Ship-Bridge Collision Resistance of Sand-Filled Steel Pipe Pile Cofferdam

Literature Overview

The 2024 paper by Fang Hai, Ju Wei, Zhu Lu, Zhang Xinchen, and Yao Pengfei in the China Journal of Highway and Transport presents an innovative collision protection system using sand-filled steel pipe pile cofferdams for bridge piers. The study combines scaled physical testing (1:25 model), nonlinear finite element simulation, and parametric analysis to evaluate the energy absorption capacity of this novel protection device. Funded by the National Natural Science Foundation of China (52078248), this research addresses a critical infrastructure protection challenge with direct implications for steel pipe design, fabrication, and installation.

Core Technical Content

Test Configuration and Results

The scaled model was designed at 1:25 scale based on an actual bridge engineering project. The test compared bridge pier models with and without the sand-filled steel pipe pile cofferdam protection device under horizontal impact loading.

Energy Absorption Mechanism

The sand-filled steel pipe pile cofferdam operates through multiple energy dissipation mechanisms:

1. Plastic deformation of steel pipe piles — the steel tubes undergo local denting and global bending, absorbing kinetic energy through plastic work.
2. Sand compaction and particle rearrangement — the confined sand absorbs energy through densification, inter-particle friction, and stress redistribution.
3. Frictional interaction — relative movement between the ship hull and steel pipes generates frictional energy dissipation.
4. Pile-soil interaction — the embedded piles transfer forces to the surrounding soil through skin friction and end-bearing.

Parametric Study Results

The numerical study examined four impact scenarios with varying ship masses and velocities:

• Ship mass range: from smaller vessels to 200,000 t class
• Impact velocity: up to 3.97 m/s (approximately 14.3 km/h)
• Peak force reduction efficiency increases with both ship mass and impact velocity
• Maximum reduction rate of 38.11% achieved for a 200,000 t vessel at 3.97 m/s impacting the SZ02# South Tower

Interpretation of Technical Points

Steel Pipe Design Considerations

From a steel pipe manufacturing perspective, this application imposes specific requirements:

Sand Infill Material Selection

The choice of sand as the infill material is significant from an engineering standpoint:

• Grain size distribution affects compaction behavior and energy absorption capacity
• Density variation influences the effective mass and momentum transfer characteristics
• Moisture content affects inter-particle friction and energy dissipation
• Compaction level determines the initial stress state and subsequent deformation behavior

The sand serves as a controllable energy absorber whose response can be tuned through material selection and installation density. This is analogous to the concept of replaceable fuses in seismic design, where the energy dissipation element can be inspected and replaced after an impact event.

Connection with Engineering Practice

This technology represents a permanent-temporary combined protection approach (永临结合), meaning the cofferdam serves both as construction dewatering during bridge construction and as permanent collision protection thereafter. This dual-purpose design philosophy has significant economic advantages:

• Eliminates the need for separate temporary and permanent protection systems
• Reduces total project cost by integrating construction and protection functions
• Provides immediate protection during the construction phase when piers are most vulnerable
• Allows inspection and maintenance access through the cofferdam structure

For steel pipe suppliers and fabricators, this application opens new market opportunities in marine and bridge infrastructure. The key engineering challenges include:

1. Ensuring adequate impact toughness of steel pipe material at potential low-temperature service conditions
2. Maintaining weld integrity through the entire service life under cyclic marine environmental loading
3. Achieving proper sand infill density during installation without introducing voids or segregation
4. Ensuring corrosion protection system compatibility with potential sand abrasion

Key Questions and Reflections

A critical question concerns the long-term performance degradation of the sand-filled protection system. After repeated minor impacts or wave loading, does the sand compact further, reducing the available deformation capacity? Does the steel pipe accumulate fatigue damage from environmental loading that compromises its impact resistance? These questions are essential for maintenance planning and design life assessment.

Another important consideration is the interaction between the cofferdam and the bridge pier during an impact event. The FE model validation shows good agreement (<10% force error), but the simplified boundary conditions in the FE model may not capture the true three-dimensional soil-pile-pier interaction, particularly for large impact events where global pier movement becomes significant.

Study Insights and Implications

This research demonstrates that sand-filled steel pipe pile cofferdams provide a cost-effective, inspectable, and replaceable collision protection solution for bridges. The 34-38% peak force reduction is substantial and can prevent catastrophic pier damage from vessel impacts. For the steel pipe industry, this validates the use of standard line pipe products (API 5L / GB/T 9711) in collision protection applications, provided that impact toughness and weld quality requirements are met. The permanent-temporary combined concept is particularly attractive for large bridge projects where budget constraints and construction schedules demand integrated solutions. Future research should focus on full-scale testing, long-term performance monitoring, and development of design guidelines for practical engineering application.