Core Technology of Steel Structure Products: Full-Process Control of High-Strength Bolt Friction Connections

In critical applications such as industrial buildings, heavy-duty bridges, and wind turbine towers, high-strength bolt friction connections serve as the fundamental load-transfer mechanism for steel structure products. This article systematically analyzes five key control dimensions of this technology:

1. Scientific Basis of Material Matching

1. Correlation Between Bolt Grades and Steel Strength

• Grade 10.9 bolts must be paired with high-strength steel plates (e.g., S690QL) with tensile strength ≥1040 MPa.

• Friction coefficient at contact surfaces must ≥0.45, achieved through grit blasting to attain Sa3-level surface roughness.

2. Hardness Control Standards for Washers

• Hardened washers require Rockwell hardness of HRC 35-45.

• Sandwich composite washers compensate for thickness tolerances (±0.3 mm).

2. Critical Parameters in Manufacturing Process

1. Precision Pretension Application Technology

• Utilizes direct tension indicators or ultrasonic bolt stress meters.

• Three-stage loading: initial 50% pre-tightening → secondary 80% loading → final tightening to 110% design pretension.

2. Hole Machining Accuracy Requirements

• Standard hole diameter tolerance: +0.3 mm/-0.0 mm.

• Slotted hole length tolerance: ≤±1.5 mm.

3. Special Treatments for Environmental Adaptability

1. Corrosion Protection in Marine Environments

• Dual protection: hot-dip galvanizing (zinc layer ≥85 μm) + fluorocarbon topcoat.

• Passes 3000-hour salt spray test per ISO 9227.

2. Low-Temperature Toughness Assurance

• Nickel-alloy steel bolts with -50℃ impact energy ≥27 J.

• Molybdenum disulfide lubricant prevents cold brittleness.

4. Quality Verification Through Advanced Testing Technologies

1. Non-Destructive Testing Methods

• Torque coefficient recheck: dynamic torque testing on 10% randomly sampled bolts.

• Phased array ultrasonic testing evaluates stress distribution uniformity.

2. Digital Monitoring Systems

• Embedded RFID chips record installation time, torque values, and operators.

• BIM-based smart alert platform cross-references design parameters with real-world data.

5. Preventive Design Against Engineering Failures

1. Fatigue Life Calculation Models

• Applies IIW FAT90 stress curves and rainflow counting for wind-induced vibration analysis.

2. Slip Control Under Seismic Loads

• Dual friction surfaces (primary + secondary) for energy dissipation.

• Post-installation slip ≤0.15 mm (EN 14399-2 compliant).