Building a covered work area with a 40' span, will this work?

[STx]

We've finally moved so now I need to build an area to work out of the elements. Budget isn't going to allow doing a fully enclosed building or a concrete slab right now so I'm just building the frame and putting a corrugated tin roof on for now. My plan is to use 2 3/8" drill stem (pipe) for the posts and rafters built sort of like a truss. I'm planning to set the posts on 10' centers (set 4' deep on concrete and with 120# of concrete per post) and the rafters on 4' centers and then bolt 2x4's onto the pipe with brackets on 4' centers to screw my corrugated tin roof onto. Initially, I'll build a 20 x 40 work area so I can cover my container, later expanding that our to 40 x 40 or 60 x 40 as funds allow.

I can get all the material I need for this as I have it designed for about $1,800 but, before I start throwing this up, I thought I'd see what you guys thought of the plan. Attached is a drawing of how I plan to frame it. We have no snow or frost line here but, it does get pretty windy. The soil is mostly sandy loam with some clay for about the first 4' and then caliche below that. If I get down to the caliche in each post hole, I should have a very solid base.

Any feedback, good or bad, is appreciated.

 

[RedNeckRacin]

I think your roof is going to be floppy. Take a look at a standard truss. Everyone focuses on the top shape, but the bottom chord all the way across the bottom is what holds the building together and keeps the walls from pushing outwards. I think you need to have a continuous chord from wall to wall and some stiffened legs to hold the top chord.

Fwiw, I'm a civil engineer by trade.

 

[STx]

I was planning to run a piece of pipe all the way along the top of the posts and then notch just a u out of the top of the pipe to set the rafter pipe into. I'm also going to run a piece of pipe along the ridge that the rafters will be notched and welded to. I think the structure should be pretty rigid, everything will be tied to everything else somewhere. I'm could do these a little more like a scissor truss, it won't add a ton of material. I'm actually going to have a fair amount of waste with the way it's laid out now. More like this.

I am concerned that 4' spacing for the roof purlins might be a little far though, I might cut that down to 2', it only adds about $300 to the materials.

 

[dickfoster]

I think your roof is going to be floppy. Take a look at a standard truss. Everyone focuses on the top shape, but the bottom chord all the way across the bottom is what holds the building together and keeps the walls from pushing outwards. I think you need to have a continuous chord from wall to wall and some stiffened legs to hold the top chord.

Fwiw, I'm a civil engineer by trade.

I agree but I'm only an electrical/electronics engineer by trade albet a retired one. Something to help hold the walls together and make the roof trusses into a complete triangle and so stiffen the entire structure.

 

[STx]

The walls will get girts when I enclose it. If it seems loose, I could add one 3' or 4' down from the top now to stiffen it.

 

[bcp]

Both designs look like you are trying for more than 14 feet clearance in the center. If this is needed, then just make the posts taller and use a simple triangular truss for the full span.

Bruce

 

[STx]

I do stack stuff pretty high inside but it's more that I hate wasting all the overhead space with regular trusses.

 

[RedNeckRacin]

Op, your walls will be plenty stiff. I was worried about the impromptu rafters trying to spread the top of the walls apart. If you had a chord to connect the tops of the walls with the same direction as the rafter it will be all the better. We have wooden trusses in our 80x40 building that are on 4ft centers so that shouldn't be a problem. I would really want to run a truss analysis to see if everything would be allright. Have you ever priced out trusses??? They are super economical and are most likely built cheaper than you can do it unless your materials are free.

 

[KennyG]

Do you know someone who is actually a structural engineer? The calculations are fairly simple, but I think this project needs to be analyzed. As a first step, I would go with a full scissor truss instead of the tie approach you started with. You are going to have a real potential for the rafter to buckle where the tie connects.

 

[STx]

Op, your walls will be plenty stiff. I was worried about the impromptu rafters trying to spread the top of the walls apart. If you had a chord to connect the tops of the walls with the same direction as the rafter it will be all the better. We have wooden trusses in our 80x40 building that are on 4ft centers so that shouldn't be a problem. I would really want to run a truss analysis to see if everything would be allright. Have you ever priced out trusses??? They are super economical and are most likely built cheaper than you can do it unless your materials are free.

I haven't yet but am going to Monday. Closest place I know of that builds them is about 120 miles away though, so delivery is going to add to the cost. I can get the material to build the pipe trusses delivered for about $120 per truss, including my consumables to weld it up.

I was originally looking at doing this with all wood but pricing the materials (minus the trusses), it comes out about $400 cheaper to do it with the steel pipe. It'll be more labor on my part but, I have the tools and more time than money right now, so that isn't a problem.

I only got to thinking about doing it this way because driving down, I saw a lot of open structures that were built this way on the side of the road. Some of them were pretty large so it seemed like it must work.