Nonlinear Analysis of Steel Pipe Concrete Composite Lattice Columns in High-Pier Large-Span Continuous Rigid Frame Bridges

Literature Overview and Engineering Context

The study by Zhan Yulin, Zhao Renda, Xu Tengfei, and Tang Chengping, published in Sichuan Building Science in 2009, investigates the nonlinear behavior of a pioneering bridge structure: the Baba Jinte Bridge on the Yaxi-Luzhou Expressway in Sichuan Province, China. This bridge represents the first application of steel pipe concrete composite lattice columns as high piers in a large-span continuous rigid frame bridge in China, marking a significant advancement in bridge engineering practice. The research was supported by the Southwest Jiaotong University Young Teacher Research Startup Project and the Sichuan Provincial Department of Transportation Science and Technology Project, reflecting the collaborative nature of the work between academia and industry.

The continuous rigid frame bridge, also known as a continuous rigid frame bridge, is a structural system that combines the advantages of continuous beam bridges and rigid frame bridges. In this system, the main girder and the pier are monolithically connected, creating a continuous structure that provides favorable load distribution and high stiffness. The use of steel pipe concrete composite lattice columns as the pier structure introduces a novel composite structural system that leverages the high strength-to-weight ratio of steel pipe concrete and the structural efficiency of the lattice configuration.

Core Technical Points and Structural Configuration

The steel pipe concrete composite lattice column, as implemented in the Baba Jinte Bridge, consists of multiple steel pipe concrete members arranged in a lattice pattern to form a column structure with high stiffness and load-bearing capacity. The lattice configuration provides several structural advantages: it distributes the loads from the bridge deck among multiple load paths, it provides redundancy in the event of member failure, and it offers favorable aesthetic properties that are important for bridge design in scenic locations.

The nonlinear analysis conducted by the authors established a three-dimensional numerical model that accounts for the composite behavior of the steel pipe concrete cross-section, including the interaction between the steel tube and the confined concrete core. The analysis was performed for both construction stages and the completed bridge state, recognizing that the structural behavior during construction can differ significantly from the as-built behavior due to the sequential loading and the time-dependent properties of concrete.

The composite action between the steel tube and the concrete core is the fundamental mechanism that provides the superior performance of steel pipe concrete members. The steel tube provides lateral confinement to the concrete, which increases the concrete's compressive strength and ductility beyond what would be achievable with unconfined concrete. Conversely, the concrete core prevents local buckling of the steel tube under compressive loading, creating a mutually beneficial interaction that results in a composite member with higher strength and greater ductility than either component alone.

Nonlinear Analysis Methodology and Results

The three-dimensional nonlinear numerical model developed by the authors incorporates several critical nonlinear effects that are essential for accurately predicting the behavior of the composite lattice column under service and ultimate limit state loading. Geometric nonlinearity accounts for the large displacements and rotations that occur in the slender lattice members, particularly under lateral loads such as wind and seismic forces. Material nonlinearity captures the elastic-plastic behavior of the steel tubes and the nonlinear stress-strain relationship of the concrete, including the progressive cracking and crushing that occurs under high compressive stresses.

The construction stage analysis is of particular importance because the structural behavior during construction can differ significantly from the as-built behavior. During construction, the lattice members are erected sequentially, and the concrete is placed and cured in stages. The time-dependent properties of concrete, including creep and shrinkage, cause progressive changes in the internal force distribution that can lead to significant secondary stresses in the completed structure. The nonlinear analysis for construction stages must account for these time-dependent effects to accurately predict the final structural state and ensure that the stresses during construction do not exceed the allowable limits for the partially completed structure.

The key finding from the nonlinear analysis is that the steel pipe concrete composite lattice column provides significantly higher stiffness than conventional pier configurations, and that the transverse connections between the lattice members play a critical role in controlling lateral deformation. The transverse connections, which may be implemented as welded or bolted steel plates, braces, or diaphragms, create a rigid framework that distributes lateral loads among all lattice members and prevents differential lateral displacement between adjacent members.

Welding and Manufacturing Considerations for Lattice Columns

The fabrication and assembly of steel pipe concrete composite lattice columns involves complex welding operations that require careful planning and execution to ensure structural integrity. The lattice configuration creates numerous connection nodes where multiple steel pipe members intersect, and each node requires precise fit-up and high-quality welds to ensure the structural continuity of the lattice framework.

The welding of the lattice members at the intersection nodes presents unique challenges compared to conventional structural welding. The three-dimensional nature of the connections, with members joining at various angles, requires the use of multi-pass welding techniques and careful weld sequencing to minimize residual stresses and distortion. The weld geometry at these nodes is complex, with potential overlap between adjacent welds, and the accessibility for inspection and repair may be limited by the lattice configuration.