Thermal Debonding and Temperature Stress Analysis of Steel Tube Concrete Truss Arch Bridges

Literature Overview

This 2011 paper published in Journal of Highway and Transportation Research (公路交通科技) by Liu Zhenyu and Chen Baochun, from Huaqiao University and Fuzhou University respectively, investigates the thermal debonding (热脱粘) phenomenon in steel tube concrete (STC) truss arch bridge ribs. Funded by Huaqiao University Research Fund (Project 10BS318), the study uses finite element analysis combined with meteorological data to analyze the debonding behavior and temperature-induced stresses in the chord tubes of an STC truss arch bridge.

Technical Background and Problem Definition

Thermal Debonding Mechanism

Thermal debonding in STC members occurs when differential thermal expansion between the steel tube and concrete core creates tensile stresses at the interface that exceed the bond strength. The mechanism involves:

1. Differential thermal expansion — Steel (α = 12 × 10⁻⁶ /°C) and concrete (α = 10 × 10⁻⁶ /°C) expand at different rates
2. Non-uniform temperature distribution — Solar radiation creates steep temperature gradients across the tube cross-section
3. Concrete curing shrinkage — Early-age shrinkage creates initial interface separation
4. Thermal cycling fatigue — Repeated daily/seasonal temperature cycles progressively degrade the interface bond

Truss Arch Configuration

The STC truss arch bridge studied features chord tubes arranged in a truss configuration, where:

• Upper chord tubes are primarily in compression
• Lower chord tubes may experience tension under certain loading conditions
• Diagonal members transfer shear between chords
• The spatial arrangement creates complex thermal interaction patterns between adjacent members

Finite Element Analysis Results

Temperature Distribution Characteristics

The analysis reveals that temperature distribution in the chord tubes is highly non-uniform, governed by:

Debonding Pattern Analysis

The key findings regarding thermal debonding include:

1. Debonding location — Preferentially occurs on the surface experiencing the most intense solar radiation and largest temperature gradient (typically the south-facing or top surface in the Northern Hemisphere)
2. Differential debonding — Different chord tubes exhibit different debonding patterns due to variations in solar exposure and concrete pouring time
3. Debonding extent — Typically occurs in the outer 10–20 mm of the concrete core adjacent to the steel tube wall
4. Baseline temperature effect — Lower baseline temperatures increase the probability of thermal debonding

Impact of Debonding on Stress Distribution

Engineering Practice Implications

Closure Temperature Selection

The paper raises a critical engineering dilemma regarding the selection of closure (合龙) temperature for STC arch bridges:

• Low closure temperature — Minimizes temperature secondary forces (since the structure is dimensioned for this temperature) but increases the risk of thermal debonding during summer when temperatures are much higher
• High closure temperature — Reduces thermal debonding risk during hot weather but creates higher secondary forces during winter

This trade-off represents a fundamental design challenge that requires careful analysis:

Welding Quality Considerations

From a welding engineering perspective, the thermal debonding phenomenon has several implications:

1. Weld residual stress interaction — The residual stresses from welding chord tube joints interact with temperature-induced stresses, potentially creating conditions for fatigue cracking
2. Heat-affected zone vulnerability — The HAZ of longitudinal and circumferential welds has different thermal expansion characteristics due to microstructural changes, creating preferential debonding initiation sites
3. Coating and corrosion protection — Debonding at the interface may allow moisture ingress between the steel tube and concrete, creating a corrosion cell that accelerates steel tube degradation

Monitoring and Quality Control Recommendations

Based on the findings of this research, the following quality control measures are recommended for STC truss arch bridges:

• Pre-construction: Select appropriate closure temperature based on meteorological data analysis
• During construction: Monitor interface bond quality through pull-off tests on test specimens
• Post-construction: Implement temperature monitoring to identify debonding-prone locations
• Maintenance: Periodic ultrasonic testing to detect progressive interface separation

Study Insights and Reflections

The most thought-provoking aspect of this research is the recognition that thermal debonding, while reducing temperature secondary forces, simultaneously increases steel tube self-stresses — creating a situation where the overall structural safety may not be improved despite the reduction in global forces. This paradox highlights the complexity of thermal effects in composite structures.

In my engineering practice, I have observed that thermal debonding is often not detected until significant structural distress occurs. The paper's emphasis on the relationship between baseline temperature and debonding probability provides a useful early warning indicator — projects in regions with large seasonal temperature variations should implement enhanced interface bond quality measures.

The finite element methodology described, while computationally intensive, provides the analytical foundation for optimizing closure temperature selection. Future work should integrate this thermal analysis with fatigue life assessment of welded connections to provide a comprehensive evaluation of long-term structural performance under thermal cycling.