Highway Gantry Processing

A highway gantry (referred to as a gantry) is a large metal structural frame installed on highways, usually spanning the road above. It consists of columns on both sides and a horizontal beam, resembling a “gate,” hence the name “gantry.” It is used to suspend traffic signs, cameras, electronic information screens, or open toll collection system equipment. It is suitable for multi-lane, high-traffic sections where roadside signs may be obscured by large vehicles.

Structural Types

• Full Gantry: The horizontal beam spans the entire road, supported by columns on both sides, similar to a bridge, suitable for multi-lane highways.
• Half Gantry (Cantilever/Butterfly): A single column supports the horizontal beam, suitable for sections with limited space or near exits.
• Truss Gantry: Uses a truss structure (round or square tubes) to provide higher rigidity and stability, often used for heavy equipment.
• Flexible Gantry: Such as Forsters Flexgantry, connected to movable concrete barriers, which can move laterally upon impact, improving safety.

Materials and Design

• Materials:
  • Steel: Mainly uses Q235 or Q345 high-strength low-alloy steel, with a yield strength of 235-345 MPa and a thickness of 4-10mm, hot-dip galvanized (thickness 60-80μm) for corrosion protection.
  • Aluminum Alloy: Lightweight design, density of approximately 2700 kg/m³, corrosion-resistant, suitable for specific scenarios.
  • Concrete: Some column foundations use high-strength concrete (C30-C40) to improve stability.
• Design Features:
  • Dimensions: Horizontal beam span of 10-40 meters (depending on the number of lanes), column height of 6-12 meters, must withstand wind loads (approximately 1.2 kN/m²) and equipment weight.
  • Structure: The horizontal beam is often a box-type or truss structure, the columns are cylindrical or rectangular, and the foundations are often pre-embedded or bolt-fixed.
  • Modular: Facilitates transportation and installation, reducing on-site construction time.
  • Safety: Must comply with wind and seismic resistance standards (such as Chinas "Highway Bridge and Culvert Design Code") and consider impact safety (such as REBLOC H4b testing).

Processing Technology Flow

(1) Design and Preparation

• Design: Use CAD or BIM software for 3D modeling, calculate loads (static, dynamic, wind), and optimize the structure. Finite element analysis (FEA) ensures strength and rigidity.
• Material Preparation: Purchase Q235/Q345 steel plates or pipes, check the surface quality (no cracks, rust), and cut to the required dimensions.

(2) Component Processing

• Horizontal Beam/Column Forming:
  • Stamping/Roll Forming: Steel plates are formed into box beams or tubular structures using hydraulic presses (1000-3000 tons) or roll forming machines, with a tolerance of ±1mm.
  • Pipe Bending: Columns or cantilever beams are bent using CNC pipe bending machines, with an angle accuracy of ±0.5°.
• Hole Processing:
  • Process mounting holes (for signboards, equipment fixation), hole diameter 10-50mm, quantity 100-300.
  • CNC Punching: High precision (±0.2mm), suitable for multi-variety production.
  • Plasma/Laser Cutting: Used for large-size holes or complex shapes, with an accuracy of ±0.5mm.
• Welding:
  • Use TIG/MIG welding or arc welding, the weld seam must be free of porosity, and the strength must reach more than 90% of the base material.
  • Use fixtures to ensure welding accuracy, with a deviation of <±1mm.

(3) Surface Treatment

• Shot Blasting/Sandblasting: Remove the oxide layer, surface roughness Ra 3.2-6.3μm, enhance coating adhesion.
• Hot-Dip Galvanizing: Zinc layer thickness 60-80μm, corrosion resistance life 10-20 years.
• Spraying: Epoxy primer + polyurethane topcoat (total thickness 80-120μm), the color is often green (China/Canada) or silver-gray, and blue is used in some scenarios (such as airport sections).

(4) Assembly and Installation

• Factory Pre-assembly: Trial assembly in the factory to verify dimensions and connection accuracy.
• On-site Installation:
  • Foundation Construction: Pour concrete foundation (C30-C40), pre-embed bolts or steel plates.
  • Hoisting: Use a crane (50-100 tons) to install horizontal beams and columns, with a deviation of <±5mm.
  • Equipment Installation: Signboards, cameras, or toll collection equipment are fixed with bolts, and the angle needs to be calibrated (such as in Quebec, Canada, where signs are tilted downwards for drivers to view).