PREDICTION OF LIMIT POINT BUCKLING IN RETICULATED METAL SHELLS
Arul Jayachandran S 1*
1Professor, Department of Civil Engineering, Indian Institute of Technology Madras, Chennai, India
The present paper deals with the nonlinear finite element formulations for the computational post buckling and large deformation analysis of reticulated shell systems using the corotated-updated Lagrangian (CR-UL) formulation. A concept of advanced/total analysis of skeletal metal structures is introduced. The purpose of the integrated formulation is to detect the progressive loss of stability and strength in the overall system. In reticulated systems, the rigid body displacements are predominant and hence their kinematics is handled through transformation matrices, which separate the strain producing (natural) deformations. The natural deformations are handled using the natural tangent stiffness. The inelastic and buckling behavior of the axial members in a reticulated system have considerable bearing on the snap-through limit points and ultimate strengths as well as control the cause of stability driven or ultimate strength driven collapse. To incorporate the inelastic behavior of the members, a mixed hardening model was adopted to account for the shift and changes in yielding parameters upon stress reversal after snap-through and possible future extension to cyclic loading. The flow rules and modified yield criterions are used in a state determination procedure inside a double loop iterative process that computes for both the geometric nonlinearity by CR-UL and the member inelasticity. The formulation is verified by the analysis a single layer dome for the roof of a petroleum tank. The analysis of some practical structures showed that area for improvement in optimizing designs without compromising safety. The examples explain how inherent safeguards against instability are present in reticulated shell structures in the real world conditions.
Limit point buckling; Reticulated metal shells