Wyndham City Council: Wedge Sreet Pedestrian Bridge
Posted under: The idea of an iconic bridge linking the Werribee CBD to Wyndham Park was conceived in 2006 and became a reality in 2013. It supports Wyndham City’s visionary plan for the development of the Werribee City Centre as the capital of the new West. The architecturally designed bridge incorporates robust materials like steel and concrete to produce a unique design creating a truly amazing experience amongst the tree tops. The bridge was complex to design and equally complex to construct. The degree of difficulty offered opportunity to develop alternative approaches and methods to bring this vibrant orange structure to life.
Introduction
The Wedge Street footbridge is the first major public infrastructure project in Council’s visionary plan for the development of the Werribee City Centre as the capital of the new West. The footbridge provides a vital link between the businesses in the CBD and Wyndham Park. The development of the business centre aspires to reorientate elements of the centre to face the Werribee River rather than turn its back on it. The project was particularly challenging due to restrictions relating to flora, fauna and hydraulic considerations. The footbridge is also a complex structure that has provided some challenges during design and construction. It has been affectionately named the ‘snake’ bridge as its winding nature resembles a snakes belly moving across the river and through the park. It takes off from the Werribee Piazza and lands in Wyndham Park at a point that is anticipated to be an entertainment space due to its natural amphitheatre setting. The completed project offers a truly unique experience for urban dwellers to enjoy the old river red gum tree tops up close and personal and take in tranquil view lines up and down the Werribee River while only metres from the Werribee City Centre.
Project Management
Wyndham City Council solely managed the project from its conception through to tender award and contract managed the construction phase. This required the Project Manager to develop a clear project plan in consultation with stakeholders and to consider the Councillors request for the delivery of an ‘ICONIC’ bridge. The Project Manager arranged a survey of the site, relevant permits (CHMP, Flora & Fauna) and initiated discussion with Melbourne Water to determine the constraints of the site. A general review of the budget was also conducted to ensure there were sufficient funds to proceed. An expression of interest brief was developed by the Project Manager and architects were sought to develop concepts for the bridge. The design by Group GSA (formerly WMCQ Architects ) was selected by Council. The Project Manager then sought structural design quotes from which Hyder Consulting were awarded the design of this complex structure. The Project Manager and Hyder Consulting met regularly to track the progress of the project and to discuss any design issues. Occasionally, the architect was also invited to provide comments on any issues that might compromise the design. The Councillors, key stakeholders and public were kept up to date on the project during this phase. A quantity surveyor was engaged during various phases of the project to ensure the project costs were not blowing out.
Once the design was complete a specialist contracts engineer was bought in to provide assistance with the development of contract documents / specifications and to be part of the tender evaluation panel. This was to help mitigate any possible risks. The tender was awarded to BMD Constructions who had the required VicRoads prequalification, OH&S and quality systems in place. While they managed the construction phase on site, Wyndham City Council continued to play a Project Manager role through the monitoring of the construction program, budget and regular attendance on site and at meetings. BMD had a full time Project Engineer on site who was supported by a Project Manager and Construction Manager. In addition, 14 sub-contractors were also engaged to complete the project. While the project was technically challenging, a large portion of its success was due to the collaboration between all stakeholders.
Flora and Fauna
A flora and fauna assessment within the Wyndham Park and surrounding riverside areas was undertaken to determine any impacts the bridge may have. Two assessments were undertaken with the first being in June 2007 and the secondary assessment during spring and summer in 2007/2008 to focus on four issues:
- The growling grass frog and other frog species
- Platypus
- Spring fauna survey
- Spring flora survey
The flora assessments revealed both state and regionally significant species in the area. These were all recorded using GPS technology and were required to be protected during the works. The bridge was carefully designed to curve and weave through the tree tops protecting the old river red gums and to minimise the necessary footprint through the established vegetation. The fauna assessment revealed a total of 49 species at the site. The assessment did not reveal the presence of the growling grass frog, however it confirmed the presence of platypus and as a result the following considerations were made:
- Restrictions were placed on construction activities within 35 meters of the river bank during October through to the end of April due to the platypus breeding and nesting season.
- Low level lighting was chosen to have minimum impact on platypuses
inhabiting the area.
Cultural Heritage Management Plan
A CHMP was required for the project given its proximity to the Werribee River. The design incorporated two piers on the banks of the Werribee River with additional piers and abutments within the flood plane. The CHMP assumed there would be varying levels of disturbance across the entire activity area from intense construction at the bridge location to minor disturbance at the site compound. The activity area had been previously assessed as being a highly disturbed site, however as part of the CHMP a complex assessment was undertaken which included sampling thirteen test pits across the site. The assessment did not find any Aboriginal cultural material during the testing.
Design Considerations
The Architect selected robust materials for all surfaces. The main deck is a coloured and textured concrete surface with a palate inspired by the trees and grasses found within Wyndham Park. Mindful of the risk of anti-social graffiti effecting the bridge, all painted surfaces were coated with anti-graffiti paint. The bridge structural section was designed to conceal conduits for the provision of power and future services. Lighting is provided by low energy LED’s fitted under the handrail creating a continuous thread of light. Together with the use of ‘riddle’ feature lighting this provides enough light on the deck without impacting on the nocturnal park life. A simple see through galvanised fin blade balustrade was chosen to allow pedestrians on the bridge to enjoy the experience without any solid fixtures blocking their view along the river and over the park . This balustrade was designed to accommodate crowd loading in anticipation of large events in the park.
