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