Crack Initiation Strength of Structural Steel Members Having Experienced Large Compressive Strain due to Buckling Deformation (2nd Report)

Abstract

It is known that compressive plastic strain deteriorates the ductility and fracture toughness of steels.So when structural members encountered buckling collapse is subjected to cyclic load, cracks may easily initiate at the concave side (compressive side) of buckling deflection.In this paper, an attempt was made to investigate the crack initiation behavior for structural members subjected to cyclic bending load after undergoing buckling collapse.For this purpose, crack initiation tests using strip specimens under cyclic bending load were performed with JIS SS 400 steel plate.For different cyclic loading conditions indicated by various displacement amplitude of the loading point, distribution of strain on specimen at the bending buckling state, and number of cycles at crack initiating was examined.For all loading cases, elastoplastic large deformation FEM analyses were also performed for the strip specimens to investigate strain and stress at crack initiation points. It was found that : (1) For the strip specimens subjected to cyclic load after undergoing buckling collapse, crack initiated earlier at the center of width on the compressive side than at the edge on the tensile side.(2) According to the FEM analyses, the largest stress was induced at the center of width on the compressive side.(3) Relationship between the strain at the crack initiation points and number of cycles at crack initiating can be expressed by a linear function on logarithmic scale.