Switching from CBF to EBF

[CG513]

New building code has changed R factor for a CBF from 5 to 3.25 which is causing an increase in overall seismic base shear of more than 30%. Our thought is to change from a CBF to an EBF braced structure to utilize the R = 7 or 8 factor and reduce overall base shear.

We understand the theory of EBF, but this structure is fully designed CBF and not sure how much redesign would be required to switch to EBF - asides from tweaking bracing angles, link beam stiffeners, etc. How much is likely to change? ie. columns, beams, foundations to ensure strength greater than the link beam itself?

Any help, tips, thoughts are appreciated.

Thank you.

 

[SteelPE]

Depending on where you are located. If you are in the US you should look at the requirements of AISC 341 (if applicable). More than likely, you will have to make changes to the bracing members and beams. From what I remember the detailing of the link is very important. The connection will need to be carefully detailed as well (in accordance with AISC 341).

 

[sandman21]

Change it to a SCBF.

 

[ATSE]

Changing from Ordinary CBF to EBF; actually very different - close to starting the design over from scratch.
OCBF has hardly any ductility. EBF is inherently better, but more expensive to design, and more expensive to fabricate due to connection requirements (overstrength). For one and two story buildings, EBF may be overkill except for very high seismic areas.

 

[Gumpmaster]

I agree with sandman. If you have to change it, going from an OCBF to an SCBF would be much more straightforward than going to an EBF.