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DSA Roof Mech. Unit

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I am dessigning the support of two pieces of roof top mechanincal units added to an existing California school building, (DSA job). The equipment has vibration isolators and is to be supported by a braced steel framed platform with the top of the platform about 1'-6" above the exsitng roof. The platform will be supported by tube steel stub columns welded to the exsting roof WF beams.

Per Table 16A-O of the '01 CBC, the a-p and R-p values I am using are per Item 3-C with an a-p of 2.5 and R-p of 3.0 EXCEPT that footnote #14 requires an R-p of 1.5, (resulting in very large horizontal forces). The DSA plan checker says that this force must be used for the design of the entire system, including the existing roof framing. I contend that it is only the attachments and anchorage based on footnote #5 of the same table.

Anyone out there dealt with DSA on this issue before?

Thanks in advance,

Larry Hauer, S.E.



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