Steel beam question

[farmer2009]

Could you not run a simple design joist pattern with the steel. Then come back over it with say 2x4's and make your nailers to hold your floor pattern. I say 2x4's based off a 16" joist spacing. Then add steel blocks where you have lots of joints to handle that stress.

I would have to agree with LD1 though. Lots of trip hazards.

 

[LD1]

To do the joist pattern like you have designed, without a post in the middle, you are going to need a substantial carrier beam. Whatever one is the full 15.15' length.

And the design of all the other joists tying RIGHT into the CENTER of that beam, puts a point load right at midspan. A point load roughly 1/2 of the total load on the gazeebo deck.

I would not design for less than a 50psf live load and 10psf dead load.

162sq ft with 1/2 of that loading right on the midspan of the long beam @ 60PSF is 4860#. Lets just call it 5k.

So, you need a beam to span 15.15' and carry a load of 5k at midspan and not deflect more than 1/2" (L/360)

Minimum I see is a C9x13.4 channel. Could drop to a 8" with a C8x18.75 but gain more weight (and will cost more). And only way to get under 8" depth is with an Ibeam. S7x20 would work. But again, heavier and more $$$

I didnt figure any loading on the rest of the beams, as it isnt going to be too significant. But wanted to see if this is still what you are planning on doing.

 

[LD1]

Could you not run a simple design joist pattern with the steel. Then come back over it with say 2x4's and make your nailers to hold your floor pattern. I say 2x4's based off a 16" joist spacing. Then add steel blocks where you have lots of joints to handle that stress.

I would have to agree with LD1 though. Lots of trip hazards.

Or just a simple joist pattern with treated 2x10's. On 16" centers they are good for spanning almost 16' with a 50PSF load.

Then lay out that crazy pattern with 2x4's laid flat (like roof purlins) which sould be quite stout with 16" joist spacing.

 

[LD1]

If you wanted to do channel on 2' centers for the joists, like farmer2009 describes or like how I described with 2x10's

For steel channel it would require c5x6.7 at a minimum for the joists. If you want to do steel, this is how I would do it. Instead of a large beam in the middle, then 3 smaller ones on each side radiating out from the middle, then even smaller ones for the remainder of the bracing. Just seems way more complicated than it needs to be.

I know you said 8' up. What is going under it? is there a reason you want the fancy pattern on the under side?

 

[farmer2009]

The advantage of steel here would be the floor thickness. With steel you would be less than 8" total. With 2x10's you would be about 12". The disadvantage would be the building weight.

He said something about firewood storage underneath. So it seams like a one roof two purpose situation. Which I understand.

One thing to throw out to the OP. In 10-15 years are you going to want to climb steps to sit on the gazebo. Or is the wife going to be able to climb up to it while pregnant. I don't know your situation but might think about some more of those scenarios. What ever fits you.

 

[crazyal]

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

This is exactly what I had in mind and why the joist layout is "crazy".

So here's a picture of what I have now. The wife has never liked the woodshed. I've seen much worse looking ones but since we both want a gazebo I thought I could move the shed and put it there. My plan is to have a bridge from the corner of the deck to the gazebo and also a set of stairs coming down towards where I took this picture from. The idea is to use the space under the gazebo to store firewood wrapped with lattice to hide the wood but allow plenty of air flow. The firewood would already be seasoned, no green would be stored under it. The shed is 12' wide and 8' deep and the opening is about 7' high.

I found a picture on the net that may give a better idea of what I'm looking to do. When I get a chance I'll use one of the on-line deck designers and do a layout. If possible I would like the floor of the deck to be at the same height as the gazebo floor, one step up would be acceptable. Because I would like to store wood under it I would like at least 6' between the floor for the firewood (this could just be wood simply laid on the ground and the bottom of the joists. A center post isn't out of the question but I figured I would see just what size channel was needed without a center post first. Also the location of the outside posts doesn't have to be exactly at the edge. But the posts will be carrying the load of the gazebo's walls and roof so they should be close, say within a foot. Otherwise I think it would be adding even more calculations to the load mix. Part of the reason I like the idea is because it's complicated. I knew figuring out would be more work but that just makes it more rewarding when you look at it. Anyone can do simple.

 

[LD1]

but I figured I would see just what size channel was needed without a center post first.

A heavier 8" or lighter 9" channel is the minimum as per my post above.

If thats acceptable, go for it.

But if all you are gonna do is store wood under neath it, Id go more conventional then make your nailers to get that fancy floor

 

[farmer2009]

Those pictures help explain why you want what you do. I think it will look really nice. If that's all the bottom will be used for I wouldn't worry about the underneath and use the double layer to frame the floor and a center post.

With the bridge out to it you won't have to worry about access.

Keep pictures coming along the way.

 

[s219]

I built gazebos for many years (built in factory, sold alongside storage sheds) and we could do the octagonal pattern floor without any of the complexity shown in the OP's plan. Lots of ways to do it. Might want to research some plans for wood gazebos and see what pops up.

 

[crazyal]

Right now I'm just in the coming up with a plan on how I want to build it. Nothing is set. Since it's basically free standing I want the posts to be steel. Two of the 3 6x6 pressure treated posts are warped on my deck. It's tied to the house and a cement footing so it's not structurally a problem but doesn't look as nice as it could. Everything from the gazebo floor up will be wood with the pressure treated 4x4 posts having a vinyl cover like I did on the deck. I've also debating using 7" c channel with a pt 2x4 laying flat on top of it around the outside edge and 2x10 for joists and blocking as needed for the decking boards. I like the idea of making the octagon out of steel because I can lay it out exactly on my shop floor and weld it up and then place it on top of the posts.

Here's a basic layout of what it will look like. It's not exact and and it just show an octagon deck, not a gazebo but it at least gives an idea.