Abstract
The identification of the modal parameters of bridges and other large civil constructions has become an important research issue. Different approaches have been proposed depending on the excitation used: ambient excitations (due to wind, traffic, …) or artificial excitations (e.g. impact test with heavy drop weights). In practice it turns out that not all modes are well excited by the ambient forces. Hence the application of an artificial actuator is advisable. The problem is that larger constructions often require large and heavy excitation devices, which are hard to manipulate. Another difficulty encountered in performing a modal analysis on large civil constructions is the necessity for a large number of high sensitivity sensors. Consequently a large number of cables has to be installed resulting in a large setup time.This paper is a proof-of-concept which demonstrates the possibility of using lightweight Pneumatic Artificial Muscles combined with the scanning laser Doppler vibrometer to perform a modal analysis on a civil structure. This combination allows for an important reduction in setup time and allows for sine testing as well as the application of broadband signals such as periodic chirps, true noise or multisines.
Highlights
Different approaches to perform a modal analysis on civil constructions such as bridges are commonly in practice [1,2,3,4,5,6,7,8,9,10,11,12]
Two consecutive measurements were performed on the ceiling of the laboratory: an Experimental Modal Analysis (EMA) measurement to prove this simple setup can give excellent results and an Operational Modal Analysis (OMA) measurement that will serve as a reference for the technique most often used in modal analysis nowadays
Comparing both figures shows that the EMA measurement results in vibration signals that are about ten times (20 dB) larger than the vibrations measured during OMA
Summary
Different approaches to perform a modal analysis on civil constructions such as bridges are commonly in practice [1,2,3,4,5,6,7,8,9,10,11,12]. Depending on the excitation used these methods are divided into Experimental Modal Analysis (EMA) or Operational Modal Analysis (OMA). Experimental Modal Analysis identification methods and procedures are forced excitation tests where the applied forces can be measured together with the response of the structure (e.g. accelerations). Applying an excitation device, is in practice often problematic when the tested structure is large. In applications where it is rather difficult to apply an artificial force Operational Modal Analysis can be used. During OMA, the very low levels of dynamic response introduced by wind and/or traffic are measured with high sensitivity transducers. In such cases, it is practically impossible to measure the ambient excitations, and
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