| Reactive powder concrete (RPC) as a green high performance concrete has incomparablesuperior performance in many aspects including super high strength, high toughness, highdurability and excellent volume stability. Reactive powder concrete is the future developmentdirection of the concrete. The application in combination structure will form RPC filled steeltubular structures. In this regard, it is of great theoretical significance and engineeringapplication value to study the RPC filled steel tubular members. In this paper, the bond-slip,interfacial bond damage performance, size effect model and impact resistance properties arestudied for reactive powder concrete filled different cross-section steel tube. The mainresearch work and innovation achievements obtained in this dissertation can be summarizedas follows:(1) The axial bearing capacity calculation of reactive powder concrete filled circular,square and round-ended steel tubular short columns were derived based on the unifiedstrength theory and thick-walled cylinder theory. By means of the theorem of the stationaryvalue of potential energy and consideration of confinement effect, the theoretical formulas ofthe composite compressive elastic modulus were decuced. The formulas can actually andreliably describe the elasticity behaviors and the confinement mechanism of the compositecolumn. The composite axial compression stiffness of RPC filled steel tube was furtheranalyzed.(2) A unified plastic limit solution with size effect was dericed by using the unified yieldcriterion and a strain gradient plasticity theory. The axial compressive strength of externalsteel pipe with size effect was conducted. The size effect rule and mechanism under differentdeformation conditions was discussed. The amendment of core RPC compressive strengthwas carried out by means of adopting Weibull statistical size effect model. The thick-walledcylinder theory with size effect for external steel pipe was conducted. The calculation formulawith size effect model and interfacial bonding strength is presented for reactive powderconcrete filled different cross-section steel tubular columns subjected to axial compressionbearing capacity. The accuracy of the ultimate capacity formula is effectively improved forRPC filled steel tubular stub columns. A number of parametric studies, including in strengththeory parameter, confinement index and RPC strength are also carried out to investigate theireffects on the analytical solutions.(3) The bond-slip constitutive model of RPC filled steel tube was approximatelysimulated by the three section line for appliying spring element in ANSYS numerical simulation. The nonlinear spring element named Combination39was adopted to simulate thebond-slip behavior between steel tube and RPC. Attention is especially paid to F-D curveselection method and characteristics of nonlinear spring element named Combination39.Combination39elements were used to simulate the three directional interactions with normaldirection, longitudinal and ring tangential direction. The axial compression bearing capacityand load-deformation curves of RPC filled different cross-section steel tubular columns weregot to use ANSYS postprocessor. The results indicated that the simulation curves were goodagreement with the trial curves. Parametric studies are carried out to investigate the influenceof RPC strength, confinement index and axial compression stiffness ratio on the ultimate axialcompressive capacity(4) The split Hopkinson pressure bar (referred SHPB) numerical simulation for RPCfilled steel tubular short column and RPC short column were conducted by LS-DYNAsoftware. The waveform diagram of stress wave, axial stress versus time, axial strain versustime and and the reconstruction of stress versus strain curves were consistent with theexperimental results which proved the rationality of finite element model. Based on thedynamic mode suggested by CEB and Malver，a calculation expression of dynamic increasefactor was deduced for RPC filled steel tube. The three-wave method and two-wave methodare given to the formula of calculate strain, stress and strain rate. The RPC strain ratehardening characteristics, specimen failure process and response of dynamic increase factorswere studied under impact loading. The effects of RPC strength, steel tube wall thickness,confinement index and other coefficients on the impact resistance are discussed through thenumerical analysis. |
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