Buckling and strength of prestressed steel stayed columns

Abstract

Prestressed steel stayed columns have been used since fiftieth of the last century to en-hance their critical and maximal capacities in compression. This research deals with cen-tral steel tube columns, one and two tube crossarms and spatial prestressed rod or cable stays. Firstly four columns made of stainless steel 1.4301 with one central crossarm and cable stays were tested up to extreme buckling deflections. The following numerical anal-ysis employed geometrically and materially nonlinear analysis with imperfections (3D GMNIA) using ANSYS software. Careful analysis was successfully validated and used to obtain optimal prestressing of stays giving maximal critical loads and maximal collapse loads of the tested columns. All the following parametrical studies cover columns of the same geometrical and nonlinear material characteristics as given or resulted from testing. This enables comparison and evaluation of the significance concerning mode and value of initial deflections, value of prestressing, number of crossarms, material characteristics, sliding of stays at crossarms and ratios of maximal collapse to critical loads. The main re-sults concerning critical loads of an “ideal column” (with amplitudes of initial deflections L/500000) and maximal loads of an “imperfect column” (with amplitudes of initial deflec-tions L/200) under various prestressings of stays are discussed in a detail. In the conclu-sions a necessity of GNIA/GMNIA considering respective mode and value of initial de-flections is emphasized (linear buckling analysis is not sufficient in such prestressed ele-ments). Also the substantial significance of activating of stays during buckling and radical increase of both critical/maximal loads by adding the second crossarm is presented.