Stay Cable Maintenance

Many cables are enclosed within a plastic sheath or protective duct, which can degrade over time or suffer damage from impact or vibration. In some cases, older duct systems lacked UV resistance, leading to material breakdown, brittleness, and severe deterioration.

Additionally, if thermal expansion and contraction are not properly accounted for, prolonged exposure to extreme temperatures can further compromise the integrity of the outer covering, affecting the cable’s long-term performance and reliability.

Duct and anchorage systems are not always fully resistant to water infiltration. When moisture enters the stays, particularly at lower or deck anchorages, it can lead to corrosion of steel components. Additionally, damage may occur due to freeze-thaw cycles. Harsh environmental conditions such as exposure to marine settings, industrial facilities, or air pollution can further accelerate deterioration.

Cable stay anchorages utilize various forms of corrosion protection, including paint systems, galvanizing, metallization, and protective coatings such as grease or impregnated tape. Without proper maintenance, these protective layers can deteriorate, leading to corrosion. If the damage spreads to structural components such as strands, wedges, or bearing plates, both structural integrity and safety may be compromised.

Over time, cable loads can fluctuate due to various factors. A loss of load in one cable may cause an unintended increase in adjacent cables, potentially leading to localized overstress in the supported structural elements.

Long cables are often equipped with dampers to mitigate vibration. These dampers may be elastomeric, hydraulic, or friction-based. Impact, unexpected vibration loading, or inadequate design, installation, or maintenance can lead to damage, even under regular use. In most cases, they are positioned at or near deck level, making them relatively accessible.

Mini-cameras and endoscopes are valuable tools for examining anchorages and ducts, allowing us to identify hidden defects. When necessary, we can create access points within the ducts and restore them after inspection. In some cases, removing anchorage caps and their internal filling materials is essential to inspect the critical area where the tensile element is anchored.

We utilize advanced technologies to assess the condition of hidden stay cable elements, including:

• Acoustic Emission Surveillance – Strategically placed sensors detect tell-tale sounds emitted during energy release when a stressed element fractures. The fracture’s location is determined based on the timing of recordings from nearby sensors.
• Magnetic Flux Leakage – Defects, corrosion, and section loss are identified by magnetizing the steel and measuring disruptions in the magnetic field.
• Ultrasonic Guided Waves – This method detects corrosion or wire breaks within a limited distance from the probe, primarily in the critical anchorage zone.
• Force Measurement – Residual force in tensile elements can be reliably determined using direct or indirect methods for individual strands, wires, or complete tendons.

Removal of accumulated deposits from ducts and clearing blockages in anchorage and formwork tube drains.

• Reapplying or renewing protective coatings on anchorage components and other metallic elements, such as anti-vandalism tubes above the deck.
• Re-tightening stuffing boxes, where present, to ensure anchorage water tightness.
• Removing and replacing anti-corrosion fillers in anchorage caps, injected areas near anchorages, and, in select cases, along the free length of cable ducts.

Replacing worn or damaged components, including bolts, fastenings, duct transition pieces, and anchorage caps, to ensure structural integrity and performance.

Replacing worn components, followed by thorough cleaning and re-sealing to restore damper functionality and performance.

An individual strand is removed and typically replaced to assess its current properties. After 10–20 years of service, this practice helps verify strand integrity and ensures its residual fatigue life aligns with expectations.

Older bridges often utilized simple plastic or HDPE pipes that were not designed to control cable vibrations or resist UV exposure. We can post-weld helical fillets onto the ducts to minimize wind and rain-induced vibration or apply specialized coverings and tape to enhance UV resistance and aesthetic appearance.

Some bridges feature cables composed of individual strands or wires without a protective duct. We can retrofit ducts to improve strand protection and enhance aerodynamic performance.

Water accumulation near anchors requires attention. Weak points often include the lower duct transition to the structure and the sealing and detailing of caps. We apply replacement seals and retrofit flexible elastomeric boots to improve water tightness, frequently supplementing this with drainage solutions as a backup.

Corrosion protection in anchorages is commonly provided by injected grease or wax. If previous injections were substandard—leading to voids, instability, or material degradation—it is essential to replace the protection. A key challenge is removing the old material, and we have developed specialized techniques to achieve reliable results.

Advances in corrosion protection systems have significantly improved over the years. As these systems have finite lifespans, periodic reinstatement is necessary. With high-quality materials and expert application, we can extend the interval between required interventions.

If installation tolerances or structural deflection were not adequately accounted for in the original design, significant bending stresses may develop, especially in larger diameter tendons. If analysis confirms that these stresses impact cable performance and fatigue life, installing a filter or deviator can help localize and minimize these unwanted effects.

Some cables experience substantial load variations or even reversals, which can cause strands to slip and lose tension if the strand, wedge, or anchor block interface fails to function correctly. Solutions include restressing with new wedges, hydraulic reseating (or “over-blocking”), and adding wedge retaining plates to restore proper tension.

In multi-strand cable systems where damage or corrosion is limited to a few strands, individual strand replacement can be a cost-effective solution. Given the complexity of this operation, Freyssinet applies its expertise and specialized tools to ensure safe and precise execution.

Security against malicious or terrorist attacks is a priority for critical and highly vulnerable assets. Drawing from our expertise in this field, we develop tailored protection solutions upon request.

Ice accumulation on cables in cold climates is now better understood. Where temporary closures are not an option, owners seek proactive solutions to address this phenomenon. Given the unpredictable nature of ice accumulation, we collaborate with clients to assess site-specific risks and propose effective mitigation measures.

While bridges with high pylons traditionally include lightning protection systems, these may not always safeguard the cables themselves. Lightning strikes have occasionally led to duct damage and, in rare cases, catastrophic failure of tensile elements. We provide repair and replacement services, along with enhanced lightning protection to prevent future occurrences.