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Bridge Reassessments – Realistic Shear Capacity Evaluation Using Arch Action Model

Gleich, Philipp A. / Maurer, Reinhard

Abstract Structural assessments of existing older German road bridges based on current German standards often uncover substantial deficits especially in terms of the required shear reinforcement in the main girders in longitudinal direction. In case of many thousand bridges built in the 1950s/1960s, the required and the existing shear reinforcement ratio can vary by factor 2 to 3 or even exceed these values. These shear deficits are only partly due to increases of traffic loads. Most of it is attributed to the evolution of structural shear capacity calculation models and especially due to the negligence of a substantial part of the concrete contribution to shear capacity. However, shear failures of existing German bridge structures have not been reported so far. As a result of these imprecise calculation models, unnecessary cost-intensive strengthening measures might have been executed in many cases. Only few representative experiments on prestressed continuous concrete beams are documented. Thus, three large-scale experiments have yet been carried out in order to gain more information about the shear load bearing behavior of such beams, using extensive measurement technique to guarantee continuous recording of structural behavior and internal forces. The overall aim was to verify an analytical arch model, which has been developed within several research projects at TU Dortmund University, based on tests and numerical simulations in order to offer more precise shear reassessment approaches for existing bridge structures. It is a matter of great public interest to investigate whether additional load bearing capacities can be applied to current approaches for shear assessments without undercutting the required safety level. The issue comes down to whether extensive, cost-intensive strengthening measures with corresponding interventions upon the traffic are in fact necessary or if it can be proved by a more precise verification procedure that the structures already possess sufficient shear capacity.