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http://www.engineersedge.com/beam_be...calculator.htm
HI.. new to this forum, and would appreciate a bit of advice. I am not an engineer. I hope to construct an overhead bridge crane in my garage that is capable of lifting 4000 lbs. The span (length of garage) is 23 feet. I would like to use two 23' long "S" flange I-beams positioned 72" apart (the cross bridge I have (rated for 4000 lbs) will not accommodate the wider flange "W" beams). I was planning on using two 23 foot long S10 x35 Beams supported at the ends. These beams have h=10", w = 4.9", inertia moment (Ix) = 147 in^4, and a section modulus (Wx) = 29.4 in^3. While the the two parallel I-beams are supporting the cross bridge, because the hoist running on the cross-bridge can be positioned to either side of the bridge, I assume each I-beam itself must be capable of supporting the full load? The cross-bridge itself weighs 1,000 lbs. I also assume I need sufficient strength to stay well clear of not only yield limit, but also stay in the range of elastic deformation. By my rudimentary calculation, centering all 5,000 lbs (load + bridge) at the center of one S10x35 generates a maximum deflection of 0.48" and a maximum stress of 11,480 psi. Is this OK for a mild steel beam? Am I over stating the stress by my assumptions?
A related question... I would prefer to use smaller i-beams if possible. Would an S8x23 or even an S7x20 do the job?? A S8x23 produces a deflection of 1.1" and a maximum stress of 20,800 psi. The S7x20 beam deflects 1.67" with a maximum stress of 27,860 psi.
What are appropriate safe limits for deflection and stress?
Thanks
JSM
Welcome to EE!
See:
http://www.engineersedge.com/beam_be...calculator.htm
Thanks.. that is very helpful. Question... can't seem to figure out what Fy is? There are three choices.. are these a property of the I-beam chosen?
jsm
Originally Posted by Kelly Bramble
In response to the last sentence in your original post, Deflection is more one of what "feels" right to the Engineer designing the beam. There is a somewhat common range of deflection to beam ratios that tend to be around the 1/300 to 1/400 marks. The cost difference in steel is between 1/300 and 1/400 is relatively little. Do a search on "beam span/deflection ratio" to get some ideas on range.
As to stress, it is not so much of an option or choice to my mind. For an overhead crane system, I would start with a Safe Working Load of 2-1/2 times actual load. So the 4000-lbs would become at least 10,000-lbs.
As a hoist or crane, you also need to consider shock-loads. Something like an unnoticed kink in a chain that at the 3000-lb lift point suddenly straightens out and bounces the load. The shock loading at that point may be more than 3-times the design load.
For 23' span and 4000-lbs, I would seriously suggest you contact a local Structural Engineer to do the design it for you. You may also need City or County Certification with those spans and loads and for those an Engineer signing off would be mandatory.
Thanks for the input... this is becoming more complicated than I first imagined. .... will consider your advice.
j
Fy = the beam "Youngs modulus". For A36 steel the youngs modulus is approximately 29 ksi (29,000 pounds per square inch).
29,000,000 psi... Young's modulus.
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