Introduction

The structural performance of buildings and protective systems under extreme loading conditions, such as air blast loads, has become an area of critical interest, particularly for infrastructure security, military applications, and high-risk industrial facilities. One innovative solution to enhance the blast resistance of concrete structures is the use of laced reinforced concrete (LRC) combined with wood cover layers. This hybrid system merges the mechanical strength of laced reinforcement with the energy-absorbing and lightweight properties of wood, aiming to improve performance under dynamic, high-strain-rate conditions.

Explanation

1. Laced Reinforced Concrete (LRC)

Laced reinforced concrete is a modified form of traditional reinforced concrete where diagonal steel bars (laces) are added between vertical and horizontal reinforcement. These lacing elements create a truss-like internal structure that:

• Enhances shear capacity.
• Improves ductility and energy dissipation.
• Provides better crack control under dynamic loading.

This makes LRC particularly suitable for resisting high-intensity, short-duration loads like those from an air blast.

2. Wood Cover Layer

Wood, particularly hardwood or engineered wood panels, can serve as an external protective cover over concrete structures. Its advantages under blast loading include:

• Energy Absorption: Wood can deform and absorb significant blast energy before transferring it to the underlying concrete.
• Delay in Stress Transmission: Wood delays the impact wave, reducing the initial shock to the structural core.
• Lightweight Nature: It adds minimal dead load to the structure.
• Easy Replacement: Damaged wood layers can be replaced more easily than structural concrete.

3. Air Blast Load

An air blast load typically results from an explosion, producing high-pressure shock waves that act almost instantaneously on a structure. Important factors in blast analysis include:

• Peak overpressure (intensity of the blast).
• Impulse (pressure over time).
• Stand-off distance (distance from explosion center to structure).

These parameters significantly influence how a structure will respond.

4. Structural Analysis Considerations

To analyze the behavior of LRC with a wood cover under blast loading, several factors must be considered:

• Dynamic material properties of concrete, steel, and wood.
• Blast wave propagation and reflection effects.
• Nonlinear finite element modeling, especially for failure modes like cracking, crushing, and delamination.
• Time-history analysis to capture transient response and stress wave interactions.

Objective of the Analysis

The goal is to understand how well the composite system of LRC with wood covering withstands air blasts, by assessing:

• Reduction in spalling and scabbing.
• Improved blast energy dissipation.
• Delay and reduction in stress transmission to the core.
• Overall structural integrity and residual strength.