Preliminary Study On Seismic Retrofitting Method Of Existing Beam Bridge

At present,China's seismic design specification for highway bridges has been issued and implemented for three generations,namely " Specification of Earthquake Resistant Design for Highway Engineering(1977)","Specification of Earthquake Resistant Design for Highway Engineering(1989)" and "Guidelines for Seismic Design of Highway Bridges(2008)".In 2012,China also issued and implemented the seismic design specification for urban bridges.The revised edition of Guidelines for Seismic Design of Highway Bridges(2008),the fourth generation specification for seismic design of highway bridges,will soon be released and implemented.With the advancement of bridge seismic design technology and the update of bridge seismic design specification,the requirements for bridge seismic design become higher and more stringent and detailed.Therefore,the seismic performance of bridges built in different periods in China is different.Bridges built before the implementation of the Specification of Earthquake Resistant Design for Highway Engineering(1977)may not have seismic design due to the lack of seismic design specifications.Bridges designed according to the Specification of Earthquake Resistant Design for Highway Engineering(1977)and Specification of Earthquake Resistant Design for Highway Engineering(1989)may also have different degrees of problems in seismic design due to the low requirements of the specifications or the lack of detailed provisions.Therefore,it is very important and necessary to evaluate the seismic performance of existing bridges and reinforce the bridges with seismic performance problems.However,at present,there is no specific specification for seismic retrofitting design of bridges in China,and the research work is insufficient.Therefore,it is necessary to carry out systematic and in-depth research in this area.Based on the above analysis,relying on the national key research and development project "Key Technologies for Improving the Seismic Performance of Existing Urban Bridges in High Seismic Intensity Zone without Interruption of Traffic",this paper carries out a preliminary study on the seismic retrofitting methods of existing girder bridges.The main research work is as follows:1.By counting the damage types and their proportion of existing girder bridges in several large earthquakes,the common damage types of existing girder bridges in earthquakes are obtained.Taking the revised edition of Guidelines for Seismic Design of Highway Bridges(2008)as the reference standard,the four generations of seismic design specifications of bridges are compared and analyzed.At first the seismic fortification standards,importance coefficient,ductility design and seismic measures of the four generations of seismic design specifications of bridges are compared and analyzed,and then a detailed comparative analysis of three specific clauses: minimum pier-beam overlap length,bearing seismic performance checking and design seismic force calculation is done.The possible types of seismic design defects of existing girder bridges built in different period in China are summarized and the possible types of seismic damage that maybe caused by these defects are analyzed.2.Seismic retrofitting methods of existing girder bridges are summarized.Seismic retrofitting methods that can be adopted and have mature technology in China are summarized,and the selection principles of seismic reinforcement methods are studied.It is suggested that appropriate seismic retrofitting methods should be selected from the aspects of reinforcement effect,traffic impact,design and construction difficulty.In view of the most common defect of seismic capacity,such as insufficient overlap length of piers and beams,the concrete selection principles of seismic strengthening methods are put forward,and the corresponding design methods are given.3.Finite element simulation analysis method is used to study the effect and scope of application of seismic strengthening of beam bridges using isolation method.By changing the pier height of the model,the seismic analysis of different pier height bridges is carried out.The seismic isolation effect of lead rubber bearing is analyzed from the aspects of seismic internal force response and displacement response of bridges,and the recommended application scope of the seismic isolation strengthening method is given.