Doubts about seismic modeling 1

[JuanTalavera]

Hello mates , this is my first post and im not native english so I might have a couple of mistakes
My doubts are the following (by the way im using ETABS 2013 13.1.1:

1- I have recently seen in some videos online that the in the section Define>Load Cases
that when adding a Response Spectrum Type Load Case, Load Type "Acceleration" they input the Scale Factor as 1 and 0.3(for the perpendicular axis) , when i usually input 9.807 or 0.3*9.807 in the perpendicular direction. Why would they use 1 or 0.3 ? By the way I define the response spectrum From File, period vs value and the Y axis of the Response Spectrum in my txt file is in function of the the gravity constant (i.e 0.8 g, yeah high seismic zone) (See Attachment #1 "Sismo"for example)

2-When modeling eccentric or concentric braced frames, I have read that you have to assign that the frame is a braced frame for designing parameters, is this true? I mean usually I thought that with just designing the elements as "Sway Special" was enough. And also I have read that you'd have to assing a "Dual System" somewhere in eatbs when you have Braced frames in a direction and SMF in the other direction, I have no info on this. I'd like to know where can I assign these parameters.
By the way, theorical question, in a inverted V eccentric braced frame with one link in the middle is it okay to assume moment connections between the link and the beams, and pinned connections between link/beam to the diagonals and pinned in the beams-column connection? That is assuming that the plastic behaviour would normally occur in the link and the bean could develop little plastic behaviour though it isn't the target

3-And the last question is, how can I define a "haunched concrete beam" ? I mean in the nonprismatic section it allows to define this kind of beam but works like a charm for steel, when using concrete sections it does seem like working properly it calculates a longitudinal reinfor. for the beam but when you look at the section after designing it uses as material the default steel assigned A992Fy50 like it was a steel beam and im sure that this must be messing the total weight of the structure. Just to be clear, the beam designs itself using the design concrete frames you can see attatchment #2 "acarteladas". Btw the I believe I have seen somewher ein etabs website in one of their "brochures" that non prismatic is available only for hot rolled steel sections.
Thanks for your time and help

 

[MrHershey]

1. Response spectrum scale factor should be larger than 1 or 0.3, typically. For IBC/ASCE buildings, it should be g*I/R. The 1 and 0.3 is just for orthogonal combination. When using it, your scale factor should then be 1.0*g*I/R or 0.3*g*I/R. [URL unfurl="true"]https://wiki.csiamerica.com/display/etabs/Scale+factor+in+RSA[/url]

2. Sway special (or sway intermediate, or sway ordinary) should only be used with moment frames. For eccentric or braced frames, you are a non-sway system. Refer to ETABS manual on design checks made for each of these categories. Would also recommend you do a backcheck of critical elements by hand if you're not sure what ETABS is doing. Not familiar with the dual system option. I believe your understanding of the fixity is correct. Beam should be modeled as continuous (moment) connections between beam/link elements. Everything else is pinned (moment released).

3. I would tend to design dapped or haunched connections by hand myself instead of relying on ETABS. It's great for system wide behavior, big picture stuff. For connections or local conditions, I wouldn't waste time trying to figure out how to get ETABS to do it right (if it even can). Find your worst reaction for each beam type and then do it by hand or automate in a spreadsheet.