CRACKING CRITERIONS FOR HARDENING CONCRETE STRUCTURES ANALYSED BY A PROPABILISTIC APPROACH

Abstract eng:
The durability of reinforced concrete structures depends, among other things, on the quality of concrete and on the presence of cracks. Cracks may occur in the early stage of hardening due to the development of stresses caused by plastic shrinkage, thermal deformation, autogenous shrinkage or a combination of these deformations. In case of durability prediction, it is often desirable to calculate the probability on cracking and the probability on a certain crack width as well. To calculate the probability of cracking and the probability on a certain crack width in a hardening concrete structure, a cracking criterion should be chosen; mostly this is a strength criterion. Quantifying the magnitude of the cracking criterion influences the results of a calculation and thus the reliability of the results considerably. In general it is assumed that a lower cracking criterion results in a safer situation. A Monte Carlo approach is used to examine this presumption. Until now, the cracking criterion was always taken as a fixed parameter, which is valid for plain concrete. However, for reinforced concrete, the cracking criterion is influenced by its reinforcement. In this paper, a level III calculation method for the probability of cracking and the probability of crack widths in hardening concrete elements is discussed. The level III calculation for the probability calculations will be achieved by using the Monte Carlo approach. With this method, the probability distribution functions of all input parameters are taken into account. As a new approach, the probability distribution functions to calculate the distribution of the cracking criterion for reinforced concrete are taken into account as well. In this calculation, the variability of the reinforcement bars are taken into account by probability distribution functions that describe the accuracy of placement of these reinforcement bars. It will be investigated how parameters like the concrete cover and reinforcement ratio influence the calculated results and which parameter contributes most explicitly to the realisation of a reliable prediction of the crack width and, hence results in an improved reliability of the prediction of durable concrete structures.

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