When to use SCBF over OCBF?

[amendale]

From reading the AISC 341 it seems to me that an OCBF would almost always be more economicaly feasible versus a SCBF to design due to SCBF capacity design requirements for beams, connections, and columns, as well as compactness restriction for braces. I understand the ductility advanatages of SCBFs but I was wondering if there are ever cases when a SCBF would make more sense economically, or if there are special cases where OCBFs are not suitable?

 

[SteelPE]

Height limitations and SDC come into play when selecting a LFRS too.

 

[IsaacStructural]

In addition to SteelPE's answer, SCBF also reduce the calculated base shear and foundation loads substantially.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[amendale]

Isaac - pertaining to your response about foundation load reduction, just wondering is the capacity of the SCBF braces considered as foundatin loads just as for other members?

 

[IsaacStructural]

I believe the connections need to be designed for the strength of the brace members, but the global design loads and uplift from seismic on the foundations will be much lower due to the use of R=6 instead of R=3.25.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[msquared48]

Check ASCE7 Table 15.4-1.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[IsaacStructural]

15.4-1 Is for Nonbuilding Structures, Similar to Buildings. but yes, 15.4-2 provides the requirements for which system is allowed for different Seismic Design Categories.

I don't think this completely answers the question though, there are cases when both systems can be used, and it is generally cheaper to use an OCBF system, but I don't believe that is always the case.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[amendale]

I guess maybe under very high seismic loads, where a high R factor would greately change the design, perhaps a SCBF would make more sense.

 

[IsaacStructural]

Well that is the basic point of a SCBF, it comes into play in high seismic zones. There is no reason to use SCBF detailing on a low rise building in a low seismic location.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)