Abstract: An efficient and robust finiteβelementβbased method for estimating nonlinear responses of complex threeβdimensional structures with partially restrained connections under dynamic and seismic loading is presented. The method is developed using the assumed stressβbased finiteβelement method in which the tangent stiffness can be expressed in explicit form and fewer elements are needed to model a structure. Geometric and material nonlinearities and the nonlinear behavior of partially restrained connections are considered. For the dynamic and seismic analyses, three major sources of damping are considered. They are viscous damping, hysteretic damping in the PR connections, and the hysteretic damping at the plastic hinges, if plastic hinges are developed in the structure. It is observed from the examples considered in this study that proper consideration of PR connections is essential in modeling the realistic dynamic and seismic behavior of structures. Numerical results show that the presence of partially restrained connections may not cause failure of a structure due to insufficient strength but may make serviceability constraints, e.g., the lateral deformation, more critical.