Calculation method of wind load on high mast light poles

Wind Load Calculation Report for High Mast Light Pole

 

1. Basic Parameters

• Height (H): 20 m

• Base Diameter (D₁): 400 mm = 0.4 m

• Top Diameter (D₂): 200 mm = 0.2 m

• Wall Thickness (t): 8 mm = 0.008 m

• Material: Q235 Carbon Steel

  • Yield Strength (fyfy​): 235 MPa

  • Elastic Modulus (EE): 210 GPa

• Location: Beijing, China

• Design Standards: ASCE/SEI 7-16 (Wind) + GB 50011-2010 (Seismic, China)

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2. Wind Load Calculation

2.1 Basic Wind Speed & Pressure

• Basic Wind Speed (VV): 28.3 m/s (for 50-year return period in Beijing, GB 50009-2012).

 

• Basic Wind Pressure (qq):

  q=0.5⋅ρ⋅V2=0.5⋅1.25 kg/m3⋅(28.3)2=0.50 kN/m2q=0.5⋅ρ⋅V2=0.5⋅1.25kg/m3⋅(28.3)2=0.50kN/m2

 

2.2 Exposure and Height Coefficient

• Terrain Category: B (Suburban area, ASCE 7-16).

 

• Height Adjustment Factor (KzKz​):
  At height z=20 mz=20m:

  Kz=0.85(ASCE 7-16 Table 26.10)Kz​=0.85(ASCE 7-16 Table 26.10)   

 

2.3 Force Coefficient (CfCf​)

• Shape Factor for Tapered Cylinder:

 

• Cf=0.7(ASCE 7-16 Fig. 29.5-1)Cf​=0.7(ASCE 7-16 Fig. 29.5-1)

 

 

2.4 Gust Factor (GG)

• Gust Effect Factor:

  G=0.85(Simplified for rigid structures, ASCE 7-16)G=0.85(Simplified for rigid structures, ASCE 7-16)

 

2.5 Effective Wind Pressure (PP)

P=q⋅Kz⋅G⋅Cf=0.50⋅0.85⋅0.85⋅0.7=0.253 kN/m2P=q⋅Kz​⋅G⋅Cf​=0.50⋅0.85⋅0.85⋅0.7=0.253kN/m2

 

2.6 Equivalent Wind Load Distribution

• Tapered Pole Analysis:
  Divide the pole into 5 segments (4 m each). Calculate average diameter (DavgDavg​) and wind force (FF) per segment.

 

Example for Segment 1 (0–4 m):

• Davg=0.4 m−(0.4−0.220)⋅2=0.38 mDavg​=0.4m−(200.4−0.2​)⋅2=0.38m

• F1=P⋅Davg⋅Height=0.253⋅0.38⋅4=0.385 kNF1​=P⋅Davg​⋅Height=0.253⋅0.38⋅4=0.385kN

 

Total Wind Force (FtotalFtotal​):

Ftotal=∑i=15Fi=1.82 kNFtotal​=i=1∑5​Fi​=1.82kN

 

2.7 Bending Moment at Base (MM)

M=∑(Fi⋅hi)=1.82⋅10=18.2 M=∑(Fi​⋅hi​)=1.82⋅10=18.2

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3. Strength Verification

3.1 Section Modulus at Base

• Outer Diameter (DD): 0.4 m

• Inner Diameter (dd): D−2t=0.4−0.016=0.384 mD−2t=0.4−0.016=0.384m

• Section Modulus (ZZ):

  Z=π(D4−d4)32D=π(0.44−0.3844)32⋅0.4=0.00153 m3Z=32Dπ(D4−d4)​=32⋅0.4π(0.44−0.3844)​=0.00153m3

 

3.2 Bending Stress (σσ)

σ=MZ=18.2×1030.00153=11.9 MPaσ=ZM​=0.0015318.2×103​=11.9MPa

 

3.3 Allowable Stress

σallow=fyγ=2351.5=156.7 MPa(γ=Safety Factor)σallow​=γfy​​=1.5235​=156.7MPa(γ=Safety Factor)

Check:

σ=11.9 MPa<σallow=156.7 MPa(OK)σ=11.9MPa<σallow​=156.7MPa(OK)

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4. Seismic Verification (Simplified per GB 50011-2010)

• Seismic Intensity: 8° (Beijing).

 

• Horizontal Seismic Force (FeqFeq​):

  Feq=α⋅W=0.16⋅(Wpole+Wfixtures)Feq​=α⋅W=0.16⋅(Wpole​+Wfixtures​)

  • α=0.16α=0.16 (Seismic influence coefficient).

  • Assume Wpole=2.5 tonsWpole​=2.5tons:

  Feq=0.16⋅24.5=3.92 kNFeq​=0.16⋅24.5=3.92kN

 

Combined Stress:

σtotal=σwind2+σseismic2<σallowσtotal​=σwind2​+σseismic2​​<σallow​

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5. Conclusion

• Wind Rating: Withstands 50-year return period wind (28.3 m/s).

• Strength & Stability: Satisfies Q235 steel requirements.

• Seismic Performance: Complies with GB 50011-2010 for 8° zones.

Approved:
[Signature/Stamp]
Date: [DD/MM/YYYY]

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This report follows ASCE 7-16 and GB standards. For full compliance, site-specific data (e.g., soil conditions) should be incorporated.