Study On The Vertical Interaction Between Static Human And Structure

In recent years, with designers’ continuous pursuit of better architectural art form as well as the upsurge of building materials of high performance, the characteristics of modern architectural structures like lightweight, long-span, low damping have become increasingly apparent. As a result, it makes vibration disaster resulted from the coupled system of the static crowd and structure gradually prominent.The vertical interaction of static body and structure is a complex, important and critical issue but still has not been fully understood. Mainly includes: 1. How the vibration of structure affects static body’s reaction and comfort; 2. How the static body influences the response and dynamics characteristics of struture. In order to solve these two key issues, we need to establish a simple, reasonable and accurate static body model. However, in order to establish this model we should first confirm the related parameters of static body.According to the research results of Dr. Dongwei Wang and theoretical derivtion,the shaking table with reasonable parameter ratio was designed. However, the practical parameters of the structure were determined by free vibration experiments.Referring to the thoughts of biomechanics, this article used shaking table to conduct forced vibration tests, as a result, the vertical resonance frequency of the static human-structure coupled system was obtained. By comparison, it is found that the resonance frequency of the system are second order and first order with and without the static human, which shows the static human is not a rigid mass block but a single degree of freedom with mass, stiffness, damping.Based on the least square and normal distribution principle, we compared the resonance frequencies of the coupled system of the static body and structure from experimental measure and from theoretical model. This paper identifies the modal mass of the static body, the coupled mass of the body and the structure are approximately 39.62% and 49.45% of total body mass, while the damping ratio,fundamental frequency of the static human are approximately 0.1217 and 4.29 Hz. Onthis basis, a continuous bar with two segments model proposed by Ji was optimized in this paper. Finally, the stiffness, mass, height distribution of this model and the model function of static body were successfully identified.This paper used a continuous-elastic bar with two segments to model the body standing on a footbridge and built the crowd-footbridge-tuned mass damper(TMD)vibration system. By simplifying the static crowd as a generalized human body, we studied the dynamic characteristics of the generalized human-footbridge-tuned mass damper vibration system and the parameter design of TMD. We identified the parameters of generalized human body through the principle of least square.Comparing with the data available from experiments, the correctness of simplifying the static crowd to a generalized human was verified. Utilizing the root-mean-square acceleration as the optimization criterion to assess the degree of human body comfort,the optimal parameters of a TMD system were discussed. On this basis, this paper then introduced the design methods of the TMD for the pedestrain bridges with the random meaning and established the differential equtions of the crowd-footbridge-MTMD system which considered multiple models and multiple TMD.In the fifth chapter, we studied the dynamic characteristics of the generalized human-structure-TMD(Tuned Mass Damper) system. Both the generalized human and the structure were simplified as a single-degree-of-freedom(SDOF) system. Then,a three-degree-of-freedom(3DOF) vibrating system with a TMD attached under the structure was built. The undamped natural frequencies, the displacement and acceleration spectra of the coupled 3DOF system were derived out. The comparison between the present 3DOF system and the 2DOF model for the structure-TMD system was studied. The results show that the generalized human-body has influence on dynamic properties of the system. When the fundamental frequency of the body is a half of that of the structure, the nature frequencies between the two models are very close. When the fundamental frequency of the structure is close to that of the body,the nature frequencies between the two models are different. When the fundamental frequency of the structure is close to that of the body and the excitation is fromwalking or jumping, the displacement and acceleration values of the structure and TMD in the 3DOF model are larger than those in the 2DOF model for some frequency ratios and mass ratios.