Large-span spatial steel structures are widely used in projects such as railway station concourses, airport terminal roofs, elevated skywalks, large exhibition hall (convention center) roof structures, and major sports stadiums. Given their typically large spans and dimensions, economic and safety considerations generally necessitate the use of integral lifting and slip-form installation techniques.
Lifting as a Single Unit: Suitable for complex, irregularly shaped steel structures with large spans. This method imposes no restrictions on lifting area, weight, or height, making it particularly advantageous for lifting heavy steel components in confined spaces or indoors (e.g., Wuhan Show Arena, Nanjing Jiangbei Civic Center).
Sliding Installation: Suitable for structures with uniform planar dimensions, elongated shapes, regular column grids, consistent curvature, and moderate height. This method effectively addresses limitations such as insufficient crane boom length and lifting capacity.
I. Overall Lifting Method Construction Process
1. Construction Process Flow
Lifting plan design → Construction preparation → Formwork fabrication, installation, and acceptance → Lifting unit assembly and acceptance → Lifting system installation → Lifting system commissioning → Load test lifting → Single-stage overall lifting (in phases) → Fine-tuning, positioning, and connection → Graded unloading lifting → Acceptance
2. Overview of Construction Process
2.1 Construction Preparation
Prior to lifting the structural unit as a whole, conduct simulation calculations and analysis. This includes:
– Impact assessment of assembly and lifting on the existing structure, reinforcement requirements, and stress analysis of lifting points;
– Design of the lifting platform;
– Stress analysis and reinforcement of the lifting section;
– Overturning resistance verification;
– Wind load calculations and collision prevention measures.
Verify and select lifting equipment and steel strands. Maintain a minimum clearance of 300mm between the lifting section and adjacent structures.
Installation and Acceptance of Mold Base
2.2 Erect an assembly jig on the ground or floor directly below the projection plane of the installation location for the lifting section. Position it according to the corbels at the upper lifting points and adjust the assembly positioning of the lower lifting section to ensure precision at the lifting interface. The assembly structure shall be pre-cambered based on construction simulation results, and reinforcement members for the lifting section shall be installed.
2.3 Install lifting frames (upper lifting points) and hydraulic lifters at the structural design elevations of the main structure (lattice columns, tower column tops).
2.4 Mount the hydraulic pump source system and guide frames (for organizing and securing hydraulic lines, steel strands, synchronous communication cables, etc.) at the upper lifting points. Connect both pump source systems and the computer synchronous control system.
2.5 Install temporary lifting attachments for the lower lifting points at the upper chord ends of the component lifting unit truss, corresponding to the upper lifting points. Install dedicated steel strands and dedicated bottom anchors between the upper and lower lifting points.
2.6 Tension the steel strands to ensure uniform force distribution across all strands. Then verify that all temporary measures for the large component lifting unit and hydraulic synchronized lifting meet design requirements.
2.7 During trial lifting, apply loads incrementally at 20%, 40%, 60%, and 80%. After confirming no abnormalities in all sections, continue loading to 90%, 95%, and 100% until the component lifts clear of the formwork. After the lifting unit rises approximately 100mm, pause the lift. Fine-tune the elevation of each lifting point on the component lifting unit to achieve a level position. Allow it to rest for 12 to 24 hours. During this period, conduct a power-off test to ensure the anti-fall locking devices and lifting slings meet performance requirements.
2.8 For the formal lift, use the adjusted height of each lifting point as the new starting position and reset the displacement sensors. Maintain this configuration throughout the overall lifting process until reaching near the design elevation. During overall lifting, primary factors affecting component lifting speed include hydraulic hose length and pump station configuration. Typically, data measurements are taken every 3–5 meters during overall lifting (measuring the lifting height at each lifting point; if necessary based on measurement results, adjust individual lifting points to ensure lifting synchronization).
Before initiating fine-tuning, switch the computer synchronous control system from automatic to manual mode. Utilize the “fine-tuning and jogging” functions of the hydraulic synchronous control system to precisely position each lifting point to the design location, meeting design and relevant code requirements for truss alignment. Re-measure relevant data, lock the hydraulic lifters, and await subsequent welding operations after structural installation.
After graded unloading is completed and the welds of the lifted structure pass inspection, synchronously unload the hydraulic lifting system equipment. Similar to the lifting process, unloading is also performed synchronously in stages: 20%, 40%, 60%, and 80%. Upon confirming no abnormalities in all areas, unloading may continue to 100%, meaning the steel strands of the lifters are no longer under tension. The structural load is fully transferred to the steel columns (main structure), and the structural loading condition transitions to the design state.
II. Key Control Measures for Large-Span Steel Structure Construction and Installation:
(1) Construction Simulation Calculations for Overall Lifting: Analyze the effects of temperature, wind loads, self-weight deformation, differential settlement, and other factors on the lifting section or entire structure. Conduct construction simulation calculations to determine these impacts and propose guiding measures, such as permissible wind force levels, pre-adjustment values for counter-deformation cambering, and unloading sequences.
(2) Assembly Platform
Based on the lifting segment and site conditions, assembly methods may include ground assembly, assembly on scaffolding, or assembly on steel platforms.
(3) Lifting Scaffolding
The lifting scaffolding structure supports the hoist and bears the entire lifting load throughout the process, making its structural design a critical focus.
(4) Lifting Reinforcement Measures: During lifting operations, temporary reinforcement may be required for the lifted structure or lifting platform to transfer loads and ensure overall stability, tailored to the structural characteristics.
(5) Lifting Point Types: Truss structures typically employ several lifting point configurations. Truss lifting points include beam-supported and welded types. When using beam-supported points, attention must be paid to the cross-sectional dimensions of the lifting beams.
(6) Lifting Synchronization Control Measures: Maintaining overall lifting synchronization is critical, typically achieved through a triple-control system: 1. Manual surveying with total stations to monitor elevation at set lifting intervals; 2. Computerized synchronization control systems; 3. Laser distance measurement systems.
(7) Wind-Resistance Tie-Down Measures: Conduct wind force calculations in advance based on the lift’s wind resistance rating. Monitor wind speeds using anemometers installed at the lift location and reference specialized weather forecasts for the lifting area. Should wind speeds exceed limits, halt lifting operations immediately. Implement wind-resistance tie-down measures by temporarily securing the structure to surrounding structures with steel cables.
(8) Lifting Monitoring Measures: To ensure safety during the lifting process, select key stress points on the lifted structural segments based on project conditions for stress-strain monitoring and bearing rotation angle monitoring. Conduct deformation monitoring at points with significant displacement to track the structural stress state throughout the lifting operation. Identify and report potential safety hazards promptly to implement corrective actions and guarantee construction safety.