×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Soil on concrete structure, DL or LL?

Soil on concrete structure, DL or LL?

Soil on concrete structure, DL or LL?

(OP)
I have a soccer field on top of a prestressed concrete parking garage. Is the soil DL or LL?  

RE: Soil on concrete structure, DL or LL?

I have always used Live load.  Especially given the soccer field nature it will be moist soil so heavier than a drier soil.  I will often use an inflated unit weight of 125-130pcf and a lower load factor (1.3 ish) instead of a dryer weight and a higher load factor (110pcf*1.6) but it ends up with a similar ultimate load.

RE: Soil on concrete structure, DL or LL?

It's soil load. It is in the IBC combinations under H. It's usually treated as LL.

RE: Soil on concrete structure, DL or LL?

I think I am in the minority. I would consider that to be a dead load with moist unit weight.

RE: Soil on concrete structure, DL or LL?

(OP)
My original thought was H also but that is defined as lateral loss due to soil.  

RE: Soil on concrete structure, DL or LL?

(OP)
Loss = load. (autoincorrect)  

RE: Soil on concrete structure, DL or LL?

@tngolfer: I would consider it as a deal load (superimposed) for  designing for strength, including proportioning of the foundations. However, for stability checks, uplift calculations etc. I would not count on it, i.e. assume it does not exist.  

RE: Soil on concrete structure, DL or LL?

I would say statistically, it's a dead load because it's known,ever-present and more predictable than a live load, thus justifying a lower load factor. I see no reason to not count it as being there for other combinations of load as DST148 has suggested, but would consider it's lowest/minimum weight in those calculations.

RE: Soil on concrete structure, DL or LL?

It's a dead load.  Use wet unit weight.

RE: Soil on concrete structure, DL or LL?

Canada it's an H load with a load factor = 1.5, which is the same as the live load factor.  The code distinguishes soil, superimposed earth, trees, etc when considered as dead loads the code requires the load factor be 1.5.  When the depth of the soil starts exceeding 1.2m in depth the load factor can be reduced to 1.25 as the depth increases.  Guess they feel if there is only a couple of feet of soil it could be removed easily hence the 1.5 load factor?

RE: Soil on concrete structure, DL or LL?

In ASCE 7-10 (and probably all the rest of the editions), Chapter 3, Dead Load is defined as weight of "...all materials of construction... including but not limited to walls, floors, roofs, ..."
By that definition, it's not a Dead Load.

RE: Soil on concrete structure, DL or LL?

When you take the live load reductions allow per the IBC will you apply them to the weight of the soil? I would not, so I would have to say that it is a dead load.
Now this is a Special-Purpose roof (2009 IBC section 1607.11.2.2) but per the 2009 IBC section 1607.11.3 Landscaped roofs. "...the uniform design live load in the landscape area shall be 20 psf. The weight of the landscaping materials shall be considered as dead load and shall be computed on the basis of saturation of the soil."  

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Soil on concrete structure, DL or LL?

Like others have mentioned I would consider it a dead load.  Seems to me that it is a "material of construction".  It's essentially, just unique flooring.  How is soil any different than a concrete topping slab, tile, etc.  Seems to me that I would design it as a dead load and use the saturated weight of the soil in the design.  This is what we have done in the past for rooftop gardens.

 

RE: Soil on concrete structure, DL or LL?

AASHTO defines it as "...dead load of earth fill" for design of tunnels, culverts, and other rigid underground concrete structures. I don't see why it would be any different under the IBC. Also, the earth fill is not transient, so makes sense that it would be a sustained dead load. Just my 2 cents...

RE: Soil on concrete structure, DL or LL?

I consider it dead load, particularly when only a percentage of only the dead load can reliably be used to resist uplift.  

For concrete detention vaults, the dead load of the soil above is used, in addition to the dead load of the vault, to prevent it from becoming bouyant.   

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Soil on concrete structure, DL or LL?

Another vote for dead load.

RE: Soil on concrete structure, DL or LL?

+1 for dead load, but considering the following:

Dry unit weight with min expected fill for 0.6D cases

Saturated unit weight with max expected fill for others

RE: Soil on concrete structure, DL or LL?

In addition to treating it a dead load with the saturated unit weight, I would suggest that you investigate ponding/flooding potential and verify any vehicle loading if not already done. I once helped on a project with a heavily landscaped roof with HS-20 loading.  

RE: Soil on concrete structure, DL or LL?

I agree that it is a dead load becasue it is permanently acting on the structure but I think that it is a highly variable dead load and should be assinged a load factor of 1.5. The unit weight of the soil is related to its compaction which cannot be assured.  

RE: Soil on concrete structure, DL or LL?

The National Building Code of Canada specifically defines soil and trees above a structure as a dead load except when it's acting as the load restraining structure (retaining walls, etc) or acts as a counteracting load in certain other ways.

The occupancy above the soil would be a live load, though.

RE: Soil on concrete structure, DL or LL?

++1 Dead load for downward gravity. This should not be reduced in load combos as it doesn't vary from time to time and will be supplemental to any true live load and won't get LL reduction factors.
+1 Live for seismic and uplift but I am on the fence about this. In a seismic event it may be liquified and unfixed, uplift is just being conservative...  Never had to deal with this before.

MAP

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources