| For decades,the coal consumption in China continues increasing.Coal gangue,as a waste residue generated during coal mining and processing,has a low application ratio.A large number of coal gangue storage has severely occupied our country’s land resources.In order to improve the comprehensive application of coal gangue,it is one of the research hotspots to prepare new building materials by using coal gangue to replace certain proportion of ordinary concrete ingredients.It is well known that the mechanical properties of concrete are greatly improved under external confinement,and the core concrete is also not easily affected by environmental factors.Therefore,the composition of steel tube and concrete could improve the strength of structural member.The axial compressive properties of coal gangue concrete and concrete-filled steel tubular short columns have been widely studied whilst the research on coal gangue concrete-filled steel tube is relatively few.Therefore,this paper studies the influence of gangue substitution rate on the bearing capacity of coal gangue concrete filled steel tubular stub and reinforced coal gangue concrete counterparts.The influence of coal gangue replacement ratio on the performance degradation of coal gangue concrete-filled steel tubular stubs has been studied.The main findings are as follows:(1)Coal gangue is used to replace the coarse aggregate in concrete,and seven groups of the specimens under different substitution rates with design strength of C45(0%,25%,50%,100%)and C60(0%,50%,100%)are prepared and the compressive strength,splitting tensile strength and elastic modulus of coal gangue concrete are tested.The analysis shows that the mechanical properties of coal gangue concrete decrease with the increase of the substitution rate of gangue.The model for predicting the strength of gangue concrete is presented.Based on the existing model,the constants for predicting the splitting tensile strength and elastic modulus of coal gangue concrete are presented.(2)According to the mixture proportion of coal gangue concrete,seven groups of reinforced coal gangue concrete and coal gangue concrete-filled steel tubular stubs have been prepared.The phenomena of axial compression test show that circle reinforced coal gangue concrete short columns show roughly the same shear failure modes with the circular ordinary reinforced concrete short column,namely a diagonal main crack.The failure modes of coal gangue concrete-filled steel tubular short columns are also roughly the same as those of ordinary concrete-filled steel tubular short columns.After removing the outer steel tube,the same inclined crack from the end of the column to the center of the column is observed.Therefore,the replacement rate of coal gangue has little influence on the failure modes of these short columns.(3)The axial compressive strength and initial stiffness of the short column decrease with the increase of the coal gangue replacement rate.The increase of improvement coefficient and confinement coefficient is due to the increase of the replacement rate of coal gangue.Because of the increase of coal gangue replacement rate,the bearing capacity degradation of coal gangue concrete-filled steel tubular short columns decreases after peak value.It shows that compared with reinforced concrete short columns,coal gangue is more likely to be used as the substitute of coarse aggregate in the core concrete of concrete-filled steel tubular short columns.(4)By considering the substitution rate of coal gangue,an improved design method of reinforced concrete and concrete-filled steel tubular short columns is proposed.The predicted axial strength of the short columns fits well with the test results.Based on the proposed formula,a full-range analysis is conducted on the behavior degradation of the stubs.The analysis results show that coal gangue should be used to prepare concrete-filled steel tube with relatively high steel strength and relatively low concrete strength. |
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