Learning Forum

[Inan]

Hi there. So I have designed a suspension bridge on ANSYS however my model is encountering very large deformations which I need help fixing. My model is working however the the displacements I get from running my model is 700.18m which is very large and incorrect. The image below shows the initial model.

[1shan]

,n Since the model has lots of connections I think you should try performing a normal modal analysis to check if all the connections and constraints are applied properly. In the first picture, the pillar that is supporting the deck looks like it is rotating quite a bit. Have you used a fixed support to constraint this? If yes please check if it has been applied properly(try this without the large deflection first). nUnfortunately, ANSYS staff can't download attachments.nRegards,nIshan.n

[Inan]

Thank you for the reply!nSo I followed your recommendation and performed a modal analysis in order to identify if there is any loose connections. Initially, I had fixed supports at the end of my bridge and at the bottom of the towers. I added fixed supports at the point where the tower and the deck connects as well. The results of my modal analysis shows that there does not seem to be any loose connections so my model is modelled properly. I am new to ANSYS so I may be mistaken.nAdding those additional fixed supports at the connection between the tower and deck has managed to give me new working results for my total deformations. The maximum has now been reduced to 17.982m however this is still large from my understanding.nMy other results however still do not work. The model looks unstable and I am encountering many errors indicated at the bottom of the image.nIs there any additional suggestions you can offer to fix this problem? Also regarding your comment on ANSYS staff cannot download attachments, are staff unable to access the attachments that I provided or you just do not download any attachments? Thank you again in advance.n

[Inan]

Thank you very much for the reply!nSo I followed your suggestion and performed a modal analysis on my model to identify if there are any loose connections. I tried with both large deflections on and off and I encountered the same results in both cases. The image below shows the results of the modal analysis. There does not seem to be any loose connections in the modal analysis. To answer your question previously, initially, I had fixed supports at the end of my bridge and at the bottom of the towers. I also added fixed supports at the connection between my deck and my tower.nWhat I noticed is each time I try and solve my model, im encountering new results each time and new errors each time. The image below shows how the model is now.nThe errors at the bottom of the screen instruct me to turn on large deflections or turn off small sliding. I followed the programs suggestions and the new results I got are shown below. The maximum displacement has been reduced to 17.89m which is a good sign, however the model is still not working and 17.89m is still to large form my understanding.n I have not managed to figure out the issue yet. I would love some additional suggestions if you know how I could fix this model. I would greatly appreciate it. Also regarding your statement on ANSYS employees cannot download the attachment, does the google docs attachment I attached not work or is staff not allowed to download the attachments at all. If there is a way for me to send the model please tell me how. I would appreciate it if someone can look deeper into the model. Thank you in advance!n

[peteroznewman]

nYou will need to define an initial stress in the main cables to represent the final tension. The main cables could have an INISTATE command to create pretension in the entire length as gravity ramps on in step 1 of the analysis. The hangars could use Bolt Pretension to lift the bridge after gravity has created tension in the main cables to level out the road surface.nThe previous paragraph was copied from my advice in one of your earlier posts. nhttps://forum.ansys.com/discussion/24024/i-need-help-identifying-why-my-results-are-out-of-scale-and-help-changing-some-elements-of-my-model#latestnMaybe you should try it.n

[Inan]

nThank you for the reply. I do not know how to use the INISTATE command so I was trying to learn from the Mechanical APDL>Advance Analysis Guide>5.6 Example problems using initial state. I added a 'Inistate, Define' command under static structure in order to assign a initial stress for each of the main cables. I looked at the solution information to identify the element ID for both of the main cable (417,418) then assigned some stress values. I don't believe I did this correctly as I'm still encountering errors in my results.nI'm not sure of the mistake I made. Would love if you can provide some guidance on this issue. Thanks again in advance. n

[peteroznewman]

There are many posts about INISTATE. Read them.nhttps://www.google.com/search?q=site%3Aforum.ansys.com+inistate&rlz=1C1CHBF_enUS900US900&oq=site%3Aforum.ansys.com+inistate&aqs=chrome..69i57j69i58.926j0j7&sourceid=chrome&ie=UTF-8n