Carrying out stressing operations for post tensioning systems in the workplace — ProQual Awarding Body Occupational Qualification Construction & Building Services Revision
This element focuses on the practical skills and knowledge required to safely and accurately carry out tendon stressing operations for post tensioning syst
Topic Synopsis
This element focuses on the practical skills and knowledge required to safely and accurately carry out tendon stressing operations for post tensioning systems on site. It covers the interpretation of project information, selection of appropriate resources, adherence to safety procedures, compliance with specifications, and time management to achieve the required structural performance and quality standards.
Key Concepts & Core Principles
- Post-tensioning systems: Understanding the components, including tendons (strands or bars), anchorages, ducts, and grout, and how they work together to prestress concrete.
- Stressing operations: Correct procedures for tensioning tendons to specified loads using hydraulic jacks, including monitoring elongation and force to ensure compliance with design specifications.
- Grouting: The process of injecting cementitious grout into ducts to protect tendons from corrosion and provide bond, requiring knowledge of mix ratios, injection pressure, and curing.
- Health and safety: Applying regulations like CDM 2015, conducting risk assessments, and using personal protective equipment (PPE) to manage hazards such as tendon failure, high-pressure equipment, and working at height.
- Quality control: Checking materials, documenting tensioning records, and inspecting completed work to meet standards like BS EN 1992-1-1 and the Post-Tensioning Association guidelines.
Exam Tips & Revision Strategies
- Present a comprehensive portfolio of evidence including annotated photos, signed witness statements, and completed stressing records for each operation.
- During assessment observations, verbalise your risk assessment and the safety measures taken before starting the stressing process.
- Review the contract specification and method statement thoroughly prior to the assessment; be prepared to explain how your actions align with these documents.
Common Misconceptions & Mistakes to Avoid
- Failing to calibrate or zero the jack/loading cell before each stressing sequence, leading to inaccurate force readings.
- Misaligning the stressing jack with the tendon axis, causing uneven loading and potential anchor failures.
- Ignoring sudden drops in pressure during stressing, which may indicate strand slippage but is often mistaken for normal equipment behaviour.
- Rushing to meet deadlines without completing the required documentation or witness checks, resulting in non-compliance with contract records.
Examiner Marking Points
- Award credit for demonstrating accurate interpretation of stressing drawings, tendon layouts, and stress data sheets without prompting.
- Award credit for correctly selecting and inspecting stressing equipment, anchorages, and personal protective equipment before use.
- Award credit for maintaining exclusion zones, displaying warning signs, and following safe systems of work during stressing operations.
- Award credit for achieving specified elongation and pressure readings within tolerance, recording results clearly and promptly.
- Award credit for minimising disruption and damage to formwork, reinforcement, or adjacent works, and for cleaning up debris immediately after operation.