Web Panel Zone Shear Equations

[SteelPE]

I am in the process of designing an canopy with a pure beam outrigger. I am being constrained by the architect to uses specific size sections, but I am in negotiations with some of his constraints. Code is IBC 2015/AISC 14th edition

My outrigger has some rather large moments at the end... and while the sections work for strength and stiffness, I am having issues with connecting the beam to the column. I am currently trying to interpret the requirements of the AISC for web panel zone shear... specifically, paragraph J10.6(a) and J10.6(b) which give different requirements if panel zone deformation has not been considered in the "frame" analysis J10.6(a) and if panel zone deformation has been considered in the "frame" analysis J10.6(b).

Well, in this instance, I don't have a "frame", so would I assume that I have to fall under section J10.6(a)? I find this section a bit confusing.

Also, as a secondary question.... why do you get increased panel zone strength if the axial load in your column is extremely large? That is slightly counterintuitive.....unless there is some sort of "confining" moment due to the axial load (sort of how axial load in a concrete column can increase the bending strength of the column).

 

[JoshPlumSE]

why do you get increased panel zone strength if the axial load in your column is extremely large?

Take a closer look at those equations.... If you compare the equations with and without axial load, they provide equal capacity at the transition point, then LOWER capacity as the axial force increases.

Regarding the different equations depending on whether panel zone deformation has been included in the analysis: This is all about drift. The idea that panel zone deformation (which is good for the ductility of seismic frames) can lead to fairly large increases in story drift.

Personally, I NEVER use the panel zone deformation included equations unless I'm doing seismic. Because, it's relying on the plastic deformation of the panel zone..... Not something you want to have in a normal gravity load situation!

The solution is usually to use a column with a thicker web, or to use a web doubler plate (expensive) if you have no other options.

 

[SteelPE]

Take a closer look at those equations.... If you compare the equations with and without axial load, they provide equal capacity at the transition point, then LOWER capacity as the axial force increases.

Yes, you are right. I programed these equations into a spreadsheet years ago. In the years since, whenever I went in to check the capacity of a connection I have always used a Pr<<<<<<Pc, so I have never really had a chance to see what happens as we approach the limit where you change equations.

In this instance, the canopy is on the end of a 900' long building in an area where Pg=50psf. We are getting some crazy amount of snow drift (just over 10'-0") on top of the balanced snow.... this is only one of many issues with what we are dealing with.