Environmental Temperature Effects on Hanger Vibration and Tension Measurement in Steel Tube Concrete Arch Bridges

Literature Overview

This paper by He Wei, Zhu Yafei, and He Rong (2016), published in Earthquake Engineering and Engineering Dynamics, addresses a critical practical problem in the maintenance and monitoring of steel tube concrete arch bridges. The study establishes a theoretical framework for hanger tension measurement that accounts for ambient temperature variations, which is particularly relevant for engineers involved in the fabrication, welding, and long-term structural integrity assessment of steel pipe components used in bridge hanger systems. The work is funded by Henan Provincial Basic and Frontier Technology Research Program (152300410241) and related provincial grants.

Core Technical Content

The authors derive the free vibration equation of hangers under variable temperature conditions based on Euler-Bernoulli beam theory, incorporating both prestress effects and thermal expansion of the steel pipe hanger members. The key relationship established is between hanger tension, temperature change, and transverse vibration frequency. The paper also analyzes the thermal over-buckling temperature rise conditions for hangers, which is directly relevant to the structural stability of slender steel pipe components under thermal loading.

Key Findings

• When ambient temperature remains constant, increasing tension results in increased natural frequencies of the same vibration mode.
• When tension remains constant, increasing ambient temperature causes a decrease in the natural frequency of the same vibration mode.
• For regions with large seasonal temperature differentials, the influence of ambient temperature on hanger tension measurement cannot be neglected.
• The proposed explicit formula incorporating temperature effects yields higher calculation accuracy and closer approximation to true values compared to temperature-independent models.

Technical Analysis from a Steel Pipe and Welding Perspective

Thermal Expansion and Steel Pipe Hanger Behavior

From a materials science perspective, the thermal expansion coefficient of structural carbon steel (typically 11.7 × 10⁻⁶ /°C per GB/T 700 and Q345 series steels commonly used in bridge construction) directly influences the hanger's effective length and thus its natural frequency. When the steel pipe hanger experiences a temperature rise ΔT, the thermal strain ε_th = α·ΔT induces additional compression that effectively reduces the axial tension in the hanger system. This phenomenon is particularly pronounced in long-span steel tube concrete arch bridges where hanger lengths may exceed 100 meters, amplifying the cumulative thermal effect.

Welding Considerations for Hanger Connections

The hanger connection welds—typically full-penetration groove welds or fillet welds joining the steel pipe hanger to anchor plates—are subject to cyclic thermal stresses during seasonal temperature variations. The coefficient of thermal expansion mismatch between the steel pipe and any dissimilar materials at the connection (such as galvanized coatings or composite dampers) can lead to fatigue cracking over time. Engineers should pay special attention to:

• Weld procedure qualification under cyclic thermal loading conditions
• Post-weld heat treatment to relieve residual stresses that may compound with thermal cycling
• Non-destructive testing (NDT) intervals adjusted for regions with extreme temperature ranges

Temperature-Compensated Tension Measurement Methodology

The explicit nature of the proposed equation is a significant practical advantage, as it eliminates the need for iterative numerical solutions during field measurements. This is particularly valuable for rapid assessment during bridge inspection campaigns where technicians need immediate tension readings to evaluate structural health.

Engineering Practice Implications

For steel pipe manufacturers and fabricators supplying hanger systems, this research highlights the need to:

1. Specify appropriate steel grades with controlled thermal expansion characteristics for hanger applications in extreme climate zones.
2. Design welding details and connection geometries that accommodate thermal elongation without inducing excessive stress concentrations.
3. Provide recommended temperature compensation factors in product technical documentation to assist bridge operators in accurate long-term monitoring.

The thermal over-buckling analysis is particularly important for slender steel pipe hangers with high slenderness ratios (L/D > 100). The critical buckling temperature rise can be estimated using the Euler buckling formula modified for initial imperfections, and this threshold must remain above the maximum expected service temperature to prevent catastrophic structural failure.

Study Insights and Reflections

This paper bridges the gap between structural dynamics theory and practical steel pipe component engineering. As a welding and materials engineer, I find the explicit formulation particularly valuable because it provides a straightforward tool for field technicians who must account for temperature effects without specialized computational resources. The research underscores that material properties—including thermal expansion coefficient, elastic modulus variation with temperature, and yield strength degradation at elevated temperatures—must be integrated into structural health monitoring protocols. For steel pipe fabrication quality control, this means that dimensional tolerances and straightness specifications for hanger pipes must be evaluated in the context of their thermal operating environment, not merely at ambient workshop conditions.