Wind damage and mechanics of flying debris

1. Wind damage and mechanics of flying debris Wind loading and structural response Lecture 2 Dr. J.D. Holmes

2. Wind damage and mechanics of flying debris • Damage due to windstorms is increasing • accounts for 70% of insured losses (difficult to separate direct wind damage from rain, storm floods) • big increases in U.S. in late 1980’s and 1990’s • Hurricanes ‘Hugo’, ‘Andrew’, ‘Georges’ $ Billions also gales in Europe : 1987($3.7bill.) , 1990 ($15bill.), 1999 ($10bill.)

3. Wind damage and mechanics of flying debris • Ferrybridge cooling towers - England, 1965 interference effects

4. Wind damage and mechanics of flying debris • Brighton Chain Pier, England, 1836 aeroelastic instability also, Wheeling Bridge, Ohio, 1854

5. Wind damage and mechanics of flying debris • Tacoma Narrows Bridge, Washington State, 1940 aeroelastic instability

6. Wind damage and mechanics of flying debris • Tacoma Narrows Bridge, Washington State, 1940 aeroelastic instability

7. Wind damage and mechanics of flying debris • Low-rise buildings - tornado and hurricane damage

8. Wind damage and mechanics of flying debris • High-rise buildings - cladding (glass) damage Hurricane ‘Alicia’, Houston, 1983

9. Wind damage and mechanics of flying debris • Wind-generated debris • generates high internal pressures • allows wind and rain penetration • danger to occupants

10. Compact Sheet l Rod t d Wind damage and mechanics of flying debris • Types of flying debris

11. Wind damage and mechanics of flying debris • Threshold of flight Compact object: aerodynamic force just balances resistance of gravity and fixity I = fixity parameter (=1, for objects resting on the ground) CF = aerodynamic force coefficient

12. Wind damage and mechanics of flying debris • Threshold of flight • The higher the value of characteristic dimension, l, or density, m, the higher the wind speed for the threshold of flight, Uf. • Example : for CF = 1, I = 1 , UF = 30 m/s (67 mph) l = 110 mm (4.3 in) for wooden object l = 20 mm (0.8 in) for stone object

13. Wind damage and mechanics of flying debris • Threshold of flight Sheet object: Rod object:

14. Wind damage and mechanics of flying debris • Time of flight and distance travelled • assume constant wind speed Accelerating force : Acceleration :

15. Wind damage and mechanics of flying debris • Time of flight : Acceleration : Time taken to reach vm: where : dimensional

16. Wind damage and mechanics of flying debris • Distance traveled : Time to reach velocity v : Distance traveled during time taken to reach vm:

17. Wind damage and mechanics of flying debris • Time of flight and distance travelled Examples : steel ball 2mm (0.315 in.) diameter timber : 100 mm(4 in.) by 50 mm (2 in.) by 1600 mm (5.25 ft.) long

18. Wind damage and mechanics of flying debris

19. Wind damage and mechanics of flying debris

20. Wind damage and mechanics of flying debris

21. Wind damage and mechanics of flying debris Sphere falls under gravity and air resistance until it impacts ground or a building

22. Wind damage and mechanics of flying debris • Time and distance to impact : Some shapes (e.g. plates, prisms) have lift – can reach heights greater than release height

23. Wind damage and mechanics of flying debris Some shapes (e.g. plates, prisms) have lift – can reach heights greater than release height

24. Wind damage and mechanics of flying debris Some shapes (e.g. plates, prisms) have lift – can reach heights greater than release height

25. Wind damage and mechanics of flying debris Some shapes (e.g. plates, prisms) have lift – can reach heights greater than release height

26. End of Lecture 2John Holmes225-405-3789 JHolmes@lsu.edu