Need an engineer-strength of wood beam?

[IHDiesel73L]

I am constructing a gate with a kind of archway over it because I want to be able to hang/hoist things from it if need be. One of the reasons I'm doing this is so that I have a place to hang deer before butchering which it can certainly handle, but I have a habit of overbuilding things, so I wonder how much I weight it will support? For example, could I lift the front end of a compact utility tractor? Could I pull a small block Chevy with it, etc...? Here is a sketchup representation of what I'm building:

I've already got the 4 x 6 posts in the ground. They are buried about 3' 6" on what seems to be solid and relatively undisturbed heavy clay soil. I dug the holes 4' deep and added 6" of gravel to the bottoms to facilitate drainage. This weekend I'll be adding the lintel on top which will consist of a 4 x 6 sandwiched between two 2 x 8s. The 4 x 6 lintel will rest on the tops of the 4 x 6 posts (a deviation from the drawing-I just decided that last night) and Timberlock fasteners will be driven through the top down into each post. After that, the 2 x 8s will be screwed to each side using 3" coated deck screws. Part of the function of the 2 x 8s is to provide a finished look, but they should also provide quite a bit of stiffness also.

I tried looking online for information about the strength of wood beams, and found lots of charts and formulas, but I really don't understand them well enough to use the information. All of the lumber is pressure treated Southern Yellow Pine. The unsupported span of the beam is 8' 1". I'm just trying to get a rough estimate of how much weight I can safely support with this. For example, a SBC with a cast iron intake, exhaust manifolds, etc...comes in at just shy of 600lbs, vs. the 7.3L Powerstroke in my truck which weighs nearly 1000lbs fully dressed :shocked: Any ideas?

 

[Chef Pa]

Maybe this will help.

First would be diy engineering:

CECalc.com - Structural Wood Calculations

A reference table (pdf)

http://www.awc.org/pdf/wsdd/c2b.pdf

Greg

 

[PapaPerk]

I am constructing a gate with a kind of archway over it because I want to be able to hang/hoist things from it if need be. One of the reasons I'm doing this is so that I have a place to hang deer before butchering which it can certainly handle, but I have a habit of overbuilding things, so I wonder how much I weight it will support? For example, could I lift the front end of a compact utility tractor? Could I pull a small block Chevy with it, etc...? Here is a sketchup representation of what I'm building:

I've already got the 4 x 6 posts in the ground. They are buried about 3' 6" on what seems to be solid and relatively undisturbed heavy clay soil. I dug the holes 4' deep and added 6" of gravel to the bottoms to facilitate drainage. This weekend I'll be adding the lintel on top which will consist of a 4 x 6 sandwiched between two 2 x 8s. The 4 x 6 lintel will rest on the tops of the 4 x 6 posts (a deviation from the drawing-I just decided that last night) and Timberlock fasteners will be driven through the top down into each post. After that, the 2 x 8s will be screwed to each side using 3" coated deck screws. Part of the function of the 2 x 8s is to provide a finished look, but they should also provide quite a bit of stiffness also.

I tried looking online for information about the strength of wood beams, and found lots of charts and formulas, but I really don't understand them well enough to use the information. All of the lumber is pressure treated Southern Yellow Pine. The unsupported span of the beam is 8' 1". I'm just trying to get a rough estimate of how much weight I can safely support with this. For example, a SBC with a cast iron intake, exhaust manifolds, etc...comes in at just shy of 600lbs, vs. the 7.3L Powerstroke in my truck which weighs nearly 1000lbs fully dressed :shocked: Any ideas?

First of all you should not use screws. You should use galvanized carriage bolts. :thumbsup:

Here's how I would make the beam... I would use two 2"x12".... and place an 8" section of the 4x6 post every couple of feet. The beam would be attached to either side of the main post with the carriage bolts. This will sandwich the main posts and beam together making a very strong structure.

The other issue you have to work out is attaching the load to the beam. The attachment must distribute the load evenly to the beam. I recommend some sort of steel plate that attaches with multiple carriage bolts.

The biggest issue I see with the set-up is side loading on the beam... not a direct vertical pull on the beam... this could cause the whole outfit to lean... so firmly mounted posts are critical... also small kickers or braces maybe needed to support the posts in this situation. An ideal design would use four posts forming an A-frame on each end. This would be very strong! But it all depends on how much loading you are carrying.

Good luck!

 

[Pipestone Kid]

The design you described (4x6 with a 2x8 on each side will hold everything you described. (listed) However, if you are a little unsure, put a strip of sheet metal on each side of the 4x6 before you add the 2x8's. When the sheet metal is held firm by the lumber, it cannot buckle and you have, in effect, created an I beam. (Two I beams to be more exact). You could lift your whole truck if you wanted.

