Bridge Structures Intensify Crosswinds, Threatening Vehicle Safety

Researchers from China have identified specific bridge configurations that significantly intensify crosswinds within the driving space of long-span coastal bridges, posing a measurable threat to vehicle stability. Published in Advances in Bridge Engineering, the study combines computational fluid dynamics simulations with wind tunnel experiments to analyze how auxiliary structures, such as pedestrian bridges and towers, alter the local wind environment. The work focuses on a twin-box girder bridge located along the coast of Fujian Province, a region where strong crosswinds are a known factor in traffic accidents involving high-sided vehicles.

The investigation addresses a critical gap in understanding how the aerodynamic properties of the bridge itself, rather than just natural wind conditions, contribute to hazardous driving zones. Previous studies often idealized bridge models or neglected auxiliary facilities, limiting their ability to capture the full scope of aerodynamic interference. By incorporating detailed auxiliary structural facilities into the experimental design, the team aimed to quantify the mechanisms by which different deck configurations influence wind speed distribution and turbulence intensity within the traffic lanes.

The study began with numerical simulations using the Fluent software to model the wind field around various cross-sectional configurations of the bridge. The researchers selected a representative cross-section that included a pedestrian bridge suspended beneath the main sea-crossing structure. To determine the incoming wind speeds for the simulations, the team utilized meteorological data indicating a wind speed of 29.1 m/s at a height of 10 meters. Applying a wind profile exponent of 0.12 for the coastal location, they calculated the wind speeds at different heights above the deck to establish realistic boundary conditions for the computational domain.

The computational domain was carefully designed to meet the requirements for driving wind environment tests, ensuring that the blockage ratio of the structure did not exceed 5%. An unstructured mesh with approximately 480,000 elements was employed, with refinement applied near the bridge deck and guardrails to capture flow details accurately. The Realizable k–ε turbulence model was used to simulate the shear flows over the bridge deck, providing a baseline for understanding how wind interacts with the complex geometry of the bridge and its appendages.

Among the tested configurations, the numerical results indicated that the equivalent wind speed generally decreased from the windward side to the leeward side of the bridge deck. Configuration 6 exhibited the highest equivalent wind speed, reaching 20.53 m/s. This configuration was subjected to the combined influence of the pedestrian bridge and a nodal structure, creating a particularly unfavorable wind environment for vehicles. Cross-Section 7, which featured a tower located nearby, showed distinct wind field variations that differed markedly from the other sections, suggesting that the presence of vertical structures can significantly alter local airflow patterns.

To validate the numerical findings and provide a more refined analysis of on-bridge driving safety, the researchers conducted wind tunnel experiments using a 1:20 scale model of the bridge. Cross-Sections 6 and 7 were selected for physical testing. The experimental setup included two Cobra probes for measuring fluctuating wind speeds and a six-component force balance to record the aerodynamic forces acting on a vehicle model. The vehicle model was positioned in different traffic lanes to assess the lane-specific aerodynamic responses under various wind directions.

The wind tunnel tests were conducted at an incoming wind speed of 10 m/s, satisfying the Reynolds number similarity criterion. The measurements focused on the wind field within the 0–5 m height range above the deck. For Cross-Section 6 under left-side incoming flow, the equivalent wind speeds decreased progressively from Lane 1 to Lane 6, with Lane 1 experiencing the highest speed of 8.45 m/s. Conversely, under right-side incoming flow, Lane 6 recorded the highest equivalent wind speed of 9.29 m/s, indicating that the windward side of the deck is consistently subjected to higher wind loads.

The aerodynamic force measurements revealed that the position of the vehicle relative to the interfering structures significantly impacted the forces acting upon it. Under left-side inflow, the pedestrian bridge located on the leeward side caused the aerodynamic forces on the leeward lanes to be significantly lower than those on the windward side. In contrast, when the wind came from the right side, both the pedestrian bridge and the viewing platform were on the windward side, leading to flow acceleration around the structures. This resulted in significantly higher aerodynamic forces and moments on the windward lanes, with Lane 6 experiencing a lateral force of -4.498 N, the highest among all tested lanes for that condition.

