Study On A Hybrid Mitigation Control On The Footbridge Based On Crowd Flow Evacuation

Currently,the footbridge with lightweight and high-strength materials has extensively emerged.Since these structures usually have the characteristics of lowfrequency and lightly-damped vibration modes,they are prone to form resonance.Therefore,it is necessary to control the excessive vibration of the structure caused by the crowd load.Although the TMD device has the advantages of mature technology and low cost,there still have the problems of limited control efficiency and detuning.As the cause of footbridge vibrations,the pedestrians are intelligent vibration receivers who can smartly react to the surrounding environment.There are a potential to use permanent(such as a bench or ligh t pole)or temporary(guardrail or emergency exit)facilities on structures apart from their primary functions to affect the pedestrian walking velocity and frequency.By smart design and positioning of these facilities,the dynamic load applied to the structure is manipulated to alter the energy input and the corresponding vibration response of the structure.In this paper,a new hybrid mitigation method based on crowd flow control and TMD is established,and the numerical and experimental results verified its damping performance.The social force model reflecting the interaction between individual pedestrians is developed,and the single and two-way crowd motion models in the scene of obstacles are established.Finally,in the interaction model,this study introduces the pedestrian perception mechanism to study the pedestrian lock-in and structural dynamic characteristics.This paper represents from the following aspects:(1)Based on the micro-social force model,the pedestrian motion behaviors such as two-way,obstacle avoidance,and transcend are simulated on the Matlab platform.According to the simulation dynamic,the crowd evolution process is discussed and the crowd motion law is analyzed.Finally,the simulation results of walking frequency,walking speed,and other motion parameters are further analyzed;(2)The moving load model and SMD model are used to simulate pedestrians and calculate the dynamic response of the footbridge.On the Matlab virtual laboratory,the crowd flow control based on placing obstacles is numerically implemented on an interior footbridge.According to the numerical response results,the vibration mitigation efficiency of the crowd control strategy is investigated.Then,the influence of different obstacle layouts and the number of obstacles on the vibration reduction rate is compared.The field tests were carried out on a steel-glass footbridge to verify the vibration mitigation performance of pedestrian control measures.Finally,the results indicate the change of the time and frequency domain response with and without the crowd flow control.(3)This study proposes a hybrid mitigation method based on the crowd flow control and the eddy current tuned mass damper to control the excessive vibration caused by the random crowd excitation.The time-varying coupling model of the crowd-structure-tuned mass damper is established,and the structure response is investigated.A virtual three-dimensional obstacle based on the pedestrian stereo vision on the laboratory footbridge is designed to avoid the accident that pedestrians may encounter caused by the actual obstacles.The vibration mitigation method is applied on an experimental footbridge under random crowd loads and then the mitigation performance is analyzed experimentally and numerically.A video camera is used to estimate the velocity and number of steps of each pedestrian.Besides,an energy analysis method is carried out to explain the vibration mitigation mechanism.The results show that the performance of the proposed hybrid mitigation method is more effective than the single mitigation method and the number and layout of obstacles determine the mitigation efficiency;(4)Based on the lateral crowd-structure coupling model,a pedestrian-structurepedestrian full path interaction model that introduces a pedestrian perception mechanism is established.In the case of a single pedestrian,the delay,lock and stop acceleration thresholds are customized,and the structural response caused by the pedestrian’s gait adjustment driven by sensing different accelerations thresholds is studied.The interaction model is used on an internal pedestrian bridge to realize the movement behavior of pedestrians such as Lock-in.The influence of crowd motion parameters on the Lock-in phenomenon is analyzed and discussed.