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Yet another I-beam question.
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Posted by: Paul Cotter ®

04/23/2008, 10:30:57
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Sorry that this question is so similar to others.

In a family home I need to span 14 foot to provide support for bedrooms above. The roof will not be supported by the beam but the attic will.

The joists resting on the beam will extend 12 foot on both sides of the beam. The construction above the beam is 'normal'.
(ie 2x4 wooden studs, 2x8 joists on 16" centres, 2x6 on 16" for attic, drywall walls, two drywall ceilings etc)

I have calculated a live load of <7000lb and a dead load of < 3000lb. What size steel beams can I use? I want to maximize my headroom and would prefer to keep the depth to 6 inches. I have free access to a W6-15 beam (moment of inertia=29.1)and want to know if this will suffice in terms of deflection. I think the permitted deflection is L/360 = 0.47".

Many thanks







Modified by Paul Cotter at Wed, Apr 23, 2008, 10:34:36


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: Yet another I-beam question.
: Yet another I-beam question. -- Paul Cotter Post Reply Top of thread Forum
Posted by: randykimball ®

04/23/2008, 22:12:26
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http://www.engineersedge.com/beam_bending/beam_bending1.htm
..is a good place to begin.




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: : Yet another I-beam question.
: : Yet another I-beam question. -- randykimball Post Reply Top of thread Forum
Posted by: Paul Cotter ®

04/24/2008, 08:32:10
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Perfect - thank you. It still took me a while. The last engineering I did was at Imperial College 35 years ago. So just to help any others that google their way here.

Deflection = 5/384 * W * L^3 / ( E * I)

for a 'normal' straight I-Beam supported at its ends and uniformly loaded. Using Imperial measurements we have.

W = Load in pounds.

L = length in inches.

E (Young's modulus or modulus of elasticity) for plain old mild steel is in the range 29,000,000 to 30,000,000 pounds per square inch.

I = (second) moment of inertia for the beam. I found this table at a site called efunda.

http://128.242.106.218/math/areas/RolledSteelBeamsW.cfm

And no - the beam is inadequate. The deflection is beyond the limits acceptable under code here in Ontario.








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