Hi Stress Experts,

Good day to everyone

I would like to clear a general doubt when inputting bridge displacements in CAESAR II.

The general view is that platform and bridge displacements at support points to be entered as follows:

For example:
vector1 vector2
Dx = 50.8500 -50.8500
Dy = 29.4800 -29.4800
Dz = 49.2000 -49.2000
Rx = 0.0000 0.0000
Ry = 0.0000 0.0000
Rz = 0.0000 0.0000

But I found in some of the analysis, the analyst has taken the following approach neglecting Rx, Ry and Rz (refer below) for all the supports except for anchor. I couldn’t get the correct explanation for omitting Rx,Ry and Rz.

vector1 vector2
Dx = 50.8500 -50.8500
Dy = 29.4800 -29.4800
Dz = 49.2000 -49.2000

There is a change in code stress values if anchor support are used which has Rx, Ry and Rz as zero and when the other supports do not have Rx, Ry and Rz values…i.e they are free to rotate…

Also the anchor supports will have enormous moments developed since it has Rx,Ry and Rz as zero while other supports don;t have rotations as zero but have translations....

I am of the view that the approach is wrong and all supports should have Rx, Ry and Rz as zero apart from translations in x,y and z directions.

Kindly share your thoughts and experiences on the above topic

Regards,
SAM.

Is the pipe free to rotate? No? Then value is required for rotation also (zero or else)

Regards,

Dear danb,
Thank you for the quick response..

I have a doubt, for Offshore piping connecting bridge and platforms, the pipes are free to rotate or not ????....If the answer is available, then values for Rx, Ry and Rz can be decided....

As mentioned earlier, two different methodologies used by stress analysts for inputting support displacements for offshore bridge piping.. Which methodology involves the real scenario....???

Also my question was whether specifying Rx,Ry and Rz as zero will have an impact on the Analysis and end results...

I earnestly solicit your suggestions.

Regards,
SAM

Ok,

Model every support with cnode and give displacements to the cnodes. Specify all values for dispacements, i.e. also 0 for the rotations.

I hope this answers your question.