Reliability of Using Smart Phones Sensors as an Experimental Instrument on Steel Bridge

Accelerometers in smart phones and “apps” that use them have a potential to determine dynamic characteristics of civil engineering structures. Damping ratio, which is a key quantity needed to design a structure, can only be identified by conducting experiments on similar structures. However smart phones have not been used as an experimental measuring tool for civil engineering structures. In this study, LIS331DLH ultra low-power high performance three axes linear nano MEMS internal accelerometer of smart phone sensor is tested with high-end expensive seismometer for deriving damping ratio of a pedestrian model steel bridge using snap-back method. Eight experiments have been conducted with various initial displacement imposed at the mid span of bridge. Measured amplitude of acceleration time histories together with numerically calculated displacement waveforms are compared in time and frequency domains. Furthermore wavelet analysis is employed to time histories to capture instant frequency changes on the vibration of structure. Finally correlation between applied initial displacement and the value of damping ratios are derived for each acceleration and displacement waveforms. Although smart sensors could not catch high frequency signals and amplitude levels as obtained from reference sensor, measured fundamental frequencies are derived similarly. The analysis carried out proves that smart phones can determine damping ratio in close proximity compared with quality accelerometers. With some drawbacks, smart phone sensors can be utilized in determining damping ratio of model steel bridge.