Viscous Damper Vibration Control for Semi-Floating System Concrete-Filled Steel Tubular Arch Bridges

Literature Overview

This paper by Peng Yihua, He Xuhui, Jing Haiquan, and Yan Lei (Journal of Railway Science and Engineering, Vol. 18, Issue 6, 2021, pp. 1504-1512) investigates the seismic energy dissipation performance of viscous dampers installed in semi-floating deck systems of concrete-filled steel tubular (CFST) arch bridges. Supported by the National Key R&D Program of China (2017YFB1201204), the National Natural Science Foundation of China (U1934209, 51708559), and the Hunan Provincial Natural Science Foundation (2019JJ50819, 2020JJ5754), the research addresses a critical seismic design issue for large-span CFST arch bridges. The study is conducted at Central South University's National Engineering Laboratory for High-Speed Railway Construction Technology.

Core Technical Content

The research focuses on a medium-deck CFST arch bridge with a calculated span of 252 m, which employs a semi-floating deck system. In this system, the main deck beam is supported by the arch ribs through vertical hangers but is not rigidly connected to the arch, allowing relative longitudinal displacement between the deck and the arch during seismic events. The viscous dampers are installed to control the deck beam's seismic response by dissipating kinetic energy through viscous resistance.

Dynamic Time History Analysis

The study employs nonlinear dynamic time history analysis to evaluate the seismic response of the bridge with and without viscous dampers. The analysis incorporates:

• Nonlinear material models for steel (CFST arch ribs) and concrete (deck beam).
• Nonlinear viscous damper models with appropriate damping coefficient and velocity exponent.
• Real earthquake ground motion records scaled to the design seismic intensity.
• Soil-structure interaction effects at the bridge bearings.

Seismic Response Comparison

The analysis reveals the following key findings regarding the effect of viscous dampers on the bridge's seismic response:

Damper Parameter Selection

The study develops a methodology for selecting appropriate viscous damper parameters (damping coefficient and velocity exponent) based on the bridge's seismic performance objectives. The selection process considers:

• The target reduction in deck displacement response.
• The acceptable increase in arch crown displacement.
• The modification of force distribution in the arch ribs.
• The damper's capacity to withstand the expected relative displacements without damage.

The viscous damper force-displacement relationship is characterized by the equation:

F = C × |v|^α × sign(v)

where F is the damper force, C is the damping coefficient, v is the relative velocity across the damper, and α is the velocity exponent (typically 0.2-1.0 for viscous dampers).

Engineering Practice Implications

This research has direct relevance to the steel pipe and fitting industry in several important ways:

1. CFST arch rib fabrication: The arch ribs of CFST arch bridges are typically fabricated from large-diameter steel tubes (300-800 mm OD) that are filled with concrete. The steel tubes may be seamless, LSAW, or spiral-welded depending on the diameter and application. The fabrication quality of these tubes directly affects the seismic performance of the bridge. Key quality requirements include:

• Uniform wall thickness within tight tolerances (±0.5 mm or ±10% of nominal)
• Freedom from surface defects (cracks, folds, laps)
• Consistent mechanical properties (yield strength, elongation, impact toughness)
• Proper concrete fill density and strength

1. Weld joint integrity: The arch rib fabrication involves longitudinal welds (for LSAW or spiral-welded tubes) and potentially circumferential welds for field splicing. These welds must achieve full penetration with uniform mechanical properties. The welding process (typically SAW for longitudinal welds and SMAW or FCAW for circumferential welds) must be qualified through welding procedure qualification (WPQ) and welder performance qualification (WPQ).
2. Viscous damper connection details: The connection between the viscous damper and the bridge structure involves critical steel components and weld joints. These connections must be designed to accommodate the full range of expected relative displacements without damage. The connection steel components (typically fabricated from structural steel plates and tubes) require careful weld design to ensure ductile behaviour under cyclic loading.
3. Seismic design standards: The seismic design of CFST arch bridges must comply with relevant standards including:

• GB 51210 (Code for Seismic Design of Highway Bridges)
• JTG/T 2232 (Specifications for Seismic Design of Highway Bridges)
• TB 10003 (Code for Seismic Design of Railway Bridges)
• Eurocode 8 (Seismic Design of Structures)

1. Quality control for seismic components: The quality assurance programme for seismic components should include:

• Material certification and mechanical property verification
• Weld NDT (UT, MT, PT) with acceptance criteria per relevant standards
• Dimensional inspection of fabricated components
• Load testing of viscous dampers to verify force-displacement characteristics
• Installation inspection to ensure proper alignment and clearance

Key Questions and Reflections

The study provides valuable insights into the seismic energy dissipation performance of viscous dampers in semi-floating CFST arch bridges but several aspects warrant further investigation. First, the long-term durability of viscous dampers under cyclic loading and environmental exposure (temperature, humidity, UV radiation) should be evaluated through accelerated aging tests. Second, the interaction between multiple dampers installed at different locations along the bridge deck should be examined, as the force distribution may be non-uniform during seismic events. Third, the effect of damper damage or failure on the bridge's seismic performance should be assessed to ensure progressive collapse resistance.

From a welding engineering perspective, I note that the connection details for viscous dampers involve complex weld geometries where cyclic loading is expected. The weld design must account for fatigue effects, with appropriate weld detail categories assigned per relevant fatigue design standards (e.g., GB/T 19830 or Eurocode 3 Part 1-9). The welding process should be optimized to minimize residual stresses and to achieve uniform microstructure in the HAZ. Post-weld treatment such as low-temperature stress relief may be beneficial for critical connections.

Study Insights and Implications

This research demonstrates that viscous dampers can significantly improve the seismic performance of semi-floating deck CFST arch bridges by reducing deck displacement responses while maintaining acceptable force distributions in the arch ribs. The developed damper parameter selection methodology provides a practical tool for engineers designing seismic energy dissipation systems for similar bridge configurations. For the steel pipe and fitting industry, the study highlights the critical importance of fabrication quality, weld integrity, and connection design in seismic applications. The research contributes to the ongoing development of seismic design guidelines for large-span CFST arch bridges and underscores the need for rigorous quality control in the fabrication and installation of seismic components.