Using a rhythmic human shaker to identify modal properties of a stationary human body on a footbridge

Abstract

Dynamic properties of the human body are basic parameters in biomechanics and many related areas. Experimental test is the most reliable manner to obtain dynamic parameters of the human body. Traditional method usually employs shaking table test or well-designed test rig driven by a mechanical shaker, which is always expensive and sometimes not available. This paper presents a simple but efficient transmissibility-based procedure for testing the dynamic properties of a human body. The excitation is generated by a human shaker with rhythmic movement acting on a flexible structure (either a footbridge or a long-span floor). Wide band excitation frequency can be generated even excite in a narrow-band owing to the multi-harmonics of the footfall force. The procedure consists of two main steps, namely, to identify the modal properties of the supporting structure and to establish the transmissibility of the human body. The human excitation force is found to be highly correlated with the body motion based on simultaneous footfall measurement and 3D motion tracking. To this end, the human excitation force is reconstructed and calibrated using the human body motion. The structural frequency response function is established using the footfall force and the bridge acceleration. Then the modal properties of the supporting structure, i.e. the vibration frequencies, mode shapes, and damping ratios and modal mass, are identified. The performance of human excitation method is checked by conventional ambient vibration testing and impact testing methods. Transmissibility of the human body is obtained by motion measurement at the supporting point and the stationary human body. The identified resonance frequency of the human body is further modified to obtain its natural frequency since the body is heavily damped. The feasibility of the procedure is demonstrated in identification of the dynamic properties of a footbridge with a stationary occupant having different postures.