Acceptable column deflection?
Acceptable column deflection?
(OP)
I am investigating the design of a replacement column. Based on current wind codes the theoretical deflection of the existing column that has been in service over 20 years would be well over 10”/100’. Wind design is driving column thicknesses. To reduce the column deflection to 6”/100’ would require substantial thickness increase and cost. When is it acceptable to exceed the guidelines of 6”/100’ deflection? Is this strictly a function of tray performance? One consulting engineer stated he had also seen 8”/100’ as a common guideline. If the existing column has been operating satisfactorily, is there any reason not to exceed the 6”/100’ guideline with customer approval? Is this typically a tray manufacturer requirment for performance guarantee?





RE: Acceptable column deflection?
One could argue that the original vessel design served well for its service life but when you replace it with a new vessel, good engineering practice (not to mention vessel regulations in most jurisdictions) would require using the most current Codes and standards. Try buying a new vessel built to the 1980 ASME Code. No fab shop that I know will agree to do this for you.
The 6"/100 ft. criteria is fairly universal. I have not seen any maximum deflection criteria from any major engineering firm or owner/user that exceeded 6"/100 ft for vertical vessels. If you have ever been on top of a 150-200 ft. vertical vessel in a stiff wind I think that you might think that 6" deflection/100 ft. is too much! One can get motion sickness or at least have a strong desire to decend fairly quickly to get off that swaying pole.
Your client may or may not want to waive their maximum deflection criteria.
KST
RE: Acceptable column deflection?
ASME STS-1-2003 "Steel Stacks" section 4.5 Lateral Deflections - "There is no practical limit placed on the maximum deflection a stack can experience"
6"/100' may be a nice rule of thumb but is not required by code.
RE: Acceptable column deflection?
RE: Acceptable column deflection?
ASME STS-1-2003 is for Steel Stacks and not Pressurised Process Columns.