Study On Mechanical Behavior Of RC Beam And Column In Colliery Environment Strengthened With Frp Reinforced Cementitious Matrix

It’s necessary to keep the high carrying capacity and reliability of buildings or structures existed on the mine ground mainly in reinforced concrete(RC)structure,for the safe production of coal or reuse of abandoned mine space.However,those structures are damaged and deteriorated after about ten years service,and need to be repaired or strengthened.Fiber reinforced polymer(FRP)is given more application in the coal mine.Fiber reinforced cementitious matrix(FRCM)can be utilized to replace epoxy resin and overcome its durability problems,while the feasibility and mechanism are not clear yet.Based on the previous foundation and combination method of physical experiments,numerical calculations,and theoretical research,the degradation regularity of RC materials and the compound action mechanism between the deteriorated concrete and corroded steel bar under the coupling effect of colliery environment and load is studied.And then the degradation of RC beam and column is studied together with the influence factors.A type of carbon fiber reinforced cementitious materials(CFRCM)suitable to the reinforcement of deteriorated RC beam and column is developed,thus the bond behavior between FRP reinforced CFRCM and deteriorated concrete is studied and the shear strength model is established.The enhancement of RC beam and column strengthened with FRP reinforced CFRCM is explored and the calculation models of carrying capacity are established.Further,a series of experimental investigation and theoretical research work have been carried,and the main contents and creative achivements are summarized as follows.1.Degradation mechanism of concrete and steel bar under coupling effects of colliery environment and load are revealed and the bond strength model between the deteriorated concrete and corroded steel bar is established.The time functions of neutralization depth,compressive strength and elastic modulus of concrete are established by numerical fitting,together with the nominal yield strength and ultimate strength of steel bar.Bond strength between deteriorated concrete and corroded deformed steel bar is established,with comprehensive consideration of compressive strength of concrete,corrosion of steel bar,crack width,and the friction coefficient between corroded steel and deteriorated concrete.2.Mechanical degradation of RC beam under coupling effect of colliery environment and load is reavled.The influence mechanism of concrete deterioration and steel bar corrosion on the mechanical behavior of RC beam is studied and then the shear carrying strength model is established.Failure mode of deteriorated RC beam changes from compression shear failure to a bending failure.The ultimate carrying capacity decreases linearly with deterioration degree,while the ductility desreases rapidly first and then slowly.As the compressive strength of concrete decreases 27.90%,the corrosion ratio of steel bar comes to 7.22% and the maximum width of expansion crack reaches 0.761 mm,thus the carrying capacity of deteriorated RC beam decreases by 28.9%,and the ductility coefficient decreases by 33.01%.Shear capacity model of degraded RC beams is established by numerical fitting,based on the compressive strength loss of concrete.3.Mechanical degradation of large eccentric compressed RC column under coupling effect of colliery environment and load is reavled together with the influence mechanism and then the carrying strength model is established.Failure mode of deteriorated RC column changes from yield of tensile steel bar to crushing of compressed concrete.The ultimate carrying strength and ductility decrease rapidly first and then slowly.As the compressive strength of concrete decreases 32.94%,the corrosion ratio of steel bar comes to 8.68% and the maximum width of expansion crack reaches 3.46 mm,thus the bearing capacity of large eccentric compressed RC column decreased by 17.66%,and the ductility coefficient decreased by29.21%.As the influence of concrete degradation on the protective layer,the relationship between corrosion cracks and peeling angle of concrete are considered,the model of bearing capacity of RC column degraded by large eccentric compression is improved,and the test results are verified.4.A type of CFRCM suitable for repair and reinforcement is developed,with the compressive strength over 30 MPa and the bending strength close to 10 MPa.The evolution law and influencing factors of tensile bond strength and shear strength at the interface of CFRP sheet or woven mesh reinforced CFRCM and deteriorated concrete are revealed.Thus,the relationship between shear strength of strengthening layer and the relative compressive strength of concrete is fitted and the maximum shear model between CFRP sheet reinforced CFRCM and deteriorated concrete is improved.5.CFRP sheet or woven mesh reinforced CFRCM increases the shear strength of RC beam and limits the development of oblique cracks effectively.Under the ultimate load,the normal section of strengthened beam is subject to bending failure.The carrying capacity of deteriorated RC beam is slightly improved with shear reinforcement only,while the maximum increase is more than 30% when the RC beam was bending and shear strengthened.The strengthening effect of CFRP sheet reinforced CFRCM is more effective than woven mesh.The ductility and stiffness of RC beams are both enhanced.6.The mechanical property of deteriorated RC column strengthened with CFRP sheet or woven mesh reinforced CFRCM is improved effectively.Under the ultimate load,longitudinal fiber composite material breaking breakage occurs to the deteriorated RC column strengthened with CFRP sheet or woven mesh reinforced CFRCM under large eccentric compression,showing a strong brittle with only one main crack.The carrying capacity of RC column strengthened with CFRP sheet reinforced CFRCM increases better,with an average increase of more than 17.50%,but the ductility is limited and decreased significantly with the increase in the number of CFRP sheets.The ductility and stiffness of RC column strengthened with CFRP woven mesh reinforced CFRCM are well improved though the carrying capacity is relatively lower.7.The mechanism of deteriorated RC beam and column strengthened with CFRP sheet or woven mesh reinforced CFRCM is analyzed,and the effect of CFRP sheet amount on the deformability and stiffness of the strengthened beam is revealed,thus the method to determine the effective utilization rate of the CFRP sheet is given.Based on deterioration of RC material and effective utilization of FRP,the models for flexural capacity of RC beam and carrying capacity of RC column under large eccentric compression strengthened with FRP reinforced CFRCM are improved.As the relationship between the effective coefficient of FRP shear reinforcement and the shear strength between the CFRP sheet and deteriorated concrete is revealed,the shear capacity model of deteriorated RC beam strengthened with FRP reinforced CFRCM is improved and verified through experimental results.