Fatigue strength of steel beams with bracket plates welded to the tension flange

Abstract

Fatigue tests under three-point bending were carried out on mild steel beams with bracket plates welded to the tension flange. The variables considered were the beam and bracket designs and the position of bracket connected. Particular attention was paid to the effect of configuration in the bracket-ends, which was varied in two distinct cases; in one the taper of the bracket end was straight and in the other it was rounded in three different ways. A good SN correlation was obtained by plotting the results in terms of bending stress range at the location of failure in the flange. This followed from the fact that the propagation of cracks across the flange exhausted the considerable part of fatigue life of beams. Thus the design details did not affect strongly the endurance of beams. However, the initial stage of cracking was sensitive to the types of bracket-ends. The fatigue crack associating with a straight bracket-end originated either from the weld toe on the flange at the bracket-to-flange junction or through the weldment, depending on the relative magnitude of two stresses suffering in the flange and in the bracket plate. The rounding of the bracket-ends prevented the occurrence of fracture through weld due to increase in the flexibility at the bracket-to-flange junction, but it did not improve the strength of crack initiation at the weld toe. It was suggested that the crack initiation of both fracture types in beams was possibly predicted from the results of comparative tests on plate specimens with longitudinal non-load-carrying fillet welds and with transverse load-carrying fillet welds.