Civil Engineering Reference
In-Depth Information
Figure 6.4
Mean internal pressure coefficient
as a function of windward/leeward open area.
The effect of building wall and roof flexibility is such as to increase the response time
according to Equation (6.18) (Vickery, 1986):
(6.18)
For 'normal' low-rise building construction,
K
A
/K
B
is about 0.2 (Vickery, 1986 and
Section 6.2.5) and the response time therefore increases by about 20%.
6.4
Nominally sealed buildings
The situation of buildings that are nominally sealed, but have some leakage distributed
over all surfaces, can be treated by neglecting the inertial terms and lumping together
windward and leeward leakage areas (Vickery, 1986, 1994; Harris, 1990).
A characteristic frequency,
n
c
,
is obtained. Pressure fluctuations below this frequency
are effectively communicated to the interior of the building.
n
c
is given by Equation
(6.19) (Vickery, 1994):
(6.19)
where
r
is the ratio of total leeward wall surface area to windward wall surface area,
a
s
the speed of sound and the other parameters were defined previously. A
w, total
is the total
surface area of the windward wall and
φ
is the wall porosity. Equation (6.19) is
essentially the same as Equation (6.18), with
τ
equal to (1/2π
n
c
).
The peak internal pressure coefficient can be estimated by:
(6.20)
