Influence of concrete cracking on service conditions of prefabricated and reinforced concrete members

Abstract

This thesis investigates the instantaneous and time-dependent behaviour of reinforced concrete slabs and the response of lifting anchors used in prefabricated construction, particularly the development of cracks and how these influence the overall structural response. In this context, four sets of experiments were carried out on a total of ten simply-supported and three continuous lightly reinforced concrete slabs as well as thirty-six prefabricated concrete panels with different lifting anchors and reinforcement arrangements. In the first set of tests, the influence of concrete age of first loading and different drying conditions on the cracking patterns, time-dependent deformation and degradation in the stiffness of the reinforced concrete slabs were investigated. A second set of experiments was carried out to investigate the influence of different levels of cracking on the time-dependent behaviour and the degradation in the stiffness of simply-supported and continuous reinforced concrete slabs introducing a particular loading system devised to load/unload the samples. A well-defined setup for measuring the relative humidity in concrete was also proposed to gain better understanding of the development of non-linear shrinkage profile in concrete over time. The experimental results were modelled by finite element method accounting for the cracking and tension-stiffening of the concrete for the instantaneous response and for time effects, such as creep and shrinkage, during the long-term behaviour. The first set of experiments on prefabricated panels was focused on the behaviour and comparison of different edge lifting anchors and their ultimate capacities. A design procedure was proposed to account for the shape of the different lifting anchors by introducing a shape modification factor for individual lifting anchors. The behaviour of different lifting anchors influenced by the additional reinforcements was investigated in the last set of experiments.