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旧 2009-09-15, 08:53 PM   #1
huangyhg
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默认 seismic horizontal irregularity

seismic horizontal irregularity
in table 12.3-1 of asce 7-05 there are five sections referenced for the type 4 horizontal irregularity (out-of-plane offsets irregularity). all of the sections referenced are the same as asce 7-02 and the source document fema 450-1/2003 edition except section 16.2.2. this section requires that a 3-d mathematical model be created of the structure. does anyone know the reason that this section was added to asce 7-05? i can find no discussion of this requirement, which adds a significant amount of cost/time to the engineering of structures with this horizontal irregularity compared to previous code editions.
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well unfortunately the nature of the code is that it is written by different people. asce 7 committee takes the fema/nehrp documents and modifies them; nehrp takes atc documents and modifies them and so on and so forth. so what ends up happening is that if a member of the asce 7 committee has a strong opinion that horizontal irregularity should require a fem model of the structure, then it will be in the code. it isn't particularly fair or accurate, but it is the way it is. i believe, but haven't looked to make sure, that simple structures such as those with a flexible diaphragm are exempt from horizontal irregularity provisions. so with hope the more complex structures would already have structural modeling.
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