Avoidance of Low Strength Failure of Connections Induced by Fibrous Cracks Initiating at Weld Toes

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There are a few examples in which welded connections show a premature failure with insufficient ductility owing to fibrous cracks extending from the weld toes under monotonic or a few cycles of reversed loading. This type of connection failure should be avoided so that building structures possess plastic deformation capacity. However, no definite criteria have been established yet to prevent such a premature failure like this. The first step to be made is to identify material's characteristic constants that govern initiation of fibrous cracks at the weld toes and unstable extension of the cracks in the through-thickness direction.In this study a model test of welded T-shaped connections under combined tensile and bending loads was performed : A tensile load was applied to a main member (a plate) ; in addition bending moments were applied to the main member by pulling an attached plate fillet-welded to the main member. The material in a narrow area at the weld toes sustained large tensi … More le strain so that cracks were initiated along the weld toes and extended the the main member. The plate thickness of the main member and the bending to tensile load ratio were in this test.The greater the plate thickness, the smaller the maximum slope of the main member at which cracks initiate and extend. This means that cracks initiate when the material at the weld toes sustains a certain critical strain. The critical strain was found to be a useful criteria to evaluate the ductility of the weld toes. The test, however, came up with difficulties in measuring accurately values of the critical at the weld toes. Now study is in progress to estimate strains at the weld toes by means of nonlinear finite element analysis.An test example of welded connections in which premature failures due to cracks were recorded with reliable data is the tubular K-joint. Based on an analysis of extensive existing data for the K-joints, a simple rule was found to identify the loading conditions and geometry of the joint under which premature failures may occur. Less