Floor truss diaphragm rigidity 2

[ugandabob]

In a multi-storey building, the diaphragm action will be provided by several horizontal trusses in each floor (the floor is grating).

Can this be modelled as a rigid diaphragm? When modelling the trusses individually, horizontal deflections are below 2 x story drift, although one level is close.

Changing to flexible will have a sizable impact on the forces in the braced frames, so I do not want to overdo it. Semi-rigid modelling not an option.


Thank you.

 

[JoshPlumSE]

Of course you can model it that way. But, if you do, how are you going to determine the forces in the horizontal trusses? You MIGHT be able to reasonably distribute the horizontal forces to your lateral system. But, that's a big if....

It's like saying "Can I analyze my vertical truss as if it were a vertical wall or would it be better to analysis it like a multi span beam".

Personally, I think the only REASONABLE way to analyze a system like you describe is to directly model the trusses and see exactly how the forces flow through the system. I can't imagine a system where this wouldn't be the easiest way to model it.

I suppose that you could get into an argument with a code official who things the horizontal truss needs to be detailed like the vertical braces. But, that is a secondary argument.

 

[phamENG]

I'm with Josh. Model the members discreetly. Only way to get an accurate idea of the load distribution. After all, you don't have a diaphragm.

 

[ugandabob]

Thanks for the responses. It's what I was expecting, just thought I would throw it out there to see if someone could bail me out and save me some design time.