Technofast – NZ Engineering News – Airport – June 2021

They tension the tower’s stay rods, using precise hydraulic force rather than torque to tension pairs of bolts supporting the slim, elegant structure overlooking the three runways of Australia’s busiest airport, which handles 44 million passengers in a typical year.

Since installation, the cost-effective, trouble- free and safe way of securing the stay rods to the foundation and post-tensioning the rods to ensure the tower’s stability has withstood winds exceeding 200kph in the nearby Sydney CBD (in 2015); daily rainfall exceeding 200mm (1998) constant deluges of salt from the seaside location and the heat of one of the worst droughts in Australia’s history.

“The nuts have been so trouble- free in service that, after 24 years from the last contact we had with the tower’s operators, we got a request from Arup Partners for information about the nuts so they could continue safeguard the ongoing stability of the structure. The nuts were so reliable in service that it was easy to forget they were there,” says Technofast CEO John Bucknell, whose company sequentially removed, refurbished and reinstalled the tensioners to extend their safety and performance even further into the future.

The tensioners enable the tower to be moved 30mm in any chosen direction to ensure perfect alignment using with the hydraulic control we established,” says John Bucknell. “Their future and past performance demonstrates the longevity of the versatile product and the range of extreme applications which can be addressed using them.” They are so quick and easy to use that nuclear power plants (and conventional plants tool use them to minimise downtime and service time on generators,” he says. Different designs of rapidly actuated sets of Technofast hydraulic nuts – including the latest EziTite designs-are used in applications as diverse as architectural and construction projects, oil and gas vertical structures, cable stays on mining and lifting equipment including draglines, and wind power generators. The latest EziTite designs further enhance the durability of the original hydraulic tensioners used at Sydney Airport.

EZITITE FEATURES INCLUDE:

• Reduced maintenance downtime
• Improved safety on the job
• Reliable and precise tensioning across multiple nuts 
• Accurate and reliable loading 
• User-friendly, requiring little physical effort
• Fast to fit and remove

They are ideal for difficult or confined spaces, where vibrational or torsional stresses are a problem and where regular maintenance requires repeated adjustment or removal of nuts.

ORIGINAL SELECTION

Technofast hydraulic nuts were originally selected for Sydney airport control tower because installation of them was so simple, safe and time-saving, while delivering a long-term durable and adjustable tensioning solution. Twelve 50mm Technofast nuts were used on the 45m-high control tower to anchor its stay rods to three concrete buttresses at its base.

After being screwed into place by hand until the base of the nut was against the working face, hydraulic pressure was applied extend the nut’s piston and push the nut body apart.

This stretched and tensioned the 80mm steel stay accurately. Threaded lockring, mounted on the piston, was then tightened to retain the induced load and the hydraulic pressure was released. The three control tower stays were tightened simultaneously by three personnel, each using a single Hydraulic hand pump with spider hoses attached to four Technofast tensioners. Pressure was raised in steps of 35bar/500psi until the designated tension of 840bar/12,000psi was reached. Once the tensioners were pumped up to the required pressure, the lock rings were nipped tight with a C spanner. About half a day was spent on the original tensioning operation, with none of the customary problems associated with conventional torque-tightened fasteners, such as metal friction and heat build-up. The Technofast nuts were safe to install because they were locked mechanically at each step of the tensioning process.

The three stays were checked and tightened if necessary every three months for the first 12 months of the control tower’s life to counteract any setting of the foundations. “This was a very simple process in which the tensioners were repressured to re- tension the stays and secure the nuts again,” says Bucknell. “Since then, maintenance requirements have been minimal. The stainless tensioners are engineered to be very resistant to corrosion from the salty air in abundance at the airport.

These are the same qualities that make them such a good choice for building sites in aggressive environments, as well as mining. energy, power and gas and water utilities”