Potential Quality Risks:

• Substandard material: The strength and ductility of the coupler material fail to meet standard requirements.
• Dimensional deviations: Internal thread size, tolerance, and length do not comply with specifications, resulting in overly tight or loose fitting with the thread end.
• Damage during transportation and storage: Thread damage caused by impact during transport, or corrosion due to humid environments.

Control Measures:

• Conduct strict inspection upon delivery, verifying certificates of conformity and test reports; perform sampling tests on mechanical properties when necessary.
• Use go/no-go gauges to check the accuracy of internal threads; reject any non-conforming batches.
• Store couplers off the ground with moisture protection; stacking height should not exceed 1.5 m to prevent deformation from excessive load.

III. Common Issues in Connection Operations and Standard Practices

Typical Operational Errors:

• Improper torque control:
  • Insufficient torque: Tightening by feel without using a calibrated torque wrench, leading to “false tightening” and structural safety risks.
  • Excessive torque: Over-tightening causes thread seizure, stripping, or deformation of the coupler and rebar.
• Incomplete connection: Exposed threads exceed allowable limits, resulting in insufficient effective connection length.
• Poor alignment: Axial misalignment or angular deviation between rebars introduces Extra stress.
• Missed or incorrect tightening: In congested reinforcement areas or during night work, connections may be missed or incorrectly tightened.

Standard Operation Guidelines:

• Always use a calibrated torque wrench and set torque values according to rebar diameter (e.g., Φ25 rebar corresponds to 260 N·m). Tighten until a “click” sound is heard.
• Clean debris from thread ends and inside the coupler before connection. After tightening, mark the junction between the coupler and rebar; exposed threads should be limited to 1–2 pitches.

• Use rebar positioning brackets to ensure alignment; adjust immediately if deviation exceeds 3 mm.

IV. On-Site Management Gaps and Optimization

Key Challenges:

• Insufficient worker skills, unfamiliarity with technical requirements, and lack of responsibility.
• Superficial technical briefings without clearly defined operational points and quality standards.
• Lack of process supervision, especially in critical steps such as thread processing and torque control.
• Disorganized material management, including poor inspection and improper storage leading to misuse or damage.

Optimization Measures:

• Provide specialized training before construction; only qualified personnel may operate. Implement “dual inspection” for critical procedures.
• Use illustrated technical briefings to clearly specify torque values and procedures for different rebar diameters.
• Establish a three-level record system (“processing–connection–inspection”), with a sampling inspection rate of no less than 10% per batch.
• Store couplers and protective caps by category with clear labeling, and apply a first-in, first-out (FIFO) system.

V. Strategies for Environmental and Spatial Constraints

Challenges in Special Conditions:

• Adverse weather: Rain or snow causes moisture and rust on threads; low temperatures reduce operational flexibility.
• Confined spaces: In beam-column joints or shear walls, dense reinforcement makes it difficult to apply torque.
• Work at height: Increases operational difficulty and safety risks, leading to non-standard connections.

Solutions:

• Suspend outdoor work during rain or snow; cover processed thread ends with waterproof sheets and dry threads with a hot air gun before resuming work.
• Use short-handle torque wrenches in dense reinforcement areas, or optimize rebar layout in advance to reserve working space.
• For high-altitude work, set up stable platforms and secure tools with fall-prevention devices to avoid one-handed operation.

VI. Technical Points for Special Rebar Connections

• Different-diameter rebar connection:
  Use matched reducing couplers to ensure compatibility between thread specifications and rebar diameters. Tighten the smaller-diameter end first, then secure the larger end; apply torque based on the larger diameter standard.
• High-strength rebar treatment:
  For high-strength rebars with poor weldability, increase cutting fluid concentration during threading to reduce processing temperature. After processing, conduct hardness testing to prevent brittle fracture due to work hardening.

Summary: Key Control Points

Quality control of straight thread rebar coupler connections should focus on three critical aspects:

1. Thread quality: Ensure precision in thread processing and proper protection of both thread ends and couplers.
2. Torque control: Every connection must be tightened using a calibrated torque wrench strictly according to standard values.
3. Process management: Establish a full traceability system from material entry to final inspection.

Through a closed-loop management approach of strict material inspection, equipment calibration, standardized operations, and process monitoring, the connection qualification rate can be increased to over 98%, providing a solid guarantee for structural safety.