ACI 350 Load Factor for Earth Loads, H

[StructuralPhil]

Per ACI 350-06, the load factor H listed in the load combinations of Section 9.2.1 "shall be reduced to 0.6 where H reduces the effect of D, L, or F."

In the case of a cantilever retaining wall, would it be appropriate then to apply a 1.6 factor to the lateral earth pressure behind the wall but only a 0.6 factor to the weight of soil on the heel of the footing?

 

[JoelTXCive]

No, I do not think so.

What I think they are saying is then when you have 2 opposing loads acting simultaneously on a member, ACI wants you reduce the load that is 'helping out'.

For example, if you are designing a wall stem; and have active earth pressure pushing the stem one direction; and at the same time you have permanent passive pressure pushing back; then you need to reduce the passive pressure down to 60% of it's full value.

 

[Celt83]

H is defined by IBC and ASCE 7 as the load due to Lateral earth pressures
I have always interpreted the weight of the soil mass as a DL which receives a reduced load factor for stability checks.



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[StructuralPhil]

Celt83 - ACI 350 defines H as "loads due to weight and pressure of soil, water in soil, or other materials, or related internal moments and forces," so it seems like they're wrapping all earth/groundwater effects into that one factor rather than breaking it out like other codes do.

 

[driftLimiter]

If the vertical pressure of soil or the vertical friction component of sloped backfilled is used to resist overturning, then I agree with @StructuralPhil these terms should have a 0.6 factor, whilst the loads causing the overturning would be higher as required.

 

[GC_Hopi]

I happen to be working on a similar loading and this snip is from ACI 350-20. It matches Celt83's interpertation.

 

[GC_Hopi]

This commentary also implies that in the "06" code the interpretation from StructuralPhil is correct.

 

[StructuralPhil]

Thanks to all for the input.

GC_Hopi, sounds like there have been significant changes in ACI 350-20, time to upgrade