Design value of a headed stud shear resistance in composite steel – concrete beams – probability-based approach to evaluation

Abstract

[EN] Conventional standard procedure used to determine the design value of a headed stud shear resistance in composite steel-concrete beams is very simple but, in fact, mathematically incorrect, particularly in the case when such connector is automatically welded and when it is working in a solid slab. According to this approach the considered value is specified as a minimum of two separate design values. One of them is related to the resistance of the stud itself while the other is associated with the failure of the surrounding concrete. In the paper presented by the authors a new algorithm which allow to evaluate this value is recommended and discussed in detail. It seems to be more accurate because it is based on the fully probabilistic inference. In such approach a new random variable is introduced, being a minimum of two other, statistically independent, random variables. Analogously as it is in the concept previously mentioned, the first random variable quantifies now the steel stud shear resistance whereas the second one – the resistance of the adjacent concrete. Consequently, the sought design value is determined as a suitable quantile of this new random variable, characterized by log-normal probability distribution. It is shown that the design value of a headed stud shear resistance, calculated in this manner, strongly depends on the variability of strength parameters, relating both to the steel of which the connecting stud is made and to the concrete of the slab. In addition, it is found that in the case when the variability of concrete strength is too high, the safety factor recommended to use in European standards is not able to provide the required safety level, acceptable by the building users. The considerations presented in the article are illustrated by a detailed computational example.