| A mineral transportation trestle bridge is widely used in industrial fields,such as metallurgy,colliery,thermal power,cement production etc,for material delivery and transmission.The structural support of transmission equipment is made of the steel structure.Material transmission is a dynamic action process,which is always in the wake of the influence in start-up and braking of conveyor belt,mineral transmission vibration and exciting vibration of traction equipment etc.Due to the dynamic excitation.The key to the design of this structure is how to evaluate the structural dynamic response correctly.This paper takes a long-span trestle structure of a cement plant as the research object,the vibration measurement was carried out to study the influence of the stressed-skin construction on the natural vibration characteristics of the truss trestle bridge.Based on the discrete element method,a dynamic model of material conveying is established and its effectiveness is analyzed,Further more,the DEM-FEM model of grid trestle bridge will be built to analysis the dynamic characteristics of the structure.The study reveals the structural response under dynamic excitation of material conveying,and proposes a dynamic influence coefficient in the design of this kind of structure,which offers a reference for structure design.The specific research contents are as follows:First,the vertical random vibration test of the grid trestle bridge structure under the full-load normal transmission condition was carried out on the large grid trestle bridge structure which this paper concerns to obtain the vertical vibration acceleration time history curve of the actual structure,and the modal analysis method is used to confirm the natural frequency of the actual structure.Second,the influence of the exterior protected construction on the natural vibration characteristics of the truss trestle is proved.According to the structural characteristics,the overall joint model and the independent grid model are constructed according to whether the stiffness of the stressed-skin construction is considered or not for modal analysis.Compared with the measured results,the result shows :Due to the stiffness and mass distribution,the self-vibration modes of the overall joint model are quite different from those of theindependent load model.Compared with the measured structure modal,the first frequency of the independent model is close to the measured one.The second and third frequencies of the overall joint model are close to the measured ones.Since the natural vibration of the structure is mainly based on the first mode,the independent model is determined as the basic model for the subsequent structural dynamic response parameter analysis.Third,the discrete element model should be built to simulate the dynamic effect of conveying materials on the grid trestle bridge structure.Three groups of parameters that affect the dynamic characteristics of material transportation are selected for analysis,the results shows : The influence of conveying volume on material conveying load is positive before it reaches critical value,and it has no effect after it reaches critical value;The influence of particle radius on material conveying load is negatively correlated;The impact of material conveying speed on material conveying load is negatively correlated.Finally,the coupling model of the discrete element and structure should be built to study the dynamic characteristics in the process of material conveying.According to the three groups of parameters that affect the dynamic characteristics of the structure in the process of material transportation,the internal force response and displacement response of the structure under various working conditions are obtained.Based on this,the recommended value of dynamic coefficient of material conveying grid trestle structure is given.This paper suggests that the design of the structure should be designed according to the dynamic coefficient under full load condition,considering the full load condition under no-load condition and under-load condition,and the dynamic coefficient at full load condition should be taken as 1.4.When the particle radius increases,a smaller dynamic coefficient can be selected,but not lower than 1.4.When the materials conveying speed is not higher than 3.5m / s,the structural dynamic coefficient should be designed and calculated according to 1.7;when the conveying speed is higher than 3.5m / s,the structural dynamic coefficient should be designed and calculated according to 1.4. |
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