🔷 Introduction

Reinforced concrete (RC) structures are widely used in both civilian and military infrastructure due to their strength, durability, and cost-effectiveness. However, under extreme loading conditions such as air blast loads—resulting from accidental or deliberate explosions—conventional RC beams may experience severe damage, including spalling, cracking, or even failure.

To improve blast resistance, advanced composite materials such as Glass Fiber-Reinforced Polymer (GFRP) bars are increasingly being explored. GFRP bars offer high tensile strength, corrosion resistance, and light weight, making them suitable for use in extreme environments. A spiral configuration of GFRP bars embedded within the RC beam offers additional advantages such as confinement, energy dissipation, and improved bonding performance.

This topic focuses on the structural behavior and analysis of RC beams reinforced with spiral GFRP bars when exposed to air blast loading. The objective is to understand how the spiral arrangement of GFRP bars influences the blast resistance, energy absorption, and overall performance of the RC beam.

🔷 Explanation of the Analysis

1. Materials and Reinforcement Configuration

• Concrete: Acts as the compressive medium in the beam. Under blast loading, it is prone to brittle failure modes such as spalling and crushing. In this example, the Johnson-Holmquist material model is selected.
• Spiral GFRP Bars: These act as tensile reinforcement and provide confinement to the concrete core, improving ductility and post-peak behavior. Their helical arrangement ensures better anchorage and stress distribution.
• GFRP Advantages:
  • Corrosion resistance (important in blast/fire conditions)
  • High strength-to-weight ratio
  • Electrically and thermally non-conductive

2. Blast Load Characterization

• Air blast load is typically modeled as a pressure-time history with a sharp rise (impulsive peak) followed by a decaying phase. In this case, the CONWEP air blast model is used.
• The load characteristics depend on:
  • Explosive type and weight
  • Standoff distance
  • Geometry and orientation of the beam

Blast loads can cause both flexural and shear failures, and the response is often dynamic and highly nonlinear.

3. Numerical/Analytical Modeling

Analysis can be performed through:

• Finite Element Modeling (FEM) using  ABAQUS to simulate dynamic response under blast loads.

4. Dynamic Response Parameters

Key outputs of the analysis include:

• Maximum deflection
• Crack initiation and propagation
• Failure modes (flexural, shear, punching, etc.)
• Energy absorption and damping

5. Design and Safety Implications

• Using spiral GFRP reinforcement can enhance the blast resistance of RC beams by improving:
  • Ductility
  • Energy dissipation capacity
  • Residual strength

🔷 Conclusion

The integration of spiral GFRP bars into reinforced concrete beams represents a promising advancement in blast-resistant design. Such reinforcement improves both the strength and ductility of RC beams, allowing them to better withstand and recover from air blast events. By using numerical simulations and experimental validations, engineers can optimize the design for real-world protective structures, ensuring safety and resilience under extreme loads.