Although the widely acknowledged shortcomings of visual inspection have fueled significant advances in the areas of
non-destructive evaluation and structural health monitoring (SHM) over the last several decades, the actual practice of
bridge assessment has remained largely unchanged. The authors believe the lack of adoption, especially of SHM
technologies, is related to the 'single structure' scenarios that drive most research. To overcome this, the authors have
developed a concept for a rapid single-input, multiple-output (SIMO) impact testing device that will be capable of
capturing modal parameters and estimating flexibility/deflection basins of common highway bridges during routine
inspections. The device is composed of a trailer-mounted impact source (capable of delivering a 50 kip impact) and
retractable sensor arms, and will be controlled by an automated data acquisition, processing and modal parameter
estimation software. The research presented in this paper covers (a) the theoretical basis for SISO, SIMO and MIMO
impact testing to estimate flexibility, (b) proof of concept numerical studies using a finite element model, and (c) a pilot
implementation on an operating highway bridge. Results indicate that the proposed approach can estimate modal
flexibility within a few percent of static flexibility; however, the estimated modal flexibility matrix is only reliable for
the substructures associated with the various SIMO tests. To overcome this shortcoming, a modal 'stitching' approach
for substructure integration to estimate the full Eigen vector matrix is developed, and preliminary results of these
methods are also presented.
The quality of test data is an important consideration in conducting field experiments on civil infrastructure. In addition to possible errors due to the experimental setup, the uncertainties due to incomplete knowledge of a structure's behavior and its interactions with the natural environment greatly affect the reliability of the system identification results. This paper discusses the uncertainties related to ambient vibration testing of a long-span steel arch bridge and possible ways to mitigate them. The consistency of the identified parameters is examined through statistical analyses.