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Effect of Deflection on Screws

Effect of Deflection on Screws

Effect of Deflection on Screws

(OP)
For a residential project that I am working on, the ceiling has deflected 3.5" due to inadequate support underneath the bearing line (poorly sistered connection with screws on the first story of a four story wood-framed residential building). We are looking to replace the joists underneath the bearing line with a beam and then increase the ceiling height slowly by jacking back to what it was before. My supervisor stated that the ceiling deflection might have yielded the screws in a way that it may not provide full capacity when the ceiling is raised. Anyone have any similar experience with this matter? Is there anything to be cautious of when raising the ceiling height back to normal? Thank you so much for your input!

RE: Effect of Deflection on Screws


1) I've not considered this myself but it is a valid point. Given enough curvature, unintended shear flow transfer between sheathing and framing could be expected to result in inelastic fastener "plowing" through the sheathing. I would expect that quite a bit of curvature would be required to cause a problem of this sort however.

2) If there are gaps between individual sheathing panels, as there are supposed to be, then this may limit the amount of fastener damage that develops since you're only dealing with the incidental shear flow in one panel vs the entire length of the framing member.

3) If you're installing a new beam, you'll likely need to fasten that to the sheathing for various reasons. This would seem like a good opportunity to get some new/fressh fasteners installed connecting the sheathing to the framing. Perhaps you can get what you need out of those such that the loss of the existing fasteners in that area is palatable.

Some questions for you:

4) Over what span of member did this 3.5" deflection occur?

5) Will this new beam be parallel or perpendicular to the existing floor joists in the area?

HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me: http://www.eng-tips.com/viewthread.cfm?qid=456235

RE: Effect of Deflection on Screws

(OP)
Thanks for the great input, KootK.

The bearing wall is basically being supported by a 2X10 DF joist sistered with (2)-2X8s running the same direction, a total span of ~22 ft but supported in the middle by a drop beam that is perpendicular to the joists. We are looking to replace the built-up beam of joists with a new PSL beam running parallel to the existing joists - just wanted to see if it is necessary to refasten surrounding joists affected by the ceiling deflection.

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