Research On Seismic Retrofit Methods For The Railway Bridge With Gravity Piers

The railway bridge is the economic lifeline of the country and lifeline projects. As thesubstructure of the bridge, piers are easily damaged under the action of earthquake. Becauseof the history of economic restrictions, in some areas with highly seismic intensity in China,there still exist massive gravity piers with low steel reinforcement. The poor ductility andenergy-dissipating capacity of this type of pier result in the deficiency of its seismic resistantcapability, which would lead to severe damage of a bridge or even collapse under the actionof earthquake. Strengthening this type of bridge piers before an earthquake, and repairingthem damaged by earthquakes can not only save money, but provide significant guarantee toconduct the relief work on time. Therefore it has been an urgent issue to propose a reliableretrofitting method for existing railway gravity piers and to study how to evaluate the seismicresistant performance of piers after retrofitting. The main contents in this paper are as follows:(1) Based on the problems of concrete gravity bridge piers, including low steelreinforcement and vulnerability under the action of earthquake, three seismic retrofittingmethods are proposed: wrapped carbon fiber sheet, wrapped concrete and wrapped steel plate.The process and method of construction for those three methods are presented, and especiallythe anchorage method of the connection between these three retrofitting materials withfoundations at the bottom of the bridge pier is detailed.(2) For those three seismic retrofitting methods, a finite element model is built and itssolving method is also studied. Bearing capacity, displacement ductility and distribution rulesof plastic zone of pier models before and after retrofitting are studied based on ANSYS thefinite element analysis software. The effect of factors such as retrofitting materials, anchorageat the pier bottom and retrofitting height is discussed; also retrofitting effects of differentmethods are compared.(3) Six sets (23models totally) of pier test models with different steel ratios are designedand built based on similarity principle of model. Seismic retrofitting on damaged pier modelsis conducted using those three retrofitting methods. Seismic performances of pier modelsbefore and after retrofitting are studied through pseudo-static test method. Hysteretic curves,skeleton curves, displacement ductility, energy-dissipating capacity and destruction mode ofpier models before and after retrofitting under action of cyclic horizontal force are acquired.Seismic performance and retrofitting effects of pier models before and after retrofitting arecompared and analyzed, verifying the effectiveness and feasibility of those three retrofittingmethods and anchorage connection methods.(4) Evaluation method of seismic capacity of bridge piers after retrofitting is alsoprovided. Simplified method of capacity curve of retrofitted pier models is established and simplified calculating formula is proposed based on finite element analysis and model test. Onthe basis of the rest service lives of existing railway bridge piers, compensation method foradjustment coefficient of seismic action considering influence of service life to elasticdemand spectrum is proposed, and inelastic demand spectrum curve considering displacementductility of retrofitted piers is established. Targets and limits values of seismic performance ofretrofitted railway gravity piers are given. A simplified evaluation method and the process ofseismic capacity of retrofitted gravity piers are put forward, and a railway gravity pier withdeficient seismic capacity is also taken as example to conduct the seismic capacity evaluation.