Dear Richard Ay,
In the help doucument of CII state that: CAESAR II forms rigid elements by multiplying the wall thickness of the element by 10. The inside diameter, and the weight of the element, remain unchanged.

How to comprehend it?

Now I suppose a pipe element its parameters below:
Out side diameter=OD
Pipe wall thickness=T
Inside diameter=ID=OD-2T
Pipe element length=L

Then this element is set as rigid (with or without weight). In order to calculate its stiffness, is it right below the new parameters?

New wall thickness=10*T
New inside diameter=ID
New OD=ID+2*10*T
New rigid element length=?

My another query is how the weight of the rigid element remain unchanged?

Regard,
Llljq

Hi Llljq

I interpret Caesar quote tike this...
1) When thickness of pipe increase for same diameter pipe, rigidity of system increase means flexibility decreases.
2) When pipe model as rigid body rather that pipe it's flexibility decreases.
3) Rigid model provide similar flexibility as when model as pipe where thickness is multiplied by 10. Means 6" pipe with 7 mm thickness when model as rigid body provide similar flexibility with 6" pipe with 7*10= 70mm thickness when model as pipe.
4) When model as rigid body weight have to calculate manually and feed manually.
5) Length feed as normal length.

Regards

Habib

Dear Habib,
Thank you for your kindly answer. But you can not explain “The inside diameter, and the weight of the element, remain unchanged”!

I persist in my point of view about inside diameter (ID) is unchanged.

I think in calculate stiffness of rigid element…
New OD=ID(unchanged)+2*10*T
New pipe wall thickness =10*T (T is the wall thickness of original pipe element)
I agree with you that L (pipe length) is unchanged.

I don’t know how to remain weight unchanged? It seems that purportless.

Regard,
llljq

Dear Habib,
Thank you for your kindly answer. But you have not explain “The inside diameter, and the weight of the element, remain unchanged”!

I persist in my point of view about inside diameter (ID) is unchanged.

I think in calculate stiffness of rigid element…
New OD=ID(unchanged)+2*10*T
New pipe wall thickness =10*T (T is the wall thickness of original pipe element)
I agree with you that L (pipe length) is unchanged.

I don’t know how to remain weight unchanged? It seems that purportless.

Regard,
llljq

A Rigid ( Vale etc. ) have a weight.
This weight do input in the Rigit Weight field.
One ought to think Caesar do not additional a pipe element weight.
Is this right ?
If this not so, then it is illogical.
Because the User must allways from his Rigid Weight to subtract Caesars calculated pipe weight.

I works often in dynamic calculation with masses on nodes.
Centers of gravity (Valve as Rigid).

Then i must for the static load case consequently works with forces one nodes (-Y direction) for the weight case. At this i set the specific weight for this element zero.

Hi llljq

Concept of rigid model is to influence stiffness matrix of piping.
Piping has it's own stiffness in axial direction, bending direction & torsion direction. Stiffness depends on piping material modulus of elasticity, length of piping, moment of inertia.
Flange or valve is much less flexible than a pipe. So when a piping system is with valve, flange attached, we can consider same stiffness of pipe to valve.
valves, flanges are much more rigid.
To accommodate this difference in flexibility rigid model concept came into picture.

As I mention earlier when thickness of pipe increase flexibility decrease.

So when certain portion of piping model as rigid Caesar consider that particular portion is stiff ( as if thickness of that portion increase by 10 times)

So rigidity only enhance at rigid portion of model, nothing to do with weight of that portion of piping ( it will not be 10 times)

You have to get weight data from vendor or from caesar database.

whatever data you feed Caesar will consider that weight only for that particular portion of piping.

Regards

Habib

dear habib,
I know what you tell me the theroy about siffness,thank you.
but please answer what my query!!
what i have said about my point of view is some bases...

please tell me you email or msn!

because my englise is poor,so some more detail point of views i can not writed here. ....




now below is my test ensample:

CII UIit is :mm

pipe OD: 108mm
pipe T: 4mm
Ta: 21℃
T1: 21℃ (in this way for simple purpose and ignore expansion displacement due to thermal expansion)
P1=0

PIPE ELEMENT: FROM 10 (ANC) TO 20
DX=2000mm

FORCE @ NODE 20 FX=-5E106N

1. I SET THIS PIPE ELEMENT AS RIGID (WITH OR WITHOUT WEIGHT)

LOAD CASE: W+F1(SUS)

NOW YOU CAN observe the displacement in the load case due to fixate FX:

DISP.X=-2.796mm

2. I CANCEL THE RIGID,AND THEN SET:

NEW OD=100+2*10*4=108mm
new T=10*4=40mm

pipe element length L=2000mm

NOW YOU CAN SBSERVE THE DISPLACENET IN THE LOAD CASE DUE TO FIXATE FX:

DX=-2.796mm


THIS MEANS THAT WHAT I HAVE POINTS: IN STIFFNES CALCULATION, CII IS SETED BELOW:
ID=original pipe element (UNCHANGED)
NEW WALL THICKNESS=10 * T
NEW OD=ID+2*10*T

THAT IS SAY, THE INSIDE DIA. IS UNCHANGED,NOT OUT DIA. AND A PIPE ELEMENT WITH NEW OD AND NEW T CAN AS SAME AS OLD RIGID ELEMENT (OLD OD AND OLD T).


THAT CAN PROVE WHAT MY POINTS ABOVE.





I don’t know how to remain weight unchanged? It seems that purportless.

Regard,
llljq

habib HAVE NOT completely understand what my pURPOSE...I THINK

WHAT YOU HAVE SAID "..So rigidity only enhance at rigid portion of model, nothing to do with weight of that portion of piping ( it will not be 10 times)" AND OTHERS , I 'M completely agree...except you think OD IS UNCHANGE.

AND HOW TO understand remain weight unchanged stated in help documents?

i hope get some imformation from coade technologist (e.g. richard ay)...

..waiting for you ...

When determining different parameters for the stiffness matrix both the cross sectional area and the section's moment of inertia must be computed. This is where the 10*t comes into play - and this is the only place. So, just to use "round numbers":

OD = 10
t = 1
therefore ID = 8

So, for the "A" and "I" of a rigid element:
ID = 8
t = 1*10 = 10
ODrigid = ID + 2*t = 8 + 2*10 = 28

So for this rigid element the "A" and "I" will be computed based on an OD of 28 and an ID of 8.

When it comes to computing the weight of the rigid - CAESAR II uses your specified input value. When it comes to the projected area for wind, CAESAR II uses the specified OD of 10.

The use of the "10t" method is so that a 12" rigid is stiffer than a 6" rigid, but not as stiff as a 20" rigid, but all rigids are stiffer than the associated (normal) pipe elements.

Dear Richard Ay,

Thank you. Your answer is my solution.