High intake tower structures exhibit significant time-varying characteristics in their seismic performance during service life due to environmental erosion and material deterioration. This paper establishes a time-varying seismic fragility analysis framework for intake towers over their full life cycle based on the incremental dynamic analysis (IDA) method. By introducing time parameters, time-varying probabilistic seismic demand models based on displacement and local damage indices are constructed, and five performance levels are defined. The research results indicate that with increasing service life, the probability of the structure reaching critical performance levels exhibits a nonlinear growth. After 40 years of service, material strength and elastic modulus begin to decline significantly, with evident degradation of seismic performance. At a seismic acceleration of 0.8 g, the probability of the 60-year-service structure reaching the slight damage limit state (LS1) has reached 99%, while the probability of reaching the collapse limit state (LS4) exceeds 25%. The local damage index results demonstrate that under the same seismic intensity, the exceedance probability of tower-side damage exceeding LS1 for the 60-year-service structure has increased by approximately 10% compared to that of the new structure (0-year service). Therefore, in the seismic design and retrofitting decision-making for intake towers, the time-varying characteristics over the entire service life must be fully considered. Particularly when the service life exceeds 40 years, seismic fortification standards should be appropriately enhanced or targeted strengthening strategies should be developed based on time-dependent fragility curves, so as to avoid underestimating long-term seismic risks. This study provides a quantifiable scientific basis for whole-life safety assessment and resilience enhancement of high-rise intake towers.
Zhang et al. (Mon,) studied this question.