Pipe Support Stiffness

[pipesvessels1]

Hi,

Does anyone have a definitive formula for calculating the 'Stiffness' of pipe supports for use in Caesaer II's restraint definition dialogue box ('Stif'.

I have used k=EA/(L^3)in the past for bending stiffness but don't know full history of this and it doesn't ring true for Major and Minor axes of UB's, PFC's etc (W Shapes, Parallel Flanged Channel)

Any help would be appreciated,

Regards,

J O'D

 

[DSB123]

JohnOD,
The formula you quote is totally incorrect assuming the A is for the Cross Sectional Area. Stiffness of supports is dependant upon the resisting section Inertia and not the area. Therefore for UB's, PFC's etc there would be a multitude of stiffnesses to consider dependant upon the direction of the pipe loading onto the support. Normally you can get away by calculating the 'Stiffness' about the major and minor axes of the section.

 

[pipesvessels1]

Thanks DSB,

Yes but how do I calculate that stiffness taking in to account varying lengths / shapes? CII defaults to 1.0e12 lb/in for some reason which it calls rigid. I want to accurately define the stiffness.

Cheers,

JOD

 

[DSB123]

JohnOD,
It depends on the construction of the supporting structure. If it's a simple cantilever then the lateral stiffness is given by:-

k = 3EI/(L^3) where L = Length of cantilever; E = the material's Elastic Modulus and I = Sectional Modulus of Section. (I will have two values for the major and minor axes)

If the support is not a simple cantilever then the "composite" stiffness may be calculated by structural methods.

Hope this helps.

 

[pipesvessels1]

Excellent, thank you!