Existing reinforced concrete frame buildings designed for vertical load only could suffer severe damage during earthquakes. In recent years, many research activities have been paid to develop reliable and practical analysis procedure to identify the safety level of existing structures. The research discussed in this paper deals with proposal of an efficient incremental procedure to estimate seismic capacity of irregular structures performing few pushover analysis (one for every relevant modal shape) and applying a series of Modal Pushover Analysis (MPA). This approach, similar to the Incremental Dynamic Analysis (IDA), replaces the Nonlinear Response History Analyses (NL_RHA) by simple pushover analyses. In this work, this idea, named IMPA (Incremental Modal Pushover Analysis), is proposed for a 3D complex building and this application is described and discussed.