Method of determining seismic action of existing structures for different continuing seismic service life

This paper introduces a method of determining the seismic action for existing structure. The method incorporates the influence of seismic hazard and the continuous seismic service life. According to the more commonly assumed magnitude distribution, attenuation laws and the earthquake record, the relation of seismic hazard to seismic action is studied. The results are in terms of a modification factors of seismic action versus design reference period (i.e., 50 years). Under the principle of all the seismic action of each fortification level have the same exceeding probability, the calculation formulas is proposed to calculate exceeding probability of seismic action, while the exceeding probability based on the continuous seismic service life is converted to the well-matched exceed probability based on the design reference period (i.e., 50 years). At last, the modification factors of seismic action for existing structure with different continuous seismic service life are given in this paper.