Return to index: [Subject] [Thread] [Date] [Author]

RE: Check for Floatation

[Subject Prev][Subject Next][Thread Prev][Thread Next]
As some others have written, I typically only include the weight of soil
projected vertically above the footing extension and consider any cone
shaped failure as adding to the safety factor. But on a few occasions I have
used cone shaped failure zones when a Geotechnical Engineer provides
guidance on the angle of failure. 

It should also be noted that the hydrostatic uplift pressure must be
accounted for in the weights used at the footing projection. This can be
accounted for by: a) using "buoyant weight" of the soil and slab projection
(i.e. unit dead weight minus 62.4 pcf); b) using the full soil weight above
the footing and considering the hydrostatic uplift pressure below the base
slab to the full width of the footing extension; or c) using full dead
weight of all components and then subtracting the volume of water displaced.
For balanced conditions they all come out the same, but the method used can
alter the safety factor calculated depending on which are considered as
"resisting" forces. 

> -----Original Message-----
> From: RajSTC(--nospam--at)aol.com [mailto:RajSTC(--nospam--at)aol.com]
> Sent: Monday, August 14, 2000 10:08 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Check for Floatation
> 
> 
> I am evaluating the adequacy of a, buried, steel storm 
> shelter manufactured 
> by a local steel fabrication shop.  In order to pass the FEMA 
> approval 
> criteria, the structure has to be checked for floatation 
> assuming that the 
> water table can rise up to the ground level.  For a box, 
> L'XW'XH', the 
> buoyancy is 62.4LWH.  The weight of the steel structure is 
> very small in 
> comparison to the buoyancy.  Additional weight has to come 
> from soil weight 
> on the extended portions of the bottom plate.  For the 
> purposes of further 
> discussions, assume that the bottom plate extends 2' beyond 
> the face of the 
> walls.
> 
> For estimating the weight of soil on the extended plate, 
> should the soil be 
> limited to 2' wide column?  It seems to me that the failure 
> of soil will be 
> in the form of a wedge, the wedge being bounded by the 
> vertical wall of the 
> structure, the 2' projection of the bottom plate, existing 
> ground surface and 
> an inclined line emanating from the edge of the extended 
> plate.  The inclined 
> line could be assumed to be at 60 deg. from the horizontal.
> 
> No site specific soil reports available.  The structure will 
> be installed 
> anywhere in Oklahoma and adjoining states.  I will put a 
> disclaimer on the 
> drawing to exclude sites that may have expansive clays, silts etc.
> 
> Any thoughts?
> 
> P. Rajendran
> Service & Technology Corporation
> 105 SW Penn
> Bartlesville, OK 74003
> Ph: 918 336 8161  FAX: 918 336 8265
> 
> ******* ****** ******* ******** ******* ******* ******* *** 
> *   Read list FAQ at: http://www.seaint.org/list_FAQ.asp 
> *   This email was sent to you via Structural Engineers 
> *   Association of Southern California (SEAOSC) server. To 
> *   subscribe (no fee) to the list, send email to 
> *   admin(--nospam--at)seaint.org and in the body of the message type 
> *   "join seaint" (no quotes). To Unsubscribe, send email 
> *   to admin(--nospam--at)seaint.org and in the body of the message 
> *   type "leave seaint" (no quotes). For questions, send 
> *   email to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
> *   send to the list is public domain and may be re-posted 
> *   without your permission. Make sure you visit our web 
> *   site at: http://www.seaint.org 
> ******* ****** ****** ****** ******* ****** ****** ********
> 

******* ****** ******* ******** ******* ******* ******* *** 
*   Read list FAQ at: http://www.seaint.org/list_FAQ.asp 
*   This email was sent to you via Structural Engineers 
*   Association of Southern California (SEAOSC) server. To 
*   subscribe (no fee) to the list, send email to 
*   admin(--nospam--at)seaint.org and in the body of the message type 
*   "join seaint" (no quotes). To Unsubscribe, send email 
*   to admin(--nospam--at)seaint.org and in the body of the message 
*   type "leave seaint" (no quotes). For questions, send 
*   email to seaint-ad(--nospam--at)seaint.org. Remember, any email you 
*   send to the list is public domain and may be re-posted 
*   without your permission. Make sure you visit our web 
*   site at: http://www.seaint.org 
******* ****** ****** ****** ******* ****** ****** ********