In the US, I'd be using AISC appendix 6 which covers both the strength and stiffness required of bracing. As one would expect, the stiffness is actually the more important parameter.
Agree with the posts above. I've actually seen 2% of the flange force referenced, not 2.5%, but in many cases the difference is negligible when it comes to choosing a brace.
I've usually used 2%... can anyone point out where 2.5% comes from? You can also refer to the Eurocodes... they address the load location relative to the shear centre in a pretty definitive manner.
It is a pretty complex issue with based both on theoretical behavior and empirical research. Like KootK said what matters isn't the axial force in the brace (which would be quite low), it is the stiffness of the brace. The AS code requires 2.5% not 2% (AS4100 5.4.3.1). Being empirical and a proxy for stiffness it isn't like there is a single correct value.
EngMann - everyone has posted some good information and food for thought, but I see you're in Pennsylvania. That makes me 99% sure you're using AISC. Pay attention to what KootK posted. Appendix 6 is the place to look.
In a nutshell:
Strength of Brace is 2% of load in flange at that point unless you're looking at the brace closest to the inflection point of a beam in double curvature, and that one is 4%.
Stiffness of the brace is related to the load in flange, the unbraced length of the beam, and the same relation to the inflection point.
As KootK said, the stiffness is usually more important the strength when designing these.
Someone on here recently linked an design article on tension bracing design. The article gives detailed examples on bracing design. I'm reposing as it may be of help.
