Research On Coupled Vibration Of Crowd-long Span Corridor Structure Based On Social Force Model

In recent years,the structural forms of long-span floors,air corridors and footbridge,etc.are becoming more popular due to the people’s increasing demands for large space structures and aesthetics as well as the support of new building materials and advanced construction technology.Compared with structures with higher stiffness and heavier mass,this kind of structure is more likely to have vibration serviceability problems.The complex random crowd excitation is the main load on this kind of structure,and it is also the most important factor to cause structural vibration.Because of the time-varying characteristics of crowd load and the complexity of pedestrian-structure interaction,when pedestrians act on structures in different states,which can not only increase the mass of the structure,but also exert the dynamic load on the structure.Most importantly,the modal characteristics of the structure are changed.It is of profound significance to consider the randomness of population and crowd-structure interaction for deeply understanding the change regulation of the dynamic characteristics and dynamic response of structures subjected to crowd action.At present,the research on the vibration response and modal change of the large span structure under the crowd load is mainly as follows: 1.many researchers consider the randomness of pedestrians in the study,but the first order mode is considered while the higher modes are ignored.2.when the finite element model is used to simulate,many regard the structure as a multi degree of freedom system while the pedestrian is considered as a consistent incentive.In order to evaluate the vibration serviceability of structures under random loads better,the following aspects are studied in this paper based on the research results of random load and pedestrian-structure interaction at home and abroad:Firstly,time-varying and moving spring-mass-damper model(SMD)is adopted to replace each pedestrian.Secondly,in two different cases of considering and not considering pedestrian-structure interaction,the mode superposition method is used to calculate the dynamic response of the structure and the change of the structure mode when pedestrians walk across the structure at excepted and resonance step frequency.Based on the social force model and statistical analysis of pedestrian traffic parameters in the field of transportation as well as the introduction of the deceleration avoidance mechanism and self stopping mechanism,the random walk process of crowd is simulated to obtain the dynamic parameters of arbitrary pedestrians at any time and establish a random crowd load model.In this model,the interaction between pedestrians and the environment,the pedestrians individual and the randomness of pedestrians in the time and space domains are taken into account.3)Based on the established stochastic crowd load model,the moving SMD model is applied to simulate the dynamic behavior of a single person,and a random crowd load model considering crowd-structure coupled vibration is established.According to the dynamic balance between the footbridge and the random crowd at any time,the governing equation of the random crowd-footbridge coupled vibration is established.The change situation of the footbridge dynamic parameters with the motion of the random crowd are solved by using the state space method,and the governing equation of coupled vibration is solved by using Nemark-β method.The effects of the random crowd load considering crowd-structure coupled vibration on the model and the evaluation results of the vibration serviceability of the steel structure corridor is discussed.4)Since the complexity of the step frequencies of crowd has influence on the higher modes of the structure under the random load of the crowd,so in order to evaluate the vibration serviceability of the structure more accurately,the change situation of the footbridge dynamic parameters with the motion of the random crowd are solved by using the differential quadrature(DQ)-integral quadrature(IQ)mixed method,and the contribution of higher modes on the vibration response is discussed.Taking a long span steel structure as an example,the modal changes of the structure calculated by the mode superposition method and the DQ-IQ mix method are compared,and the vibration comfort evaluation is carried out.