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The Structural Engineer

In assessing the local stability of simple retaining walls, conventional design methods require that independent assessments are made of sliding, overturning, and bearing capacity, with the width of the wall base being determined by the most critical of these considerations. It is shown that these three considerations can be interrelated by using an integrated design method. This method indicates that the selection of high values of angle of base friction, as permitted by the current Code of Practice for earth retaining structures, can lead to unacceptably low factors of safety on bearing capacity when due account is taken of load eccentricity and inclination. An introduction is made to design using partial coefficients, or load factors, and it is shown that a partial coefficient of 1.4 to 1.5 is required on the tangent of the internal angle of shearing resistance to obtain conventional factors of safety of the required value. Adoption of the Danish Code factor of 1.2 appears to lead to conventional factors of safety less than 2. Finally, wall design using compaction theory is introduced where some account is taken of the high lateral earth pressures induced by compaction plant. It is shown that the resulting high lateral thrust has a potentially dramatic effect on factors of safety against sliding and bearing capacity. Under these circumstances, there is a likelihood of the wall sliding, in which case the lateral thrust is reduced to the active value. Despite this, bending moments at the base of the wall stem are still higher than those obtained using a quasi-hydrostatic distribution of lateral earth pressure, since bodily wall translation is associated with a parabolic pressure distribution. This leads to an elevation of the line of active thrust which can readily account for a 50% increase in the design bending moment. Professor T.S. Ingold introduction The conventional process of wall design involves

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The Structural Engineer

Dr. L. A. Clark (M) (University of Birmingham): The authors are to be congratulated for developing design aids which should greatly reduce the design time of a popular form of concrete bridge construction (i.e. M-beam bridge decks). The test data obtained from the four bridges at various stages of construction are particularly valuable, since, to the writer’s knowledge, no previous data have been obtained for either fullsize or true model M-beam bridge decks.

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The Structural Engineer

A significant feature of multistorey sway frames is the drastic effect of horizontal deflections on their stiffness. This applies particularly with tall and irregular frames, where controlling the sway, to satisfy limit state recommendations, is more difficult than satisfying strength and instability requirements. In this paper a simple, but accurate, method is presented for the design of these frames. An equation is first derived to define the most economic profile of a frame in its deformed position. A practical design method is then presented in which the member sizes are calculated so that the storey deflections, as given by the profile, are satisfied exactly. The method is fast because it does not depend on the analysis of the frame with preselected sections and thus removes the need for the explicit solution of any simultaneous stiffness equations. Instead, it proportions the members in the most economic manner, using current market prices, and calculates the required column sections. A design procedure is given so that all the recent BSI recommendations for the limit state design of steel sway frames are satisfied. The results of an investigation into the design of sway frames are then reported, in conjunction with a number of examples. Professor K.I. Majid and S. Okdeh

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The Structural Engineer

The design rules in British Standards relating to bridges and buildings for lateral torsional buckling of beams are summarised. Attention is focused on the torsional restraint requirements at the supports for achieving the ultimate design limit state. The results of an experimentol investigation carried out using hot rolled universal beam sections under the action of a central point load applied at the top flange level are presented. The beams were tested to failure with different degrees of torsional restraint stiffness at the supports and the results compared with the design values obtained from British Standards. B. Bose

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