In the Harmonic Analysis there is no direct option to include Static Dynamic Combination as it is availble in other dynamic cases, so in my opinion in order to check the stresses we have to combine manually the pure dynamic case with static case. Is i am right, can anybody throw some light on this.

Regards
Ashvin Bhagat

The stress from a harmonic load has not a static character. You dont have a static stress limit.
Its a question of fatique.
The static stress ist here a middle stress and do not have influence to the Fatigue.

The stresses from a dynamic load cannot have a static character , it does not matter which type of dynamic analysis you perform.For example if you have Slug Flow or Water Hammer type of loading, a fatigue analysis is more justified than the simplistic scalar stress summation ( SUS+OCC) requirement of B31.3,although we cannot do a Harmonic analysis for those type of loadings.

When I started Dynamic analysis, I asked this question to COADE as to why the Static-Dynamic combination option is not available in CAESAR II for Harmonic Analysis,however the reply I got was " it is just not programmed that way in CAESAR II".

My suggestion to you will be ( in this matter I fully agree with Ohlinger) that you perform a Fatigue analysis on the line of SEC VIII DIV 2 Appendix 5.Make sure the data is realistic.


Anindya Bhattacharya

Perhaps saying "it is just not programmed that way in CAESAR II" was a nice way of saying, as you point out, that summing a high cycle stress amplitude with sustained stresses is inappropriate.

I believe we have a very good approach to harmonic analysis now with inclusion of fatigue curves and a definition of load cycles. I would caution against the use of the VIII-2 Appx.5 fatigue curves as these are from polished bar tests. I prefer to use a fatigue curve based on the (B31.3) cyclic reduction factor (f) or simply a maximum stress from OM-3 or API618.