Application and Analysis of Steel Tube Concrete Dumbbell-Shaped Section Arch Bridges

Literature Overview

The paper by Chen Lirong and Chen Baochun (2016), published in the Journal of Guangxi University (Natural Science Edition), presents a comprehensive survey of steel tube concrete (CFST) dumbbell-shaped section arch bridges. The authors collected extensive data from existing constructed bridges across China to establish statistical ranges for key design parameters including rise-to-span ratio, span-to-height ratio, section aspect ratio, and material properties. This study was supported by the Ministry of Housing and Urban-Rural Development's engineering construction standard formulation plan (2011-1-59), underscoring its role in standardization efforts for this bridge type.

Core Technical Parameters and Statistical Findings

The study reveals several critical statistical trends that are highly relevant to steel pipe selection and fabrication:

The dumbbell-shaped section, which consists of two circular steel tubes connected by a central web plate, represents a hybrid structural concept that leverages the confined concrete behavior of circular CFST elements while achieving a rectangular overall profile suitable for deck integration. From a steel pipe manufacturing perspective, the consistent h/d ratio near 2.5 across all span ranges indicates that pipe diameters and wall thicknesses can be standardized effectively across projects, simplifying procurement and welding inspection protocols.

Interpretation of Section Force Characteristics

The dumbbell section concentrates compressive forces in the two outer steel tubes during normal loading conditions, while the central web primarily transfers shear between the tubes. This force distribution pattern has direct implications for welding quality requirements:

• The upper chord tubes experience sustained high compressive stresses combined with bending, making weld integrity at tube-to-web connections critical for long-term performance.
• The lower chord tubes serve as the primary tension members during construction phases before concrete hardening, requiring careful control of residual stress in the longitudinal welds of ERW or HFW pipes.
• The web plate-to-tube fillet welds are subject to cyclic loading from traffic and wind, necessitating fatigue assessment in accordance with Eurocode 3 or AASHTO LRFD fatigue categories.

Engineering Practice Implications for Pipe Fabrication and Welding

Based on the statistical findings, several practical recommendations emerge for steel pipe suppliers and fabricators:

1. Pipe geometry standardization: With h/d consistently around 2.5, pipe diameters in the 400–800 mm range with wall thicknesses of 12–25 mm dominate the market for medium-to-large span CFST arch bridges. Fabricators should prioritize seamless or HFW pipes meeting ASTM A515 or GB/T 8163 specifications for these applications.
2. Welding process selection: The connection welds between circular tubes and web plates typically require full-penetration groove welds with SMAW or FCAW processes. For wall thicknesses exceeding 20 mm, multi-pass welding with appropriate interpass temperature control (below 250°C for carbon steel) is essential to prevent HAZ softening.
3. Non-destructive testing requirements: Given the criticality of tube-to-web connections, 100% UT examination of groove welds and MT or PT of fillet welds should be mandated. The confined concrete environment means that any weld defect is effectively unreparable after concreting, making pre-concreting inspection absolutely essential.

Key Questions and Reflections

The statistical approach adopted by the authors provides valuable empirical data but raises important questions from a materials and welding perspective. The study does not address how pipe manufacturing method (seamless vs. HFW vs. LSAW) affects the long-term performance of dumbbell sections under sustained compressive loading. In practice, the anisotropy of rolled plates used in LSAW pipes can influence the buckling behavior of thin-walled tubes under high confinement pressures. Furthermore, the effect of pipe surface roughness on the bond strength between steel tube and core concrete deserves more attention, as this directly affects the composite action efficiency.

Study Insights and Implications

This literature provides a solid empirical foundation for the preliminary design of CFST dumbbell-section arch bridges. For welding engineers involved in bridge fabrication, the key takeaway is that the geometric regularity of this section type allows for the development of standardized welding procedures, consistent NDE protocols, and predictable quality assurance plans. The consistent aspect ratios across span ranges mean that qualified welding procedures developed for one project can be readily transferred to subsequent projects with minimal requalification, provided that wall thickness ranges remain within the original WPS parameters. Future research should integrate pipe manufacturing quality indices into structural performance models to establish clear traceability between material origin and structural behavior.