[CEUS-earthquake-hazards] no "right" answer

[Wang, Zhenming]

These are very interesting. But these comparisons are based on hazards (ground motion and wind speed), not risks. There are some efforts on risk comparisons (Harris, 2006; Malhutra, 2006; Luco, 2006). It would be more interesting to see a detail risk comparison between wind and seismic loads for some common buildings, such as a single family home and a 5-story concrete building in the New Madrid area.

Thanks.

Zhenming


-----Original Message-----
From: jacob at ldeo.columbia.edu [mailto:jacob at ldeo.columbia.edu]
Sent: Saturday, February 16, 2008 10:55 AM
To: Joe Tomasello
Cc: Wang, Zhenming; ceus-earthquake-hazards at geohazards.usgs.gov
Subject: Re: [CEUS-earthquake-hazards] no "right" answer

Joe, Zhenming, all:

Re wind vs seismic:

When NYC discussed seismic codes in the 90s, several studies were published by
then NCEER (later MCEER) that addressed this comparative issue. For regular
buildings the cross-over from seismic to wind load dominance occurred (for NYC
code winds = 100mph) generally for heights between 10 and 20 stories, where
below 10 stories generally seismic loads controlled the design, above 20
stories wind generally controlled, and between 10 and 20 stories it depends on
the details of shape and materials (i.e. mass) of the buildings.

For highly irregular buildings, because of torsional loads, seismic dominates
over wind more prominently.

There can exist peculiar situations: if you have a tall UN-HQ-curtain-like
building, tall, and narrow in one direction, and long in the other: wind loads
control design along the "short axis" of the building, seismic along the "long
axis", since the wind loads depend on the surface area availble, while seismic
depends on the inertial forces, and hence the mass of the building as seen
along a given axis.

Klaus Jacob
=====================