The design wind pressures for buildings of all heights in
lb/ft2 is determined according to the following equation:
p = q G Cp - qi(GCpi)
| (27.3-1) |
The current implementation assumes that building is
enclosed and sealed, so that internal pressures cancel each other. Therefore,
the wind pressure equation becomes
where
G | = | Gust-effect
factor (26.11). For rigid buildings, it is either 0.85 or it can be calculated
according to Section 26.11.4. For flexible buildings, it is calculated
according to Section 26.11.5. Methods given in both Sections are implemented.
|
Cp | = |
External pressure coefficients (Figure 27.3-1). A value of 0.8 is used for
Windward wall and an interpolated value is used for Leeward wall (Figure
27.3-1)
|
The velocity pressure, q (lb/ft2), is
calculated as follows:
| (26.10-1) |
where
Kz | = |
velocity pressure exposure coefficient (26.10.1) and it is determined based on
exposure type (user input) and height above ground (see Table 26.10-1).
Alternatively, it is allowed to use the following for
Kz:
In which zg and
α are defined in Table 26.11-1. The equations given above are
used in this implementation.
|
Kzt | = | topographic factor
(26.8.2). It can be a user input value or alternatively, it can be calculated
from
in which K1,
K2 and γ
for K3 are user input values . If
Kzt is provided directly, it is used
for all heights. Otherwise, variation in Kzt is considered according to Equation
26.8-1.
|
Kd | = | wind directionality
factor (26.6) (user input). It is determined from Table 26.6-1. For building
type structures, Kd is given as 0.85.
The value is hard-coded in the implementation (i.e., you are not allowed to
enter a value for Kd). |
Ke | = |
ground elevation factor (26.9) (user input) |
V | = | Basic wind
speed (Section 26.5) (user input) |