Study On The Influence Of Temperature Stress And External Load On The Cracking Of The Foundation Pillar Of The Transmission Tower And The Preventive Measures

As the voltage level of transmission lines continues to increase,more stringent requirements are put forward for the carrying capacity of the transmission structure.The transmission tower is an important structure in the UHV transmission line.The upper part of the tower has a large load,and the foundation bears all the upper load.The load directly acts on the column.The column plays the role of safely transmitting the upper load to the foundation.In the UHV transmission line There have been cracks in the foundation pillars of some projects.This paper will analyze the causes of cracks in the foundation column from two aspects of temperature stress and external load,carry out theoretical analysis and numerical simulation,and propose corresponding anti-cracking measures.The main research content and results include the following three aspects:(1)Starting from the basic theory of concrete temperature field and temperature stress,considering the influence of age,curing temperature,pouring temperature and concrete creep on the hydration heat stress of the foundation column,compile the corresponding APDL calculation program for the water transmission tower foundation column.Numerical simulation of the temperature field and temperature stress in the process of chemical heat release is carried out,and the temperature stress field distribution of the temperature field of the foundation column is obtained.Due to the different heat dissipation conditions,the temperature difference between the center and the edge of the foundation column is large,and the maximum temperature and the maximum stress appear in At the center of the column,the heat release is basically completed 28 days after pouring,and the temperature of the column tends to be consistent with the ambient temperature.Under the three heat generation functions,the maximum tensile stress in the column during the age is less than the tensile strength of the concrete,so it is unlikely that the temperature stress will cause the column to crack.Reinforcement can improve the thermal conductivity of the foundation column,and the configuration of appropriate temperature steel bars can enhance the crack resistance of the column,and propose comprehensive preventive measures against temperature cracks in the foundation column.(2)In the calculation,the constitutive relationship between concrete and steel is considered,combined with ABAQUS simulation calculation,to analyze the damage development process of the foundation column under tension and compression loads.When the column is compressed,the load directly acts on the concrete surface of the column through the bottom surface of the flange.There is stress concentration at the connection between the upper surface of the column concrete and the flange.As the load increases,the internal microscopic cracks in the concrete continue to expand,and the cracks start from the edge of the flange.The concrete extends to the side of the foundation column,and finally the component fails;under the action of the uplift load,the load is transmitted downward through the anchor rod and gradually decreases from the proximal end to the distal end.Due to the inconsistent deformation of the anchor rod and the concrete,Therefore,there is a relative displacement between the two,the concrete near the top of the anchor rod is seriously damaged,and cracks occur around the anchor rod.As the uplift load increases,the bond between the anchor rod and the concrete fails until the anchor rod is pulled out.(3)The use of composite stirrups to strengthen the foundation column can restrain the lateral deformation of the concrete,inhibit the development of concrete cracks,make the stress field of Saint-Venant uniform,effectively improve the bearing capacity,stiffness and ductility of the column,and inhibit the development of damage.Reduce concrete cracks.For the structural measures of arranging diamond-shaped stirrups at the center point of the outer stirrups,when the column width-to-height ratio is 1:2,by comparing the spacing,diameter and other factors on the bearing capacity and damage of the concrete column,a spacing of 100 mm and diameter are given.The best arrangement of 12 mm diamond stirrups.