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RE: Wind Loads-UBC vs. ASCE

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The IBC 2000 has a table with equivalent speeds (Table 1609.3.1)
Fastest Mile(mph)===> 3 sec Gust(mph)
    70                  85
    75                  90
    80                  100
    85                  105
    90                  110
    100                 120
    105                 125
    110                 130
    120                 140
    125                 145
    130                 150
    140                 160
    150                 170
Linear interpolation is permitted

-----Original Message-----
From: Padmanabhan Rajendran [mailto:rakamaka(--nospam--at)yahoo.com]
Sent: Wednesday, March 07, 2001 8:16 AM
To: seaint(--nospam--at)seaint.org
Subject: Wind Loads-UBC vs. ASCE


ASCE 7-98 wind map shows maximum "3 sec. gust wind
speed" of 150 mph, whereas according to UBC 97, the
maximum "Basic Wind Speed" is limited to 130 mph. Is
there any correlation between the two terms? If not,
is there any formula for extrapolating wind stagnation
pressure for basic wind speed in excess of 130 mph,
while using UBC 97?

2. ASCE 7-88 showed the gust factors, gz, as a
function of the height 'z' along the height of the
structure.  However, ASCE 7-98 gives a single value
for gz (Sec. 6.5.8). Quick calculation indicates that
the force due to wind would be less, if calculated
with 7-98 provisions. The reduction is not
insignificant. Were the provisions of 7-88 overly
conservative or is there something in error in 7-98?

Rajendran

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