Knee brace for pony truss with underhung floorbeams.

[PPMcGG]

Does anyone know a good book or website for help on designing knee braces, or their effect on top chord stability? I have Stability Design Criteria by Galambos but it only mentions knee braces. Another question is does anyone know where I could find a way to calculate the top chord stability (or spring constant) based on just welding the underhung floor beams to the bottom chord?
Any help would be appreciated.

Pat McGregor
EIT

 

[bridgebuster]

See if this helps

http://www.eng-tips.com/viewthread.cfm?qid=208780&page=1

 

[bridgebuster]

Also, try

http://books.google.com

and search for "pony truss"

 

[PPMcGG]

Thank you for the replies, I had already looked through AASHTO so I know what need to be checked. I guess my real question is about knee braces and how they actually brace the system and interact with the normal pony truss spring constant (stiffness) equation. Do you know anything about that?

 

[bridgebuster]

The spring constant equation doesn't take into account knee bracing; therefore: "h" should be as shown.

Looking through some old books, there's no discussion of the bracing, although it's shown on some drawings. I would say ignore it; you'll be on the conservative side.

 

[PPMcGG]

So what is the actual point of the knee braces for the underhung floor beams? They attach the floor beams to the verticals, but what positive effect does that actually have on the system?

 

[bridgebuster]

My guess is that they used the knee bracing to brace the upper chord.