In the paper the results of an analytical study of the behavior of braced and unbraced frames and subassemblages is presented. The analysis assumes elastic perfectly plastic member response and includes the effects of axial loads on frame deformations, axial loads on member stiffness, axial shortening of columns, finite column width, and hinge reversal. The results of the analysis show that the lateral stiffness of braced and unbraced frames designed under similar conditions were approximately the same. The analysis shows that the PΔ effects significantly reduce the load carrying capacity of both types of structures, especially when these units are required to provide lateral support to more flexible frame units.