Experimental Study On Working Performance Of Concrete-shaft Composite Anchor

The research object of this paper is concrete-shaft composite anchor (Hereinafter referred to as composite anchor),The composite anchor is made up by a concrete shaft, shaft of steel wire rod steel and corrosion protective layer.This experiment uses the long spiral drilling pressure pouring concrete technology form concrete rod body,and then implanted reinforcement made from composite anchor which has the advantage of high bearing capacity, low cost, good durability, the craft is simple, fast construction speed, saving steel, cement, etc.Paper through theoretical analysis elaborated the basic principle of composite bolt stress.And study of composite anchor load-bearing characteristics and key technology solutions of the problem through the full scale test on site.The study of composite anchor a total of three types, which are full length bonded composite anchor, full length free composite anchor, half free segment length of composite anchor.In view of the need to study, the test is divided into three groups,The first group is the bond anchorage test of bar reinforcement and grouting body,which is to study of bonded composite bolt load transfer mechanism of component and determine the reasonable bonding length.The second group is the total length of free section at the bottom of the anchor rod fixed end bearing capacity of concrete compression test,which is to research the fixed end the actual stress distribution of bearing plate and determine reasonable fixed end force structure.The third group is a basic test of composite bolt, which discusses three types of composite bolt under the action of pulling force of load-bearing characteristics.This paper studies the three kinds of composite anchor shaft of the internal force distribution, the load transfer mechanism, bearing capacity and deformation characteristics, shaft and soil around the pile side friction distribution and three composite anchor in this a few aspects of the similarities and differences.In addition, as a result of the composite bolt hole perfusion process is the same as the ordinary long spiral drilling pressure filling pile, the paper also studied the composite anchor rod and the connection between the ordinary long spiral drilling pressure filling pile.The bar reinforcement bond anchorage experiments shows:(1) Located in the steel pipe and steel 3,5,7 beam of steel strand,When the bond length of the steel strand and grouting body not less than 4 m steel strand,The bond anchorage failure does not occur within the rod body, the ultimate bearing capacity of the steel strand as control factors.(2)The average ultimate bond strength between steel tube and concrete shaft is 1.1?1.45N/mm2?The full length free period of composite anchor fixed end bearing capacity of concrete experiments shows:(1)The diameter of 400 composite anchor,behind the concrete pole into ?220 bearing plate and bar reinforcement and adopt construction process of similar long spiral pressure after pouring pile embedded reinforcing cage.which is reasonable and feasible.(2) C25 concrete shaft, when the bearing plate is 200 mm diameter and set the spiral reinforcement, the ultimate bearing capacity of bearing plate above the concrete compression is 1400 kN.The composite anchor basic experiments shows:(1)The stress of shaft concrete (tension, compression),which have an effect on composite anchor of the uplift ultimate bearing capacity and shaft displacement.In this experiment, the ultimate bearing capacity of the composite bolt, the shaft compression than tensile more than 8.3%, The peak of displacement, the shaft compression than tensile little about 18%. (2) The composite anchor with half free segment length.the concrete compression in the free section of shaft, the shaft concrete of the bonding period range, the upper Compression and the lower tension.As opposed to not free period of anchor rod, with free period of peak tensile stress of the anchor rod body concrete significantly reduced, The mechanical model can reduce the occurrence of shaft concrete crack, and ensure the durability of composite anchor.(3) Composite anchor with free period of should appropriate to minimize the bond length under the premise of assurance of bonded bar reinforcement anchoring reliable, So it can maximum increase shaft concrete compression section, maximum uplift bearing capacity and the best concrete stress, achieve the goal of optimization design.(4) The anchor head displacement is greater than the peak of displacement in the composite anchor with free period.It should be according to the control requirements for composite foundation deformation anchor prestress at engineering application.Based on theoretical analysis and the field test, this paper puts forward the half free segment length of composite anchor optimization design train of thought.This paper provides estimates of composite anchor limit bearing capacity formula and gives specific Suggestions and problems that should pay attention to when the composite anchor applied in actual engineering,Paper also proposed the further research and development of the technology.