When to use overstrength factor

[StructEngneer]

Dear all,

After reading the ASCE7-05 I could not find when I should use over strength factor. I have project which is in high seismic zone i.e. california.Can I use redundancy factor,how different it is from over strength factor.

 

[JAE]

Do a search on this site for this topic - been discussed before - basically you use the OS factor on critical, brittle connections, etc. The various material specifications outline when to use it (i.e. AISC).

The OS factor is completely different from the redundancy factor. The redundancy factor tries to reflect the overall level of redundancy in the structure's bracing system (i.e. more, smaller braces are better than one big brace).

The OS factor attempts to oversize non-ductile portions of the structure (like bolted connections) so that the first yeild failure occurs in the more ductile elements first, avoiding sudden, brittle failures during a seismic event.

 

[StructEngneer]

Thanks JAE for the help. I read older post and it was quiet helpful.So all my X bracing connection will be designed for overstrength factor,even my column will be designed for over strength facror as R=3.25. How abt my beams? do i need to design my beams for redundancy of 1.3 as my sesimic design category is D and IBC states to use redundancy factor of 1.3 for seismic design category D,E and F .If yes can I just have redundancy of 1.3 on all my perimeter beams, bracing and columns( here column will not be included as OS will govern) and not internal beams as internal beams will will not fail in seismic.

Thanks in advance