Zhuojin Pipe Fitting Co., LtdFinite Element Analysis of Lateral Impact Resistance of Square Steel Tube Concrete Members with Built-in CFRP Profiles
Literature Overview
This 2022 paper by Li Guochang, Liu Lu, and Yang Zhijian from Shenyang Jianzhu University presents a comprehensive finite element investigation into the lateral impact behavior of square steel tube concrete (STC) members reinforced with built-in I-shaped carbon fiber reinforced polymer (CFRP) profiles. Supported by the National Natural Science Foundation of China (Grants 51878419 and 51938009), the research was published in Advances in Steel Construction. The work addresses an emerging structural concept where CFRP profiles are embedded within the concrete core of square steel tubes to enhance impact resistance.
Methodology and Technical Approach
The study employs ABAQUS explicit dynamic analysis to simulate the full impact process. A critical aspect of the methodology is the incorporation of strain rate effects on material properties, which is essential for accurate impact simulation. The Johnson-Cook constitutive model is typically used in such analyses to account for the strain rate sensitivity of both the steel tube material and the concrete core.
The parametric study varies four key parameters:
- Impact energy level
- Steel ratio (composite steel content)
- Shear span ratio
- Material strength (concrete and steel)
Key Technical Results
| Parameter Variation | Effect on Mid-Span Deflection | Effect on Peak Impact Force | Effect on Energy Dissipation |
|---|---|---|---|
| Impact energy (increase) | Increases | Increases significantly | Increases |
| Steel ratio (increase) | Increases | Increases significantly | Increases |
| Shear span ratio (increase) | Increases | Increases | Increases |
| Concrete strength (increase) | Minimal effect | Minimal effect | Moderate increase |
| Steel tube yield strength (increase) | Moderate increase | Increases significantly | Increases |
| CFRP profile presence | Reduces deflection | Increases capacity | Enhances dissipation |
Technical Discussion
The finding that peak impact force is barely influenced by concrete strength but is significantly affected by steel tube yield strength and steel ratio is particularly noteworthy from a pipe engineering perspective. This suggests that the steel tube shell dominates the dynamic load transfer mechanism during lateral impact. The concrete core primarily contributes to post-yield energy absorption rather than initial load resistance.
For steel pipe manufacturers supplying tubes for impact-resistant structural applications, this research indicates that increasing the yield strength of the steel tube (e.g., selecting API 5L X70 instead of X52, or using Q355 instead of Q235) provides more benefit for impact resistance than increasing concrete strength. This has direct implications for material selection in projects requiring impact protection, such as offshore platforms, bridge piers in ship-impact zones, and industrial structures subject to blast loading.
The incorporation of CFRP I-profiles within the STC cross-section represents an innovative hybrid approach. CFRP profiles offer high specific strength and stiffness without adding significant self-weight, and they do not corrode. However, their brittle failure mode requires careful consideration of ductility requirements. The study demonstrates that CFRP profiles enhance both energy dissipation and deformation capacity, suggesting that the steel tube and concrete core effectively constrain the CFRP profile against buckling and delamination during impact.
Engineering Practice Integration
In the context of steel pipe manufacturing, the integration of CFRP profiles within steel tube concrete members raises several quality control considerations:
- Pipe dimensional accuracy: The internal bore of the square steel tube must be sufficiently precise to allow CFRP profile placement and concrete placement without voids. For square tubes produced by box welding (HFW or SAW), dimensional tolerances per EN 10219 must be verified.
- Weld quality of box sections: Any weld defects in the box section (porosity, incomplete fusion, undercut) could serve as stress concentration points during impact loading. Non-destructive testing (NDT) per EN 10217-2, particularly phased array ultrasonic testing (PAUT), is recommended for critical applications.
- Residual stress management: The welding of box sections introduces residual stresses that may interact adversely with dynamic loading. Stress-relief welding or post-weld heat treatment should be considered for impact-critical applications.
Study Insights
The parametric study reveals that the shear span ratio significantly influences the failure mode transition between flexural and shear-dominated behavior. For practical design, maintaining a shear span ratio above 2.0 ensures a more ductile, flexure-dominated failure that maximizes energy absorption. This is consistent with general reinforced concrete design philosophy but has specific implications for STC members where the steel tube provides inherent shear confinement.
The research contributes to the growing body of knowledge on hybrid composite-steel-concrete structural systems and provides a validated FE methodology that can be adapted for other impact scenarios, including vehicle impact, falling object impact, and blast loading of steel tube concrete structures.