I think the beam will be be operating under a tensile load as it will  
be located under the ramp structure that will no doubt want to buckle  
in it's center.  Or that is to say the worst case load would be a  
point load at the center of the ramp I think.  The point of the beam  
would be to stiffen the ramp from underneath.  The ramp has two 1  
inch side bends to stiffen it.

Rest assured that any completed design will be tested at 3X of  
maximum load and I will definitely apply side loading of 500 lbs to  
verify the design is stable.  Of course all the testing will be  
conducted while I lay under the beams and look for signs of failure. **

cc   (  ** just kidding  )

> On Feb 24, 2008, at 9:30 PM, Carl Denk wrote:
>
> I assume that the "beam" is vertical and carries compression loads  
> only.
> Then it would proper nomenclature (structural engineering) would be
> column (a beam is bending loads like a floor beam). The most efficient
> crossection likely would be round tube, with square tubing a close
> second. After reading the links, without a drawing, I'm at a lost as
> what this looks like. Sounds like you are trying to make a composite
> structure, and where there is compression, buckling will be likely
> unless sufficient lateral (sideways) support is supplied, and At this
> point would suggest extreme caution.
>
> 85% of structural failures are details (connections, etc.) and not  
> main
> members like beams or columns failing. Just read yesterday that the  
> I-35
> bridge in Minneapolis failure, the very likely cause, several gusset
> plates buckled due to insufficient thickness. A piece of heavy  
> paper on
> edge on the table top, push down on the top, no double the  
> thickness (as
> one piece, not 2 layers) and push down and notice the force should  
> be 4
> times.
>
> If thinking composites, check out the home built airplane material
> suppliers.
>   http://www.wicksaircraft.com/catalog/product_cat.php/subid=1/ 
> index.html
>
> I'm very familiar with the composite materials, having built a 200  
> mph,
> 1000 mile range 3 place aircraft that we flew for 1100 hours  
> everywhere
> from Grand Canyon to New York City and Florida. There are many  
> modes of
> failure, and expertise is necessary. Could liken to the issues of  
> wiring
> a simple house vs. OP-AMP design.
>
> Composites are not very forgiving, a bump and it's junk. I'm thinking
> would be better sticking to steel or aluminum. The weight of the
> explorer sounds about correct for empty, could easily hit 5000 lbs. I
> would think. 20 gallons of fuel alone would be 120 lbs. My Bronco  
> weighs
> in over 5000 lbs. empty, and not unusual to see 5600 lbs. leaving the
> recycling yard scale.
>
> Cedric Chang wrote:
>> I have bought a pair of Harbor Freight steel ramps ( item #
>> 55424-5VGA ) that will support 1000 pounds ( say the specs ).    They
>> are 6 feet by 228.6 mm.  ( Ever since Russell showed me how, I now
>> mix measurement units )    Anyway, I want to attach a beam to the
>> bottom of each ramp that lays flat in storage and swings down in use
>> to give each ramp more ability to support mid-span weight.
>>
>> I can think of two questions.......
>> Q1 :  What would be a low cost material that is strong and
>> lightweight ?  easy to cut ?
>> Q2 :  What is the optimal shape for such a beam ?  a triangle ? some
>> kind of hyperbolic thing-a-ma-jig ?
>>
>> Update:  I wrote up a concept paper on this idea.  It is located at
>> http://oh-dog.com/ramp/concept.pdf
>> Take a look and tell me if I have I fluffed the math or structural
>> concepts.
>>
>> Thanks
>> CC
>>
>> If I make a zillion money units off this idea, proceeds will go to
>> the old - age - engineers fund.
>>
>>
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