COMPUTER AIDED ANALYSIS OF BIAXIALLY LOADED ELASTIC COLUMNS

Abstract

It has always been of great practical importance to predict the behaviour of axially compressed thin walled steel compression member in a steel structure such as a transmission tower,a building frame, an aircraft structure or a space frame. The load coming on such members is generally eccentric either in one plane or in both. Moreover,the cross section of these member can be either symmetric or asymmetric. While symmetric cross section are some what easy to analyse, the asymmetric cross section poses more difficulties. Also such thin walled members have low bending and torsional stiffness and try to bend or twist as, load is applied. All these things contribute to a '3D Behaviour' or 'Space Behaviour'. Historically these members have been treated as one dimensional for analysis. Because of large no. of assumptions, the analysis may not represent the true state of stress thus requiring a larger factor of safety in the design. • Extensive work has been done in the past on eccentrically loaded thin flanged columns 'and now with the advent of FEM and digital computers a renewed interest has developed on this issue. The problem of eccentrically loaded column is one of having Geometrical Non Linearity and attempts have been made to analyse using one dimensional or two dimensional elements. A Finite Element Analysis involving 3 D element is not reported anywhere. A 3D FEM computer program using 20 noded brick element for (iv) geometrically non linear problem has been developed. In general ,data preparation for 3D problem is tedious, time consuming and susceptible to human errors. A generalised Mesh Generator based on 'Isoparameteric Super Element' concept has been developed in which a band width reduction algorithm has also been incorporated. A simple post processor showing deflected shape of the discretised solid is also developed. Lastly , few examples have been solved, and results are substantiated by available experimental results.