Study On The Vibration Characteristics Of Floor Slabs Caused By Random Crowd Loading Based On Cellular Automata Model

With the development of lightweight and high-strength materials,the form of building structures has been optimised and large-span floor slab structures are often used in public buildings.Most of these buildings have a soft structure with a low self-oscillation frequency and are susceptible to resonance with pedestrians,which not only affects the comfort of pedestrians,but also to a certain extent the safety of large-span floor structures.In addition,such buildings generally have a large flow of people,in the event of an accident,there is a problem of evacuation,and when the crowd evacuation caused by the building vibration,not only will cause panic,intensify the difficulty of crowd evacuation,but also easy to cause serious safety accidents.Therefore,the study of the vibration response of floor slabs caused by crowd evacuation has certain theoretical value and practical significance.In this paper,the study is carried out from two aspects: the single person load model and the crowd trajectory simulation.A multi-degree-of-freedom single-person bipedal walking model is established by combining the human biological force model and the effect of human-structure dynamic interaction;a classroom pedestrian evacuation model is established based on the principle of metacellular automata;finally,the vibration response characteristics of the floor slab under the pedestrian evacuation condition are investigated by establishing a finite element structural model of the floor slab,considering the single-person bipedal walking force model and the pedestrian evacuation trajectory.The main research work of this paper is as follows.(1)A new human dynamics model considering both the biological force model and the human-structure dynamic interaction is proposed by combining the coupled vehicle-bridge model theory.Considering the bipedal walking model of the human body,the human body is divided into three mass blocks,representing the torso and legs of the human body,and the dynamic response of the human body and the dynamic response of the structure under the multi-degree-of-freedom single person bipedal walking model is obtained by the Newmark-β method.(2)Based on the principle of meta-cellular automata,a classroom pedestrian evacuation model was established by considering the social attributes of pedestrians and the influence of the surrounding environment on pedestrians,using static fields to simulate the influence of the surrounding environment and dynamic fields to simulate the social attributes of pedestrians.The effect of familiarity optimisation on the evacuation time of the model was analysed under setting different parameter working conditions,and the pedestrian evacuation path map and trajectory coordinates were also obtained.In addition,the numerical simulation results show that the evacuation time of pedestrians is positively correlated with the initial number of evacuations,and as the initial number of pedestrians grows to a certain threshold,the influence of surrounding pedestrians on each other will become more and more serious,and the congestion phenomenon will become more and more serious.In addition,the initial position of pedestrians will also have a certain impact on the overall evacuation time and efficiency.(3)A finite element model of the floor slab structure is established,and the vibration response characteristics of the floor slab structure due to crowd loading during pedestrian evacuation are analysed by combining the multi-degree-of-freedom single-person bipedal walking model and crowd evacuation trajectory coordinates;the vertical vibration characteristics of the building floor slab are investigated under the variation of pedestrian parameters(step frequency,density,path and step width)and floor slab thickness considering different influencing factors.Among them,the change of pedestrian cadence will have the most significant impact on the vertical vibration response of the floor slab.