| Ultra high performance concrete(Ultra high performance concrete,UHPC for short)is a new cement-based material,which has the ultra high strength and excellent durability.However,the ductility of UHPC is poor,and its failure belongs to brittle failure.The UHPC was injected into the steel tube to form the UHPC filled steel tube,which can effectively overcome the shortcoming of this material brittleness.It give full play to the excellent performance of each material,and this application prospect is very broad.The interfacial bond between steel tube and UHPC is the premise of the two materials working together.Therefore,the bond behavior is one of the important research problems of UHPC filled steel tube.At present,there are many researches on the bond behavior of Concrete-filled steel tube around the world,while there are few researches on the bond behavior of the UHPC filled steel tube,which are still in the initial stage.There are still some shortages in the experimental research and theoretical analysis of the bond behavior of UHPC filled steel tube.In this context,the bond performance of UHPC filled steel tube is studied by means of experimental research and theoretical analysis.It mainly includes the following contents and conclusions:1.Experimental study on interface bonding and sliding performance of UHPC filled square steel tube: A total of 21 specimens were designed,including 18 UHPC filled square steel tube specimens and 3 Concrete-filled square steel tube specimens for contrast.The failure pattern of the specimen after loading was observed,and the load-slip curve,bond failure load,load-strain curve and strain distribution curve of the specimen were analyzed.The results show that the interface friction in the square steel tube is not evenly distributed inside the steel tube,but mainly concentrated in the corner of the steel tube.The degree of corrosion on the inner surface of the steel tube under thermal curing was more serious than that under natural curing;The load-slip curves are divided into two types: one has obvious peak points,the other has no obvious peak points,The slippage of the loading end is about 1～3mm for the two types of curve bond failure loads.The slippage at the loading end corresponding to the bond failure loads of two types is about 1～3mm;The longitudinal strain of steel pipe is basically distributed by exponential function.2.Research on calculating the bond strength of UHPC filled square steel tube:Based on the experimental study of UHPC filled square steel tube,the existing formulas and specifications are compared,and the factors affecting the bond strength are analyzed.On this basis,the formula for calculating the bonding strength of UHPC filled square steel tube is established by means of semi-theoretical and semi-empirical methods.The results show that the interface bond strength of UHPC filled steel tube is larger than that of Concrete-filled steel tube.The existing bond strength formula for the UHPC filled steel tube is no longer applicable,and the values of existing norms for UHPC filled steel tube structure tends to be conservative;The ratio of width to thickness,the compressive strength of UHPC and the ratio of length to width can decrease,increase and decrease the bond strength respectively.The formula is in good agreement with the experimental data,which provides reference for the related research.3.Research on the constitutive model of UHPC filled square steel tube: Based on the experimental study of UHPC filled square steel tube,the average bond stress development curve is simplified in sections,and the interface bond stress and internal slip development in each stress stage are discussed.The piecewise function is used to express the bond slip constitutive of the UHPC filled square steel tube.By means of factor analysis and theoretical derivation,the coordinate formula of each characteristic point of the curve and the curve expression of the ascending and descending sections are given.The distribution of bond stress is analyzed by the longitudinal strain distribution of steel pipe.The results show that the average bond stress slip curve can be divided into five stages of bond stress development.The composition of bond stress and internal slip is different in each stage.The exponential function,hyperbolic function and linear function are used to describe the constitutions in sections.The constitutive model of UHPC filled square steel tube is in good agreement with the experimental results. |
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