Rigid Diaphragm modelling in 3D

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Rigid Diaphragm modelling in 3D

Post  sagarmjadhav on Thu Mar 15, 2012 6:52 pm

Hello Sir,

I am trying to model a 12 storey RCC SMRF in Ruaumoko-3D.I want to make use the rigid diaphragm action for the slabs.According to manual I have to slave all the nodes of the storey with the master node which should be at the center of the mass.but I dont have a node modelled exactly at the center of mass.Is there any other option ?

Thanks & Regards,
Sagar

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Re: Rigid Diaphragm modelling in 3D

Post  Domenico on Thu Mar 15, 2012 7:42 pm

I do not see why the master must be at the centre of mass of the slab. It whould not be any difference from what node you use as master, unless there are numerical implications I ignore.

Try using different master nodes and see if results change?
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Re: Rigid Diaphragm modelling in 3D

Post  sagarmjadhav on Thu Mar 15, 2012 8:07 pm

Sir,
Thanks for the reply .
Okay I shall try and see if the results change.
But are you implying to select any node on that storey as a master node and just slave the remaining nodes on the storey(in my case I am slaving Ux,Uz Dof's)

Sagar

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Re: Rigid Diaphragm modelling in 3D

Post  sagarmjadhav on Wed Mar 21, 2012 5:49 am

Sir I have checked and found that no matter what node I select as master node the behavior is the same.But also found that even if I do not slave the nodes on a slab with a particular master node,this doesnt change the natural time period of the structure.I donno what may be the reason for this.

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rigid floor modelling

Post  Athol Carr on Thu Mar 22, 2012 6:49 am

If masses and rotational inertias are applied to the nodes on the floor then any node may be used as the master node, The other masses and the products of there radius of gyration squared will be summed together with the rotational inertias to give the total mass and rotational inertia of the floor. The statement of using the centre-of-=mass as the master node would be appropriate if you only applied the one mass and rotational inertia to the floor.

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Asking abot rigid diaphragma

Post  ng_92 on Mon Dec 02, 2013 2:22 am

Hello sir,
I'd ask about modelling rigid diaphragm on my model
The problem is that I don't have any node located in the center of the mass,
so I add a new node located in the center of the mass in which that node has
break a beam, so I divided that beam into two elements. I used that new node as master node.
In this model, I work with default global axes where the plan view is on the X-Z view. So I slave
other nodes with UX,UZ, and RY DOFs. The WEIGHTS parameter filled are WX,WZ, and MY.
The question is whether such way is valid, since I met no error on running the data, but I found that
the mode shapes is weird.
That's all the question from me, thanks and regards, Ng

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asking about rigid diaphragms

Post  Athol Carr on Thu Dec 26, 2013 7:48 am

Any node could be used as a master node. Slaving should not change the natural periods of free vibration, unless there is something wrong with the slaving or your rotational inertias. The slaving will eliminate many of the high frequency modes as you have reduced the total number of degrees of freedom. If you want to use the centre of mass as the master node, no problem, just create a node at that location, slave the other nodes to it ( the two horizontal degrees of freedom and the rotation about the vertical axis. As no members are directly connected to the node, fix the vertical displacement and fix the rotations about the two horizontal axes.

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Re: Rigid Diaphragm modelling in 3D

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