| Typically, locally slender cross-sections are avoided in the design of hot-rolled steel structural elements, but completely avoiding local buckling ignores beneficial post-buckling reserve that exists in this mode. With appearance of high and ultra-high yield strength steels, this practice may become uneconomical, as local slenderness limits for sections to remain compact are function of the yield stress. It is postulated that continuing effort towards fuller understanding of hot-rolled steel cross-sectional local stability and more accurate accounting of web-flange interaction will create a more robust method for the design of high yield stress structural steel cross-sections that are locally slender.;First, studying the slenderness limits that are currently defined by the AISC (2005) Manual of Steel Construction in Table B4.1 of its Specification as a single value for each type of element indicates a single value of elastic local buckling coefficient. Finite strip analysis was performed on all the sections of the AISC's shape database under different loading conditions and the analysis showed that coefficients fall in a wide range, and it can be extremely approximate to represent the whole range with a single value. Based on the exact values for elastic local buckling coefficients, a series of simple empirical equations were developed and used to construct a table which is essentially a proposed alternative to AISC's Table B4.1.;A series of nonlinear finite element analyses is used to compare three design methods for locally slender steel elements: (i) AISC, (ii) AISI-Effective Width, and (iii) AISI-Direct Strength Method (DSM). Design strength formulas of chosen methods are provided in common notation, highlighting the role of cross-section stability, and showing that different methods take very different approaches predicting the strength of locally slender sections. Nonlinear finite element analysis parameter studies were performed to understand and highlight the parameters that lead to divergence between capacity predictions of different design methods. Role of cross-section details, imperfections, residual stresses, and material yield stress and parameters are examined. Finally, stress distributions at failure and cross-sectional strain distributions are used to propose improvements to DSM so it may be applied to structural steel. |
