Seismic Response Analysis And Hybrid Simulation Of Human-structure Interaction System

In recent years,considerable research efforts have been made on the topic of human-structure interaction(HSI),especially after the London Millennium Footbridge event,in which due to pedestrians walking large bridge deck vibrations caused panic among the crowd.Many school buildings were severely damaged or even collapsed in Wenchuan Earthquake when the classrooms were full of students with heavy crowd loads.This caused concerns regarding the role of emergency evacuation in structural failure.To quantitatively evaluate the effects of human-structure interaction,a spring-loaded inverted pendulum(SLIP)is proposed which applies to running and walking on vibrating surfaces.Shaking table tests were conducted in which the participants move on a treadmill excited laterally or longitudinally by a shaking table.Then a crowd-structure interaction model is established considering the variability between humans,and the model is applied to the analysis of seismic responses of the crowd-structural system.The main work and conclusions are as follows:1.A 3-D SLIP model for simulating humans running on the horizontal vibrating floor is established.PD control for the leg force and foot moment is employed to achieve the desired values for the height and forward running speed of the center of mass,and P control is used to maintain limited lateral speed.Numerical results show the robustness of the control methods which are stable even subjected to large disturbances.Shaking table tests were conducted in which the participants ran on a treadmill excited laterally or longitudinally by a shaking table.The test results show that the HSI increased with the excitation level,and synchronizations were observed mainly in the cases of longitudinal excitations.The HSI can be interpreted as an equivalent additional mass and negative damping to the structure for the lateral direction,while additional mass for the longitudinal direction.The numerical simulations are compared with the experiments,and it demonstrates that the model describing human behaviors agrees well on both the stationary and moving treadmill.2.A SLIP model with roller foot is established that can simulate human walking under longitudinal floor excitation.Human walking tests were conducted on a stationary treadmill or a longitudinally vibrating treadmill excited by a shaking table.The walking test results indicate that the HSI in the longitudinal direction can be interpreted as an equivalent additional mass and damping.When the excitation frequency is close to the pacing frequency,the pacing frequency tends to keep with the excitation frequency.Compared with the test results,the model can describe the characteristics of human longitudinal walking force well.The model can represent the beating and synchronous responses subjected to longitudinal excitations.The influence of different control parameters on human behavior is analyzed,and the results show that the interaction force increases with control parameters.3.The 3-D SLIP and 3-D rigid inverted pendulum(IP)models are established to describe human walking behaviors under lateral floor excitations.The k_p control is proposed to maintain the stable walking of the 2-D linear inverted pendulum,and the spectral radius analysis method is applied to determine the range of the control parameter that satisfies the stability conditions.A comparative study on model responses of 2-D linear IP,3-D rigid IP,and 3-D SLIP walking on stationary and vibrating surfaces is conducted.The results show that the equivalent coefficients obtained by 3-D SLIP are in good agreement with tests.The 3-D rigid IP and 3-D SLIP can reflect the phase pulling and synchronization when the excitation frequency is close to the step frequency,which is consistent with tests.4.Real-time hybrid testing was conducted for simulating the seismic responses of the crowd-structure system.The testing showed that the step frequency changed significantly when subjected to ground vibrations.Synchronization occurred when the step frequency is close to the structural vibration frequency,resulting in a large increase in the structural responses.When the human step frequency is far away from the structural frequency,the human walking has little influence on the structural response.5.Based on the SLIP model,the crowd-structure interaction model is established considering the variability between humans.The influences of crowd movement on structural seismic responses are analyzed.The simulation results show that crowd movement has a great influence on structural responses.Under the 70Gal horizontal earthquake excitation,the influence of crowd walking on the structure is 37.8%at the maximum and 12.1%on average larger than that when there is no crowd.The influence of crowd running on the structure is increased by24.2%at the maximum and 5.4%on average.Human step frequencies changes due to the vibration of the structure after the HSI is taken into account,which leads to an increase in the synchronization rate of the crowd,and the influences of the crowd on the seismic response of the structure increases accordingly.