Key Techniques for Unloading of Super-Large-Scale Irregular Hyperbolic Steel Roof Structures

The unloading schemes of steel roof structures vary significantly due to factors such as the complexity of the structural system， the scale of the structure， and the boundaries of the construction process. The quality of unloading schemes is often qualitatively analyzed by comparing the deformations at local key joints and the additional stress ratios of members in the completed roof structure. However， changes in local joints and members cannot fully and accurately reflect the overall structural changes. To address the shortcomings in the effectiveness and accuracy of conventional data representation methods， this paper proposed a design principle based on feasibility， economy， and technical rationality. It adopted the comprehensive minimum residual sum of squares of deformations and stress ratios of all joints in the completed and designed steel roof structure as a quantitative evaluation index to assess the quality of unloading schemes. Furthermore， the criteria and calculation formulas for different deformation and stress ratio indications were provided. Taking the steel grid roof of the T5 Terminal at Xi’an Xianyang International Airport as an example， a comparison of batch-by-batch and level-by-level unloading schemes was conducted. Through a comparative analysis of the deformations and stress states of all members throughout the unloading process corresponding to different schemes， the unloading sequence from the middle to the east and west was selected as the initial scheme for construction planning. The comparison results showed that while the unloading sequence had a relatively minor impact on the completed structure after closure， the different force transmission paths during the unloading process significantly affected the stability of small-section members， making them prone to compressive instability during construction. A comparison between the unloading scheme adopted during the implementation phase and the preferred initial scheme verified the reliability of the proposed technical rationality evaluation method for unloading schemes. To address safety concerns throughout the unloading process， this paper proposed quality and safety control techniques that incorporate internal force control， deformation control， and synchronization control of unloading operations for all structural members. The unloading scheme design principles were simple and easy to implement， while the analysis method exhibited strong data representation and high accuracy. It comprehensively considered the effects of different unloading schemes on the deformations and stresses of all members throughout the unloading process. Additionally， the quality and safety control techniques were highly targeted and operable.