Wind Load Calculation Report (As per
ASCE 7-16)
Advance Design of Steel Structures
CV597
Submission date: April 19, 2021
Prepared By
SYED MUNEEB HAIDER
21L-7054
Resource Person
Dr.Tauqir ahmed
Assistant Professor
Civil Engineering Department
National university of computer and emerging sciences
Lahore
Table of Contents
Wind Loads ………………………………………………………………………………………………1
1. Procedure for the calculation of wind load as per ASCE 7-16 for open
steel shed…….…………………………………………………………………………………......1-15
1.1 Determine the basic wind speed, V
1.2 Determine wind load parameters
• Wind directionality factor, 𝐾𝑑
• Exposure category
• Topographic factor, 𝐾𝑧𝑡
• Ke = Ground elevation Factor
• Gust factor, G
• Enclosure classification
• Internal pressure coefficient, 𝐺𝐶𝑝𝑖,
1.3 Determine velocity pressure exposure coefficient, 𝐾𝑧 𝑜𝑟 𝐾ℎ
1.4 Determine velocity pressure, 𝑞𝑧 𝑜𝑟 𝑞ℎ, see equation below.
1.5 Determine external pressure coefficients, 𝐶𝑝 or Cn
1.6 Determine wind pressure, p, on each building surface (open, enclosed and
partially enclosed).
1.7 Flow Chart
2. Wind loads for industrial building (excel result).…………………………….16-19
3. Comparison of results with commercial software.…………………………19-22
3.1 MBS (Metal building software) result
3.2 SAP2000 Result
4.References…………………………………………………………..……………………………23
Wind Loads
Structures block the flow of wind and the wind’s kinetic energy is converted into potential
energy (into pressure), which causes a wind loading.
The effect of wind on a structure depends on the
•
density and velocity of the air
•
angle of incidence of the wind
•
shape and stiffness of the structure
•
roughness of its surface
For design purposes, wind loadings can be treated using either a static or a dynamic approach.
1. Procedure for the calculation of wind load as per ASCE 7-16 for open steel
shed
1.1 Determine the basic wind speed, V
Basic wind speed in Pakistan is shown in Figure. The basic wind speed is based on statistical
data
Statistical data (V)
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1.2 Determine wind load parameters
•
Wind directionality factor, 𝐾𝑑, see Table 26.6.1
Wind directionality factor, Kd
•
Exposure category for each wind direction considered, the upwind exposure shall be
based on ground surface roughness that is determined from natural topography, vegetation,
and constructed facilities.
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Exposure Categories
•
Topographic factor, 𝐾𝑧𝑡, see Figure 26.8-1.
𝐾𝑧𝑡 = (1+𝐾1𝐾2𝐾3)2, where 𝐾1, 𝐾2 and 𝐾3 are given in Fig. 26.8-1.
If site conditions and locations of buildings and other structures do not meet all the conditions
specified in Section 26.8.1, then Kzt =1.0.
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Topographic factor Kzt
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•
Ke = Ground elevation Factor
This factor accounts for the height above mean sea level
Ground elevation factor, Ke
1. The conservative approximation Ke =1.00 is permitted in all cases.
2. The factor Ke shall be determined from the above table using interpolation
•
Gust factor, G
The gust-effect factor for a rigid building or other structure is permitted to be taken as 0.85.
Condition of natural frequency
The approximate lower bound natural frequency (na), in hertz, of concrete or structural steel
buildings meeting the conditions of Section 26.11.2.1 is permitted to be determined from one of
the following equations
For structural steel moment-resisting frame buildings,
na =22.2∕h0.8 (26.11-2)
For concrete moment-resisting frame buildings,
na =43.5∕h0.9 (26.11-3)
For structural steel and concrete buildings with other lateral force-resisting systems,
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na =75∕h (26.11-4)
If na is greater than 1 then G = 0.85
•
Enclosure classification
1. Open Building
A building having each wall at least 80 percent open. This condition is expressed for each wall
by the equation Ao ≥ 0.8 Ag where
Ao = total area of openings in a wall that receives positive external pressure
Ag = the gross area of that wall in which Ao is identified
2. Partially Enclosed Building
A building that complies with both of the following conditions:
•
•
The total area of openings in a wall that receives positive external pressure exceeds the
sum of the areas of openings in the balance of the building envelope (walls and roof) by
more than 10 percent.
The total area of openings in a wall that receives positive external pressure exceeds (0.37
m2) or 1 percent of the area of that wall, whichever is smaller, and the percentage of
openings in the balance of the building envelope does not exceed 20 percent.
3. Enclosed Building
Building that has the total area of openings in each wall, that receives positive external pressure,
less than or equal to 4 sq ft (0.37 m2) or 1% of the area of that wall, whichever is smaller. This
condition is expressed for each all by the following equation:
Ao < 0.014 or 4 sq ft (0.37 m2), whichever is smaller, where A and A are as defined for Open
Buildings.
