WIND CODE-IS 875-PART 3
- 3. GIST INTRODUCTION WIND EFFECTS METHODS OF CALCULATING WIND FORCE 1 2 3
- 5. GENERAL TERMS IN WIND CODE 1. WIDTH,w 2. DEPTH,l 3. HEIGHT,h 4. OCEAN CURRENT 5. SOLIDITY RATIO 6. GUST 7. GRADIENT VELOCITY 8. PRESSURE & SUCTION 9. DESIGN WIND SPEED
- 6. Wind speed at 5 to 10 kmph is called breeze. Wind speed at 50 kmph is called strong wind. Wind speed more than 80 kmph is called very strong wind.
- 7. Vz = Vb. k1. k2. k3 in m/s Vb = Basic wind speed in m/s k1 = Probability factor (risk coefficient). k2 = Terrain height and structure size factor. k3 = Topography factor. DESIGN WIND SPEED VZ
- 8. DESIGN WIND PRESSURE PZ The design wind pressure, Pz = ½ ρ Vz2, ρ = Density of Air = 1.225 Kg/m3 Pz = ½*1.225*Vz2 = 0.6Vz2 Pz = Design wind pressure in N/m2 Vz = Design Speed in m/s
- 9. WIND PRESSURE AND FORCES ON BUILDINGS AND STRUCTURES 1) The building / structure is taken as a whole. 2) Individual structural elements such as roofs and walls. 3) Individual cladding units such as sheeting and glazing including their fixtures.
- 16. TORNADOS
- 22. TERRAIN CATEGORY - 1 TERRAIN CATEGORY - 2 TERRAIN CATEGORY - 3 TERRAIN CATEGORY - 4
- 23. CLASS OF A BUILDING Class A : Size of the structure is less than 20m Class B : Size of the structure between 20 to 50m Class C : Size of the structure greater than 50m
- 27. The effect of topography will be taken as when upwind Slope < 3 deg k3 = 1.0 Slope > 3 deg k3 = 1.0 to 1.36 K3 – TOPOGRAPGHY FACTOR
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- 33. DYNAMIC EFFECTS OF WIND Guidelines for det.Problems of wind induced oscillations: 1) Height / Min.Lat Dim > 5 2) If natural frequency in the first mode is less than 1.0Hz Fundamental Time Period, T = 0.1 n ,n=number of storeys, T = 0.09H/√d, Natural Frequency = 1/T, 45m
- 34. 800 ft Tall Building 2 ft2 ft Neutral Position Oscillates in the opposite direction Oscillates in the direction of wind WIND DIR 13 2
- 36. PRESSURE COEFFICIENT METHOD Wind Load , F = (Cpe – Cpi) x A x Pd Cpe – External pressure coefficient Cpi – Internal pressure coefficient A – Surface Area of Structural Element Pd – Design Wind Pressure
- 37. Buildings with small openings(< 5% of wall area) Cpi = 0.2 Buildings with medium openings (5% to 20% of wall area) Cpi = 0.5 Buildings with Large openings (> 20% of wall area) Cpi = 0.7 Cpi – INTERNAL PRESSURE COEFFICIENT
- 54. Cp FOR e - 1.25 IF OVERHANG SLOPE - 1.00 IF OVERHANG HORIZONTAL - 0.75 IF OVERHANG SLOPES UPWARDS
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- 58. FORCE COEFFICIENT METHOD F = Cf x Ae x Pd where, F = Force in N Cf = Force coefficient from Fig.4 Ae = Effective Frontal Area in m Pd = Design Wind Pressure in N/m
- 59. FORCE COEFFICIENTS FOR CLAD BUILDINGS
- 61. SINGLE FRAMES: FORCE COEFFICIENTS FOR UNCLAD BUILDINGS
- 62. MULTIPLE FRAMES: FORCE COEFFICIENTS FOR UNCLAD BUILDINGS
- 63. Frame spacing ratio = c/c of frames/Least dimensions MULTIPLE FRAMES
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- 65. GUST FACTOR METHOD Fz = Cf*Ae* Pz* G Fz = Along wind load on the structure at any height z Cf = Force coefficient for the building Ae = Effective frontal Area for the height z Pz = Design pressure at height z due to hourly mean wind obtained as 0.6Vz^2 G = Gust factor