Reliability of nonlinear framed structures

The assessment of reliability for framed steel structures is approached by the determination of limit state surfaces in load space. Surfaces corresponding to initial yield, plastic hinge formation and mechanism formation or structural instability are found by an incremental loading procedure along proportional load paths from the point of expected values. A previously derived stiffness matrix for wide-flange steel members subject to elasto-plastic bending and derived from moment-thrust-curvature equations is utilized. The nonlinear frame response is based on a tangential stiffness matrix for which each cross section of a member may experience various degrees of partial plastic behavior. A recent model for the nonlinear behavior of connections reflecting moment and axial force coupling due to noncentroidal rotation is also incorporated. Turkstra's rule of load combination permits the inclusion of arbitrary point-in-time as well as lifetime maximum probability distributions of live and wind loads.