4. Enclosed Building
It is a building that is not classified as open or partially enclosed.
•
Internal pressure coefficient, 𝐺𝐶𝑝𝑖,
Internal pressure coefficient GCpi
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1. Plus, and minus signs signify pressures acting toward and away from the internal
surfaces, respectively.
2. Values of (GC,) shall be used with q, or qh as specified.
3. Two cases shall be considered to determine the critical load requirements for the
appropriate condition: (i) a positive value of (GCi) applied to all internal surfaces (ii) a
negative value of (GCi) applied to all internal surfaces
1.3 Determine velocity pressure exposure coefficient, 𝐾𝑧 𝑜𝑟 𝐾ℎ
Note that 𝐾ℎ is constant and calculated for mean height of the building, while 𝐾𝑧 varies with
heights measured from the base of the building.
Velocity pressure coefficient
Notes:
1. The velocity pressure exposure coefficient K, may be determined from the following formula:
For l5ft ≤ z ≤ zg
Kz = 2.01(z/zg)2/α
For z < 15 ft.
Kz = 2.01 (15/zg) 2/α a 2.
α and zg are tabulated in Table 26.11-1
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Terrain exposure constants
Linear interpolation for intermediate values of height z is acceptable.
1.4 Determine velocity pressure, 𝑞𝑧 𝑜𝑟 𝑞ℎ, see equation below.
𝑞𝑧=0.613𝐾𝑧𝐾𝑧𝑡𝐾𝑑Ke𝑉2(N/m2); Vin m/s
qz = 0.00256 𝐾𝑧𝐾𝑧𝑡𝐾𝑑Ke𝑉2 (Ib/ft2); Vin mi/h
where:
𝑞𝑧 = velocity pressure calculated at height z, (N/m2)
𝑞ℎ = velocity pressure calculated at mean roof height h, (N/m2)
𝐾𝑑 = wind directionality factor
𝐾𝑧 = velocity pressure exposure coefficient
𝐾𝑧𝑡 = topographic factor
Ke = Ground elevation Factor
𝑉 = basic wind speed, in m/s
1.5 Determine external pressure coefficients, 𝐶𝑝 or Cn
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External pressure coefficients, Cp
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1.6 Determine wind pressure, p, on each building surface (open, enclosed and partially
enclosed).
1. 𝑝=𝑞𝐺𝐶𝑝 − 𝑞𝑖(𝐺𝐶𝑝𝑖)
where:
q = qz for windward walls evaluated at height z above the ground.
q = qh for leeward walls, sidewalls, and roofs evaluated at height h.
qi = qh for windward walls, sidewalls, leeward walls, and roofs of enclosed buildings, and for
negative internal pressure evaluation in partially enclosed buildings.
qi = qz for 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 26.12.3. For positive internal pressure evaluation, qi may conservatively be evaluated at
height h (qi =qh).
G = gust-effect factor; see Section 26.11. For flexible buildings, Gf determined in accordance
with Section 26.11.5 shall be substituted for G.
Cp = external pressure coefficient from Figs. 27.3-1, 27.3-2, and 27.3-3.
(GCpi) = internal pressure coefficient from Table 26.13-1.
2. 𝑝=𝑞𝐺𝐶𝑝 (for open building)
The net design pressure for the MWFRS of open buildings with monoslope, pitched, or troughed
free roofs in lb/ft2(N/m2), shall be determined by the following equation:
𝑝=𝑞𝐺𝐶n
where
qh = velocity pressure evaluated at mean roof height h using the exposure as defined in Section
26.7.3 that results in the highest wind loads for any wind direction at the site.
G = gust-effect factor from Section 26.11.
CN = net pressure coefficient determined from Figs. 27.3-4 through 27.3-7
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Net Pressure coefficients, Cn
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1.7 Flow Chart
Determine wind flow
speed ‘V’
Determine wind
Load parameters
Determine Velocity
Pressure coefficient
Kz and Kh
Determine
Velocity Pressure
qz and qh
Determine external pressure
coefficient Cp
Calculate wind pressure “p” on each
building surface
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2. Wind load for industrial building (Excel result)
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3. Comparison of results with commercial software
Note:
1. MBS (Metal Building Software) software follows MBMA (Metal Building System
Manual) and this manual refers to ASCE and according to this manual wind load acts in
both transverse and longitudinal direction of building but some values of surface
coefficient may differ from values available in ASCE because of that answers may differ
2. In field we always follow MBMA because MBMA is derived from ASCE and MBMA
simplify ASCE code for steel buildings.
3. In SAP2000 wind load is applied on global axis instead of local axis so results may differ
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3.1 MBS (Metal Building Software) result
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3.2 SAP2000 result
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4. References
•
ASCE (7-16)
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