size-dependent punching shear failure of thick reinforced concrete slabs

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Experimental investigations of reinforced concrete (RC) slabs with significant thickness still represent a major challenge in civil engineering. Above all hardly manageable dimensions of test specimen, associated self-weights, and appropriate test-loads are responsible for conventional test-setups and concepts currently facing true limits. This explains why undamped intensive international research on the punching shear behavior of RC slabs has been limited to comparatively thin members and thus does not cover the total practical range of recent application that probably rises further in the future. Despite these experimental deficits semi-empirical design rules (EC 2, ACI 318, MC 2010) have been derived from the available data basis and must be applied to cases beyond the intended scope. Thus, extrapolation of experimental results is necessary which introduces additional uncertainty to prognoses of the punching shear failure due to the size effect. Whether potential safety issues arise thereof and how big these might be cannot be quantified without testing thick RC slabs. Also physically well-interpretable models based on these data which have been proposed yet need further verification by large scale tests. The general concept continuously developed and enhanced in the previous project phases aims to resolve the deficit directly, enabling for punching shear tests of really thick RC slabs for the first time. Inspired by numerical simulation, experimental demands concerning space, test-setup, devices and loads are significantly reduced accounting for (multiple) symmetry of specimens consequently. This allows for testing of clearly thicker RC slabs employing the infrastructure already at hand. Once having successfully minimized unintentionally stiff friction-links in the current phase and having restricted to demonstrate the test set-up´s validation of functionality to 30 cm thick RC slabs as directed by the reviewers before, now 70 cm thick RC slabs shall be finally tested. At first, this requires to build the adequate and large-scale concrete-made supports finally, which have been deferred so far. Next is to consequently verify the then up-scaled concept employing appropriate but symmetrically reduced beams again. Finally, the proposal contains two test series. The first enables to quantify the size effect by testing of strictly and truly up-scaled RC slabs without reinforcement while the second one captures the different potential failure mechanisms of reinforced concrete slabs experimentally.