Seismic Behavior Research Of Irregular Bridges Considering Bearings Friction Sliding And Structural Pounding

Irregular bridge is main selectable program as bridge structure crossing complex terrain,which is largely applied in our country.The internal force coupling effect and structural collapse mechanism of the bridge become remarkable and complicated due to its irregular shape and height of piers incorporates.Contrary to the Northride earthquake in America,and the Hyogoken-Nanbu earthquake in Japan,the seismic disasters in Wenchuan earthquake mainly included girder sliding,expansion joint damaged,slipping side retainer fracturing,etc.However,slight cracks were just appeared in piers,that was because the friction sliding effect of laminated rubber bearing reduced seismic force transformed to piers.So it is important to systematically study the effect on seismic behavior of bearing friction sliding and structural pounding for irregular bridge.It is based on theoretic research,shaking table test,and scientific test methods,seismic behavior of irregular bridge were studied under seismic excitation concerning bearing friction sliding and structural pounding in the paper.The main contents and achievements are as follows :(1)Shaking table test and numerical analysis were carried out on the seismic-resistance and seismic-isolation system of irregular curved bridge,and the crack propagation law and damage mechanism of two models were studied.The relations of natural frequency and damping ratios of two systems varying with seismic intensity were studied by analyzing characteristic parameters of measuring points on structure.The experimental data of acceleration and strain indicates that the seismic-isolation system has better behavior under seismic action.Displacement of girder and top of pier in the experiment indicates that radial and tangential displacements should be rigorously restricted for the seismic-isolation system of irregular curved bridge as to avoid the girder drops.(2)Taking an irregular curved bridge in the shaking table test as a research object,a space-coupling model concerning bearing friction sliding was constructed,and the impacts of bearing stiffness and frictional ratio on dynamic response of the kind of bridge were studied.Results shows that bearing sliding can largely dissipate seismic energy,reduce bending moment at the bottom of pier,thus avoid the appearance of plastic hinge at the area;the initial bearing stiffness and frictional ratio should be chosen accorrding specific structural style,which have a great significance on acceleration shock absorption rate of an irregular curved bridge.(3)The basic concept and basic mechanics model of the irregular curved bridge floating seismic system were been proposed.The working mechanism of the system and failure mode of the irregular curved bridge with the floating system were discussed.Through the numerical analysis of the acceleration response of the top of pier and the top of the beam in the shaking table test,it indicated that the seismic performance of the floating seismic system was good and can be used to seismic design of a curved bridge in the high seismic intensity area.(4)Impacts of frequency spectral characteristics of seismic waves and input dimensions on structural dynamic response and damage mechanism of the irregular Y-shaped bridges were studied by shaking table test.Results showed that the most unfavorable earthquake input was along branch straight bridge when the acceleration response of the pier top was calculated;relative displacement of adjacent girders and pounding force were accelerated when input dimension of seismic waves was increased;the demand can be satisfied by inputing seismic in two directions when calculating strain at the bottom of the pier;seismic response of the structure will be increased when seismic frequency spectral was in a broad distribution and seismic wave amplitudes were closed in every term.(5)Taking an irregular Y-shaped bridge in the shaking table test as a research object,spatial analysis model was established to study the impact on the seismic behavior of Y-shape irregular bridge concerning bearing friction sliding and structural pounding.The results showed that displacement and internal force at the top of the pier would decrease while girder generated larger impulse acceleration,when only considering pounding of expansion joint influence;as taking bearing friction sliding and pounding of expansion joint into consideration,the relative peak displacement at the top of the fix pier and adjacent girders both decreased,impulse acceleration of girder may increase or decrease;pounding in longitudinal direction will arise for Y-shape bridge under longitudinal seismic wave.However,there was not only the pounding along the bridge,but also transverse pounding should not be ignored.It had a great influence on calculation results of pounding of expansion joint with the choice of structure calculation models.(6)According to the shaking table test of multi-dimension seismic input based on structure with four classes of variable parameters,the impact of seismic intense and dimension on pounding force of adjacent structures were studied.On the basis of experimental results,four kinds of impact elements were used in the numerical simulation of the impact force in the pounding process,and the applicable scope and the advantages and disadvantages of different pounding units were discussed.Combined with shaking table test and numerical calculation method,the effects of pounding stiffness,pier height,pounding clearance,mass ratio of adjacent girders,and restitution coefficient on pounding response of the structure were studied.(7)Based on structural dynamic principles,a simplified dynamic mechanical model with multiple degrees of freedom was established for an irregular multi-span simply supported concrete bridge,dynamic equation of the model was derived according to Lagrange’s equations.Seismic behavior of irregular bridge concerning nonlinear influences of abutment stiffness,bearing friction sliding,structural pounding under traveling wave based on program using Runge-Kutta methods was analyzed to instruct the seismic behavior of this kind of bridge.