truss issue

[dan.suciu488718]

hi,
I am building a frame with 5 bays and 6 oppenings which has a truss roof system.
I have introduced the trusses using the library option, and edited them to my conformation.
I think i am doing something wrong, because when i load the truss element I get relatively large bending moments in the bars, also in nodes, ... and what i thing is a big axial force .
My question is if i need to set some releases for the bars, or if the current approach is the correct one.
The project is for my bachelors degree.
I have attached the project file bellow,loaded on 2 frames(just for test pupose)

Thank you in advance,
Dan,Suciu

[marcin.rakus]

hello,
Modeling truss usually assumes released joints at the end of truss members. There are two approaches in RSA to obtain such result: first one is of course giving releases (menu/geometru/releases) at the bars (pinned-pinned most likely) - this method allows to perform typical static analysis of the structure, and the second one is to use truss attribute on bars (menu/geometry/additional attributes/advanced bar attributes), but in this case non-linear analysis comes into consideration.
You can peek similar structures in Examples attached to RSA (eg. 2D frame-RC.rtd).

[dan.suciu488718]

hi,
thank you for the reply,
I have chosen to put releases on the truss nodes,however I am having a hard time understanding the difference between linear and non-linear analysis (maybe language difference), but does it refer to first and second order analysis, where you take into account buckling ?
thank you in advance

[Serhan_BAKIR]

Non-linear analysis for truss systems is overkill unless you have tension only braces to prevent out of plane buckling. You should define end releases for truss bars assuming that connection nodes do not transfer bending moment. At this point attention is needed in axis definitions, i.e. release for x axis refers to torsional release of the member.

If you will design your steel truss system per LRFD code, pay close attention to top chord calculations. Hand calculations must be done for each unique element (top, bottom chords web elements) in order to get a grip to what Robot is doing.

In your structure you should introduce purlins and braces aswell but before complicating the model optimize your basic truss beforehand and understand its behavior thoroughly.