paper several reinforced concrete slabs have been analyzed through analytical and numerical procedures according to the Model Code 2010 prescriptions and following the Dutch guidelines. The analytical and numerical results obtained have been compared with experimental results. Parametric studies have also been carried out on the slabs in order to focus on the main sensitive parameters that influence the results obtained from numerical simulations and in order to obtain reliable and, at the same time, safe results. The main indications of the guidelines for reinforced concrete slabs are presented in the paper