Width of Rec tubing

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How much does the width of Rec tubing effect the load rating for a vertical load?in other words, If I have for example a 3"x1.5" rec tubing, would hold the same vertical load as a 3"x2" rec tubing with the same wall thickness and the 3" section in the vertical orientation? If not, what is the difference in load rating, and why?also, how do I determine the different load ratings for different sizes of materials at differing lengths?There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:The 2" tube would hold more, because the top and bottom flanges have more total material. You need to think of this as a truss. The top and bottom chords ( flanges) are either in tension or compression. The sides just keep the two separated. The more material area you have in the top and bottom at a given distance from the center line or neutral axis, the more load the member will take in bending. You can gain that material 2 ways. One you make the top and bottom wider ( within reason due to buckling if it gets too wide and unsupported) or you make it thicker. So in theory, 1.5" wide by 1/4" thick would have approximately the same area as 2" wide by 3/16" thick ( the extra distance from center of the material would change the specs somewhat) All this is assuming that the height of the tube was the same and you were ignoring the little bit of material in the side walls. This is why "heavier" beams the same approximate size can take more load. Usually the top and bottom flanges get both wider and thicker.( You can gain more bending strength for a given member in one other way, add to the distance from the center line. Taller members are more resistant to bending with thinner top and bottom chords because the distance from neutral is greater. Sort of like a lever, it's distance times strength. so 1/8" or possibly even 1/16" wall 3" tall tube may be stronger than your 2" tall tube.)As far as how you figure out what loads they can take, either you crunch the numbers like an engineer would, or you go to a reference table and look up the specs that some one else has already done most of the math on, then plug those numbers into your bending calculations. Things get more complicated depending on how a structure is supported and where loads are applied, so you really can't just pull numbers from a chart and use them unless the loads are simply supported on each end, and have simple loads applied.What exactly are you trying to figure out?Last edited by DSW; 09-17-2012 at 04:42 PM..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I was under the understanding that it was the vertical sides that were the supporting sides and the horizontal sides were more or less just there to keep the vertical sides apart. Yes if the different widths were of different wall thicknesses the thicker would hold more. but if they are the same thickness than there would be no difference in the amount of support they would give. or at least be nominal. Thus the reasoning behind channel having top and bottom flanges. the flanges are there to keep the Vertical section in line and maintain it's support capabilities. as opposed to Angle where it doesn't have that extra support for the vertical section and is more likely to deform and lose it's support capabilities.Also why rectangular tubing will support more weight with the longer side set vertically than it would with the shorter side vertically.There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:Originally Posted by ThorsHammerYes if the different widths were of different wall thicknesses the thicker would hold more. but if they are the same thickness than there would be no difference in the amount of support they would give. or at least be nominal. .
Reply:A simple experience shows previous explanations : Places a plastic or wooden ruler, between supports at both ends. Then apply a force with your finger at the center of the rule First in one position and then the other Look what happens...Mauricio
Reply:Here are a couple of calculators that may help:http://www.wa4dsy.com/robot/bendingFor example... 1000 lb center load on a 48 inch span... ridiculous I know. 3" high by 1.5" wide will deflect 0.59" with a bending stress of 34733 lbs.3" high by 2.0" wide will deflect 0.48" with a bending stress of 28269 lbs.Not a huge difference... if 20% isn't huge. Now roll that tube on it's side...1.5" high by 3" wide will deflect 1.93" with a bending stress of 56655 lbs.2.0" high by 3" wide will deflect 0.94" with a bending stress of 37012 lbs.On it's side the difference is 50%. I imagine if you bumped the 1.5x3 span it would bend.
Reply:Originally Posted by ThorsHammerYes if the different widths were of different wall thicknesses the thicker would hold more. but if they are the same thickness than there would be no difference in the amount of support they would give. or at least be nominal.
Reply:I'm obviously doing something wrong with the calculator. The only answer it's giving me is "NaN".There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:Thor FYI all those calculators are showing numbers for cantilevered beams with point loads on the end ( ie the diving board example in the link). Numbers would be different for a "normal" beam use where it's supported on both ends. If nothing else, this will give you something to compare one to another even if it will not give you exact numbers for what I assume you probably are looking for..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Forhire, in your bend calculations, can you explain why the bending stress is so much higher for the 1.5" tubes than the 2" tubes?what would the deflection be if they had the same bending stress as the 2" tubes?I'm sure this is just me not knowing the right vocabulary for given stresses, just trying to wrap my head around it.There are no problems. There are only solutions. It's your duty to determine the right one.Hobart Handler 210Airco 225 Amp MSM Stinger
Reply:Stress (s) can be equated to the load per unit area or the force (F) applied per cross-sectional area (A) perpendicular to the force as shown in the Equation belowWhere: s = F/As = stress (psi or lbs of force per in.2)F = applied force (lbs of force)A = cross-sectional area (in.2)
Reply:Originally Posted by ThorsHammerForhire, in your bend calculations, can you explain why the bending stress is so much higher for the 1.5" tubes than the 2" tubes?what would the deflection be if they had the same bending stress as the 2" tubes?I'm sure this is just me not knowing the right vocabulary for given stresses, just trying to wrap my head around it.