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ASCE 7 Nonbuilding Structure - OCBF or STMF?

ASCE 7 Nonbuilding Structure - OCBF or STMF?

(OP)
See attached sketch. Non building structure SDC D. I want to classify this lateral system as an Ordinary Concentrically Brace Frame per ASCE 7-10 Table 15.4-1 but it is obviously not a classic OCBF configuration. Could this system be classified as an OCBF or would one be forced to try it meet the requirements of a Special Truss Moment Frame? If it can not be an OCBF, what disqualifies it?

RE: ASCE 7 Nonbuilding Structure - OCBF or STMF?

I think that a third option might be your best bet: Ordinary Moment Frame. At the proportions shown, I expect that the lion's share of your energy dissipation will come by way of flexural behavior in the trusses rather than shear behavior in the bracing.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: ASCE 7 Nonbuilding Structure - OCBF or STMF?

(OP)
Are you suggesting dropping R from 1.5 to 1 for recognition of moment frame behavior of slender braced frame; but still design and detail as typical OCBF per AISC 360? Also sketch should have shown X braces as K bracing not permitted OCBF...

RE: ASCE 7 Nonbuilding Structure - OCBF or STMF?

I apologize, I'll have to rethink this. I didn't pick up on your SDC D and was actually thinking OMF R=3.5. Clearly, that won't be allowed.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: ASCE 7 Nonbuilding Structure - OCBF or STMF?

I struggle with this but I think that I'd vote for inverted pendulum, non-building structure, not similar to buildings, R = 2.0. That assumes that your mech unit thing embodies much of the weight of the system.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: ASCE 7 Nonbuilding Structure - OCBF or STMF?

You are creating a MT-OCBF, multi-tiered ordinary concentric braced frame, AISC 341-16 has requirements using an R=3.25. Cant remember off the top of my head but I dont think you can use that style of built-up column with STMF.

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