Failure Modes of Precast Segmental Concrete-Filled Double-Skin Steel Tube Piers Under Large-Scale Explosion

Literature Overview

Published in Explosion and Shock Waves (Vol. 43, No. 11, 2023), this comprehensive study by Xia Mengtao and colleagues from Southeast University's Ministry of Education Engineering Research Center for Explosion Safety Protection investigates the failure modes of precast segmental concrete-filled double-skin steel tube (PS-CFDST) piers under large-scale field explosion tests. The research is supported by multiple National Natural Science Foundation grants, China Postdoctoral Science Foundation, and Jiangsu Provincial Natural Science Foundation.

Structural System Description

The PS-CFDST pier system is designed for precast bridge substructure applications where blast resistance is a critical design requirement. The key structural features include:

Double-skin steel tube: An inner and outer steel tube with concrete infill, providing enhanced confinement and blast energy absorption.
Precast segmental construction: The pier is assembled from precast segments connected by post-tensioned prestressing tendons.
Post-tensioned prestressing: High-strength steel tendons provide axial pre-compression to the assembled pier, improving resistance to lateral blast loads.

Design Parameters

Parameter	Description
Structural type	Double-skin steel tube concrete-filled
Assembly method	Precast segmental with post-tensioning
Loading condition	Large-scale ground surface explosion
Analysis method	Field explosion test + LS-DYNA finite element simulation
Key variables	Axial load level, tendon modeling approach, segment joint behavior

Key Findings from Explosion Testing

Failure Mode

The dominant failure mode observed was overall pier failure caused by post-tensioned prestressing tendon rupture. This is a critical finding because it identifies the prestressing system as the governing weak link in the PS-CFDST pier under extreme blast loading, rather than the steel tube or concrete core.

Damage Distribution

Segment joint shear slip: Significant shear displacement was observed at the bottom joint of the pier body, indicating that joint integrity is a critical design consideration.
Core concrete damage: Concrete damage concentrated at segment joints and at locations where prestressing tendons compressed the concrete, suggesting stress concentration effects.
Steel tube response: The double-skin steel tube maintained relatively better integrity compared to the concrete and prestressing components.

Numerical Simulation Insights

The LS-DYNA finite element analysis provided additional insights:

The modeling approach for prestressing tendons has a significant influence on the predicted dynamic response of the precast segmental pier. This underscores the importance of accurate tendon material modeling and boundary condition representation in blast simulation.
Increasing axial load reduces lateral deformation and bottom shear slip, thereby improving the overall blast resistance of the PS-CFDST pier. This finding has direct implications for design optimization — higher precompression levels can enhance blast performance.

Welding and Fabrication Considerations

For the double-skin steel tube fabrication in this application:

Fabrication Aspect	Technical Requirement
Outer tube welding	Full-penetration butt welds for blast load transfer
Inner tube welding	High-quality welds to maintain confinement integrity
Inter-tube connection	Robust structural connections to prevent relative displacement
Segment end preparation	Precision-cut pipe ends for proper joint alignment
Weld inspection	Full NDT coverage (UT + RT) for critical welds

The double-skin steel tube configuration requires careful welding sequence planning to minimize residual stresses in both tubes. The inner tube should be welded first, followed by the outer tube, with intermediate stress-relief treatments if necessary. The connection between the inner and outer tubes must be designed to accommodate differential thermal expansion during welding while maintaining structural continuity during blast events.

FMEA Analysis of Critical Failure Modes

Failure Mode	Severity	Occurrence	Detectability	RPN	Mitigation
Prestressing tendon rupture	10	6	5	300	Increase tendon redundancy and ductility
Segment joint shear failure	9	7	4	252	Improve joint shear key design
Steel tube local buckling	7	4	6	168	Increase tube wall thickness
Concrete spalling at joints	6	5	7	210	Add joint sealant and confinement
Tendon-concrete bond loss	8	3	6	144	Use bonded tendons with corrosion protection

Study Insights and Engineering Recommendations

This research provides essential data for the design of blast-resistant precast bridge piers using the PS-CFDST system. The identification of prestressing tendon rupture as the governing failure mode is a pivotal finding that should redirect design attention toward tendon protection and redundancy. For steel pipe fabrication engineers, the double-skin steel tube technology represents an advanced manufacturing challenge that demands high-precision welding, rigorous quality control, and thorough non-destructive testing. The finding that increased axial load improves blast performance suggests that optimizing the prestressing level is a viable design strategy. However, the study also reveals that the modeling assumptions for prestressing tendons in numerical simulations significantly affect predicted behavior, which means that analytical design methods must be validated against physical test data. Future work should explore tendon protection strategies, such as incorporating sacrificial layers or ductile tendon materials, and should investigate the long-term performance of precast segmental joints under cyclic blast-like loading conditions.