• Structural Engineering and Mechanics
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• v.14 no.2
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• pp.119-133
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• 2002

A beam-column fiber element for the large displacement, nonlinear inelastic analysis of Concrete-Filled Steel Tubes (CFT) is implemented. The method of description is Total Lagrangian formulation. An 8 degree of freedom (DOF) element with three nodes, which has 3 DOF per end node and 2 DOF on the middle node, has been chosen. The quadratic Lagrangian shape functions for axial deformation and the quartic Hermitian shape function for the transverse deformation are used. It is assumed that the perfect bond is maintained between steel shell and concrete core. The constitutive models employed for concrete and steel are based on the results of a recent study and include the confinement and biaxial effects. The model is implemented to analyze several CFT columns under constant and non-proportional fluctuating concentric axial load and cyclic lateral load. Good agreement has been found between experimental results and theoretical analysis.

• Structural Engineering and Mechanics
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• v.11 no.2
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• pp.123-132
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• 2001

An improved version of the Element-free Galerkin method (EFGM) is presented here for addressing the problem of transverse shear locking in shear-deformable beams with a high length over thickness ratio. Based upon Timoshenko's theory of thick beams, it has been recognized that shear locking will be completely eliminated if the rotation field is constructed to match the field of slope, given by the first derivative of displacement. This criterion is applied directly to the most commonly implemented version of EFGM. However in the numerical process to integrate strain energy, the second derivative of the standard Moving Least Square (MLS) shape functions must be evaluated, thus requiring at least a $C^1$ continuity of MLS shape functions instead of $C^0$ continuity in the conventional EFGM. Yet this hindrance is overcome effortlessly by only using at least a $C^1$ weight function. One-dimensional quartic spline weight function with $C^2$ continuity is therefore adopted for this purpose. Various numerical results in this work indicate that the modified version of the EFGM does not exhibit transverse shear locking, reduces stress oscillations, produces fast convergence, and provides a surprisingly high degree of accuracy even with coarse domain discretizations.