Bridge protection: Weigh In Motion and Structural Health Monitoring combine to prevent collapses

Bridges are essential to a functioning infrastructure, but their durability is often compromised by the frequent passage of overweight trucks. The implementation of precise measurement technology for bridge protection is critical in detecting and mitigating structural issues at an early stage. On the Brooklyn Queens Expressway in New York such a system is currently employed. Here, Weigh In Motion (WIM) sensors from Kistler not only monitor commercial vehicles automatically, but are also used for direct enforcement of truck weight. 

In the U.S., over 250,000 bridges are more than 50 years old, with 150,000 deemed deficient or obsolete. If any of these deteriorate further, authorities may need to close them, causing significant traffic disruptions. Modern technologies, such as Weigh In Motion (WIM)  and Structural Health Monitoring (SHM) or condition monitoring offer a solution. 

Direct enforcement of truck weight in New York

Especially overloaded vehicles exert immense stress on road surfaces and overall structures. As vehicles get heavier, the stress on the bridge increases exponentially, with overweight trucks causing far more damage than those that comply with regulations. Unfortunately, weight restrictions are often ignored, limiting their effectiveness in protecting bridge integrity – this is where commercial vehicle enforcement comes in. 

To address this issue, Weigh In Motion solutions from Kistler assist Departments of Transportation (DOTs) and bridge owners worldwide. The New York City DOT (NYSDOT), for instance, launched the nation’s first automated WIM direct enforcement program on the Brooklyn Queens Expressway (BQE) to tackle the problem of overweight trucks. This system allows the DOT to directly enforce truck weight limits using WIM data alone, marking it the only such enforcement site in the U.S. 

The Weigh In Motion system uses piezoelectric sensors, providing highly accurate, maintenance-free data unaffected by temperature changes. The robust quartz crystals withstand axle loads of 30 tons or more, with a high natural frequency and excellent linearity. Seamlessly integrated into the pavement, these sensors enable fast, non-intrusive installation and real-time vehicle weight monitoring at speeds up to 120 km/h. This technology not only helps with monitoring traffic loads, but also supports bridge owners assess structural health and plan for maintenance or weight-based tolling to prevent overload damage. 

Structural Health Monitoring of bridges

Combining the WIM system with Structural Health Monitoring (SHM) provides bridge engineers with an enhanced solution. SHM measurement systems are based on accelerometers, strain gauges, and other types of sensors which are placed at key points on the bridge. For instance, accelerometers may measure vibrations in the center of the concrete piers or monitor the whole structure to register any significant changes in the bridge’s natural frequency, which indicates possible damage. The quality of the results depends on the sensitivity, frequency range, temperature stability, and linearity of the sensors. Measurement expert Kistler offers accelerometers with a wide frequency range of 0 to 1500 Hz and an operating temperature range of –55 to +125°C. 

Structural health monitoring systems allow real-time monitoring of bridge movement, vibration and deflection, while WIM systems collect live load data from both regular and overloaded trucks. This comprehensive approach enables precise calculations of a bridge’s remaining life expectancy beyond standard load assumptions. 

Looking ahead, Weigh In Motion and Structural Health Monitoring systems could be further augmented with third-party technology to gather detailed data from multiple locations, offering deeper insights into heavy traffic patterns across states. AI technology plays a crucial role in aggregating and analyzing large data sets, facilitating data-driven traffic management to enhance the road safety and protect highways, and bridges. In the future, Kistler solutions and a network AI-supported camera technology could provide even more detailed data, enabling transport authorities to trace the exact routes of overloaded vehicles, track uninsured motorists, and issue tickets.