| Along with the advance of science and technology,construction industry standard has been considerable developed.All kinds of tall,large span,quaint building works come one after another,too.In the other hand,traditional building materials and building structures have become increasingly difficult to meet people’s needs.Therefore,the development and application of new building materials and structures has become one of the hot spot that engineering and technical personnel carry out scientific research.Subsequently,the concrete filled steel tube(CFST),lightweight aggregate concrete and micro-expansion concrete technology came into being,which has been widely used in engineering practice,and achieved good economic and social benefits.This paper combines the above three kinds of technology as a whole,composed of micro-expansion lightweight aggregate concrete filled steel tube(hereinafter referred to as MELA-CFST),give full play to their respective advantages and make up for their shortcomings.In order to study basic mechanical properties of the MELA-CFST,this paper carried out the following research:(1)Analyzing the influence of expansive agent dosage on concrete strength and free deformation of specimen through micro-expansive lightweight aggregate concrete mix ratio test.Experimental study shows that adding an appropriate amount of expansion agent can not only compensate shrinkage of lightweight aggregate concrete and prevent cracking,but also improve the compactness and strength of concrete.However,an excess of expansion agent will not conducive to the further improvement of concrete strength.(2)Making 24 MELA-CFST stub column specimens,observing the strain of the specimens under the condition of limited expansion for 60 days,and analyzing the influence of expansive agent dosage to performance of restricted expansion of lightweight aggregate concrete.Experimental results show that in the range of test parameters,the greater the expansive agent is,the more obvious shrinkage compensation of core concrete is,the hoop compressive stress of steel due to shrinkage of core concrete is also smaller,sometimes even hoop tensile stress is also produced.(3)Having an axial compression test on the MELA-CFST stub column specimens and analyzing the results by decomposition analysis to discuss the stress-strain relationship of steel tube and core micro-expansive lightweight aggregate concrete respectively.Experimental results show that increase steel ratio and strength of core concrete can greatly improve the combined strength and stiffness of the specimens;adding an appropriate amount of expansive agent can improve the confining force of steel tube on core concrete,and makes the confining force appeared in advance when the specimens under axial loading.On the basis of experiment,obtained the strength criterion of core micro-expansive lightweight aggregate concrete under the three-dimentional stress states by fitting.As well as,by the comparative analysis of various formulas,the formula of ultimate bearing capacity which is suitable for MELA-CFST stub column was put forward.(4)Establishing the constitutive relationship model of steel and concrete under threedimensional stress.Respectively using the method of synthesis and the practical formula for numerical analysis to get the stress-strain curves of the MELA-CFST stub column specimens,and comparing it with the curves obtained in the test.The results show that the flexible working stage of MELA-CFST is longer than that of ordinary CFST,and the composite elastic modulus is below than ordinary CFST under the same parameters.The practical formulas which obtained by modification in the existing research results can better react the axial compression failure process of the MELA-CFST,but some relevant parameters are not suitable for the MELA-CFST which has a low steel ratio. |
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