Detection of Damage in a Lattice Mast Excited by Wind by Dynamic Measurements

The paper illustrates the effectiveness of monitoring the dynamic response of a system for detection of damage herein using an output-only assessment scheme. The system is a 20 m height steel lattice mass excited by wind and the mast is instrumented with accelerometers picking up dynamic responses under ambient loading conditions. The paper presents the instrumentation and considerations regarding layout of instrumentation and strategies for acquisition and processing of data. Damage in the mast is provoked using a hacksaw and the cross sectional area of one the diagonals of the mast (one located close to the foundation) is gradually reduced by sawing deeper and deeper into the diagonal. During the process of introducing damage to the mast, its dynamic responses are recorded. By postprocessing these recordings, the changes in dynamic characteristics of the mast with the size of damage are identified. By studying the recorded variations it seems reasonable to conclude that by implementing a vibration monitoring system on the mast it would be possible to reliably detect a damage corresponding to less than a 50% loss of cross sectional area of the diagonal. This would allow for issue of a warning of a potential progress towards structural collapse prior to its occurrence.