Research On Mechanical Connection Of 500MPa High Strength Rebars

Since the 70’s of 20 th century, Europe, the United States and Japan have developed the mechanical connection technology of rebars, and established a series of technological standards accordingly. Compared with other countries, the mechanical connection technology of rebars was developed relatively late in our country. In the late 1980 s, according to the Japan’s pressed coupling sleeve connection of rebars, our country developed the technology of rebar’s pressed coupling sleeve connection. Then, the taper threaded connection and the parallel thread connection of rebars occured in the 1990 s. By far, the mechanical connecton technology is largely applied to the connection of rebars with low and medium yield strength, but there are few study and application on the mechanical connection of 500 MPa or higher strength reinforcement bars.Comparing the advantages of different mechanical connection technologies, the study in the paper is based on the rolled parallel thread connection of rebars with ribs stripped, which has excellent connection performance. According to the mechanical requirement of the parallel thread connection, the size of the threaded coupler was designed. And the standard parallel thread connection specimens applied to 500 MPa high strength rebar were made on the basis of the designment. Through a series of experiments such as monotonic tension test, high strength cyclic load test and large deformation cyclic load test as well as the finite element method, the influence of the threaded coupler’s size on the behavior of the mechanical connection was investigated.The main conclusions of this paper are shown as follow:(1)The parallel threaded coupler size of different diameter rebars is determined on the basis of theoretical calculation. The experiments show that the couplers designed by the method in this paper satisfy the constant strength requirement of rebar connection, the connection strength meets the level I connection that standard requires.(2)Once the size of coupler satisfies the requirement that the break of thread occurs after the failure of rebar, the strength of connection mainly depends on the rebar’s ultimate strength. And the coupler’s length and diameter have little influence on the strength of connection.(3)Overlong coupler can make the installment of rebar connection difficult, so that the length of coupler less than the double length of 13 threads of rebar is appropriate.(4)The ratio of coupler length and rebar diameter be controlled in the range of 1.6~1.8 is advisable.(5)The guide on the design and construction of 500 MPa high strength rebar parallel thread connection is compiled, which provide the reference for the industrial production of coupler.