Impulse Response Technique: A Valuable Non-Destructive Method to Detect Flaws

Impulse Response (IR) is a nondestructive testing technique in which “mobility” of the structural member under investigation is determined. Mobility is a complex ratio of particle velocity and the applied force. The test involves striking the surface of the structure with an instrumented hammer and measuring vibration response of the member. The time-domain data of the instrumented hammer (applied force) and the vibration sensor are collected and transformed into the frequency domain by the signal analyzer. The mobility of the member is obtained by calculating the transfer function of particle velocity and the applied force. The value of the mobility can be used to assess the condition of the member on a comparative basis. Tests can be performed on a variety of construction materials such as concrete, masonry, ceramic, thin steel or aluminum plates. The method has been successfully used to determine slab-on-grade support conditions, delaminations, voids, existence of grout under the machinery base plates or in concrete blocks or clay bricks. This paper presents a description and the equipment used in the method. In addition, case studies will be presented to show how the method was applied to document the internal conditions.