Study On The Basic Mechanical Properties And Durabilities Of FRP-Steel Composite Material

Fiber reinforced polymer (FRP) is increasingly being used for retrofit and repair of structures, due to its light weight and high strength. But, the structures strengthened with FRP have brittle performance significantly, which bad for the structures’seismic performance. Based on the research background and sponsored by the Natural Science Foundation of China (51108355) and Natural Science Foundation of Hubei Province (2011CDB269), a new material using FRP and steel sheet has been put forward, namely FRP-Steel composite material, which give full play to the mechanical behavior of FRP and steel, significantly improve the strength, ductility and rigidity of the single reinforced material. Experimental researches have been carried out in the mechanical properties of the FRP-Steel composite material under the laboratory environment and the elevated temperature environment, the bond property between FRP and steel under the elevated temperature environment, the durability of the FRP-Steel composite material under wet-dry cycles, which can be summarized as follows:1、Thirty-six specimens of FRP-Steel composite material were made by hand, and then the tensile tests were conducted, including fiber type (Carbon fiber, glass fiber and basalt fiber), the fiber layers, the steel thickness and the laying method of FRP and steel. The results indicate that:(1) CFRP-Steel composite material has high strength and better plastic performance. GFRP-Steel composite material has better ductility after steel yielding;(2) When FRP layers in a certain range, with the steel thickness increasing, FRP-Steel composite materials have an increasing trend in the basic mechanical performance, while the relative increase is reduced, and when the steel thickness exceed4mm, the reduce speed increase.(3) More symmetry and uniform the laying method is, more better the mechanical performance has. Based on the results, an analysis under the mixing rule is developed to predict the mechanical performance of FRP-Steel composite material, the calculation results have good agreement with the test results.2、Sixty-six specimens of CFRP-Steel composite material and GFRP-Steel composite material were exposed to elevated temperature environment at30℃～120℃, and the tensile tests of specimens were conducted. The results indicate that the basic mechanical performance of the specimens gradually decreases with the increase of temperature, and the decrease is more pronounced at glass transition temperature of adhesive. Based on the results, a degradation model is developed to predict the elasticity, the modulus after steel yielding, the yield strength and the fiber breaking strength of FRP-Steel generalized composite material at elevated temperature, and the calculation results have good agreement with the test results.3、Performance of FRP-steel bonded interfaces under elevated temperature (30℃～120℃) conditions according one hundred and fifty-three double shear specimens are investigated. There are two FRP-steel double shear models for different research purpose.(1) The FRP-steel double shear model I test results indicate that:1) The failure mode gradually change with the increase of temperature;2) The ultimate strength and bond stiffness of the specimens gradually decrease with the increase of temperature, and the decrease is more pronounced under the glass transition of adhesive. Based on the results, a degradation model under elevated temperature of FRP and steel bond stiffness is developed by using modified Arrhenius analysis, the calculation results have good agreement with the test results;(2) The FRP-steel double shear model II test results indicate that:1) The ultimate strength gradually decrease with the increase of temperature;2) The failure mode is mainly FRP and steel peeling off;3) On the basis of research achievements of FRP and concrete bonding interface, the bonding shear stress-local slip model of FRP and steel under different temperature is development, the ultimate bonding load formula of FRP and steel is put forward, and the calculation results have good agreement with the test results.4> Durability of CFRP-Steel composite material under aggressive environmental conditions such as wet-dry cycles according one hundred and twenty specimens are investigated. The results indicate that:(1) The environmental conditions further reduce the yield strength and fiber breaking strength. However, no significant change the elastic modulus and the modulus after steel yielding of the one-sided laying CFRP-Steel composite material.(2) The environmental conditions further reduce the yield strength, fiber breaking strength, elastic modulus and the modulus after steel yielding of the bilateral laying CFRP-Steel composite material.(3) The mechanical performance of bilateral laying specimens has further reduce than the one-sided laying specimens. Based on the results, a modified regression analysis is developed to predict the long term durability performance of CFRP-Steel composite material, the model calculation results have good agreement with the test results. The fiber bresking strength regression model of CFRP-Steel composite material is put forward to predict the service life of CFRP-Steel compsite material under wet-dry cycles environment.