| Concrete filled steel tube(CFST)is a member of the steel tube and concrete bear the load together that is filled with concrete.Its superior performance depends on the cooperation of steel tube and concrete,however,the interaction mechanism between the two materials is complicated.In the process of load transfer,Steel tube and concrete bear the load together and coordinate deformation,the interfacial bonding force especially the shear bond strength plays an extremely important effect.Due to the high temperature,the material properties of steel pipe and concrete are deteriorated,in addition,the expansion and deformation of the steel tube and concrete are inconsistent,which may lead to the deterioration of the interface performance.So that the stability and bearing capacity of structures has been falling.At present,the study on the interfacial behavior of CFST under normal temperature and fire is carried outat home and abroad,but,there is no report on the interfacial bonding behavior of CFST under fire.Based on the above background,in this paper,the interfacial bonding behavior of concrete filled steel tube under constant temperature is studied.The main work and achievements are as follows:(1)The test of 23 concrete filled steel tubular columns under constant high temperature was carried out,the temperature-time curve and load-relative slip curve are obtained.analyzed the effects of constant temperature,thickness ratio and slenderness ratio on the average bond strength and load slip curve.Test results shows that constant temperature has significant influence on the average bond strength of CFST specimens at the temperature between 20℃ and 900℃ and average bond strength decreases with increasing temperature at first,then increases,and reduces at last;Average bond strength decreases with the increase of the ratio of length to diameter of CFST specimens;With the increase of the thickness ratio,the degree of average bonding strength is relatively small.(2)According to the analysis results,the key factors that affect the bond strength betweensteel pipe and concrete of CFST under constant temperature are determined,and return to the average bond strength and the relative slip value formula of the peak load.On this basis,the interfacial bond stress slip relationship model of CFST under constant high temperature is obtained.The relationship model is compared with the experimental results,and the rationality of the relationship modelis verified.(3)Setting up finite element model of concrete filled steel tubular column under constant temperature,the applicability and rationality of the model are verified by the related experiments. |
PDF Full Text Request