AS1170.4 Earthquake Combination Cases

[Anonymous]

Hi Guys,

I recently posted a question in regards to completing earthquake design using equivalent staitc method in Robot. I was able to succesffully complete an analysis but dont believe that the combination and load cases created are entirely correct. I believe the load cases and combination cases are to be as follows:

Earthquake Load Case =

1. + EQx (Positive X direction applied at +0.1b)
2. + EQx (Positive X direction applied at -0.1b)
3. – EQx (Negative X direction applied at +0.1b)
4. – EQx (Negative X direction applied at -0.1b)
5. + EQy (Positive Y direction applied at +0.1b)
6. + EQy (Positive Y direction applied at -0.1b)
7. – EQy (Negative Y direction applied at +0.1b)
8. – EQy (negative Y direction applied at -0.1b)

Where b is the plan dimension of the structure at right angles to the direction of the action.

Earthquake Load Combinations =

1. (1) + 0.3(5)

2. (1) + 0.3(6)

3. (1) + 0.3(7)

4. (1) + 0.3(8)

5. (2) + 0.3(5)

6. (2) + 0.3(6)

7. (2) + 0.3(7)

8. (2) + 0.3(8)

9. (3) + 0.3(5)

10. (3) + 0.3(6)

11. (3) + 0.3(7)

12. (3) + 0.3(8)

13. (4) + 0.3(5)

14. (4) + 0.3(6)

15. (4) + 0.3(7)

16. (4) + 0.3(8)

17. (5) + 0.3(1)

18. (5) + 0.3(2)

19. (5) + 0.3(3)

20. (5) + 0.3(4)

21. (6) + 0.3(1)

22. (6) + 0.3(2)

23. (6) + 0.3(3)

24.(6) + 0.3(4)

25. (7) + 0.3(1)

26. (7) + 0.3(2)

27. (7) + 0.3(3)

28. (7) + 0.3(4)

29. (8) + 0.3(1)

30. (8) + 0.3(2)

31. (8) + 0.3(3)

32. (8) + 0.3(4)

Where (_) = load case

Has anyone else come across this??

Cheers.

[Artur.Kosakowski · Accepted solution]

You can define both positive and negative eccentricities for seismic cases and then use Newmark combinations in the same way I indicated in http://forums.autodesk.com/t5/robot-structural-analysis/earthquake-design-using-as1170-4-australia/m... .Then you can delete the combinations you consider as "excessive". 

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[Anonymous]

Thanks Arthur..... I think these combination cases should be looked at again and updated in the next version!!

[Anonymous]

Hi Arthur,

I also believe the issue Petar raised regarding the earthquake combinations under AS1170.4 is correct.

The number of combinations that needs to be considered is much more than what Robot is currently analysing under Equivalent Static Method.

Similar to Modal Analysis, the Equivalent Static Analysis should allow seismic case groups to include "X+Y-" "X+Y+" "X-Y-" and "X-Y+".

Please confirm that this issue will be rectified in the next robot revision.

Thanks,

Alvin

[Artur.Kosakowski]

Hi Alvin,

I'm not in the position to tell what was and what wasn't introduced in the new version before it has been released.

[Anonymous]

Hi Arthur,

Thanks for your reply. Can you please raise this issue to the Robot software development team?

Thanks

Alvin

[Artur.Kosakowski]

I have already notified them. 

[Anonymous]

Hi,

Did we get a solution for the raised issue related to EQ combinations? I have the same questions.

Regards,

Rajeev