| In the field of reinforced concrete(RC)structure strengthening,with the characteristics of high peel resistance and resistance to external adverse factors,nearsurface mounted(NSM)CFRP bar has been proved to be a new strengthening technique superior to the traditional externally-bonded strengthening technique.At present,the adhesives used in the NSM CFRP bars are mostly organic epoxy resin or inorganic cement mortar materials.Although the former has good strengthening effectiveness,the organic adhesive is toxic and harmful during curing,having poor high temperature resistance and fire resistance.The latter one has poor strengthening effectiveness and large energy consumption in the production,failing to meet the requirements of green energy saving.In order to overcome the disadvantages of epoxy resin and cement mortar,the alkali-activated geopolymer mortar with rapid hardening,early strength and environmental-friendly was proposed to be used in RC beams flexurally strengthened by NSM CFRP bars.In addition,in order to reduce the debonding failure and further improve the mechanical performance of RC members,a new type of CFRP strip winding anchorage system was proposed and studied in this paper.In this paper,the experimental investigation,finite element verification and theoretical analysis were combined.Firstly,the basic investigation on the interfacial bond behaviour of 21 specimens was carried out,and the influence of the types of adhesive,groove width and the number of anchorage on the ultimate pull-out load was studied.Moreover,on the basis of the investigation on the bond behaviour,the system was applied to RC beams flexurally strengthened by inorganic adhesive-based NSM CFRP bars.5 RC beams were fabricated to experimentally investigate the flexural behaviour.The influence of the types of inorganic adhesive,bonding length and anchorage on the flexural behaviour of RC beams strengthened by inorganic adhesive based NSM CFRP bars was studied.The main contents are as follows:(1)The experimental study on the interfacial bond behaviour of NSM CFRP barsinorganic adhesive-concrete was carried out on 21 specimens to reveal the influence of adhesive types,groove width and anchorage system on the failure mode and loaddisplacement curve of NSM CFRP bars system.The results showed that the ultimate load of epoxy resin specimen was the highest,and the ultimate load of cement mortar specimen was 33% of the geopolymer specimens.Furthermore,the ultimate load increased by only 3% with the groove width increased by 20%,and the ultimate load increased by 14%,25% and 28% with 1,2 and 3 anchorage number,respectively.In addition,a reasonable average bond stress slip model was fitted by regression analysis.(2)Based on the experimental study of bond behaviour,the cohesive element of ABAQUS software was used to simulate the bond behaviour of inorganic adhesivebased NSM CFRP bars.Compared with the test results,the rationality of using cohesive element to simulate the bond behaviour of inorganic adhesive-based NSM CFRP bars was proved.(3)5 RC beams were designed and fabricated to study the flexural behaviour of RC beams strengthened by inorganic adhesive-based NSM CFRP bars.The influence of the types of inorganic adhesives,the bond length of CFRP bars and the anchorage system on the failure mode,load-deflection curve,strain,stiffness,ductility and energy consumption of RC beams were investigated.The results showed that the debonding failure of cement mortar specimen was the most serious,and the ultimate flexural load of specimens with short bonding length was the lowest.In addition,the failure modes of specimen with anchored-CFRP bar was light,and the corresponding ultimate flexural load and energy consumption of the anchorage strengthened beam were the highest.(4)Based on the experimental investigation of strengthened RC beams,the finite element simulation of RC beam strengthened by inorganic adhesive-based NSM CFRP bar was carried out.The simulation value was fitted with the experimental value,and a reasonable finite element model of strengthened beam was proposed.In addition,based on the current theoretical model of NSM strengthening beams,the ultimate flexural load and deflection of the beam were predicted and calculated.It was proved that the theoretical calculation model recommended by the code can be utilized for the flexural design of beams strengthened by inorganic adhesive-based CFRP bars system.(5)Based on the finite element model of the strengthened beam,the finite element parametric analysis of strengthened RC beam was carried out.The influence of the groove dimension,the diameter of CFRP bars(strengthening amount)and the type of FRP bars(elastic modulus)on the failure mode and flexural behaviour of the strengthened beam were analyzed,and the finite element results were compared with the corresponding theoretical results. |
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