Dynamic Response Analysis Of Bridge Structure Under Dynamic Load

Bridge structures under dynamic load may produce a series of problems such as vibration,deformation and destruction.Due to complexity and variety of actual bridge engineering,simple supported girder bridges are widely used because of its low cost,simple construction,prefabrication,quick construction and simple and reliable structure system.This paper will simplify the bridge structure as simple girder,Its dynamic response analysis is more detailed,and its research results can also be widely applied to simply supported girder bridges,providing necessary foundation for dynamic topology design in initial stages of conceptual design.First of all,from mechanical dimension of the simply supported beam stress and displacement,made the following research:the strength of simply supported beam to the structure of its impact,in which changes in force to follow the sinusoidal distribution;force acting on simply supported beams.The influence of position change on the structure;the effect point of force and the influence of the force magnitude on the simply supported beam at the same time.In conclusion,the following research results are obtained:First,the response of the simply supported beam to the force magnitude is the largest at natural frequency and decreases to both sides,and at a low frequency,the response of the beam to its response to the frequency response of the load is synchronous.While at high frequency,the response delay of simply supported beams is more obvious.Second,when the load moves,the response of a few nodes shows the first increase and then decrease at the moving speed accelerates.If the load is withdrawn,the response does not disappear instantly,but continuously changes,and its value is even larger.Thirdly,when the force and acting point of the simply supported beam are all changing,the response of the velocity to the load is the most obvious when the load is moving slowly.When the load is medium,the response of the angular frequency is the most significant;When the load motion is very fast,the angular frequency and speed will cause corresponding responses,which can not be neglected in actual research.Secondly,modal analysis and transient dynamic analysis of simply supported beams,that is,based on the discrete method,the nodes of the simply supported beams are divided and then the moving loads are applied to the corresponding nodes.Then the modal analysis is started to analyze the moving loads And the corresponding changes of the natural frequency of the simply supported beam structure;then add the simple harmonic load,and change the location of the moving load,expand the transient dynamic analysis,get the maximum node displacement state,the displacement value of each node and do the absolute value deal with.In the meantime,two types of results are compared.When a moving load is applied to a simply supported beam,the mode shapes and natural frequencies of the beam change similarly.The frequency of the beam can not be changed when the moving load is applied to the formation of the beam.The change of the beam frequency is most obvious when applied to the peak of the formation.After the localized harmonic load is applied to the beam,the absolute value of the transient displacement is compared with that without the moving load,The sum of the former will always be greater than the latter.On the basis of the above,the damper is placed on the simply supported beam,and transient dynamic analysis and damping modal analysis are carried out.It is pointed out that the damping position is different and the frequency changes accordingly.The natural frequency without damping is not dependent on the damping Change the position of the device.When there is damping,the sum of the absolute values of deflection at each point changes.The greater the damping coefficient,the more obvious the change.Finally,the theory and analysis of stress wave are introduced into the research of this topic,the theoretical wave velocity of longitudinal wave and bending wave are analyzed in details,and the corresponding wave velocity value is obtained.As a result,validated and compared,in the analysis,the acquired P-wave propagation velocity is valid and credible,but the obtained bending wave propagation velocity has a large error from the theoretical value.