The lifeblood of our infrastructure: How modern bridge testing ensures safety and durability

Bridges are a vital part of our infrastructure, transporting people and goods safely across rivers, valleys and other obstacles. Steel bridges in particular, known for their high load-bearing capacity and durability, play a central role in rail and road transportation. But even these robust structures are not immune to aging or wear and tear.

The average lifespan of a steel bridge is usually between 80 and 120 years, depending on the construction method, load and environmental influences. Day after day, they are exposed to dynamic loads and climatic effects. These factors can significantly impair the load-bearing capacity and operational safety of steel bridges. The most significant loads include:

• Elevated traffic load: Heavy goods traffic is putting more strain on bridges than originally planned (160,000 times more than a car)
• Dynamic loads: Vibrations and oscillations caused by traffic can lead to fatigue cracks in the steel.
• Corrosion: Moisture, road salt and pollutants can attack and weaken the steel.
• Material fatigue: Prolonged repeated stress weakens the microstructure of the material.
• Extreme events: Accidents, floods or earthquakes can cause additional damage.

Optical emission spectrometry (OES) is a proven method for analyzing the chemical composition of steels. It can be used to precisely determine the content of carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), nitrogen (N) and other elements. This chemical analysis is the first step in identifying the steel and determining its properties. Mobile OES is especially suitable for this, as it results in only minor destruction and can be conducted on site. This eliminates the need to remove bridge material for laboratory analysis. 

The analysis results form the basis for determining which raw materials were used to build the bridge, such as puddle steel or materials based on a newer method. More modern processes such as the Bessemer or Thomas process involve less phosphorus, making the life expectancy of the material longer than that of puddle steel. Although phosphorus is necessary in order to increase the steel’s strength and hardness, an excessive phosphorus content leads to brittleness and makes the bridge more vulnerable to cracking. Once the raw materials used and the suitability for welding have been determined using OES, the next steps can be planned. This is why mobile OES is becoming increasingly important for bridge inspections.

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The bridges are assessed and classified on the basis of numerous aspects such as structural stability, traffic safety or durability. Based on these results, appropriate measures are taken as needed: 

• Welding repairs to eliminate cracks
• Reinforcement with additional beams or slabs
• Coatings for corrosion protection
• Replacement of damaged components

Digitalization and the use of innovative technologies are set to make bridge maintenance even more effective in the future. Combining precise measurements, modern data analysis and advanced repair techniques helps to guarantee the safety and longevity of bridges, enabling them to continue playing their vital role in our infrastructure. For a real-world example, we can look to the pilot project Smart City Dortmund. In this project, sensors have been installed at five selected bridges in the German city of Dortmund. The sensors measure inclination, strain, cracks and temperature in real time and continuously provide data on the condition of the bridges. The aim is to be able to monitor these bridges continually and enable predictive maintenance. Real-time monitoring thus makes constant risk management possible, which not only increases safety but also optimizes the control of traffic flows. In addition, continuous data analysis allows realistic cost plans to be drawn up for future renovations, which can deliver significant cost savings in the long term.

Bridge testing is more than just a routine technical process – it is crucial to maintaining our infrastructure. With methods such as mobile OES, systematic material analysis, and digital monitoring solutions, we can not only avoid acute hazards, but also effectively extend the service life of our bridges – for greater safety, efficiency and sustainability in the transportation sector.