Study On Seismic Behavior Of Reinforced Concrete Column Under Low Cyclic Loading After Freez-thaw Cycles

This thesis is mainly to study the effect of freeze-thaw cycles on the seismicbehavior of reinforced concrete columns. Based on data regression analysis andtheoretical model deduction, experimental study and numerical simulation calculation,the degradation of mechanical properties and the constitutive model of concrete areexplored, the variation of the indexes of reinforced concrete column under low cyclicloading after freez-thaw cycles, such as strength, stiffness, ductility and energydissipation are studied.In this paper, the mechanical performance testing data of concrete afterfreez-thaw cycles are collected and analyzed, the index of relative compressive strengthof freezing-thawing damaged concrete is introduced, and the relationships betweenrelative compressive strength and initial elastic modulus, peak strain, peak tensile stressand biaxial compressive strength are established; the mathematical expressions of thecomplete stress-strain curve of the freezing-thawing damaged concrete are suggestedand the equations' parameter calculation formulae are discussed; based on the isotropicelastoplastic damage theory, the expressions of damage model parameters aresuggested.An experimental investigation on the seismic behavior, which included6freezing-thawing damaged reinforced concrete columns and2un-damaged reinforcedconcrete columns, is presented in this paper. The effect of frost-thaw cycle times andaxial compression ratio on the seismic behavior of the freezing-thawing damagedreinforced concrete columns are considered. The research shows that, under the sameaxial compression ratio, the shape of load-deflection hysteretic curves changes fromspindle shape to arch and the number of hysteretic curves at failure decrease with the increase of cycle of freezing and thawing; the change of stiffness and strengthdegeneration of the specimens are not obvious when the cycle of freezing and thawingis little, while the seismic indexes of the specimens, such as strength, stiffness,displacement ductility and energy dissipation, degraded obviously after300timesfreeze-thaw circle; under the same cycle of freezing and thawing, the ultimate bearingcapacity and initial stiffness increase, the degeneration of stiffness and strength expedite?the displacement ductility and energy dissipation rapid decrease with the increase ofaxial compression ratio.Based on the concrete elastoplastic damage model which has been suggested inthis paper, a numerical simulation calculation was carried out for the experimentalspecimens by using the finite element software ABAQUS, the degradation mechanismof the seismic behavior of reinforced concrete column under low cyclic loading afterfreez-thaw cycles is studied.