Seismic Performance of Precast Concrete Bridge Piers with Embedded Steel Tubes

Literature Overview

The paper by Du Qing, Wang Junnan, and Qing Longbang, published in Building Technology in 2017 (Vol. 48, No. 8, pp. 830–832), investigates the seismic performance of precast concrete bridge piers with embedded steel tubes and prestressed steel strands. Funded by the Hebei Province Natural Science Foundation (E2014202257), this research from the School of Civil Engineering and Transportation at Hebei University of Technology presents quasi-static test results and finite element simulations of precast composite columns under cyclic loading.

Core Technical Content

Test Configuration and Results

Three concrete specimens with embedded steel tubes and prestressed steel strands were designed and tested through quasi-static experiments to investigate the cyclic response of precast composite columns. Key findings include:

• The ADINA solid finite element software was used to simulate the precast concrete bridge piers.
• The model test results showed good agreement with calculated results.
• High prestress composite columns possess higher strength and better energy absorption capacity.

Structural System Description

The precast bridge pier system incorporates:

Implications for Steel Pipe Manufacturing and Welding in Seismic Applications

Steel Tube Material Requirements for Seismic Applications

The embedded steel tubes in precast concrete bridge piers serve critical functions under seismic loading:

• Confinement of concrete core: Steel tubes provide lateral confinement that prevents concrete spalling and maintains structural integrity under cyclic loading. The confinement pressure depends on steel tube yield strength and wall thickness.
• Ductility enhancement: Steel tubes provide ductile behaviour that allows energy dissipation through plastic deformation. Material selection must ensure adequate elongation and strain hardening capacity.
• Crack control: The steel tube acts as a crack arrestor, limiting crack propagation in the concrete core. Surface quality and dimensional accuracy affect this function.
• Prestress transfer: In systems with prestressed strands, steel tubes may serve as tendon ducts or anchorage components, requiring specific material and manufacturing specifications.

Welding Quality for Seismic Applications

Welding in precast concrete bridge piers with embedded steel tubes presents unique challenges:

• Seismic qualification requirements: Welds must maintain ductility and energy dissipation capacity under cyclic loading. Weld procedures should be qualified for low-cycle fatigue and ductile fracture resistance.
• HAZ property control: The heat-affected zone of welds connecting steel tubes must exhibit properties comparable to the base metal. Softening or embrittlement in the HAZ can create weak links under seismic loading.
• Residual stress management: Welding residual stresses can interact with seismic loads to accelerate crack initiation. Post-weld stress relief or controlled welding sequences should be employed.
• Weld geometry and accessibility: In precast applications, weld accessibility may be limited. Weld procedures must be qualified for the actual welding positions and access conditions.

Manufacturing Quality Control for Seismic Steel Tubes

Steel tubes for seismic applications require enhanced quality control:

1. Material testing: Tensile testing, Charpy impact testing, and elongation verification at specified temperatures.
2. Dimensional verification: Wall thickness, diameter, and straightness verification through ultrasonic testing and dimensional inspection.
3. Surface quality: Magnetic particle testing (MT) for surface defects that could initiate cracks under cyclic loading.
4. Weld inspection: Radiographic testing (RT) or ultrasonic testing (UT) for volumetric weld defects.
5. Residual stress assessment: Strain gauge or neutron diffraction measurement of residual stresses to verify stress relief effectiveness.

Confinement Mechanism and Manufacturing Interface

The confinement provided by steel tubes is directly related to manufacturing quality:

Defect Analysis and Seismic Performance Implications

Manufacturing defects can significantly compromise seismic performance:

• Wall thickness non-uniformity: Creates localised stress concentrations that can initiate buckling under cyclic loading. Tubes with thickness variations exceeding ±10% of nominal should be rejected.
• Surface defects: Act as crack initiation sites under reversed cyclic loading. Surface defects exceeding specified limits should be repaired or the tube rejected.
• Weld defects: Lack of fusion, porosity, or cracks in welds connecting steel tubes create weak links that can fail prematurely under seismic loading. Full volumetric NDT is recommended for critical welds.
• Residual stress accumulation: From manufacturing and welding, can reduce the effective ductility of the steel tube. Residual stress levels should be verified and controlled through stress relief procedures.

Engineering Practice Recommendations

For the manufacturing of steel tubes for precast concrete bridge piers with seismic requirements:

• Material specification: Specify steel grades with verified mechanical properties, including yield strength, tensile strength, elongation, and impact toughness at service temperatures.
• Weld procedure qualification: Qualify welding procedures for cyclic loading conditions, including low-cycle fatigue resistance and ductile fracture resistance.
• Dimensional tolerances: Enforce tight tolerances on wall thickness, diameter, and straightness to ensure consistent confinement and load distribution.
• Surface quality: Specify surface finish requirements and implement inspection protocols to detect and control surface defects.
• Residual stress control: Implement post-weld stress relief procedures and verify residual stress levels through measurement.
• System-level testing: Conduct system-level cyclic loading tests to verify the interaction between steel tubes, concrete, and prestressed strands.

Study Insights and Manufacturing Perspective

This research demonstrates the effectiveness of embedded steel tubes in enhancing the seismic performance of precast concrete bridge piers. The finding that high prestress composite columns possess higher strength and better energy absorption capacity validates the design approach and highlights the importance of steel tube quality.

From a manufacturing perspective, the key insight is that the seismic performance of precast concrete bridge piers is fundamentally dependent on the quality of embedded steel tubes. The confinement mechanism that provides ductility and energy dissipation is directly related to steel tube material properties and dimensional accuracy. Any manufacturing defects that compromise these properties will directly reduce seismic performance.

The good agreement between FE simulation and experimental results validates the numerical modelling approach, but from a manufacturing standpoint, the critical takeaway is that the simulation assumptions must be verified through material testing and dimensional inspection. The model's accuracy depends on accurate input parameters, which must be obtained through rigorous quality control of manufactured steel tubes.

The research also highlights the importance of prestress in enhancing seismic performance. For steel tube manufacturers, this suggests that tubes serving as tendon ducts or anchorage components require specific manufacturing specifications to ensure proper prestress transfer and long-term durability. Surface finish, dimensional accuracy, and material properties must all be controlled to ensure effective prestress application and maintenance.

This study ultimately reinforces the principle that seismic design effectiveness depends on manufacturing quality. The theoretical benefits of embedded steel tubes in precast concrete bridge piers can only be realised if the tubes are manufactured to specifications that ensure consistent material properties, dimensional accuracy, and defect-free construction. Quality control protocols should be applied with particular emphasis on parameters that directly influence confinement effectiveness and cyclic loading resistance.