Secondary beams in ETABS 1

[Blackstar123]

Hi all
I am confused about secondary beams option in ETABS. As to my knowledge, secondary beams are those which rest on another beam (called primary beam). These beams have pinned supports unlike other beams which have continuous moment release.
My 1st question is what if i draw a "secondary beam (according to above definition)" like other beams as line object in ETABS. What difference does it make?? After all in actual structure who can say that this beam has pinned support or fixed.. These are all our idealization.. Isn't it??
My 2nd question is what type of beam is this which rests on column at one end and at beam at the other end.?? Should i also consider it as a secondary beam?
Thank you in advance for any help.

 

[pkjr618]

Hi Blackstar123,

You're thinking way too much about this, IMHO. Secondary beam is just a term used by the program to help us draw the structure.

Thanks and best regards.

 

[Blackstar123]

Thank you pkjr618 for the reply. I got your point but what about the support condition?? Beam drawn by these two commands have different end support condition. Could you give a practical example in which we would want the beam to have pin or fixed support?

 

[pkjr618]

Typically, we'd like to assign a fixed end condition for beams that are part of the lateral load resisting system of our structures so that they will resist moments induced by lateral load such as wind and earthquake. On the other hand, we might want to assign a pinned end condition on beams which are not part of the lateral load resisting system. We do this because having every beam and girder as ductile members would prove to be expensive rather than having these secondary beams serve only one purpose as the gravity load resisting system of the structure.

Besides, you can always change the member end condition of the secondary beam utility if you want it fixed or pinned accordingly. Thanks to dadomago75 for helping me better understand the idea in the above paragraph.