Mass normalized mode shape identification of bridge structures using a single actuator-sensor pair

Identifying mode shapes of bridge structures typically require a dense array of stationary sensors to accurately capture mode shapes with appropriate spatial resolution. An alternative approach is developed here, which requires only a single pair of actuator and sensor. The mode shape identification involves, first, identifying the natural frequencies and modal damping ratios, followed by an estimation of the mass normalized mode shapes components at the excited and measured degrees of freedom. An input-output balance is employed with a series of inputs and outputs obtained from a sequence of tests. The sequence of tests include exciting and measuring at different locations along the bridge, using either a roving actuator and/or a roving sensor; the requirement for a unique identification is that the roving actuator and sensor must be collocated in at least one of the tests. The performance of the proposed method using different types of responses, namely, displacement, velocity, and acceleration, is assessed using numerical simulations. The effect of different types of errors in the identification process is also studied. The method is finally applied to experimental data obtained from laboratory scale tests.