| The vertical rotary construction technology has been widely used in the installation of the arch tower of cable-stayed bridge,but it is seldom used in the construction of the "A" steel tower.The upper tower segment of "A" shaped steel tower has a certain internal inclination Angle with the main pivot hinge,resulting in the main pivot hinge bearing a huge horizontal component in the vertical rotation process of the steel tower,which has a higher construction safety risk.In order to understand the mechanical response of the rotating structure and provide data support in the construction safety risk control,this paper analyzes the stress state of each component of the rotating system in the vertical rotating process of the "A" shaped steel tower by using two methods of finite element simulation and engineering monitoring,and explores the general mechanical law of the vertical rotating of the "A" shaped steel tower.After calculation and analysis,the conclusion is as follows: the vertical rotation of steel tower is the most unfavorable condition at the beginning;Under the most unfavorable conditions,the mechanical performance of each component of the rotary system meets the design requirements in finite element analysis and engineering monitoring.When the steel tower rotator is in place,the transverse stiffness of the steel tower increases obviously,while the transverse stiffness of the composite beam decreases obviously.The environmental excitation method is used to solve the composite beam vibration modes.The comparison between the measured and simulated vibration modes shows that the vibration modes are similar in shape,but the measured vibration modes are less frequent.The research content of this paper is as follows:(1)Summarize the key construction technologies of vertical rotation of "A" shaped steel tower,analyze the overall and local mechanics of the rotation system structure by using finite element software Abaqus,Midas Civil and Midas FEA NX,and solve the most unfavorable working conditions and stress distribution and stress overlimit degree of the main structure during the rotation process.Compare the calculation results of different software and analyze the reason of difference.(2)The vertical rotating process of steel tower was divided into two stages: before and after the rotating body was in place.Midas Civil was used to calculate the vibration shapes of composite beams before and after the rotating body and their corresponding frequencies.The frequency variation trend was observed and the reasons for the changes were analyzed.Considering the influence of downwind load on composite beams under Marine environment,the critical wind speed of wind induced flutter is solved.According to the variation of the annual wind speed and direction in Huangdao District of Qingdao,the possibility of the main beam flutter during the vertical rotation of the bridge tower is determined.(3)The change of structural load and constraint is analyzed through the stress time history data of structural measuring points.Judging the structure safety according to the measured stress.The measured stress data and simulated stress data under the most unfavorable conditions are compared to analyze the reasons for the difference in data.The longitudinal and transverse stiffness changes of steel tower and composite beam are analyzed by using the acceleration data of measuring points.The environmental excitation method was used to solve the vibration mode of the composite beam,and the vertical stiffness of the composite beam was analyzed.The simulation mode and the measured mode shape and frequency were compared,and the reasons for the difference were analyzed.According to the simulation and measured data,the safety of key components in the process of rotation is determined,the most unfavorable working condition of the steel tower in the process of rotation is analyzed,and the change of structural load and constraint information in the process of reverse rotation is summarized.The research content of this paper provides data reference for the construction safety of vertical rotating steel tower of "A" shape. |
