Windsor Bridge

Windsor Bridge

Client: Georgiou Group

Location: Windsor, NSW

Duration: September 2020 – March 2021

Structure Overview

The Windsor Bridge was built in 1874 over the Hawkesbury River and consisted of eleven spans ranging from 9.8 to 13.5 metres. It was 143 metres long and 6.1 metres wide with two traffic lanes. The bridge’s main structure used reinforced concrete precast beams featured a separate cantilever footway added in 1968. The deck had eight longitudinal beams fixed to RC pier headstocks with dowels. The piers were made up of cast-iron cylinders, connected by concrete diaphragms and steel bracing. The bridge’s height was raised by 2.4 meters in 1897 by extending cast-iron piers, and Pier 10 was rebuilt using Australia’s first precast concrete beams. In 1921-22, the timber elements were replaced with reinforced concrete.

Scope of Works

Mainline was engaged by Georgiou Group to demolish the 143-metre composite concrete and cast-iron bridge over the Hawkesbury River.

The demolition scope encompassed:

• Demolition of the existing bridge, excluding the permanent works structures.
• Remove existing bridge piles to 500mm below riverbed level.
• Retain Windsor South Span 1 and carefully remove walkway, bitumen surfacing, curbing and sundry services.
• Maintain, without compromise, all flora, fauna and built form, abutting South and North bridge road approaches.
• No access from South Windsor end.

Equipment Deployed

The demolition of the Windsor Traffic Bridge, one of Australia’s oldest, required “handle with care” treatment. The bridge had significantly deteriorated. Design of custom plant and equipment was needed to brace, lift, and contain the structures during demolition. The equipment deployed included custom made specialised equipment, including:

• LiftnRoll design and built lifting platform.
• Customised bridge deck Airbag transport system.
• Self-erecting Pier Cradle for bracing, containment, and base cut.
• Airbag floatation pack (AFP) fitted to the cradle to transport columns to shore.

Plant:

• 180 tonne capacity double-action hydraulic lift platform
• Modular Flexi barge
• 240T mobile crane
• Various Bulk transport trucks
• Hyundai 36t Excavator
• Hyundai 48t Excavator
• 5 Tonne Forklift.
• 2x 6-metre workboats
• Dive team and diving apparatus
• Various concrete cutting equipment /Road Saws, wire & hand saws

Project Highlights

• Winner – 2021 World Demolition Award
• Elimination of cranes on barges through innovative, custom designed equipment
• An Australia first bridge deconstruction methodology was utilised
• Project completed with zero LTIs
• Greater than 99% of materials were recycled or repurposed

Operational Challenges and Solutions

The Windsor Bridge presented a unique opportunity for innovation and deconstruction processes. Extensive and variable structural deterioration, flood scoured riverbed levels (up to 5 metres variation), Covid-19 lockdowns, tidal river waters and a local protest group all made for a uniquely challenging contract experience.

We eliminated the need for heavy lift cranage and loaded barge movements on water with:

• The introduction of Mainline custom LiftnRoll apparatus, was the first key driver to raise 120 tonne integral bridge spans to roadway height, for transport to shore on roller airbags.

Zero foreign materials entered the waterway with:

• Absolute minimal concrete cutting on roadway to separate spans, and zero cutting of piers in-situ
• Strict environmental controls on the waterway, on the bridge deck, and on the shoreline.

We cut columns 500 mm below the riverbed, containing the fractured cast iron caissons, and integrated floatation transport by:

• Using a self-erecting, steel frame
• Our Airbag Floatation Pack was the second key driver having four key functions: (i) create the basal shear point for caisson severance; (ii) cradle the cast iron columns as a strongback; (iii) buoyancy and transport to shore; iv) self erection by buoyancy adjustment.

Maintaining team morale:

• Being exposed to daily public protestor scrutiny over 5 months was challenging. We maintained a vigilant non-contact task focus.