Integrated Anchor Design And Performance Study For Large-tonnage FRP Cable

In order to solve the performance defects of steel cable,such as self-gravity and corrosion degradation,using new material to replace steel cable is considered to be an effective solution.Owing to the excellent characteristics of fiber-reinforced polymers(FRPs),such as the small weight,high tensile strength,corrosion and fitague resistance,they are widely applied in the repair and reinforcement of existing structures.Because FRP cables are anisotropic materials,their transverse strength is much lower than their longitudinal tensile strength,so how to achieve effective anchoring of FRP cables is a difficult problem.At present,most of the existing researches focus on single load transfer component(LTC)or single FRP cable anchor systems(CASs)design,but lack of integrated anchorage design based on load transfer medium and different cable material.In this paper,LTC material modification,parameter analysis of anchor force,design and performance evaluation of different FRP cables and disclosure of anchor failure mechanism were studied.The conclusions of this study are as follows.(1)Optimization design and performance improvement of the LTCs.In order to realize the performance design of the LTC,four kinds of modified resin-based LTCs were proposed.The modified materials included quartz sand,garnet sand,single microfiber,hybrid sand-microfiber and hybrid long-short microfiber.The compressive strength,elastic modulus,load-displacement curve,failure mode,failure mechanism and ductility of the modified resin with different contents were studied.Comparing to the compressive strength of the plain resin,those of the LTCs modified by quartz(LTCQs)and the LTCs modified by garnet(LTCGs)increase by 9% and 8%,respectively,whereas their elastic moduli increase up to 227% and 218%,respectively.The maximum compressive strengths of LTCGF-8,LTCGF-13,and LTCCF-7 were 48%,51% and 40% higher than that of plain resins,respectively.The maximum elastic moduli of LTCGF-8,LTCGF-13,and LTCCF-7 were 254%,254%,and 211% higher than that of plain resins,respectively.A cubic polynomial fitting model can appropriately describe the relationship between the compressive behavior and microfiber content of the LTCSF.The compressive strengths and elastic moduli of the LTCQFs and the LTCGFs can be increased simultaneously with the increase in the microfiber content,and their relationship could be described by a cubic polynomial fitting model.The maximum compressive strength and elastic modulus of the LTCSFs were 127.7 MPa and 10.4 GPa,increasing by 51% and 271%,respectively,relative to the plain resin values.LTCMGF-8 showed an optimal compressive strength and ductility.(2)Study on mechanical performance of small-tonnage BFRP cables.The mean anchor efficiency of three Φ4-37 shallow-ribbed BFRP cables was 101%.Optimizing the manufacturing technology and assistant tools could increase the fatigue life of the BFRP cable up to 4.9 times(398,962 times)compared with previous experiments.The fatigue failure mode of the ribbed BFRP cable with winding anchor were all split failure on the cable in the free portion.The fatigue life ofΦ4-37 shallow-ribbed BFRP cable could be increased to 696321 times by using casting anchor and improved ribbed BFRP tendon(with reduced rib height and rib width),but the failure mode was still the splitt failure of free-portion cable.The fatigue life of the BFRP cables could reach 2 million times by using segmented variable-stiffness casting anchor and pultrusion plain round cable,without splitting or local wire breaking.The elastic modulus increased slightly with the increase of fatigue times.The static anchor efficiency of the plain round BFRP cable could reach 110% after 2million times of fatigue.(3)Theory and FE analysis of large-tonnage FRP CAS.The formula of cable anchor force deduced verifies that the improvement of compressive strength and elastic modulus of LTC was the premise of cable anchoring force improvement.The anchor force increased linearly with the increase of anchor length and cone angle(keeping the thickness of loading end unchanged).However,the relationship between anchor force and the change of cone angle(keeping the thickness of free end unchanged)and the change of loading end and free end thickness at the same time was nonlinear,and the growth trend of anchor force would gradually slow down.The designed large-tonnage horizontal tension system could stably carry 500 tons of cable force.The radial displacement of BFRP cables at the loading end increased with the increase of single tendon spacing,while the radial stress and radial displacement decreased with the increase of the thickness of the LTC.Cone angle and anchor length had the greatest influence on the axial displacement,but the least on the radial displacement.The parameters of large-tonnage BFRP CAS are N = 4,S = 1.5mm,T = 10 mm,L = 400 mm and θ = 5.5°,respectively.(4)Static behavior of large-tonnage BFRP cables.The failure modes of Φ7-37 BFRP cable andΦ4-127 BFRP cable were a rupture failure in the free portion.No damage was found in LTCs after loading.The load of the BFRP cables increased with displacement increasing linearly.As the load increased,the maximum axial strain of two types of BFRP cables in the free portion increased with load increasing.The mean ultimate load and the mean anchor efficiency of Φ7-37 BFRP cables were 1919 k N and 95%,respectively.The mean ultimate load and the anchor efficiency of Φ4-127 BFRP cables were 2419 k N and 93%,respectively.From the loading end to the free end,the shear stress of the center BFRP tendon first increases rapidly,then decreases slowly,then increases gradually again,and finally decreases quickly.The axial strains and shear stress of the BFRP cable in the anchor zone are consistent with the FE results,and are proved to follow linear and quartic functions,respectively.(5)Static behavior of large-tonnage CFRP cables.From the loading end to the free end,the shear stress of T-1 in the anchor zone initially increased rapidly,then increased slowly,and finally decreased rapidly.The maximum shear stress was always at the free end of the outermost-layer LTC.The along shear stress of the LTC increased from the inner-layer LTC to the outermost-layer LTC.As the load increased,the maximum tensile strain difference of T-1 at the loading and free ends increased.By optimizing the parallel tendons into dispersed tendons in the anchor zone,the anchor efficiency of the CFRP cable was improved from 60% to 91%.Correspondingly,the cable force was improved from 2684 to 4070 k N.The change in the tendon spacing had a slight effect on the dispersed CAS.The increase in the anchor length and decrease in the conical angle effectively avoided the notch effect of the dispersed cable in the anchor zone.The cable force and anchor efficiency of Φ4-91 CFRP were 3393 k N and 93%,respectively.(6)Failure mechanism analysis and optimization design of FRP CAS.For FRP tendons,the radial compressive stress,as well as the relative radial displacements,were found to be nearly identical at different positions in the same cross section.The positions of the outermost-layer FRP tendons and the section near the loading end of anchorage are the maximum stressed positions.Excessive tension-bending stress and radial compressive stress lead to anchor failures of the FRP cable.The tension-bending stress is induced by the axial displacement lag of the FRP cable,whereas the radial compressive stress is caused by the inner cone angle of the anchorage.To meet the preparation,dimensional and mechanical requirement of the anchorage,the spacing of the FRP tendons should be as small as possible.Changing the inner cone form is benefit for reducing the radial compressive stress and radial displacement,but not the tensile stress difference between the inside and outside and axial displacement.Conducting the radial variable stiffness of the LTC is the most effective method.This method was also validated in different tendon diameters and number of tendons.