Problem Building Structures and Public Safety: the Case of Hong Kong

When designing continuous concrete bridges incorporating precast, pretensioned beams, problems of interpretation of design requirements arise at the continuous supports when considering the serviceability limit state. These problems are associated with the tension induced in the tops of the precast beams at their ends as a result of hogging bending and with the tension induced at the bottom of the in situ concrete crosshead as a result of long-term sagging bending in the absence of live load. These problems are discussed and design proposals made. Professor L.A. Clark and I. Sugie

Twenty high strength concrete deep beams with various top-to-bottom loading ratios were tested to failure. Two types of web reinforcement were investigated: type ‘a’ web pattern with verticul web reinforcement ratio pv at 0.48% and type ‘b’ web pattern with pv at 1.43%. Detailing of the web reinforcement followed the recommendations given by the UK CIRIA Guide, which would seem to be the only design document for deep beams subjected to combined top-and-bottom loading. It is found that the CIRIA detailing rules help to ensure ductility in the behaviour of the specimens, and this in turn yields consistent ultimate shear strengths irrespective of the loading condition imposed on the beams. Comparisons with test results also show that the CIRIA predictions are both conservative and consistent. K.H. Tan, Professor F.K. Kong and L.W. Weng

Winner of the Institution's annual Kenneth Severn Award, Rena Vogelzang, answers President Brian Uy's essay question on structural efficiency, embodied carbon and maintaining public safety.