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 Beam: W caculation for reinforcement of joists with W6 Post Reply Forum
Posted by: smegal ®

02/07/2006, 21:51:17

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I want to reinforce 2 x 10 joists with a W6 I-beam. I am trying to find the correct calculation for a 10 ft i-beam length under the joists where the uniform load is 8000#. I am restricted to W^ because of surrounding structures.

Ituitively it does not seem that the I-beam would have to support all of W. Please check the drawing which shows a ledger board support on one end and the foundation on the other end.

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 Re: Beam: W caculation for reinforcement of joists with W6 Re: Beam: W caculation for reinforcement of joists with W6 -- smegal Post Reply Top of thread Forum
 Posted by: swearingen ® 02/08/2006, 13:15:39 Author Profile eMail author Edit There are a few other pieces of information needed to answer your question definitively, but I'll work with what you've given so far.Some assumptions: 1. The 8000# is distributed evenly over the joists. 2. The joists are 10' long from ledger to foundation. 3. The ledger is continuously supported and has the same deflection characteristics as the other end.The key here is the relative stiffness of the joists versus the W6. I would calculate the stiffness of the joists and the W6 as a function of distributed load per inch of deflection. I would then ratio the total load using this stiffness comparison. For example, if you put 100 lb/ft on the W6 and you calculate a deflection of 0.32", then the stiffness is 312.5 lb/ft /in. If you're joists come in at 75 lb/ft /in, that means that approximately (312.5 / (312.5 + 75)) = 81% of the load will go to the W6. To understand how this works, think about it in the extreme: if the joists were rubber bands, the W6 would take practically all of the load. If the joists were W36 steel beams, the W6 would see next to nothing.Now, if my assumption that the ledger is not fully supported, and is a wooden beam parallel to the W6, then things get worse for the W6.Note that if properly supported, a W6x16 or larger will hold 8000# as a POINT LOAD in the center of a 10' span, which is way worse than what you have. You may be OK as is with the assumptions I've made.

 Re: Beam: W caculation for reinforcement of joists with W6 Re: Re: Beam: W caculation for reinforcement of joists with W6 -- swearingen Post Reply Top of thread Forum
Posted by: smegal ®

02/08/2006, 23:28:33

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I should have said that I am not an ME but should have been in light of my current situation (unemployed).

Max span for 2x10 is around 14ft and that is what I have. The ledger is somewhat over supported as you can see below. I found the following facts and I apoligize if you already know this but the Module of Elasticity for these joists on 16 in centers is 1.2 based on 1.E06 lb/sf. The bending value for this joist is 1036 lb/sq inch. The table also has L/360 deflection maximum at .5 in.

I hope this helps in addition to my post. I may end up using 3 2x6 fastened together unless a W6x? can be used. Thanks again.

 Re: Beam: W caculation for reinforcement of joists with W6 Re: Re: Beam: W caculation for reinforcement of joists with W6 -- smegal Post Reply Top of thread Forum