What are the precision control techniques for the installation of large-span steel structures?

Large span steel structures are widely used in large-scale engineering construction such as high-speed railway stations, large conference centers, bridges, sports venues, etc. due to their advantages of light weight, large span, good seismic performance, and flexible shape. The installation accuracy directly determines the load-bearing stability, safety, and service life of the structure. Due to the large size, heavy weight, complex spatial shape of large-span steel structural components, and the influence of multiple factors such as construction environment, lifting technology, and temperature changes, the difficulty of controlling installation accuracy is relatively high. If the precision control is not in place, quality hazards such as component misalignment, node connection deviation, and structural deformation are prone to occur. This not only affects the aesthetic appearance of the structure, but may also lead to stress concentration, exacerbate structural damage, and even cause safety accidents. Based on industry standards and engineering practices such as the "Construction Specification for Manufacturing and Installation of Highway Steel Structure Bridges" (JTG/T 3651-2022), the precision control technology for large-span steel structure installation revolves around five core links: pre construction preparation, component processing precision control, on-site installation precision control, construction process monitoring, and later precision review. Various technologies work together to build a full process precision control system, ensuring that installation quality meets design and specification requirements, and promoting high-quality construction of large-span steel structure projects.
The precision control of large-span steel structure installation follows the core principles of "precise control, full process control, dynamic adjustment, and collaborative adaptation". The core goal is to control the installation deviation of components within the allowable range of specifications, ensure balanced structural stress and coordinated deformation, and balance construction accuracy and engineering economy. The selection of precision control technology should be based on the type of steel structure (pipe truss, steel truss, steel frame, etc.), span size, component weight, and construction environment. Targeted optimization schemes should be used to avoid blindly applying processes, ensure that technical measures are scientifically feasible and effective, and meet the practical needs of engineering applications.

Pre construction preparation is the foundation of precision control, and the core is to avoid precision hazards from the source through measures such as scheme optimization, measurement system construction, and material control, laying the foundation for subsequent installation precision control. The focus covers three key aspects: construction scheme optimization, measurement control system construction, and component entry inspection.

The optimization of the construction plan needs to be combined with the actual engineering situation, clarify the precision control objectives and targeted technical measures. In the scheme design phase, BIM technology is fully utilized to simulate the entire construction process, construct a three-dimensional information model, and identify issues such as component collisions and insufficient installation space in advance. The lifting sequence, lifting point setting, and assembly process are optimized to provide scientific basis for precision control. For the commonly used construction mode of "ground assembly+overall lifting" for large-span steel structures, it is necessary to accurately calculate the lifting parameters and develop a lifting strategy of "lifting point oil pressure balance, structural posture adjustment, and displacement synchronization control" to ensure a smooth and accurate overall lifting process. At the same time, the plan needs to clarify the precision control indicators for each link, such as component installation plane position deviation, elevation deviation, node connection deviation, etc., to provide standards for precision control during the construction process.

The construction of a measurement control system is the core prerequisite for precision control, which requires the establishment of a high-precision and fully covered measurement network. High precision total stations, level gauges, laser locators, 3D laser scanners, and other equipment are used. The angle measurement accuracy of the total station is not less than 1 second, and the point cloud positioning accuracy of the 3D laser scanner is better than 1mm, ensuring accurate and reliable measurement data. Before construction, it is necessary to lay out and calibrate the measurement reference points, establish a horizontal control network and an elevation control network, clarify the positioning coordinates and elevations of each component, and ensure the uniformity of the measurement reference points. At the same time, professional measurement personnel should be equipped, detailed measurement procedures should be developed, measurement frequency and review requirements should be clarified, to avoid the accumulation of measurement errors and provide guarantees for subsequent installation accuracy control.

The on-site inspection of components is the first checkpoint to control accuracy, and it is necessary to strictly verify the machining accuracy and quality of components. Large span steel structural components are often manufactured using factory and CNC precision manufacturing. When entering the site, the specifications, models, and dimensions of the components need to be checked, with a focus on testing indicators such as component length, cross-sectional dimensions, hole spacing deviation, weld quality, and component verticality. The hole spacing deviation of the components must be strictly controlled within ± 0.5 millimeters. Three dimensional laser scanning technology is used for comprehensive inspection of key components, comparing the deviation between the design model and the actual components. Unqualified components are strictly prohibited from entering the site for use. At the same time, check whether there are defects such as deformation and rust on the surface of the components, and correct the slightly deformed components to ensure that they meet the installation accuracy requirements.

The precision control of component processing is the fundamental guarantee for installation accuracy. The core is to ensure that the dimensions, shapes, and node accuracy of the components meet the design requirements through standardized processing techniques, with a focus on precision control in the three stages of cutting, welding, and assembly.

The precision control of cutting requires the use of high-precision processing equipment such as CNC cutting and 3D drilling machines, strictly following the design drawings for precise cutting, controlling the deviation of cutting size, and avoiding problems such as size deviation and inclined cutting during the cutting process. Before cutting, the raw materials need to be pre treated to eliminate internal stress and prevent deformation during subsequent processing and installation. For complex components such as bidirectional bending and large cross-sections, specialized processing equipment is required to ensure the accuracy of the component forming and meet the requirements of spatial installation.

Welding accuracy control requires standardized welding processes to reduce the impact of welding deformation on accuracy. For thick plate welding, welding robots are used for operation, strictly implementing preheating before welding (80-120 ℃) and interlayer temperature control processes to avoid problems such as shrinkage deformation and weld cracking during the welding process. Implement 100% ultrasonic testing on first level welds to ensure uniform and reliable weld quality, while controlling weld height and width to avoid component connection deviation caused by weld protrusion. After welding is completed, the components should be corrected in a timely manner to eliminate welding deformation and ensure that the flatness and verticality of the components meet the requirements.

