Study On Seismic Behavior And Damage Analysis Of Recycled Concrete Filled Circular Steel Tubular Columns Under High Axial Compression Ratio

Recycled concrete-filled steel tube structure is a new type of composite structure.At present,certain experimental research has been carried out on recycled concrete-filled steel tube structure at home and abroad.The research shows that due to the compactness of steel tube and the restraint effect of steel tube on core concrete,it can effectively solve the defects of recycled concrete in mechanical properties and durability,and recycled concrete-filled steel tube can not only show high bearing capacity,It also has good seismic performance.However,at present,there are few studies on the seismic hysteretic behavior and damage performance of recycled concrete-filled steel tubular columns under high axial compression ratio at home and abroad.In order to study the seismic performance of recycled concrete-filled circular steel tubular columns under high axial compression ratio,In this paper,two concrete-filled circular steel tubular column specimens and five recycled concrete-filled circular steel tubular column specimens were tested under horizontal low cyclic loading.The failure mode,hysteretic behavior and damage performance of recycled concrete-filled circular steel tubular column specimens under high axial compression ratio were analyzed,The following conclusions are drawn:(1)Recycled concrete-filled circular steel tubular columns with high and low axial compression ratio will experience elastic,elastic-plastic rising stage and elastic-plastic falling stage under horizontal low cyclic loading.When the specimen with low axial compression ratio is damaged,a rotatable plastic hinge will be formed at the bottom of the column,the bulging phenomenon is serious,and the recycled concrete is crushed,which belongs to typical compression bending failure;However,when the specimen with high axial compression ratio is damaged,the bulging phenomenon is not obvious,and there is no obvious plastic hinge rotation at the bottom of the column,which belongs to instability failure.(2)The hysteretic curve of the specimen with low axial compression ratio is relatively full and has good deformation capacity and energy dissipation capacity;The hysteretic curve of specimens with high axial compression ratio will drop suddenly,and the horizontal bearing capacity is high,but the ductility and energy dissipation capacity are weak.In the case of high axial compression ratio: the addition of recycled aggregate has no effect on the shape and trend of hysteretic curve;With the increase of wall thickness,the hysteretic curve is fuller,and the ductility and energy dissipation capacity of the specimen will also increase;With the increase of slenderness ratio,the bearing capacity decreases,but the ductility increases.(3)The stiffness degradation curve of each specimen shows a trend of fast in the early stage and slow in the later stage.The initial stiffness of the specimens with high axial compression ratio is large,and the stiffness degradation curve is steep.In the later stage,the stiffness of the specimens with high and low axial compression ratio is gradually close.In the case of high axial compression ratio,the change of recycled aggregate substitution rate has little effect on the stiffness of the specimen;With the increase of slenderness ratio,the stiffness of the specimen is obviously low;With the increase of wall thickness,the initial stiffness of the specimen increases,and tends to be consistent with the specimen with thinner wall thickness in the later stage.(4)The bearing capacity and deformation of recycled concrete-filled circular steel tubular columns under high and low axial compression ratio will be affected by P-Δ The influence of the second-order effect is small in the elastic stage and significantly increased in the elastic-plastic stage.P-Δ The influence of the second-order effect on the specimens with high axial compression ratio is significantly lower than that on the specimens with low axial compression ratio.In the case of high axial compression ratio,the influence of second-order effect on circular steel tube ordinary concrete is slightly lower than that on circular steel tube recycled concrete;The thicker the wall thickness of the specimen is,the more serious the influence of the second-order effect is;The larger the slenderness ratio of the specimen,the more serious the influence of the second-order effect.(5)The calculated values of the bearing capacity and flexural stiffness of the specimen are obtained from various codes and standards at home and abroad.After comparing with the measured values of this test,it is concluded that under the condition of low axial compression ratio,the calculated values of the compressive bending capacity and lateral stiffness of the circular steel tubular recycled concrete column calculated by using the national standard GB 50936-2014 are in good agreement with the test values;In the case of high axial compression ratio,the compressive bending capacity and lateral stiffness of recycled concrete-filled circular steel tubular columns calculated in various specifications are small,which need to be properly enlarged.(6)The equivalent plastic hinge length of each specimen in this experiment is calculated by concrete crushing method and section curvature method.Finally,it is concluded that under the condition of low axial compression ratio,the equivalent plastic hinge length of the specimen is in the range of(0.2 ～ 0.3)h;In the case of high axial compression ratio,the plastic hinge is not fully formed because the specimen tends to have compression bending instability failure,so the length of plastic hinge calculated by this method is not accurate.(7)Four seismic damage analysis models are used to calculate and analyze the damage index D of each specimen in this test.Based on the classification of the seismic level of the building structure,combined with the damage index value calculated by the seismic damage analysis model mentioned above and the failure mode of the specimen during the test,the damage quantitative index of the seismic performance level corresponding to the concrete-filled circular steel tubular column under high and low axial compression ratio is given.