Post-Yield Flexural Properties of Tubular Members

In order to carry out inelastic dynamic analyses of steel offshore platforms under earthquake excitations, flexural members are generally modeled by assuming the formation of plastic hinges at the ends when the corresponding moments exceed a limiting value. In this work, static solutions are obtained for the yield and post-yield properties of tubular members in flexure by making use of experimental moment-curvature relationships that are available in nondimensional form for several levels of axial load acting on the section. The objective is to determine improved properties for the point hinges by considering the spread of yielding. These properties are the equivalent yield moment at zero axial load, the post-yield stiffness expressed as a fraction of the corresponding elastic stiffness, and an interaction diagram giving the yield moment as a function of the axial load. The sensitivity of response to variations in these properties is also examined by analyzing an example platform.