Eccentricy on C-shape profile - Bending Moment

[Barau]

Hello,

I have a doubt related to the following problem. The picture attached shows a c-shape profile and its centre of mass. The column-beam is attached by fasteners at each extremity. Normal forces are applied on this element comming from the attachements. The same normal force (Fn) creates, due to the eccentricity , a bending moment ( M = Fn x y). That's my question actually. The lever arm that I have to consider is the value of y or (y - t_w/2)? I was considering the value of y, however, when I remember how the loads are distributed on fastened plates, I get confused. Due to the centre of mass not actually be on the neutral line of the web explain this? I appreciate any clarification. Thanks

 

[structSU10]

Are you refering to a torsional moment applied to the channel due to the load? For a channel, the CG does not coincide with the shear center, so the eccentricity for torsion is w.r.t. the shear center.

Is this just a simple shear connection? Is the channel oriented the way you show it? What direction is the force Fn in relation to the channel? I can't picute what you mean exactly.

 

[BAretired]

The problem is not clear. If Fn is an axial force applied at the face of the channel, there is an eccentricity of y to the c.g. of the section. Bending moment would be Fn*y if deflection is neglected. If deflection is considered, M = Fn(y + d) where d is deflection.

BA

 

[Barau]

Thanks BAretired, sorry for not being so clear exposing the problem, but you helped with your statement. Thanks again.

 

[rb1957]

not that it matters much ('cause the difference is small) i think the moment is Fn*y
assuming Fn is horizontal (in the x-direction) ... i see the reaction to Fn on the shear face of the fasteners
there are many things that affect this ...
as you've noted, does the beam deflect ?
how can the beam react torque at the ends ?
how is the beam loaded ?

form the simple sketch, i'd say the x- reaction is at y=0, and from there draw a free body ...
where's the load applied ?
this is balanced by couples, presumably at both ends.
deflections can affect reactions.