ultimate flexural strength of plate girders under the effect of weld crack in flange toe

the plate girders are used in important structural systems. the earlier design of plate girders was restricted to their critical bukling capacity. experimental and theoretical studies show the plate girders with vertical stiffners can carry load over than their critical buckling loads and then in modern design codes is permitted to use post- buckling capacity of them. in this case the out- of- plane bending stresses is associated in web panel and then some fatigue cracks may appear under the effect of cyclic loading. in this paper the influence of cracks in weld toe of flange is investigated using nonlinear finite elament analysis of the models of vertically stiffened plate girders. the ultimate bending capacity of beams is estimated using the well know finite element code of lusas. the effect of crack length, ratio of web slenderness and crack location are investigated in this study. the ultimate capacity of such plate girders is calculated under initial geometric imperfections. the obtained results in this study show that cracks with length of 30 cm can reduce maximum 18% in ultimate bending capacity. also the results are compared with the recommendations of the modern design code of alsc- lrfd.