Weird results of calculating arc constructions (innormal bending moment)

[Anonymous]

Hello!

Sorry for my English, it's not very good 🙂

I'm very fresh with using Autodesk Robot program. I'm now finishing University in specialisation of civil engineering.

I have a Diploma research about an 100-years old bridge. I tried to make a flat construction in Robot which is adequate to real one and i have two big problems here.

One is unnormous huge bending moment, few times more value than a longitudinal N force, which is very weird in arc constructions (it's missing its puropse ;). I don't know how to interpretate this because it's absolutely weird to me.

And second one is the tension from bending moment is completely wrong calculated from bending moments, cause with normal calculations it should be about 15 MPa , not 0,85 🙂 (Simple division of bending moment by strenght ratio of the profile). Am I interpreting results wrong, or it's some issue?

I'm attaching rtd file with my case,

Thank You very much for further help!

Kind regards to You all,
Maciek

PS. Sorry for bad placing the loads, just use first case, it's all made in "own weight" because i program was showing me only results from 1 section of loads, i am very fresh in this and learning this program only by myself.

[Rafacascudo]

You can crrate combinations on menu Load through dialog window or table (edit tab).
When you select more than 1 load case, NTM diagram shows an envelope diagram of the choosen cases

[me1205377]

if i understand you correctly 

go to  Loads >> Manual combinations >> New >> give it a combination name >> ok >> click on any case number  from "case list" and chose a factor eg: 1.2 or 1.6  then click on the " >" symbol.   repeat the last few steps for as many load cases you wish to "combine" in a load combination then click apply 

[Artur.Kosakowski · Accepted solution]

Hi @Anonymous

But i still don't know how to combine two cases into one result, because i can see the NTM for case 1 or case 4 etc, but when i check in the cases list for ex. 1 4 , it's still results of one of them, and i can't see combined NTM. Must i sum them, or there is some way to activate them simultanousely?

Because i don't see any difference in N force depending of variant of load (2x240 kN or 1x320 kN). Moments are changing when i choose for ex. 1 4 or 1 5, but N force - not.

See this video:

See also: https://forums.autodesk.com/t5/robot-structural-analysis-forum/moving-load-in-combinations/td-p/7662...

If one or more of these posts answered your question, please click Accept as Solution on the posts that helped you so others in the community can find them easily.

[Anonymous]

Thank You all of You again very much for Your help and answers, i managed to finish my Diploma research about bridge 🙂

I hope the bug in program would be fixed soon, because i think Robot is a very handy and helpful tool with solving Engineery's problems 🙂