بررسي رفتار كمانش ناپايدار در گنبدهاي شبكه يي كم ارتفاع و ارائه ي روشي براي تحليل مسير پس كمانش

ASSESSMENT OF UNSTABLE BUCKLING BEHAVIOUR IN SHALLOW RETICULATED DOMES AND PRESENTATION OF A METHOD FOR ANALYSIS OF THE POST-BUCKLING PATH

For design puiposes, the stability of any structure be­ing designed is of paramount importance. The fact that it is possible to perform an analysis ou a space struc­ture, which shows that the stresses in that structure are all below those permissible for the materials used in its construction, is. in itself, no guarantee that when tho structure is loaded it will not collapse. In order to de­termine this, it is necessary to find out if the structure b stable under the action of the applied loads. The secondary paths, > specially in unstable buckling, can play the most important role in the collapse of the structure. In this paper, an attempt is made lo automatically calcu­late the bifurcation path of shallow lattice domes. This calculation is performed in a two stage analysis of the space stiucture. without introducing any geometrical im­perfections. The method is implemented in a combined materially and geometrically nonlinear finite element analysis computer program, based on an incremental /iterative Newton-Raphson solution procedure. In the first sta^e analysis, the proportional live load factors, at which critical points occur, are determined and the pri­mary path is obtained. In the second stage analysis, the perfect stiucture is led towards the lowest bifurcation path, using the technique described in the paper. The resulting theoretical predications are verified by existing experimental observations on a model dome