  Limit analysis is a computationally efficient tool to assess the resistance
and the failure mode of structures but does not provide any information on the
displacement capacity, which is one of the concepts which most affects the
seismic safety. Therefore, since many researchers did not consider limit
analysis as a possible tool for the seismic assessment of structures, its
widespread employment has been prevented. In this paper this common belief is
questioned and the authors show that limit analysis can be useful in the
evaluation of the seismic performance of frame structures. In particular, to
overcome the limitation on the possibility to evaluate the displacements of a
structure based on a limit analysis approach, an approximated capacity curve is
reconstructed. The latter is based on a limit analysis strategy, which takes
into account the second order effects, and evaluates the displacement capacity
considering a post-peak softening branch and a threshold on the allowed plastic
rotations. Then, based on this simplified capacity curve, an equivalent single
degree of freedom system is defined in order to assess the seismic performance
of frame structures. The proposed simplified strategy is implemented in a
dedicated software and the obtained results are validated with well-established
approaches based on nonlinear static analyses, showing the reliability and the
computational efficiency of this methodology
