Based on ASCE7-10 provisions, seismic forces are calculated based on 2% probability of exceedance within a 50-year period (a mean recurrence interval of about 2475years). Due to the short remaining lifespan of the existing building which results in a relatively low probability of extreme load exposure, the use of these values for design may be excessively conservative.
In one of our studies we asked ourselves this question too. We used the following equation, which describes failure probability: P=1-e^(-Tlife/Tcalc), where Tlife is building service life and Tcalc - relative frequency. If I'm not mistaken this is
Poisson distribution.
If you use this information in some articles, please make a reference [Areschenko, T. S., Prokopovich, S. V., Sabirova, O.B. Frolova, E. D. Setting the Seismic Input Level for Estimating the Seismic Resistance Capacity of Facilities in Performance Based Designing, Natural and technogenic risks. Building Safety, 4(35), 2018].
https://eurocodes.jrc.ec.europa.eu/doc/WS_335/report/EC8_Seismic_Design_of_Buildings-Worked_examples.pdf
Saeed Mojtabazadeh
I couldn't find any specific reduction factor for short term life span design, in the Technical Report provided. I would appreciate it if you could mention any specific page number or chapter that I can refer to.
Sergey Prokopovich
Thank you for your response.
Would you please provide me with the paper you've mentioned?
Park, Ji-Hun. "Seismic hazard level reduction for existing buildings considering remaining building lifespans." Earthquake Engineering and Engineering Vibration 18.3 (2019): 649-661.
Seismic hazards for the evaluation and retrofit of existing buildings can be reduced on the basis of equivalence in the probability of exceedance between existing and new buildings as given in the following.
1-(1- λ new)L new = 1-(1- λ exist)L exist
where Lexist is the expected remaining building lifespan for an existing building and Lnew is the expected whole building lifespan for a corresponding new building which is built with the same structure and at the same site hypothetically. Also, λexist is the annual rate of exceedance of the seismic hazard level applied to the evaluation and retrofit t of the existing building and λnew is the annual rate of exceedance applied to design of the corresponding new building.
The Technical Report given by Saeed Mojtabazadeh describes the method of setting the design values on pp 6-10. This report works with peak ground accelerations.
If you work with other chartacteristics, first, you have to calculate the failure probabilty. When it's done, you take a database of values of these special charachteristics and do the statistical analysis: find the distirbution law and parameters of distirbution. After, you must calculate the value corresponding to the failure probability using the distirbution law. We've just made the same operation with CAV and Arias value. If you want, I could send you the paper on using this method.
Our papers on setting of design values using failure probability.
Dear Saeed Ghaemian
The provisions of ASCE 7-10 is in line with performance objectives defined in ASCE 41-13, such that in addition to Probability of Exceedance (return period), collapse risk is also considered in providing seismic hazard maps (provided in ASCE 7-10) . So these seismic hazard maps are derived for 4 seismic hazard levels including BSE1, BSE2, BSE-1N and BSE-2N (according to performance objectives in ASCE 41-13) and it can not be clearly stated that each map belongs to which return period ( 475 y and 2475 y).
Consequently, no formula is provided in ASCE 7-10 for relationship between spectral acceleration parameters ( Sxs and Sx1 in seismic hazard maps) in other returned periods compared to common returned periods (475 y and 2475 y).
If you want to calculate the spectral acceleration parameters for each returned period, you have to use the formula proposed in ASCE7-5, which uses the spectral acceleration parameters for 475 y in the formula.
regards, Majid.
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