1 ACCEPTED SOLUTION
Accepted Solutions
The step @YT_4948 is missing is using prestress analysis. The standard linear analysis uses superposition so the sag of the guys due to gravity does not account for pretension - it is done independently. I have attached a complete example for a tower with guy wires modelled as beam elements that includes the incorrect and the correct prestress techniques for the static and the modal cases. Also an example for the buckling case is included but you would need to suppress the beams for that example. This is Creo 10 so hopefully you can upgrade to see it.
FYI this is a similar technique as that used for stringed musical instruments.
Wind and Gravity + Pretension = WRONG ANSWER
Run pretension first, and then Prestress static and you get correct results.
First/LH case below has the check box to include the results from the pretension run.
The increase and decrease in tension in the wires due to the wind load are also correct and there is no exaggerated sag due to gravity.
I believe if solid elements were used, a non-linear analysis would provide correct final results without the need for a pretension analysis step. Also, with non-linear analysis you can time-stagger the loads, accomplishing the pretension in another way.
The step @YT_4948 is missing is using prestress analysis. The standard linear analysis uses superposition so the sag of the guys due to gravity does not account for pretension - it is done independently. I have attached a complete example for a tower with guy wires modelled as beam elements that includes the incorrect and the correct prestress techniques for the static and the modal cases. Also an example for the buckling case is included but you would need to suppress the beams for that example. This is Creo 10 so hopefully you can upgrade to see it.
FYI this is a similar technique as that used for stringed musical instruments.
Wind and Gravity + Pretension = WRONG ANSWER
Run pretension first, and then Prestress static and you get correct results.
First/LH case below has the check box to include the results from the pretension run.
The increase and decrease in tension in the wires due to the wind load are also correct and there is no exaggerated sag due to gravity.
I believe if solid elements were used, a non-linear analysis would provide correct final results without the need for a pretension analysis step. Also, with non-linear analysis you can time-stagger the loads, accomplishing the pretension in another way.
Good question, as the circled box can be confusing.
Unchecked - The prestress study is run first as part of the prestress-static and both result are available under the same single study folder structure.
Checked- Means you have already run the prestress study and have a result folder so you are asking to not rerun that study but to continue onward with the 2nd part of the prestress-static study. This does a check to make sure the model is the same and will not run successfully if it detects changes. I find on occasion Creo detects a change when there was not any change. (probably related to geometry problems / approximations)
I prefer unchecked because if I change the model I need to rerun both studies anyway. It is more for saving that analysis time for rerunning the prestress study that the checked option is there. However, if you have multiple Prestress-Static scenarios that all use the same input prestress study by checking the box they could all refer to a single prestress run rather than each running them as part of their own study.
For running multiple studies as part of single study this is the option._1
This would be for a larger sequence of studies that you want to collect together for example based on a specific design variant. (Run modal, several static, buckling, etc as one study called "MyDesign1")
when results are pulled for the study, there will be multiple analysis to pick results from.
