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RE: ASCE 7-98 Wind Pressure Questions
- To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
- Subject: RE: ASCE 7-98 Wind Pressure Questions
- From: "Carter, Charlie" <carter(--nospam--at)aisc.org>
- Date: Sun, 3 Nov 2002 07:13:11 -0600
>In C6.5.5 of ASCE 7-98, it states that
design for applications
>of serviceability, design using maximum likely events, or
>applications, wind speeds associated
with the mean recurrence
>intervals other than 50 years may be used by
>design pressures by the factors in Table
C6-3. Has anyone
>used this clause to justify using smaller
(or larger) pressures?
Yes. One example I can remember is in AISC Design Guide
10 Erection Bracing of Low-Rise Structural Steel Frames. There is a discussion
of exposure period for an erected steel frame, which is comparatively much
shorter than the exposure for that same frame in the completed building.
Therefore, one can take advantage of the factors in the table you referenced to
adjust the same basic wind exposures to use a lesser wind load in design for the
erection phase. It does not, however, reduce the wind load on the final
question, in ASCE 7-98, the directionality factor
separated from the load factor and is now included in
velocity pressure. Consequently, the velocity
>is reduced by
0.85 while the new load factor is increased from
7-95) to 1.6. My question is why weren't the ASD
affected? Are the wind pressures now lower
with 7-98 than with 7-95?
I asked the same question. No answer received to date.
I think you are correct that the ASD combinations should have been affected as
well. I will inquire again and report back if I get an