Key Construction Techniques for Steel Truss of Transfer Floor in Super High Rise Tower

The transfer floor of super high-rise tower in Hangzhou West Railway Station TOD project adopts the reinforced steel-concrete structure with large steel truss prefabricated, and the construction quality of the steel truss is crucial for the long-term performance of the structure.To ensure precise control of steel truss construction, three key technologies for steel truss construction are carried out. Firstly, based on the basic parameters of steel structure segmented weight, lifting arm length, lifting capability, the suitable tower crane model is selected through comparative analysis of lifting weight. Theoretical analysis and load bearing capacity verification of the basement roof is conducted. With the consideration of load distribution on simply-supported two-way slabs, the bearing capacity of the basement roof at the most unfavorable state during the driving conditions is analyzed. The site load deployment is clarified and the steel structure lifting capacity meets the requirements. Secondly, a three-dimensional model of the steel structure is built and information are integrated. Based on visualized complex steel structure model, the difficulty of pouring construction is judged by checking the enclosed compartments. In the original plan, two closed compartments are formed due to the interlacing of multiple web plates and transverse partitions; and a secondary pouring construction method was designed by grouting the closed compartments first and then uniformly pouring other steel reinforced concrete structures. Based on three-dimensional model and the principle of improving pouring quality, the concept to enlarge pouring holes on the top surface of the steel column diaphragm, remain flow holes on the inner cabin web, and change the outer sealed plate to several battens is proposed and discussed carefully, thereby greatly reducing the enclosed space. At the same time, the diaphragm holes enlarged, one-time-concreting shaping plan is proposed by changing the concrete flow direction from top to bottom, as an alternative method of secondary pouring plan from bottom to top, optimizing the steel structure structure to ensure pouring molding. Finally, with consideration of the lifting capacity of tower crane, the construction and installation process of the steel truss structures is designed. Based on the truss installation process, analyze the components that affect mid span deformation is analyzed and calculate the key parameter of mid span camber in the process is calculated. The initial preset height of the bed frame should be composed of three parts of displacement, those are, the mid span deflection caused by the self weight of the half truss when supported by the bed frame, deflection caused by the self weight of the overall truss after welding and dismantling the bed frame, and displacement designed at the mid span for the pre-arch structure when reinforced concrete is considered in the structural design. A three-dimensional solid nonlinear finite element model is established by ABAQUS, and the deflection of 16.2 m span truss structure under the construction state considering the support stiffness for the aforementioned key construction processes.The results show that when installing the half truss, the maximum mid span deflection of the structure is 6.41 mm; after removing the jig frame, the structure undergoes a further downward deflection of 1.53 mm in the span. Therefore, based on the finite element calculation results, the pre arch value is determined to be 24.1 mm, which is approximately 1.5/1 000 of the span. This article determines the tower crane model through numerical analysis, optimizes the steel structure layout through three-dimensional models, and clarifies key construction parameters through numerical simulation, ensuring the accuracy and quality of truss layer construction. The relevant experience can be used as a reference for similar projects.