Study On The Confining Modelling,axial And Seismic Performance Of Pre-damaged Concrete Columns Repaired With Textile Reinforced Concrete(TRC)

As important elements in buildings,concrete columns could bear vertical and lateral forces.Once they are severely damaged,it may endanger human life and property.In the "double carbon" policy,repairing damaged concrete columns can not only improve the buildings’ safety and usability,but also has great significance to social developmentce.Textile reinforced concrete(TRC),as a cementitious composite composed of textile and fine-grained concrete,has good application prospects in the field of repair and reinforcement because of the advantages of light weight,high strength and corrosion resistance.In the so far,there are few research on damaged reinforced concrete(RC)columns repainred with TRC.Therefore,the mechanical and seismic performance of TRC repaired concrete columns were studied from the two levels of materials and components in this dissertation.The methods of physical experiment,mathematical statistics and theoretical analysis were used in the research.The main research contents and conclusions are as follows:(1)The damage evolution laws of TRC confined undamaged concrete under monotonic axial load were analyzed.The mechanical properties on undamaged concrete confined by TRC was studied,including factors such as the TRC layers,concrete strength,and cross-section shape.The results indicate that the peak stress and peak strain of the confined concrete increase with the increase of TRC layers.TRC has the best confinement effect on the circular cross-section.In the case of the same cross-section shape,as the concrete strength increase,the increase range of peak stress and peak strain of TRC confined concrete decreases,due to the weakening of the confinement effect of TRC.(2)Based on statistical analysis results,it is clarified that the stress-strain curve of TRC-confined concrete has the hardening and softening characteristics.The concrete with strong confinement has strain hardening characteristics,while the other has strain softening characteristics.For the TRC confinment system,the failure mechanisms are analyzed,and the working mechanisms under different sections are revealed.Based on the Sargin model,a new closed mathematical expression is deduced to describe the stress-strain curves of TRC-confined concrete.Further,the existing strength and weakness judgment models of confined concrete are evaluated with the statistical data.The critical limit value is modified and the modified confinement ratio is adopted with 0.045 in this paper.By establishing the strength model and axial strain model of TRC-confined concrete,a design oriented unified stress-strain constitutive model of TRC confined concrete is presented.The results indicate that the model can better show the strain hardening and softening characteristics of confined concrete.(3)Based on the axial compression test of TRC-confined pre-damaged concrete,the failure modes of TRC constrained damaged concrete were clarified,and the effects of preloading level and TRC layers on the compressive strength,axial deformation capacity and energy dissipation of TRC-confined pre-damaged concrete were analyzed.The results showed that compared with the unconfined pre-damaged specimens,the axial compressive strength and corresponding axial strain of TRC-confined pre-damaged concrete have an increasing trend with the increase of TRC layers,and the capacity of energy dissipation and deformation are improved.Moreover,it has significant effects with smaller pre-damage degree.Then,the damage evaluation index of concrete is given.By considering the influence of preloading on concrete strength,damage factor was introduced,and the strength and strain models for TRC confined pre-damaged concrete were ontained.Futher,based on the presented model above,the stress-strain constitutive model of TRC confined pre-damaged concrete was obtained.(4)Through the axial compression test of pre-damaged RC columns repaired with TRC,the strengthening effect of TRC was studied.The research factors include the preload level,TRC layers and slenderness ratio.Moreover,the damage evolution law and failure mechanism of damaged RC Columns strengthened with TRC are clarified.The experimental results show indicate that under the same amount of reinforcement,the bearing capacity of TRC-strengthened pre-damaged RC columns decreases with the increase of preloading level.Compared with the pre-damaged specimens without repairation,the bearing capacity and deformation performance of the pre-damaged RC columns repaired by TRC are improved with the increase of TRC layers.With the increase of slenderness ratio,the axial peak strain and ultimate strain of damaged RC columns repaired with TRC decrease.When the preload level does not exceed the peak load,three layers of TRC can be used to restore the RC column to the initial bearing capacity.Then,based on the strength model of TRC-confined pre-damaged concrete,the strength model of pre-damaged RC columns repaired is established by considering the effect of longitudinal reinforcement,stirrup and TRC.At the same time,the strain model considering the double confinememt of TRC and stirrup is presented.Furthermore,the stress-strain constitutive model of pre-damaged RC columns repaired with TRC is given.(5)The variation laws of bearing capacity,stiffness,deformation and energy dissipation accumulation of quantitatively pre-damaged RC columns repaired with TRC under low cycle loading are analyzed.The effects of TRC layers,axial compression ratio,shear span ratio and stirrup spacing on the seismic behavior of quantitative pre-damaged RC columns repaired with TRC are clarified.The damage evolution mechanism and failure mechanism of repaired RC columns are revealed.The experimental results indicated that TRC could reduce the length of the plastic hinge zone of pre-damaged RC columns and improve the failure modes of the specimens with large axial compression ratio and small shear-to-span ratio.The yield load and peak load of the specimens with larger axial compression ratio and smaller shear span ratio are increased.The deformation capacity of the specimen is poor and the stiffness degradation is fast after reaching the peak load.The accumulated energy consumption is less when the specimen failed.Therefore,the seismic performance of the specimen with larger axial compression ratio and smaller shear span ratio is poor.For the specimen with smaller stirrup spacing,the hysteretic curves of the repaired column is full.The energy dissipation capacity is improved.The stiffness degradation ratio is smaller.And the deformation capacity performs better.Compared with the undamaged RC columns without strengthening,the bearing capacity of the pre-damaged RC columns after repairation could restore to its initial level as with the increase of the number of strengthened layers.Moreover,the stiffness increases slightly,and the energy dissipation capacity and ductility are significantly improved.(6)Based on the stress-strain constitutive relationship of TRC-confined pre-damaged concrete presented in this paper,the calculation method of characteristic points(yield point,peak point and failure point)on the degenerated trilinear skeleton curve were discussed through section performance analysis.The hysteretic rules of the restoring force model is defined.Therefore,the restoring force model of pre-damaged RC columns repaired with TRC is established.The results show that the hysteresis modelling is in good agreement with the experimental curves.There are 112 pictures,31 tables and 224 references in this paper.