Wind load calculation
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Wind Load Design Code: GB/T 50009-2012 “Code for Loads on Building Structures”; NB/T 47041-2014 “Tower-type vessels”, Article 7.6; GB/T 12337-2014 “Steel spherical storage tanks”, Article 6.5. Wind load: Wind load force = standard wind pressure × area exposed to wind; Wind bending moment = wind load force × distance from centroid. Basic wind pressure w0 = 1/2ρv02; Air density ρ = 1.25 kg/m3. Shape coefficient for towers K1 = 0.7; Shape coefficient for spherical tanks K1 = 0.4. Wind-induced vibration coefficient K2i = 1.7 (for H ≤ 20 m). Equivalent width of ladders K3 = 400; Equivalent width of operating platforms K4 = 600. Relative positions between ladders and pipelines at the top of the tower: 180°, 90°.1. Along-wind direction: The direction of wind is the same as the direction of vibration. Wind load Pi = K1K2iq0filiDei ×10^-6. Bending moment at cross-section 0-0: MW0-0 = p1l1/2 + p2(l1 + l2/2) + p3(l1 + l2 + l3/2) + …… Bending moment at cross-section I–I: MWⅠ–Ⅰ = pili/2 + pi+1(li + li+1/2) + pi2(li + li+1 + li+2/2) + ……
2. Cross-wind direction: The direction of wind is perpendicular to the direction of vibration. Cross-wind-induced vibrations should be considered when H/D > 15 and H > 30 m. Critical wind speed: Vci = Do/(0.2Ti) ×10^-3. Wind speed at the top of the tower: V = 1.265(ftq0)^1/2. If V < Vc1, no vibration is considered. When Vc1 ≤ V < Vc1, vibrations of the first mode occur. When V > Vc1, vibrations of both the first and second modes occur. Calculation of amplitude during resonance: Reynolds number Re = 69VD0. Bending moment at any cross-section J-J: McaJ-J = (2π/Ti)^2 YTiΣmk(hk-h)φki.
3. Maximum bending moment along-wind direction: Maximum bending moment at cross-section I–I: MmaxⅠ–Ⅰ = MwⅠ–Ⅰ + Me (along-wind bending moment + eccentric load). MEⅠ–Ⅰ + 0.25MwⅠ–Ⅰ + Me (seismic load + 0.25 times the along-wind bending moment + eccentric load). Maximum bending moment at cross-section 0–0: Mmax0–0 = Mw0-0 + Me (along-wind bending moment + eccentric load). ME0-0 + 0.25Mw0-0 + Me (seismic load + 0.25 times the along-wind bending moment + eccentric load).
4. When considering cross-wind-induced vibrations: Maximum bending moment at cross-section I–I: MmaxⅠ–Ⅰ = MwⅠ–Ⅰ + Me (combined wind-induced bending moment + eccentric load). MEⅠ–Ⅰ + 0.25MwⅠ–Ⅰ + Me (seismic load + 0.25 times the combined wind-induced bending moment + eccentric load). Maximum bending moment at cross-section 0–0: Mmax0–0 = Mw0-0 + Me (along-wind bending moment + eccentric load). ME0-0 + 0.25Mw0-0 + Me (seismic load + 0.25 times the combined wind-induced bending moment + eccentric load)