Application of Dynamic System Identification to Timber Bridges

Abstract

A method of global nondestructive evaluation for identifying local damage and decay in timber beams was developed in previous analytical studies and verified experimentally using simply supported beams in the laboratory. The method employs experimental modal analysis and an algorithm that monitors changes in modal strain energy between the mode shapes of a damaged structure with respect to the undamaged structure. A simple three-girder bridge was built and tested in a laboratory to investigate the capability and limitations of the method for detecting damage in a multimember timber structure. The laboratory tests showed that the method can correctly detect and locate a simulated pocket of decay inflicted at the end of a girder as well as detect a notch removed from the midspan of a girder. The tests showed that the method can correctly detect damage simultaneously at two locations within the bridge, but also that large magnitudes of damage at one location can mask smaller magnitudes of damage at another location. When a calibrated baseline model is used to represent the undamaged state of the bridge, the results show that the method of nondestructive evaluation is able to detect each case of inflicted damage, but with some increase in localization error.