During the installation of channel steel frames, ensuring verticality and horizontal accuracy is crucial for structural safety and functional achievement. A technical system must be built from four dimensions: foundation treatment, installation process, measurement control, and adjustment/correction.
Foundation treatment is the prerequisite for accuracy control. The stability of the channel steel frame depends on the flatness and elevation accuracy of the foundation plane. Before construction, the foundation must be thoroughly cleaned to remove laitance, oil, and other impurities. A laser level should be used to verify the foundation elevation to ensure the error is within acceptable limits. For embedded parts, parallelism and straightness must be strictly controlled. For example, in subway power supply systems, the parallelism and straightness deviation of the embedded channel steel along its entire length must not exceed specified values to prevent frame distortion due to uneven foundations. During foundation pouring, non-shrinkage, slightly expanding cement mortar should be used for secondary grouting to prevent foundation settlement from affecting the frame's horizontality.
The standardization of the installation process directly affects the achievement of accuracy. The assembly of the channel steel frame must follow the principle of "overall before parts," prioritizing welding into a complete frame before installation. During welding, key nodes are first tack welded for fixation. For example, multiple tack welds are made at frame joints. The frame squareness is adjusted by measuring the diagonal dimensions. After confirming that everything is correct, full welding is then performed to reduce the impact of welding deformation on verticality. For pole installation, the joint position and connection method must be strictly controlled. Except for the top layer, where lap joints can be used, all other pole joints must use butt joint fasteners. Adjacent joints should be staggered to avoid concentration within the same span, maintaining the overall stability of the frame.
Measurement control is the core means of ensuring accuracy. Verticality detection requires multi-dimensional verification using a laser plumb line and a theodolite. For example, in the installation of high-rise steel structures, when using the internal control method, auxiliary control points need to be set up inside the building. A standard point is emitted by a laser instrument. Multiple laser points are projected onto the target at each rotation of a certain angle. The intersection point is taken as the reference point to ensure vertical transmission accuracy. Levelness testing relies on high-precision levels to monitor the elevation of each node in the frame in real time. For example, during steel beam installation, the height of the supports and the distance from the corbel to the column base are measured, and shims are used to adjust to the design elevation, preventing frame tilting due to elevation deviations.
Adjustment and correction are crucial for accuracy optimization. For installed channel steel frames, a "whole-to-local" correction sequence should be adopted, prioritizing overall verticality and levelness adjustment before fine-tuning local nodes. For example, during single column installation, the deviation between the column head centerline and the positioning axis is measured, and torsional deformation and axial displacement are calculated. The column base position is then adjusted accordingly to eliminate torsional deformation. For frame deformation caused by welding or external forces, jacks and steel wedges can be used for forced correction. For instance, when the verticality of a steel column exceeds the tolerance, adjusting screws and steel wedges are used to gradually adjust it to the design requirements.
Environmental factors are equally important to control. Construction should be avoided on foggy or cloudy days when visibility is poor to prevent direct sunlight from causing thermal expansion and contraction deformation of the steel structure. Laying out the lines should ideally be done before sunrise or after sunset. For horizontal swaying caused by internal climbing or attached tower crane operations, laying out operations must be suspended until the structure is stable before measurement can be performed to avoid affecting accuracy due to vibration.
Controlling the verticality and horizontality of the channel steel frame installation is a systematic project that requires multi-dimensional collaboration, including foundation treatment, process specifications, accurate measurement, timely calibration, and environmental control, to build a comprehensive accuracy assurance system.
