Calculator (Fatigue) 5-4w

Please follow the procedure to calculate the fatigue for each case/member/section.
(note: both input files must be derived from Microstran V8 v8.10m)

Please note, all fields are mandatory

Step 1:
Select input files

Select 'Member Forces' file(Axial, My, Mz): This is the analysis report file generated by Microstran program.
Select 'Library' file(A, Zx, Zy): Select the .asc file you wish to use.
Background:
This program was developed in accordance with Section 11 of AS 4100-1998 with the assistance of
Microstran V8.10m finite element analysis software to carry out the structural fatigue strength calculations.
Please refer to the corresponding section of the AS 4100 for more details on the fatigue assessment.

Any individual structural member or welded detail, or a group of members or welded details, can be assessed
for its fatigue strength.

The Detail category and Capacity factor of the structures have been taken into account in this program.

However in the program, the Thickness effect was not considered for plate thickness greater than 25mm (Section 11.1.7).

Operator should check that in all stress cycles, the magnitude of the design stress shall not exceed fy (yield stress)
and the stress range shall not exceed 1.5fy (Section 11.1.4).

Fatigue strength for shear stress needs to be checked manually, as Microstran program does not export shear calculation
results than can be easily utilised by this program.
Calculation Procedure:
1. for each individual member /segment / load case, read the member forces (axial force, bending moments My and Mz)
from the Microstran report file.
2. read the member section properties (cross section area A and section modulus Zx and Zy) from the Microstran library file.
3. calculate the member stresses: ie axial force / A, My / Zy, Mz / Zx.
4. combine the above stresses.
5. obtain the maximum stress along the member length.
6. calculate the Nsc corresponding to the above maximum stress.
Nsc = (frn3 X 2 X 106)/(ff3)
OR
Nsc = (f55 X 108)/ff5
7. fatigue for each individual load case = load cycles/corresponding Nsc
8. sum fatigue values from step 7. for all load cases. (Section 11.8.2)
Hints:
To generate the report file in Microstran, follow the following steps.
1. After analysing the model in Microstran, select Reports => Input/Analysis...
On the pop up window:
under Structure: do not select anything.
under Loading/Results: only select Member forces.
under Style: select Along members ----> and put in the number of segments you wish.
The larger the number the more detailed results the program will produce.
Then still under Style: only select Sort by... Node/section ----> Member results
on the next pop up window, select the load cases specifically created for Fatigue Designs
on the following pop up window, select what ever you would like to include in the report file.
Hit OK to leave the pop up window.

2. Again inside Microstran, select File => List/Edit File...
On the pop up window:
under Analysis select Report.

3. After the file comes up, save the file as whatever name and wherever you would like to use in the future.

4. The Library file is the Microstran section library file used in the analysis of the model.
It used a file extension of .asc and locates in the Lib sub folder under the Microstran folder.