الفهرس 
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Abstract
During the past few years, the space (3-D) structures consisting of double¬ layer grids become a very common and suitable way for covering large areas because they are widely accepted as efficient large span structures, In spite of the advantages of space structures, sudden and progressive collapses have been experienced, and it has been found that the major problem facing these structures is the brittle type of failure caused by buckling of critical compression chord members consequently.
This research is concerned with the nonlinear analysis and stability for a kind of these structures, which consists of two way orthogonal vierendeel girder, named CUBIC. Space Frame System. Since this system criminates the need for diagonal members, it provides space for accommodation or machinery within the roof structure, In addition, easy access is available to service runs.
A simple derivation of the tangent stiffness matrix of the CUBIC Space Frame chord member (a mid-span hinge element) has been done, the stability functions of this chord member was derived in terms of the common stability functions of the prismatic member.
A nonlinear finite element program has been modified to consider both the two types of members of the CUBIC Space Frame, which are the chord member with midspan hinge and the vertical ordinary member (spacer). Several examples were solved and compared with published results to verify the program after modification.
To show the effect of the relative geometrical dimensions and support conditions on the behavior of the CUBIC Space Frame system, a parametric study has been done to investigate the relations of its resistance, deflection and behavior with the variation of the relative values of its different dimensions.
Finally recommendations for analysis and design of the system are given.