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Definitions of seismic force resisting systems per Table 12.2-1 ASCE7-10

Definitions of seismic force resisting systems per Table 12.2-1 ASCE7-10

Definitions of seismic force resisting systems per Table 12.2-1 ASCE7-10

(OP)
I am having difficulty interpreting which design coefficient applies in the following case: This is a 2 story wood framed structure in a FEMA coastal zone, Design category E. The lower story, which is unoccupied due to the flood elevation, cannot have walls other than breakaway walls in the direction of the wave action. I have therefore used wood braced frames using steel tension rods as braces. The wood columns of the frames cantilever vertically to resist lateral forces on the upper story. In the perpendicular direction shear walls are allowed and used to resist shear on the lower story and for both directions on the upper story. My theory is that A-13, "Bearing walls with wood structural panels" is appropriate for all but the one direction on the lower floor, and A-15 "Bearing walls using flat strap bracing" is the closest definition for the remaining condition. The only other definition that is close is G-7, "Timber frame", which is not permitted in design category E. Although not technically a "flat strap bracing" system the concentric rod bracing is at least as efficient and robust. I would therefore use the more restrictive R coefficient of 4 for the A-15 description. The plan examiner disagrees, saying table 12.2-1 does not allow the use of steel rods so must be designed with moment frames. So the question is, "is this a timber frame or a bearing wall with steel bracing?" I believe the structure as a whole will react more like a bearing wall system than a timber frame system and would like to save the expense of using moment frames. I welcome input.

RE: Definitions of seismic force resisting systems per Table 12.2-1 ASCE7-10

Your post is slightly hard to follow. Flat strap bracing is for light-framed cold formed steel not wood framed walls. Rods would also not qualify as flat strap bracing if you were to use them in a cold formed wall. If you are using tie rods you can use them in a Ordinary Concentric braced frame (OCBF) configuration and utilize them as tension only bracing. SO the plan checking is correct and incorrect as tie rod could be used in an OCBF.

RE: Definitions of seismic force resisting systems per Table 12.2-1 ASCE7-10

(OP)
Thank you. I think by OCBF you mean ordinary steel braced frame which would not apply to a heavy timber frame using steel rods for tension bracing, I believe. If that is the case I can use steel headers and columns, of course, but I am trying to find a definition that would apply to the braced timber frame solution I described. I guess the answer is there is none.

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