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Re: Multiple loads on a pad foundation question
- To: <seaint(--nospam--at)seaint.org>
- Subject: Re: Multiple loads on a pad foundation question
- From: "Raymond Shreenan" <rshreenan(--nospam--at)adelphia.net>
- Date: Thu, 18 Jan 2007 19:59:27 -0800
Find the resutant location of both loads for all
conditions of live load and dead load and design the footing or pad for the soil
bearing that creates the worst punching shears and moments on the footing.
Another approach if you have the space is to determine the footing size
on the maximum total load for both columns and locate the center of the
footing at the resultant location of the maximum column loads and then check
soil bearing for DL one column and DL + LL the other column.
i hope this helps.
----- Original Message -----
Sent: Thursday, January 18, 2007 2:31
Subject: Multiple loads on a pad
I am designing a pad foundation
for a prefabricated steel building. The steel building is used in the middle
of a wood building that is a private school for a local church. I have the
deflection calculations for the steel building (story drift) and am using
proprietary Hardy Frames to control the drift around the core of the wood
building. Using the building separation analysis of UBC 1633.2.11 (similar in
CBC) I come up with an allowable building separation of
This creates one problem for me.
The wood structure is designed as a typical slab on grade. All four walls
surrounding the center of the building are bearing (except for the steel
building in the middle). I will integrate the turn-down edge of the slab (or
interior grade beam for bearing walls). There are a number of pads that will
have a reaction from heavy timber loads that need to rest on the same pad
footing as the columns for the steel building rests. If the foundations are
placed in a monolithic pour I have to design the pad food for both a
concentric load from the steel building and another eccentric load from the
wood building. So the question is how to address the analysis? I?m using one
of the typical foundation design programs that allow only one load whether it
is eccentric or concentric.
So my question is if it is
feasible to locate the eccentricity of the resultant of both loads by
proportional interpolation? There is no uplift on the structure since the
steel building is fully enclosed in the wood structure and a flexible membrane
or flashing is used to seal the gap between the two structures. This allows
movement without worry about pounding between the two structures. The design
is based on worst case allowable deflections rather than actual deflections
which is calculated by the steel building manufacturer and controlled by the
stiffness of the Hardy Frames. The question is really limited to identifying
the bearing point or its eccentricity on the pad footings due to two column
loads applied within about 12-inches of each other center to center.
P.S. I am not the Engineer in
Responsible Charge on this project. The project was designed by another
engineer who I am consulting for. He will wet seal the design and I will seal
(along with him) the separation calculations as well as the pad foundation