The Rotating scaffolding in the dome of St Paul's Cathedral

The response of reinforced concrete to shear forces depends on the transfer of shear across cracks. If aggregates fracture when cracks are formed, shear resistance is likely to be reduced and the loss of strength is likely to be a function of crack width and thence, in some cases, member depth. The analysis of new test results reported here, and others available from the literature, shows that, with limestone aggregate, the shear strengths of members without shear reinforcement are often below characteristic resistances calculated according to EC 2 and other recent recommendations. A considerable proportion of the experimental strengths can be below design resistances. The deficits of resistance are greatest where high concrete strengths are combined with relatively large effective depths. The same phenomenon appears to occur with other aggregates, but to a lesser extent. Members with shear reinforcement are similarly likely to be affected but to an extent less than that in members without shear reinforcement P. E. Regan, BSc, DIC, PhD, CEng, FIStructE Consultant I. L. Kennedy-Reid, BSc, MEng, CEng, MICE, MIHT Atkins – Highways and Transportation A. D. Pullen, BSc(Eng), ACGI Dept. of Civil and Environmental Engineering, Imperial College London D. A. Smith, BEng, CEng, MICE Atkins – Highways and Transportation