Two Level Truss 1

[slickdeals]

Folks,

Please help me with the following question.

I have a truss that has a truss for a top chord and truss for a bottom chord. Diagonals span between the top chord of the bottom truss and bottom chord of the top truss.

There are two trusses that span between supports. I have steel framing between the trusses supporting slab on metal deck.

In my model, I have the deck (modeled in ETABS as membrane) extending all the way to the outside trusses.

Under dead loads, the top of this truss system will be under compression and the bottom under tension.

What effect will the floor slab now under tension have on the chord forces? The program will not take into account the effect of this on the chord forces.

What is the suggestion for this kind of a truss system where you have a floor slab and a roof slab?

Thanks

 

[MiketheEngineer]

What in the world is this??

Each truss may have compression in the top chord and tension in the bottom chord. In other words - they are acting rather indpendently.

Now when you tie the trusses together - a whole new set of things may happen. I might just design them as two separate trusses and assume that the diagonals really don't do much.

And depending on how they are attached - they very well might not do much.

 

[slickdeals]

Mike,
I totally agree with you that each truss will have a compression in the top chord and tension in the bottom chord.

However, what effect will the slab that connects into these trusses have on the compression chord force transfer.

The roof slab will definitely be in compression. The floor (at the lower truss) maybe in tension.

Should the slab be taken into helping distribute the compression chord forces from the bottom truss?

I know it is confusing......

Thanks

 

[kslee1000]

It sounds interesting, why not to provide a sketch to clarify the system you have to get more ideas.

 

[JAE]

kslee1000 is right - we have this real nifty Engineering.com post-a-sketch feature at the bottom of each reply box - put some drawings together and post them on this thread.