Zhuojin Pipe Fitting Co., LtdSHPB Testing of High-Temperature Concrete-Filled Steel Tube Reactive Powder Concrete
Literature Overview
Guo Zhikun, Chen Wanxiang, Jiang Meng, and Zou Huihui (2017), from the State Key Laboratory of Explosion Shock Protection and Disaster Mitigation at the PLA University of Science and Technology, investigate the dynamic mechanical properties of concrete-filled steel tube reactive powder concrete (CFST-RPC) specimens after exposure to high temperatures using the Split Hopkinson Pressure Bar (SHPB) technique. The study, funded by the National Natural Science Foundation (Grants No. 51378498, 51578541) and Jiangsu Provincial Natural Science Foundation (Grant No. BK20141066), examines the effects of strain rate and temperature on the dynamic compressive behavior of CFST-RPC and plain RPC specimens.
Core Technical Approach
The SHPB test employs 75 mm diameter bars to conduct split Hopkinson pressure bar experiments on specimens at room temperature and after exposure to 200°C and 300°C. The strain rate range covers typical impact conditions encountered in blast and impact loading scenarios. The study compares the dynamic behavior of CFST-RPC specimens with plain RPC specimens to isolate the contribution of the steel tube confinement to the post-fire dynamic performance.
| Test Condition | Strain Rate Effect | Temperature Effect | Failure Mode |
|---|---|---|---|
| Room temperature | Toughness increases with strain rate | Baseline | Ductile (CFST-RPC) / Brittle (RPC) |
| 200°C exposure | Toughness increases with strain rate | Moderate degradation | Ductile (CFST-RPC) / Brittle (RPC) |
| 300°C exposure | Toughness increases with strain rate | Further degradation | Ductile (CFST-RPC) / Brittle (RPC) |
Key Findings and Engineering Implications
The results demonstrate that after high-temperature exposure, both the toughness and relative toughness of CFST-RPC specimens increase with strain rate, and at the same strain rate, they increase with the fire exposure temperature. This counterintuitive finding suggests that the steel tube confinement becomes more effective at higher temperatures as the concrete core loses strength and relies more on the steel tube for load-bearing. The energy absorption capacity of CFST-RPC increases with fire exposure temperature, while plain RPC shows minimal sensitivity to temperature. The failure mode remains ductile for CFST-RPC and brittle for plain RPC across all temperature conditions.
From a steel pipe manufacturing and welding perspective, this research has critical implications for the fire-resistant design of CFST structural members. The steel tube must be designed to maintain its mechanical properties at elevated temperatures, which directly influences the steel grade selection and welding procedure. High-strength steels such as Q460 or Q550 may experience significant strength reduction at 300°C, necessitating thicker wall sections or fire-protective coatings. The weld quality is equally critical, as welds are typically the weakest link in terms of high-temperature performance. Welding consumables must be selected to ensure adequate ductility and toughness at elevated temperatures, and post-weld heat treatment may be necessary to relieve residual stresses that could exacerbate thermal cracking.
Study Insights and Reflections
This research is particularly relevant for infrastructure in fire-prone environments, such as petrochemical facilities, nuclear plants, and offshore platforms. The finding that CFST-RPC maintains ductile failure even after high-temperature exposure is encouraging for structural safety, as ductile failure allows for energy dissipation and prevents catastrophic collapse. The SHPB testing methodology provides a reliable means to characterize the dynamic properties of composite materials under extreme conditions, which is essential for blast-resistant design. Engineers should consider these findings when specifying steel tube grades and welding procedures for CFST members in high-risk environments, ensuring that both the base material and the welds can withstand the combined effects of fire and impact loading.