Correct panel calculation model to distribute lateral loads AND vertical loads correctly.

[dareB7FAD]

I am trying to model precast concrete planks supported non-compositely on steel beams at both ends.  The planks are on a ramp, thus although they are flat, they are not ‘horizontal’. I am unable to get a panel calculation model to give the correct distribution of load.

The correct distribution of vertical load onto the beams is given by using a cladding panel calculation model.

However, as the decking is not acting as a diaphragm, the lateral deflections are huge.

Under lateral load only, it is obvious that the floor deck is not acting as a diaphragm

When I specify the panel as Stiffened, I get the error message below:

I have tried the other panel calculation methods to resolve this anomaly.  The Shell calculation method for example appears to introduce the required in-plane stiffness to the slab

but the bending moment in the beam is incorrect.

Is there a panel calculation model which will give the correct vertical load distribution AND allow the in-plane stiffness of the floor to be correctly included?

[Simau]

@dareB7FAD 

As claddings act only to transfer loads, try using dummy bars to simulate diaphragm effect

And for horizontal bracing set the bars as "ignore"

To avoid instabilities you need to use fixed supports, or to add vertical bracings

[dareB7FAD]

Thanks @Simau for this.

Now, does it mean that the setting below is not implemented in Robot?  Or is there an error in the implementation?

 Because this setting gives the error message in my first post.

Surely all it needs to do is what has just been suggested by @Simau then??

On the issue of dummy elements, any guidance as to their choice?  The lateral drift is sensitive to the stiffness of these elements. Less so, the column moments

On the ‘ignore’ setting,  I presume it means loads should not be distributed to these elements but the stiffness should still be considered in the analysis?

Many thanks
p.s there shouldn't be instability errors with the boundary conditions in the original post

[Simau]

@dareB7FAD 

Now, does it mean that the setting below is not implemented in Robot? Or is there an error in the implementation?

This setting is only for panels, not for claddings

On the issue of dummy elements, any guidance as to their choice? The lateral drift is sensitive to the stiffness of these elements. Less so, the column moments

The choice of dummy elements is not so critical, their role is to transfer the horizontal forces to the columns

On the ‘ignore’ setting, I presume it means loads should not be distributed to these elements but the stiffness should still be considered in the analysis?

Correct

[dareB7FAD]

Thanks @Simau

The reason I did not accept this as solution is you saying ‘the choice of dummy elements is not so critical; their role is to transfer the horizontal forces to the columns’.

I might be missing something.

With CHS508x10, I get the lateral drift below:

With CHS 323.9x10, the drift is more than double

May be I am missing something? Your assistance is appreciated.

[Simau]

@dareB7FAD 

You are right,

I forgot to specify to set these dummy bars as "truss".

You'll see that the the choice is not critical