Archiveof AppliedMechanics 64 (1994) 472-479 9 Springer-Verlag 1994 Post collapse behavior of square and rectangular tubes compressed symmetrically between two platens N. K. Gupta, A. Khullar 472 Summary Square and rectangular slender sided tubes of aluminium and steel were laterally compressed between two rigid platens in an Instron machine. Their post collapse load-com- pression curves and histories of deformation are presented for typical specimens. An analysis is presented to compute the post collapse load-compression curves by assuming that stationary plastic hinges are formed at the middle and the ends of vertical arms and that the horizontal arms bend into convex inward continuous arcs. Results obtained from the analysis compare well with the experiments. Nach-Kollaps-Verhalten yon quadratischen und rechteckigen Rohren, welche syrnmetrisch zwischen zwei Platten zusammengedriickt werden 0bersicht Schlanke, quadratische und rechteckige Rohre aus Muminium und Stahl wurden zwi- schen zwei starren Platten in einer Instron-Maschine zusammengedrfickt. Ffir einige typische Proben werden die Last-Verformungs-Kurven und das Deformationsverhalten nach dem Kol- laps aufgezeichnet. Es wird ferner eine analytische Methode vorgestellt, welche es gestattet, die Nach-Kollaps-Kurven zu berechnen; sie basiert auf der Annahme plastischer Flieflgelenke in der Mitte und an den Enden der Vertikalarme und auf der Voraussetzung, dab die Horizontal- arme in konvexen Bogenstficken gebogen werden. Die theoretischen Ergebnisse stimmen gut mit den experimentellen Resultaten (iberein. 1 Introduction Study of the plastomechanics of thin walled tubes under lateral compression has received con- siderable attention in recent years. In the case of square tubes, their post collapse behavior un- der lateral compression, between two platens of narrow width placed orthogonally to the tube or by an orthogonally placed indenter when the tube is resting on a flat base, has been ana- lyzed by Gupta and Sinha [1, 2] by assuming the formation of stationary and rolling plastic hinges. Bending collapse of these tubes was analyzed by Kecman [3]. For symmetrical collapse of square tubes in a 'ring' mode between two platens, Sinha and Chitkara [4] determined the collapse load from a stability analysis of the vertical members, They assumed that the collapse of square tubes occurred with the formation of four stationary hinges, one each in the middle of each of the four sides. In an earlier paper [5], a two stage analysis for the elastic collapse load of these tubes was presented. It was shown therein that the collapse of the tube into a mechanism occurs with the formation of stationary plastic hinges at the mid-height of the vertical arms and the tube cor- ners, Fig. l(b). In this paper, we present an analysis for computing the deforming geometry and the post collapse load versus compression (relative vertical platen displacement) curves for both square and rectangular tubes which are subjected to in-plane symmetrical com- pression between two rigid platens. Several experiments were performed on as-received tubes of different sizes and made of alu- minium and mild steel. Aluminium tubes were also tested in annealed state. Their load-com- pression curves and histories of deformation were studied. Received July 28, 1993, revised version 24 January 1994 Professor N. K. Gupta, Dr. A. Khullar Applied MechanicsDepartment Indian Institute of Technology, Delhi Hauz Khas,New Delhi 110016,India