Aspects of sequential instability of structures.

The use of multi-component light-weight structures has increased considerably during recent years. Collapse of such structures may be propagated by progressive failures of their components and the load-deflection curves of these structures may be characterised by a number of limit points. The fundamental mechanics of sequential collapse behaviour of these structures is presented herein. Expressions relating the loads and deflections are derived for a general structural system. The family of curves obtained describes the essential characteristics of the sequential instability behaviour of large redundant structures. Simple structural systems displaying the complete set of characteristics are presented and investigated in detail. Large-deflection elastic buckling models and a plastic buckling model are considered. It is found that member behaviour and connectivity between the members have extremely important effects on the structure behaviour. The theoretical work is supported by experimental evidence. Tests are performed on a model structure subjected to large elastic deformations. High strength steel is used to construct the model to ensure elastic behaviour throughout. An extensive and thorough experimental investigation is carried out to obtain the complete set of equilibrium characteristics. The experimental results are in complete agreement with the general and detail theoretical work. The theoretical critical behaviour of the models investigated in this thesis is shown be governed by Thom's Swallowtail Catastrophe and this is verified by the experiments. These structures exhibiting a series of limit points in their load-deflection curves are prone to demonstrate dynamic snap under dead loading. As a consequence, the concept of dynamic snap is examined. The occurrence of premature global failure due to dynamic snapthrough is deduced from a study of the form of the potential surface. An investigation is also made of the important effect of initial imperfections on the sequential buckling process. It is shown that the presence of imperfections may markedly change the form of a collapse sequence for particular structural systems. The use of "Force Limiting Devices" to improve the collapse characteristics of structures liable to sequential instability is also investigated.