Study On The Flexural Performance Of Box Type Concrete Beams Strengthened With Different Type

Transport facilities is an important infrastructure to ensure national economy and social development,as an important part of reinforced concrete bridge in the traffic facilities is particularly important.Because of survey,design,construction,time and so on a variety of reasons,coupled with the increasing highway traffic,the withstood load of highway and bridge is becoming more and more serious,and widespread lack of bearing capacity.Many of the existing bridges has been unable to meet the requirements of modern traffic,even in the normal use state,many buildings and bridges has been out of age and the emergence of the extended service now.In this case,the simplest way is to demolish.But our country is a developing country with limited economic conditions,all the reconstruction is bound to cause a great waste of social.Bridge strengthened is the economic and efficient strengthened method,the passage aiming at steel plate strengthened,angle steel strengthened,CFRP strengthened(carbon fiber)three common kinds of in strengthened engineering,studying on the performance of flexural behavior and strengthening effect factors of box type concrete beams.18 box type concrete test specimen was designed in the experimental,considering the different concrete strength,reinforcement ratio,amount of strengthened,U stirrup spacing of four parameters,and effects of these four parameters is studied on the failure pattern of test specimen strengthened,stiffness,bearing capacity,mid span displacement,strain.Through the comparison of mid span strain,deflection relationship,bearing capacity,mid span displacement,stiffness and the development of crack after the test specimen strengthened,analysis the stress performance of the above three kinds of strengthened methods,and according to the existing strengthened standard about bending calculation formula of bearing capacity of strengthened concrete test specimen,verify the formula of calculating the bearing load of the box type beam strengthened.The main contents are as follows:To study on variation law of bending stiffness,bearing capacity,displacement,steel plate and steel strain of box type concrete test specimen strengthened with steel plate,the test results were studied.The research results show that,the flexural behavior of test specimen can be well improved with steel plate strengthened.The performance shows that the compressive concrete was crushed,tensile steel and steel plate was yield and the peeling failure phenomenon between steel plate and concrete didn't occurre.The elastic stage,the stiffness of standard test specimen and strengthened test specimenare basically the same;in yield phase,the stiffness of strengthened test specimenis significantly improved.The yield load and ultimate load are improved obviouslyby steel plate strengthened.Steel plate strengthened belongs to a passive strengthened way,so have little influence on the cracking load.After Steel bar yield,the strain of steel plate grows rapidly and can limit steel bar strain,which means making full use of the reinforcement material,achieve good reinforcing effect of steel plate strengthened.To study on variation law of bending stiffness,bearing capacity,displacement,angle steel and steel bar strain of box type concrete test specimen strengthened with angle steel,the test results were studied.The research results show that,the angle steel strengthened is a passive reinforcement way,and the size of angle very small,not effective package on the test specimen bottom surface,so is little effect on the cracking load the test specimen.Steel angle strengthened can effectively improve the yield load and ultimate loadof test specimen.Steel angle strengthened can improve the ductility of the test specimen,mainly because the standard test specimenon the bottom configuration longitudinal steel bar is less,the failure phenomenon of strengthened test specimen shows the phenomenon of reinforced test specimen.On the elastic stage,the stiffness of standard test specimen and strengthened test specimenare is basically the same;on the yield phase,the stiffness of strengthened test specimen is significantly greater than the standard test specimen.Before cracking of concrete,the strain of steel bar and angle steel of test specimen strengthened with angle steel are no significant difference,can stress together;angle steel is yield before the steel bar,the effect of box type concrete test specimen with angle steel is remarkable.To study on variation law of bending stiffness,bearing capacity,displacement,CFRP and steel bar strain of box type concretet est specimen strengthened with CFRP,the test results were studied.The research results show CFRP strengthened has small effect on the cracking load because CFRP belongs to a passive reinforcement way and such materials is very thin,at the early stage of loading CFRP role is very small.CFRP strengthened can effectively improve the yield load and ultimate load of test specimen,give full play to it's high strength properties,play a good reinforcing effect.CFRP strengthenedhas little effect on test specimen stiffness before test specimenyield,the test specimen stiffness improves after yield.The ductility of CFRP strengthened test specimen was reduced,but generally meet the requirements.Box type section beam is one of the section widely used in bridge,with excellent properties.Presently experiments and relative research theory are concentration on the rectangular or T shaped,but less research on the box type beam.Through this research can fill the blank on steel plate,angle steel,CFRP strengthened bending test,provide test data and theoretical basis for box type concrete beam strengthened.