Dynamic Testing and Vehicle-Bridge Coupled Vibration Analysis of CFT Stiffened Skeleton Basket-Handle Arch Bridge

Literature Overview

The study by Shi Zhou, Xia Zhaoguang, and Ge Yumei (2006), published in the Journal of the China Railway Society, Vol. 28, No. 4, pp. 95-101, presents full-scale dynamic testing and vehicle-bridge coupled vibration analysis of a 140-meter span railway steel tube concrete (CFT) stiffened skeleton basket-handle arch bridge. The research employs the ambient vibration method (pulsation method) for measuring self-vibration characteristics, and conducts dynamic load tests with test trains traveling at various speeds and performing braking maneuvers at designated locations.

Core Technical Content and Methodology

The CFT stiffened skeleton basket-handle arch bridge represents an advanced bridge type that combines the structural efficiency of CFT arch ribs with the aerodynamic and aesthetic advantages of the basket-handle (tied-arch) configuration. The stiffened skeleton system provides additional lateral and torsional stiffness to the arch, which is particularly important for railway bridges subject to dynamic train loading.

Dynamic Testing Methodology

The dynamic testing program included the following components:

1. Ambient vibration testing (pulsation method): The self-vibration characteristics of the bridge were measured using ambient traffic excitation, with accelerometers deployed at strategic locations on the bridge deck and arch ribs. The natural frequencies, mode shapes, and damping ratios were extracted from the measured time-history data using spectral analysis techniques.
2. Dynamic load testing: Test trains passed through the bridge at multiple constant speeds, and braking maneuvers were performed at specified locations. The strain, displacement, and acceleration time-history responses of the bridge span structure were recorded under each test condition.
3. Vehicle-bridge coupled vibration analysis: The measured dynamic responses were compared with theoretical predictions from vehicle-bridge coupled vibration calculations, which account for the dynamic interaction between the moving train and the bridge structure.

Key Dynamic Performance Findings

Dynamic Amplification Factor Analysis

The dynamic amplification factor (DAF) represents the ratio of the dynamic response to the static response under moving train loads. The research findings indicate:

• The measured dynamic responses and dynamic amplification factors are in good agreement with the theoretical vehicle-bridge coupled vibration calculation results.
• Both the measured and calculated dynamic responses exhibit consistent trends with increasing train speed.
• The dynamic amplification factor increases with train speed, as expected, but remains within acceptable limits for all tested speed ranges.

Self-Vibration Characteristics

The ambient vibration testing revealed the following self-vibration characteristics:

• Multiple vertical, lateral, and torsional modes were identified within the frequency range of interest.
• The first-order vertical frequency and lateral frequency provide the primary dynamic response characteristics for train-bridge interaction.
• The damping ratio of the bridge structure was determined from the decay of free vibration after the test train passed, providing critical input for dynamic analysis.

Engineering Practice Implications

Steel Tube Fabrication for Arch Ribs

The arch ribs of the CFT basket-handle arch bridge are fabricated from steel tubes that require careful attention to the following aspects:

1. Tube geometry and tolerances: The arch rib steel tubes must meet strict geometric tolerances to ensure proper alignment and load distribution in the arch structure. Ovality, straightness, and dimensional accuracy are critical parameters.
2. Welding of arch segments: The longitudinal and circumferential welds in the arch rib steel tubes are subject to combined compressive and bending stresses. The weld quality directly influences the arch rib's load-bearing capacity and fatigue resistance. Full-penetration butt welds with 100% NDE inspection (RT or UT) are recommended for primary structural welds.
3. Corrosion protection: Railway bridges are exposed to atmospheric corrosion, and the steel tube arch ribs require appropriate corrosion protection. The interior of the CFT arch ribs is protected by the concrete core, while the exterior requires coating or galvanization. The coating system must be compatible with the concrete placement process.

Vehicle-Bridge Interaction Considerations

The dynamic testing results have important implications for the design and maintenance of CFT arch railway bridges:

• The vehicle-bridge coupled vibration analysis confirmed that the bridge structure can safely accommodate the expected range of train speeds and braking conditions.
• The dynamic amplification factor should be included in the design load calculations for the arch ribs, deck, and hangers.
• Regular dynamic testing should be conducted as part of the bridge maintenance program to monitor changes in dynamic characteristics that may indicate structural degradation.

Summary

This research provides comprehensive dynamic characterization of a 140-meter span CFT stiffened skeleton basket-handle arch railway bridge through full-scale dynamic testing and vehicle-bridge coupled vibration analysis. The results confirm that the bridge possesses good vertical and lateral stiffness, adequate structural strength, and satisfactory overall dynamic performance under various train operating conditions. The good agreement between measured and calculated dynamic responses validates the vehicle-bridge coupled vibration analysis methodology for this bridge type. The findings support the applicability of CFT stiffened skeleton basket-handle arch bridges for large-span railway applications, with important implications for steel tube fabrication quality, welding standards, and dynamic design considerations.