Demand Curve
For determination of demand curve one has to collect the following data
- PGA of different return period
- Soil profile
- Response analysis of structure.
Usually 3 different return periods of earthquake are used in such analysis. 45 yrs, 475 yrs and 2475 yrs. The higher the return period, the stronger the ground shaking.
Return period of earthquake can be rewritten as
475 yrs probability of 1 earthquake = 100%
50 yrs probability of 1 earthquake = 100x50/475 = 10 %
similarly,
2475 yrs probability of 1 earthquake = 100%
50 yrs probability of 1 earthquake = 100x50/2475 = 2 %
So, 45 yrs = 100% probability in 50 yrs
475 yrs = 10% probability in 50 yrs
2475 yrs = 2% probability in 50 yrs
Return period of earthquake can be rewritten as
475 yrs probability of 1 earthquake = 100%
50 yrs probability of 1 earthquake = 100x50/475 = 10 %
similarly,
2475 yrs probability of 1 earthquake = 100%
50 yrs probability of 1 earthquake = 100x50/2475 = 2 %
So, 45 yrs = 100% probability in 50 yrs
475 yrs = 10% probability in 50 yrs
2475 yrs = 2% probability in 50 yrs
Best way of determination of demand curve is CMS method (Conditional Mean Spectrum). For better understanding of CMS method you can watch the following video by Sir Jack Baker.
In our study
Fig 1: Conditional Mean Spectrum (CMS) for SA(0.2sec) at 2475 yr
Similarly we have to find the CMS at 0.3 sec and for different return period. This way we use a proper demand curve.
