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

Fri Feb 15 08:46:51 MST 2008

The demarcation line of where wind load controls the design is dependent on
the seismic load and the mass (weight) of the building. Wood buildings
without masonry veneers that fall into design categories A,B, and sometimes
C (see tables 9.4.2.1a and b ASCE 7) Most all other types of buildings,
e.g., concrete, steel frame etc wind will normally control only in Design
Category A. As a rule of thumb, I start to look for seismic to control the
building design Ss approaches 0.20g or as Sd approaches 0.10g.  The
residential code may be a bit different; however our experience has shown
that the R-IBC generally follows the regular IBC code.

Bear in mind that there are prescriptive requirements for buildings in all
design categories A-F.  However in design categories A and B these are
usually minimal and are systemic in any good structural design. 

As an example of how far reaching this code is, normally you would think of
Nashville as being "seismically quiet."  However we did an 8 story concrete
shearwall hotel built in 06-07 designed under the IBC 2003. It fell in
Design Category B, Sds = 0.218, Sd1=0.098. Base shear for seismic was more
than twice that of wind. The net effect was to add considerable cost to the
building above that would have been required by the Standard Building Code
even though it is likely that seismic would have controlled - the forces
would have approached those of wind and the wind loads would have been
lower. 

Joseph Tomasello, PE

5880 Ridge Bend Rd.

Memphis, TN 38120

Phone:

(901) 761-2016 office

(901) 821-4968 direct

(901) 412-8217 mobile

From: Wang, Zhenming [mailto:zmwang at email.uky.edu] 
Sent: Friday, February 15, 2008 7:15 AM
To: Joe Tomasello
Cc: ceus-earthquake-hazards at geohazards.usgs.gov
Subject: RE: [CEUS-earthquake-hazards] no "right" answer 

Joe,

I have been told by some structural engineers that it is wind load, not
seismic load that governs the structural design in most parts of Kentucky
(central and eastern). Have you done any design analysis on these? It would
be interesting to see the load comparisons.

Thanks.

Zhenming  

  _____  

From: Joe Tomasello [mailto:JT at ReavesFirm.com] 
Sent: Thursday, February 14, 2008 12:39 PM
To: 'Seth Stein'; WrightLa at usa.redcross.org
Cc: Wang, Zhenming; ceus-earthquake-hazards at geohazards.usgs.gov;
cfostel at conwal.com
Subject: RE: [CEUS-earthquake-hazards] no "right" answer 

Seth, et al:

This firm has been involved with recovery efforts of the tornado strikes of
February 5, 2006.  The tornado damage shown in the attached is perceived by
the locals to be the primary day to day threat from natural hazards.  

The failure mode is rather simple; the wind lifts the roof deck and buckles
the joists, which in turn pulls inwardly on the top of the precast panels
causing them to fall (see Image 647 and 307).  Evidence indicates that the
lateral force resistant system remained standing (see Image 313), however a
majority of the building collapsed. This design is pre-1997 NERHP, but
included seismic considerations. It's unlikely that additional seismic
resistance required by 1997 NERHP would affect the outcome. 

What I'm suggesting is that contrary to the accepted convention (more
seismic is better), we think there can be a case made that seismic design
does not cure all the ills created by the various different natural
disasters as advertised by FEMA.

Image 647 - shows failure mode

Image 313 - Shows seismic bracing

Image 307 - Shows failed panels large warehouse

-----Original Message-----
From: ceus-earthquake-hazards-bounces at geohazards.usgs.gov
[mailto:ceus-earthquake-hazards-bounces at geohazards.usgs.gov] On Behalf Of
Seth Stein
Sent: Wednesday, February 13, 2008 7:58 PM
To: WrightLa at usa.redcross.org
Cc: zmwang at email.uky.edu; ceus-earthquake-hazards at geohazards.usgs.gov;
cfostel at conwal.com
Subject: Re: [CEUS-earthquake-hazards] no "right" answer

Both are problems, but in the US severe weather kills about 500 people per
year and earthquakes kill about 10. Another way to look at this is that
every 6 years severe weather has the same net effect as the 1906 San
Francisco earthquake.

Seth Stein

William Deering Professor

Department of Earth and Planetary Sciences 1850 Campus Drive Northwestern
University, Evanston, IL 60208

(847) 491-5265 FAX: (847) 491-8060 E-MAIL: seth at earth.northwestern.edu
http://www.earth.northwestern.edu/people/seth

On Wed, 13 Feb 2008 WrightLa at usa.redcross.org wrote:

> When earthquakes don't happen, tornadoes are a bigger problem.

> 

> 

> 

> The recent loss of life due to tornadoes is horribly tragic, and not 

> to be belittled by any means, but the loss of life that could be 

> caused by an 1811 quake in the NMSZ beggars the imagination.

Joseph Tomasello, PE

5880 Ridge Bend Rd.

Memphis, TN 38120

Phone:

(901) 761-2016 office

(901) 821-4968 direct

(901) 412-8217 mobile

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