Fatigue Assessment of Orthotropic Steel Bridge Decks: Fid-Bau Portal

Fatigue Assessment of Orthotropic Steel Bridge Decks

Beales, C. / Cuninghame, J. R.

Fatigue failures have occurred in the steel orthotropic decks of several bridges in Europe, some after little more than a decade in service. This has led not only to expensive inspection and repair procedures but has also highlighted the difficulty of assessing these decks, which lie outside the scope of most design codes.

Test procedures have been developed at TRRL which have been used to determine the fatigue lives of welded connections on particular bridges. The data collected and experience gained have led to a greater understanding of the behaviour of orthotropic decks which can be used for a more general assessment of fatigue lives. In particular, the influence of factors which are not easy to model mathematically, such as the effect of the surfacing, can be evaluated.

This paper describes the experimental techniques and the application of these procedures to the deck of the Severn Crossing.

Load tests, with a vehicle of known axle weights, are used to determine the influence surface of stress at the welded connections. Tests carried out with the bridge deck surfacing removed are compared with similar tests on the surfaced bridge with the asphalt at summer and winter temperatures. Where such trials on actual bridges are impractical, data may be obtained from laboratory tests on a full-scale deck panel. The merits of the different methods are discussed.

Fatigue tests on full-scale specimens representing sections of the bridge deck are used to determine the weld classification of the connection.

Any views expressed in this paper are not necessarily those of the Department of Transport.

A computer program developed at TRRL applies the procedures of BS 5400 (Part 10) to the measured stresses and the S—N data to estimate fatigue lives. Fatigue lives have also been estimated from stress spectra obtained under traffic loading.

The research highlights the sensitivity of the calculated fatigue lives to the position of the wheel tracks and to the asphalt surfacing. It is concluded that, for ‘worst case’ conditions, few connections in the decks of existing long span bridges meet the 120-year UK design life for fatigue.