Bottom Flange Brace Uplift

[BH6]

What would be the "best"/standard detail for bracing the bottom flange of a W beam when you need to brace for uplift (steel deck on compression flange). I am seeing some options but not really any standard.

 

[jayrod12]

A plan view of the entire thing would, as usual, gain more insightful answers.

The number of braces you would need to take the bottom chord buckling load into the diaphragm to be delivered to the lateral load resisting elements is something you as the designer would need to determine.

As a note, the brace load of roughly 2% would potentially be cumulative. So determine what a reasonable load would be to transfer through these braces and up to the deck, and then determine how many beams can be braced by that amount of load. That would allow you to determine the appropriate number of braces.

Is there not someone in your office familiar enough with these ideas that you could run it past?

One thing to note, depending on the current size of the beams, and the amount of uplift you're dealing with, I at times find it's cheaper in the long run to just increase the beam size so it works unbraced for the full length. You need to realize that for both flange bracing and bottom chord bridging, you're introducing many additional connections. And the connections are generally the most expensive part of the entire thing.

And, depending on what kind of finish you are providing on the steel, e.g. galvanizing, any additional connections just start costing more and more once you account for touch-ups required on site.