The spread plasticity models that are generally used for nonlinear analysis include the uniform, linear, and, more recently, power spread plasticity models. Because all of these models are formulated from a linear moment diagram subjected to lateral loading apart from the effect of gravity loading, it has been assumed that the predefined shape of their curvature extends from the two ends of the element. This assumption can lead to incorrect outcomes in nonlinear analysis. In this study, a distributed plasticity model is developed that considers the effects of both gravity and lateral loading. To derive the proposed model, the unit load theory based on the principle of virtual work is used, and a general formulation is prepared to achieve the stiffness matrix of each beam-column element with the different flexibility properties along it. To confirm the accuracy of the proposed methodology, seven numerical examples are assessed. It is demonstrated that the results of the proposed model differ from the linear flexibility model when using only one element for each member, although the difference can be decreased by subdividing the individual structural members into more than one element. The accuracy of the proposed model is corroborated through comparison with experimental results.
