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RE: ibc 2000 seismic design values

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I agree with Jake - and also agree with Jen that the code is not as clear as
it could be here. Unfortunately, the 2003 IBC didn't do anything to clarify
this. 

Note that "Q" is defined as "the effect of horizontal seismic forces" and
"D" is defined as "the effect of dead load". Since the effect of dead load
is vertical, it is implied that the second term relates to vertical effects.
But it would help if this were more explicitly stated. 

Nevertheless, there could be other interpretations: since dead load (mass)
has lateral inertia effects due to earthquakes, the "effect of dead load"
could also be interpreted as a lateral force. And in some circumstances,
vertical earthquake effects can directly cause an increase in lateral force,
e.g. the effective weight of fluids can be increased by vertical
accelerations which in turn cause higher lateral fluid forces. 


William C. Sherman, PE 
(Bill Sherman) 
CDM, Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)cdm.com
 

> -----Original Message-----
> From: Jake Watson [mailto:jwatson(--nospam--at)utahisp.com] 
> Sent: Thursday, July 22, 2004 7:43 AM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: ibc 2000 seismic design values
> 
> The second term in the "E" equation (0.20*Sds*D) should be 
> considered vertical.  V is horizontal.  At least that is how 
> I have interpreted the definitions.  Look at the definitions 
> in the front section of CH 16.
> 
> HTH,
> 
> Jake Watson, P.E.
> Salt Lake City, UT
> 
> -----Original Message-----
> From: Jen Wadsworth [mailto:JWadsworth(--nospam--at)TricoEngineering.com]
> Sent: Thursday, July 22, 2004 7:28 AM
> To: 'seaint(--nospam--at)seaint.org'
> Subject: ibc 2000 seismic design values
> 
> 
> In section 1617, equation 16-28 is for obtaining "E" when the 
> effects of gravity and seismic ground motion counteract. 
> Equation 16-29 is for obtaining "E" when the effects of 
> gravity and seismic ground motion are additive. When do they 
> counteract and when are they additive?
> What is the difference in "V", the base shear and "E"?? When 
> do we use V and when do we use E??
> 
> JWadsworth
> 
> 
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