Gauge Newsletter September 2015 | Page 31

KASUN DHARMASIRI Department of Civil Engineering (Fourth Year) Rail’s safe structure system on a bridge • Source: http://alliancesensors.com situations where post structural integrity damping ratios etc. The vibration charac- is of concern. teristics could be extracted from the time history data collected from acceleration As explained earlier, the damage detec- transducers employed in specific locations tion methods in use mostly depend on of the structure excited either by artificial visual inspection. However, it is difficult means or free vibration, after analysis. In to detect damages in the structure using order to assess damage, a comparison has visual inspection until the damages in the to be made between two structural health structure have turned out to be promi- states. However, researches are being car- nent; say spalling of concrete in the soffit ried out to use the non-linear behavior surface, cracking and other deformations. to identify damages rendering the need to compare two structural health states Furthermore, use of visual inspection has redundant. certain limitations such as accessibility issues and visibility issues, which may It is evident that use of VBDD to detect deem the method useless in certain cases. damages is a possibility and if not com- To address these issues, various dam- pletely replace, adopt it as a complemen- age detection techniques have emerged tary method to detect damages along with during the past years such as acoustic visual inspection. or ultrasonic, magnetic field, x-ray, radiographic, eddy current and vibration based damage detection techniques. References 1. Brownjohn, J.M.W., 2007. ‘Structural Vibration Based Damage Detection (VBDD) health monitoring of civil infrastructure’. has a greater potential mainly because it Philosophical Transactions of the Royal is a non-destructive method, addresses Society A: Mathematical, Physical and issues related to accessibility and visibil- Engineering Sciences 365, 589–622. ity of damages and can be programmed 2. Chang, P.C., Flatau, A., Liu, S.C., 2003. to run autonomously. The basis of VBDD ‘Review Paper: Health Monitoring of is that dynamic response of a structure Civil Infrastructure’. Structural Health changes with damages it has accumulated Monitoring 2, 257–267. over its service life. This is based on the 3. Wang, L., Chan, T.H., 2009. ‘Review of hypothesis that due to damages, the stiff- vibration-based damage detection and ness of the structure alters (drops) leading condition assessment of bridge struc- to changes in vibration characteristics tures using structural health monitoring’. such as modal frequencies, mode shapes, In:QUT Conference Proceedings. Source: http://en.wikipedia.org Gauge Newsletter University of Peradeniya 31