Computing redistribution moments in the plastic stage by using linear analysis

摘要

In this research, a suggested linear model was investigated to analyze the plastic stage for indeterminate skeletal steel structures.rnThe aim of this model is to facilitate the analysis of the structure element in the plastic stage without resorting to therncomplicated calculations of the material nonlinearity. The suggested model was represented by considering the full plasticrnsections in the element as a concentrated plastic hinge. The plastic hinge was modeled instead of the plastic zones as a pinrnsupport or an intermediate hinge with a rotational spring. Computing the stiffness of rotational spring was based on thernacceptance criteria in the nonlinear static analysis according to FEMA 356 (2000). The linear structural methods can be usedrnafter that to calculate the deformations and moments in plastic stage. In this paper and due to the simple cases which are analyzed,rnthe forced method of structural analysis can be used. But for structural elements which are more complicated than thernpresent cases where the plastic hinges are separated on more positions, the finite element analysis is the best. The suggestedrnmodel can be used to predict the mechanism of failure, to evaluate the deformations after occurring the plastic moment asrnwell as to compute the elastic redistribution moments. The suggested model was verified by comparing the experimentallyrnand analytically results of steel beam deformations which made by El Damatty (J Steel Compos Struct 3:421–438, 2003)rnwith the obtained results of the suggested model, and the suggested model gave good results. Moreover, a W-shaped fixedrnsteel beam was analyzed by finite element method by using ANSYS program, the suggested model and elastic analysis torncompute the induced moments in plastic stage and evaluated the elastic redistribution moments. The suggested model gavernmatching values of the induced moments of the fixed compared with the finite element results.