Eccentric Compressive Performance of Bolted-Welded Joint Composite Components for Large-Span Rigid Frame Steel Tube Concrete Arch Bridges

Literature Overview

This research paper investigates the eccentric compressive mechanical performance of a novel bolted-welded joint composite component designed for large-span rigid frame steel tube concrete (STC) arch bridges. The study combines experimental testing, finite element analysis, and theoretical modeling to characterize the load-bearing capacity, deformation behavior, and failure modes of the joint under eccentric compression. The composite component integrates bolted connections and welded connections in a hybrid arrangement, combining the advantages of both connection types to achieve improved structural performance.

Structural Design and Configuration

The proposed joint component is designed to connect steel tube concrete arch ribs to the rigid frame structure of the bridge. The component consists of a steel sleeve that encases the end of the steel tube concrete arch rib, with bolted connections providing the primary load transfer mechanism and welded connections providing additional restraint and stiffness. The hybrid bolted-welded configuration is intended to combine the ductility and ease of field assembly of bolted connections with the stiffness and continuity of welded connections.

The eccentric compression loading condition is particularly relevant for arch bridge joints because the actual loading state rarely involves pure axial compression. Eccentricity arises from load eccentricity, geometric imperfections, and construction tolerances, and can significantly reduce the load-bearing capacity of the joint. The study systematically investigates the effect of eccentricity ratio on the joint performance, providing design guidance for practical engineering applications.

Test Specimen Parameters

Experimental Results and Analysis

The experimental program involved testing full-scale joint specimens under eccentric compression loading. The specimens were instrumented with strain gauges, displacement transducers, and load cells to capture the complete load-deformation response. The test results revealed several important characteristics of the joint behavior.

Under pure axial compression (eccentricity ratio of zero), the joint exhibited a well-defined elastic stage followed by a gradual yielding stage and a stable plastic stage. The ultimate load capacity was significantly higher than the theoretical axial capacity of the steel tube concrete arch rib alone, indicating that the joint provides additional load-bearing contribution through the interaction of the sleeve, bolts, and welds. The failure mode under pure axial compression was characterized by local buckling of the steel tube wall near the joint interface, with the concrete core providing significant confinement and load-carrying capacity.

As the eccentricity ratio increased, the load-bearing capacity decreased progressively, and the deformation behavior became more asymmetric. The tension side of the joint experienced bolt elongation and potential slip, while the compression side experienced increased local deformation and possible crushing of the concrete. The study found that the joint maintained ductile behavior up to eccentricity ratios of 0.15, with only a gradual reduction in capacity. However, at eccentricity ratios exceeding 0.20, the joint exhibited a more brittle failure mode with sudden capacity loss.

Load Capacity vs. Eccentricity Ratio

Finite Element Analysis

The finite element model was developed using shell elements for the steel components and solid elements for the concrete core. The bolted connections were modeled using spring elements representing the bolt stiffness, while the welded connections were modeled using tie constraints. The concrete material was modeled using a constitutive model that accounts for confinement effects, while the steel material was modeled using an elastic-plastic constitutive relationship.

The finite element results showed good agreement with the experimental results, validating the modeling approach. The stress distribution analysis revealed that the bolt forces were not uniformly distributed, with higher forces developing in bolts located on the compression side of the joint. This non-uniform bolt force distribution is an important design consideration, as it means that the bolt group cannot be assumed to share the load equally.

The weld stress analysis showed that the welds experienced significant stress concentrations, particularly at the weld toe where the weld transitions to the base metal. The maximum weld stresses were observed under eccentric loading conditions, with the tension side welds experiencing the highest tensile stresses. The study recommends that weld quality control be particularly stringent for eccentrically loaded joints, with emphasis on achieving full penetration and minimizing weld defects.

Relevance to Pressure Vessel and Cladding Engineering

While this study focuses on bridge engineering, the fundamental principles of hybrid bolted-welded connections are directly applicable to pressure vessel fabrication. In clad plate pressure vessels, the connection between the cladding layer and the backing plate is essentially a bonded-welded interface, and understanding the load transfer mechanisms is critical for ensuring structural integrity. The eccentric loading analysis provides insights into how asymmetric loads affect the bond strength and stress distribution at the clad-backing interface.

The study's approach to combining experimental testing with finite element analysis is a methodology that can be directly applied to cladding interface characterization. Engineers working on bimetal pressure vessels can adopt similar approaches to study the stress distribution at clad-backing interfaces under various loading conditions, including thermal stresses, internal pressure, and external mechanical loads.

Study Insights and Recommendations

The most important finding from this study is that the hybrid bolted-welded joint configuration provides significantly improved performance compared to either bolted-only or welded-only connections. The bolts provide the primary load transfer capacity while the welds provide additional stiffness and restraint, resulting in a joint that is both strong and ductile. This hybrid approach is consistent with the philosophy used in clad plate fabrication, where the combination of mechanical bonding and metallurgical bonding provides superior interface integrity.

The study also highlights the critical importance of eccentricity in joint design. In pressure vessel applications, thermal expansion differences between dissimilar metals can create significant eccentric loads at interfaces. The findings suggest that joint designs should be evaluated under eccentric loading conditions, not just pure axial loading, to ensure adequate safety margins. The recommended maximum eccentricity ratio of 0.15 for acceptable ductile behavior provides a useful design criterion that can be adapted for pressure vessel interface design.

For engineering practice, the recommendations include careful attention to bolt preload control, weld quality assurance, and consideration of eccentric loading effects in design calculations. The hybrid connection approach offers a promising solution for applications requiring both high strength and good ductility, and the methodology developed in this study can serve as a template for evaluating similar hybrid connections in pressure vessel and cladding applications.