If R =3 in Steel Frames

[syrupmaker]

If I take R = 3 for a steel frame, what exactly does that really mean I can and cannot do as far as member design and connection design is concerned?

Thanks in advance

 

[Taro]

See IBC Table 1617.6.2. Using R=3 means that you satisfy all applicable requirements in the AISC ASD or LRFD Specification, but you do not satisfy the additional requirements in the AISC Seismic Provisions. Use of this system is not allowed for Seismic Design Categories D, E, or F. It is commonly used for areas that do not have high seismic loads.

 

[CSEllc]

You also have larger seismic forces since "R" is in the demoninator in the seismic load equations.

I would rather design for "lower" seismic forces and detail it properly.

 

[samdamon]

Syrupmaker-

in regions of relatively low seismicity and when considering low rise construction (say three stories or less) using R=3 makes a lot of sense from both the Engineer's and Owner's perspectives. For the engineer, design and detailing requirements become simpler when using R=3. This saves design time and will also tend to simplify construction. For the Owner, the conservativeness of using R=3 (which may or may not result in slightly larger member sizes in moment frames, and thus possibly higher material costs) will probably be more than offset by savings in the cost of detailing and fabrication, IMHO.