If sustined stress is calculated in two conditions and load case is formulated as shown below then what shall be the correct way of defining Load case for Operating stress check (APPENDIX P)(AS SHOWN BELOW A,B,C)


1. W+P1+T1(OPE)
2. W+P1(SUS)
3. T1(EXP)
4. L1-L2(EXP)(ALGEBRIC)
5. L1-L3(SUS)(ALGEBRIC)

OPERATING STRESS CHECK LOAD CASE
*********************************
A)W+P1+T1

B) L4+L5 (SCALAR)

C) L4+L2 (SCALAR)

Dipanjan ,

I have not yet read appendix P ( except what I read at the website of Becht Engineering), but my straight question to you is why do you think B and C should be ?

Concept of linearity and superposition is the basic concept that one should understand before running the computer program.

Regards

Anindya ,

Appendix P defines operating stress as calculated stress at any condition including the effect of all sustained loadings and displacements.

So in this context which sustain condition to consider "as installed" or "operating config."

Dipanjan,

First, what do you specifically mean by " which sustained case to consider"?

You want a stress at a temp, where the effect of thermal ,dead wt. and other loadings if any will be there.

So what do you think the program will do?

It will load the sytem with a load vector which will include thermal load, dead wt and all other forms of loading that are applied in that load case.

Considering non linearity, the system stiffness matrix ( I hope you are aware of what is meant by a "stiffness matrix" )will be arrived after series of iterations.They will find out which supports are active , perhaps what you are referring as" which sustained case to consider".

Displacements will be solved as [P]*{F] where [P] is the load vector and [F] is the flexibility matrix ( inverse of stiffness matrix although the program does not invert the matrix, solves by gaussian elimination).

Displacements and stresses are related by:
[S]=[E][B][D]

Where [S] is the stress vector, [E] is the elasticity matrix, [B] is the strain- displacement matrix and [D] is the displacement vector.

In contrast if you are asking for a stress corresponding to strain range, the stress will be

[E][St]where [E]is elasticity matrix and [St] is strain vector corresponding to that strain range.

Your question is relevant only where there is a range in question and not a particular load case.

Regards