Mechanical Behavior And Reliability Of Steel-Concrete Composite Beams Considering Durability

Steel-concrete composite beams are widely used in Bridge Engineering. With the growth of service time, the durability damage will occur gradually for composite beams’main components such as steel beam, concrete slab, reinforcement and stud, and it leads to the mechanical property deterioration of composite beams, such as failure mode transforming, carrying capacity declining, stiffness degradation, ductility reducing and so on. So the reliability index will be reduced gradually and service life will decline in service period for composite beams. To insure safety operation and to provide technology basis for durability design, service life prediction, reinforcement and rebuilt, it is very necessary to carry out research on the mechanical behavior of steel-concrete composite beams considering durability damage. This research project is supported by National Natural Science Foundation under the Project No.50878216"Durability Research of Steel-concrete Composite Beams " and the Research Fund for the Key Program of Ministry of Railways the Project No.2007G031"Research on Durability Technical Measures of Steel-concrete Composite Beams ". Centering on the essential scientific problems existing in durability research on steel-concrete composite bridges, aiming at improving the durability,the systematical and in-depth study have been carried out which includes the mechanical behavior of corrosion stud and stud shear connector after stud corrosion,flexural capacity and time-dependent reliability of composite beams in which stud suffer durability damage.The main research works include as follows:(1) By penetration test of chloride ion for3section types’stud shear connectors under artificial climate environment were carried out, penetration path of chloride ion for stud shear connectors was studied, chloride resisting properties of3section types’stud shear connectors was compared, and erosion rule of chloride ion for combined surface of composite structures was build up.(2)The corrosion studs have been obtained by artificial climate accelerated corrosion method and galvanostatic accelerated corrosion method. Through corrosion studs’ tensile test, the degradation mechanism of mechanical behavior has been studied and quantitative relationship models of nominal yield strength, tensile strength, elongation and modulus of elasticity vs. corrosion rate for corrosion stud. And on the basis of research achievement above, the constitutive model of corrosion stud has been build.(3)Through regression analysis of push-out tests which were conducted by scholars at home and abroad, the calculation formula of shear bearing capacity for stud shear connectors has been build up in which interact influence of stud and concrete was considered. According to the formula, the analysis and comparison on push-out test results which were conducted in this paper has been performed. The computational model of load-slip curve of stud shear connector has been set up. Based on the experimental researches of10stud shear connectors in which stud suffered corrosion, failure model, shear capacity and load-slip curve have been obtained. And on the basis of analysis at experimental results above, The computational model of shear capacity, shear stiffness, ultimate slip and load-slip curve for stud shear connector in which stud suffered corrosion.(4) The galvanostatic accelerated corrosion tests of14steel-concrete composite beams were carried out and the experiments on flexural behavior were conducted. Based on test results, the research on fracture characteristics, fracture distributing, deformation development characteristics, strain distributing in mid-span section, relative slip of joint surface, ductility and stiffness, were carried out.(5) On the basis of flexural strength model of corrosive steel-concrete composite beams considering influence of corrosive cracks in concrete cover, with considering of the effect of shear connection degree on bending capacity after stud corroded, by introducing coordination coefficient of corrosive stud and concrete, adopting simplified plastic theory, by integrate of test results in this paper, the flexural strength model considering combined corrosion effect has been put forward. The validity and rationality of model has been validated thought example analysis.(6) Based on flexural capacity ultimate stage, the analysis method of time-varying reliability for steel-concrete composite beams was put forward, which considered stud corrosion and time-dependent characteristics of load effect. The time-dependent reliability analysis for a steel-concrete composite beams bridge was conducted under de-icing salt condition, and the factors that influenced the reliability index of steel-concrete composite beams were investigated.