In this study the seismic risk of five storey existing reinforced concrete building in Athens is investigated.

In this study a new measure of strong ground motion duration, with special application in pulse-like dynamic time-history analysis, is proposed.

The special interest produced by near-field directivity records and their effect on structural response has given a new significance in the velocity time history, its pulse-like content and relevant parameters and indices.

According to this study the duration of the inherent pulse-like content is used in order to define the limits of the strong ground motion duration, expected to produce a structural response almost identical to that affected by the total duration of the ground motion.

 Two duration levels, the total duration and a truncated one, equal to that of the inherent velocity pulse, are used as seismic excitation for a particular of medium to high rise reinforced concrete buildings.

The results for the response displacements and forces are quite close permitting the acceptance of the pulse duration as the strong ground motion time interval at least for pulse-like records.

Near-fault records have high frequency content. In addition, in the positive directivity the records may contain large amplitude velocity pulse of long duration.

These characteristics affect the response and design of both high frequency and long period structures.

The long period pulse in near-fault records may cause strong fundamental mode response of long period structures. In addition, the high frequency content of the same record may coincide with the second (or higher modes) resulting in severe overall response of the structure.

In traditional seismic design procedures, the high frequency content of near fault records has been accounted for in the development of the seismic design spectra.  

 Eventually, The results show fairly good agreement, showing that the truncated records can be used instead of the original ones for the calculation of the elastic and the inelastic response, reducing significantly the computational time.