Revised probability of exceedance for N. America

[VoyageofDiscovery]

Through a recent conversation with a seismologist, I understand that Codes are moving toward a 2% in 50 years vs. the typical 10% in 50 years we have been using. Canada's NBCC is now implementing this new probability and thus I anticipate much higher loads. Has anyone noticed this recently in the rest of N.America or have any comments.

VOD

 

[Qshake]

Yes there has been a trend for this and it's been evolving for some time.

The 2% in 50 years is aimed at the moderate seismic zone with infrequent events. As you know there are some zones that boast very high accelerations but don't occur or haven't occured in recent recorded history. Three examples of this are New Madrid area in the Central US, Seattle, WA and lastly Charleston, SC.

There is very much resistance to this and many agencies are settling on a 1000 yr return period rather than the 2500 yr. period.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[Taro]

It's really not as bad as it might seem at first. Yes, the ground motion is based on a 2%/50yr event. But the design acceleration is only 2/3 of the calculated acceleration. This tends to bring down the design forces to the ballpark of what we were using before. The 2/3 factor is used in place of the 1.5 factor of safety against collapse that was traditionally assumed when using the 10%/50yr event.

 

[LSThill]

Question? RE: TID-7024 NUCLEAR REACTORS AND EARTHQUAKES for Base Shear and Overtruning moment

Please "what is the new difference":

2%/50yr event? and or 10%/50yr event?