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Stability analysis of a spaceframe structure Oberti, Andrea Luca

Abstract

Two theories for the stability analysis of a spaceframe structure are presented: the first uses only Livesley stability functions, the second includes in addition the effects due to chord rotation and flexural end shortening of a member. The critical condition is defined by the load which makes the tangent stiffness matrix of the structure become singular. Three methods for obtaining the critical load are presented: determinant plot, Southwell plot, and load-deflection curves. The analysis is carried out for the plexiglass model of an actual conical spaceframe, made of glulam timber, and built for the storage of potash. The overall critical load for this structure is found to be in satisfactory agreement with the experimental results obtained in previous model tests. Some additional effects, such as geometric imperfections in the joint coordinates and different member end-fixity conditions are investigated. The concept of effective length for a member is introduced to present the results obtained by varying the height/span ratio of the structure. Finally some design suggestions are given for structures of this type. The analyses were made using spaceframe programs based on the stiffness method, modified to include stability effects. An IBM 360/67 computer was used for the calculations.

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