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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