Strain Rate Effect Of Materials On Seismic Response Of Reinforced Concrete Frame-wall Structure

The reinforced concrete structures are widely used and required to resist dynamic loads when subjected to seismic loading during the period of its active service. In recent years, the reinforced concrete structure may suffer distress under the action of unforeseen strong earthquake which is often occurs. Reinforcing steel and concrete are both sensitive to strain rate, hence, the mechanical properties of them will be changed by the strain rate effect. The mechanical properties, deformational properties and failure mode of reinforced concrete structures and members will be changed, too. There is very little research about the effects of strain rate on reinforced concrete materials, members and structures subjected to seismic loading. In this paper, the strain rate sensitivities of microconcrete and galvanized wire, the effects of strain rate on reinforced concrete shear walls and structures under seismic loading were investigated. A shaking table test of reinforced concrete shear wall structure was also carried out. The main aspects of research work in this thesis are listed as follows:(1) The dynamic compressive properties of miroconcrete which is most popular used in dynamic model test for replacing concrete are experimentally investigated under the strain rate of earthquakes. Based on the tested results, the dynamic increasing factor (DIF) of compressive strength and elastic modulus which are function of strain rate are obtained by regression analysis. The uniaxial compressive constitutive model of the microconcrete with strain rate effect is fitted by using the compressive stress-strain relationship of concrete in the China code for design of concrete structures (GB50010-2010). The dynamic compressive properties of microconcrete are analyzed in finite software ABAQUS by using the damaged plasticity model and the presented uniaxial compressive constitutive model of the microconcrete. The comparison between the numerical results and tested results show that the presented model can describe the dynamic properties of microconcrete very well.(2) The galvanized wires are often used to simulate the reinforcing steel in the dynamic model test. The dynamic tensile test on galvanized wires are carried out, and the mechanical and deformation properties of galvanized wire under the seismic strain rate are investigated. Based on tested data, the relationship of dynamic increasing factor of yield strength and tensile strength which are function of strain rate-are gotten. According to the comparison with the reinforcing steel models, the dynamic tensile properties of galvanized wire and reinforcing steel are very similar. In the dynamic model tests, it is feasible for using the galvanized wires to simulate the reinforcing steels.(3) A three-story reinforced concrete frame-wall shaking table test model is designed and made on the basis of the similarity theory, and bi-directional shaking table experiment was carried out. The seismic response and failure mode of reinforced concrete frame-wall structure are investigated by the shaking table test. Meanwhile, the tested results which are obtained from the shaking table test provide evidence for the nonlinear seismic response analysis of the reinforced concrete structure.(4) Reinforced concrete shear wall is the typical member in reinforced concrete structure. The research about the dynamic properties of shear wall is relatively scarce. In order to understand the effects of strain rate on the dynamic properties of reinforced concrete shear wall, the finite element model of reinforced concrete shear walls are established in the software ABAQUS. The numerical simulation of the dynamic properties of reinforced concrete shear walls under different strain rates are carried out, which consist of different height-to-width ratio and axial compressive ratio. The numerical results provide theoretical basis for the dynamic experiments of the reinforced concrete shear wall.(5) The research about strain rate effect of materials affected on the response of reinforced concrete structure under seismic loading is limited, hence, the elastoplastic seismic response analysis with strain rate effect of reinforced concrete structure are studied. Based on the uniaxial compressive constitutive model of microconcrete with strain rate effect, the dynamic fiber beam element subroutine of microconcrete in software ABAQUS is given. The finite element model of reinforced concrete frame-wall structure in the shaking table test in this paper is established, and the elastoplastic seismic response analysis with strain rate effect is carried out by using the dynamic fiber beam element subroutine of microconcrete. The numerical results are consistent with the tested results, and the comparison between the numerical results and tested results show that the dynamic response of reinforced concrete shaking table model can simulate by the dynamic fiber beam element subroutine of microconcrete in software ABAQUS accurately. The calculated results with strain rate effect and without strain rate effect are compared with eachother, and results show that the case with strain rate effect is more accurate. Meanwhile, a finite element model of high-rise shear wall structure is established and the effects of strain rate on the dynamic response of the model under seismic loading are investigated. The results show that the effects of strain rate are more obvious with the increasing peak value acceleration of input motion. Hence, the strain rate effect should be considered properly in the seismic design and analysis.