| As a kind of geological disaster with strong destructiveness,earthquake damages bridge structures far more than other disasters.As a common structural form of highway bridges,single-column pier bridges are often strengthened with typical antioverturning strengthened measures due to their insufficient anti-overturning performance.However,there are few studies on the influence of these anti-overturning reinforcement measures on the seismic performance of single-column pier bridges.In addition,with the significant increase in the number of high-magnitude potential source areas in China,especially the introduction and application of the idea of fortifying against extremely rare earthquakes,the existing single-column pier bridges need seismic reinforcement.In this thesis,a single-column pier bridge in service is taken as the engineering background.The dynamic elastic-plastic time-history analysis method is used to study the seismic performance of the unstrengthened bridge.Then,the influence of typical anti-overturning strengthening measures on the seismic performance of the single-column pier bridge is explored.And the key problem of insufficient seismic performance is clarified.Based on the concept of energy dissipation,two new strengthening methods are proposed,which are to replace the connection device with the X-type energy dissipation device and replace the concretefilled steel tube(CFST)column with the energy dissipation auxiliary column.Finally,the goal of double improvement of the anti-overturning and seismic performance of single-column pier bridges is achieved.The main research contents and conclusions are as follows:(1)To obtain the seismic performance of typical single-column pier bridges in service under frequent,rare and extremely rare earthquakes,the dynamic elastic-plastic model of the single-column pier bridge was first established.Then the natural vibration characteristics of the single-column pier bridge were analyzed.And the far-field and near-field typical ground motions were selected to carry out the dynamic elastic-plastic time-history analysis.The seismic responses such as plastic hinge angle,pier bottom shear,pier top displacement and support shear under frequent,rare and extremely rare earthquakes are obtained.Finally,the seismic performance is analyzed by comparing with the standard limit value.The results show that the lateral stability of single-column pier bridge is poor.The bearing shear of the unstrengthened single-pillar pier bridge under extreme earthquake in far-field condition does not meet the specification requirements.The angle of plastic hinge area,the displacement of pier top and the shear force of support all exceed the limit value of seismic specification under near-field earthquake.Near-field earthquakes are more harmful to the single-column bridge than far-field earthquakes.(2)Aiming at the problem of insufficient seismic performance of the singlecolumn pier bridge in service under rare or extremely rare earthquakes,the influence law of existing typical anti-overturning strengthened measures on seismic performance of the single-column pier bridge was examined.And whether the reinforcement measures of concrete filled steel tube(CFST)auxiliary column and steel cap beam can improve the seismic performance of the single-column pier bridge was determined.The seismic performance of the single-column pier bridge strengthened with CFST auxiliary columns and steel-covered beams is obtained by time history analysis.And the seismic performance is compared with that of the single-column pier bridge before strengthening.The results show that one or more seismic responses of the singlecolumn pier bridges after strengthening do not meet the specification requirements.The near-field earthquake is more harmful to the single-column bridge than the far-field earthquake.After the strengthening of the CFST auxiliary columns,the plastic hinge angle,the displacement at the top of the pier and the shear force at the bottom of the pier all decrease.But the shear force at the bottom of the pier increases.The maximum plastic hinge angle of the strengthened single-column pier bridge decreases slightly.But the corresponding bending moment increases,which shows that the development degree of the plastic hinge is improved.The rest of the seismic response is similar to that of the unstrengthened single-column pier bridge.(3)Because of the phenomenon that the current typical anti-overturning strengthened measures do not improve the seismic performance of single-column pier bridges,a new strengthened method is proposed to replace the connecting device with an X-type lead extrusion damper between the CFST auxiliary column and the original pier.The structure,working principle and arrangement of the X-type viscous damper are introduced in this thesis.Through parametric analysis,the auxiliary column which is most suitable for the X-type viscous damper of the bridge is obtained and applied to the single-column pier bridge.The damping effect of the reinforcement method of adding energy dissipation connection is explored.The results show that,the singlecolumn pier bridge with ordinary connecting device between the CFST auxiliary columns,the addition of a X-type damper under far-field earthquake can significantly reduce the maximum response values of plastic hinge angle,pier bottom shear,pier top displacement and support shear.And the maximum damping ratio of seismic response is between 26.9 %～45.6 %,and all meet the requirements of the specification.Under near-field earthquakes,the maximum damping rates of plastic pivot angle,pier bottom shear,pier top displacement and support shear are is between 27.6%～43.8%.However,the shear force at the bottom of the single-column pier bridge after reinforcement still exceeds the standard limit.(4)To further improve the problem of pier base shear exceeding the limit when the auxiliary columns of X-type lead extrusion dampers are installed.A new strengthened method of replacing CFST columns with energy-dissipation auxiliary columns is proposed,which can not only meet the requirements of anti-overturning of single-column pier bridges,but also greatly improve the seismic performance.The structure,working principle and arrangement of the new type of energy dissipation auxiliary column are introduced in this thesis.Through parametric analysis,the energy dissipation auxiliary column with optimal parameter combination is obtained and applied to the single-column pier bridge.The seismic response of a single-column pier bridge with energy dissipation auxiliary columns is analyzed,and its damping effect is compared with that with CFST auxiliary columns.The results show that,compared with the single-column pier bridge with CFST auxiliary columns,the addition of energy dissipation auxiliary columns under far-field earthquake can significantly reduce the maximum response value of pier bottom shear,pier top displacement and support shear,and the maximum damping rate is between 16.3%～48.0%.And all seismic responses meet the specification.Under near-field earthquakes,it has good damping effect on plastic hinge angle,pier bottom shear,pier top displacement and support shear.The maximum damping rates are is between 26.6%～51.3%,and all seismic responses meet the standard limits. |
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