Identification of spatial modes through instantaneous vibration direction

Directional vibrations (i.e., directional swaying mode motions and/or torsional mode motions) exist widely in many civil structures such as high-rise buildings and offshore platforms which are exposed to random dynamic loads like winds or ocean currents. These motions may result in directional damages (e.g., fatigue damages) of these structures. Thus, there is a need to identify such directional vibrations. This paper presents a new method for the identification of spatial modes through analysis of the instantaneous vibration direction. This method is based on responses from accelerometers installed at several floors while only one bi-axis accelerometer is required at each floor. It is thus of great practicability and very convenient for engineering applications.