A mechanical modeling approach for the simulation of partially restrained (PR, or semirigid) steel and composite connections subjected to any loading regime is described, and verification studies utilizing this approach are presented. This paper first presents a description of the advantages and drawbacks of a previously published component model, which served as the basis for developments discussed here. An original mechanical model is then introduced and described in detail. This model is capable of taking into account the influence of all the main deformation components, including slip in the bolts, partial interaction between the concrete slab and steel girder, shear deformation of the panel zone, and cracking and crushing of the slab. The model also evaluates the energy dissipated by each component, leading to a clear understanding of the connection behavior. Preliminary validation analyses are then presented and discussed. Results indicate that this approach can predict the complex behavior of PR composite connections well, and that the computation effort is minimal when compared to more sophisticated approaches.