| Coal gangue is the appendage of mine excavation,because it has some pollution to the environment,most of it is Centralized piled up,which not only affects the space utilization of mining area,but also increases the management cost.Coal gangue is used as coarse aggregate of concrete and combined with thin-walled steel and FRP material to form composite column members,when applied to underground environment such as mine,on the one hand,FRP can protect the internal structure from the damage of wet and complex underground environment;on the other hand,the lightweight property of gangue concrete and thin-walled steel is also conducive to the light transportation and rapid construction in underground.For columns,compared with the ideal stress state of axial compression,eccentric compression is more close to the engineering practice.However the mechanical behavior of this new type of composite column with coal gangue as aggregate subjected to eccentric load is not clear.Therefore,in this paper,FRP-gangue concrete-thin-walled steel double-walled solid column bias mechanical properties and its influence factors were studied,and the bias bearing capacity calculation formula considering eccentricity and slenderness ratio reduction was proposed,which provided theoretical reference for engineering practice.Firstly,the bias tests of 24 composite columns and axial compression tests of 4composite columns were carried out.Considering the influence factors such as eccentricity,length-diameter ratio,FRP layers and fiber direction,and concrete strength,the failure mode and stress mechanism of composite column under bias were explored.The results show that the FRP-coal gangue concrete-steel double-wall solid column has good ductility,in which the FRP is the outermost constraint,and the final failure of the member is marked by the fracture of FRP.The steel tube is the internal constraint in the member.Its function is mainly reflected in the circumferential tension,which constrains the core concrete,rather than the function of the tensile steel bar in the reinforced concrete column.The load eccentricity is the most important factor affecting the bias bearing capacity and deformation of the composite column,followed by the aspect ratio and the FRP layers.Bidirectional fiber FRP can improve the ductility of the column,but not the bearing capacity of the column.Then,the finite element model of the composite column was established by using the finite element software ABAQUS,and its validity was verified by comparing with the test results.Based on the test,the influencing factors of the bias performance of the composite column were further analyzed.The results show that,in addition to reducing load eccentricity,increasing the strength of concrete or decreasing the length-diameter ratio of columns can increase the bearing capacity of biased columns.In different section forms,the internal steel pipe offset to the tensile side can improve the mechanical properties of the bias composite column,and can weaken the influence of load eccentricity increase on the bearing capacity of the column,but if the offset of the steel pipe is too large,the opposite effect will be achieved.Appropriately increasing the diameter of steel tube is also an effective method to increase the bias bearing capacity of composite column.Finally,by fitting the experimental data in this paper,the constraint effectiveness coefficient of the existing FRP constrained concrete is revised,and the new concrete strength model is applied to the biased columns,and the bearing capacity formula of double-tube coal gangue concrete columns with an FRP external tube and a thin-walled steel internal tube subjected to eccentric load is proposed considering the eccentricity and the reduction of length to diameter ratio.The accuracy of the formula is verified by comparison with the finite element resultsThere are 55 figures,18 tables and 70 references in this paper. |
PDF Full Text Request