Strain Capacity of Cross-Section Elements and the Role of Local Slenderness in the Rotation Capacity of Structural Steel

The objective of this paper is to demonstrate how element (e.g. flange) local slenderness may be used to predict element strain capacity, and in turn, the element strain capacity may be used to predict member rotational capacity in structural steel members. Member plastic hinge rotation capacity has an important role in the design of steel structures, and while implicit understanding of the rotation capacity has sufficed in the past, as inelastic direct analysis methods are adopted in conventional as well as seismic design more explicit treatments are needed. It is hypothesized that the member rotation capacity, for rotations limited by local buckling, may be determined based on comparing the strain demands based on the distance to the neutral axis, against the strain capacity determined as a function of the element local slenderness. To test this hypothesis a comprehensive series of material and geometric shell finite element collapse analysis are performed in ABAQUS on component elements (plates) and structural steel members. The finite element analysis confirms the hypothesis, and also demonstrates the importance of additional factors, such as depth-to-length (shear-to-moment) in predicting the rotational capacity. The analyses are compared to existing code provisions for both conventional and seismic design and recommendations for potential improvements are made.  

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