2% in 50 Years deducted from 10% in 50 Years 1

[MaxJasper]

Hi experts,
How can I calculate 2% in 50 years from the following map which is 10% in 50 years? Let's say just for Santiago. Thanks.

Max.

 

[shemp]

You would need more information to obtain the gound acceleration for a 2% probability of exceedance in 50 yr. What is needed is a seismic hazard curve. This relates the ground acceleration to probabilities. The relationship is not linear due to many things such as seismicity and ground attenuation relationships.

I'm not sure if you're actually looking for Santiago's ground acceleration, or if you just want to know how to convert accelerations due to varying probabilities. But, for what it's worth, the US Department of Defense has the following ground accelerations for Santiago for 2% exceedance in 50 yrs.:

Ss=1.65g (ground acc. for buildings w/period of 0.2s)
S1=0.75g (ground acc. for buildings w/period of 1.0s)
These values are probably very approximate and conservative, though.

Hope this helps you out a little.

 

[MaxJasper]

Shemp,
Thanks a lot for the info.
Do you have a bit of explanation on Ss & Si quantities and how they are used?

Many more thanks,
Max.

 

[shemp]

Max,
The Ss and S1 values are spectral accelerations at building periods of 0.2s and 1.0s, respectively. This system is used in the NEHRP references, FEMA 368 and FEMA 369 (which you can order for free), and also in the IBC. You can look at these or another seismic design reference to get a better understanding.

Shemp

 

[ludvik]

I don't believe it is possible to convert between 2500 year and 500 year earthquakes without specific knowledge of your area, especially soil conditions.

In new york, there is factor of 2 difference between 500yr and 2500yr, whilst in California it is 2/3. The answer is it depends.

Michael Ludvik

 

[MaxJasper]

Hi again,
Is there any American building code which stipulates on a procedure for calculating PSHA for a locality?

Max.