Distributed Structural Damage Generated by High-Frequency Ground Motion

Abstract

Underground explosion generates high-frequency, short-duration, and large-amplitude ground motions which may cause damage to nearby surface structures. The commonly used damage assessment method in earthquake engineering cannot capture local damages and propagation properties of stress wave produced in a structure by such high-frequency ground motion. In the present study, damage assessment is developed at the material level for reinforced concrete structure excited by underground-explosion-induced ground motion. A numerical method of wave propagation in nonlinear and composite media is adopted to assess wave motion and structural damage of a two-story frame located at different surface distances from the underground explosion epicenter. A fracture indicator determined by equivalent tensile strain is defined to assess concrete damage, and a plastic indicator based on effective plastic strain is used to identify the plastic state of reinforcement. Ground velocity at the structural supports is used as input. The proposed material model is implemented in a commercial software \IAUTODYN\N through its user-supplied subroutines. Distributed concrete damage induced by high-frequency response is simulated. The effect of vertical ground motion is illustrated clearly. The numerical results show that the current design code based on ground motion peak particle velocity alone is rather conservative.