Ultra-High Performance Steel Tube Concrete Bridge Structure Design and Analysis

Literature Overview

This paper by Gong Yunxia and colleagues from Chang'an University, Chongqing University, and Yunnan Provincial Design Institute, published in the Journal of Highway and Transportation Research and Development (2024, Vol. 41, No. 6), presents a comprehensive design study of ultra-high performance steel tube concrete (UHPC-STC) composite bridge structures. The research was supported by the National Natural Science Foundation of China (Grant 52008026), the China Postdoctoral Science Foundation (Grant 2021M692746), and a central university research project. The study focuses on medium-span underpass bridges and proposes three bridge type schemes: composite truss girder bridge, tied-arch bridge, and cable-stayed slab bridge, all utilizing UHPC rectangular steel tube concrete as the primary load-bearing structural members.

Core Technical Approach

The research promotes the application of UHPC rectangular steel tube concrete composite structures as the primary load-bearing members of bridge structures, leveraging their high bearing capacity, high durability, construction convenience, and high prefabrication degree. The study creatively incorporates carbon fiber reinforced polymer (CFRP) hanger rods, CFRP prestressing tendons, and cold-formed rolled U-shaped cross beams combined with UHPC bridge deck panels. Finite element analysis was performed on each design structure to evaluate strength, stiffness, stability, and dynamic characteristics, with all verification results meeting code requirements.

Material and Fabrication Considerations

The use of UHPC in combination with steel tubes introduces significant fabrication and welding challenges that differ from conventional CFST applications. UHPC, with compressive strengths typically ranging from 120 to 200 MPa, requires specialized concrete technology including high-volume powder systems, optimized particle grading, and superplasticizers. The steel tubes used for UHPC-STC members are typically rectangular or square cross-section welded steel pipes, fabricated from high-strength structural steel grades such as Q345B, Q420, or higher.

The welding of rectangular steel tubes for UHPC-STC members requires careful attention to several factors. First, the high compressive strength of UHPC imposes greater hoop stresses on the steel tube, which means that the welds in the steel tube must be designed to withstand higher internal pressures. The longitudinal and transverse welds in rectangular steel tubes are subject to complex stress states that include membrane tension, bending, and shear. The welding procedure must ensure full fusion and adequate penetration to prevent weld defects that could initiate under the combined action of UHPC confinement pressure and structural loads.

Second, the CFRP components (hangers, prestressing tendons, stays) introduce additional fabrication complexity. CFRP materials have significantly different mechanical properties and thermal expansion characteristics compared to steel. The connection between CFRP components and steel structures requires specialized anchorage systems that can transfer loads without stress concentrations that could damage the CFRP. The welding of steel connection plates to the steel tube members must be performed with controlled heat input to avoid thermal distortion that could affect the alignment and fit-up of CFRP components.

Structural Performance Analysis

The finite element analysis results reveal distinct performance characteristics for each bridge type. The simply supported composite truss girder exhibits good dynamic characteristics with moderate stiffness and stability. The continuous composite truss girder offers more balanced member utilization and higher material efficiency, though with relatively lower vertical stiffness. The tied-arch bridge provides high vertical stiffness but suffers from relatively poor transverse stability. The cable-stayed slab bridge combines high vertical stiffness with good transverse stability, though at a significantly higher material cost.

The dynamic characteristics of the simply supported composite truss girder are particularly favorable, with natural frequencies well above typical vehicle-induced excitation frequencies, minimizing the risk of resonance. The stability analysis confirms that all proposed structures meet the buckling resistance requirements under both serviceability and ultimate limit states. The use of CFRP components contributes to weight reduction and corrosion resistance, which is particularly beneficial for bridge structures exposed to harsh environmental conditions.

Engineering Practice and Technical Economic Analysis

The technical economic analysis provides a valuable basis for bridge type selection. The continuous composite truss girder emerges as the most economically favorable option with a material cost ratio of 0.97 relative to the simply supported truss girder baseline. The tied-arch bridge is slightly more expensive at 1.02, while the cable-stayed slab bridge is significantly more costly at 1.83. However, the economic comparison must be balanced against construction performance and aesthetic considerations. The composite truss girder bridge offers superior construction performance due to its modular, prefabricated nature, while the tied-arch and cable-stayed bridges provide more distinctive architectural aesthetics.

From a welding and fabrication perspective, the prefabrication degree of the composite truss girder bridge is the highest, which aligns with modern construction trends toward off-site fabrication and rapid on-site assembly. The rectangular steel tube concrete members can be fabricated in workshops under controlled conditions, ensuring consistent weld quality and dimensional accuracy. The on-site assembly primarily involves mechanical connections and grouting, minimizing the need for field welding. This approach reduces the risk of weld quality issues associated with field welding conditions such as weather, accessibility, and operator fatigue.

Study Insights and Conclusions

This research represents a significant advancement in the application of UHPC and CFRP materials in bridge engineering through the innovative use of UHPC rectangular steel tube concrete composite structures. The study demonstrates that these advanced materials can be effectively integrated into bridge design to achieve high bearing capacity, high durability, and high prefabrication degree. From a fabrication and welding standpoint, the key challenges lie in ensuring the integrity of steel tube welds under high UHPC confinement pressure and in designing reliable CFRP-steel connection systems. Engineers should establish comprehensive fabrication quality assurance programs that include weld procedure qualification for high-pressure confinement conditions, specialized CFRP anchorage testing, and rigorous dimensional control of prefabricated components. The economic and technical analysis provides a clear basis for bridge type selection, with the continuous composite truss girder offering the best balance of cost, material efficiency, and construction performance. This research opens new possibilities for lightweight, durable, and rapidly constructable bridge structures that meet the demands of modern transportation infrastructure development.