10h Australian Small Bridges Conference 2021
Outcomes of a collaborative approach – Newcastle Inner City Bypass early works shared path bridge
Nathan Roberts, Technical Director, Aurecon Dave Mockett, Associate, Aurecon Chutiwat Poolsilapa, Bridge Engineer, Aurecon Miguel Wustemann, Director, KI Studio
ABSTRACT
Transport for NSW are currently developing the detailed design for the Rankin Park to Jesmond (RP2J) section of the Newcastle Inner City Bypass (NICB). This is the final link of a western motorway for the City of Newcastle. As an early works package for this project, an existing at grade signalised pedestrian crossing has been replaced with a shared path bridge and ramps. The bridge comprises a steel tied arch main span and concrete ramp and stair approaches. The general arrangement of the bridge has been strongly influenced by underground utilities. The bridge crosses Newcastle Road, one of the main routes into the Newcastle Central Business District (CBD). This is a busy route which currently accommodates approximately 60,000 vehicles per day. Hence, urban design was considered an important factor in the design resolution of the structure. The asset owner, engineer and urban designer collaborated closely together during the detailed design phase to refine the design and create a new landmark as part of the approach into the city centre. Digital technologies such as 3D modelling and virtual reality were used to help visualise the design and to communicate the proposal to stakeholders. Construction is now nearing completion. This paper will outline the design of the bridge, focusing on the development of urban design refinements and digital technology employed as part of the delivery.
1 INTRODUCTION
The NICB is part of Transport for NSW’s (TfNSW) long-term strategy to provide an orbital link within Newcastle’s road network. This link will connect the Pacific Highway at Bennett’s Green to the Pacific Highway at Sandgate. Sections of the bypass have been opened progressively since the early 1980’s. Once complete, the route will provide improved traffic flows across the western suburbs of Newcastle, connecting key regional destinations.
The road network surrounding the proposed link currently suffers from traffic congestion and delays at key intersections. Contributing to congestion in the area was an existing signalised mid-block pedestrian crossing of Newcastle Road. The signalised crossing facilitated pedestrian movements between suburbs to the north, and parkland, cycling and public transport routes to the south. The crossing was frequently used and when triggered, resulted in traffic queuing back to the NICB / Newcastle Road intersection to the west, causing significant congestion during peak times.
To improve safety and alleviate congestion caused by this crossing, a grade separated crossing has been constructed. This comprises a steel arch main span with a composite concrete deck. The main span is connected to the existing path network with cast in-situ concrete ramps and precast concrete stairs. The ramps connect to the bridge with Coles Street (a local service road) and Newcastle Road on the northern side, and to Jesmond Park and Newcastle Road on the southern side. Stairs also provide pedestrian access to bus stops on Newcastle Road.
Located to the south of the bridge site is the existing east-west Jesmond cycle path. This is a busy route that is used by pedestrians and cyclists for recreation and commuting. The proposed RP2J section of the NICB will impact this route during construction. A new grade separated crossing is proposed for the east-west cycle path as part of the main NICB works. Construction of this will be staged to allow continued access, however completion of the Newcastle Road shared path bridge as an early works project has also provided an alternative route that can be utilised during construction of the main RP2J project.
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A locality plan showing key features in the vicinity of the project is shown in Figure 1 below. An aerial view artist’s impression of the completed project is also provided in Figure 2 below.
Figure 1- Locality plan
Figure 2- Indicative artist’s plan view of the project showing proposed features
2 BRIDGE SITE AND CONSTRAINTS
The topography at the project site comprises sloping ground from the northern suburbs of Jesmond and North Lambton down towards Newcastle Road. This results in Coles Street being elevated above Newcastle Road with a level difference of approximately two to three metres. Before construction of the project, a vegetated batter existed between Coles Street and Newcastle Road. At the location of the existing signalised mid-block crossing, a concrete block retaining wall and ramp provided access between Coles Street and Newcastle Road.
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Newcastle Road runs east-west at the bridge location, following a natural low point between higher ground to the north and south. It runs parallel to Dark Creek which is currently a concrete lined channel, located immediately south of Newcastle Road in Jesmond Park. Historically Dark Creek meandered in a north westerly direction before crossing Newcastle Road near Jesmond. To the east, Newcastle Road rises uphill. The bridge crossing is located at the base of this rise near the Newcastle Road intersection with Steel Street. West of the crossing location Newcastle Road is relatively flat towards Jesmond. A view of the bridge site prior to construction is shown below in Figure 3.
Figure 3- View of main span alignment from southern side prior to construction. View from Jesmond Park with Steel Street on the right
2.1 Traffic
As discussed previously, Newcastle Road is one of the busiest routes in the city, providing connectivity between the M1 Motorway and Hunter Expressway to the Newcastle CBD. Other major generators of traffic near the project are the John Hunter Hospital (a major regional hospital in NSW) and the University of Newcastle. Traffic data recorded in 2014 indicated that approximately 60,000 vehicles per day used the section of Newcastle Road at the bridge location. Consequently, traffic was a major constraint for construction and the design of the bridge and approaches needed to minimise disruptions to Newcastle Road.
Coles Street on the northern side of the site also presented challenges. The location of the northern ramp was constrained between Coles Street and Newcastle Road. This required partial closure of the local road during construction. Multiple residential dwellings and a church rely upon Coles Street for access. Consequently, the project needed to ensure access (at least one way) was maintained along the local road during construction.
