Hi,everybody!
assumption in the following(In Ceasar using B31.3 Code):

L1 = W + P + T + D (OPE)

L2 = W + P (SUS)

L3 = L1 - L2(EXP) ,and combination method:algebraic

we always use L3 to check the themal expansion stress, but take little attention to the combination method.

here,wo use the algebraic method In order to be consistent with the B31.3 Code.

but My question is that why can not we use the scalar method for L3 combination method.
is that the bending moment using the algebraic combination method is always greater than using the scalar method in mathematics ? the equation is :
(M1x*M1x + M1y*M1y + M1z*M1z)(M2x*M1x + M2y*M2y + M2z*M2z)>=
(M1x*M2x + M1y*M2Y + M1z*M2z)(M1x*M2x + M1y*M2Y + M1z*M2z)

can anyone tell me the real consideration in physics?

In the "Static Load Case Editor", read the "help text" on the Combination Methods - there are examples that should answer this question.

hi,Richard Ay
thank you for your reply!
the help manunal you point out i have even read it.
it only introduce the difference between algebraic and scalar combination method in mathematics .

what i want to know is that why the B31.3 code use the algebraic method to evaluate the thermal expansion stress in physical sense and not the scalar method.

why can not we caluate the code stress in L1 case and separately caluate the the code stress in L2,then getting the thermal expansion stress by L1 code stress substracted L2 code stress.

don't tell me that L1 code stress directly substracted L2 code stress is inconsistent with B31.3 code which i have even know.

i want to know the theory in physics.

Scalar combination (a CAESAR II term) is usually applied to stress summations (e.g. sustained plus occasional) and algebraic combinations apply to range calculations (e.g. from installed to operating).
A scalar stress combination performs operation on the stress magnitude (no sign). An algebraic stress combination includes the sign. You may ask how do you get a signed stress when the moments are combined SRSS. We combine the signed moments to calculate the resultant stress instead.

hi ,Dave Diehl
thank you for your reply!

maybe you don't not understand what i want to know.

what you say in caesar's help manunal is clear and consisten with the code.

My question has nothing to do with the caesar sofeware.

what i want to know is the judgement method for thermal expansion stress in B31.3 code is Se which can be got using the algebrical?

why doesn't the B31.3 code use SE got by L1 code stress directly substracted L2 code stress to check the thermal expansion stress?

Lanxuedream you said that you know about Code n standards but do you understand it? Because if you understand, you must be know that ASME B31.3 do not address about "operating stress" (except as non mandatory at appendix P) thats why CAESAR do not give you code stress and allowable stress in the output if you use ASME B31.3. That also one answer of your question why we cannot Calculate "directly" expansion stress (L3) by calculate code stress of L1 (W+P+T+D) and then add it with L2 (W+P) in scalar, because ASME B31.3 do not address about Operating Stress.
I hope that answer your question, thanks.

TENGKU SYAHDILAN
PfcE Indonesia

hi,LNG!
Thank you for your explanation.
You said exactly what I want to know.
I want to know exactly why the B31.3 Commission don't define the "operation stress" as the sustain stress ,and then calculate the expansion stress form the result of the "operation stress".
Doesn't it meet with Reality?
If not, why they do not check the expansion stress in this way but in which well known?
can any one help me?

The B31.1/B31.3 (and similar) Codes are setup to evaluate stress based on the recognized failure modes: primary and secondary (for details on this refer to Markl's papers).

The Primary stress state/failure mode is force based, where the load does not change with system displacement. The "Sustained" case is the load case for the evaulation of this state.

The Secondary stress state/failure mode is displacement (thermal) based, where the loading is cyclic. The "Expansion" case is the load case for the evaluation of this state.

So from a "stress point of view" you only need to evaluate these two load cases (ignoring Occasional which is also Primary). The Operating case is necessary for restraint design, limit checks, and as a computational component for the Expansion case. However, the stresses from the Operating case are neither primary or secondary, and therefore this case is not a Code Compliance case.

Read the "sticky topic" at the top of this Forum on this same subject.