Title: Precast Concrete U-Beam Dapped Ends

Author(s): Leslie A. Clark, Baljeet Gill, and Howard Taylor

Publication: Structural Journal

Volume: 86

Issue: 6

Appears on pages(s): 723-727

Keywords: beams (supports); bridges (structures); composite construction (con-crete to concrete); construction joints; loads (forces); models; plastic theory; precast concrete; pretensioning; structurrri design; tests; webs (supports).

DOI: 10.14359/9231

Date: 11/1/1989

Abstract:
Precast concrete U-beams are used extensivet’y in the U.K. for medium-span bridge decks. The precast beams act compositely with an in situ concrete top slab. If it is necessary to incorporate a dapped end in a U-beam, considerable manufacturing and design difficulties arise because of the shape of a U-beam. With regard to manufacture, expensive modifications have to be made to the steel molds used in the precast factory. Design problems arise because the reaction forces tend to push the U-beam webs apart. To overcome the manufacturing problems, a new end detail has been developed that does not require modification to the steel molds. However, the new detail created additional design problems. The development of the new detail was carried out by an initial program of theoretical work and model testing. Once a design method and a feasible method of construction had been developed, tests on full-size U-beams were performed at a precast concrete factory. These tests confirmed the results of the model tests but revealed some further difficulties, which were resolved, and a satisfactory detail was finally achieved.