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 Subject: Wide Flange Beam strength Category: Science > Physics Asked by: mrstu2570-ga List Price: \$2.00 Posted: 21 Feb 2005 17:17 PST Expires: 23 Mar 2005 17:17 PST Question ID: 478387
 ```I am constructing a slow pull machine to test various climbing gear and i need to know if a wide flange I beam size:12, weight perfoot:14, depth of section:11.91, flange width:3.97, flange thickness:.225, web thickness:.200 will be able to width stand an electrical winch mounted on one end and pulling a fixed point on the other end of a 15ft section and max loads reaching 700lbs (30kN)``` Request for Question Clarification by redhoss-ga on 21 Feb 2005 19:16 PST ```How is the beam oriented and what is the distance from the outermost part of the beam to the centerline of the pulling force. The orientation of the beam determines whether you are bending it in the weak or strong axis.``` Clarification of Question by mrstu2570-ga on 21 Feb 2005 19:25 PST ```The beam will be oriented on its side so the winch and fixed point will be bolted through the top of the flange on either end of the 15ft section. So the winch will be at point 0 and the winch cable will run down to an attachment point at 15ft. Again the max load will be 30kN. Will the beam bend?```
 ```Hello mrstu2570, you ask if the beam will bend and the answer is absolutely yes. When you apply any load to any steel shape it bends some amount. This is called deflection. If a beam is loaded above the yield strength of the steel, it not only deflects (bends), but will permanently remain bent. However, if the load is small enough that the stress is less than the yield strength of the steel, the beam will return to the original shape. I think I understand your description of how the winch will be mounted and the anchor point attached. You are loading the beam on its strong axis. The properties that determine the "strength" of a beam are its section modulus and moment of inertia. For your beam (12WF x14#) those properties are: Sx = 14.8 in.^3 Ix = 88 in.^4 Sy = 1.18 in.^3 Iy = 2.34 in.^4 Comparing Sx and Sy you can see why I wanted to know how you were mounting the winch and anchor. The beam is more than 12 times as strong when loaded about the x axis (as you are doing). We don't know the exact distance from the flange of the beam to the centerline of the winch cable, but surely it won't be more than 12 inches. The bending moment in the beam would be: M = 700# x 18 in. = 12,600 in.# The 18 in. number comes from adding the 12 inches to the distance from the flange of the beam to the neutral axis (centerline) of the beam. The stress in the steel is then found: S = 12,600 in.# / 14.8 in.^3 = 851 psi The yield strength of structural steel is normally 36,000 psi. Comparing 851 to 36,000 you can see that there is no danger in doing any damage to your beam. The beam will deflect some when you are testing, but you will probably not be able to notice the movement. Here is my best guess at how much it will actually deflect. d = (12,600 x 15 x 12)/(48 x 29,000,000 x 88) = .0000185 inch I think the beam you are using will work just fine and hope that this explanation hasn't confused you too much. Let me know if you have any questions. Good luck with your testing, Redhoss```
 mrstu2570-ga rated this answer: `Fast response with a great answer and explanation!!`