Redundancy factor for SDC D Non-building structure

[FRACH23]

I was caught up in a doubt if my interpretation of ASCE7-10 redundancy factor is correct. I was designing a piperack. As being non-building structure, i took redundancy factor of 1.0 as per Code's Section 12.3.4.1 item 4. However, Section 12.3.4.2 says that if it's at SDC D~F (mine is at SDC D), rho should be 1.30. I hope I could get confidence from your opinion. Thanks a lot.

 

[insajn]

Far as I know, any non-structural object that is permanently fixed on a structural element should be designed as a structural element in many of the limitations in the code ( generally speaking ).

My advice is just take it as "1.3" ( it's the worst case ). And I think that piperack is a structural element. Cladding of a building is considered as a non structural element, but piperack isn't.

 

[wannabeSE]

FEMA P-751 2009 NEHRP Recommended Seismic Provisions: Design Examples includes a pipe rack in part 13.2. Here is an excerpt

13.2.3.6 Redundancy factor. Some nonbuilding structures are designed with parameters from Standard Table 12.2-1 or 15.4-1 if they are termed “nonbuilding structures similar to buildings”. For such structures (assigned to Seismic Design Category D, E, or F) the redundancy factor applies. Pipe racks, being fairly simple moment frames or braced frames, are in the category similar to buildings. Because this structure is assigned to Seismic Design Category D, Standard Section 12.3.4.2 applies.

Considering the transverse direction, the seismic force-resisting system is an ordinary moment resisting frame with only two columns in a single frame. The frames repeat in an identical pattern. Loss of moment resistance at the beam-to-column connections at both ends results in a loss of more than 33 percent in story strength. Therefore, Standard Section 12.3.4.2, Condition (a) is not met. The moment frame as described above consists only of a single bay. Therefore, Standard Section 12.3.4.2, Condition b is not met. The value of ρ in the transverse direction is therefore 1.3.

 

[FRACH23]

thanks guys, especially with wannabeSE's FEMA P-751. I now realized that judgement of structure, being similar to building or not, shouldn't be taken literally, but rather as to how the frame behaves.