Slender plated girders are usually composed of slender webs and compact flanges. In order to increase
their capacity, they are stiffened with transverse and longitudinal stiffeners of different shapes. Thin
plated girders used to support loads over long spans develop significant post-critical resistance after
the plate buckling occurs. To achieve better understanding of longitudinally stiffened plated girders
subjected to high bending moments and shear forces, four experimental tests on large scale test
specimens were performed. The results of these tests were used to verify the numerical model, which
was employed for further parametric studies. With numerical simulations the influence of initial
imperfections and residual stresses on the capacity of girders was investigated. Initial imperfections
were considered as actual measured initial imperfections, as positive buckling modes and as deformed
shapes, based on preliminary nonlinear calculations of perfect girders. Residual stresses were
considered with a simplified stress pattern where the level of compression stresses was varied. The
final residual stresses were determined on the basis of residual stresses measured in the tested girder.
With a verified simplified numerical model a parametric nonlinear analysis was systematically carried
out to determine the resistance of longitudinally stiffened plated girders. Based on 630 numerical
simulations a new equation for interaction at high bending moments and shear forces, as well as the
section, where the check should be performed is proposed. An extensive reliability analysis of five
different design models was made, i.e., the EN 1993-1-5 interaction model, the proposed new model,
the gross cross-section bending resistance model and two models, which are a combination of the first
three. The purpose of this reliability analysis is to determine partial safety factors and study the
adequacy of the EN 1993-1-5 resistance model. The studies have shown, that the capacity of
longitudinally stiffened plated girders can satisfactory be determined according to EN 1993-1-5 under
the condition, that the check is made at a distance hwi,max/2 and that the gross cross-section bending
capacity includes safety factor �M1 = 1,1. Finally, the influence of the tension field action on
intermediate transverse stiffeners was studied. Two tests on a full scale girder were performed to
determine the axial forces in transverse stiffeners. Parametric study, where the influence of stiffener’s
stiffnesses on the girders limit capacity was investigated, followed. The EN design rule for axial forces
in transverse stiffeners, proved to be conservative, thereby a new design rule for rigid intermediate
transverse stiffeners, based on the minimum flexural stiffness of a stiffener is proposed.
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