Project-1
Using regular approach for building of all heights in chapter
26 and 27 , determine the basic wind pressures for a commercial
building with 15 feet eave height. The building is rectangular in
plan with dimension 45 ft by 40 ft, gable roof with angle =26.6
and the mean roof height h= 20 ft. It is assumed that the
building is located in a flat terrain with exposure B in all directions
and it is enclosed. Draw the wind pressures on walls and roof and
show the values.
CHAPTER 27 WIND LOADS ON BUILDINGS_MWFRS (DIRECTIONAL PROCEDURE)
Table 27.2-1 Steps to Determine MWFRS Wind
Loads for Enclosed, Partially Enclosed and
Open Buildings of All Heights
Step 1: Determine risk category of building or other
structure, see Table 1.4-1
Step 2: Determine the basic wind speed, V, for the
applicable risk category, see Figure 26.5-1A, B
or C
9, = velocity pressure calculated using Eq. 27.3-1 at
height z
9n = velocity pressure calculated using Eq. 27.3-1 at
mean roof height h.
The numerical coefficient 0.00256 (0.613 in SI)
shall be used except where sufficient climatic data are
available to justify the selection of a different value of
this coefficient for a design application.
27.4 WIND LOADS MAIN WIND
FORCE-RESISTING SYSTEM
Step 3: Determine wind load parameters:
> Wind directionality factor, K., see Section
26.6 and Table 26.6-1
> Exposure category, see Section 26.7
>> Topographic factor, K,, see Section 26.8 and
Table 26.8-1
> Gust Effect Factor, G, see Section 26.9
Enclosure classification, see Section 26.10
> Internal pressure coefficient, (GCpi), see
Section 26.11 and Table 26.11-1
27.4.1 Enclosed and Partially Enclosed
Rigid Buildings
Design wind pressures for the MWFRS of
buildings of all heights shall be determined by the
following equation:
p = 460 – 9(GC) (lb/ft?) (N/m') (27.4-1)
where
Step 4: Determine velocity pressure exposure
coefficient, K, or Ki, see Table 27.3-|
Step 5: Determine velocity pressure q, or 9, Eq. 27.3-1
Step 6: Determine external pressure coefficient, Cor Cw
Fig. 27.4-1 for walls and flat, gable, hip.
monoslope or mansard roofs
► Fig. 27.4-2 for domed roof's
Fig. 27,4-3 for arched roofs
» Fig. 27.4-4 for monoslope roof, open building
> Fig. 27.4-5 for pitched roof, open building
Fig. 27.4-6 for troughed roof, open building
>> Fig. 27.4-7 for along ridge/valley wind load
case for monoslope, pitched or troughed roof,
open building
Step 7: Calculate wind pressure, p, on each building
surface
Eq. 27.4-1 for rigid buildings
Eq. 27.4-2 for flexible buildings
Eq. 27.4-3 for open buildings
g = 9, for windward walls evaluated at height z
above the ground
9 = 9 for leeward walls, side walls, and roofs,
evaluated at heighth
9= 9, for windward walls, side walls, leeward
walls, and roofs of enclosed buildings and
for negative internal pressure evaluation in
partially enclosed buildings
91 = 9for positive internal pressure evaluation in
partially enclosed buildings where height z is
defined as the level of the highest opening in
the building that could affect the positive
internal pressure. For buildings sited in
wind-borne debris regions, glazing that is not
impact resistant or protected with an impact
resistant covering shall be treated as an
opening in accordance with Section 26.10.3.
For positive internal pressure evaluation,
9. may conservatively be evaluated at height
hq = 4x)
G = gust-effect factor, see Section 26.9
C = external pressure coefficient from Figs.
27.4-1. 27.4-2 and 27.4-3
(GC) = internal pressure coefficient from Table
26.11-1
9 and 4, shall be evaluated using exposure
defined in Section 26.73. Pressure shall be applied
27.3.2 Velocity Pressure
Velocity pressure, 93, evaluated at height z shall
be calculated by the following equation:
4, = 0.00256K KYK V (Ib/nt") (27.3-1)
In SI: 4 = 0.613KK,K,V (N/m?); V in m/s]
where
K = wind directionality factor, see Section 26.6
K. = velocity pressure exposure coefficient, see
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