Sizing bridge beams

[deezler]

Agree Lou that those are robust bridge options, but how do you carry and move them into place across an active creek? A crane or telehandler? Lotta logistics there, vs constructing something piece by piece.

 

[LouNY]

A trailer could still be on axles, dump bed would actually slide fairly well, maybe a couple of "ski's".

 

[2manyrocks]

Agree Lou that those are robust bridge options, but how do you carry and move them into place across an active creek? A crane or telehandler? Lotta logistics there, vs constructing something piece by piece.

One option is to temporarily place a couple of logs over the creekbed and then drag the trailer frame over the logs. Then remove the logs.

 

[Rockbadchild]

I went to my local trucking company and bought a retired flat bed for $700 even if you pay double that still going to be cheaper then beams and decking.

see below for my thread,

bridge construction on a budget

good morning TBN members, Id like to share my bridge construction of last summer perhaps it will give ideas to folks with similar project in the future and getting constructive feed back … there is a small creek splitting my property preventing me to access the back end which constitute of...

www.tractorbynet.com

 

[Rockbadchild]

Structural wasn't my strongest class so I am not even going to attempt to calculate it... What is P.T. 5 2x8 ? like tubing? and laminated?? just against each other? regardless the case is I would go with two I beam instead and something like 4'' wide x 6'' tall and that would be as overkill as it can be.

 

[LD1]

Structural wasn't my strongest class so I am not even going to attempt to calculate it... What is P.T. 5 2x8 ? like tubing? and laminated?? just against each other? regardless the case is I would go with two I beam instead and something like 4'' wide x 6'' tall and that would be as overkill as it can be.

Yup. Even a little W6x12 I-beam (matches your 4"w x 6"h specs) would be stronger than the proposed wood.

Just ONE of those 168lb beams could support the WHOLE 3000lb tractor right at midspan.

 

[jonsstihl]

I built a similar bridge 10 foot span, out of two 8x8 hemlock beams and 2x8 hemlock decking about 10 years ago. at the time I had my b7800 and it worked OK but over the years one beam failed due to rot.

I just rebuilt it with steel beams doubled up so i used two steel beams per side so four beams total with the same size 2x8 decking. they are six inch steel beams I think W15 (not sure) I doubled them up to match tire tread widths of all my stuff ranging from ATV to an old manure spreader used as a wood trailer that is wider than the tractor.

I also more than doubled my tractor weight in those ten years. b7800 was approx 3000 with a loader and my L4740 is atleast close to 8000lbs with the loader and filled tires. I get what feels like zero deflection when I cross the steel frame bridge with my L4740.

I hate doing stuff twice. my time is worth something, I vote for steel especially for your longer span.

 

[Rockbadchild]

Ho I see so P.T. 5 or 6 2x8x14 = 5 or 6 pressure treated 2x8 x 14 ... I thought it was P.T. 5 was steel grade.. ok so keep in mind you get most of the strength from the height not the with but the way to make beams is to have plywood (half inch or 3/8) in between each 2x8's and nails (6inch apart in a zipper pattern) and glued together... I am sure you would be fine with what you have as long as its glued and proper nails in with the plywood in between.

 

[LD1]

Ho I see so P.T. 5 or 6 2x8x14 = 5 or 6 pressure treated 2x8 x 14 ... I thought it was P.T. 5 was steel grade.. ok so keep in mind you get most of the strength from the height not the with but the way to make beams is to have plywood (half inch or 3/8) in between each 2x8's and nails (6inch apart in a zipper pattern) and glued together... I am sure you would be fine with what you have as long as its glued and proper nails in with the plywood in between.

The plywood adds nothing more than mass to the beam. Its no stronger or no weaker that equivalent sized dimensional lumber.

In otherwords.....if he builds a beam with 4 2x8's and 3 pcs of 1/2" plywood in between.....making the total beam 7.5x7.5......it would have the same strength as if he just skipped the plywood all together and used 5 2x8's.

And plywood.....even marine grade.....is the last thing I'd want for a wet-location beam.

The reason why plywood became so popular with built-up beams is because nominal sizes. .....

A 2x4 wall is 3.5" thick........a doubly ply header is only 3. So a slice of plywood makes the beam 3.5" wide.
A 2x6 wall is 5.5" thick......a triple ply header is 4.5"......so two slices of plywood make it 5.5.

I am guessing that somewhere along the lines.....someone saw it and mis-understood the purpose of the plywood....and now it seems to be preached as gospel about how much stronger it makes things. But it doesn't add any more than an equivalent size dimensional lumber.

 

[Rockbadchild]

The plywood adds nothing more than mass to the beam. Its no stronger or no weaker that equivalent sized dimensional lumber.

In otherwords.....if he builds a beam with 4 2x8's and 3 pcs of 1/2" plywood in between.....making the total beam 7.5x7.5......it would have the same strength as if he just skipped the plywood all together and used 5 2x8's.

And plywood.....even marine grade.....is the last thing I'd want for a wet-location beam.

The reason why plywood became so popular with built-up beams is because nominal sizes. .....

A 2x4 wall is 3.5" thick........a doubly ply header is only 3. So a slice of plywood makes the beam 3.5" wide.
A 2x6 wall is 5.5" thick......a triple ply header is 4.5"......so two slices of plywood make it 5.5.

I am guessing that somewhere along the lines.....someone saw it and mis-understood the purpose of the plywood....and now it seems to be preached as gospel about how much stronger it makes things. But it doesn't add any more than an equivalent size dimensional lumber.

I disagree, although I agree with the wet location beam, that's a very good point... the wood grains of any planks are longitudinal, the plywood keep the grains bonded uniformly together, so it doesn't separate under stress.