Dynamic Response of CFRP-Concrete-Steel Tube Composite Structures Under Low-Speed Lateral Impact

Literature Overview

Liu Ye, Wang Rui, and Li Zhigang from Taiyuan University of Technology published this research in the Chinese Journal of Explosives and Shock Waves (2018, Vol. 38, No. 4), investigating the dynamic response of Carbon Fiber Reinforced Polymer (CFRP)-concrete-steel tube composite structures under low-speed lateral impact. Supported by the National Natural Science Foundation (51378290), the study employs ABAQUS finite element modeling validated against experimental data, followed by orthogonal analysis of seven influencing parameters.

Technical Background and Application Context

Low-speed lateral impact represents a critical loading scenario for transportation infrastructure, including bridges, viaducts, and protective barriers. Unlike high-speed impact where dynamic material effects dominate, low-speed impact (typically below 15 m/s) involves quasi-static material response with significant geometric nonlinearity and progressive damage accumulation. The CFRP-concrete-steel tube composite system combines the high tensile strength and damage tolerance of CFRP, the compressive strength of concrete, and the ductility and energy absorption capacity of the steel tube.

The composite structure configuration typically involves a steel tube filled with concrete and externally wrapped with CFRP layers. This arrangement leverages the confinement effect of CFRP on concrete, the hoop reinforcement provided by the steel tube, and the synergistic energy absorption mechanisms of all three materials.

Finite Element Model and Validation

The ABAQUS model incorporates:

• Johnson-Cook or similar strain-rate-dependent model for steel tube
• Concrete Damaged Plasticity (CDP) model for concrete core
• Hashin or Puck failure criterion for CFRP layers
• Contact algorithms for interfacial interactions
• Explicit dynamic solver for impact simulation
• Mesh sensitivity analysis for convergence

The model was validated by comparing numerical predictions with experimental results, demonstrating good agreement in predicting impact force-time histories, displacement responses, and damage patterns. This validation confirms the model's capability to simulate the complex failure mechanisms in CFRP-concrete-steel tube composites.

Orthogonal Analysis Results

The orthogonal analysis examined seven factors: impact height (energy), hollow ratio, CFRP layer number, CFRP orientation, steel tube wall thickness, concrete strength, and specimen geometry.

Key findings from the analysis:

1. Impact height (directly related to impact energy) is the dominant factor controlling peak impact force, as expected from energy balance principles.
2. Hollow ratio is the primary factor affecting plateau impact force, with the optimal range between 0.3 and 0.7 where impact resistance increases with hollow ratio.
3. Residual deflection is governed by the combined effect of multiple parameters, indicating that structural stiffness degradation after impact is a complex multi-factor phenomenon.
4. CFRP layer orientation significantly affects the energy absorption mechanism—axial-oriented layers resist penetration while hoop-oriented layers provide confinement.

Process and Design Optimization Insights

The hollow ratio finding is particularly significant from a manufacturing and design perspective. A hollow ratio between 0.3 and 0.7 represents an optimal balance between material efficiency and impact resistance. Below 0.3, the structure is too massive and the concrete core provides most of the resistance. Above 0.7, the steel tube and CFRP must carry excessive loads without adequate concrete confinement.

For CFRP application, the layup sequence and orientation must be carefully designed. A balanced layup with both axial and hoop layers provides optimal multi-directional resistance. The number of CFRP layers must be optimized to avoid premature debonding while ensuring adequate tensile capacity.

Engineering Practice and Quality Control

From a fabrication standpoint, the quality of CFRP-concrete-steel tube composite structures depends on several critical factors:

1. Steel tube surface preparation: The exterior surface must be properly cleaned and prepared for CFRP bonding. Any oxide scale, mill scale, or surface contamination will compromise the adhesive bond strength. Shot blasting to Sa 2.5 standard is recommended.
2. CFRP layup quality: Vacuum infusion or hand layup with controlled resin content must ensure void-free composite layers. Delamination defects in CFRP significantly reduce impact resistance.
3. Concrete placement: The concrete must be placed without voids inside the steel tube. Vibration and compaction must be adequate to achieve uniform density. The concrete-steel tube interface must achieve proper bond through surface treatment or mechanical interlock.
4. Curing and bonding: The CFRP must be applied after concrete has achieved sufficient strength (typically 70% of design strength) to prevent damage during handling.

Study Insights and Reflections

This research demonstrates the effectiveness of CFRP-concrete-steel tube composite systems for low-speed lateral impact protection. The orthogonal analysis methodology provides an efficient approach to identifying critical design parameters without exhaustive parametric studies. The finding that hollow ratio optimally ranges between 0.3 and 0.7 has direct implications for structural design optimization, enabling significant material savings without compromising impact performance. Engineers designing impact-resistant composite structures should consider the multi-scale damage mechanisms—from CFRP fiber failure at the micro level to steel tube collapse at the macro level—and design for progressive failure modes that maximize energy absorption. The validated finite element model provides a powerful tool for design optimization and performance prediction under various impact scenarios.