Rosson, Barry T.

This research investigates the development and performance of a new closed-form stiffness matrix for a beam element that assumes a second-order stiffness variation over the regions of beam-columns with partial yielding. Stiffness reduction occurs due to yielding of the cross-section of W-Shapes under certain conditions of residual stress, moment, and axial load. Currently, inelastic material models assume a linear stiffness variation over the beam element length, even though it is well known they vary nonlinearly over the partially yielded regions. To evaluate the performance of the new stiffness matrix, two beams and four frames were analyzed using MASTAN2 considering five load increment and nine element conditions. Discussion and recommendations are provided regarding the parameters that influence the modeling results and the ability of the new stiffness matrix to consistently provide better results than the original stiffness matrix with an assumed linear stiffness variation.