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Wind damage and mechanics of flying debris. Wind loading and structural response Lecture 2 Dr. J.D. Holmes. Wind damage and mechanics of flying debris. Damage due to windstorms is increasing accounts for 70% of insured losses

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Wind damage and mechanics of flying debris l.jpg

Wind damage and mechanics of flying debris

Wind loading and structural response

Lecture 2 Dr. J.D. Holmes


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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.)


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Wind damage and mechanics of flying debris

  • Ferrybridge cooling towers - England, 1965

    interference effects


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Wind damage and mechanics of flying debris

  • Brighton Chain Pier, England, 1836

aeroelastic instability

also, Wheeling Bridge, Ohio, 1854


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Wind damage and mechanics of flying debris

  • Tacoma Narrows Bridge, Washington State, 1940

aeroelastic instability


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Wind damage and mechanics of flying debris

  • Tacoma Narrows Bridge, Washington State, 1940

aeroelastic instability


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Wind damage and mechanics of flying debris

  • Low-rise buildings - tornado and hurricane damage


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Wind damage and mechanics of flying debris

  • High-rise buildings - cladding (glass) damage

Hurricane ‘Alicia’, Houston, 1983


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Wind damage and mechanics of flying debris

  • Wind-generated debris

  • generates high internal pressures

  • allows wind and rain penetration

  • danger to occupants


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Compact

Sheet

l

Rod

t

d

Wind damage and mechanics of flying debris

  • Types of flying debris


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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


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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


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Wind damage and mechanics of flying debris

  • Threshold of flight

Sheet object:

Rod object:


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Wind damage and mechanics of flying debris

  • Time of flight and distance travelled

    • assume constant wind speed

Accelerating force :

Acceleration :


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Wind damage and mechanics of flying debris

  • Time of flight :

Acceleration :

Time taken to reach vm:

where :

dimensional


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Wind damage and mechanics of flying debris

  • Distance traveled :

Time to reach velocity v :

Distance traveled during time taken to reach vm:


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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





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Wind damage and mechanics of flying debris

Sphere falls under gravity and air resistance until it impacts ground or a building


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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


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Wind damage and mechanics of flying debris

Some shapes (e.g. plates, prisms) have lift – can reach heights greater than release height


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Wind damage and mechanics of flying debris

Some shapes (e.g. plates, prisms) have lift – can reach heights greater than release height


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Wind damage and mechanics of flying debris

Some shapes (e.g. plates, prisms) have lift – can reach heights greater than release height


End of lecture 2 john holmes 225 405 3789 jholmes@lsu edu l.jpg
End of Lecture 2John Holmes225-405-3789 [email protected]


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