Overall Stability Analysis Of Multi-story High Rise Steel-frames

With the development of economy in our country, steel frame structure has been more and more widely used in industry. In order to analyze the stability of steel structure, we should firstly focus on the overall stability of the steel frame. However, the current method effective length is based on the calculation on stability of the column instead of the steel frame. Considering the impact on the inner force caused by deformation, the analysis based on the inner force of the steel frame structure has been revised in the new edition of Code for design of steel structure (GB 50017-2003). In this revision, second order elastic analysis onthe equationη=ΣN.Δu/ΣH.h>0.1 of steel frames structure has been raised. Inthe process of second order elastic analysis, the horizontal load is added to column top to deal with the influence on inner force caused by various defects of structures and levers.This thesis points out a theoretical analysis of the ultimate load-carrying capacity and deformation of the un-braced ideal steel frames. It evaluates the practicality of the book Code for design of steel structure (GB 50017-2003) in analysis the internal force of steel frames, and gives some suggestion on the structure analysis and design of steel frame.The ANSYS as a finite software is taken as mechanical analysis approach combined with geometric and material non-liner. The result shows that the both conform to each other. It simulates the whole process of elastic-plastic behaviour of ultimate bearing capacity and is compared with results of the other documents, and the analyzed method has been definitely proved practical.Through analysis of some examples, with the methods of first order elastic analysis, second elastic analysis and the notional load approaches recommended in the book Code for design of steel structure (GB50017-2003) and other methods, it carries act a comparative analysis of the frame structure. The result shows first order plastic analysis would be taken in calculation of the frame structure whenη<0.1. However, whenη>0.1 andη<0.25, the second order elastic analysis would be taken and the imaginary horizontal load is dealt with the defects of frame structures, or the method in this thesis would be taken. The analysis result obtained through the methods of the first order elastic analysis is much smaller than the result obtained through the method of the numeric analysis in this thesis whenη>0.25, we should increase the deflective rigidity of the frame structure. We get the conclusion meanwhile, after considering the second order effect, the horizontal deflection of the frame becomes larger; and affections of second order effect should be considered on the multi-storey and high building frame.