 

[biggerten]

I agree with PapaPerk, side loading needs to be a concern, if the weight starts shifting it'll either want go over or want 'rack' - somw gussets would help with the racking, and I like the A-frame idea as well. Also, sandwiching the sheet metal is a good idea, you could sandwich plywood instead of the sheet metal, too. Also, something to keep the beam from 'rolling' off of the posts.

 

[Brad_Blazer]

Uh, the strength in an I-beam is not in the web, it's in the top and bottom flanges.

It looks like the described beam is good for about 1 ton using Fb=1000psi and derating the distributed load by a factor of 5/16 for a point load in the center. A lot depends on the lumber grade. Make sure the top sheds water so it doesn't deteriorate. The strength is in the top and bottom fibers of the wood so don't cut any notches, especially near the center where the bending stress is greatest.

The top beam will also tie the posts together to resist any fence tension and the cantilever weight of the gate.

 

[bironacad]

Maybe this will help.

First would be diy engineering:

CECalc.com - Structural Wood Calculations

A reference table (pdf)

http://www.awc.org/pdf/wsdd/c2b.pdf

Greg

I like how everyone is leaving this alone, lol,:thumbsup:

 

[IHDiesel73L]

I like how everyone is leaving this alone, lol,:thumbsup:

I looked at it but unfortunately I don't possess the math skills to utilize the information. I'm sure I could do the calculations if I knew what numbers went where.

Uh, the strength in an I-beam is not in the web, it's in the top and bottom flanges.

It looks like the described beam is good for about 1 ton using Fb=1000psi and derating the distributed load by a factor of 5/16 for a point load in the center. A lot depends on the lumber grade. Make sure the top sheds water so it doesn't deteriorate. The strength is in the top and bottom fibers of the wood so don't cut any notches, especially near the center where the bending stress is greatest.

The top beam will also tie the posts together to resist any fence tension and the cantilever weight of the gate.

Thanks! It sounds like you know how to utilize the information bironicad referenced below. I looked at those tables but I don't how to plug in what numbers where in order to come to the conclusion you did. Would you mind showing the calculation that led you to that number? I'm not sure of the grade of the lumber, I just know that it's Southern Yellow Pine. Would the grade be stamped right on it? I could always call the lumberyard and ask I suppose. I will be locating the load point in the center in the form of a large eye bolt of the appropriate working load drilled through the beam and secured at the top with a nut and a very large washer. As for the load rating itself I doubt I would ever try to lift more that 1000lbs (if that even), its just nice to know how overbuilt it is :laughing:

 

[flusher]

I am constructing a gate with a kind of archway over it because I want to be able to hang/hoist things from it if need be. One of the reasons I'm doing this is so that I have a place to hang deer before butchering which it can certainly handle, but I have a habit of overbuilding things, so I wonder how much I weight it will support? For example, could I lift the front end of a compact utility tractor? Could I pull a small block Chevy with it, etc...? Here is a sketchup representation of what I'm building:

I've already got the 4 x 6 posts in the ground. They are buried about 3' 6" on what seems to be solid and relatively undisturbed heavy clay soil. I dug the holes 4' deep and added 6" of gravel to the bottoms to facilitate drainage. This weekend I'll be adding the lintel on top which will consist of a 4 x 6 sandwiched between two 2 x 8s. The 4 x 6 lintel will rest on the tops of the 4 x 6 posts (a deviation from the drawing-I just decided that last night) and Timberlock fasteners will be driven through the top down into each post. After that, the 2 x 8s will be screwed to each side using 3" coated deck screws. Part of the function of the 2 x 8s is to provide a finished look, but they should also provide quite a bit of stiffness also.

I tried looking online for information about the strength of wood beams, and found lots of charts and formulas, but I really don't understand them well enough to use the information. All of the lumber is pressure treated Southern Yellow Pine. The unsupported span of the beam is 8' 1". I'm just trying to get a rough estimate of how much weight I can safely support with this. For example, a SBC with a cast iron intake, exhaust manifolds, etc...comes in at just shy of 600lbs, vs. the 7.3L Powerstroke in my truck which weighs nearly 1000lbs fully dressed :shocked: Any ideas?

Take three 2x8s the length you need to span the distance between your posts and use them to fabricate a glulam/nail-lam beam. Use exterior grade wood glue and a lot of C-clamps to glue the 2x8s together and then use 16p cold dipped galvanized nails to nail them together.

 

[Pipestone Kid]

Uh, the strength in an I-beam is not in the web, it's in the top and bottom flanges.

It looks like the described beam is good for about 1 ton using Fb=1000psi and derating the distributed load by a factor of 5/16 for a point load in the center. A lot depends on the lumber grade. Make sure the top sheds water so it doesn't deteriorate. The strength is in the top and bottom fibers of the wood so don't cut any notches, especially near the center where the bending stress is greatest.

The top beam will also tie the posts together to resist any fence tension and the cantilever weight of the gate.

If the strength of an I beam is not in the web, why does a 12 inch beam have a greater load capacity than an 8inch? Try taking the web out and see how much it holds.