ABSTRACT
non-linear stiffness equation is the incremental perturbation method. The section of tubes is divided into six elements each area of which is concentrated to a point, as shown in Figure 10(a). Figure 10(b) shows an analytical model of double-tube members. An outer tube whose initial deflection at midspan is 1/10000 is tied to an inner tube by eight connectors. In order to simulate the contact between the inner tube and the outer tube, the connectors are assumed to have the load N - axial deformation u relation as shown in Figure 10(c). The stress - strain curve of the outer tube is modeled in four segments and that of the inner tube is bilinear.
