Arul Jayachandran S

The nonlinear behavior of space structures has been researched by various authors using the total and updated Lagrangian formulations. In this paper, a corotated-updated Lagrangian (CR-UL) formulation is used for studying the postbuckling behavior of steel reticulated systems. This formulation is used since space truss elements contain large components of rigid body displacements. The global tangent stiffness is derived from the corotation (CR) principle and the local (natural) tangent stiffness is derived using the updated Lagrangian (UL) finite element formulation. A state determination procedure is used for including the inelastic behavior with mixed hardening. Here members are assumed to reach the material strength limit state, which is reasonable in large span space structures based on serviceability governed design, with no consideration made for member buckling. The effect of bolt slip in the member joints is included by using a sudden slip model under the service loads. The global nodal displacements and coordinates are updated based on the analytical model of the bolt slip displacement using a simple affine transformation. The effect of bolt slip on the global displacements and member forces has been studied and compared with the results of previous authors.

Traditional analysis of transmission line tower structures gives good estimate of ultimate strength but deflection estimates are much less than actual deflections measured from tests. This is caused by additional deflections due to joint properties like bolt slip in splices and splice plate deformations. These two displacement contributing factors are difficult to include in analysis. Prototype tower testing in test beds, which provides design strength evaluation and actual deflections is expensive. This paper presents a simple analytical procedure which captures not only the ultimate load and associated deflections but also the additional deflections because of bolt slip in leg splices. The formulation incorporates a corotational updated Lagrangian procedure in finite element analysis framework. The additional deflections are integrated into a nonlinear analysis formulation used for reticulated structures which also considers member buckling and yielding. To demonstrate the applicability of the formulation, towers which were experimentally tested in test beds are studied and the results are compared with strength and deflection measurements. The formulation has been demonstrated to be a reasonable alternative to expensive proto type testing.

The inelastic buckling of columns is difficult to model analytically. Methods like FEM or approximate closed form expressions are presently available but they are unsatisfactory for reasons mentioned in this paper. In this study, the inelastic buckling of columns is modelled to reflect the true curves upto the ultimate load prior to and except the rapid unloading. The method aims to be a helpful supplement to assist in predicting failure loads and modes during experimental testing of columns in intermediate slenderness ranges. The method combines the iterative Newmark's approach for eccentrically loaded columns with the arc-length displacement control scheme to direct the load increments. The results obtained are verified with known behaviour of column buckling with respect to slenderness, mode of failures, imperfections etc. The method simulated the load-deflection and failure mode of columns of various slenderness with reasonable accuracy.

In the construction of single layer domes and vaulted structures manufactured ball-node type connections are widely used. These ball-nodes deform due to the action of a three-dimensional state of stress while offering their resistance. These deformations result in a loss of connection stiffness, which influences the overall stability of these domes, and is usually ignored in the analysis. This work presents an investigation on the effect of ball-node deformations in the inelastic post-buckling behavior of domes and vaulted structures. A model for the load-deformation properties of the ball-nodes has been proposed in this study, in the lines of EC3-8. This connection flexibility model is integrated into a corotated-updated Lagrangian finite element formulation. Results for single layer domes and a braced barrel vault are presented. Although the present investigation deals with ball nodes only, the computational framework is still relevant for other type of connections of space structures, with modifications.