A lateral resisting system with knee brace?
A lateral resisting system with knee brace?
(OP)
we are designing a government office building in an area of low seismic and wind loads. so we picked a lateral resisting system with shear only connection between beam and column, and a diagonal brace between them as shown in attached pdf.
I have some questions:
1. is this a right computer model for the framing (in pdf file)?
should I use fixed connection for column to footing?
Does H/400 drift limit for wind sounds right?
2. The wind load will control the design but I still have to add those seismic information in structural notes. so
What is seismic force resisting system per ASCE 7 Table 12-2-1 for such framing?
Building frame system:
steel eccentrically braced frame, non-moment resisting,
connections at columns away from links,
or Ordinary steel concentrically braced frame,
or Steel System not specifically detailed for seismic resistance...?
Thanks.
I have some questions:
1. is this a right computer model for the framing (in pdf file)?
should I use fixed connection for column to footing?
Does H/400 drift limit for wind sounds right?
2. The wind load will control the design but I still have to add those seismic information in structural notes. so
What is seismic force resisting system per ASCE 7 Table 12-2-1 for such framing?
Building frame system:
steel eccentrically braced frame, non-moment resisting,
connections at columns away from links,
or Ordinary steel concentrically braced frame,
or Steel System not specifically detailed for seismic resistance...?
Thanks.






RE: A lateral resisting system with knee brace?
Keep in mind that your connections should still be designed to Omega*Eh. Since Omega is the same as your R value, that essentially means you are designing your connections as if your structure remains perfectly elastic during the seismic event.
Therefore, seismic will actually control your connection design whenever your wind loads are less than 3 times your calculated seismic force.... A lot of people miss that.
Josh
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
They are considered OMF. Design guidelines are also given
RE: A lateral resisting system with knee brace?
I can't really expand on the answers given above for most of the questions expect to say H/400 sounds a little conservative.
I have done a few frames like this in the past, low seismic region however. However I would not use a HSS or steel angle, reasons, HSS walls are limited in bending and steel angle in compression are not effective.
Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
I have done the moment connection with the beam sitting on top of the column.
I use the procedure in AISC Design guide 16 for flush moment-end plate connections, just change the forces around to meet my conditions. But don't be surprised if you get thick plates and/or large bolts during your design.
I typically only do it when the lateral loads are small otherwise the numbers get out of end
RE: A lateral resisting system with knee brace?
"Where does it say you have to use omega for the connections when using R=3?"
That's just the basic theory behind seismic design. Though reviewing the AISC Seismic Design handbook, I found the quote (in Part 2: systems utilizing R = 3):
"Members and connections of braced-frame systems with R=3 need only comply with the Specification. The Seismic Provisions are not required for use in the design of braced-frame systems when R is take as equal to 3."
Therefore, it appears that the connection design does not necessarily need to be design for that overstrength force. I'm not sure that I would personally be comfortable with that if it were my project. But, I'm not sure there is a code provision which explicitly prohibits it.
RE: A lateral resisting system with knee brace?
Do you also apply omega on the connections for R=3 in SDC A and B? I have never heard of this before.
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
DHKpeWI
RE: A lateral resisting system with knee brace?
RE: A lateral resisting system with knee brace?
Check drift under strength level seismic loads using amplication factor Cd and compare to ASCE 7-05,
Table 12.12-1.