LRFD Geotechnical/Foundation Design
LRFD Geotechnical/Foundation Design
(OP)
A soil report we received reads:
...we recommend over excavating 18-inches and using the following Maximum Factored Bearing Resistances:
Service Limit State – 3.0 ksf
Strength Limit State – 6.0 ksf
Are the two limit states derived from a common Ultimate Bearing Capacity? Or is their no correlation between the values?
Also, does anyone have a reference/glossary of terms for structural engineers? In everyday office conversations I keep interchanging nominal with ultimate and girder with stringer etc... it's bad.
...we recommend over excavating 18-inches and using the following Maximum Factored Bearing Resistances:
Service Limit State – 3.0 ksf
Strength Limit State – 6.0 ksf
Are the two limit states derived from a common Ultimate Bearing Capacity? Or is their no correlation between the values?
Also, does anyone have a reference/glossary of terms for structural engineers? In everyday office conversations I keep interchanging nominal with ultimate and girder with stringer etc... it's bad.






RE: LRFD Geotechnical/Foundation Design
Amazon has several civil engineering dictionaries available, but I might recommend just doing a google search on specific terms, as you'd likely get better information that way.
RE: LRFD Geotechnical/Foundation Design
RE: LRFD Geotechnical/Foundation Design
You need to get a copy of the AASHTO LRFD code and look at Chapter 3. That is where the limit states and relevant load combinations are defined. If your project is transportation related in any way, you better check that the design code you should be using is AASHTO LRFD. If it is, you should find someone who is familiar with it to do the design. If not, then you should ask the geotech to reword his recommendations in "building lingo" so that there is absolutely no confusion on your part when doing structural design. While the others above are on the right track, there are subtle differences between AASHTO and IBC geotech analysis, and you should ask the geotech to adjust his wording accordingly - you should not guess his intent. Also, the AASHTO load combinations to be used with the "strength" limit analysis have different load and reduction factors than the IBC load combinations. I find it strange that the geotech would be using AASHTO terminology on a non-transportation project. Usually it is the other way around (not many are familiar with AASHTO unless you are in the bridge design world) and we always ask them to convert to AASHTO terminology (eg. "service" and "strength" level recommendations). If they refuse to do so or don't understand what we are talking about, we suggest to the owner that they find another geotech who knows what they are doing.
Good luck.
RE: LRFD Geotechnical/Foundation Design
This IS in fact a transportation project. And our office does have a copy of the AASHTO LRFD; it was my mistake for not adding any context to my question, I forget not everyone works transportation.
Soils/geotechnical engineering is not one of my strengths, I was only asking if the two "allowable" bearing pressures are related.
e.g.:
Service Limit State = (f1)(f2)(f3)(qu)
Strength Limit State = (f1)(f2)(f3)(qu)
While skimming through AASHTO it did not become apparent to me.
RE: LRFD Geotechnical/Foundation Design
Clansman
If a builder has built a house for a man and has not made his work sound, and the house which he has built has fallen down and so caused the death of the householder, that builder shall be put to death." Code of Hammurabi, c.2040 B.C.
RE: LRFD Geotechnical/Foundation Design
RE: LRFD Geotechnical/Foundation Design
RE: LRFD Geotechnical/Foundation Design
Something to the effect of:
"I think I may have flip-flopped the words for the service and strength bearing pressures"
Luckily, it was a lack of understanding on the authors part, and they had not made such an egregious error in a final report.