Experimental Research On Self-compacting And Self-stressing Concrete-filled Rectangular Steel Tubular Stub Columns Under Axial Compression

Nowadays,large-span structures and high-rise buildings are booming,concrete filled rectangular steel-tube structures are increasingly used in structural engineering.However,it requires a lot more research works in order to show the advantages of it in the practical application of civil engineering.Based on the actual demands,this paper has carried out in-depth research on several must-solved problems.The authors made in total of 14column samples of self-compacting and self-stressed concrete filled rectangular steel-tube to conduct the axial bearing capacity test to obtain the following conclusions:(1)According to the respective characteristics of self-compacting concrete and self-stressed concrete and its application in practical engineering case,this paper decided to adopt the method of mixing expansion agent and ordinary cement to make the self-compacting and self-stressed concrete for this test.Two types of self-compacting and self-stressed concrete are tested:Self-compacting and self-stressed concrete with expansion agent UEA(P1 type);Self-compacting and self-stressed concrete with expansion agent UEA,HCSA(P2 type).Through tests,it is concluded that the self-compacting capacities and self-stressed values of both types can meet the requirements.In the axial compression bearing capacity test,the compression bearing capacity value difference of two types is small,and both types can be can be used in future tests.(2)Same self-compacting and self-stressed concrete is poured into three rectangular steel tubes of different cross-sections.Different cross-section forms represent different reinforcement ratios and different aspect ratios.According to the axial bearing capacity test results,the rectangular steel-tube cross-section with large reinforcement ratio has high compression bearing capacity,but these two values didn't form proportional relationship.Different aspect ratios have different axial bearing capacities.(3)In order to facilitate the use in actual engineering,based on the data obtained from the axial compression test,this paper derives the application formula after the equilibrium theory.The comparison between the results calculated by the formula and the test results shows that the correlation between the two types of concrete is good,and the difference of both types is about±10%,which can be used as a reference in the application.The calculated value of ultimate axial compression bearing capacity of self-compacting and self-stressed concrete filled rectangular steel-tube samples raised 30%compare to the calculated value in Code for Design of Composite Structures(JGJ 138-2016)and Technical Specifications for Structures with Concrete-filled Rectangular Steel Tube Members(CECS159:2004).(4)The damage state of self-compacting and self-stressed concrete filled rectangular steel-tube short columns after the ultimate bearing capacity test is basically consistent with the ordinary concrete filled rectangular steel-tube short columns,but its elastic phase can reach more than 85%of the ultimate loading N_u,and the ductility rate is lower than that of ordinary concrete filled rectangular steel-tube.