# Fatigue analysis with JIS standard book

1. Jun 8, 2017

### Ridzuan

Dear guys
can somebody explain, what is actually the following terms, used in fatigue analysis:

1. Mean stress correction factor
2. Plate thickness correction factor
3. Redundancy factor

Thanks guys. you are the best...

2. Jun 8, 2017

### Staff: Mentor

Please post links to the reading you have been doing so far about those terms, and ask specific questions about what you are not understanding in that reading. Thanks.

3. Jun 8, 2017

### Ridzuan

I am doing design review for RTG crane, manufactured by MITSUI Paceco. In the technical document submission, they are providing the fatigue analysis. I am cross checking the analysis with JIS standard book, JISB8821:Calculation standards for steel structures of cranes. The equations as below:

Mean stress correction factor, Cr
= 1.3 (1-R) / (1.6-R)
= 1.0
R is stress ratio

Plate thickness correction factor, Ct
= 4√ (25 / t)
= 1.0
t is plate thickness

Redundancy factor, ƴ
= 1.0

The Japanese took the Cr, Ct and ƴ value as 1.0 and use the values as input into the GT-STRUDL program.

4. Jun 9, 2017

### kotaro yamashita

Hi! Ridzuan. I'm an engineer of a Japanese crane maker.

If the structure is exposed to reversed stress, R takes a negative value.
Reversed stress state is not favorable for the fatigue strength.
To reduce allowable stress range(Δσr), Cr is calculated by above formula.
But if R is zero or more, then it is not reversed stress state, and Cr is regarded as 1 and the reducing won't be done.

Also, the thicker plate is the worse fatigue strength.
If t is more than 25 mm, Δσr is reduced by Ct.
For 25 mm or less, Ct is regarded as 1.

γ can take a value within 0.80 to 1.25, it is considered from the influence of corruption of the structure, importance of the part, and ease of inspection.
It affects the design stress amplitude (Δσd).
Except for unusual circumstances, We often use 1 as γ.

5. Jun 9, 2017

### Ridzuan

Hi Kotaro Yamashita. Nice to know you. I think i've found the right person, japanese crane maker engineer.
Thanks for the clarification. You are explaining very well.
Can you define those 3 terms in layman term... i am a mechanical engineer but i found it is hard to understand... a simple example will do.