| With the increasing voltage level of transmission tower,it is necessary to study the strength and stability of the double flat arm derrick in order to ensure the safey and efficiency in construction of transmission tower.The magnitude of the wind load seriously affects the stability of the double flat arm derrick.Most of the general stability studies under static loading,the effect of dynamic loading on stability is usually ignored.In this paper,the height of the double-flat arm is 162 m,the wind area of the two-arm is large and the wind load has a great influence on the stability of the double flat arm derrick.Therefore,it is very important to study the anti-wind stability of the double flat arm derrick.The main research work and results are as follows:The equivalent static analysis of the double flat arm derrick is carried out.According to the performance parameters of the double horizontal arm holding rod,the finite element model is established by using ANSYS and the frequencies and modes of each order are obtained by modal analysis.The equivalent static analysis is carried out under the working and non-working conditions of the double flat arm derrick.It is found that the maximum displacement of the double flat arm derrick occurs at the end of the flat arm under each working condition.The maximum stress of the waist ring increases gradually with the increase of the height of the rod body and the maximum stress of the flat arm occurs in the tower material of the leeward side connected between the flat arm and the rod body.The most dangerous condition under non-working condition is that the wind direction angle is 45 degrees when the flat arm turns 0degrees and the most dangerous working condition is the partial load hoisting(4t/0t).The displacement of the double flat arm derrick,the horizontal arm,the waist ring and the stress distribution of the shaft can be obtained and the reference basis for the design and reinforcement of the double flat arm derrick can be provided.The wind vibration response of the derrick is analyzed,the linear filtering method is used,the simulation program of fluctuating wind load is compiled by MATLAB,and the wind vibration response is analyzed by time domain method.Compared with the displacement and stress values Calculated by static wind load,it is concluded that the displacement and stress values under fluctuating wind load are larger than those under static wind load,and the equivalent static method can not reflect the randomness of wind load.The stability analysis of the derrick is carried out,the characteristic value buckling analysis is first carried out,the non-linear and initial defects of the material are the second carried out.Curve of the derrick,and the BR criterion is applied to obtain the instability of the derrick whenthe average wind speed is 56m/ s.At this time,the displacement of the end of the flat arm is up to 1.2m,and The dynamic increment method is adopted.According to the criterion of displacement,it is concluded that under the action of a pulsating wind load with an average wind speed of 39m/s,the derrick is unstable,and the stability of the static wind and The pulsating wind is compared and analyzed,and it is concluded that the design of the fluctuating wind taking into account the wind vibration coefficient in the specification is not safe.The wind vibration coefficient obtained by dynamic time history analysis is compared with the wind vibration coefficient calculated according to the load Code of Building structure,and the results are as follows: due to the sudden change of mass and wind shield area,The value of wind The sound coefficient obtained by time history analysis at flat arm is 26.5% larger than that calculated according to the code.In the design of this kind of derrick,it is suggested that the value of stroke vibration coefficient should be improved,especially at the flat arm of the holding rod,and the value of wind vibration coefficient should be considered and increased separately. |
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