ABSTRACT
Based on the insights of Chapter 3, a numerical model should be able to incrementally describe the structural behaviour of a construction from the linear elastic stage, through cracking and crushing, until complete loss of strength or stability. Only then is it possible to control the serviceability limit state, fully understand the failure mechanism and assess safety. With this aim, material characterization should include a complete stress-strain behaviour description considering the observed experimental failure modes, stiffness degradation and energy dissipation.
The goal of the present chapter is the description of the main materials encountered in existing civil engineering structures. Essential material properties are discussed according to their experimental behaviour. In this regard, it must be stressed that data are also available in codes of practice, although mainly focused on concrete and steel. Far less information is usually available for timber and masonry due to their heterogeneity and diversity of construction techniques, which makes generalization complex. The incomplete material characterization is particularly felt in case of nonlinear analysis, which should be primarily considered for understanding the behaviour of existing structures. The recommendations presented in this chapter are not intended as a substitute to detailed material investigation and testing (in situ or on material sample, when possible), being the careful judgement of the analyst required at every level of the structural assessment. Sensitivity analyses should also be used to determine the influence of specific material parameters in the assessment outcome. This can be of support in judging the effectiveness of additional tests to refine material and structural characterization. Finally, information about safety assessment is introduced in the last section of the present chapter. Aspects such as cyclic behaviour, creep, shrinkage, moisture movement or thermal expansion are not discussed in the present text, despite their possible relevance in the evaluation of structural performance.
