Using inertial measurement units originally developed for biomechanics for modal testing of civil engineering structures

Abstract

This paper explores the use of wireless Inertial Measurement Units (IMU) originally developed for bio-mechanical research applications for modal testing of civil engineering infrastructure. Due to their biomechanics origin, these devices combine a triaxial accelerometer with gyroscopes and magnetometers for orientation, as well as on board data logging capability and wireless communication for optional data streaming and to coordinate synchronisation with other IMUs in a network. The motivation for application to civil structures is that their capabilities and simple operating procedures make them suitable for modal testing of many types of civil infrastructure of limited dimension including footbridges and floors while also enabling recovering of dynamic forces generated and applied to structures by moving humans. To explore their capabilities in civil applications, the IMUs are evaluated through modal tests on three different structures with increasing challenge of spatial and environmental complexity. These are, a full-scale floor mock-up in a laboratory, a short span road bridge and a seven story office tower. For each case, the results from the IMUs are compared with those from a conventional wired system to identify the limitations. The main conclusion is that the relatively high noise floor and limited communication range will not be a serious limitation in the great majority of typical civil modal test applications where convenient operation is a significant advantage over conventional wired systems.

Enhanced sparse component analysis for operational modal identification of real-life bridge structures

“…The damping ratios were derived from the free decay parts using the logarithmic decrement method and the fitted envelopes are indicated as red lines in modal response plots. The estimation results of modal parameters are given in Table 1 compared with those by the NExT/ERA method in [40]. The frequency estimates match very well with difference within 0.3%.…”

“…Station Road Bridge in Figure 6(a) is a steel girder bridge with 36 m span near Exeter St David's railway station. A modal test was performed on the bridge (also reported in [40]) using two types of sensors,…”

“…The mode shapes estimated from QA data using NExT/ERA procedures in [40] are taken as the reference to evaluate the estimation accuracy of the enhanced SCA method. For QA data, all the extracted five modes indicate high similarity with the reference and the modal assurance criteria (MAC) reach over 99.96%.…”

“…Based on four channel measurement, mode shape vectors of the third bending and first torsion modes (Figure 9 markers denote the mode shape ordinate of the north side of the bridge (TP1~3) and solid lines with 'x' shaped markers denote the mode shape ordinate of the south side of the bridge (TP4~6). The modal assurance criteria (MAC) compared with the mode shapes estimated by NExT/ERA method using QA measurement data [40] are given in the subplot titles.…”

“…Although the estimated damping ratios are much smaller than the values by the NExT/ERA method, the estimates from free-decay signals in this study could be reliable since the fitted envelops of damped vibration curves in Figure 10(e) to (i) match very well with the actual ones. Table 1 Modal frequencies (f) and damping ratios (  ) of the first five modes estimated by the enhanced SCA method and the NExT/ERA procedure [40]…”