Current designs of steel orthotropic bridge decks commonly use V section longitudinal stiffeners which are continuous through the transverse diaphragms. An assessment has been made of the fatigue performance of a butt welded splice joint used to make the site a connection between lengths of stiffener. Fatigue tests were carried out on sections of deck containing a full size stiffener plate joint. Endurance was found to depend only on stress range, though fatigue crack growth was slower where the applied stress cycle was mainly compressive. Transverse butt welds on a backing bar are placed in class F in the British Standard for bridge design (BS 5400 part 10) but splice joints using this type of weld gave results which were within class C. The high fatigue strength is attributed mainly to a favourable disposition of residual stresses in the splice joint welds and to the absence of penetration defects in test specimens. Taking account of fatigue data in the literature for this type of joint, and the difficulty of detecting weld root defects in thin plate, together with the fact that such joints are made under site conditions, it is recommended that splice joints of the type tested be treated as class D for design purposes provided high standards of welding and non-destructive testing are adopted. Fatigue lives have been estimated for a splice joint in a typical modern bridge deck under design traffic loading. Assuming class D fatigue strength a design life of 21 years was calculated for a joint in the traffic lane of a bridge carrying one million commercial vehicles per year. A method of fatigue assessment for welded joints on existing bridges, based on recorded service stress history, was used to assess a splice joint in a bridge deck. The recorded data indicate that the bridge is currently carrying approximately half its design traffic loading and that the fatigue life of some splice joints may be reached in 55 to 70 years depending on traffic growth. Those joints fabricated to the same standard as the test specimens are unlikely to suffer fatigue damage. (A)

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