ODERBRÜCKE PROJECT INSIGHTS (3/4)
Implementation of CFRP Hangers: Testing, Approval, and Manufacturing Excellence
The decision to implement CFRP hangers in the bridge design was not without significant challenges, requiring extensive testing and rigorous approval processes to ensure the safety, durability, and performance of the final solution. Given that CFRP hangers had never been used in a railway bridge before, a systematic approach was necessary to validate their viability under real-world conditions.
Validation Through Comprehensive Testing
The structural integrity and reliability of the CFRP elements were initially verified through a series of laboratory and real-world tests, executed at the prestigious EMPA research facility in Dübendorf, Switzerland. These tests focused on demonstrating the ability of CFRP hangers to withstand the demanding conditions typically encountered by railway bridges, such as high-frequency dynamic loads and long-term fatigue.
Fatigue Testing
One of the primary concerns with any structural component is its ability to withstand repeated loading without degradation over time. To address this, long-term cyclic loading tests were conducted on the CFRP hangers. These tests replicated the repeated stresses that occur with every train passing over the bridge, simulating years of service life in a matter of weeks. The results confirmed that the CFRP hangers had exceptional fatigue resistance, a key advantage over steel, which is prone to fatigue failure under continuous cyclic loading.
Static Load Tests
In addition to the fatigue testing, full-scale static load tests were performed to confirm the strength and reliability of the CFRP hangers under extreme loading scenarios. These tests subjected the hangers to much higher loads than they would ever encounter during typical operational conditions, ensuring that they could withstand potential accidental overloads without compromising structural safety. The static load testing reinforced the confidence that the CFRP hangers would perform reliably throughout their service life.
Expert Review and Structural Design Validation
Beyond the laboratory testing, the design and performance of the CFRP hangers were closely reviewed by independent experts. Prof. Dr.-Ing. Gerhard Hanswille, a renowned authority in engineering, provided an expert review of the results. Additionally, Schlaich Bergermann Partner (SBP), the engineering firm responsible for the overall structural design, played a critical role in calculating the load distribution across the structure and confirming the viability of the CFRP solution. With their extensive expertise in lightweight and high-performance structures, SBP was integral in ensuring that the use of CFRP hangers did not compromise the bridge's safety or functionality.
Securing ZiE Approval for the CFRP Hangers
Given the innovative nature of the CFRP hangers, it was crucial to obtain the necessary approval for their use in a railway bridge. In Germany, this required the “Zustimmung im Einzelfall” (ZiE), a special approval granted for individual cases involving new or innovative materials and systems. This approval was essential to demonstrate that the CFRP hangers met all regulatory and safety standards for railway infrastructure.
As part of the ZiE application, a comprehensive testing program was conducted, and the results were presented to the relevant authorities. The extensive testing, conducted by EMPA Dübendorf and thoroughly reviewed by independent experts, ultimately proved that the CFRP hangers met or exceeded all required safety and performance criteria for use in the demanding environment of a railway bridge. Remarkably, the outstanding fatigue strength of the carbon hangers was highlighted during testing when a hydraulic cylinder used to test the system failed due to fatigue, while the CFRP cables remained unaffected. This performance served as a strong testament to the exceptional durability and resilience of the carbon fibre hangers.
Manufacturing and Construction Excellence
Following successful testing and approval, the next critical phase of the project was the production and installation of the CFRP hangers. The manufacturing process was executed by Carbo-Link AG, a leader in the production of CFRP components, ensuring that every hanger met the exacting standards of precision, quality, and performance required for such a demanding application.
Precision in Prefabrication
One of the key advantages of using CFRP materials in the bridge hangers was the ability to achieve high precision in their prefabrication. Carbo-Link AG’s state-of-the-art manufacturing process allowed for the production of the CFRP cables to exact specifications, ensuring that minimal on-site adjustments would be necessary. This level of precision was essential for maintaining the integrity and performance of the structure, as even slight deviations from the design could affect the load distribution and performance of the entire system.
Efficient and Rapid Installation
The installation of the CFRP hangers was remarkably efficient. Thanks to the reduced weight of the CFRP cables, the installation process was streamlined. Using a mobile lift, the team was able to manually install the hangers, including the prestressing process, in just seven days. This rapid installation significantly reduced the construction time, leading to cost savings and minimizing disruption to the surrounding area. The reduced weight of the CFRP hangers also eliminated the need for heavy machinery, further simplifying the installation process.
Logistical Advantages
The use of CFRP also provided logistical benefits. Unlike steel cables, which are heavy and cumbersome to transport and handle, the CFRP hangers were much lighter, making them easier to move and install. This lighter weight reduced transportation costs and allowed for more efficient handling on-site, minimizing the complexity of logistics and the associated costs.
Looking Ahead
With the successful testing, approval, and manufacturing of the CFRP hangers, the project team has laid the foundation for a future in which lightweight, high-performance materials revolutionize the way we approach infrastructure design and construction. The innovative use of CFRP not only enhances the safety and performance of the railway bridge but also sets a precedent for the use of advanced materials in future infrastructure projects.
Stay tuned—next week, we’ll bring you the final part of this series, which will explore the impact of these innovations and look ahead to future applications of CFRP technology in infrastructure.
