ASCE 7-05 MCE vs. ASCE 7-10 MCEr 1

[StructureMan44]

The tables for Ss and S1 were revised between ASCE 7-05 and 7-10. In the commentary of 7-10 (C11.4) it states that "The basis for the mapped values of the MCEr ground motions in ASCE/SEI 7-10 is significantly different from that of the mapped values of MCE ground motions in previous editions of ASCE/SEI 7. These differences include use of (1) probabilistic ground motions that are based on uniform collapse risk, rather than uniform hazard;..."

What is the difference between "uniform" collapse risk and "uniform" hazard?

 

[Gumpmaster]

Here is a good paper that explains it. Uniform Risk vs Uniform Hazard

 

[Gumpmaster]

The summary, as I understand it, is that the previous seismic maps provided a uniform seismic hazard such that the earthquakes had a 2% probability of exceedance in 50 years. The new maps provide a uniform risk of collapse for a selected collapse probability.

There's a bunch of statistical voodoo to go from one to the other.

The part that I don't quite grasp is what is the uniform risk of collapse based on? There are regional differences in construction methods and standards as well as large variations in construction type and quality based on when the structure was built (which also varies by region). I'm not quite sure how they capture this in the maps. Maybe someone can educate me.