What size channel do I need for this? I can't find the numbers I need.

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I am building a steel trailer. This will be a copy of one I built in Aluminum with 12" 2.96 X .300 C channel and 3X6X1/4 box channel. I'm waiting for my engineer friend to call back, but can anyone hazard an educated guess on what size material I need for similiar properties in steel, or tell me where to find this information? My metal sales guy seems to think that 15lb/ft 10" C will be enough, but I'm not sure about that.Thanks!
Reply:Will this help? Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:If you're not up to the math, WICH I'M DEFINITLEY NOT, you might try this chart for a good ballpark figure.  http://www.cousesteel.com/AndysPlace/SteelChart.htmlI'm assuming these are static loads.  Live loads will vary, and vehicle loads would vary even further due to the severe impact and twisting.  But remember, most stuff is overbuilt to satisfy lawyers, and engineers (who sometimes either overdo it, under do it, or completely get it wrong.  Not saying they're bad, just human).  Also you should note that carrying capacity is for a SINGLE piece of channel, a trailer has 2 channels."Any day above ground is a good day"http://www.farmersamm.com/
Reply:In tensile strength Aluminum and Steel are pretty close so you would want the same cross section.  But for stuff like trailers you are more concerned with bending so to compare structural aluminum and steel you need to look at the modulus of elasticity and moment of inertia.  Since steel has 2.9 times higher modulus you can get the same amount of deflection in beam with moment of inertia that is 1/2.9 of the aluminum.  This is Ix or Ix-x in most materials charts and the units are in^4.  Look up the moment of inertia for the aluminum and divide by 2.9, then find a steel that lower moment of inertial.