Requirements for a Geo Report Seismic C+ 1

[DJYork]

Also, posted question in Geotech area, but not sure which area it better applies, geo or structural.

According to 1802.2.6 & 7 of the IBC, it is required to have a Geotech Report for seismic categories C and above. Is there something that is acceptable for a Geotech report not be performed if a more stringent analysis is used? I was informed there was such an entry, but I am unable to find it.

FYI, this is more of an office discussion instead of me trying to design without a Geotech Report.

 

[TDAA]

If the soils are unknown, use D unless the building official states it is less. It is in there somwhere.

 

[mrMikee]

Section 1615.1.1 in the second paragraph it says use Site Class D unless the building official determines that E or F soil is likely present, provided soil properties are unknown.

-Mike

 

[DJYork]

Sorry, maybe I did not state the question clear. The above posts are refer to the Site Class (which it is acceptable to use D), but I am referring to the Seismic Design Catagory C and above as stated in 1802.2.6 & 7.

 

[JAE]

DJYork,

What do you mean by [blue]"a more stringent analysis is used"[/blue]? Do you mean a more stringent geotechnical analysis, or a more stringent structural analysis?

 

[DJYork]

Well, it seems a little difficult to put into words, but I'll try.

If you have a seismic design category less than C (for seismic purposes) the IBC does not require a Geotech report per 1802 (my understanding). So if you have a seismic design category in C or above are there values, assumptions, or provisions that the code allows if you still do not have a Geotech report.

It is somewhat ambiguous question, since the design values do not have a great deal to do with the seismic design category.

It a short version is there any way to design a foundation/building without a Geotech report (by code) if the design category is above C.

Again, this is a long story how this question came about in our office, but I want to reiterate that we are not trying to design without a soils report.

 

[JAE]

I guess I'd question your statement that with Category C you have to do a "Geotech report".

What the text of IBC 2000 says is, [blue]"Where a structure....Category C in accordance with Section 1616, an investigation shall be conducted, and shall include an evaluation of the following potential hazards resulting from earthquake motions: slope instability, liquefaction, and surface rupture due to faulting or lateral spreading."[/blue].

Those are three distinct items that simply need to be "evaluated" by the geotech, and, I presume, reported back to the design team to consider. Its not saying here that a full geotech report is required. That's taken care of in 1802.1.