SUBSTRUCTURAL ISOLATION METHOD FOR DAMAGE DETECTION IN CIVIL STRUCTURES

Abstract

Structural health monitoring (SHM) is the process of evaluating a structure with the use of sensors to provide an accurate representation of its current condition. Damage is identified, located, and quantified in order better understand the deterioration of the structure and allow for informed decision-making. Vibration-based damage detection uses accelerometers to measure the response of the structure due to ambient or applied loads and calculates modal properties based on the measured response. These modal properties (natural frequency, mode shape, modal damping) are functions of properties of the structure (mass, stiffness); thus, a change in modal properties can be an indicator of damage. Only a portion of each structure was investigated, using a process called substructuring. Substructuring is the process of studying only a small section of the structure and identifying local behavior. Using measurements from the boundaries of the substructure, a virtual force was calculated to restrain the boundary to zero response. The response of the isolated substructure was calculated by superimposing the (measured) global response with that from the applied virtual supports. The natural frequencies of the isolated substructure were then calculated and compared to the expected (undamaged) frequencies. A significant difference between the two indicated damage within the substructure. The substructural health monitoring technique is validated using a spring-mass and modeled beam. Local frequencies are shown to be sensitive to local damage, insensitive to damage outside of the substructure, and change with the severity of damage.