bridge engineering and extreme events: wind effects on bridge decks
TRANSCRIPT
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AVI GORI
JULIANNE CRAWFORD
WIND EFFECTS ON SHORT SPAN BRIDGE DECKS
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HISTORY OF WIND EFFECTS ON BRIDGES
❖ Tacoma Narrows Bridge in 1940
❖ Hood Canal Bridge in 1979
❖ Sabo Pedestrian Bridge in 2012
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HISTORY OF WIND EFFECTS ON BRIDGES
❖ Tacoma Narrows Bridge in 1940
❖ Hood Canal Bridge in 1979
❖ Sabo Pedestrian Bridge in 2012WHAT IS WIND’S EFFECT ON SHORT SPAN BRIDGES?
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AASHTO Wind Equations
Where:
PB = Base Wind Pressure (ksf)
VDZ = Design wind velocity at design elevation Z (mph)
Where:
V0 = Friction velocity for various upwind surface characteristics (mph)
V30 = Wind velocity at 30.0ft above low ground (mph)
VB = Base wind velocity of 100 mph at 30.0ft height (mph)
Z = Height of structure at which wind loads are being calculated (ft)
Z0 = Friction length of upstream fetch (ft)
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DERIVATION OF THE AASHTO VELOCITY EQUATION
Wind velocity (u) depends on elevation (Z), atmospheric conditions, air density, etc.
Derived relationship:
k empirically found = 2.5 for stable conditions
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Derivation of the AASHTO Pressure Equation
The theoretical equation for pressure is proportional to density and velocity (U) squared
The theoretical drag force equation is found by multiplying by surface area (A)
Equations Used in Our Model:
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OUR WIND MODEL
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CONTRIBUTION OF WIND TO:
1. SHEAR ABOUT CENTER SPAN DUE TO LATERAL WIND LOAD (DRAG)
2. MOMENT ABOUT CENTER SPAN DUE TO VERTICAL WIND LOAD
(LIFT)
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MODEL ASSUMPTION
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❖ Wind Pressure
○ Deck Height
○ Surface Conditions
❖ Deck Type
❖ Angle of Attack
❖ Deck Thickness
❖ Span Length
VARIABLESWhere:
PB = Base Wind Pressure (ksf)
VDZ = Design wind velocity at design elevation Z (mph)
Where:
V0 = Friction velocity for various upwind surface characteristics (mph)
V30 = Wind velocity at 30.0ft above low ground (mph)
VB = Base wind velocity of 100 mph at 30.0ft height (mph)
Z = Height of structure at which wind loads are being calculated (ft)
Z0 = Friction length of upstream fetch (ft)
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❖ Wind Pressure
○ Deck Height
○ Surface Conditions
❖ Deck Type
❖ Angle of Attack
❖ Deck Thickness
❖ Span Length
VARIABLES
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VARIABLES
❖ Wind Pressure
○ Deck Height
○ Surface Conditions
❖ Deck Type
❖ Angle of Attack
❖ Deck Thickness
❖ Span Length
SLAB
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VARIABLES
❖ Wind Pressure
○ Deck Height
○ Surface Conditions
❖ Deck Type
❖ Angle of Attack
❖ Deck Thickness
❖ Span Length
GIRDER
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VARIABLES
❖ Wind Pressure
○ Deck Height
○ Surface Conditions
❖ Deck Type
❖ Angle of Attack
❖ Deck Thickness
❖ Span Length
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VARIABLES
❖ Wind Pressure
○ Deck Height
○ Surface Conditions
❖ Deck Type
❖ Angle of Attack
❖ Deck Thickness
❖ Span Length(t)
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VARIABLES
❖ Wind Pressure
○ Deck Height
○ Surface Conditions
❖ Deck Type
❖ Angle of Attack
❖ Deck Thickness
❖ Span Length
(L)
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SENSITIVITY ANALYSIS
SLAB GIRDER
Deck Thickness: 56.8in
Deck Height: 30ft
Angle of Attack: 45°
Span Length: 60ft
Deck Thickness: 16in
Deck Height: 30ft
Angle of Attack: 45°
Span Length: 30ft
TYPICAL SLAB TYPICAL GIRDER
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SENSITIVITY ANALYSIS
SLAB GIRDER
Deck Thickness: 39-72in
Deck Height: 15-60ft
Angle of Attack: 0-180°
Span Length: 50-125ft
Deck Thickness: 10-24in
Deck Height: 15-60ft
Angle of Attack: 0-180°
Span Length: 28-40ft
VARIABLE RANGES VARIABLE RANGES
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RESULTS SYNTHESIZED
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LOCATION
FINDINGS
SUMMARY
IN OPEN COUNTRY AND COASTAL ENVIRONMENTS, THE
CONTRIBUTION OF WIND IS NON-NEGLIGIBLE
LATERAL WIND FORCES COMPRISE A SUBSTANTIAL PORTION
OF THE TOTAL LATERAL FORCES
MOMENT: ANGLE OF ATTACK
SHEAR: SPAN LENGTH
LATERAL LOADS