Does surcharge fall under the category of LL?

[mfstructural]

I'm doing some studying now for the SE and in practice we have always thought of the surcharge as a LL....applying the appropriate ASD factors. However, I'm going through some examples now and the solutions in the book do not reduce the surcharge. The particular LC I'm looking at has a .75LL factor. However, the surcharge is not being reduced. I am missing something?
Thanks

 

[hokie66]

It probably depends on what type surcharge you are talking about. Any superimposed load can be called a surcharge. Probably the most common use of the term "surcharge" is for superimposed loading behind a retaining wall, but that wouldn't fit with a .75LL factor.

 

[mfstructural]

thx for the reply. Yes I'm talking about a superimposed load behind a retaining wall in addition to the active soil pressure on the retaining wall. So the .75LL doesn't apply to a surcharge load? Is the surcharge then considered a Hydrostatic load and the 1.0 factor applies?

 

[hokie66]

Not sure if I understand your question, but a uniform surcharge behind a wall results in an additive active pressure for the full height of the wall, which is the (uniform load) x (active pressure coefficient). I don't know where the .75 comes from.

 

[mijowe]

If the surcharge load is due to a surface live load, then the surcharge is a live load and live load factors would apply.

 

[dcarr82775]

I agree with mijowe, if the surcharge is from LL, the LL factors apply.

 

[mfstructural]

Ok, got it. It basically depends on the source of the load. Thanks

 

[Splitrings]

The active pressure coefficient may be 1.0 if the surcharge is applied quick enough in saturated soils. Pore water pressure carries the load equally in all directions.

As mentioned above, there several possible surcharge loads; sloping backfill, vehicular live loads, building loads, etc. I would only consider dynamic loads as live loads and apply the LL factor to them.

 

[DST148]

@mfstructural: Like you mentioned in your last post, it depends on the source of the load. However, for lateral earth pressure and pressure of bulk materials, load factor for H would apply, regardless of the source of the load.