Study On The High Strength Steel Wire-CFRP Externally Prestressed Cable Imposed On The Continuous Girder Bridge

The speed of bridge construction in China has slowed down,while the bridge disasters frequently occur,the problems of insufficiency of bearing capacity and fatigue damage in bridge,which has served for a long time,has been gradually exposed.The keynote of bridge construction in China has changed from construction to maintenance.Under this background,the reinforcement of bridge serving for a long time has become a hot topic in the field of bridge research in China.There are many repair and reinforcement cases based on bridges in service at home and abroad.External prestressed reinforcement system has gradually became the main method of bridge reinforcement because of its advantages of active reinforcement,clear force transmission route and fungibility.The traditional external prestressed cables consist of high strength steel strand and CFRP tendons,while these two materials have their respective defections.On this background,a new kind of external prestressed cable composed of high strength steel wire and CFRP material has been put forward in this program.This external prestressed cable combines the advantages of the ductility and lateral shear resistance of the steel wire and the durability of CFRP.Based on the principle of cooperative deformation for composite materials,the model of tensile process of composite bar has been predicted.The tensile test of composite bar has been carried out.By comparing the analysis of test results and the theoretical model,the results indicate that composite bar performs as expected in the stage of elastic stage.After the strain reaches the ultimate strain of the carbon fiber,ductile stage was not distinct as expected.The stress and strain curves of samples drops separately in the end,which indicates that the mixtion of steel wire has contributed certain ductility.Then,the PC continuous box girder bridge with insufficiency in bearing capacity and several cracks has been analyzed,using finite element software Midas-Civil.The results of modeling analysis for the bridge in bearing capacity are consistent with the statistics of routine monitoring.The results shows that the stress in the bottom of the cross section in the middle bridge span is beyond limitation,so is the stress in the top of the cross section in the middle pier.That is to say,the cross section is insufficient in flexural capacity in those areas.In this case,linear external prestressed cable is imposed on the girder to strengthen the bridge,which consists of 8 beams of 15-?15.24 high strength steel wire with CFRP composite external prestressed cable in the top of middle pier and the same prestressed cable in the bottom of the middle span.After the calculations and analysis,the bearing capacity of this bridge satisfies the stress requirements of the bearing capacity of the ultimate state of the bridge normal use and bearing capacity limited stated,while realizing the control of the deflection in the midspan.Finally,by the means of the analysis of finite element modeling,another two kinds of external prestressed cable materials,CFRP composite cable and steel strand,have been compared with steel wire with CFRP prestressed cable.It turns out that under the same tension control coefficient 0.7,steel strand,CFRP cable and high strength steel wire with CFRP composite cable perform differently in the loss of prestress,deflection control,promotion of flexural bearing capacity,and the stress control of cross section through the whole girder.The result shows that CFRP performs better on the deflection control and the bending stiffness.However,composite wire and steel strand is better on the stress control of cross section through the whole bridge.When the prestress loss causing by the prestress relaxation appears,both CFRP and composite cable show a trend of increasing deflection amplitude,while the increase of steel strand remains unchanged.