1. Slippage of Tendon Due to Rust on Anchorage, Strand, or Wedge

The principle of self-anchoring systems relies on the teeth/grooves on the wedge gripping the steel strand, and the wedge effect created as the clamp is drawn into the conical hole of the anchor, thereby locking in the prestress. If rust or other contaminants fill the teeth/grooves, preventing proper grip on the strand, or if the teeth themselves are corroded, reducing their strength, slippage may occur.

Additionally, rust on the strand surface or inside the anchor hole can create undue resistance, affecting the wedge’s engagement and potentially leading to slippage! If such conditions are found, it is imperative to replace the affected strands and anchors. Remind construction personnel to avoid installing anchorages too far in advance to prevent rust formation.

2. Mixing Components from Different Manufacturers

On some projects, components from different manufacturers might be present due to procurement reasons. In such cases, extreme caution must be exercised! The design angles for the mating surfaces of anchors and wedges typically differ between manufacturers and must absolutely not be mixed. Mixing them can have dire consequences! Furthermore, the dimensions of limit plates vary by manufacturer, including hole patterns and limiting depths. Using mismatched components significantly increases the risk of serious incidents.

3. Blockage in the Anchor Plate’s Internal Duct

This issue occurs frequently yet is often overlooked. The strands pass through the anchor and the duct within the anchor plate. If residual concrete debris inside the anchor plate duct contacts the strands, it can cause uneven stress distribution or even bending of the strands. This situation highly predisposes the strands to fracture! Alarmingly, the problem might not manifest during tensioning itself; the wedge or strand could suddenly fail and be ejected at a later time, posing an extreme safety hazard.

4. Incorrect Installation or Omission of the Limit Plate

The limit plate is a critical component during tensioning. During installation, ensure the anchor seats fully and evenly within the limit plate’s recess. Each hole of the anchor must align perfectly and pass freely through the corresponding holes in the limit plate. The strands must not contact the edges of the limit plate holes. The limiting depth must strictly match the specification provided by the manufacturer. A limiting depth that is either too large or too small can readily lead to problems.