Validation of proof loading methods: With a basis in collapse testing and stop criteria crack evaluation

Safe proof loading of concrete bridges requires reliable stop criteria. Such criteria must ensure sufficient margin to the ultimate resistance and may be based on observations from advanced testing. In particular, the identification of thresholds related to pre-stressed and non-shear-reinforced slab structures is currently ongoing with an addition of specific focus on potentially brittle failure modes of such structures. This paper presents representative examples of identifying stop criteria and target load thresholds using a combination of laboratory- and in-situ testing. Responses from recently tested structures and structural elements will be presented to enable discussion and perspectivation. The presented test results show measurable warning with sufficient margin from crack initiation to stop criterion. It was additionally seen that the target load often may be the governing threshold when proof load testing.