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Re: Soils Reports (continued)

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Dave-
You're correct--it's very confusing. However, the language is 1615.1.1 seems fairly clear also: "When the soil properties are not known...Site Class D shall be used unless the building official determines determines that Site Class E or F soil is likely..."
Chuck

Dave Adams wrote:
Chuck,

There is a difference between "site class" (1613.5.2) and the "allowable
load bearing values for soils" (1804.2) and the confusion comes in the
terminology.  Rather than "S-sub-D", the common "assume this class if
you don't have a soils report" is not simply called "D" -- however, we
also have a "seismic design category D", where we MUST have a soils
report to do anything anymore.  They are two completely different things
using the same identification:  "Site Class D" is based on a series of
specific parameters listed in Table 1613.5.2 that will have some bearing
on the behavior of that soil under seismic loading.  However, this
raises a good question:  If the site class definitions are based on soil
behavior during an earthquake (at least a snapshot basis), and we can
simply ASSUME "D" (no soils report) unless geotechnical data shows
otherwise ... Why are we forbidden to assume a particular class of soil
material according to Table 1804.2 if we happen to find ourselves in SDC
D?  These decisions are both based on seismic performance and behavior,
yet we are allowed to assume in one case, but forbidden from assuming in
the other.  Unless I am totally off base ...

In terms of the inspection requirements I see for residences (R-3 &
U-1), 1704.1 "Exception 3" allows us to avoid the inspection
requirements unless the building official deems otherwise.  This means
we do not have to have special inspection of shear walls, diaphragms,
drag struts, anchor bolts, or hold-downs if the sheathing fastener
spacing is 4" or less on center ... But our wood-frame commercial
buildings still require this level of inspection (all shear walls, all
diaphragms, all collectors on a periodic basis) in SDC C and above.
Unless I am totally off base ...

Dave



-----Original Message-----
From: Chuck Utzman [mailto:chuckuc(--nospam--at)pacbell.net] Sent: Tuesday, February 05, 2008 5:16 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Soils Reports (continued)


Dave-
I'm in an on-going dialog with our local CBO in an attempt to convince him to allow the EOR to continue our past practice of using S_D unless he has some reason to suspect the presence of poor soil, ground water, etc. (as listed in 1802.2.1 thru 1802.2.6) at the site. (some local CBO's apparently have agreed). One citation is:
The 2006 IBC Structural/Seismic Design Manual states of pg. 4 "Without a

geotechnical investigation, Site Class D shall be used."
Chuck Utzman, P.E.
p.s. It looks like the EOR will have the discretion to decide what needs

Special Inspection for residential work (Sec. 1701.1 exception 3).  Am I

reading that right?

Dave Adams wrote:
One other thing I noticed and am wondering if PERHAPS there is a
misprint in the IBC.
ASCE 7-05 allows the building official to WAIVE the requirement for a site-specific soils report for ALL seismic design categories C - F (Section 11.8.2) ... unless I'm missing something, which is entirely possible. IBC Section 1802.2 does NOT allow the building official to waive the soils report requirement for SDC D - F. Is the "exception" listed at the beginning of 1802.2 POSSIBLY in error, as it restricts the user to 1802.2.6 (SDC C)? ??????????


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