Structural Health Monitoring Based on Vibration Signature Analysis
The concept of using heterogeneous sensor measurements to obtain insight into the condition of structures and systems under arbitrary dynamic environments has been a subject of great interest to the science and engineering community for many decades. Its scope covers a wide spectrum of applications ranging from monitoring the health of aerospace structures to detecting damage in civil infrastructure systems. As an example, as early as 1970 the offshore industry evaluated the utility of this concept for monitoring the condition of offshore platforms, but found it impractical because of the limitations in computational capacity of the period. Due to the challenging nature of the technical problems associated with this topic, over the past 30 years substantial research efforts have been undertaken by many researchers in many areas related to this broad, interdisciplinary field. More recently, there has been a resurgence of interest in the field due to the remarkable advancement in sensor technology and computational power and the economic feasibility of deploying sensors and associated data acquisition systems in conjunction with PCs to provide dense networks of measurements, with much higher spatial resolution than had previously been feasible.
However, in spite of these remarkable developments on many fronts, there are still major technical hurdles that need to be overcome before the approach under discussion becomes useful for practical application.
While there are many techniques and approaches involved in the nondestructive evaluation (NDE) of structural systems, they can all be broadly categorized as local or global methods, or alternatively, micro or macro methods. The first category includes methods designed to provide information about a relatively small region of the system of interest by utilizing local measurements. The second category uses measurements from a dispersed set of sensors to obtain global information about the condition of the system. Clearly, the two approaches are complementary, with the optimum choice of method highly dependent on the scope of the problem at hand and the nature of the sensor network. An overview of NDE approaches for condition assessment is available in Housner et al.
The NDE methodologies for structural health monitoring will be used to leverage the major investment that the Federal Emergency Management Agency (FEMA) has made by the deployment of an extensive state-of-the-art sensor network in a critical facility in Southern California (the Long Beach Public Safety Building). The building, which is currently undergoing a $30M seismic retrofit, has already been instrumented with high-resolution strong motion accelerometers, and will be instrumented in the near future with an array of other sensors: conventional strain gages, fiber-optic strain gages, acoustic emission sensors, and laser-based sensors for floor displacement measurements. The timing of the retrofit provides a unique opportunity to obtain field data on the changing structural characteristics as the retrofit progresses in time.