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PTB-4-2013 Eample E4.3.7 mystery variables

PTB-4-2013 Eample E4.3.7 mystery variables

PTB-4-2013 Eample E4.3.7 mystery variables

(OP)
The ASME Code Section VIII Division 1 solution method presented in Example E4.3.7 of PTB-4-2003 provides and equation for the combined force factor f2 that consists of variables FS [axial force] and MS [net section bending moment] for which I am unable to locate a specific reference to in Part UG or mandatory Appendix 1. I am particularly interested in any specific Code reference to the underlying reasoning for the numerical sign convention assigned to these loads in this example.

RE: PTB-4-2013 Eample E4.3.7 mystery variables

This is simply a strength of materials calculation. As noted in the Code f2 is the axial load per unit width of circumference. The axial load is a combination of the axial force and the bending moment. The first half of the equation is converting the force into force per unit width by dividing by the circumference. The second term is converting the bending moment into force per unit width by dividing by the section modulus/thickness.

For the numerical sign convention, the bending moment causes compression on one side of the tower and tension on the other. Therefore, a plus or minus is used to determine the maximum and minimum loadings. It is important to check the negative moment as if the junction will be in compression under pressure, the Code requires a more detailed analysis.

RE: PTB-4-2013 Eample E4.3.7 mystery variables

Be aware PTB-4 has been revised and republished in 2012 and 2013.

RE: PTB-4-2013 Eample E4.3.7 mystery variables

(OP)
Thanks for the quick responses. I have the 2013 edition, simply made a typo. Referencing back to my original query, I must assume then the Code has used PTB-4 to introduce and define the two variables Fs and Ms as well as the combined load equation, as opposed to Part UG or Appendix 1-5? In Figure E4.3.7 would the axial forces be acting downward? Would the net bending moments be acting counterclockwise? Or is the signage and directions even of relevance?

RE: PTB-4-2013 Eample E4.3.7 mystery variables

The Code absolutely will NOT use PTB-4 to do anything, particularly something as important as introduce new variables. The response provided by pdiculous963 it's also the response that I would give.

Remember that the Code is not a design guide. Good engineering practice must be followed to comply with the rules. That's what you are seeing in PTB-4.

RE: PTB-4-2013 Eample E4.3.7 mystery variables

As the Code applies to a wide range of vessels with unlimited loading scenarios, the Code does not define Fs and Ms. The designer is expected to use engineering principles to determine the unit forces f1 and f2. The author of the document arbitrarily used Fs and Ms to designate axial force and overturning moment for the equations.

The axial forces are due to weight of the tower, so yes they act downward. The bending moment is likely due to wind load, so it would act as an overturning moment.

RE: PTB-4-2013 Eample E4.3.7 mystery variables

(OP)
Thanks again. Please accept my apology for my poor choice of words. It was certainly not my intention to imply that the purpose of PTB-4 is, or should be, anything beyond its title of "Section VIII Division 1 Example Problem Manual".

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