| It shows that precast structures have a prospect of utilization in our construction industry. It is significantly important for the whole structure to ensure that the joints of precast frame structure have a good seismic behavior and don't fail prior to other members. Engineered cementitious composites (ECC) is a class of high performance cementitious composites with ultra-high toughness and excellent energy dissipation. The seismic resistance of structures can be significantly enhanced with the substitution of ECC. Due to higher cost of ECC compared with normal commercial concrete, application of ECC for a whole structure is essentially uneconomic. This paper proposes to involve ECC only in the connection zone of precast frame joint, which is expected to obtain highest performance/cost. The specific contents are as follows:(1) Two ways of precast frame beam-column connection are proposed in this paper based on the research and by an innovative use of the ECC in the connection zone. Then,2 ways of assembly are optimal designed by the nonlinear finite element software of ATENA. The result shows that the stress can be reliably transfer from longitudinal rebar of beam to connection rebar when the overlap length reaches a certain degree. Additionally, the bond stress between rebar and concrete have an influence on the mechanical behaviors of joints. However, it can be ignored when the bond stress reaches a quarter to normal bond stress.(2) Based on the proposed assembly schemes above,9 precast joint and 2 monolithic joint are designed for the experiment. The production process and test program of the specimen are introduced in detail. The seismic performance of 11 specimen in terms of failure mechanism, hysteresis curve, strength, stiffness, ductility, energy dissipation and strain are studied through the pseudo static test. According to the test results, 2 ways of assembly both have a reliable connection. Besides, the specimen involved ECC exhibit better energy dissipation because of the full hysteresis curves. Moreover, the stress of stirrups in ECC specimen is lower than those in concrete specimen at the same load level, which indicates that the substitution of ECC can enhance the shear capacity of joint and partially replace the function of stirrups in the joint.(3) The nonlinear analysis software of OpenSees which is developed by PEER are employed to conduct the numerical analysis. The finite element models are established based on fiber section and macroscopic element of beam-column joint. Then 5 models are calculated and parametric analys are studied. The calculation results show that the hysteretic loops from the simulation results exhibit good agreement with the experiment results. However, according to the envelope curves from simulation result, the initial stiffness of simulation is slightly larger than that of experiment. The uniaxial material of ECC provided by OpenSees is effective to simulate the seismic performance of the steel reinforced flexural members. With the increase of compressive strength of ECC, yield load and peak load of different joint models increase differently. Models involved ECC exhibit higher yield load and peak load than concrete models at the same compression level. Modulus reduction of ECC material has a slight reduction on the initial stiffiness and strength of joint models.(4) In the end of this paper, based on the experiment and simulation result, some relevant suggestions for design and construction of the assembly scheme proposed above are presented. |
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