Citation

Zaman M, Ghayamghamian MR. Bull. Earthq. Eng. 2019; 17(7): 3777-3799.

Copyright

(Copyright © 2019, European Association on Earthquake Engineering, Publisher Holtzbrinck Springer Nature Publishing Group)

DOI

10.1007/s10518-019-00625-0

PMID

unavailable

Abstract

The basic goal of earthquake resistant building design codes is to provide life safety in the event of extreme earthquake loading and to reduce the seismic risk in the long run. In the most building codes including Iranian building code (Standard No. 2800), design basis earthquake is defined as an earthquake with 10% probability of exceedance (PE) in 50 years. Such an approach leads to buildings with unknown reliability, meaning that the probability of exceedance from the specified limit states in the service lifetime is not known. Furthermore, the regions with the same mapped peak ground acceleration (PGADBE) and different hazard curves, may have different seismic risks. Therefore, life safety is not uniformly provided across the entire region. Here, an attempt is made to estimate PGADBEs based on the uniform collapse risk approach for Tehran megacity. The building capacity and PGA hazard curve for 354 grids in Tehran are computed. Then, the risk-adjusted design PGA at different grid points are calculated by optimizing risk integral using the acceptance criteria of 1% in 50 years for ordinary usage buildings (risk category II). The computed risk-adjusted design PGAs vary from 0.33 g in the east to about 0.45 g toward west, south, and north. Meanwhile, the proposed mapped PGADBE in standard 2800 is a constant value of 0.35 g for the whole region. To preserve a uniform collapse risk, risk-adjustment factors to modify the mapped PGADBE are introduced. Furthermore, the maximum considered earthquake (MCE) required to evaluate the acceptance criteria is found to be in the range of 1.5% to 2.5% PE in 50 years. The PGAs with 2% PE in 50 years provide nearly uniform acceptable probability of collapse for buildings classified in risk category II. In addition, it is found that the buildings' seismic importance factor (I) also needs to be revised from 1.2 to 1.3 for seismic risk category III, and from 1.4 to 1.6 for seismic risk category IV to preserve the 0.5% and 0.25% collapse risk in 50 years, respectively. The outcomes also revealed that the sensitivity analysis with regard to the uncertainty of buildings' collapse fragility curve can be ignored for buildings in risk categories I and II, while it needs to be performed for buildings in risk categories III, and especially IV. Finally, the estimated PGA hazard curves of the Tehran megacity are approximated by the cubic functions to expedite the future risk assessment studies in Tehran megacity.

Language: en