Analysis Of Vehicle-bridge Coupling Dynamic Characteristics Of Cracked Beam Bridge

Highway is the basic part of China’s comprehensive three-dimensional transportation network,which undertakes more than 70% of the traffic volume every year.As an significant part of China’s highway system,highway bridges are also facing huge challenges.During the actual operation of the small span reinforced concrete bridge,or due to vehicle overloading,design errors and other uncontrollable factors,the main beam has different degrees of damage,and cracks are one of its main damage forms.The apprearance of cracks will affect severely the static and dynamic performance of the bridge,and the vehicle load,as one of the most key loads in the service process of the bridge,has a great influence on the service performance of the cracked bridge.This paper takes the cracked simply-supported beam bridge as the research object,and studies the mechanical properties of the cracked simply-supported beam bridge under moving load.The main research contents are as follows:(1)By comparing various crack types,it is established that the crack type in this article is an I-type open crack.The beam bridge model with a constant cross-section crack is established by the finite element software Abaqus.The element type is C3D8 R solid element,and the through wedge shaped crack is used to establish the crack.Using a continuous equivalent stiffness model for cracked beams,the relationship between structural stiffness and crack depth was derived,which compares the results of both methods to verify the correctness of crack settings in the finite element model.(2)Using a finite element model of a simply supported beam with constant cross-section cracking to discuss and analyse the influence of crack depth,crack width,and crack location on the dynamic characteristics of a cracked beam.The results show that the crack depth hurts the dynamic characteristics of the structure most,and the vibration frequencies of each order decrease with the increase of the crack depth;within the allowable crack range in design specifications,the crack width has almost no effect on the vibration frequency of the structure;the influence of the crack location on the vibration frequency increases or decreases with the distance from the vibration mode node.(3)Based on the damage identification theory of long gauge strain influence lines,damage identification of finite element cracked simply supported beams subjected to moving constant forces is performed,and the structural cracking section stiffness is compared with the equivalent continuous stiffness model.The error is small,and further decreases as the crack depth increases.On this basis,a damage identification program for cracked beam bridges under moving constant forces is compiled using Matlab software.The results show that the crack depth has the greatest impact on the dynamic stiffness of the structure.As the crack depth increases,the dynamic stiffness continuously decreases,while within the allowable crack range,the crack width has almost no impact on the dynamic stiffness of the structure;Through normalization,it is found that the speed and magnitude of the moving constant force have a small impact on the dynamic stiffness of the structure.(4)Taking the Duzhuang River East Branch Bridge in Lankao County,Henan Province as the research object,Abaqus was used to establish a finite element model of a single span single cracked simply supported hollow slab with different damage levels,extract its first ten modes,and compile a 1/4 vehicle cracked beam bridge coupled vibration response and damage identification program.The results show that the reasonable selection of the length of the long gauge element is one of the key factors for local damage identification.When the crack parameters are the same,the overall damage of the structure increases with the increase in the number of cracks.However,when the relative distance of the damage location is small,the local damage generated may be greater than the condition with more damage numbers but larger distance.Vehicle traveling speed,vehicle weight,and bridge structure damping ratio have a significant impact on bridge vibration response.Vehicle speed has no obvious regularity,and the impact of vehicle weight on bridge dynamic response is approximately a quadratic function.Appropriate increase in damping ratio can reduce adverse effects of dynamic response and reduce safety hazards.