Re: Data needed
- From: wfhabicher@xxxxxxxxxxx
- Date: Fri, 28 Dec 2007 10:13:44 -0800 (PST)
On Dec 28, 11:57 am, "SteveB" <deserttrave...@xxxxxxxxxxxxx> wrote:
"Carl Byrns" <carl.by...@xxxxxxxxxxx> wrote in message
news:%U5dj.111996$eh4.25630@xxxxxxxxxxx
"SteveB" <deserttrave...@xxxxxxxxxxxxx> wrote in message
news:r47e45-lq9.ln1@xxxxxxxxxxxxxxxxxxxx
I want to put up eight three inch square by .120" thick posts twenty feet
long, about two foot into concrete piers. Four of them would form a 7'
square in the center, the other four would form a larger square of about
15". I want to stand them on end. This is for a hot tub/observation
platform.
Where can I find the compression strength of that tubing? I'm sure this
is going to be way strong enough, as the spa is about 300 gallons. So,
that's a little under 3,000# for spa and water. There would be multiple
bracing on the posts, both to each other, on the horizontal and on the
diagonal. I believe a simple box with an X in the middle would give it
sufficient strength to keep any lateral movement to a minimum. 1/4"
would be over double the price, and overkill, IMHO.
Steve
Better see if your local building code allows this.
-Carl
We have the following local policy on sheds and outbuildings that are not
insulated, electrified, or are built on weekends:
Steve
Steve,
3000 lbs + 6 burly friends + beer :-)), 20 feet up in the air,
requires engineering.
Is your area prone to storms, ice build-up, earthquakes, etc.? Then
you would have to consider that, also. What are soil conditions
like? Sand, mud, bed rock? Will this tower be free-standing or be
attached to an existing structure?
I take it that the four outer posts are to support a surrounding
deck? If so, consider a design with four posts only: say 4" x 4" x ?
or 6" x 6" x ?. ( My GUESS is that it would take 6" x 6" x ?? for
this app.) These four posts would support the tub AND a cantilevered
deck. Don't forget the safety railing!!
While column buckling failure is ONE consideration, other modes of
failure are torsional collapse (the tower twists during collapse), and
tower shear failure (the structure moves sideways during collapse,
legs "hinging" at the base). Both of these modes of failure are
resisted by shear (diagonal) bracing.
Buckling failure is wrapped up in the formula Kl/r (slenderness
ratio) where "K" is a factor depending on the column end conditions,
"l" is the UNBRACED length of the column, and "r" is the section's
radius of gyration. Most structural design handbooks have listings of
Kl/r ranging from a low of 20 to a high of 200 with a corresponding
allowable compressive stress in the steel, which varies only a little
with the yield strength of the steel.
In my jurisdiction (Ontario, Canada) such a structure would require
stamped and certified drawings by a licensed Professional Engineer to
get it past the city building department.
A year or so ago a fellow called me because he wanted to put a hot tub
on an extension to an existing deck. The city building department
told him it would have to be "engineered" with stamp and signature of
P.Eng. on the dwgs. He nearly choked when I explained to him what he
was in for. And his deck was only 3' or 4' off the ground!
Let us know what you decide to do!
Wolfgang
.
- References:
- Data needed
- From: SteveB
- Re: Data needed
- From: Carl Byrns
- Re: Data needed
- From: SteveB
- Data needed
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