How do you optimize the shape and orientation of bridges and towers to reduce wind drag and lift?

1 Wind drag and lift

Wind drag and lift are two components of the aerodynamic force that wind exerts on a structure. Wind drag is the force that acts parallel to the wind direction, and tends to slow down or resist the movement of the structure. Wind lift is the force that acts perpendicular to the wind direction, and tends to push or pull the structure away from its original position. Both wind drag and lift depend on the shape, size, and surface roughness of the structure, as well as the wind speed, direction, and turbulence.

2 Shape optimization

One way to reduce wind drag and lift is to optimize the shape of the structure, so that it minimizes the separation and reattachment of the wind flow around it. Separation and reattachment create vortices and pressure differences that increase the drag and lift forces. A smooth, streamlined, and tapered shape can reduce the separation and reattachment, and thus the drag and lift. For example, a circular or elliptical cross-section is more aerodynamic than a square or rectangular one, and a slender or curved tower is more aerodynamic than a bulky or flat one.

3 Orientation optimization

Another way to reduce wind drag and lift is to optimize the orientation of the structure, so that it aligns with the dominant or prevailing wind direction. This way, the structure faces the minimum wind resistance, and reduces the chances of cross-wind effects. Cross-wind effects occur when the wind hits the structure at an angle, and create oscillating forces that can cause vibrations and instability. For example, a bridge deck should be oriented parallel to the main wind direction, and a tower should be rotated to face the wind.

4 Wind tunnel testing

A useful tool for optimizing the shape and orientation of bridges and towers is wind tunnel testing. Wind tunnel testing is a method of simulating the wind conditions and measuring the wind effects on a scaled model of the structure. Wind tunnel testing can help you evaluate the aerodynamic performance of your design, identify potential problems, and compare different alternatives. Wind tunnel testing can also help you calibrate and validate numerical models and computational fluid dynamics (CFD) simulations.

5 Wind load codes and standards

A final aspect of optimizing the shape and orientation of bridges and towers is to comply with the wind load codes and standards that apply to your project. Wind load codes and standards are sets of rules and guidelines that specify the minimum requirements for designing structures to resist wind forces. Wind load codes and standards vary by region, country, and type of structure, and are based on historical data, statistical analysis, and engineering judgment. Wind load codes and standards can help you ensure the safety, reliability, and durability of your structure.

6 Examples of optimized bridges and towers

To illustrate how shape and orientation optimization can reduce wind drag and lift, here are some examples of bridges and towers that have applied these principles. The Millau Viaduct in France is the world's tallest bridge, with a streamlined deck and pylons that reduce the wind drag by 50%. The Burj Khalifa in Dubai is the world's tallest building, with a slender and tapered shape that reduces the wind load by 40%. The Shanghai Tower in China is the world's second tallest building, with a twisted and curved shape that reduces the wind load by 24%.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?