It is necessary to understand the development of a comprehensive composite beam-column fiber element for large displacement nonlinear inelastic analysis of concrete-filled steel tube (cft) columns. The bond/slip formulation represents the interaction between concrete and steel over the entire contact surface between the two materials. Thus, the modeling accounts for the two factors that causes the slippage between steel shell and concrete core. The first factor is the difference between axial elongation of the steel shell and the concrete core, and the second is the difference between curvatures in the cross section for the concrete core and the steel shell. These effects are integrated over the perimeter and are added to the virtual work expression of the basic element. Furthermore, the constitutive models employed for concrete and steel are based on the results of a recent study and include the confinement and biaxial effects. A 13-degree of freedom (dof) element with three nodes, which has five dof per end node and three dof on the middle node, has been chosen. The quadratic lagrangian shape functions for axial deformation and the quartic hermitian shape functions for the transverse directions are used. The model is implemented to analyze several cft columns under constant concentric axial load and cyclic lateral load. The effect of semi- and perfect bond is investigated and compared with experiments. Good correlation has been found between experimental results and theoretical analyses. The results show that the use of a studded or ribbed steel shell causes greater ultimate strength and higher dissipation of energy than the columns with nonstudded steel shells.
The use of composite fiber materials for civil engineering structures experienced its first peak in the 1950s and 60s. Today's increased use of composite fiber materials is partly attributable to the development of the pultrusion process, a special technique that allows for the production of composite fiber elements in shapes commonly used in steel or aluminum construction. A ceramic-based composite fiber material (1) formed by disposing a premolded body (5), which is obtained by weaving fiber bundles (3) each of which is formed by bundling a plurality of ceramic fibers (2), in a matrix of a ceramic material, and characterized in that a first ceramic matrix m1 is formed in an inner space of each of the fiber bundles (3) and the portion in the vicinity of an outer circumference thereof, a second ceramic matrix m2 being formed in an inner space, which is other than these fiber bundles (3), of the premolded body (5) and an outer circumferential portion thereof. This material is also characterized in that ceramic fiber of a volume ratio vf of not less than 10 % is complexed in a reaction-sintered matrix.
