Bracing vs. Mz on Rafter

[RRufino]

Hello,

I'm writing today because i need your help to understand what is happening in the following model: http://we.tl/jB117lnBG8

It's a industrial steel structure, traditional single bay frame, i've considered x-bracing on roof and wall modelled by tension bars. On bracing system i've square hollow sections to functioning as truss chords.

I'm verifying this model by using nodal loads on columns top and i´m realizing that bracing system is not getting all forces induced by loads. Instead, model is taking advantage of rafter's out of plane stiffness so i'm getting Mz on rafters when, by concept, i was expecting to get only axial effort induced truss functioning.

I'm i doing something wrong? How can i model the traditional behavior of an bracing system?

(i've tried to release Rz on rafter bars between chords and behavior seems ok, but i got the feeling that i shouldn't need to do that),

Thanks in advance,

RRufino

[tony.ridley]

the 100x100 strut is putting force into the portal rafter in it's minor axis. so you will get bending.  For example, a similar vertical truss..........

[RRufino]

Hi,

Thanks Tony, i had already realized that.

How to approach this on day by day work? Break rafter bars on intersection with other truss bars, release Rz on rafter and on steel create member with all rafter bars?