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WIND - Gust response factor for flexible or dynamically wind sensitive structures

WIND - Gust response factor for flexible or dynamically wind sensitive structures

WIND - Gust response factor for flexible or dynamically wind sensitive structures

(OP)
ASCE 7-05 AND 7-10 have some pretty complicated equations for Gust response factor for flexible or dynamically wind sensitive structures. The variables that are illusive are n1"building natural frequency" and ß "damping ratio, percent of critical". I can't find how to arrive at numerical values for these variables. (I'm using ASCE 7-05, but 7-10 looks very similar).

Has anybody had experience using this set of equations? And have you ever arrived at a Gust Response Factor that is greater than one?

It has been suggested that it would be conservative to assume the value of one, but I'm wondering whether or not that is actually truly a conservative approach. I'm analyzing for anchor bolts to support a vertical "knock out drum" that stands 40 foot tall and whose diameter is 6.06 feet at the base and necks down to 3.5 feet at about mid-height.

Thank you in advance for responses.

RE: WIND - Gust response factor for flexible or dynamically wind sensitive structures

ASCE 7-10: See page 521 for a discussion on damping values as percent critical for wind calculations. For natural frequency (first mode) 7-10 added section 26.9.3 which includes approximate equations to estimate n1. 7-05 does not contain this to my knowledge. You may model your structure in an appropriate analysis software to find the first mode frequency also. If your structure is simple enough, you may find other equations that are suitable as well, depending on how simple you can break it down to.

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