Recommendations for Assessment of Reinforced Concrete Slabs: Enhanced structural analysis with the finite element method

Report, 2021

Reinforced concrete structures show a pronounced non-linear response, with cracking of concrete for service loads and reinforcement yielding and concrete crushing at ultimate load. With non-linear finite element (FE) analysis, the structural response can be captured, and such analyses have shown great potential to reveal higher load carrying capacity compared to simplified and linear analysis methods. A multi-level structural assessment strategy, developed in previous research, provides a framework for more advanced, successively improved analysis of reinforced concrete slabs.

This report provides recommendations for practicing structural engineers on structural assessment using FE analysis. The focus is on enhanced assessment with non-linear FE analysis, and the scope is reinforced concrete slabs with limited membrane effects. The intention is to facilitate the use of non-linear analysis in engineering practice by providing detailed recommendations on how such analyses can be made to provide increased understanding of the structural behaviour and reliable estimations of the load-carrying capacity of concrete slabs. However, the framework presented is general, and the approach can in many aspects also be used for other types of reinforced concrete structures. The recommendations given here are based on previous research performed by the authors, information from literature and engineering judgement based on practical experience. They are intended to give conservative estimates of the load-carrying capacity, fulfilling the required safety level.

The report includes a thorough description of the assessment strategy. The global safety format recommended for non-linear analysis is presented and its application for different assessment levels is described. Furthermore, recommendations on how to take deterioration into account are given. Non-linear FE analysis of concrete structures is presented together with general advices for its application. Furthermore, general recommendations are presented for simplified and linear analysis, corresponding to today’s practice.

For assessment with non-linear FE analysis, detailed recommendations for use in engineering practice are presented. Advices are given on idealization of the structure, choice of material models, determination of material parameters, modelling and analysis. Furthermore, the evaluation of structural response, determination of load carrying capacity and response under service conditions are described. For non-linear analysis with shell elements, resistance models on higher Level-of-Approximation according to Model Code 2010 are used. Finally, examples are showing the application of the strategy on two slabs tested in laboratory and one bridge deck slab.