SH20 Footbridge Opens

in Motorways by Jon C — May 17, 2010 at 3:09 pm | 2 comments

The distinctive blue and white footbridge providing improved access for cyclists and walkers between Hillsborough and Onehunga over SH20 will be officially opened on Wednesday afternoon.

The 3.5m-wide cable-stayed bridge upgrades access between Seacliffe Road in Hillsborough and Beachcroft Avenue in Onehunga, and was a community-based component of the NZTA’s Manukau Harbour Crossing project- the local community insisted on always being a link over the motorway at this point.

It’s wider than the existing bridge, which is also too low and has supporting piers that are in the way of motorway widening.

The old footbridge will be removed on Thursday night.

From the north, the new bridge will act as a gateway to the Manukau Harbour area and from the south, the gateway to Auckland’s central suburbs.

The full Manukau Harbour Crossing Project is expected to be completed by the end of August this year, 7 months ahead of schedule.

The cable- stayed design - the facts:

• The steel superstructure of the bridge is supported by stay cables which transfer loads to a tall steel pylon.
• The pylon is inclined 10 degrees to the west to give a distinctive appearance.
• The bridge has two main spans - a 17m span which passes over the Queenstown Road offramp and a 47.6m main span over the northbound and southbound lanes of the South-western Motorway.
• The spans are also supported by concrete columns at either end and by the steel pylon.
• At the western end, the bridge connects directly to Seacliffe Road via a short concrete ramp.
• At the eastern end, there is a 31m-long curved concrete ramp that has been constructed to bridge a Watercare Services sewer and to link to Beachcroft Avenue.
• Steps at the start of the ramp give walkers direct access to the Onehunga Harbour Reserve and a new path across the reserve to the Lagoon.

Construction- the facts:

• The bridge was constructed in the stages:
• Foundations: Piles are constructed beneath the ground, to a depth 8 to 14m.
• Pile diameters ranged from 600mm to 1m and were constructed from reinforced concrete.
• Earthworks have been undertaken at the eastern end of the bridge to raise the ground level, ready for the new ramp.
• Pylon: The pylon was transported to the site in two parts.
• It was then assembled and craned into position at the eastern end of the bridge.
• It has two legs in an A-frame, with each leg anchored by a pile. The height of the pylon is 32 metres from ground level.
• It rises 25 metres above the deck of the bridge.
• Columns: Concrete columns were constructed in situ above the piled foundations.
• Truss: Two prefabricated steel truss spans support the bridge’s concrete deck panels and were installed at night under a full motorway closure.
• Cables: The main steel truss is connected to the pylon by stay cables.  The cables are partially stressed to transfer the bridge’s weight to the pylon.
• Deck: Pre-fabricated concrete deck units were transported to the site and craned into position.
• A second stage of stressing of the stay cables was carried out to lift the bridge into its final position.
• The cable- stayed design:  The steel superstructure of the bridge is supported by stay cables which transfer loads to a tall steel pylon.  The pylon is inclined 10 degrees to the west to give a distinctive appearance.

Tags: Beachcroft Ave bridge Hillsborough NZTA Onehunga Seacliffe Road SH20