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RE: Load Factor Question

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Arvel –

 

Yes, of course, settlement is an issue. That’s why I attempted to have this discussion circumvent the “foundation type” issue, because this has been discussed ad nauseum. I added language to my contract (with the architect) to instruct the owner that leveling the building after an event is probable (which he has done). FWIW, according to the geotech, the differential settlement will be between 3 and 8 inches. But the price of the property was right!

 

When you ask “is your stress envelope of the mat actually into the liquefaction layer”, I’m not sure what you’re asking. A stress envelope (to me) is an analytical concept while the liquefaction layer is a physical one. The liquefaction lens is 10-20 feet below the surface.

 

Regards,

 

T. William (Bill) Allen, S.E. (CA #2607)

ALLEN DESIGNS

Consulting Structural Engineers

http://www.AllenDesigns.com

V (949) 248-8588

F (949) 209-2509

 

-----Original Message-----
From: Arvel L. Williams, P.E. [mailto:awilliams(--nospam--at)gwsquared.com]
Sent: Friday, February 04, 2005 11:45 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Load Factor Question

 

Mr. Allen,

 

Wouldn't sudden settlement from densification of the liquefiable lens be your biggest problem following an event?  Then it would be a matter of the slab being stiff enough to distribute the live and dead loads during the event as it settles.  Also, is your stress envelope of the mat actually into the liquefaction layer? 

 

By the way, I like the stiff mat for a lightly loaded wood frame structure.  No argument on that from me.

 

As for using the reduced K value, your approach looks good to me.

 

-----Original Message-----
From: Bill Allen, S.E. [mailto:T.W.Allen(--nospam--at)cox.net]
Sent: Friday, February 04, 2005 1:36 PM
To: seaint(--nospam--at)seaint.org
Subject: Load Factor Question

I am working on a project that has a liquefaction potential. There is a lens of good soil then a lens of liquefiable soil then a lens of good soil. Based on the strata, the geotechnical engineer has said that a mat foundation is acceptable. For the design of the mat, he has given me a reduced modulus of subgrade reaction (k) to represent what the soil might act like during the event. For the purposes of this question, there is no alternative to the foundation type because that issue has been beat to death and it would be a waste of cyberspace to discuss alternatives. The question here is just related to load factors.

 

The structure is a one story wood framed building. The only loads on the building are D, Lr, W and E.

 

Here is what I intend to do.

 

  1. I use the unreduced k value for the D+Lr and the D+Lr+W cases.
  2. I use the reduced k value for D+Lr+E load cases.
  3. After the event, the results from question 1 are still valid.

 

Does anyone disagree with the above approach?

 

Thanks,

 

T. William (Bill) Allen, S.E. (CA #2607)

ALLEN DESIGNS

Consulting Structural Engineers

http://www.AllenDesigns.com

V (949) 248-8588

F (949) 209-2509