Sam Key Points and Difficulties in the Processing and Fabrication of Steel Structure Spiral Stairs

Sam 1. 3D Space Modeling and Lofting

Sam     - BIM Reverse Modeling: It is necessary to construct an accurate 3D model based on design parameters (rotation radius, tread angle, central column diameter). Use parametric modeling with BIM or Rhino + Grasshopper to verify the spatial geometric relationships and avoid interference between the tread plate, the central column and the handrail.

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Sam     - Segmented Lofting Strategy: Discretize the spiral line into multiple broken lines. Use a numerically controlled cutting machine to perform special-shaped cutting on the tread plate and the supporting beam, and mark the spatial positioning points (such as the welding coordinates of the tread plate and the central column).

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Sam 2. Material Selection and Pretreatment

Sam     - Main Structural Materials: For the central column, seamless steel pipes are preferably selected (such as Φ200×10mm Q345B). The tread plate is made of 8 - 12mm anti-slip checkered steel plate, and the handrail support is made of Φ50×3mm stainless steel pipe.

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Sam     - Anti-corrosion Pretreatment: For outdoor stairs, the steel needs to be sandblasted to remove rust (Sa2.5 level) and pre-coated with primer to avoid damage to the coating during subsequent welding.

Sam 3. Welding Deformation Control

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Sam     - Design of Workpiece Fixtures: Use an adjustable-angle circular welding fixture to fix the tread plate and the central column to ensure that the inclination angles of each tread plate are consistent (for example, each step rotates 10°).

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    - Optimization of Welding Sequence: Adopt a symmetric skip welding process (such as welding the inner side weld first and then repairing the outer side weld), and control the interlayer temperature ≤ 150°C to reduce thermal deformation.

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Sam 4. Assurance of Assembly Precision

Sam     - Virtual Pre-assembly: Obtain the actual dimensions of the components through a 3D scanner, simulate the assembly in the software, and then carry out physical assembly after correcting the errors.

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    - Setting of Positioning Reference: Take the plumb line of the central column as the reference, and use a total station to calibrate the three-dimensional coordinates of the end points of each tread plate (the error is controlled within ±2mm).

Sam II. Technical Difficulties and Solutions

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Sam 1. Cold Bending and Forming of Spatial Curved Beams

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Sam     - Difficulty: The spatial double curvature of the spiral handrail makes traditional roll forming difficult.

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Sam     - Solution: Adopt segmented cold bending (the length of each segment ≤ 1.5m) + use a numerically controlled pipe bender to precisely control the bending radius, and reserve a 2mm finishing allowance at the interface.

Sam 2. Structural Stability under Asymmetric Loads

    - Problem: The rotating staircase is prone to lateral torsion under eccentric loads.

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    - Countermeasure: Pour C40 micro-expansive concrete (filling rate ≥ 90%) inside the central column, and at the same time, add triangular diagonal braces (such as L100×10 angle steel) at the cantilever end to form a spatial truss system.

Sam 3. Control of Tread Plate Flatness

    - Challenge: Welding thermal deformation causes undulations on the surface of the tread plate (common error is 3 - 5mm).

Sam     - Process Improvement: Use CO₂ gas shielded welding (current 180 - 220A, voltage 24 - 28V), and use a hydraulic straightening machine to perform local flattening treatment on the tread plate after welding.

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Sam 4. Transportation of Special-shaped Components and On-site Installation

Sam     - Bottleneck: The overall spiral structure cannot be transported at one time and needs to be hoisted in sections.

    - Modular Design: Decompose the staircase into a central column module (for overall transportation), a tread module (with every 3 steps as a unit), and a handrail module. Use high-strength bolts (grade 10.9) for on-site connection, and inject structural adhesive at the joints for sealing.

III. Key Indicators for Quality Control

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Sam 1. Dimensional Tolerance

Sam     - The verticality deviation of the central column ≤ H/1000 (H is the total height)

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Sam     - The height difference between adjacent tread plates ≤ 3mm

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    - The straightness deviation of the handrail ≤ 2mm/m

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2. Mechanical Properties

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    - Static Load Test: Apply a load of 1.5kN/m², and the deflection ≤ L/250 (L is the span)

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Sam     - Natural Frequency Detection: Avoid resonance with the human walking frequency (1.6 - 2.4Hz)

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3. Durability

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Sam     - The thickness of the hot-dip galvanized layer ≥ 85μm (outdoor environment)

Sam     - The adhesion of fluorocarbon spraying ≥ 5MPa (tested by the cross-cut method)

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Sam IV. Application of Innovative Processes

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Sam 1. 3D Printing of Positioning Molds: Use nylon materials to print the spatial positioning fixtures for the tread plate to improve the assembly efficiency.

Sam 2. Robot Welding: For repetitive weld seams (such as the connection between the tread plate and the central column), use a six-axis welding robot, and the weld penetration depth reaches more than 70% of the thickness of the base metal.

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Sam 3. BIM + AR Technology: Overlay the 3D model onto the construction site through augmented reality devices to provide real-time guidance for the installation and positioning of complex nodes.

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Conclusion

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The processing of steel structure spiral stairs is essentially a combination of precision machinery manufacturing and architectural art. It is necessary to achieve the quality objectives through digital modeling, process innovation and strict process control. It is recommended to carry out 1:1 local entity prefabrication at the initial stage of the project, and then start mass production after verifying the process feasibility.