Seismic Behavior And Design Method Of ECC/RC Composite Columns

Engineered Cementitious Composites (ECC) is a high toughness composite material with pseudo strain hardening and multiple cracking properties. Substitution of conventional concrete with ECC in concrete structures can significantly improve the seismic performance. However it is usually proposed to be used selectively in the key parts of the structure because of the high cost of the imported PVA fiber produced in japan. In order to be widely applied to the practical structures, it is very necessary to substitute part of the expensive Japanese PVA fibers with the domestic PVA fibers for obtaining high performance price ratio. An optimal design for the fiber volume content of hybrid PVA-ECC was analyzed based on the ECC design theory. The ECC/RC composite columns were composed of the optimized hybrid PVA-ECC formwork. In this paper, seismic performance and design method of ECC/RC composite columns are comprehensive studied through experimental studies and numerical simulation,which provides an alternative for seismic design of structures.The feasibility of domestic PVA-ECC was firstly studied based on the micromechanics model. An optimal design for the fiber volume content of hybrid PVA-ECC was analyzed, taking both compressive strength and tensile strain capacity into account. The mechanical behavior of hybrid PVA-ECC was obtained through the four-point bending test and uniaxial compressive test. Experimental results indicate that the strain hardening and multiple cracking behavior of hybrid PVA-ECC are observed in the test, and the long-term compressive strength is distinctly increased.A calculation model was proposed according to the complete stress-strain curve obtained from prism specimens of hybrid PVA-ECC. This study provides material parameters and theoretical models for practical application of hybrid PVA-ECC.Experimental results showed that ECC/RC composite columns with multiple cracks had better ductility. Moreover, shear capacity of columns improved with the decrease of shear span ratio. However, stiffness, displacement ductility ratio, and energy dissipation become smaller.In addition, with the increase of stirrup ratio, stiffness, displacement ductility ratio, and energy dissipation become bigger. Four ECC/RC composite columns and one RC column were designed to study their seismic performance.Based on the experiment results, damage and mechanical characteristics of ECC/RC composite columns under low reversed cyclic loading are studied. Hysteretic hoops, skeleton curves, stiffness degradation and energy dissipating capacity are analyzed. Variables such as materials, stirrup ratio and shear span ratio have been considered in this experiment.This article describes modeling approach which can take column’s shear deformation into account in modeling based on OpenSEES software.The proposed constitutive model was coded into OpenSEES software and applied to simulate the component tests, the simulation results showed good agreement with the experimental results. Based on experiment, the parameters of the test are extended and enriched. The influence of axial compression ratio, stirrup ratio and thickness of ECC layer on seismic behavior of ECC/RC composite columns were studied in detail.The basic methods and corresponding design procedures of Performance-Based Seismic Design have been summarized based on capacity spectrum method.The seismic behavior of an ECC/RC composite frame was evaluated through the pushover analysis based on the software of ZeusNL, and its seismic behavior was compared with those of reinforced concrete frame and ECC frame. Results indicate that using ECC/RC composite columns as well as substitution of concrete in the beam-column joints with ECC is an effective way to improve the structural capacity and ductility, and to reduce the storey drift with relatively large plastic deformation and to relive the earthquake damage.