Temperature Load Analysis of Concrete-Filled Steel Tube Arch Bridges

Literature Overview

The research by He Xiongjun, Wen Wusong, and Hu Zhijian (Wuhan Jiaotong University and Wuhu Bridge Command of the Ministry of Railways, 2000) addresses the temperature load analysis of concrete-filled steel tube (CFST) arch bridges. Funded by the Wuhan Jiaotong University Provincial Training Fund, this study establishes a theoretical framework for analyzing arbitrary temperature loads on CFST composite materials, based on engineering practice accumulated over nearly a decade of CFST arch bridge development in China.

Thermal-Mechanical Coupling Analysis

CFST arch bridges are sensitive to temperature variations because the steel tube and concrete core have different coefficients of thermal expansion. When subjected to temperature changes, the differential expansion generates internal stresses that can significantly affect the structural behavior.

The differential expansion between steel and concrete generates interface stresses that can lead to:

• Separation of the steel tube from the concrete core at high temperatures.
• Compressive stresses at the interface during cooling.
• Cumulative damage over thermal cycles.

Arbitrary Temperature Load Analysis Theory

The authors propose a theoretical framework for analyzing arbitrary temperature loads on CFST composite materials. The key aspects of the theory include:

1. Temperature field distribution: The temperature distribution through the cross-section is assumed to be linear or nonlinear depending on the boundary conditions and heat transfer characteristics.
2. Strain compatibility: The strains in the steel tube and concrete core must be compatible at the interface, considering the differential thermal expansion.
3. Stress-strain relationships: The material constitutive models account for temperature-dependent elastic properties and plastic behavior.
4. Boundary conditions: The arch boundary conditions (fixed, pinned, or semi-rigid) significantly affect the temperature-induced stresses.

Structural Response to Temperature Loads

The temperature response of CFST arch bridges includes both global and local effects:

Global effects:

• Axial force changes due to differential expansion of the arch ribs.
• Bending moment redistribution between the arch ribs and deck systems.
• Vertical displacement of the arch crown.
• Horizontal thrust changes at the supports.

Local effects:

• Interface stresses between the steel tube and concrete core.
• Local buckling of the steel tube due to compressive thermal stresses.
• Cracking of the concrete core due to tensile stresses.
• Distortion of the arch cross-section.

Engineering Practice and Design Considerations

For CFST arch bridge design, temperature loads must be considered in accordance with relevant standards:

The temperature gradient across the arch rib cross-section can be significant, particularly for wide CFST arch ribs exposed to solar radiation. The top surface temperature may exceed the ambient temperature by 20-40 degrees Celsius during summer conditions, while the bottom surface may remain closer to the ambient temperature.

Welding and Fabrication Implications

From a fabrication perspective, the temperature load analysis has several implications:

• Welding residual stresses can interact with thermal stresses, potentially leading to premature fatigue failure at welded joints.
• The welding sequence should be planned to minimize asymmetric residual stresses that could compound with thermal loads.
• Post-weld heat treatment may be required to relieve residual stresses in critical connections.
• The welding procedure should account for the temperature-dependent material properties of the steel tube.

For CFST arch bridges, the steel tubes are typically fabricated from high-strength steel (Q345 or Q420) and welded into the required arch shape. The welding process introduces residual stresses that can reach 60-80% of the yield strength in the heat-affected zone. When combined with thermal loads during service, these residual stresses can reduce the fatigue life of the structure.

Key Questions and Reflections

The study from 2000 predates many recent advances in computational methods and material characterization. Modern finite element analysis software can more accurately model the thermal-mechanical coupling behavior of CFST arch bridges. However, the fundamental theoretical framework proposed by the authors remains valid and relevant.

A significant limitation of the study is the lack of experimental validation of the proposed theory. Temperature load testing on full-scale CFST arch bridges is challenging due to the difficulty of controlling and measuring temperature fields in outdoor conditions. Future research should incorporate long-term monitoring data from instrumented CFST arch bridges to validate and refine the theoretical models.

Study Insights and Implications

This research provides a foundational theoretical framework for analyzing temperature loads on CFST arch bridges. The recognition that arbitrary temperature loads must be considered in the design of CFST composite structures is essential for ensuring structural safety and serviceability. Engineers involved in CFST arch bridge design should integrate temperature load analysis into their structural analysis models, considering both uniform and gradient temperature effects. The interaction between welding residual stresses and thermal stresses should be carefully evaluated, particularly for welded connections that are critical to the structural integrity of the bridge.