| The connection between the wind turbine tower and the foundation is the most critical part of the wind turbine tower structure,the stress state of connection is complicated.Once damage occurs,the transmission path of the tower structure to the foundation will be changed or interrupted,which will cause the collapse of wind power tower system,and causing huge economic losses.Currently,the domestic and foreign research of concrete-filled steel tube wind turbine tower foundation connection section and related standards cannot be directly adapted to the design and calculation of the corresponding connection section.Therefore,it has a great theoretical significance and practical value to study the failure mechanism,ultimate bearing capacity,control indexes and parameters of the wind turbine tower structure and it's foundation connection.In this paper,a 2MW horizontal-axis variable-pitch wind turbine tower structure in Baiyun Obo(Inner Mongolia)is selected as the research object,and the load of this research is based on "Guide and Explanation of Wind Power Equipment Tower Structure Design" and the wind power system calculation software GH Bladed,and get the design value of the internal force of each tower leg.Chose the design value of the large internal force of the tower's tensile column limb as the control load,and deeply analyzed the model of the connection structure between the wind power tower and the foundation.This paper analyzes the engineering case where the base ring is pulled out integrally under the external force in actual engineering,with reference to the design experience of the combined structure and steel structure nodes at the present stage,in this article the basic ring connection of the existing conical tower has been improved to two different types of connections,the reinforced ring connection section and the PBL connection section.Those connection sections are proposed to solve the problem that the tower foundation ring has been pulled out in actual engineering.The finite element simulation and finite element parameter analysis were carried out on the reinforced ring connection section,and the effects of the number of rib plates,the height of the reinforcement section and the thickness ratio of the upper and lower ring plates on the mechanical performance of the connection section were analyzed.The simulation results show that:(1)With the increase of the number of reinforcing ring ribs,the maximum value of stress in the high stress zone of the connection section remains unchanged.With the increase of the number of ribs,the high stress area of the connection section tends to decrease significantly,and the axial deformation of the connection section decreases with the increase of the number of ribs;(2)With the increase of the height of the reinforcement section,the stress distribution and deformation of the connection section have changed significantly.The area of the high stress area decreased significantly with the increase of the height of the reinforcement section,and the maximum stress value did not change with the change of height.(3)With the increase of the thickness ratio of the upper and lower ring plates,the stress distribution form of the connection section under each parameter is basically similar,but the deformation resistance of the connection section increases with the increase of the thickness ratio.Among them,when the thickness of the upper ring plate is increased from25 mm to 30 mm,the axial tensile deformation of the connecting section only decreases by0.01 mm,indicating that when the thickness of the upper ring plate is greater than 25mm(that is,the thickness ratio of the upper and lower ring plates is greater than 1.667),The influence of the anti-deformation ability has been negligible.In the actual engineering design,the thickness ratio of the upper and lower ring plates can be selected from 1 to1.667.The finite element simulation and finite element parameter analysis are performed on PBL-type connection sections.The effects of the number of perforated steel bars in each row of the PBL connection section,the diameter of the perforated steel bar and the length of the perforated steel bar on the mechanical properties of the connection section were analyzed.Simulation results show:(1)With the increase of the number of PBL shear keys in each row,the maximum stress value of the connection section gradually decreased,and due to the continuous weakening of the steel plate part of the reinforcement section,the high stress zone was transferred from the upper part of the foundation ring to the first row of steel bar through-holes near the load point between steel plates.In order to ensure the safety of the connecting section,the ratio of the arc length to the radius of the steel plate between the steel bar through-holes should not be less than 0.2618;(2)With the parameter changes of different diameters of the perforated steel bars,the stress distribution of the connection section has little difference.The effect of the diameter of the perforated steel bar on the stress distribution of the connection section is negligible.Under the effect of large displacement,the maximum bearing capacity of the connection section of the four perforated steel bars is not large.The bearing capacity of the connection section under the diameter of the four perforated steel bars increases slightly with the increase of the diameter of the steel bars.The bearing capacity difference of the connection section under the diameter of each perforated steel bar does not exceed 1%,and the bearing capacity of the connection section under each diameter has a high safety reserve.Considering the bearing capacity,plastic deformation energy and structural cost comprehensively,it is recommended to select the diameter of the perforated steel bar with reference to the diameter of the main reinforcement bar in the core area,and use the formula to calculate the bearing capacity;(3)The perforated steel bar length parameters are 100 mm,150mm,200 mm,and250mm.According to the results of the finite element simulation,the bearing capacity and plastic deformation capacity of the connecting section when the perforated steel bars are200 mm and 250 mm in length are improved compared to the previous two types of perforated steel bars.Considering the bearing capacity,plastic deformation capacity and structural cost of the connecting section In terms of factors,the ratio of the length of the perforated steel bar to the radius of the connection section should not be less than 0.68(200/293)when designing the PBL connection section.According to the simulation data in this paper,the formula of the ultimate bearing capacity of PBL shear key single bond was improved,and the calculation method of ultimate bearing capacity of the connecting section was obtained.Comparing the improved formula with the results of finite element simulation,the theoretical calculation formula can accurately obtain the ultimate bearing capacity of the PBL-type connection section,which can provide a reference for engineering design. |
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