Incorporation of pre-existing cracks in finite element analyses of reinforced concrete beams without transverse reinforcement

Cracking in reinforced concrete (RC) bridges and other structures is common and not necessarily detrimental. However, some cracks may grow past specified limits and, aside from aesthetic and durability aspects, may influence the ductility and structural capacity of an RC member. This is not generally reflected in current assessment methods and, therefore, improved methods are needed. The aim of the current work was to develop a modelling methodology to incorporate pre-existing cracks into finite (FE) analysis for improved structural assessments. Two different approaches were investigated: (1) weakening the continuum elements at the position of a crack and (2) introducing discrete crack elements with weakened properties. In both approaches, a total-strain based model was used in the continuum elements. These modelling approaches were applied to analyses of experiments, in which concrete beams had been pre-cracked and tested in four-point bending. The pre-existing cracks led to differing failures limiting the deformation capacity, plus varying ultimate capacity and ductility. In the current study the weakened-elements approach captured the failure characteristics, ultimate capacity and ductility more accurately than a standard FE analysis without cracks included; the discrete-crack approach, on the other hand, did not. Furthermore, the bending stiffness differed between the experimental tests and the FE analyses. Damaged bond properties and closure of cracks in the compressive zone were identified as probable causes. Moreover, the choice of shear retention used for the weakened elements was shown to noticeably affect the predicted capacity and ductility. In conclusion, the weakened-elements approach was the most straightforward to implement. It was less time-consuming and led to better agreement with experimental results, compared to the discrete-crack approach. Based on this study, the weakened-elements approach is regarded as a promising approach for the structural assessments of tomorrow.

Automated summary

Cracking in reinforced concrete structures can affect ductility and structural capacity, highlighting the need for improved assessment methods. The study found that using weakened elements was more effective in capturing failure characteristics and capacity compared to the discrete-crack approach.