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RE: Canvas patio covers and the code????

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Ed,
thanks for your comments - I concure about the live load, but since I did
not have to prove the structure and was only hired to deal with the uplift
it became a moot point.
In our area it is much harder to get the depth of the foundation due to the
extremly rocky conditions. Most of our soils is decomposed granite
culminating in bedrock condition farther down. This results in a sandy soil
with a lot of larger than stone size fragments. In addition, if I exceed 5'
of depth, the contractor must conform to OSHA regulations for shoring. It's
much easier to create a shallow pad than a deep pier. Expansive soil is not
an issue in "most" of our valley although liquification area's do exist
which might do better with a deeper foundation if this were other than a
secondary structure.

BTW, I did go to the site yesterday to see the non-conforming structure that
was to be replaced. After seeing it, I would not recommend that the system
be used. It is surely not conforming and is simply a welded 1" sq x 1/16"
thk tube steel parallel chord "ladder-truss" sturcture that is constructed
in two sections 10' x 20'. The two sections joined by tack weldw at the 20'
side and the column at the junction of the two panels was omitted at the
front side to allow easier acess to the car. Although there was no noticible
deflection parallel to the front, there was a deflection at the sides that
was compensated by adding two temporary columns. I should add that the
canvas had not been installed as yet since the structure will be modified to
accomodate the pads, a connection to the house and the setback required by
the city.

I stood on one end and literally shook the structure to see how flimsy it
was. I would question how it will behaves laterally with as much flexibility
as I was able to create. Considering the potential cyclic motion, I wonder
(without having to run the numbers) if it will hold up in an earthquake. I
suspect it will since it is extremely lightweight.

After reviewing the system, I would recommend that it not be connected to
the residence but remain free-standing to allow it to fail rather than tear
away from the residence. The columns are TS2x2x1/8" from what I can see.
This is a real looser as far as I'm concerned and wonder how this company
survived for so long. I can only guess that they never pulled permits and
never got caught - imagine their luck!

Dennis

-----Original Message-----
From: Ed.Haninger(--nospam--at)fluordaniel.com [mailto:Ed.Haninger(--nospam--at)fluordaniel.com]
Sent: Thursday, August 27, 1998 10:14 AM
To: seaint(--nospam--at)seaint.org; Dennis S. Wish PE
Subject: Re: Canvas patio covers and the code????


     Dennis,

     Just as a point of reference, I designed a canvas covered wood frame
     structure for a school in central Orange County.  I remember using
     ASCE 7 with a design speed of 85 mph (3 second gust) which resulted in
     about 15 psf uplift.  I used a 1.5 uplift factor to provide the proper
     stability ratio.  (BTW - some don't feel the 1.5 factor applies - I
     do)  I remember getting foundation loads and sizes about what you
     have.  We used 1 ft dia by 6 ft deep drilled piers.  The worst column
     had about a 225 SF tributary area.  The building department had a
     consultant check it over.  The consultant thought that the roof live
     load should be 20 psf (like a solid roof), but I talked him into
     accepting the 5 psf load I used.  Other, than that the building dept
     was happy.  This was a one-of-a-kind design so the owner did not have
     any "under-designed" structures to compare to.  They were happy.

     Ed Haninger
     Fluor Daniel


______________________________ Reply Separator
_________________________________
Subject: Canvas patio covers and the code????
Author:  "Dennis S. Wish PE" <wish(--nospam--at)cwia.com> at fdinet
Date:    8/26/98 6:08 PM

(snip)....Am I missing something or is there a specific code requirement
(UBC) that makes structures like this exempt from code requirements? If the
numbers are typical of other canvas installations, how do the local
engineers address the political side of the issue so that we are not accused
of trying to create a market or putting some merchant out of business?

Dennis Wish PE