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Wind Engineering for Façade Pressures in High Rise Towers

Bhami M Ilyas

Regional Business Manager

CPP, Inc.

Codes and Standards?

The two ‘fathers’ of wind engineering : Professor Alan Davenport (l) and Professor Jack Cermak (r)

Wind tunnel testing of New York World Trade Center Towers at CSU

in Fort Collins by Professor Jack Cermak in early 1960s

Alan Davenport Wind Loading Chain

The Bigger Picture

Typical components in Wind engineering

Façade Pressures

Structural Loads

Pedestrian Comfort

Typical anemometer

GRADIENT WIND

GRADIENT WIND

Zg = HEIGHT OF GRADIENT WIND

Ug= GRADIENT WIND SPEED

Zo= AERODYNAMIC ROUGHNESS

Z= Metres

1< Zo < 5m

SUBURBAN OPEN COUNTRY FLAT TERRAIN

GRADIENT WIND

GRADIENT WIND

URBAN

0.1< Zo < O.5m

0.01< Zo < O.05m

0.001< Zo <

O.005m

Classical boundary layer profiles

400 m

300 m

200 m

100 m

LESS GUSTY

MORE GUSTY

MORE GUSTY LESS GUSTY

Boundary Layer Wind Tunnel

CP =Pressure at Surface Tap

Reference Pressure

PTAP

For Bluff Bodies:

(CP)Full-Scale = (CP)Model

PREF = ½ V2

Pressure Coefficients – the basis of wind tunnel testing

Along-wind Cross-wind Torsion

Types of wind-induced response

Wind

Drag Factors

0.6

0.3

1.5

1.2

2.0

1.5

2.2

Drag coefficients

Shaping Options

Softened corners

Tapering and setbacks

Varying cross-section shape

Spoilers

Porosity or openings

Along-wind Cross-wind

(Drag) (Lift)

Two types of dynamic response visible

Along-wind Response

Cylinder Vibration

Fluid flow

Interference effects

Add a Twist….

Vortex shedding

D = 1

D = 3

D = 5

CFD simulation of vortex shedding with three different cross-wind dimensions.

Note that this simulation also describes a constant cross-wind dimension but three different wind speeds (U = 5, 3, 1 from top to bottom)

The effect of shape on response

The Wind Tunnel Procedure

3D Pressure Data PresentationFabrication and Testing

Test Model Design

3D Data Presentation

Presentation Model Design(engineers design how the data is used/zoned/presented)

Troubles?

Wind tunnel results of pedestrian wind conditions

Lawson Comfort Ratings