Thermal Stress Analysis in Continuous Rigid Frame Bridges Using Finite Element Modeling

Introduction

Thermal actions play a critical role in the long-term safety and durability of modern bridge structures, particularly continuous rigid frame bridges constructed with prestressed concrete box girders. Daily temperature variations, solar radiation, and environmental exposure create complex temperature gradients that induce internal stresses, often leading to cracking and reduced service life if not properly accounted for in design.

This research explores how temperature gradients influence stress distribution in a continuous rigid frame bridge using advanced finite element analysis (FEA). By understanding these thermal stress mechanisms, engineers can develop more resilient bridge designs. Visit https://www.civilenvironjournal.com/index.php/acee for more peer-reviewed research in civil and environmental engineering.

Understanding Thermal Stress in Box Girder Bridges

Continuous rigid frame bridges are particularly sensitive to temperature effects due to:

• Large span lengths
• Box girder geometry
• Poor thermal conductivity of concrete

Temperature differences between the interior and exterior surfaces generate self-balanced stresses, which can exceed concrete tensile strength and cause surface cracking.

Key mechanisms include:

• Vertical and horizontal temperature gradients
• Nonlinear temperature distribution across box girder sections
• Constraint effects from diaphragms and webs

Finite Element Modeling Approach

The study employed Midas Civil and Midas FEA software to simulate thermal stress behavior at both global and local levels.

Whole Bridge Analysis

• Modeled using beam elements
• Based on Chinese bridge design temperature gradients
• Evaluated stress variation under temperature rise and cooling scenarios

Zero Block Detailed Analysis

• High-resolution solid modeling of the critical zero block region
• Refined temperature gradient input
• Accurate capture of stress concentration zones

A detailed analysis can be found in our main journal article published by Annals of Civil and Environmental Engineering.

Key Findings from the Study

The numerical simulations revealed several important observations:

• Linear relationship between temperature gradient amplitude and thermal stress
• Upper box girder surfaces experience compressive stress during heating, while lower surfaces experience tensile stress
• Cooling conditions reverse the stress pattern
• Stress magnitude varies across bridge sections in the following order:
  Mid-span root > quarter-span > side span

Zero Block Stress Distribution

• Maximum thermal stress occurs between transverse diaphragms
• Diaphragms reduce longitudinal stress transfer but increase transverse restraint
• Surface stresses dominate within the top 20 cm of the box girder roof

Impact of Improved Temperature Gradient Control

Reducing the internal–external temperature difference significantly improves structural performance:

• ~60% reduction in thermal stress at the center of the zero block
• ~75% reduction at the ends of the zero block
• Improved temperature control directly lowers crack risk and enhances durability

According to guidance emphasized by organizations such as the American Society of Civil Engineers (ASCE), controlling environmental loading effects is essential for extending bridge service life and maintaining structural safety.

Engineering Implications and Design Considerations

Based on the findings, the study highlights several practical recommendations:

• Enhance surface reinforcement in box girder roofs
• Optimize diaphragm spacing to balance stress redistribution
• Consider temperature mitigation strategies during design
• Incorporate refined temperature gradient models in FEA

For broader insights into sustainable infrastructure research, explore resources available at civilenvironjournal.

Access the Full Research Study

The complete technical analysis and methodology are available in the published research article:
Read the full study at https://doi.org/10.29328/journal.acee.1001002

Conclusion

This study demonstrates that thermal stresses significantly influence the structural behavior of continuous rigid frame bridges. Advanced finite element modeling reveals that strategic control of temperature gradients can dramatically reduce stress levels, minimize cracking, and improve long-term performance. These insights provide valuable guidance for bridge designers, researchers, and infrastructure engineers.

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