Type 4 Horizontal Irregularity

[josta]

There is a short thread on this over at the ASCE forum but no responses so I'll try it here....

With a Type 4 Horizontal Irregularity, is 3D modeling really required (ASCE 7-05, 12.7.3, second paragraph)?

I have a garage with a room above; the front wall of the upstairs room is inset about 4' from the front wall of the garage below. Normally I'd use a floor/deck diaphragm to transfer the horizontal loads to the front wall of the garage, and a beam under the upstairs wall for the uplift connections of the upstairs wall.

12.3.3.4 outlines how we need to increase the forces due to irregularities, but it makes no mention of the 3D modeling.

Table 12.6-1 (7th box down) states that the Equivalent Lateral Force Analysis is permitted for use on certain irregular structures, including Type 4. It doesn't say 3D modeling is required.

Further, Table 12.3-1 for Type 4 irregularities references the above as well as 12.7.3, and the latter is where it says 3D modeling is required.

It seems contradictory....the RCE plan checker says 3D modeling is not required, but the lateral analysis program I'm using gives me a warning message saying that it IS required. HELP!

 

[josta]

Anybody?

 

[josta]

Nobody knows?

 

[OldPaperMaker]

josta,
I don't think that there is any way to do a 3-D ananlyis of light frame construction (your garage). In addition,the structural resistance in the z direction would be very difficult to quantify.
If the building official sez it is not required I suggest that you just take his suggestion and run with it.

 

[StructuralCA]

Josta,
If it is just two stories, you can use Section 12.14 (Simplified Alternative Structural Design.) Then you can use flexible diaphragm using 12.14.5. Absent rigid diaphragm and given that there are no moment connections between floors and walls in wood buildings; 3D analysis is basically the same as 2D analysis in two different directions.

BTW, which software are you using?

 

[josta]

StructuralCA, thank you for your response. I use "Lat Pro" engineering software; it uses the "equivalent lateral force procedure".