Construction
The bridge, consists of 100 tonnes of steel and 450 cubic meters of concrete. It meanders 140 meters across the Werribee River and into Wyndham Park. The bridge is founded on 26 x 750mm and 4 x 900mm bored concrete piles, constructed in varying ground conditions including basaltic rock and on the riverbank. Sitting above the bored piles are six pile caps. Supporting the deck are the architecturally designed North and South
abutments, two piers and a blade wall, with the longest span between piers being 37 meters over the river. These piers and blade wall feature a geometric pattern that was achieved through the use of bespoke form-liners. The bridge deck is made of six steel girder sections weighing up to 45 tonnes. The segments were uniquely shaped on a large radius tapered trapezoidal to triangular in nature, incorporating the architectural rib patterning into the steel superstructure. Alternate access into Wyndham Park is provided by a 3 meter wide cast-insitu concrete spiral staircase.
Pier 1 & 2
Piers 1 & 2 are founded on six 750mm diameter bored pile foundations with pile caps, located directly on the banks of the Werribee River. Given the direct proximity and environmental sensitivity of the river a sheet pile coffer dam and floating silt curtain was constructed to protect the river and surrounds during construction of the piers. During construction water quality monitoring was continuously undertaken which confirmed no changes in the water quality.
Steel Girder Fabrication
The complex structure was fabricated off-site using over 3,000 shop fabrication drawings to achieve the 2mm tolerance on all splice joint bolt holes. The bridge girders were fabricated in six uniquely shaped sections on a large radius and tapered from a trapezoidal to a triangular shape, each section weighing up to 45 tonnes. To achieve accurate fabrication of the bridge sections surveyed templates and jigs were set up on the shop floor to assemble the girders. The use of 3D modelling, surveying and photogrammetry of the girder sections during fabrication was utilised to determine their accuracy. The splicing of bridge sections was also undertaken on the shop floor to mitigate any on-site misalignments. The above measures proved to be successful when the girders where erected on-site safely and without complications.
Handling & Transportation
Access to Wyndham Park provided a challenge for the girders to be safely delivered to site and erected. This was due to the site being restricted on both sides of the Werribee River by retail outlets, main road access through the Werribee CBD, the large number of protected river red gums and an overall tight work zone. The size and shape of the six girders also added to the transport difficulties. The following measures were undertaken to ensure safe delivery and erection of the girders:
- Individual lifting procedures were developed including proof engineered lifting points, crane pad analysis, lifting studies, centre of gravity modelling and rotational analysis.
- Traffic management planning including Memorandums of Authorisation (MOA) from VicRoads and the transportation of the units at night.
- Detailed safe work method statements were developed and implemented.
Due to the size and shape of the segments they were floated to site upside down. Utilising a two-crane lift sequence the segments were placed on temporary cradles constructed on the ground on site. In order to minimise risks, the spliced segments were connected on the ground in cradles which ultimately reduced the number of major crane lifts from six to four. Each spliced girder section had approximately 120 nuts and bolts which had to align with splice plates on both the outside and inside of the girder. Mid span and structural support towers were also designed, proof engineered and constructed to support the segments in the air until concrete diaphragms were cast and cured to support the girder loading. The cradles and structural support towers were designed to allow components of the bridge deck to be installed at ground level. Permanent handrails, bridge deck formwork, electrical conduits and trays were all able to be installed prior to the girders being lifted into position. This improved site safety due to a significant reduction in the requirements for work to be undertaken at heights and also provided fall protection for the remaining above deck works.
Sustainability
A site specific Environmental Management Plan (EMP) was developed to protect all aspects of the Werribee river, including flora and fauna, within the construction footprint and surrounding areas. Key risk areas were identified and the following mitigation measures were adopted:
- Installation of silt fences erected along the banks of the river and also along the perimeter of the site to prevent silt runoff from stockpiles.
- Construction of a sheet piled cofferdam and floating silt curtain.
- No servicing of plant was undertaken on-site.
- Compound location, parking of plant, waste bins and concrete wash bays were all located more than 30 meters from the edge of the river.
- Preventative grading of the Northern side of the site was undertaken to ensure run-off fell away from the river.
- Stockpiles were sealed with a rough surface to prevent dust.
- Landscaping of the Northern abutment was undertaken at the earliest opportunity.
- Hessian cloth was wrapped around the permanent handrails to prevent debris from falling off the bridge deck.
- Revised methods and sequencing of pouring of concrete over the river was undertaken to ensure there were no spillages into the water.
The following measures were implemented on site and proved successful as the project was delivered with no adverse impact to the site.
- Protection of old river red gums.
- Frequent water quality testing and monitoring.
- Construction of rock beaching on the river banks around piers 1 & 2.
The Contractor actively sought to undertake sustainable practices and adopted re-use and recycle methodology wherever possible. Opportunities included:
- Re-use of excavated material from Pier 2 as topsoil across the project.
- Breaking up and re-using the basalt that was excavated during the bored piling operations , for rock beaching of the river banks.
- The importation of material from a local site to be used for the type-B backfill material for the reinforced earth wall.
- Waste concrete from the concrete wash out bay was broken up and used as haul roads throughout the site. The material at project
completion was removed and sent for recycling. - Recycling skips for timber and steel were utilised on the site.
Community
The construction of the Wedge Street Bridge provides a number of benefits to the community including the following:
- A unique and distinct theme for the Werribee CBD.
- Direct access into Wyndham Park helps to promote the park which was largely a forgotten reserve tucked away behind the CBD. It is proposed that more events will be held in the park in the future and the bridge could provide a backdrop to events such as concerts and markets.
- A recreational opportunity whereby pedestrians and cyclists can obtain uninterrupted views of the Werribee River and its surrounds.