Mechanical Performance of Hollow Sandwich Steel Tube Concrete Members Under Lateral Impact Loading

Literature Overview and Context

The paper by Shi Yanli, He Jiaxing, Xian Wei, and Wang Rui from Lanzhou University of Technology and Taiyuan University of Technology, published in 2019 in the Journal of Lanzhou University of Technology, investigates the mechanical behavior of hollow sandwich steel tube concrete (HSSC) members under lateral impact loading. The study was supported by the National Natural Science Foundation of China (Project No. 51768038), the Lanzhou Science and Technology Project (2019-1-61), and the Gansu Provincial Collaborative Innovation Team (2018C-08). The authors developed a finite element model using ABAQUS that accounts for the contact relationships between the steel tubes, the concrete, and the impactor, and validated the model against experimental data from a typical specimen.

Core Technical Content and Model Development

The hollow sandwich steel tube concrete member consists of two concentric steel tubes with a concrete core and a hollow space between the inner and outer tubes. This configuration offers several advantages, including enhanced energy absorption, improved impact resistance, and reduced weight compared to solid-filled steel tube concrete members. The finite element model developed by the authors includes:

• Explicit contact modeling between the outer steel tube, inner steel tube, concrete core, and impactor
• Appropriate material models for the steel tubes and concrete under dynamic loading conditions
• Validation against experimental data from a typical test specimen
• Parametric analysis of key geometric and material parameters

The key findings from the parametric analysis are:

1. The hollow ratio has a significant influence on the peak impact force, with higher hollow ratios leading to higher peak forces
2. The hollow ratio also affects the local deformation at the impact zone, with higher hollow ratios leading to greater deformation
3. The axial compression ratio significantly influences the plateau value of the impact force and the deformation development
4. For the same hollow ratio, the cross-sectional form of outer circle-inner square exhibits superior impact resistance compared to the double circle configuration

Interpretation of Technical Points

The hollow sandwich steel tube concrete configuration represents an innovative approach to structural design that leverages the advantages of both steel and concrete while optimizing the use of materials. The hollow space between the inner and outer tubes serves multiple purposes: it reduces the overall weight of the member, provides additional energy absorption through the deformation of the hollow space, and allows for the installation of utilities or additional reinforcement.

The impact loading scenario is particularly relevant for structures that may be subjected to accidental loads, such as vehicle impacts, falling objects, or blast loads. The ability to predict the structural response under impact loading is critical for the design of protective structures, including bridge piers, building columns, and industrial equipment supports.

The finite element model developed by the authors captures the complex interaction between the steel tubes and the concrete core under dynamic loading. The contact modeling is essential because the steel tubes and concrete can separate under impact loading, leading to complex contact and separation behavior. The material models used for the steel tubes and concrete must account for strain rate effects, which are significant under dynamic loading conditions.

The finding that the hollow ratio significantly affects the peak impact force is consistent with the principle that a higher hollow ratio reduces the effective cross-sectional area and stiffness of the member, leading to greater deformation and higher impact forces for a given impact energy. However, the increased deformation also means that the member absorbs more energy before failure, which is beneficial for impact resistance.

Integration with Engineering Practice and Welding Considerations

The fabrication of hollow sandwich steel tube concrete members involves several critical welding and forming operations:

The welding of the steel tubes is critical because the welds must withstand the impact loading without failure. The heat-affected zone of the welds may have different mechanical properties compared to the base metal, particularly in terms of ductility and toughness. Under impact loading, the welds may be the weakest links in the structure, and therefore require careful design and quality control.

The concrete placement in the hollow sandwich configuration is also challenging. The hollow space between the tubes must be filled with concrete without creating voids or honeycombing. The concrete mix must have adequate workability to flow into the confined space, and the vibration procedure must be effective in consolidating the concrete without damaging the steel tubes.

The parametric analysis provides valuable insights for the design optimization of HSSC members. The finding that the outer circle-inner square configuration offers superior impact resistance compared to the double circle configuration suggests that the cross-sectional geometry can be tailored to optimize the impact response. The square inner tube provides additional stiffness and load path continuity, which contributes to the improved impact resistance.

Key Questions and Reflections

The study raises several important questions for the steel pipe fabrication and welding industry. First, the study does not address the fatigue behavior of HSSC members under repeated impact loading, which is relevant for structures that may be subjected to multiple impact events. Second, the study does not discuss the long-term effects of corrosion on the impact performance of HSSC members, which is important for structures exposed to aggressive environments. Third, the parametric analysis is limited to the parameters investigated, and the influence of other factors such as impact angle, impact velocity, and temperature on the impact response remains unclear.

The study provides valuable insights into the impact behavior of HSSC members, demonstrating that the hollow ratio, axial compression ratio, and cross-sectional form are the key parameters influencing the impact response. The finding that the outer circle-inner square configuration offers superior impact resistance is particularly significant for design optimization, as it suggests that the cross-sectional geometry can be tailored to achieve the desired impact performance.

Study Insights and Implications

The paper provides a comprehensive analysis of the mechanical performance of hollow sandwich steel tube concrete members under lateral impact loading, demonstrating that the hollow ratio, axial compression ratio, and cross-sectional form are the key parameters influencing the impact response. The finite element model developed by the authors, validated against experimental data, provides a reliable tool for predicting the impact behavior of HSSC members under various loading conditions. For the steel pipe fabrication and welding industry, the study reinforces the importance of high-quality manufacturing of the steel tubes, with particular attention to welding quality, geometric tolerances, and material certification. The finding that the cross-sectional geometry can be optimized for impact resistance suggests that the design of HSSC members can be tailored to specific loading scenarios, offering a flexible and efficient structural solution for impact-resistant applications. The study serves as a valuable reference for engineers and fabricators working on HSSC structures, providing both experimental data and analytical tools for design and quality control. The innovative hollow sandwich configuration offers a promising approach to impact-resistant structural design, combining the advantages of steel and concrete while optimizing the use of materials and the structural response under dynamic loading.