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The cost of M-beam decks may be reduced by increasing the beam spacing to 2 m. However, as this calls into question the strength of the standard 160 mm slab under the action of the abnormal vehicle wheel loading, a series of relevant tests on a 1/3 scale model was carried out. The main variables were the percentage of steel reinforcement and the spacing of the beams. Twenty panels were tested and all failed in a punching shear mode. A detailed analysis of results has shown that the ultimate capacity of bridge slabs is greatly enhanced by compressive membrane action and the failure load is virtually independent of the percentage transverse reinforcement. A method of predicting the ultimate capacity, in which it is assumed that bridge slabs are fully restrained laterally, is proposed. This is based on a modvied punching shear equation with the enhancement due to compressive membrane action accounted for by an equivalent percentage rein forcement parameter, the actual slab reinforcement being neglected. Excellent correlation is achieved with the model tests and with the results of relevant tests reported in the literature. J. Kirkpatrick, G.I.B. Rankin and Professor A.E. Long
Steel lighting columns are typically constructed from thin-walled tubes of circular or octagonal cross-section, and usually have an access hole in the region of high bending moment. The paper describes a series of tests to failure in pure bending on such tubes, some with and some without an access hole. The access hole was always at the position of extreme-fibre compression-the critical case. Twelve specimens were tested, using a purpose-built loading rig. The results give a quantitative indication of the weakening effect of an access hole, and have formed an essential basis for the development of design formulae described in a companion paper published, also in this issue of The Structural Engineer. S.A. Baban and G.H. Little