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The fatigue endurance of welded joints is reduced as section thickness increases and several design codes incorporate fatigue strength correction factors based on the section thickness of the base plate of the joint. Such corrections substantially reduce the stress range which a fatigue loaded welded joint can be allowed to carry.
A small amount of recent work has shown for realistic joint configurations, where the thickness of the attachment is less than that of the base plate, fatigue life may be increased. Insufficient data were available to quantify this effect and hence establish reliable design criteria for such non symmetrical joints. Consequently this programme of fatigue tests was set up to help rectify this situation and relax the detrimental design limitations currently imposed on fatigue loaded steel structures containing thick section welded joints.
The work was carried out using a BS4360 Grade 50D steel and a higher strength structural steel, RQT501. Base plate thicknesses of 25 and 50 were used with attachments ranging from 10 to 50 mm. The fatigue tests were carried out in bending and axial tension. A small number of tests were carried out on joints improved by weld toe grinding.
The beneficial influence of reduced attachment thickness has been demonstrated in both bending and tension for the Grade 50D steel in the as welded condition and the higher strength steel in the PWHT condition. Residual stresses at the weld toe influenced the results for the higher strength steel which showed no effect of attachment thickness in the as welded condition. n.

Additional information

Authors: BATESON P H, British Steel, Swinden Laboratories, Rotherham (GB);LINDLEY C, British Steel, Swinden Laboratories, Rotherham (GB)
Bibliographic Reference: EUR 15839 EN (1996) 153pp., FS, ECU 16.50
Availability: Available from the (2)
ISBN: ISBN 92-827-7198-9; ISSN
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