How can wind loads be accounted for in bridge design?

1 Wind engineering basics

Wind engineering is a branch of engineering that studies the interaction between wind and structures, especially buildings and bridges. Wind engineering involves measuring and modeling the wind characteristics, such as speed, direction, turbulence, and gusts, as well as the aerodynamic forces and responses of structures. Wind engineering also applies the principles of fluid mechanics, dynamics, and statistics to design structures that are safe, stable, and efficient under wind loads.

2 Wind load types and effects

Wind loads can be classified into two main types: static and dynamic. Static wind loads are the steady-state forces that act on the structure due to the mean wind speed and direction, which can cause bending, shear, and torsion in the bridge elements. Dynamic wind loads are the fluctuating forces that result from the wind turbulence, gusts, and vortex shedding, which can induce vibrations, resonances, and instabilities in the structure. These wind loads can have various effects on bridges, such as serviceability, strength, fatigue, and stability. For example, they can affect the comfort and functionality of bridge users by causing excessive displacements or accelerations; they can exceed the capacity of bridge components or connections by causing large stresses or strains; they can reduce the lifespan of bridges by causing cyclic damage or cracking due to repeated loading and unloading; and they can compromise the stability of bridges by causing buckling, fluttering, or galloping due to aerodynamic instability.

3 Wind load analysis steps

Structural engineers need to perform a wind load analysis when accounting for wind loads in bridge design. This process consists of four main steps: wind climate assessment, wind load estimation, wind load combination, and wind load effects evaluation. Wind climate assessment involves determining the design wind speed and direction for the bridge site based on historical data or regional maps. Wind load estimation involves calculating the wind pressure or force coefficients based on empirical formulas or numerical simulations. Wind load combination combines the wind loads with other loads according to the load cases and factors specified by the design codes or standards. Finally, wind load effects evaluation analyzes the structural response and performance of the bridge under the wind loads using analytical methods or software tools.

4 Wind load design standards

Structural engineers must adhere to design standards or codes that provide guidelines and criteria for wind load analysis and design in order to ensure the safety and reliability of bridges under wind loads. The most commonly used wind load design standards for bridges include AASHTO LRFD Bridge Design Specifications from the US, EN 1991-1-4: Eurocode 1: Actions on Structures - Part 1-4: General Actions - Wind Actions from Europe, and GB 50009-2012: Load Code for the Design of Building Structures from China. These standards provide basic wind data, wind actions, wind load coefficients, dynamic effects, load factors, and load combinations for buildings and bridges.

5 Wind load mitigation strategies

Structural engineers can adopt various mitigation strategies to reduce the adverse effects of wind loads on bridges, such as shape optimization. This involves modifying the shape, size, or orientation of the bridge sections to reduce wind drag, lift, or vortex shedding effects. Structural damping is another strategy which involves adding devices or materials that dissipate the wind-induced energy and reduce bridge vibrations or resonances. Lastly, aerodynamic control involves installing devices or features that alter the wind flow around the bridge or create counteracting forces, like spoilers, flaps, or jets.

6 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?