An upper-bound plastic analysis for shear

Abstract

This paper describes the calibration of a two-dimensional (2D) plasticity-based upper-bound analysis model for the assessment of shear in reinforced concrete beams. This work is part of an ongoing research effort at the University of Cambridge, aimed specifically at the assessment of shear in existing concrete bridges. Due to ductility limitations in concrete, full strength may not be achieved along the assumed lines of discontinuity during collapse, as assumed in a plasticity analysis. For this reason, an ‘effective strength’ of concrete is introduced, which is simply a fraction of the compressive cube strength of the concrete. In order to develop a suitable overall (3D) collapse analysis technique for concrete beam-and-slab bridges, it is necessary to determine this effective strength of concrete in each of the beam and slab portions. Here, a 2D beam shear collapse model, and an associated expression for the effectiveness factor for the concrete, are formulated and calibrated against several test results. Restrictions on the use of this model are established and it is concluded that such an analysis technique is eminently suitable for extension to the more general 3D collapse problem in existing concrete beam-and-slab bridges.