WIND CODE-IS 875-PART 3

PRESENTATION ON WIND CODE-IS 875 PART 3

1. Storm imogen,8 th feb,2016

2. Impact of wind on the design of structures in industry BY SS / KRN

3. GIST 1 2 3

4. WHAT IS WIND ?????

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 V b = Basic wind speed in m/s k 1 = Probability factor (risk coefficient). k 2 = Terrain height and structure size factor. k 3 = Topography factor. DESIGN WIND SPEED V z

8. DESIGN WIND PRESSURE P z The design wind pressure, Pz = ½ ρ Vz 2 , ρ = Density of Air = 1.225 Kg/m 3 Pz = ½ *1.225*Vz 2 = 0.6Vz 2 Pz = Design wind pressure in N/m 2 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.

10. TORNADOS

11. CYCLONES THUNDERSTORMS

12. TERRAIN CATEGORY - 1 TERRAIN CATEGORY - 2 TERRAIN CATEGORY - 3 TERRAIN CATEGORY - 4

13. 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

14. CLIFFS RIDGES HILLS ESCARPMENTS

15. 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

16. BREAK…

17. 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

18. 800 ft Tall Building 2 ft 2 ft Neutral Position Oscillates in the opposite direction Oscillates in the direction of wind WIND DIR 1 3 2

19. 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

20. Cpi – INTERNAL PRESSURE COEFFICIENT

21. Cp FOR e - 1.25 IF OVERHANG SLOPE - 1.00 IF OVERHANG HORIZONTAL - 0.75 IF OVERHANG SLOPES UPWARDS

22. BREAK…

23. 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

24. FORCE COEFFICIENTS FOR CLAD BUILDINGS

25. SINGLE FRAMES: FORCE COEFFICIENTS FOR UNCLAD BUILDINGS

26. MULTIPLE FRAMES: FORCE COEFFICIENTS FOR UNCLAD BUILDINGS

27. Frame spacing ratio = c/c of frames/Least dimensions MULTIPLE FRAMES

28. BREAK…

29. 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