The Transport and Road Research Laboratory (TRRL) has been involved in research into aspects of the behaviour of the Severn Crossing since 1963, some three years before the structure was opened to traffic. Early work, concerned with the performance of surfacings, traffic loadings and traffic induced stresses, led to the prediction that fatigue cracking would occur in welded connections in the steel deck. Cracks first appeared in 1971; then in 1977, cracking occurred in the trough to cross-beam and trough to deck plate joints. The early predictive work was followed by research to devise methods of repairing and strengthening the structure. Orthotropic steel decks are beyond the scope of the bridge design code (BS 5400) because of the difficulty of classifying the fatigue strength and of determining the local stress at the welded joint. Much of the experimental effort was therefore directed to fatigue testing and stress measurement. This Paper also describes TRRL research on the performance of the cables, corrosion of the steelwork, temperature effects, wind effects, and specific work on the profilometry of the decks, stiffness of the diaphragms, movement at shear key bearings, inspection of the deck welds and properties of de-icing materials. The Paper provides an overview of TRRL's involvement.
