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IBC 2000 Wind Design

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In trying to apply wind design per IBC 2000, several questions have come up:

1. IBC Section 1605.3.1.1 states that increases in allowable stresses for
materials may not be used for allowable stress design with the load
combinations of Section 1605.3.1. A 0.75 reduction factor is allowed only
when two or more transient loads are combined. As I interpret this, when
designing a CMU wall for out of plane wind load, one can no longer allow a
1/3 increase in allowable stress - is this correct? (Section 2107.1
references ACI 530 for masonry design but deletes Section of ACI
530, thus deleting the increase in allowable stress allowed by that code.)
Is there a reason that design per IBC 2000 is more conservative that past

2. IBC Table 1609.6.2.1(2) lists two load values within each column and row
as tabulated. Where does the code define what these two values represent?
One is positive and one is negative - I believe that they are windward and
leeward wind pressures, but I don't see where the code explains what the two
values represent. 

3. In this code (and in ASCE 7), it appears that the leeward (suction)
pressure is higher than the windward pressure. Under previous UBC codes, the
windward pressures were higher than the leeward pressures. Why does wind act
differently under the newer codes?  

William C. Sherman, PE
Camp Dresser & McKee, Inc.
Denver, CO
Phone: 303-298-1311
Fax: 303-293-8236
email: shermanwc(--nospam--at)

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