Lateral restraints for trusses

[StoyanAndreev]

In Eurocode 3 (EN 1993) is there a procedure to calculate the reactions in lateral restraints of compressive members (columns, truss chords) or compressive flange of beams? I am currently designing a single-story industrial building and I want to use the purlins as lateral restraints of the compressive chord of the roof truss.

 

[charliealphabravo]

I'm not familiar with Eurocode 3 but at the theory level I was taught that the reaction to laterally restrain a compression member was 2% of the force in the compression member. I think this was meant to be an alternative to doing a P-Delta analysis. I have since heard other rules of thumb and it is not hard to imagine scenarios where the restraining force could be higher or lower. I'd be interested to hear what others have to say.

 

[StoyanAndreev]

I found the procedure in Eurocode 3 - it is based on the initial arc imperfection of the chord in lateral direction. The uniform lateral force is qd=8*(e0+d)*Ned/(L^2) where Ned is the compression force, L is the length of the chorc, e0 is the arc imperfection and d is the deformation due to horizontal loading in elastic analysis. If there are X-braces to bare the wind, then d=0, e0 is about L/500, so qd is much smaller than the 2% rule. In older bulgarian design code the equation gave 1% of Ned/X where X is the buckling ratio.