Issue 17

Traditional green oak timber framing, connected with the all-timber pegged mortice and tenon joint, is enjoying a revival in the UK. However, innovation is restricted by a lack of design guidelines or design methods for the strength analysis of such frames. This paper presents results from tests on four full-scale green oak cross-frames with different brace arrangements and also presents a model for strength prediction. The importance of pull-out strength (peg loaded in double shear normal to its longitudinal axis) of pegged connections is highlighted and proven through frame tests. Influence of tensile knee-bracing on frame behaviour is confirmed by the physical testing. J. D. Shanks. MEng, PhD Engineer, Buro Happold, Bath, UK P. Walker, BSc, PhD, MIEAust, CPEng Dept. Architecture & Civil Engineering, University of Bath, Bath, UK

The works to replace and widen the Bishop’s Bridge Road Bridge whilst maintaining normal operation of Paddington station presented significant engineering challenges. The bridge crosses 13 rail tracks (eight with 25kV overhead electrification) and two LUL surface lines at the platform ends on the approach to Paddington Station and the Paddington branch of the Regents canal. Quite apart from the physical constraints of the site, both above and below ground, the design was required to allow for future developments including links to the new deck. The contractor’s novel solution of lifting the existing 800t, 65m span Bowstring Bridge before launching the new, 3200t deck beneath it and then lowering the old bridge onto the new structure to take it away on a transporter, required additional transitory phases during construction to be addressed in the design of the structure. This paper describes the development of the project concept, the various constraints identified and the effect these and the innovative construction method, imposed on the final design for the main bridge structures. Jo’ Kenward, BEng (Tech) Hons, CEng, FIStructE, MICE, MIHT Technical Director, Hyder Consulting Ltd Alan Monnickendam, BSc (Hons), CEng, MICE Partner, Cass Hayward LLP