| Due to the rapid development of economic construction,the consumption of natural building materials is enormous.In addition,the renewal of old buildings which are close to the useful life.More and more waste materials such as waste concrete are produced,which can cause great harm to environment and society.Therefore,taking natural building materials alone is not a wise move,and it is of great environmental and economic benefits to make full use of waste concrete.Because of the high,large span and other structures of building space requirements,so the use of concrete-filled steel tube structure more,and the self compacting concrete has good working performance that without vibration and uniform density.It is urgent to study the self compacting concrete structure of steel tube,and there are few researches on the axial compression bearing capacity of self compacting recycled concrete filled steel tubular columns.On the basis of previous studies,use the test and ANSYS simulation to study it,and specific contents are as follows:(1)study influence in different proportions of the slag powder and silica fume(1:1,3:1,9:1)and the different substitution rate of the recycled aggregate(0%,25%,50%,75%,100%)on the performance,compressive strength and elastic modulus to the self compacting recycled concrete,using the comprehensive test method.Experimental results show:when the replacement ratio of recycled coarse aggregate is 50%,and the ratio of slag powder and silica fume is 3:1,where the performance is the best,compared with the ratio of slag powder and silica fume in 1:1 and 9:1,the expansion degree respectively increases by 4.47%and 8.18%,the slump respectively increases by 1.90%and 2.68%,and T500 decreases by 18.18%and 25%.With the increase of recycled coarse aggregate replacement ratio and the ratio of slag powder and silica fume,the elastic modulus of self compacting recycled concrete increasingly decreases.When the ratio of slag powder and silica fume is 1:1,compared with the self compacting concrete,the elastic modulus of the self compacting recycled concrete decreases at least,and recycled aggregate replacement rate are 25%,50%,75%,100%,respectively decreasing by 4.68%,8.43%,13.75%,17.5%.Therefore,the increase of the proportion of silica fume can compensate for the decrease of the elastic modulus of the self compacting recycled concrete;At the age of 3 days,when the ratio of slag powder and silica fume is 1:1 and the replacement rate of recycled coarse aggregate is 50%,where compressive strength is the highest,partly increasing by 2.27%and 1.66%,compared with the ratio of slag powder and silica fume in 3:1 and 9:1;At the age of 7 days,when the ratio of slag powder and silica fume is 9:1 and the replacement rate of recycled coarse aggregate is 50%,where the 7 days compressive strength is the highest,partly increasing by 5.59%and 0.85%,compared with the ratio of slag powder and silica fume in 1:1 and 3:1;At the age of 28 days,when replacement ratio of recycled coarse aggregate is 50%,where the compressive strength reduced is the least,and the ratio of slag powder and silica fume is 1:1,3:1,9:1,respectively the compressive strength of 28d decrease by 0.36%,2.53%and 3.83%;When the ratio of slag powder and silica fume is 1:1,and the replacement ratio of recycled coarse aggregate is 50%,where the 28d compressive strength is the highest,partly increasing by 3.29%and 5.69%,compared with the ratio of slag powder and silica fume in 1:1 and 3:1.Thus,we propose the optimal mix proportion of 1m3C40 self compacting recycled concrete material,and optimal mix ratio is that cement:fly ash:slag powder:silica Fume:natural aggregate:recycled coarse aggregate:sand:water:water reducer are 250:150:50:50:500.4:510:742.56:153.93:12.5.(2)Axial compression test of the short columns that self compacting recycled concrete filled with the steel tubular shows that the failure mode of axial compression specimens all are shear failure,they form the waist drum of the deformation characteristics in the middle of columns.The axial compression bearing capacity of the short columns that self compacting recycled concrete filled with the steel tubular is slightly lower than that of self compacting concrete filled steel tubular short columns;The maximum displacement at the maximum load is about 6?10mm,with the increase of the compressive strength of self compacting recycled concrete,the ultimate bearing capacity of the short column is larger and the smaller the corresponding displacement;The stress-strain curve and the load-displacement curve of self compacting recycled concrete filled steel tube and self compacting concrete filled steel tube are similar,with the replacement ratio of recycled coarse aggregate,the ratio of slag powder and silica fume increasing,in the elastic stage,the slope of the load longitudinal displacement curve and rigidity of the self compacting recycled concrete filled steel tubular short column gradually decrease.With the increase of the ratio of slag powder and silica fume,the ultimate bearing capacity of recycled concrete short column with self compacting steel tube is reduced gradually;With the increase of recycled coarse aggregate replacement ratio,the ultimate bearing capacity of the self compacting recycled concrete short column decreases first,then increases and then decreases;When the replacement ratio of recycled coarse aggregate is 50%and slag powder and silica fume is 1:15 the ultimate bearing capacity of which is 1161KN,compared with 3:1 and 9:1,the ultimate bearing capacity of which respectively increasing by 3.5%and 2.4%;In the bearing capacity aspect,there is little difference between self compacting recycled concrete filled steel tubular short column and steel tube recycled concrete short column;Compared with steel tube recycled concrete short columns,self compacting recycled concrete in steel pipe is feasible;Under satisfy the condition of bearing capacity and considering the maximum utilization of recycled coarse aggregate,construction schedule and cost,the optimum replacement ratio of recycled aggregate is 50%,thenthe corresponding bearing capacity is 1.08%higher than steel tube recycled concrete short columns;The ultimate bearing capacity of 15 self compacting recycled concrete filled steel tubular short columns are obtained by static load test;By calculating,the calculated value of DBJ13-51-2003 is close to the experimental value,and their ratio is from 0.71 to 0.99,and the mean value is 0.96,the coefficient of variation is 0.03,and the safety is the lowest;finding relationship between component confinement effect coefficient and improving coefficient of concrete bearing capacity,using that curve for the regression analysis and fitting of curve,the correctional calculation formula of the ultimate bearing capacity of self compacting recycled concrete filled steel tubular short column is proposed:ND =(27.25?2-49.71? + 24.27)fckAc + fyAs.(3)From simulation results and experimental results,we can conclude that the average value of the ratio is 1.019,the coefficient of variation is about 0.008,the deviation is about 5%,and the failure form is the same as the test result;The results show that it is feasible to use the finite element ANSYS to analyze the axial compression of steel tubular short columns with self compacting recycled concrete. |
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