The Development of a Design for a Precast Concrete Bridge Beam of U-Section

Tests are described of a quarter-scale concrete simply supported bridge deck composed of U-section pretensioned beams and in situ top slab. The bridge behaved linearly at design and up to one third overload. No serious deterioration of load distribution occurred after equivalent full HB loading was repeated 2000 times at midspan in both central and eccentric positions with respect to the longitudinal centre line. Two-dimensional analysis using plate theory was found to be adequate in predicting longitudinal beam moments. The finite strip method was found to be efficient in analysing both transverse and longitudinal stresses. An ultimate load test was carried out and the cracking and collapse load factors were satisfactory. A.R. Cusens and J.L. Rounds

Dr. G. Somerville (M): I have a few questions I would like to ask regarding the two methods of analysis which were finally selected, namely, the equivalent grillage and the space frame analysis.

From a detailed research and development programme, information relevant to mostphases of the design process for concrete box-girder bridges has been derived. First, a synthesis of past designs has enabled certain features to be identified, related to the geometry of the structure and likely bounds placed upon them, thus facilitating the initial selection and proportioning of the structure. Secondly, relevant methods of analysis have been surveyed and recommendations made on their suitability in different'circumstances for treating the serviceability conditions iri the structure. Associated with this is a parameter study to highlight the significance of warping stresses and transverse flexural stresses in relation to the longitudinal flexural stresses. Finally, the treatment of the ultimate strength of these structures is discussed. B.I. Maisel, R.E. Rowe and R.A. Swann