Need a book? Engineering books recommendations...

# FOS forOvtg clarification

• To: seaoc(--nospam--at)seaoc.org
• Subject: FOS forOvtg clarification
• From: <MSSROLLO(--nospam--at)aol.com>
• Date: Thu, 25 Jun 1998 22:03:44 EDT

```I have got several responses concerning the background of this problem (wind
loading, type of fdtn etc) and would like to clarify this.  I really
appreciate all the responses.

I am trying to find a consensus on whether the vertical load should be
considered an overturning force or not.  For sake of this, I will say that the
The foundation is poured on top of the ground.  Therefor there is no passive
soil pressure present.  Once there is somewhat of a consensus on this, I would
like to change the problem a little, such as the force is a DEad and wind
force and that the column is a little off-center.

For now though, I am concerned with a centered column with a 10k upward load

#1.  Is the vertical force an overturning force?..and why/why not
#2.  What would be the correct calculation for FOS about the right toe as

I have included the original posting below.....Thanks again for the help...I
am trying to fine tune a footing program that at least models what a consensus
of experienced engineers beleive.  I was hoping this group would at least
clear up whether the force is an overturning one or not and the correct
calculation for the FOS.

have a question regarding the correct factor of safety for overturning for a
foundation subjected to an uplift force.  For purposes of this discussion,
assume I have a single footing with a horizontal force or 3 kips (to the
right) and a upward vertical force of 10 kips, both applied at the center of
the top of the footing.

Assume the footing is 15 kips in weight and is 8'x 6' x 2' thick. Pardon the
phony graphics, I am using AutoBadd.

^ 10k
|
|
------> 3k
---------------
|             |
|             | 2'
|             |
---------------
8'

1.	In calculating the FS for overturning, is it correct to call the 10k load
an overturning load?  The load is at the center of the foundation and does not
actually induce any overturning except if you do statics about a toe.  The
load itself actually does not cause overturning.  Even statics claims that is
overturns about both sides simultaneously.  I realize that the footing weight
is always a stabilzing force in both directions of rotation.

2.	Assuming you do think it should be included as an overturning force, would
the correct calcualtion be Movtg = 3x2 + 10x4 = 46 and Mstab= 15x4 = 60,
therefore FS = 1.304   OR is the correct one: Movt = 3x2=6 and Mstab=
(15-10)x4=20  FS = 20/6 = 3.333.  By definition, it would appear that the 1.3