The assembly accuracy control needs to be carried out on the factory's dedicated tire frame, and a modular tire frame system that matches the component shape should be built to ensure accurate assembly benchmarks. During the assembly process, a total station is used to monitor the position and angle of the components in real time, with a focus on controlling key indicators such as the cross angle of the tie rods, the opening position of the node plate, and the concentricity of the bolt hole group. The cross angle of the tie rods can be accurately measured through total station measurement, 3D laser scanning technology, and other methods to ensure that the deviation from the design angle meets the specification requirements. After assembly, a comprehensive inspection of the overall dimensions of the components is carried out, and any deviations exceeding the standard are adjusted in a timely manner to ensure that the assembly accuracy of the components meets the on-site installation requirements.

On site installation accuracy control is the core link of accuracy control, which needs to be combined with lifting technology, node connection and other links to accurately control the installation position, elevation and posture of components, focusing on three aspects: lifting accuracy control, node connection accuracy control and structural deformation control.

The control of lifting accuracy requires optimizing the lifting process, selecting suitable lifting equipment, setting lifting points reasonably, and ensuring a smooth lifting process of the components. For steel trusses, pipe trusses, and other components weighing over a thousand tons, a hydraulic synchronous lifting system is adopted. Through CAN bus control and three-level control mode, independent real-time monitoring and adjustment of each hydraulic elevator are achieved to meet millimeter level fine-tuning requirements, ensuring the overall synchronous lifting of the components and precise adjustment of the aerial posture. During the lifting process, measurement personnel track and monitor the entire process, provide real-time feedback on component position deviations, adjust lifting parameters in a timely manner, avoid component tilting or displacement, and ensure the accuracy of component lifting and positioning. The installation position error of large steel trusses can be controlled within 5 millimeters.

The precision control of node connections should focus on the accuracy of bolt connections and welding connections. High strength bolt connections must strictly follow the standardized operation process of "initial tightening, re tightening, and final tightening", controlling torque deviation within ± 10% to ensure smooth bolt penetration and firm connection. At the same time, check the accuracy of bolt hole alignment to avoid connection deviation caused by bolt hole misalignment. Welding connections need to ensure that the welding joints are aligned, control the joint gap and misalignment, monitor welding deformation in real time during the welding process, adjust the welding process in a timely manner, and avoid node deviation caused by welding deformation. For node connections in concealed areas, industrial endoscopes are used for inspection to ensure that the connection accuracy meets the requirements.

Structural deformation control requires targeted prevention and control measures to reduce deformation caused by various factors during the construction process. Reasonably arrange the installation sequence during the construction process, adopt the process of "partitioned flow, symmetrical installation, and graded unloading", and avoid structural deformation caused by excessive local stress; For large cantilever steel structures, temporary tie rods are used to assist in the positioning and stability of overweight components. Finite element software is used to simulate the internal forces and deformations during the lifting process, and a scientific lifting sequence is developed to gradually form the structure's own stress system. At the same time, control the construction load to avoid structural deformation caused by load concentration and ensure stable posture during structural installation.

Monitoring the construction process is an important guarantee for precision control. The core is to monitor the displacement, deformation, and stress during the structural installation process in real time through regular monitoring, detect deviations and adjust them in a timely manner, and focus on deformation monitoring, stress monitoring, and environmental monitoring.

Deformation monitoring adopts equipment such as building deformation monitoring robots and displacement meters, and uses non-contact technology to dynamically monitor the deformation and displacement of each installation point. The robot has advantages such as millimeter level accuracy and real-time feedback control, and can achieve one click reporting of monitoring data. The monitoring content includes component settlement, horizontal displacement, deflection, and node deformation. The monitoring frequency is adjusted according to the construction stage. During the lifting and node connection stages, monitoring is carried out every 12-24 hours. If deformation exceeds the standard, reinforcement and adjustment measures are taken in a timely manner to control the development of deformation. For large-span trusses, it is necessary to accurately control the deflection within the allowable design range.

Stress monitoring uses stress sensors and other equipment to collect real-time stress data of components and nodes, analyze the structural stress state, avoid stress concentration causing structural deformation or damage, adjust construction parameters based on monitoring data, and ensure balanced structural stress. Environmental monitoring focuses on temperature changes, which can easily cause thermal expansion and contraction of steel structures, leading to deformation. Real time monitoring of environmental temperature is necessary to adjust installation accuracy according to temperature changes and avoid deviations caused by temperature stress.

Post installation accuracy review is the final checkpoint to ensure that the installation accuracy meets the standard. It is necessary to conduct comprehensive accuracy testing and review after the steel structure installation is completed. Using 3D laser scanning technology to scan the entire steel structure, obtain structural point cloud data, compare and analyze it with the design BIM model, and comprehensively verify the deviation of indicators such as component installation position, node connection, and structural deformation. Develop a special rectification plan for areas with deviations exceeding the standard, adjust and correct them in a timely manner, and ensure that all indicators meet the design and specification requirements. At the same time, keep accurate detection records and establish a comprehensive accuracy control file to provide reference for subsequent project acceptance and maintenance.

The precision control technology for the installation of large-span steel structures needs to run through the entire process of component processing, on-site installation, and later review. Each link should be coordinated and controlled, strictly following industry standards, and optimizing technical solutions based on actual engineering conditions. With the application of intelligent construction equipment and new measurement technologies, the precision control and standardization level of large-span steel structure installation continue to improve. Through the scientific use of BIM simulation, hydraulic synchronous lifting, intelligent monitoring and other technologies, installation deviations can be effectively controlled, various quality hazards can be avoided, and the safe and stable operation of large-span steel structures can be ensured, providing strong support for large-scale engineering construction.