For Cross-Section 7, the presence of the tower introduced a different aerodynamic dynamic. Under right-side inflow, the tower acted as a shield, causing a sudden drop in wind speed in Lane 6. The equivalent wind speed in this lane decreased to 6.06 m/s, which was 28% lower than the 8.44 m/s observed in Lane 2. However, as the airflow passed the tower, a local acceleration zone formed on the leeward side, resulting in increased aerodynamic forces on vehicles in the third lane. This finding highlights the complex nature of wind-structure interactions, where a structure can simultaneously shield some areas while accelerating flow in others.

The most critical scenario was identified as Cross-Section 6 under right-side inflow, where Lane 6 reached an equivalent wind speed of 9.29 m/s. This condition poses the greatest threat to vehicle stability due to the combined effects of high wind speed and aerodynamic interference. The results demonstrate that auxiliary structures can create localized zones of high wind intensity. The non-uniform wind field distribution, characterized by higher speeds on the windward side and lower values on the leeward side, underscores the need for detailed aerodynamic assessment in bridge design.

The findings provide a theoretical reference for vehicle safety assessment on bridge decks and the optimization of wind barrier designs. By identifying the specific configurations that lead to the most adverse wind conditions, the study offers practical insights for engineers seeking to mitigate wind-induced risks. The integration of numerical simulations and wind tunnel testing allowed for a comprehensive analysis of the vehicle-bridge system, capturing the aerodynamic interference between the vehicle and the bridge that simplified models often miss.

To replicate the full-scale structure accurately within the laboratory, the physical models were fabricated using engineering materials selected to mirror actual structural behavior. The central crash barrier was produced through proportionally scaled three-dimensional printing, supported by steel posts and railings formed from three-millimeter ABS plates. For the main girder segment, researchers constructed the shell using four-millimeter wooden panels mounted onto an aluminum-and-wood framework, while the suspended pedestrian bridge mirrored these construction materials with identical steel posts and ABS railings. Because the full-scale vehicular bridge spans a maximum width of 45.5 meters, the one-to-twenty scaled model measured 2.275 meters wide. The model length was fixed at 4.5 meters to maintain a length-to-width ratio below two, which effectively curbed unwanted wake interference while holding the tunnel blockage ratio to 4.5 percent.

The experimental instrumentation relied on specialized hardware to record airflow behavior and vehicle force responses simultaneously. Wind velocities were captured by two Australian-manufactured TFI Cobra probes, each measuring 155 millimeters in length with a 2.6-millimeter head width, capable of recording wind speed to within 0.3 meters per second and yaw angles within one degree through a 16-bit analog-to-digital sampling system. Aerodynamic loads on the truck model were gathered by an ATI Industrial Automation six-component balance machined from high-strength aviation aluminum, featuring measurement resolutions of 1/32 newton along the x-axis and 16/N along the y-axis. To prevent the physical connection hardware from disturbing the approaching airflow, the team positioned a custom mounting base entirely inside the hollow box girder, coupling it to the vehicle model through a custom vertical rod.

Across the tested scenarios, vertical wind velocity profiling was evaluated at ten discrete elevations ranging from 0.5 to 5.0 meters in full scale, corresponding to scaled test heights between 0.025 and 0.25 meters above the deck surface. Under Condition 1 with left-side winds on the section without the tower, the vehicle in Lane 1 endured an aerodynamic drag of -0.512 newtons and a lateral force of -3.766 newtons. When evaluating the tower configuration under identical left-side inflow in Condition 3, the vehicle in Lane 1 recorded an aerodynamic drag of -0.642 newtons, a lateral side force of -3.943 newtons, and a lift force of -0.213 newtons, accompanied by a rolling moment of -0.765 newton-meters, a pitching moment of -0.075 newton-meters, and a yawing moment of 0.204 newton-meters.

Subject of Research: Aerodynamic interference of bridge auxiliary structures on wind fields in driving spaces

Article Title: Effects of surrounding interference on the wind field in the driving space of bridge deck

Article References: Guo, M., Hou, H., Yang, J., Lin, J., Lian, J., & Lin, L. (2025). Effects of surrounding interference on the wind field in the driving space of bridge deck. Advances in Bridge Engineering, 6(1), Article 41. https://doi.org/10.1186/s43251-025-00191-3

Image Credits: AI Generated

DOI: 10.1186/s43251-025-00191-3

Keywords: bridge aerodynamics, wind tunnel testing, computational fluid dynamics, vehicle safety, crosswind effects, twin-box girder, aerodynamic interference, wind barrier design, coastal bridges, equivalent wind speed, flow separation, turbulence intensity, vehicle stability, aerodynamic forces, bridge deck wind field