Wind on Retaining Walls in IBC 2009 vs 2012

[FreeCrowbars]

In section 1807.2.3 Safety factor the wording has not changed between the 2009 IBC and the 2012 IBC. It reads:

Retaining walls shall be designed to resist the lateral action of soil to produce sliding and over-turning with a minimum safety factor of 1.5 in each case. The load combinations of Section 1605 shall not apply to this requirement. Instead, design shall be based on 0.7 times nominal earthquake loads, 1.0 times other nominal loads, and investigation with one or more of the variable loads set to zero. The safety factor against lateral sliding shall be taken as the available soil resistance at the base of the retain...

In regards to wind loads:

In 2009 IBC the wind maps are Basic Wind speeds (example 90mph for a huge portion). At the bottom the notes say "these are nominal wind speeds"

In 2012 IBC the wind maps are Ultimate Wind speeds (example 115 mph for a huge portion). At the bottom of the map the notes also say "these are nominal wind speeds"

So why did the "Safety Factor" wording stay the same using "nominal" between 2009 IBC and 2012 IBC but the wind map wording "nominal" corresponds with the change between Basic and Ultimate wind speed (varying with safety factors)? Are "Other Nominal Loads" not including wind? What's the deal here?

 

[TehMightyEngineer]

I recall this being addressed in an errata or something. Short version is I recall the intent being retaining walls designed under ASD and thus the wind loads need to be reduced to ASD levels. In IBC 2012 there's an ASD conversion table in there for things like windows and such that require ASD level wind speed maps.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL, HI)
American Concrete Industries

https://americanconcrete.com/

 

[azcats]

I'm working thru validating our new retaining wall software and was just figuring out how they approach the sliding and OTM FS. Ultimately, if you input strength level wind loads, they are factored by 0.6 for service loads when computing the factors of safety and the actual soil pressures.