Optimization of Hanger Tensioning Schemes for Steel Tube Concrete Arch Bridges

Literature Overview

Fu Jinlong and Huang Tianli (2016), from Central South University, published a study in Bridge Construction on the optimization of hanger tensioning sequences for steel tube concrete (SC) arch bridges. Supported by the National Natural Science Foundation of China (Grant 51478472), this research proposed five basic tensioning patterns and established rationality criteria for evaluating tensioning schemes. Using MIDAS Civil finite element modeling, the authors analyzed eleven specific tensioning schemes applied to a real SC arch bridge project, comparing structural stress states and hanger control forces.

Core Technical Findings

The study identified three primary tensioning strategies and their structural implications:

Tensioning Strategy	Structural Response	Practical Assessment
Symmetric sequential tensioning	Local stress concentrations in arch ribs and hangers	Easy to construct but risks overstressing local components
Symmetric alternating tensioning	More uniform stress distribution across components	Better structural safety but requires more complex scheduling
Multi-batch tensioning	Significantly reduced component stresses and control forces	Optimal for high-stress bridges; combines sequential and alternating approaches

Key Recommendations

For symmetric sequential tensioning, tensioning should proceed from the arch springing zone toward the crown zone to prevent excessive stress in the arch foot region.
For symmetric alternating tensioning, starting from a four-zone division or the arch springing zone ensures more uniform stress development.
Multi-batch tensioning, which divides the total hanger force into several increments, can reduce peak component stresses by 20–35% compared to single-batch tensioning.

Interpretation of Technical Points

Rationality Criteria for Tensioning Schemes

The authors defined rationality criteria based on:

Maximum component stress ratio (actual stress / allowable stress) should not exceed 0.8.
Maximum hanger force deviation from design value should be within ±5%.
Structural deformation should be symmetric and within specified tolerance limits.
Construction feasibility and safety margins must be maintained throughout the tensioning process.

Finite Element Modeling Considerations

The MIDAS Civil model incorporated geometric nonlinearity to account for large displacements during hanger tensioning, as well as material nonlinearity for the steel arch ribs and concrete cores. The steel tube concrete arch ribs were modeled using shell elements with composite material properties, while hangers were modeled as truss elements with initial prestress applied incrementally.

Integration with Engineering Practice

For bridge engineers and construction managers, this study provides a systematic framework for planning hanger tensioning operations:

The tensioning sequence directly affects the final stress state of the bridge; improper sequencing can lead to permanent damage or premature fatigue.
Multi-batch tensioning requires careful coordination of jacking equipment and monitoring systems, as each batch must be completed before the next begins.
Real-time monitoring of arch rib stresses and hanger forces during tensioning is essential to detect deviations from predicted behavior.
The study's rationality criteria can be adopted as acceptance criteria for tensioning scheme design in similar SC arch bridge projects.

Practical Case Considerations

In the case study bridge, the multi-batch symmetric alternating tensioning scheme reduced maximum arch rib stress from 312 MPa to 248 MPa (a 20.5% reduction) while keeping hanger control forces within 3% of design values. This demonstrates the significant benefit of optimized tensioning sequencing for structural safety and serviceability.

Study Insights and Reflections

This research bridges the gap between theoretical structural optimization and practical construction sequencing. The key insight is that the path to the final structural state matters as much as the final state itself—different tensioning sequences lead to different residual stress distributions and deformation histories. From a quality control perspective, this underscores the importance of detailed construction planning and real-time monitoring. Engineers should treat hanger tensioning not as a simple mechanical operation but as a critical structural event requiring the same analytical rigor as design calculations. The methodology presented here can be extended to other cable-stayed and arch bridge types, including steel tube concrete cable-stayed bridges and composite arch bridges, providing a transferable framework for construction optimization.