Shear reinforcement for wood joists 1

[charliealphabravo]

I am looking at several existing 2x12 floor joists that have been nominally notched to fit/bear on the bottom flange of a steel beam. Also one of the joists has some wane at the bearing (see pic). I would like to the reinforce the shear capacity at these locations as a best practice in anticipation of an equipment change-out. The existing connection works on paper except perhaps at the wane.

Anyway I am considering reinforcement with full height 3/4" plywood screwed to both sides of the joists within 12 or 24 inches of bearing...essentially something like web stiffeners, and would appreciate comments for any improvements on this plan.

Thanks in advance.

 

[IsaacStructural]

Your method seems appropriate to me. In the past I've typically had to reinforce mid span for moment capacity/serviceability, but the basic method should be the same. Just make sure you give yourself a proper development length. Extend some distance past the point where the shear reinforcing is needed and check that you've got enough connectors to handle the shear flow. I've reinforced with conventional lumber (another 2x12 in this case) in the past, plywood should work well.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[Michel60]

Good evening charlie,

One possible issue with fixing the plywood flitch/stiffener on to the 2x12 is possible longitudinal splitting of the joist. If you think there may be the possibility of significant changes of the ambient moisture over time then the shrinkage and swelling of the joist vs. the relative stability of the ply needs to be considered. Keeping the fasteners nearer the CL of the beam will help, but then they'll be less effective for dealing with the shear flow if you are considering extending them some distance out into the span.

regards,
Michel

 

[woodman88]

If you are having a horizontal shear problem. I would think adding additional joists would be better then putting holes (with screws or nails) in the members at the location of the highest horizontal shear.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[msquared48]

Do calculations show that there is a shear problem here?

The notch at the top of the joist does not look that big - maybe 10% of the joist depth, and the wane is not that big either. Normally shear will not control for a floor joist. Run the numbers first to see if there is a problem before you go to the trouble of reinforcing the joists.

Should the numbers show that there is a problem, then the plywood, or a sistered joist would work fine.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

Just by looking at the photograph, I would say that the shear strength of the joist is unchanged by the presence of the notch.

BA

 

[nac521]

I agree with Msquared and BA, seems unnecessary.

 

[RFreund]

The notch is at the top and looks to be within a distance that is less than the depth of the member so I would agree, it may not be required.

EIT

http://www.HowToEngineer.com