Multiple Reference Impact Testing of Bridges Using a Network of Low-Cost Dynamic Exciters

Multiple Reference Impact Testing (MRIT) is a form of Experimental Modal Analysis (EMA) that can be used to identify the dynamic properties of full-scale bridges. These dynamic properties include natural frequencies, mode shapes, damping ratios, modal scaling and modal flexibility. Since these system properties that are directly related to the mass and stiffness characteristics of a structure, impact test measurements can be used to quantitatively characterize condition of a structure. Over time, changes in the properties can be monitored and evaluated as indicators of damage or deterioration. Instrumented hammers and drop masses are typically used to perform MRIT by providing impulsive dynamic excitation to a structure. The corresponding vibration responses are measured using accelerometers. This approach has a number of practical and experimental shortcomings, including that the testing is time consuming, the impulsive forces produced can be variable, it interferes with the normal operation of the structure, and it is not suitable for continuous monitoring applications. The research herein, evaluates a new method for performing MRIT testing by comparing it to a conventional MRIT testing method. A small-scale and inexpensive excitation device is roved amongst spatially distributed input points to provide dynamic excitation. The excitation device can be inexpensively deployed in large numbers on a structure and programmed to produce a sequence of impulsive dynamic forces. This approach has several important advantages over conventional MRIT testing. For instance, total testing time is reduced, the impulsive forces produced are more repeatable, the testing can be accomplished without affecting the normal operation of the structure, and most importantly, it is amenable to long-term and continuous monitoring applications. The new MRIT approach is evaluated on both a large-scale laboratory model and full-scale bridge structure. The dynamic characterization results for both structures are compared with those obtained by the conventional MRIT approach using instrumented impact hammers