AVI GORI

JULIANNE CRAWFORD

WIND EFFECTS ON SHORT SPAN BRIDGE DECKS

HISTORY OF WIND EFFECTS ON BRIDGES

❖ Tacoma Narrows Bridge in 1940

❖ Hood Canal Bridge in 1979

❖ Sabo Pedestrian Bridge in 2012

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?

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)

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

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:

OUR WIND MODEL

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)

MODEL ASSUMPTION

❖ 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)

❖ Wind Pressure

○ Deck Height

○ Surface Conditions

❖ Deck Type

❖ Angle of Attack

❖ Deck Thickness

❖ Span Length

VARIABLES

VARIABLES

❖ Wind Pressure

○ Deck Height

○ Surface Conditions

❖ Deck Type

❖ Angle of Attack

❖ Deck Thickness

❖ Span Length

SLAB

VARIABLES

❖ Wind Pressure

○ Deck Height

○ Surface Conditions

❖ Deck Type

❖ Angle of Attack

❖ Deck Thickness

❖ Span Length

GIRDER

VARIABLES

❖ Wind Pressure

○ Deck Height

○ Surface Conditions

❖ Deck Type

❖ Angle of Attack

❖ Deck Thickness

❖ Span Length

VARIABLES

❖ Wind Pressure

○ Deck Height

○ Surface Conditions

❖ Deck Type

❖ Angle of Attack

❖ Deck Thickness

❖ Span Length(t)

VARIABLES

❖ Wind Pressure

○ Deck Height

○ Surface Conditions

❖ Deck Type

❖ Angle of Attack

❖ Deck Thickness

❖ Span Length

(L)

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

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

RESULTS SYNTHESIZED

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