Presumptive Load-Bearing Values
Presumptive Load-Bearing Values
(OP)
I need some guidance..
Section 1806 of the 2009 IBC addresses presumptive load bearing values (displayed in Table 1806.2).
Does anyone know if these Qult or Qall values? Anyone have a source for this info?
Thanks
Section 1806 of the 2009 IBC addresses presumptive load bearing values (displayed in Table 1806.2).
Does anyone know if these Qult or Qall values? Anyone have a source for this info?
Thanks





RE: Presumptive Load-Bearing Values
In Section 2906, it also refers to these values as "allowable", and not to be exceeded unless there is data available to suggest a higher value - soils test implied.
In section 2908 (b) and (c) for piling, there is a reference to "Method 1" where the "allowable" load for the pile is determined by a load test, the allowable not exceeding 50% of the yield point. OK for that too.
Although I could find no specific statement here relating to yield vs allowable for soil, I think the testing methodology for pile is a definite hint to the "allowable" vs "yield" values.
All the allowable values from the table are letting you do is forgoing the expense of a soils test in lieu of being conservative regarding the soil bearing values. So. yes, the soil can probably take more load if properly classified according to the tables. However, that is all relative, for it will also settle more to achieve that value.
Mike McCann
MMC Engineering
RE: Presumptive Load-Bearing Values
Chapt 29 now concerns Plumbing Fixtures. All of the Soils and Foundations stuff is in Chapter 18.
Based on your response my feeling is that presumptive loads refer to allowable (not ultimate) loading.
This is what I needed to know.
Thanks again
RE: Presumptive Load-Bearing Values
I was just referring to an older code verbage that would be closer to the original intent.
Cheers.
Mike McCann
MMC Engineering
RE: Presumptive Load-Bearing Values
RE: Presumptive Load-Bearing Values
. . .shall be used with allowable stress . . .
RE: Presumptive Load-Bearing Values
1806.1 says to use the values in the table if you are designing with ASD
You can increase the values in the table by a third if you are designing with LFRD
It is not related Qall vs Qult
I agree with msquared48 and BigH that, from the context, this is a Qall number. I don't see this explicitly addressed in the IBC.
RE: Presumptive Load-Bearing Values
RE: Presumptive Load-Bearing Values
RE: Presumptive Load-Bearing Values
After reading BigH's post, it seems as though the Qall is the allowable bearing pressure based on deformation/settlement. Whereas, the Qult might be the maximum bearing pressure based on soil failure (shear failure?). Unfortunately, I assumed they were values to be used in structural design.
I apologize for any impertinence on my part. My only experience has been using the design values and recomendations in soils reports provided by a geotech.