Reinforcing existing Beam 2

[rfd23]

I have existing W8x18 beam. I need to reinforce this beam due to change in span. I did some research on welding of plates to wxisting beam. Most of the time we weld horizontal plate on bottom of bottom flange or weld a vertical plate along web, welded to undrside of top flange and top of botom flange.
Can I use two vertical plates on both sides of web and welded to web. depth of plates would be to suit welding and k of beam.
All thoughts are greatly appreciated.

 

[kslee1000]

Ok, your load is correct. I figured out the original design was governed by deflection, which was limited to L/800 for total load (ie. 2.2 klf).

Now, let's get to your trouble, assuming there is only wall above/along the proposed 16'-3" span (no column on 2nd floor in the middle). Again, design will be controlled by deflection. Let's find out required Ix.

Del = 5WL^4/384EIx = L/800
Ix = 4000W(L^3)(144 in2/ft2)/384E
= 4000(2.2)(16.25^3)(144)/384(29000)
= 488.3 in4

W8 - NG
W10x88, Ix = 534
W12x58, Ix = 533
W14x48, Ix = 485

Note, if there is a column in the middle, the situation is getting much worse.

One other thinking is to replace the top floor wall with lighter one to reduce the dead load, thus the deflection. (The existing wall needs to be removed for new beam construction, if the owner elect to go ahead for the new proposal).

Well, I think now is the time for the owner to make tough decision based on how much he is willing to spend - 2 new foundations, 2 new columns (old might work, but does not look promising), 1 new beam, 1 new wall.

Good luck. Keep us posted.

 

[BAretired]

rfd23,

I can't open your file because I don't have Excel 2007. Sorry.

BA

 

[kslee1000]

BA:

See attached PDF.

 

[ChipB]

Hmm...My 2 cents

Reinforcing the existing beam:
It's never good to mix hot work (welding) around a combustible source (wood). the beam itself will get very hot.

I have had good success with the attached sketch. You are essentially eliminating the beam supporting the first floor framing, but still supporting the load bearing wall above, and still sending the forces to your new footings.

 

[kslee1000]

Chip:

Good work. But it seems the owner does want adding any column in between the lengthened span (16'-3").

 

[BAretired]

Thanks for the pdf, kslee. The floor live loads seem a bit high to me, but I am basing my opinion on the Candadian code. For residential occupancy, we would design the Main Floor for 40 psf and the Second Floor for 30 psf. This would reduce the total live load by 349.5 plf.

I cannot comment on the snow load as I don't know the location, but 30 psf seems reasonable.

Just to clarify the arrangement of beams. From left to right will we have 8'-2", 16'-3, 8'-2"?

BA

 

[kslee1000]

BA:

I figured the W8x18 has a flexural strength to resist the moment resulted from either 3.6 klf (Fb =0.66 Fy), or 3.27 klf (Fb = 0.6 Fy) uniform load. Both are high when check deflection - using 2.2 klf, for 8.17' span, the deflection turns out to be 0.123". For 8.17' span, it represents L/797, round off to L/800. So, looks like his load is accurate.

 

[rfd23]

Thanks every body for these useful feedback.
I will keep you posted whenever we reached to any decision.

 

[BAretired]

rfd23,

We will await your further comments.

BA