help in choosing member elemets

[Mahdisadeghi84]

Dear all
Hello
I am modeling a cellphone tower and I got confused in choosing the right element member for my model...!
As I understood all of my member, except three main columns, behaves as a truss (please see pic1 and pic2) but when I modeled them as truss elements, I got instability error!
I wondered if I can change my truss members to infrmDB (or infrmFBBH) and release the end moments.
Regarding to (pic1 and pic2) what do you think as a best element member in SeiemoStruct to use (in this case)?
Notice that: pic1 is a side view and pic2 is top view of the tower.

Best,
Mehdi

pic1: http://s5.picofile.com/file/8108191618/pic1.jpg
pic2: http://s5.picofile.com/file/8108191792/pic2.jpg
my model: http://s5.picofile.com/file/8104034576/5.jpg

[seismosoft]

The best element to use for the braces is indeed the truss element. Using a frame element with end-releases is generally unstable when inelasticity appears. Further the analysis with frame elements is much slower than the analysis with truss elements. Further, the best element type for the main columns is the force-based element.

Regarding the instability error, have you tried running eigenvalue analysis? This is a good way to check if all parts of the structure are correctly connected (e.g. the trusses with the main columns).

Finally, make sure to connect all elements at the joints.

SeismoSoft Support

[seismosoft]

One more thing: for the very short members that we can see in Sections A-A and B-B use the DB element type.

SeismoSoft Support