VSL SSI 200 Stay Cable system reflects the VSL development of stay cable technology aimed at providing the best available solution for the ever-changing and complex technical demands in this area. The system offers a high fatigue resistance, outstanding corrosion protection, possibility to monitor tendon forces, as well as the possibility to adjust, inspect or replace the stay cable strands. At present, VSL is able to offer even faster installation of stay cables and reduced stay diameter.
The system main features are as follows:
- High fatigue resistance of 200 MPa at 45% of the tendon capacity over 2,000,000 load cycles;
- High degree of corrosion resistance due to the multilayer corrosion protection;
- An extruded coating providing an excellent strand corrosion protection during construction;
- Individual strand encapsulation and sealing in anchorages;
- Compact lightweight anchorage easy to install under crowded conditions;
- Easy installation of the strands into the erected stay pipe (single strand installation);
- All strands are parallel with no risk of twisting;
- Single strand stressing;
- No requirement for on-site cable grouting;
- Easy tendon force monitoring and adjustment throughout the cable’s service life;
- Ability to remove and replace individual strands without dismantling the installed anchorages;
- System adapted for the future installation of anti-vibration dampers.
High degree of corrosion protection
The system provides for a multilayer corrosion protection, which guarantees a long service life. At the same time, it makes possible to check the system throughout its service life and easily replace stay cables in case of need, which meets the strict requirements for stay cable systems. Individual parts of the system are divided into 2 categories. Replaceable and easily accessible parts of the system are regularly maintained in 15-25 years intervals; for the irreplaceable parts the full functionality and reliability is required for the whole period of designed service life of the structure, i.e. 50 – 100 years.
The system uses stay cables composed of parallel 7-wire high-tensile strands with Ø 15.2 or 15.7 mm with tight HDPE coating filled with grease or wax according to VSL specification, external HDPE pipe, pre-cast anchorages and the so-called deviators absorbing transverse forces caused by the stay cable rotation. The corrosion protection of anchoring elements is designed for 100 years of service life in the most aggressive environment.
Full individual strand encapsulation
The individual encapsulation of each strand eliminates the migration of corrosion between individual strands. The full encapsulation of strands is attained using protective caps and sealing anchorage details. The functionality of this sealing may be checked at any time during the designed service life of the system. SSI 2000 system guarantees that the quality level of protection of individual strands from factory is maintained along the whole length of strands, from ”wedge to wedge”, as well as in the area around the wedges, where the protective coating of strands from factory must be removed during installation.
A stay pipe of required length is erected with the first strand, the so-called “master strand”, and the strand is fitted into anchorages at both ends. The master strand is partially stressed, which eliminates the sagging of stay pipe. The remaining cable strands are then pulled through the pipe in cycles, affixed to the anchor and partially stressed. This system of installation guarantees the parallelness of installed strands. The stressing is done using a computer-controlled automatic stressing device with entered structure characteristics ensuring the stress uniformity after the last strand is installed. The stressing usually proceeds in several steps: optimally at elimination of the necessity to reduce the stay cable force, which can only be done using the multistrand jack, preferably only using a lightweight monostrand jack. Then follows the final tuning of the stay cable stressing force and completing works such as fitting of the anchorage caps and their protecting by pressure injections of grease or wax, fitting of deviators and connection of the steel reducer with a HDPE pipe to the sleeve leading through the load bearing structure.
The standard system configuration may be adjusted according to the parameters of any particular project. Individual strands are supplied in HDPE pipe sheathing with protective grease as standard. Although it is not required with respect to the service life, strands can be supplied zinc-coated.
Stay pipes can be manufactured in virtually any colour, with double helical ribs on the surface suppressing the weather-induced vibrations. The stay cable system can be also equipped with anti-vibration dampers, even after the installation is completed, e.g. following the structure behaviour monitoring.