Seismic Performance Test of Round-Ended Stainless Steel CFST Bridge Piers

Literature Overview

This experimental study by Zhao Qiuhong and colleagues from Tianjin University, published in 2022 in the Journal of Hunan University, presents a comprehensive pseudo-static testing program for round-ended concrete-filled stainless steel tubular (CFRST) bridge piers. The research, supported by the National Natural Science Foundation of China (51678406, 51878447), addresses the seismic performance of a novel structural system that combines the corrosion resistance of stainless steel with the structural efficiency of CFST construction, offering particular advantages for marine and coastal bridge applications.

Test Specimen Configuration

The study examines six test specimens with varying parameters:

The hollow sandwich configuration features an inner stainless steel tube within the outer tube, with concrete filling the annular space between them, creating a dual-tube confinement system.

Failure Modes and Ductility Performance

The experimental results reveal consistent failure patterns across all specimens:

• Primary failure mode: Bulging of the outer steel tube at the pier base, accompanied by localized concrete crushing at the bottom section.
• No sudden failure: All specimens exhibited gradual degradation of load-carrying capacity, indicating good ductility and warning before collapse.
• Hysteretic behavior: Full and plump hysteresis loops without significant pinching, demonstrating excellent energy dissipation capacity.

The ductility coefficient and energy dissipation capacity of CFRST specimens exceeded those of conventional CFRT (carbon steel) specimens, despite similar peak loads and initial stiffness values. This finding is particularly significant because it demonstrates that stainless steel CFST piers can achieve superior seismic performance without sacrificing initial structural stiffness.

Comparative Performance Analysis

CFRST versus CFRT (Stainless Steel vs. Carbon Steel)

Hollow Sandwich versus Solid CFRST

The strong-axis loading of hollow sandwich specimens outperformed solid specimens across all metrics, while weak-axis loading showed a mixed result where peak load and stiffness increased but ductility slightly decreased due to inward buckling of the inner tube's flat segment.

Horizontal Bearing Capacity Calculation

The authors propose a calculation method for the horizontal bearing capacity of CFRST bridge piers, validated against the experimental results with good agreement. The calculation approach considers:

1. The flexural resistance of the outer stainless steel tube.
2. The contribution of the concrete core, accounting for the enhanced confinement from the stainless steel tube.
3. The interaction between the outer and inner tubes in the hollow sandwich configuration.
4. The effect of axial load on the flexural capacity through P-Δ effects.

Engineering Practice Significance

The findings of this study have direct implications for bridge engineering practice:

• Corrosion resistance: Stainless steel CFST piers eliminate the need for protective coatings and cathodic protection systems, significantly reducing maintenance costs over the bridge lifecycle.
• Seismic design: The superior ductility and energy dissipation of CFRST piers make them particularly suitable for seismic zones, where deformation capacity is critical for preventing collapse.
• Marine applications: The combination of corrosion resistance and seismic performance makes CFRST piers ideal for coastal and offshore bridges exposed to both chloride-induced corrosion and seismic hazards.
• Weight optimization: The hollow sandwich configuration provides an alternative to solid sections, offering weight reduction while maintaining or enhancing structural performance.

Key Technical Challenges

From a manufacturing and construction perspective, CFRST bridge piers present several challenges:

• Stainless steel welding requires specialized techniques to prevent sensitization and intergranular corrosion in the heat-affected zone.
• The round-ended tube geometry requires precision forming processes to maintain dimensional accuracy and avoid localized thinning.
• Internal concrete placement in hollow sandwich configurations requires careful consideration of access and vibration methods.
• Quality control of internal welds and concrete-concrete interfaces in the sandwich configuration requires advanced non-destructive testing methods.

Study Reflections

This study represents a significant advancement in the understanding of stainless steel CFST structural systems for bridge applications. The experimental evidence clearly demonstrates that stainless steel CFST piers can achieve equal or superior seismic performance compared to carbon steel alternatives, while offering substantial advantages in durability and maintenance. The hollow sandwich configuration shows promise for further weight optimization, though the weak-axis performance degradation due to inner tube buckling suggests that geometric optimization is needed for this configuration. The proposed calculation method provides a practical tool for engineers, though further validation with additional experimental data across a wider range of parameters would strengthen confidence in its application. The study's focus on round-ended tubes, which are increasingly used in modern bridge design for their aesthetic and structural advantages, ensures practical relevance for current engineering practice.