Unlocking the Secrets of Long-Term Creep in Concrete-Filled Steel Tube Bridges
When it comes to modern bridge engineering, few projects have captured global attention quite like the Tian’e Longtan Bridge in China.
Stretching across the Hongshui River with a world-record arch span of 600 metres, it stands as a symbol of engineering ambition and precision. Yet, behind its grandeur lies a challenge that continues to puzzle engineers: how to ensure the long-term stability of concrete-filled steel tube (CFST) structures when subject to complex internal stresses.
Concrete-filled steel tubes are the backbone of such massive arch bridges, combining the compressive strength of concrete with the tensile resilience of steel. However, as spans increase, the core concrete often experiences internal debonding when encased by steel, creating potential weak points. Expansion agents have been introduced to offset early shrinkage, but the long-term creep behaviour of this material inside steel tubes has remained largely uncharted territory.
The Study Behind the Breakthrough
To tackle this question, a joint research team from Guangxi University, Guangxi Polytechnic of Construction, and Dongguan University of Technology launched a comprehensive study entitled Long-term creep behaviour of expansive agent core concrete in full-scale concrete-filled steel tube from the world’s largest span arch bridge study. The project focused on understanding how expansive agent-modified concrete behaves when confined within large-scale CFST specimens.
The researchers split the radial expansion of core concrete into two stages: debonding and restriction. By drawing on elastic and linear creep mechanics, they devised a mathematical model capable of describing both stages seamlessly through piecewise functions. This model was then tested against full-scale CFST specimens derived from the Tian’e Longtan Bridge.
Testing Full-Scale Specimens
The research went beyond laboratory samples, conducting 114-day measurements on CFST specimens measuring 0.92 metres in diameter, 12 metres in length, and 0.01 metres in wall thickness. Some specimens included expansion agents, while others did not. This dual testing approach allowed the team to validate the creep model under real-world construction conditions.
The results were telling. A debonding gap of 0.142 mm formed before the initial setting of the core concrete. Overall radial expansion reached 290.1 × 10⁻⁶, with 158.3 × 10⁻⁶ absorbed to close the debonding gap, and 131.8 × 10⁻⁶ contributing to self-stress in the steel tube. Over a six-month period, the radial creep stabilised, leaving a residual expansion of 26.4 × 10⁻⁶ and residual self-stress of 0.119 MPa.
Why Expansion Agents Matter
One of the critical findings of the study was the role expansion agents play in maintaining stress consistency within CFST. Without expansion agents, axial deformation revealed that constraining forces from the steel tube diminished towards the core due to localised yielding. By contrast, specimens with expansion agents showed a more uniform distribution of stress, effectively mitigating weak spots.
This suggests that expansion agents not only counter early shrinkage but also contribute to the long-term load-bearing stability of CFST structures. As bridges like Tian’e Longtan push the boundaries of span and design, such insights are invaluable.
Implications for Future Bridge Construction
The significance of this study extends far beyond a single bridge. As civil engineers continue to design and build record-breaking spans, understanding material behaviour over decades becomes mission-critical. Creep, often overlooked in early design phases, can alter the internal stress balance, potentially leading to durability concerns if left unaddressed.
By incorporating the deformation data of laboratory specimens into the full-scale model, the research team created a practical tool that aligns closely with field measurements. This alignment strengthens confidence in predictive models used during the design of future CFST bridges.
A Global Context
While this research was based in China, the implications resonate internationally. Across the globe, from Europe’s vast rail viaducts to Africa’s emerging transport corridors, CFST technology is gaining traction for its efficiency and resilience. The addition of expansion agents, coupled with an informed understanding of long-term creep, could redefine how such projects are approached.
For policymakers and investors, this offers reassurance that large-scale CFST structures can be designed with a higher degree of certainty regarding their service life. For construction professionals, it highlights the importance of adopting new material strategies backed by rigorous research.
Bridging Innovation with Durability
The paper, authored by Zheng Chen, Changjie Wu, Ben Chen, Yang Yang, Weiying Liang, Yunchao Tang, and Jielian Zheng, not only presents ground-breaking findings but also sets the stage for future investigations into long-term material performance. By proving that laboratory and field data can align, the team has paved the way for more predictable, safer, and more durable CFST bridges.
“The introduction of laboratory specimen deformations improves the practicality of the model, and the results show a good agreement between the measured data and the model” the authors concluded, underscoring the importance of bridging theory with practice.
Building Confidence in the Future
As global infrastructure faces the dual pressures of rapid growth and the need for long-term resilience, studies like this shine a light on the path forward. The Tian’e Longtan Bridge is more than a record-breaking span; it is a proving ground for new engineering frontiers.
By mastering the subtleties of concrete creep and the benefits of expansion agents, the industry is better equipped to deliver the next generation of megastructures with confidence.
