VQ/I

[Koohbanani]

thread507-500044
When designing a uniformly distributed beam (with V=0 at mid-span and maximum at ends), I think one could use the average of the Shear obtained from the shear diagram to design the needed nails to transfer the horizontal shear. In all text books that I've looked at, they use the entire shear amount, but their example uses a cantilevered beam with a single point load at the tip. This scenario does call for using the entire V, but for simply supported beams with uniform loads, that seems to be an overkill. Any thoughts?

 

[phamENG]

Yeah, it's overkill....everywhere except the the outer quarters of the span where you'll exceed the shear capacity of your connections and cause a failure in the beam.

 

[driftLimiter]

The shear flow is proportional to the shear at each location on the beam, so you could definitely feather down the amount of shear connectors as you go in towards the center of the beam, and still satisfy the shear flow equation. If you use the average shear for all fasteners, then the fasteners near the support no longer would satisfy the shear flow equation.

 

[DaveAtkins]

If you use the average shear for all fasteners, then the fasteners near the support no longer would satisfy the shear flow equation.

This is consistent with shear flow theory, but I wonder if one could take liberties with this, as is done with the design of composite steel beams. With composite steel beams, the shear studs between support and midspan are chosen to resist the total shear, not the shear per foot at the support. If this were done with wood design, you would have to assume the nails near the support reach their maximum capacity, then deform a bit, allowing the shear to flow to the nails closer to midspan.

DaveAtkins

 

[271828]

To do that, you would need to know that the nails in the highest shear regions are ductile enough to redistribute load to the other nails. That's what's done for headed stud shear connectors in steel-concrete composite beams.

 

[phamENG]

For that, you'd have to guarantee a mode III or mode IV failure (NDS Dowel Fastener failure modes) in the nails. Not always easy to do. And really, you'd have to limit it to IV or the angle of the nail into one of the members would change, resulting a reduced shear capacity which means you'd need additional redistribution. Doesn't feel worth it.

 

[driftLimiter]

I think the best way to handle this reg' number of fasteners is to transfer all the shear at each of of the beam with a big group of fasteners, then just have nominal connection between the plates in the middle portion of the beam.