Search

In this article, the mechanical properties and material characterisation of graphite tailings concrete, in which graphite tailings are replaced as sand were investigated. The results showed that the concentration of graphite tailings has influence on the comprehensive performance of concrete. Simultaneously, the graphite tailings have an important improvement on reducing the mesostructure distribution and micro-crack density of cement-based materials. However, high content of graphite tailings can result in the growth on defects and significantly reduces strength properties. How to solve the adverse effect of high content of graphite tailings on reduced mechanical strength of concrete or taking full advantage of this material property and characteristics of graphite tailings is an urgent problem to be solved in the future research for practical engineering applications such as road subgrades, coastal breakwaters and so on. [ABSTRACT FROM AUTHOR]

Fourteen reinforced concrete-filled steel tubular (RCFST) short columns were heated following the ISO 834 standard fire condition including cooling phase, of which two specimens were used to measure cross-sectional temperatures, and the others were loaded to failure after cooling to room temperature. The temperatures of the typical cross-sections during the fire exposure, and the axial load versus displacement curves, were measured. Effects of heating time and reinforcement ratio on the residual load-bearing capacity, compressive stiffness and ductility coefficient were discussed. Six more RCFST short columns, unexposed to fire, were tested as comparative specimens to identify the effects of fire on the residual properties. Finally, a design formula was proposed for predicting the residual load-bearing capacity of RCFST columns after exposure to high temperatures, based on relevant codes or technical specifications. The study reveals that the RCFST short columns have high bearing capacity and good ductility, even though after fire exposure. Heating time has more significant effects on the compressive stiffness and ductility than the load-bearing capacity. The load-bearing capacity, the compressive stiffness and ductility after exposure to temperatures increase with the increase of ratio of reinforcement. The results predicted by the design formula were in good agreement with the test results and lie on the safe side. [ABSTRACT FROM AUTHOR]

The typical cross-sectional temperature distribution of concrete-filled square hollow sections (SHS) in single surface, opposite-two-surface,, three-surface and four-surface fires was investigated in this research. The axial deformation and mid-height deflection versus time curves were analyzed respectively, to clarify the mechanism of the columns in different fire conditions and the influence of the fire boundary conditions. Conclusions can be draw from the theoretical analysis results. For concrete-filled SHS columns subjected to opposite-two-surface and four surface fires, the thermal distribution is axially symmetric, inducing dual-axisymmetrical temperature strains and temperature stresses. The mechanisms of the columns are similar to the condition in room temperature. While being exposed to one-surface or three-surface fires, the columns have monosymmetric temperature distribution, which causes load eccentricities and the mechanism of the columns different from those in room temperature. The column bends towards the exposed side first, then the opposite direction. Compared with the non-uniform temperature deformation and load eccentricity, which are caused by non-uniform temperature gradients, the number of surfaces exposing to fire is the key factor that influences the fire resistance of concrete-filled SHS columns. Thus in most cases, the fire resistances are increasing in turn from four-surface, three-surface and opposite-two-surface to single surface fire. However, in some special cases, for instance when the slenderness ratio A < 30, the fire resistances of composite columns are smaller in three-surface fire than those in four-surface fire. The potentional danger therefore should be induced if using the current related codes, which are based on four-surface fire condition. [ABSTRACT FROM AUTHOR]