Probabilistic steel stress–crack width relationship in R.C. frames with smooth rebars

Structural assessment of existing reinforced concrete (R.C.) constructions results from a combination of experimental (determination of material properties and rebar detailing) and numerical evaluations (static and/or dynamic nonlinear analyses under design loads). In this framework, estimation of reinforcement stress levels can give useful information about the actual response of the structure under applied loads, but generally requires invasive and expensive operations. This paper presents an insight on the assessment of relationships between crack width and reinforcement stress in the critical regions of existing concrete buildings, such as column base or beam–column joints, reinforced with smooth rebars. The proposed method is based on a refined numerical procedure that combines advanced modelling of the steel rebar and computation of relationships between observed/monitored crack patterns and uncertainties affecting relevant structural parameters. The main numerical aspects of the deterministic approach to crack width estimation, validated against specific experimental results, are discussed. In addition, a regression analysis is used to derive probabilistic estimation of the reinforcing steel stress. In summary, a promising example of integration of numerical and experimental knowledge is presented, enabling monitoring systems to cover not only global features of the constructions, but also local relevant parameters.