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This study deals with the progressive collapse of full scale square-on-square double-layer space truss (DLST) systems. The failure of certain space structures in recent years, ranging from a lattice dome in Romania, Burcharest 1963 to the DLST in Hartford USA, 1978 and the recent collapse of the Sultan Zainal Abidin Stadium, a double-layer space frame constructed in Malaysia, 2009, gives an insight into how sensitive some space structures are to progressive collapse. These tragic incidents have provided very valuable lessons for designers of the importance of understanding progressive collapse in these structural configurations. By understanding what caused such failures engineers may avoid any reoccurrence and in addition help to develop safer structures. Hence, a study of this particular problem has been conducted and the results obtained are presented in the thesis. Evaluation on the consequences of progressive collapse leads to the determination of structural Vulnerability Index due to sudden loss of an individual member (Case 1) or losses of members progressively (Case 2). In order to trace the collapse behavior a nonlinear analysis subject to increasing applied load was used. However, it is difficult for engineers to perform this nonlinear analysis due to its complexity. Hence, a simple linear analysis as an alternative method was used whereby assessment of Vulnerability Index using linear analysis is carried out using two different approaches, i.e. Rate Factor and Probabilistic Approach. Since a DLST has large number of members which correspond to a large data set, hence, these two proposed approaches are suitable. A close statistical correlation between both approaches indicates that there is a high correlation between both approaches. To ensure reliability of the proposed approaches, their results are compared using nonlinear collapse analysis and the results are found to be in good agreement. The solution strategy used to analyse the full scale models was first tested using small scale models. The numerical results of the small scale models have been verified with pre-existing experimental results and good agreements between the results are obtained. Behavior of each DLST member and also the overall structural behavior can be obtained from the nonlinear analysis. There are three different boundary conditions of the DLSTs considered. Vulnerability of the DLSTs susceptible to progressive collapse are identified and then are compared for the identification of efficient structures. The Vulnerability Index of the DLST helps engineers to discover failures that may occur due to damage or loss of its members. |
