Portable garage strength enhancements
Projects
General information
This portable garage is 24' long and 10' wide.  It was purchased at a wholesale club.  Tents like this are
used widely in this area and fail regularly during the winter. Our typical winters yield 75"-100" of snow,
ever year has at least one 12" storm and 20"+ inches in a single storm probably every other year.  
Furthermore, the snow does not melt so the snow pack frequently reaches 36" at some point during the
winter.  
I thought the tent would fail with a heavy snow load by pushing the point of the tent toward the ground.  
A close friend of ours had one that failed due to snow load and it failed in a different mode than I would
have expected.
As the snow slide off the roof it piled next to the side, causing a load on the side that failed the tent with
the point getting farther from the ground and the sides collapsing inward.

Modifications
Like many projects there was no original intention to put the amount work that ended up being put into
the project.  But once you're started, for just a little more work you can do it right.  Repeat this thinking
several times and you can easily double the time it takes to do a project.  Alas it will be done right or it
least better than it would have been if you didn't do the extra work.  In this case the inspiration was not
having the tent collapse; wrecking the tent and the contents.
Legs - Each side of the tent has five locations where the
leg touches the ground.  Rather than have the legs
simply sit on the ground I wanted them secured to the
ground.  I buried a 4x4x24" on end at the location of each
leg. The legs were leveled with a 2x4 spanning the 4x4
and adjusting the hole depth or 4x4 length.  When all of
the 4x4 were level the tent feet were lag bolted into the
center of the 4x4's.
Cross cables - Strength comes from crosses
(or triangles as I tell kids).  Cable was
criss-crossed throughout the inside of the
tent.  (The best price for cable was 50' dog
runs at Home Depot.  The lady gave me a
funny look when I bought several of them.)  I
didn't cut any of the cable This is not the most
efficient use of cable (vertical runs of cable to
get the the top of the tent don't add strength,
when the tent is history I will still have 50'
cables for the next project).  The cables are
wrapped around the legs (through holes,
under cross members, etc.) and then cable
clamped to itself so the length of each cross
can not change (that is important). Along the
sides of the tent there are two crosses and
one at each end of the tent.  The cable for the
door is bundled up during the warmer months
unless a big thunderstorm is predicted.
Roof support - Each roof
panels 6' by 6', I was affraid
the material would not be able
to support a heavy load of
snow.  Though I planned to
sweep the snow off the roof, it
had to be able to handle wet
snow while I was at work or
away for a weekend.  I decided
it was cheap insurance to add
extra roof supports by stringing
nylon rope dividing each roof
panel into thirds.  Again I
chose not to cut the ropes.  
Based on how much the roof
droops and the tension in the
ropes when the roof is loaded I
think it was a good idea.   
Winter maintenance
I clear the snow around the perimeter of the tent on a regular basis.  I pull the snow off the roof with a
push broom and then clear that snow away.

You didn't address the failure mode where the walls collapse
If by now if you might be thinking no modifications have been made to address the failure mode stated
above where the walls collapse in and the point of the roof gets higher.  You're right, I made no
modifications to address that failure mode.  Outside of adding rigid members to the inside of the tent I
didn't think of a good way to modify the tent.  By the time I thought about putting rigid members across
the peak of the tent (forming little triangles at the top of the tent) I had the tent largely constructed and
was unwilling to drill bolt holes so close to the tent cover and risk puncturing the cover.  Fortunately I
have found clearing the snow from the perimeter to be sufficient.

Expected failure mode
It is clear to me the first thing that will fail on this tent is the cover itself. While it is not in a sunny location,
the sun is still brutal to anything that has to withstand it day after day. November 2006 marks the second
year the tent has been up, I'll be surprised if the cover makes it four years.  Maybe I'll have that real
barn constructed by then!
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