| The main parameters to evaluate the flexural behavior of the steel beams, are flexural strength and rotation capacity. Current seismic design procedures implicitly permit the inelastic structural deformations under strong ground motions for economic reasons. In fact, ductility is used as a parameter for evaluating the available inelastic performances of structures. The factors that affect the ductility of these members are the section dimensions, support conditions, type of loading, manufacturing distortions(imperfections and residual stresses) and material properties.This research aimed at investigation of ductility and moment capacity of I-section flexural members made of high strength steel in ultimate state. Flexural tests on six fullscale I-shaped beams were carried out, three with hybrid sections and three with homogeneous sections, made of conventional and high-strength steels grades(Q345 and Q460), subjected to the constant moment about their major axis to verify numerical models. Three-dimensional nonlinear finite element models were established and verified with the current experimental results accounting for material nonlinearity and manufacturing distortions. Stress-strain relationships obtained from tensile coupon tests were incorporated in the finite-element model. Close agreement was achieved between the test and finite element analysis results in terms of moment-rotation response and ultimate strength. A comprehensive parametric study was conducted for a wide range of parameters.Compactness and lateral support configuration provisions for design of steel beams are formulated so as to ensure that the resulting beam exhibits an appropriate behavior. Results have shown that using the high strength steel in cross sections subjected to bending has a significant effect on flexural behavior. In this paper an attempt was made to study on influence of flange and web slenderness as well as lateral support spacing of homogenous and hybrid welded I-sections on member ductility.A new theoretical-based method was proposed to determine the rotation capacity for uniform moment loading type based on an equivalent plastic moment. A comparative study was carried out between the results of this method and numerical study to ensure the accuracy of the proposed method.Cross-section classification is a significant concept in the design of flexural steel members as it addresses the susceptibility of a cross-section to local buckling and defines its appropriate design resistance. In fact, the section ductility concept is employed in the most of the current steel design codes where section behavior is governed by the buckling of flange or web plates for which independent limitations are imposed. This assumption is unreasonable because, obviously, the flange is restrained by the web and the web is restrained by the flanges, so the interaction between the two local buckling modes must be considered. Thus, section behavioral classes should be substituted by the concept of member behavioral classes. Current research proposes a classification of flexural members based on the rotation capacity at the member level for the new version of the Chinese steel design code which takes into account the interaction between local and local–overall buckling modes.Based on the obtained results from the parametric study, a new method was proposed to determine the moment resistance of I-beams with hybrid and homogeneous sections based on the slenderness in which design procedure is directly independent from the section classification, considering local and overall interaction instabilities. In fact, the main goal of this ductility based method is to simplify the current design procedure of steel members subjected to bending. A comparative study was performed between the proposed method with EC3 and AISC and results show a close agreement of the current work with EC3. |
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