Difference between "Design by Rule" and "Design by Analysis"? 1

[mandarkardekar]

What is the difference between "Design by Rule" and "Design by Analysis" in Sec.VIII Div.2?

When we have to apply either of them?

 

[TGS4]

Design by Rule (Part 4) provides rules on how to design a pressure vessel to Section VIII, Division 2 using closed-form equations and other strict rules. Protection against the most common failure modes are assumed to be achieved when the rules are followed - fatigue generally excepted.

Design by Analysis (Part 5) provides rules on using numerical analysis (typically finite element analysis) to design a pressure vessel to Section VIII, Division 2. There are rules to explicitly demonstrate Protection Against five failure modes: Plastic Collapse, Local Failure, Collapse From Buckling, Cyclic Service: Ratcheting, and Cyclic Service: Fatigue.

Design By Analysis requires specialized knowledge and experience that takes years of practice to build, working with sophisticated computational/numerical models. Design By Rule can generally be performed using much simpler computer programs, but nevertheless requires knowledge and expertise.

 

[davefitz]

TGS4 is correct. The design by rule method has a more conservative approach, and might lead to an uncompetitive design in some cases, compared to the design by analysis method . One may also opt to use the design by analysis method if a complex design needs to depart from the standard design by rule method in order to incorporate a design feature that does not explicitly meet the design by rule method yet its use would be more competitive. But the design by analysis method is not to be used as a loophole; one really does need to be qualified by education, experience , licensure, and insurance bonding.

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