Dynamic Mechanism Research And Random Vibration Analysis Of Reinforced Concrete Bridge Under Multi Point Earthquake Excitation

It is very easy for the large span or multi span bridges to be destroied under the earthquake,in the current bridge seismic research,it is generally considered that the excitation on the bridge is uniform excitation,that is,the seismic action of each bearing is exactly the same,this assumption often misestimates the damage mechanism and state of the earthquake action to the bridge.In fact,due to the comprehensive effcts of various factors,such as the randomness of real ground motion and the effect of different site effects,the seismic action of reaching the bridge supports is different,that is,the excitation of the bridge in the earthquake action is non-consistent,at this time,the dynamic response of large span or multi span bridges may be significantly different from the results of uniform excitation.With the continuous development of the theoretical research of bridge engineering,it is an urgent problem to discuss the mechanical mechanism of bridge under non uniform excitation.Due to the comprehensive influence of focal mechanism,site effect,propagation way of ground motion and dispersion effect,the seismic action of a certain point is highly stochastic and uncertain.And the method of characterizing the three elements of the basic characteristics of the ground motion is also relatively macroscopic and rough.In view of this,The characteristics of dynamic time warping algorithm are further explored.Based on the dynamic time warping algorithm,an index that can comprehensively evaluate the waveform variation and characteristics evolution of different seismic waves is proposed.Systemly consider the influence of time difference,amplitude intensity,signal to noise ratio and space-time distribution,etc,the variation of the dynamic time regularization distance under the influence of various factors is obtained,It can be used as a criterion to judge whether the earthquake is reasonable and standard.The analytical solution of dynamic equation and response of bridge structure under non uniform excitation is analyzed in this paper,the general form of the participatory coefficient of the generalized mode of vibration is obtained,for different structural forms under different loading forms,The concrete forms of different modes of vibration mode participation are obtained.It is found that the vibration mode participation coefficient is not only related to the structure form,but also is related to the load form,that is,the value of the participation coefficient of the vibration type is influenced by the structure form and the effect of the external load.In view of the present situation that the bridge response law under the non uniform excitation is less studied in the seismic analysis of the bridge,three span and five span continuous beam bridges are respectively taken as examples,the bridge is subjected to lateral vibration and the bridge is subjected to vertical ground motion,the study of dynamic response mechanism of bridge under non uniform earthquake excitation is carried out.Through the reasoning and analysis of bridge dynamic equation and response analytical solution under non uniform excitation,all factors affecting the dynamic response of bridge are obtained,it is divided into two types of internal causes influenced by the bridge itself and the external causes influenced by the external action load through the study of various influencing factors,the external causes are mainly composed of the distribution mode and amplitude of the input acceleration combination and displacement combination,the internal factor is dominated by the variation of the span ratio,the modulus of elasticity and the moment of inertia of the section.The displacement response of the bridge is taken as an example,the distribution of the most unfavorable combination and favorable combination is obtained when the dynamic response of the bridge appears at the most unfavorable and favorable conditions.Then,the influence of different factors on the dynamic response of the bridge is deduced by the program analysis.The dynamic time history analysis of the bridge main girder model is carried out,and the rationality of the combination effect distribution is verified in time domain.Finally,the relationship between the DTW distance distribution of each combination is calculated,and the distribution rule of DTW distance is obtained.In this paper,the combined distribution of acceleration and displacement in the most unfavorable and favorable conditions is obtained by programming analysis,The random vibration analysis of the bridge main beam model is carried out,the relationship between the displacement response value of bridge under the condition of the most unfavorable combination,consistent excitation and favorable combination is verified in frequency domain,the rationality and correctness of the combined distribution effect are verified.In this paper,the present traditional uniform modulation ground motion model can not fully characterize the partition stationarity of the time frequency two domain,and affects the present situation of the accuracy of the random vibration analysis of the bridge structure.A non uniform modulation ground motion model is established by multimodal smooth envelope and nonstationary noise signal.The model can fully reflect the fluctuation and attenuation characteristics of ground motion in time domain,and its spectral characteristics are also close to the real signal.On this basis,a random evolution model of non stationary ground motion is established based on time and frequency variables.The analysis results show that the above two models are superior to the homogeneous modulation model in the time domain and frequency domain.The statistical conversion power spectrum and statistical conversion power spectrum plus white noise are obtained through statistics of real seismic data,the vertical excitation analysis of three span continuous beam bridge is carried out by spectral analysis.Compared with the traditional power spectrum,it is found that the traditional power spectrum will amplify the structure response at low frequency,and the structural response will be underestimated at the high frequency stage.