Steel beam question

[crazyal]

So I'm thinking of building a gazebo next summer. It'll be a 14' octagon about 8' off of the ground. I'm going to use steel tube on top of cement tube footings. There's going to be white lattice around the base and I'll use the space to store firewood. All the weight from the gazebo structure will rest directly on the steel posts. My question is about the sub floor. I was thinking of using C channel. Te flooring will be Tigerwood (to match my deck) and can span up to 24" between joists. This picture is kind of rough but it gives an idea how I was planning on laying out the c channels. The load this should see would be maybe 3000 lbs (12 people and the weight of decking) spread across the entire deck. My local steel supplier can answer basic questions about deflection but this is out of his comfort zone. Each side would be approx 6' and also would be c channel. This, of course, will be welded together. Only one channel will be a solid piece (it could be a S beam) but the rest would weld to it. I'm planning on welding a plate to the bottom of the beams where the joints are. So what size c channel would be needed?

 

[CurlyDave]

How far is the sub floor going to be above grade?

Most people would design the floor of the gazebo to the same criteria as a deck, which would be about 100 lb/square foot in most jurisdictions.

If it were a 14' square, it would have 196 sq feet of area, and I would design for a 20,000 lb load. This is a lot more than the 3000 lb load you are thinking about.

While I like the idea of the joist structure you show, it is not particularly easy to calculate. I would think long and hard about a more conventional framing plan with joists on 16" centers, which would be a lot easier for the average engineer to understand and calculate.

 

[s219]

Yeah, I have to agree -- what you're proposing would take Finite Element Analysis on a computer to figure loads and size the members. Try to simplify it if you can. And why are you building out of steel? Gazebos are easily made from PT lumber. Built a few dozen myself.

 

[EddieWalker]

Pretty design, but not very practical. With only a 14 foot span, I would build three beams and run your joists on top of the beams. This gives your joists a 7 foot span, which makes it very strong

 

[LD1]

I agree, you are over complicating the joists.

And even so, it is impossible for anyone to calculate that out because you did not say where the posts are going to go, and how many of them, etc.

I am "assuming" one post at each point of the octagon? But I dont like to make assumptions then give bad advise based off a wrong assumption

 

[Budweiser John]

I don't see any advantage to steel framing in this case. Conventional wood framing is cheaper and easier to attach the decking to. The finished flooring pattern will drive the joist lay out and setting the assembly on concrete piers is superior to treated wood posts set in the ground.
To further preserve the framing assembly I always treat cut ends by brushing on "Coppertox" before assembling. Cutting strips of roofing ice and water shield or using a window wrap such as "Vicore" placed on top of the joists provides a seal between the decking and joist adding years to life expectancy of the structure.
Ramblings from years of building new decks and rescuing old structures B/4 potential collapse.
B John

 

[NorEaster]

The reason joists are run that way in a gazebo is to allow the decking to be placed in a pattern, picture it as 8 triangles, whose points are at the center.

 

[BHD]

put a support in the center of the floor joist and your problems are solved, the max span then is 7 foot,

for the floor, just run the joist across the unit at the desired spacing and do not worry about the fancy web type construction, much like this picture, http://www.diyonline.com/graphics/gaz-fig6.gif

unless your desire if for a fancy pattern in the floor planks,

I my self is cheap enough I would most likely pour a concrete deck, (possibly stained or colored and stamped, or rolled), made one of these a number of years ago, does a nice job, Noble Coat on Quick Imprint Rolled Concrete | Quick Imprint Systems LLC

A center support would solve 98% of your worries if you used any kind of joist system, and the cost would be considerable less as lighter materials could be used,

 

[Mysfyt]

You are way over thinking this. Spiderman would be proud of your design I'm sure!



Something like this is all you need if you really want to make it out of channel. I'm not an engineer, just a guy who works with this material every day. Good luck!

 

[LD1]

The reason joists are run that way in a gazebo is to allow the decking to be placed in a pattern, picture it as 8 triangles, whose points are at the center.

View attachment 439690

That makes sense why you want the fancy joists now.

I may try to do some load figuring.

However, as nice as that design looks, I dont like it for practical reasons. When I build a deck, I try not to have ANYWHERE on the deck where 2 boards are butting up. Cause over time, as things change, they never seem to line up and cause trip hazards. I like full length deck boards.

IE: IF I was doing a full length of the house deck, like say an 8'x40' or a 12' x 40', my joists run the long span, and deck boards will run the short span as to not have any butt ends meeting in the middle. Your design is going to create ALOT of that.