End Deflection Control Ling Methods for Lifting Construction of Irregular Grids

For the integral lifting construction of irregular grid structures with "sharp corners" at the ends， the method of adding lifter in the "sharp corners" area is generally adopted to control its deflection. Although this method can effectively control the deflection in the "sharp corner" area at the end of the grid， the lifting reverse force of the lifter at that location is often small， resulting in a low contribution of the overall grid lifting process and a waste of construction costs.Therefore， based on a segmented lifting project in Central Zone C of Xianyang Airport， this study investigated control methods for end deflection during the lifting construction of irregular grid structures.Two methods for controlling the end "sharp corner" deflection of irregular grid structures have been proposed， including after lifting in place and during the lifting process. The former method uses machinery such as car cranes and chain hoists to apply vertical loads to the "sharp corners" area with large deflection， after the grid is lifted into the target place， causing the structure in that area to arch upwards， thereby reducing the deflection of that area. This method is convenient for construction but requires high construction site conditions. The latter method involves setting up a support frame on the upper part of the structure in high-stiffness areas and using steel wire ropes to secure the "sharp angle" area， thereby reducing its deflection during the lifting process. This method can compensate for the shortcomings of the deflection control method， which is highly limited by on-site construction conditions after the lifting process.This paper analyzed the effects of two deflection control methods through construction simulations， and also analyzed the influence of factors such as the pretension force of the steel wire rope， the height of the support frame， and the position of the tensioning node on effectiveness of the deflection control methods during the lifting process. The results showed that： 1） the difference between the structural deflection and component stress by the deflection control method after lifting in place， and by the lifters was very small， indicating that the deflection control method after lifting in place had a small impact on the structure； 2） when using the deflection control method during the lifting process， the pretension force of the steel wire rope was positively correlated with the control effect， indicating that the control effect could be improved by increasing the pretension force of the steel wire rope； the height of the support frame was positively correlated with the control effect within a certain height range， after exceeding a certain height， the impact of the support frame height on the control effect gradually decreased and then even exhibited a negative correlation； when the steel wire rope tensioning node was set in an area with high structural stiffness and stringent deflection control requirements， the control effectiveness was optimized， and increasing the number of tensioning nodes and evenly arranging them within the node area could improve the control effectiveness； 3） the two deflection control methods proposed in this paper for post-lifting and during-lifting stages was proved to be feasible and cost-reducing.