| Coal drop tube structure is one of the important structure in determining whether or not the storage and transportation system can operate normally.In the design process of more than 30 coal drop tube structure which were built in China,the main existing problems include:during calculation of static lateral pressure,the design code for building structure of coal preparation plant emphasizes that theory of static lateral pressure of coal drop tube structure should reference for the lateral pressure theory of silo stored material and active earth pressure,but because of the different structure type and working condition,it leads that there is larger difference between the theory of static lateral pressure of coal drop tube structure and the theory of silo and active earth pressure;because the coal drop structure does not exist as a separate structure during use,there are a lot of stored coal inside and outside of it,so the influence law of seismic response of the interaction system between stored coal and the coal drop tube should be furthered research on earthquake;the high temperature of spontaneous combustion generated by the stored coal in the coal storage shed will also cause serious damage to the wall of coal drop tube.These above problems lead to serious hidden dander in the coal drop tube structure.If the structural damage will affect the normal operation of the entire storage and transportation system,it may even cause the coal mine to stop production and cause huge economic losses.In this paper,coal drop tube structure has been taken as the research object,and the author has been deeply studied on the distribution law of static and dynamic lateral pressure and the thermal stress of wall of coal drop tube on different storage coal conditions through the methods of theory analysis,model experiment and numerical simulation.The specific research contents and conclusions are as follows:(1)Obtained the distribution of static lateral pressure and temperature stress through the testing of the structure model experiment.The testing results of static lateral pressure of the coal drop tube structure with a scale of 1:40 through indirect measurement show that:the lateral pressure distribution of coal drop tube structure under the inside and outside full stored coal conditions is different from the result calculated by the formula of the design code of coal preparation plant building structure.Furthermore,the pressure of coal dropping windows is significantly larger than that of other regions.The outside coal heating has an obviously influence to the temperature stress of the wall near heating area,and the effect of the area near the coal dropping windows is slightly greater than other area.(2)Demonstrated the rationality of finite element model through the comparison of model test results and numerical results.For the first time,hypo-plastic constitutive theory was introduced into the finite model of stored coal.And the two finite element model of coal drop tube and cylinder wall structure are built by the h-p constitutive for stored coal,elastic-plastic constitutive for concrete and friction contact element as the attaching element between the face of coal and concrete.After compared experimental test result and numerical analysis result,the two results are very similar.Furthered demonstrated the rationality of finite element model and hypo-plastic constitutive model for inside and outside stored coal.(3)Using the numerical simulation as a supplementary method for the model experiment that the experiment testing condition is insufficient,the distribution law of the static lateral pressure of the various stored coal condition is obtained.The eight stored coal condition finite model of coal drop tube structures and cylinder wall structure were built,the distribution law of static lateral pressure of coal drop tube structure under different coal stored conditions after the numerical simulation calculation.It is further verified that the static lateral pressure distribution of coal drop tube structure does not match the existing theoretical formula because of the presence of the coal dropping windows,and the area near the coal dropping windows has been concentrated obviously.The distribution law of the static lateral pressure in the middle region of the coal dropping windows is gradually decreasing along the vertical direction from top to bottom and accompanied by the undulating distribution of the waves.In particular,the stress changes most obviously at the height range from 6m to 16m.(4)Through the research on the interaction system between stored coal and coal drop tube,the influence law of the seismic response under stored coal to the coal drop tube structure has been concluded.A separate finite model of coal drop tube and 11 finite models of interaction system between the stored coal and coal drop tube structure under 11 different stored coal condition were built,get conclusions of structural dynamic characteristics and the law of the seismic response through the dynamic characteristics calculation for all the calculation models and the time-history analysis of the coal drop tube structure under the adjusted earthquake wave of EL-CENTRO.The total amount of inside and outside stored coal of the coal drop tube structure has a great influence on the frequency and vibration mode of the structure,especially when the coal height reaches over 20m.The acceleration and acceleration amplification factor,the displacement between the layers and the displacement angle between the layers of a separate finite model of coal drop tube increase with the increasing of the structure height,but the stress response is just the opposite.However,the changes of the amount of inside and outside stored coal has more significant influence of the seismic response of the entire structure,and the seismic response of the entire structural system has increased with the increasing of the amount of stored coal.(5)Using the numerical simulation as a supplementary method for the model experiment that the temperature rise process cannot reach the actual ignition point,the distribution law of the wall’s temperature field and temperature stress is obtained.For the model test process,the loading temperature cannot reach the natural burning point temperature of the stored coal.Assuming that all or some of the lateral stored coal are spontaneous combustion,using the theory of heat conduction and finite element,the thermal analysis to the wall of coal drop tube on the region of coal spontaneous combustion was calculated using the sequential coupling indirect,and it was concluded that the high temperature of the coal spontaneous combustion has a significant influence on the temperature field and temperature stress of coal drop tube,and it cannot be ignored.The 0.15m thickness range along the radial direction and the range of 5° to 7° outside the coal spontaneous combustion area along the circumferential direction have a greater influence.Temperature stress has stress concentration phenomenon near the coal dropping windows,when the temperature reached to 300℃,the maximum tensile stress of the wall has reached 2.83MPa,exceeding the concrete design tensile strength.The above conclusions on the distribution of static and dynamic pressure and temperature stress of the coal drop tube structure were applied to the engineering practice in a coal mine in Shaanxi.Till now,the structure has been in normal service for 14 months,and the accumulated amount of dropping coal has been reached to 3.7095 million tons,and no potential safety hazards such as cracks and deformations occurred,further demonstrating that the entire thesis has made active and meaningful explorations to improve theoretical research on the structure of the coal drop tube,providing a valuable reference for engineering application.There are 109 figures,25tables and 204 references in this paper. |
