Modifying a Joist header

[Mechanimal]

I currently have a Joist header (2 ply 2x8 SPF) that spans 10ft that supports 9 joists (2x8) with 5 being 70in long and 4 being 84in long. No joist hangers on the joist to header connection just 3 nails from the back of the header into the joist.

The previous owners of the house had done some modifications in the basement and I'm only guessing there might have been a load bearing wall beneath the joist header so approximately 2in away from the joist header a beam was placed below it (3 ply 2x8 with a 2x4 top plate).

I would like to remove this beam as it cuts into my headroom in my basement. I have measured the deflection of the beam using wire attached to either end of the beam and measured multiple points to determine the low spot. The deflection I measured was 5/32" which using a uniform load assumption gives a loading of about 205plf which is close to my estimate of 220plf.

I don't want to remove the existing joist header so to carry the load and minimize deflection I intend to add 2 more 2x8s SPF gr. 2 and through bolt this modified joist header (now it would be 4 ply 2x8) with 1/2" bolts, qty: 2 spaced 16in apart. And after I remove the lower beam reinforce the joist connections with joist hangers (manufacturer: USP JUS28).

The only thing I'm having a hard time finding any information on is regarding side loaded beams. The joist hanger manufacturers have some derating tables but are there any design guidance regarding one side loaded flush beams or joist headers? I'm not sure if I will have a load path issue with 4ply 2x8 beam if only one face is loaded.

 

[frv]

I'll beat everyone else to it: hire a structural engineer.

This can be simple. Or not. In any case, the first thing the structural engineer is going to tell you is to fix the connection of the joist to the header.

Estimating the load based on deflection is not a good idea generally, but especially in wood. The modulus of elasticity varies widely not only between members, but even within a single member.

In any case, hire a structural engineer and they'll walk you through this.

 

[Mechanimal]

Thanks for the tip, yes I agree estimating load based on deflection measurements is not good but as I had stated I first estimated a load based on what was being supported above and by measuring it it provided the feedback that I was in the ball park. I believe this is an appropriate approach since even a structural engineer can only estimate the loading on the floor which in turn can be correct or incorrect regardless of who does it. The safest approach is to ridiculously over estimate the loading and then design over sized beams and provide impractical procedures to install the new system so that if it doesn't work you can always blame the installer...

I'm just asking if anyone knows of any reference material to determine if there are any negative effects for a beam that is side loaded on one side.

 

[ztengguy]

What if the beam was shear controlled? I think you can run a torsion analysis if the beam isnt fully braced, but that would depend where its nailed too.

Wood is very forgiving to build with. Im not sure how removing the beam would be beneficial when the joists are the same depth.

Perhaps a sketch?

 

[msquared48]

ztengguy: The floor joists are probably resting on top of the header.

Sounds like the OP wants to make this into a flush beam condition with the joists framing to the side of the header. If that is the case, in that the header will have to be removed anyway, why not replace it with a solid stick? Then the nailing problem is removed, not the torsion, but this type of framing is done all the time in residences with no torsional worries.

Mike McCann
MMC Engineering

 

[Mechanimal]

Attached is the beam / joist arrangement as built

 

[msquared48]

OK. With the overhang, there is no way to make this a flush beam condition unless the cantilevered portion can be eliminated. If it is supporting an outside wall above, then it cannot.

If you want a slightly shallower beam though, try replacing the header with a PSL or microlam.

Mike McCann
MMC Engineering

 

[Mechanimal]

Attached is what I would like to do. The beam is resting on a steel beam on one end and load bearing wall on the other end.

The stress level in the beam is low, I'm more concerned about deflection and that is why I want to increase the moment of inertia without increasing the depth of the beam (or joist header). I'm just concerned with connecting 4 2x8 together and having the beam loaded on one side. That's why I was thinking of through bolting it. I am following the NDS 2005 chapter 11 guidelines so I know the bolts can handle the loading but practically I want to verify that the load path for this beam makes sense and the through bolts are the best choice for this design.

 

[Mechanimal]

Sorry the joists that are connected to the beam are not cantilevered but supported at their ends.

 

[ztengguy]

What would you do for the connection at the steel beam end, just block up up with something?

Your getting outta DIY'r area here, spend 300$ for a couple hours of a engineers time and have it done right. There might be things your not seeing that he or she would.

 

[Mechanimal]

As I mentioned previously the beam is sitting on top of the beam....

 

[dhengr]

As long as you have considered and resolved all the important details, you should be good to go. However, you are the only one here who can see those details, and you’re not revealing them so far; and there’s little incentive for us to try to pull them out of you, just so we can waste our time giving away free engineering. Whatever you do, don’t involve a real Structural Engineer who can look at the actual conditions, make some engineering judgements about the situation, understand the code requirements, etc., “since even a structural engineer can only estimate the loading on the floor which in turn can be correct or incorrect regardless of who does it.” Many Structural Engineers who do this kind of work are not “incorrect regardless,” nonetheless, you might just as well save some money and do your own guessing, it’s your house.

 

[Mechanimal]

Thanks I managed to find what I was looking for on my own. I think you have misunderstood my question (original question: "The joist hanger manufacturers have some derating tables but are there any design guidance regarding one side loaded flush beams or joist headers?"), I was only looking for someone to point me to some reference material regarding this design because that's what I was looking for. Instead the replies I received were "...get a structural engineer..." or "..how are you going to do this...". If you think I am looking for someone on an internet forum to tell me how to design something you must be crazy!

 

[4thorns]

Thanks I managed to find what I was looking for on my own.

Care to share your findings Mechanimal? I did some searches but couldn't find anything. We use built up wood girders in residential design constantly. Short spans that have been engineered in the past. Anything over and above the norm gets engineered. Just curious to see what you found.

Doug

 

[ztengguy]

Glad you found what you need. Good luck with your project.