Reliability-based evaluation of bond strength for tensed lapped joints and anchorages in new and existing reinforced concrete structures

The definition of design equations from semi-empirical or empirical models is a matter of fundamental importance in structural engineering. The direct application of partial safety factors for materials strength in such models is not appropriate in order to obtain design formulations coherent with some level of reliability, as empirical or semi-empirical formulations are calibrated adjusting empirical coefficients to fit a set of experimental data. Therefore, applying partial safety factors on material properties alone does not allow a correct estimation of structural reliability. In this paper, a reliability-based design bond strength relationship for tensed lapped joints and anchorages in reinforced concrete structures is derived applying a consistent reliability format. The semi-empirical model for mean laps and anchorages strength calculation proposed in fib Bulletin No 72 is studied. The probabilistic calibration of this model is performed defining the related model uncertainties, grounding on an extensive experimental database and distinguishing between new and existing structures. As a conclusion, the design expression for bond strength proposed by the authors is compared to current standards and its implications in laps and anchorage design in reinforced concrete structures are analyzed.