another wind load question
 

another wind load question
i am reviewing the wind loads used in the design of several buildings at our plant. the wind speed used in the design is 120mph (asce-7 02). my question is, this is the 3sec gust, so how can i relate this back to the saffir-simpson scale which is based on a 1min average. the nws says the 3sec. gust is generally 20-25% higher meaning my building is only good for 95mph sustained winds?? this brings me down to a cat. i hurricane not a cat. iii? anybody??
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table 1609.3.1 in the ibc shows the corresponding fastest mile wind speed to the 3-second gust wind speed. the v3s is in the range of 15 to 20 mph more than the vfm.
-mike
the 3 sec gust wind is the basic wind speed v
fig 6.1 in asce-7 is also at 33 ft above ground for category c exposure (open terrain, with scattered obstructions having heights generally less than 30 ft.).
velocity pressure coeffient (kz and/or kh) is used to adjust to various heights.
gust effect factor g is used to modify the applied wind pressure based on gust intensity. (doesn't apply in this case).
there is a mean hourly wind speed in asce-7 in eq 6-12
vz = b(z/33)**? x v(88/60) that converts the 3 sec gust to a sustained wind.
jmendler:
i have a table from florida 2004 statewide emergency shelter plan - table g-1. equivalent basic wind speeds.
saffir-simpson hurricane intensity scale:
hurricane category 1 =
asce-7 90mph (3-second gust) = 75mph fastest-mile = 74mph 1-minute sustained
hurricane category 2 =
asce-7 120mph (3-second gust) = 100mph fastest-mile = 96mph 1-minute sustained
hurricane category 3 =
asce-7 140mph (3-second gust) = 120mph fastest-mile = 111mph 1-minute sustained
jmendler,
look in the commentary of asce 7-02; figure c6-2. this is the durst curve, and you can use it to get a ratio of v1min to v3sec.
from that graph, v3-sec/v3600sec = 1.525
v1-min/v3600sec = 1.24
v1-min/v3600 = v1-min/v3600sec / v3-sec/v3600sec = .813
i'm not sure if you can use the ibc table 1609.3.1 to do this, it only relates vfm to v3-sec, and does not involve v 1-hour at all.
regards,
chichuck
this link explains it...
catagory 5 huricane equals to asce 07-02 195mph wind, i am not sure if the figures and equations for cp, kz, qz, etc. still applies. asce 7-02 wind map only goes up to 150mph.