Experimental Study On The Anchorage Performance Of A New Internal Casing Type Anchorage For CFRP Wire Strands

CFRP(carbon fibre reinforced composite material)has the advantages of high strength,good stiffness,light weight,corrosion resistance and fatigue resistance,etc.It can replace steel cables in bridge structures,thus improving the durability,corrosion resistance and spanning capacity of bridge structures.However,CFRP materials are anisotropic and have low shear and lateral compressive strengths.Traditional anchorage systems are unable to provide good anchorage performance,making it difficult to anchor them.In this paper,based on the systematic summary of existing anchorage systems,a new form of anchorage is improved and analysed and studied.Main research content:(1)Clamped anchorage has a large stress concentration,easy to cause damage to the CFRP tendons,and is only suitable for anchoring single tendons,anchoring filament strands need to use clamping group anchor,anchoring performance discrete;bonded anchorage is more suitable for anchoring CFRP filament strands,bonding medium and tendons under stress coordinated deformation,anchoring performance improved;composite anchorage structure process is complex,not conducive to engineering applications.(2)The internal tapered bonded anchor has an uneven distribution of radial pressure in the longitudinal direction and stress concentration.A casing with a gradual cutting slit is placed inside the anchor barrel to improve the reasonable force in the longitudinal and transverse directions of the wire strands by using the change in the width of the cutting slit.(3)Simulation analysis was carried out using finite element software.By comparing six groups of models with different parameter sizes,optimization and improvement were carried out to determine the anchor model with the optimum size parameters;various mechanical parameter indicators were analysed in detail for the optimum parameter model,including axial stress of the wire strand,radial extrusion stress,anchor barrel yield stress,bond medium stress,casing stress,load displacement relationship,to provide reference for the static load test.(4)Based on the above analysis and research,the anchorages were manufactured and compared with static load tensioning tests to measure displacement,stress and load carrying capacity parameters,and a detailed analysis of this was carried out.Main research conclusions:(1)Clamping type anchors have significant stress concentration and are prone to damage to CFRP bars.They are only suitable for anchoring a single bar material,and for anchoring wire strands,clamping type group anchors need to be used,resulting in high dispersion of anchoring performance;Bonded anchors are more suitable for anchoring CFRP strands,where the bonding medium and reinforcement deform harmoniously under stress,resulting in improved anchoring performance;The complex process of composite anchor structure is not conducive to engineering application.(2)The internal tapered bonded anchor has an uneven distribution of radial pressure in the longitudinal direction and stress concentration.A casing with a gradual cutting slit is placed inside the anchor barrel to improve the reasonable force in the longitudinal and transverse directions of the wire strands by using the change in the width of the cutting slit.(3)Using finite element software to analyse the model with wire spacing and sleeve wall thickness as variables,the results show that the anchorage system with smaller wire spacing and larger sleeve wall thickness has a more reasonable stress distribution;by comparing the internal tapered anchorage and the internal casing anchorage with the same dimensional parameters,it is obvious that the improved internal casing anchorage has a better stress distribution than the internal tapered anchorage,indicating the effectiveness of the new anchorage in improving the anchorage performance.(4)Through the static tensile test of the anchorage system with 19 CFRP wire strands of5 mm diameter,the load-bearing capacity of the inner casing anchorage was greatly improved,and the maximum anchorage efficiency coefficient could reach 113%,which relieved the excessive squeezing pressure at the small hole end of the inner cone anchorage and avoided the problem that the wire strands were easily sheared off in the anchorage area near the small hole end,so that the stress distribution tended to be reasonable;the wire spacing was 1～2mm The smaller the spacing,the better the anchorage performance;the thickness of the casing is in the range of 4～6mm,the larger the wall thickness,the better the anchorage effect;the preload has a significant effect on the anchorage performance,and the anchorage efficiency of the preload is significantly higher than that of the non-preload.