| Engineered Cementitious Composite (ECC) is a kind of high performance fiber reinforced cementitious composite (HPFRCC) which exhibits ultra-high tensile ductility, tensile strain hardening and fine multiple cracking behavior. Due to the prominent tensile performance, ECC become an ideal material to improve the shear behavior of structural members and seismic behavior of structures. A systematic study on ECC at material level, component level and structure level is conducted adopting the approaches consisting of theoretical analysis, experimental investigation and numerical modeling.1. At material level:(1) A mix proportion optimal design has been conducted for ECC, based on micromechanics and particle packing theory. In addition, the mix proportions were adjusted according to the fluidity and workability of the paste during the mixing in practice. Finally, six groups of mix proportions were determined for preparing specimens in this study.(2) Directly tensile tests for 3 groups of specimens have been conducted, and the test results show that all the prepared ECC specimens exhibit good tensile ductility and different levels of multiple cracking behaviors, and most of the specimens exhibit strain capacities over 3%.(3) Assuming that the flaw size and fiber statistical distribution follow normal distributions, a numerical simulation of multiple cracking process for ECC under uniaxial tension has been applied. The accuracy of the modeling has been verified by comparing the simulated result with the tensile test data in terms of cracking stress, cracking strain, peak stress and strain capacity.(4) Uniaxial compression tests and four point bending tests for 6 groups of ECC specimens have been conducted, and the test results show that all the prepared ECC specimens exhibit good tensile and compressive ductility and the compressive strengths are greater than 30MPa.2. At component level:(1) Experimental observations have been done on six steel reinforced ECC (RECC) columns and one reinforced concrete (RC) column under the combined action of constant axial load and reversed cyclic lateral load. Failure mode, hysteretic curves, backbone curves, displacement ductility and energy dissipation, stiffness degradation, et al have been studied for different test columns. Test results indicate that RECC columns show better seismic performance in terms of ductility, energy dissipation capacity, and damage tolerance, compared with RC columns. With the same shear span-to-depth ratio, axial load level, and transverse reinforcement ratio, the failure mode of RC column is flexural-shear, while ECC column failed by flexure. With the decrease of shear span-to-depth ratio, the yield strength and shear strength of RECC columns increase, but the displacement ductility decreases. The decrease of transverse reinforcement ratio leads to a slightly decline in terms of the load bearing capacity, deformation capacity and energy dissertation for RECC columns. However, the decreasing amplitude is not quite significant, which indicates that the fiber bridging effect in ECC can provide shear resistance effect and confinement instead of part of transverse reinforcement.(2) Theoretical calculation approaches for the flexural strength and shear strength of RECC columns have been proposed in this study. By employing the approaches to analyze the tested RECC columns, it can be concluded that the proposed calculation method can predict the flexural and shear strengths of RECC columns with reasonable accuracy.(3) The flexural and shear deformation of RECC column before yielding have been analyzed. The flexural deformation was analyzed using strip method, while the shear deformation was calculated with truss-arch model. By employing the proposed methods to analyze the deformation of tested RECC columns, it can be concluded that the strip method and the derived calculation method for effective shear stiffness of RECC columns can respectively predict the flexural and shear deformation of RECC columns with good accuracy.(4) A uniaxial cyclic constitutive model for ECC was proposed (named SHCC01). The proposed constitutive model comprises tensile and compressive backbone curves, unloading-reloading schemes, and the transition between tension and compression. The proposed cyclic constitutive model was coded into the OpenSees platform and applied to fiber section nonlinear beam-column element to simulate the responses of RECC flexural members. The simulation results indicate that the proposed model is reasonably accurate in simulating the mechanical properties of ECC material and the cyclic behavior of ECC flexural element.(5) A numerical modeling method for simulating shear-critical RECC members was put forward based on the softened membrane model (SMM), which is named softened membrane model for ECC (SMMECC). The proposed model SMMECC includes uniaxial cyclic constitutive models of ECC in compression and tension, softening phenomenon and Poisson effect of cracked ECC. The SMMECC was coded into the OpenSEES platform to simulate the structural responses. Verification of the proposed model is provided through the analysis of RECC columns, RECC beam, RECC shear walls and ECC/RC composite walls subjected to reversed cyclic loading. The simulation results indicate that the SMMECC is reasonably accurate in simulating the mechanical properties of shear-critical reinforced ECC members in terms of backbone curve, initial stiffness, yielding point, peak point, the descending brunch of the load-displacement curve, and pinching effect.3. At structure level:(1) A group of increment dynamic analysis (IDA) for a RC frame, an ECC frame and an ECC/RC composite frame has been applied. By comparing the IDA response curves, story drift distribution and plastic hinge distribution, the structural response and seismic performance of the three types of frames under different ground motion intensity levels have been assessed. The limiting values of maximum story drift for the three types of frames at 5 performance levels have been determined. In addition, a performance-cost analysis has been applied, the analysis indicated that the ECC frame has the highest deformation capacity and the best seismic performance, but the construction cost is too high; while the ECC/RC composite frame takes less construction cost by reducing the use of ECC, and its seismic performance is also significantly improved compared to the RC frame.(2) The seismic performance of a RC frame with RC short columns and an ECC/RC composite frame with RECC short columns has been analyzed. The IDA response curves and story drift distribution of the two frames are compared, and the comparison results indicate that the short column effect leads to weak story and causes concentrated damage, and consequently decrease the seismic performance of the whole structure. Replacing the RC short columns with RECC short columns can improve the seismic performance of the structure and let the deformation capacity close to normal RC frame. |
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