Cylinder takes the stress out of bridge project

The Tauranga Harbour Bridge project, one of the largest transport projects ever constructed in New Zealand, will by 2010 provide continuous four-lane access from Takitimu Dr in Tauranga through to Mount Maunganui, including a duplicate harbour bridge and a four-lane flyover.

“Use of the cylinder to stress the concrete beams on site will not only make the work quicker but also simpler, as the ability to apply large loads means less tendons are required. Stressing work can be potentially hazardous, and having less stressing operations to perform will make it safer,” says Post Tensioning and Grouting supervisor, John Grant.

In addition to achieving the required outcome for the project constructor, Fletcher Construction, the stressing cylinder will be used in ongoing construction and civil engineering projects. Similar cylinders were used on the London Eye, for example, and also the Dubai Highway in the United Arab Emirates.

The stressing cylinders are used in prestressing operations for the stressing of single and multi-strand systems. Many, including the 900-tonne jack are equipped with hydraulic nose cones which, after the cylinder’s initial extension, push the locking wedges in place mechanically while the cylinder retracts then extends again to repeat the operation as many times as necessary for the job in hand.

Depending on the user requirements, multi-strand stressing heads of any configuration can be supplied. Stressing cylinders are tested for both safety and function, and can be calibrated for the stressing load required.

Jonel Hydraulics Enerpac product manager, George Pavletich, says Jonel supplied and fitted inner guide tubes for the high tensile strand to pass through — “This shortens set-up time by a considerable amount before the stress is applied. It means there is no need to manually line up the strand to the wedge head assemblies.

“We also modified the cylinder’s wedge plate and fixed it to the ram, which means everything is in place to make it quick and simple to perform the task.”

An anti-rotational guide was also fitted, which stops the ram from rotating during the extending process. Jonel Hydraulics also supplied and fitted Enerpac high flow couplings and adaptors to suit the customer’s pump.