Pass through factored loads at columns

[tdawgye]

Hi There,

I received a question from the structural steel supplier asking to provide pass through factor loads at typical columns for a project. The building has a conventional brace frame seismic force resistant system. I have about 600kn of horizontal factored seismic force going through the column line on each side of the building (each brace frame resists 200kn of the load). How can I find the pass through factored load at each column? Would it vary from column to column depending on the number of bays away from the brace frame, or would it be spread equally across every column?

Thank you

 

[jayrod12]

Is there enough diaphragm capacity including the connection to the beams over the bracing to only account for the diaphragm depth for the braced bays? If so, the beams outside of the braced bays do not need to act as collectors and therefore there would be no pass-through forces.

However if for diaphragm capacity, or connection strength between the diaphragm and the braced line, you need more than the 3 bays, then you would have a pass-through force equal to however much load you need to move into the braced bays from the unbraced bay beams. (Hopefully that's clear enough)

 

[tdawgye]

Hi Jayrod, I think im having trouble understanding what you said. The diaphragm shear capacity is spread evenly along the entire gridline at around 10kN/m. (600kN of seismic load on this side divided by 65m, which is the width of the building))

 

[jayrod12]

If you need the entire length of diaphragm then there will be pass thru loads. They start at zero at the end of the walls and grow at a rate of 10kn/m. So by the time you get to the braced bays you should have roughly 33% of the total 600 kn as a compression/tension load left of the left brace and 17% of the 600kN right of the right brace assuming equal bay spacing.

 

[tdawgye]

Thanks for your help.