Moving load combinations

[mark.martin.se]

From 14 load cases I have 4 moving load cases (crane cases)! The workshop I'm working on is 140 meter long, and the moving load step I entered is 1,0 m!

My problem are the load combinations! As I understand it, the program calculates moving loads by applying it as static load at each step, in my case 1,0 m. Doing so, I have the incredible number of 72,000 combinations, which is insane!!!

How can I avoid this and make my calculations faster?

Any suggestions would be highly appreciated!

Regards!

[tngv75955631]

Robot can model only 1 moving load case from a start point to the end point. There is an animatic function you can the point load moving. Robot don't produce many moving load case at every 1m step as the other program.

[mark.martin.se]

The 4 crane load cases I'm using aren't working simultaneously at the same time!

The software makes from each crane load case approximately 140 static cases, which multiplied per 4 gives me 560 cases,...plus dead load, snow, wind, temperature!!

In total, around 72,000 combinations!???

[Rafacascudo]

I think it´s much more than that. If the cranes are working simultaneously ,than it would be 140x140x140x140=384,160,000 possible combinations of cranes positions.
Robot will not combine 2 or more moving load cases and find the max or min values for reactions or internal forces.
You´ll have to make all the combinations combining only 1 moving load and all the static cases.
Then for this moving load case you will have ,let´s say 10 load combinations.For these 10 load combinations you can get max and min values for any reaction/internal forces.
Use the Robot tables/ forces/envelope tab for this. Then find the max or min value for the same reaction/internal force for each of the remaing 3 moving load cases.
Use excel to sum them up.
Envelope tab gives the cocomitant forces for each max or min values

[mark.martin.se]

The crane cases are not applied simultaneously! I have 1 crane load per combination!

Attached to this post is the list of half the combinations that the software generated! (couldn't upload xls file larger the 1 MB!!!)

I just don't understand why does it have to be like this?! The other 3D structural analysis program I'm using is working on the same principal and managed to generate around 600 combinations!

My load cases are:

1. Dead
2. Snow
3. Wind -0,2
4. Wind -0,3
5. Wind L->R
6. Wind R->L
7. Wind D->U
8. Wind U->D
9. Crane L
10. Crane R
11. Crane L+H
12. Crane R+H
13. Temperature 1
14. Temperature 2

1. is combined with all cases
2. is combined with all cases
3. is combined with all cases except 4.
4. is combined with all cases except 3.
5. is combined with all cases except 6., 7. and 8.
6. is combined with all cases except 5., 7. and 8.
7. is combined with all cases except 5., 6. and 8.
8. is combined with all cases except 5., 6. and 7.
9. is combined with all cases except 10., 11. and 12.
10. is combined with all cases except 9., 11. and 12.
11. is combined with all cases except 9., 10. and 12.
12. is combined with all cases except 9., 10. and 11.
13. is combined with all cases except 14.
14. is combined with all cases except 13.

Here's one of the conbinations from the attached xls file:

ULS/7182=1*1.35 + 9/132*1.50 + 6*1.50 + 4*1.50 + 14*1.50

What does it mean "9/132"??? I suppose it's the crane case n.9 on the 132nd meter!? For instance, this comb. can influence only the last part of the workshop (may be the last 3 or 4 frames)! Calculating it for the rest of the structure is pointless and time consuming! How can I avoid this?

[Rafacascudo]

Ok, sorry ,I misunderstood.

You don't need to generate the 140 individual load cases for each moving load case.
Combine the pure moving load case ,like Crane L(not crane L + ,or crane L -) with all the other static load cases.
Case ULS/58 would be = Dead*1.35+Crane L*1.50 =(1*1.35+9*1.50)
Maybe you have to set this combinations manually

Then after you run the model , you'll get (Dead*1.35+Crane L*1.50)+ and (Dead*1.35+Crane L*1.50)- which will give you max and min values for the desired reaction or internal force.
Using the tables you can select all moving load combinations , and use the envelope tab to check the max and min values and its correspondents for any bar internal force , reactons or deformation you desire.

When using the graphic window , Dead*1.35+Crane L*1.50 will give you the combiantion values on each of the 140 load positions(use the small icon beside the cases dropbox to select the load position.
(Dead*1.35+Crane L*1.50)+ or - will give you the envelope diagram for de desired internal force, reaction or deformation

Hope it helps

PS: I counted 54 combinations for each moving load case. So the total would be 216 moving load combinations

[mark.martin.se]

Thank you rammedeiros!

I'm trying not to generate 140 individual load cases from each moving load case, but unfortunately I don't know how to do it (that's the issue), 'cause weather I select automatic EN code combination or manual code combinations the software converts my crane load cases into individual cases!!!!!!!

The number of combinations I should have is 450!.....attached to the post is a *.txt file the other structural program generated, and which I think is correct (combined in there is the pure moving load case)!

[Rafacascudo]

Use the combination table on Load/combination table ,edition tab.
Create them manually using the the 4 pure moving load.You can use excel to help generate them.

[dratsiox]

You can also use the influence lines.
Solve the crane girders indepedently and find the load-position which is worst.

Try not to use full automatic combinations.
With the simplified combinations you can reduce the number of the cases that have to be checked

[mark.martin.se]

I'm really disappointed about RSA and moving load combinations! If I have to create my own static loads out of moving loads (which seems to be the only way), or create influence lines (which in 3D models no one is using for ages) than I'll rather make my static analysis separately for each element (that's definitely faster, the old "good " 2D analysis, step by step), or simply use some other structural analysis tool!

I'm just furious, 'cause I lost precious time with geometry and load cases! The documentation is so poor and pointless for any "serious" job! When the owner of the program was ROBOBAT at least I knew whom can I write my complaints or questions to, there was some kind of support! Now, as I see it, a so called Autodesk "subscriber" has to wait a week before anyone (if so) replies! I just ask myself why did Autodesk buy Robot at first place!!!

A big THANK YOU to all forum members that commented this thread!