Investigation into backprop forces and deflections at St George Wharf

Abstract

The first part of the paper shows that good estimates of backprop forces are obtainable from the Cardington building if the slab stiffness is reduced to allow for cracking. This is significant since it resolves an apparent inconsistency between the author's work on deflection and Beeby's work on forces in backprops. The second part of the paper investigates the forces in backprops and slab deflections at St George Wharf, London. The work was carried out to investigate the validity of design procedures based on research at Cardington that have been widely disseminated in Best Practice Guides and elsewhere. Measured and predicted backprop forces and deflections are shown to compare well at St George Wharf which increases confidence in the Cardington research. The paper also describes the backpropping arrangement used at St George Wharf for construction of the 600 mm thick transfer slab at the 15th floor. The backpropping arrangement was designed using the traditional assumption that loads are equally shared between floors since the frame contractor could not justify the design using the improved methods developed by Beeby from research at Cardington. Back analysis shows that the design can only be justified if preload is taken into account in the backprops.