Issue 10

A new float glass plant has been constructed inside the boundaries of the Cowley Hill Works of Pilkington Brothers Limited, St. Helens. The site of the plant was extremely varied due both to the natural topography and geology and to the man-made obstructions of a very large industrial tip and massive foundations for an old process. J.D. Harris and A.E. Johnson

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

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.

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

The development is described of a design for a range of precast concrete bridge beams of U-section which strive for economy of construction and structural efficiency. Methods of analysis for the effect of concentrated loads have been investigated including finite element techniques from which simple methods for design office use have been derived. Standard construction details are proposed in the paper and there are examples given of how U-beams may be used in superstructures. Tendered costs are also given for two projects already under construction. E.C. Chaplin, R.J. Garrett, J.A. Gordon and D.J. Sharpe