Estimating wooden ramp strength

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I have steel ramps, but they are very short and suitable for my [low] trailer only.
I am considering making ramps from wooden boards. Specifically, picture a ramp that looks like a letter I in cross section. The wide part of the I is a 2x8. On the top and bottom of the I, there would be 2x4s. The "I", of course, would be laid flat for use.
Here's the ascii graphic:
. . |==========| ~ ~
The 2x4s would be screwed to the 2x8 with wood screws, and reinforced with glue.
My question is, what would be the strength of this ramp if it was, say, 8 ft long. Specifically, how much load could I place in the middle for some reasonably low deflection (like 1-2 inches).
thanks
i
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Ignoramus20839 wrote:

It is simply a 3x3-1/2 beam for estimating purposes. You can forget the 2x8 in the horizontal as it is conservative to do so.
I don't have a link ottomh, but a google will find any number of beam deflection engines.
Use SYP or fir for higher modulus and, of course, be sure it is defect-free timber.
Depending on length and weight desired, going w/ 2x6 tapered some for the ends might be more suitable at the expense of a little more weight/heft/bulk...
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Two thoughts...
Why not just take the 2 X 8's and test them. Put them on a block of some kind on the ground and roll whatever you plan to use them for onto them and observe the deflection. This would be simple and just cost the price of a couple boards.
I have seen a number of ramps that have a metal end on them specifically designed for a ramp. I think that would be much more compace and work better than your proposed 2 X 4 ends. I don't know where to purchase them, but they are out there because I have seen them in use many times.
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On Thu, 25 Oct 2007 11:45:15 -0400, "Lee Michaels"

Even your local borg will probably have aluminum "ramp ends" for 2x8 and 2x10 lumber. They can be secured to a trailer or truck tailgate by means of holes in the aluminum pieces and pins that go through those holes and into matching holes you drill in the trailer or tailgate. The 2x8 version has worked fine for me with 8 foot lumber for lawnmowers and snow throwers (heaviest item is about 160lbs). I never drilled holes in the tailgate of my 18 year old truck and I don't plan to drill holes in the tailgate of the new truck either ;-)
Just FYI, the 1989 Nissan pickup was better built (both assembly and design) than the 2008 Tacoma is. The wind noise was lower (after 18 years) than the new one and the speedometer was more accurate. The Tacoma reads 5% high (factory spec is +/- 7%). That 5% error will take away 5% of the warranty coverage (3000 miles of a 60000 mile warranty). It's all drive-by-wire and the only physical correction is a slightly larger tire size (70 series -> 80 series is 5% increase). The dealer hasn't done anything yet, except the usual "Im sorry. What would make you happy?" and then not following up. The dealer will get one more chance at fixing it, then I'll file a "Lemon Law" complaint (also covers things that reduce the value of the vehicle) - which they must respond to in writing. At least the error will be documented for any future warranty claims...
John
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John wrote:

I didn't drill holes in my tailgate either. What I do do though, is use cargo straps wrapped around each ramp and secured to the bumper to keep the ramps from slipping off. It wakes you up real fast when a ramp slips out while you're backing a riding mower out of the truck...

If the dealer hasn't done anything call the regional factory rep. The calibration is an easy adjustment with a proper scan tool and would take a competent tech about 5 minutes if they just go by tire measurements and 10 minutes if they measure the actual rolling radius of the tires.
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Home Depot sells the ramp ends pretty cheap. They're in the Outdoor Garden department.
--

-Mike-
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Mike Marlow wrote:

I have a set of those. They work fine with 2x8's getting my 500 pound wide cut mower in and out of my 4x4 Tacoma twice a year.
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Ignoramus20839 writes:

Might be stronger/lighter/cheaper if you attached some steel angle (hidden at Home Depot on the electrical aisle) to the 2x8, or to slices of a sheet of 3/4 plywood.
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Ignoramus20839 wrote:

Using spruce pine and ignoring the 2x8, the sagulator gives a deflection of .7" for 500lbs of load in the center of a single 8' ramp.
Chris
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OK, this is great. What does your sagulator say about 1000 lbs load?
also, what would it say if I replaced 2x4s with 2x6s?
I appreciate your help . Thanks a lot.
i
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Ignoramus20839 wrote:

Google "sagulator" and experiment to your heart's content...
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I thought that sagulator was a PC program. It is great! I have it bookmarked and am now experimenting!!!
Looks like with 2x4x, the deflection of a 1,000 lbs load in the middle will be about 2 inches, which is too much.
However, with 2x6s, the deflection will only be 0.36 inches, and 0.7 inches with 2,000 lbs center load.
So, it seems, that a ramp made to the shape of letter I, could easily let me deal with 2,000 lbs wheeled loads. (such as a dolly on casters)
i
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Ignoramus20839 wrote:

Well, when you're dealing with that kind of loads, don't forget the supporting ends, joint strength and fasteners, point loading of a caster on the 2x ramp, the downward force of the load back down the ramp running over whatever is in the way, the load limit on a truck tailgate, etc., etc., etc., ...
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Well, absolutely. Plus the 2x8 may crack on the middle under such a load.
i
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Ignoramus20839 wrote:

For what I expect would be better strength, rigidity and protection from potential defects in dimensional lumber, try making a glued and screwed box beam. Something like a top surface layer of three layers of 3/4" plywood, two or three 2x4 members inside the box, and another layer of 3/4" ply on the bottom. You'd need two sheets of 3/4" ply, six 2x4s and a lot of glue and screws to make two 1' wide ramps. If you want cleats at the sides to help keep wheels from running off, apply strips of 1x2 to the top surface along the edges.
Bad ASCII art:
## ## ################## ################## ################## ## ## ## ## ## ## ## ## ## ##################
BTW, the extruded aluminum ramp ends are called "Ramparts" and sold many places including Depot and Lowe's.
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I think that it is going to be kind of big. But I will think about it. By the way, I heeded your advice and bought the HF load balancer a year ago. I will check those ramparts, I am sure that I will need them. But maybe I will make them.
i
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wrote:

A box beam of plywood and 2X's would make an excellent ramp, but you've got the functions of the plywood and sawn lumber reversed. The plywood should be the vertical webs and the 2X's the top and bottom plates. The 2X's carry the tension and compression loads; the plywood resists the shear between the tension and compression members.
--
Ned Simmons

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Ned Simmons wrote:

The 2x's could be replaced with ply as well, however using the 2x4s just makes construction easier. The main point is in putting engineered lumber i.e. plywood in the positions of stress, eliminating the potential for an undetected flaw in the dimensional lumber from causing a catastrophic failure. Indeed, the engineered I joists for building construction have begun to shift to engineered lumber for the top and bottom chords of the I joists in place of the earlier dimensional lumber.
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wrote:

No question about that.

But there is stress in both the webs and flanges. With a little care in selecting the 2Xs you're unlikely to have a problem using them in tension or compression for the bottom and top plates. Any hidden defects, or overloading, are much more likely to cause a failure along the grain if they're subject to shear. The criss-cross grain of the plywood makes it the better choice for carrying the shear in the webs.
--
Ned Simmons

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Holy Cow!!! Talk about over engineered! Three layers of 3/4" ply? Expensive and heavy.

And get a second truck to follow along and carry the ramps. But - no doubt they will be strong.
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