Analysis Of Damper Parameters And Study Of Seismic Vulnerability Of Long-span Suspension Bridge

With the rise of seismic isolation design and the improvement of structural seismic requirements,viscous dampers are widely used in long-span suspension bridges,and play an important role in the vibration control of suspension bridges.The parameters of dampers directly affect the control effect of energy dissipation and vibration reduction.In the process of daily use,oil leakage is a common disease of damper.With the leakage of damping medium,the working state of damper changes,which increases the uncertainty of bridge and damper under the action of earthquake.Therefore,to discuss the influence of damper parameters and health status on the seismic response of the structure,and to carry out the vulnerability analysis of the damper under the earthquake action,is a key issue related to the normal work of the damper and the safe use of the bridge,so it is necessary to carry out relevant research.Based on this,this paper carried out the following work:(1)In order to study the influence of parameters of viscous damper on the seismic response of suspension bridge,the nonlinear time history analysis method was adopted.Based on SAP2000 finite element analysis software,the whole bridge model of single tower special-shaped suspension bridge was established,which considered the nonlinearity of material structure,the nonlinearity of viscous damper,the verticality effect of main cable and the interaction of pile and soil.The longitudinal position of main beam was determined under multi-level damping coefficient C and damping index α.The main conclusions were as follows:Under different damping coefficient and damping index,the fluctuation range of seismic response index was obviously different,the longitudinal displacement fluctuation of main beam was 84.52%,while the transverse shear fluctuation of tower bottom was only 1.7%;the variation trend of seismic response of different structures was obviously different,from the point of view of damper parameter Optimization:longitudinal displacement of main beam,longitudinal displacement of tower top and longitudinal bending moment deviation of tower bottom tended to take the small value toward C,and the larger value for α;the transverse shear force at the tower bottom tended to take the large value for C,and the smaller value for α;finally,chose C =2000k N·s / m,α = 0.4 as the quasi optimal parameter of the bridge damper.(2)Considering the frequent oil leakage of viscous dampers in the actual bridge engineering,a simple and reasonable mechanical model was needed to describe the oil leakage of dampers.Based on the summary of various mechanical models of dampers,the advantages and disadvantages of each model and its application scope were pointed out.At the same time,the existing damper oil leakage model was introduced,and the limitations of this model in frequency and quantitative description were analyzed.Then,based on the classical Maxwell model,by modifying the damping coefficient and equivalent energy dissipation stiffness,a simple mechanical model considering the damper oil leakage was proposed,and the quantitative definition of the damper oil leakage degree was realized.(3)In order to study the influence of damper oil leakage on the seismic response of suspension bridge,four damper models of 0%(intact),10%,20%,40% oil leakage were defined with the selected damper quasi optimal parameters as default values.The nonlinear time history analysis method was used to discuss the influence of different damper oil leakage on the seismic response and damper working state of suspension bridge.The main conclusions were as follows:The energy dissipation effect of the damper was not only affected by the damper parameters,but also related to its working state.When the limit state was not considered,the influence of oil leakage from the damper on the seismic response of various structures was different,and the hysteretic energy dissipation characteristics of the damper would be significantly changed.When the oil leakage of the damper increased from 0% to 40%,the output of the damping force of the damper decreased by 34.57%,and the displacement of the damper increased by 12.6%,which greatly changed the working energy consumption state of the damper and increases the uncertainty of the damper under the earthquake action.It was necessary to carry out the seismic performance evaluation of the damper based on the probability reliability.(4)In view of the lack of damper damage index in the existing research,referring to the limit state test of large tonnage viscous damper and domestic and foreign codes,two damage indexes of damper based on strength and displacement were defined for the first time,and three damage states are defined under each damage index,which were "over limit work","medium damage" and "complete failure ".(5)In order to study the vulnerability of viscous damper of suspension bridge under earthquake,the fitting curve method based on the capacity demand ratio model of damage index was selected as the generation method of vulnerability curve,and the influence of oil leakage of damper on the exceeding probability of each damage index,the damage index of strength damage index,displacement damage index and the damage index of strength displacement joint control were considered.The main conclusions were as follows:(1)Considering the oil leakage of the damper,the vulnerability curves of the damper were obviously different under different damage indexes of 0%,10%,20% and40%.With the increase of oil leakage,at the level of PGA of 1.5g,the probability of over limit and damage failure of damper based on the strength damage index of damper was significantly reduced,and the probability of "complete failure" of damper under this index was reduced from 14.82% to 0.03%;meanwhile,the probability of over limit and damage failure of damper based on the displacement damage index of damper was significantly increased,and the probability of "complete failure" of damper under this index was significantly increased.The probability of "complete failure" increased from 29.35% to 38.4%.(2)Considering the joint control of the two damage indexes,with the increase of the oil leakage of the damper,the damage exceedance probability of the damper under the medium damage level changed from the strength index to the displacement index,and the joint exceedance probability decreased by 51.2% from 56.13%;the damage exceedance probability of the damper under the complete damage level was strictly controlled by the displacement index,and the joint exceedance probability increased from 29.35% to 38.4%.In this paper,the sensitivity analysis of the seismic response of long-span special-shaped suspension bridge was carried out to provide reference for the relevant design;a simple and easy damper parameter model considering oil leakage was proposed to quantitatively discuss the impact of damper diseases.On this basis,two damage indexes of the damper are proposed for the first time and vulnerability analysis was carried out,hoping to evaluate the health of the following large tonnage viscous dampers Estimation,reinforcement and detection of viscous damper,and special design of viscous damper provide certain reference data and design basis.