How does heat affect flax footbridges
Marco Manconi defended his PhD thesis at the Department of Built Environment on March 25.
Bridges experience stress and deformation due to temperature changes caused by daily and seasonal fluctuations, as well as solar radiation. Research shows that these thermal effects can be as significant as, or even greater than, mechanical loads.
For his PhD research, Marco Manconi examined the thermal behavior of a flax-reinforced polymer (FRP) footbridges, addressing the challenges of moving from small-scale lab tests to real-world applications.
The research centers on a 15-meter flax-reinforced polyester footbridge in Almere, Netherlands, part of the Interreg Smart Circular Bridge (SCB) project. Completed in May 2022, this bridge is equipped with 82 fiber optic strain sensors and 8 thermocouples connected to an Internet of Things (IoT)-based structural health monitoring (SHM) system. This setup allows for real-time tracking of structural information and provides crucial data to validate computational methods.
Temperature effects and modeling
Manconi鈥檚 research includes a detailed approach to understanding how temperature affects flax-reinforced composite structures.
He turned to advanced modeling techniques that account for solar radiation, shading effects, and changing weather conditions. Data from specialized instruments like pyranometers and pyrheliometers were integrated for precise temperature predictions.
The analysis used by Manconi combines Honeybee Radiance software for solar radiation studies with Abaqus software for heat transfer simulations, linked by a custom Python script to ensure compatibility between data models.
Two key research aspects
Manconi鈥檚 research focused on two key aspects of temperature effects on structures made from flax fibers. First, he studied how heat moved through sandwich composite structures with insulating cores. Second, he looked at ways to compensate strain measurements from fiber optic sensors for temperature effects.
His focused on the thermal behavior of FRP bridges made from sandwich elements with foam cores. These cores, combined with the low thermal conductivity of flax fibers and polyurethane foam, create unique challenges in heat dissipation and temperature distribution.
Weather conditions
To test the proposed methods, Manconi and his colleagues used data collected from the Almere footbridge under various weather conditions.
He analyzed 18 years of meteorological data to identify extreme weather scenarios using statistical techniques. This allowed him to predict extreme temperature and solar radiation levels over a 50-year period.
Simulating temperature changes
Once Manconi validated the thermal model with real-world measurements, it was then used to simulate how temperature variations lead to stress in the bridge structure.
The analysis showed that thermal loads generated tensile, compressive, and shear stresses amounting to 20-26% of the material's strength limits. Advanced failure prediction criteria were applied to assess when and where damage might initiate under these complex stresses.
Another highlight of the research was the process by which the manufacturing process for the bridge was monitored with embedded sensors to track temperatures and residual strains during production over seven days.
Challenges unique to natural fiber composites were identified, emphasizing the need for further optimization of manufacturing processes to improve quality and consistency in large-scale flax composite structures.
Significant contribution
The research of Manconi and his colleagues makes a significant contribution to sustainable infrastructure by advancing knowledge about natural fiber-reinforced composites in structural applications.
It sheds light on how these materials behave under thermal stress and underscores the importance of comprehensive monitoring systems for ensuring their durability over time.
By developing a sophisticated framework for analyzing temperature effects under varying conditions, Manconi鈥檚 work addresses an important gap in understanding how flax-based composites perform in real-world structures like bridges.
Title of PhD thesis: . Supervisors: Faas Moonen, Patrick Teuffel, and Sandra Lucas.