The project brief originally required the bridge to be constructed with a vertical clearance of 5.5 m in accordance with AS 5100.1 (1). Early in the detailed design phase, further discussion regarding vertical clearances identified concerns about the potential sterilisation of high clearance routes to the Newcastle CBD. TfNSW assessed over size / over mass records for Newcastle Road and identified that the largest vehicle which had historically used the route required a vertical clearance of 5.9 m. Consequently, the clearance criteria was revised to achieve a vertical bridge clearance of 6.0 m in accordance with the AS5100.1 (1) requirements for pedestrian bridges on a high clearance route.
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In addition to constraints and criteria imposed for road traffic, the bridge needed to comply with AS 1428 (2) for access and mobility, and the Austroads Guide to Road Design Part 6A (3) for shared paths to ensure functionality for cyclists and pedestrians.
2.2 Utilities
Numerous existing services were present at the proposed bridge site. Where possible the bridge design proposed to maintain and protect existing services, however relocation was required for some assets. Key utility constraints are outlined below:
• Significant communications assets comprising eight 100 mm diameter ducts (stacked in two rows of four) are located on the southern side of Coles Street, between Coles Street and Newcastle Road. This is a major asset providing Telstra, Optus and NBN connections to the Newcastle CBD and consequently relocation would be a significant undertaking. As a result, the design was modified to leave this asset in place and to protect it accordingly. • Numerous Low Voltage (LV) and High Voltage (HV) aerial electrical conductors together with an aerial communications route were present between Newcastle Road and Coles Street. To facilitate construction of the bridge these were relocated to the northern side of Coles Street. • A 375 mm diameter watermain is located in Jesmond Park on the southern side of Newcastle Road. This main is parallel to Newcastle Road. The existing location of the water main clashed with the southern ramp for the bridge and consequently the main was relocated further south into Jesmond Park. • Other small water and gas lines in Coles Street were also relocated for footpath and pavement works.
3 DESIGN DEVELOPMENT
A high degree of collaboration between the design team, urban designer and TfNSW throughout the design led to improved aesthetic and maintenance outcomes for the project. The same team was involved throughout the concept and detailed design with Aurecon and KI Studio undertaking the engineering and urban design respectively, working with the project team from TfNSW. The following sections outline the development of important features of the design.
3.1 Concept design development
3.1.1 Alignment
During the concept design two alignment options were considered for the shared path route over Newcastle Road. A minimum three metre clear width was adopted for the shared path for each option.
The first option comprised a square crossing located near Steel Street. This option adopted main span pier locations that allowed for potential future widening of Newcastle Road to six lanes. On the northern side of Newcastle Road a ramp extended to the west tying into a retained landing area between Coles Street and Newcastle Road. On the southern side of Newcastle Road a ramp extended to the east. Stairs were provided at either end of the main span from the grade separated crossing down to Newcastle Road level. As noted above, this alignment was selected for the project. The alignment is shown above in Figure 2.
The second option comprised a skew crossing located further west of Steel Street. On the northern side this option had ramps in either direction to connect users to Coles Street. On the southern side, a single ramp extended to the west. The skewed option was proposed to provide a better alignment for cyclists. However, it was rejected as it resulted in a longer main span and an undesirable visual outcome with the span being orientated at an angle to road users. Figure 4 below illustrates this option.
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Figure 4- Skew alignment option
3.1.2 Main span
In order to achieve traffic clearance whilst minimising the length of approach ramps, options for the main span were limited to through type structures such as arches and trusses. TfNSW have recently developed a standard form of tied arch pedestrian bridge that has been used in several locations in Sydney. The TfNSW project team expressed a preference to adopt this type of structure for the main span. Consequently, following some initial discussions, this type of structure was selected for the concept. Potential amendments that could be made were noted for further investigation during the detailed design stage.
The tied arch form used by TfNSW for other recent projects consists of a through steel tied arch structure with the top and bottom chords formed by square and rectangular hollow section members. A composite concrete deck is cast in-situ on stiffened steel plates spanning between hollow steel cross members. The top chords are braced at mid-span. A fully shielded safety enclosure with a translucent roof and anti-climb screening is provided for the full length of the bridge.
The concept proposed the main span to be supported on blade piers founded on bored concrete piles socketed into rock. The total length of the main span was 34.2 m.
3.1.3 Approach ramps
The concept design progressed with bridge approach ramps comprising elevated structures for most of the approach length. These elevated ramps connected with a shorter earth retaining structure at the low end (hereafter referred to as the abutment ramp). Both ramp structures were proposed to be constructed using cast in-situ reinforced concrete. The transition location between the two was based on achieving a minimum 2.2 m vertical clearance between the elevated ramp soffit and the finished ground level.
The trapezoidal elevated ramp was proposed to be supported with central circular columns which were integral with the ramp. Proprietary bike safe balustrades were proposed for the approach ramps.
Elevated ramp columns were founded on single bored concrete piles socketed into rock. The abutment ramps where designed with shallow foundations on weathered rock.
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At the northern side, an L-shaped retaining wall was proposed along Newcastle Road in order to provide a landing area, allowing cyclists to transition onto Coles Street (which was proposed as a shared zone) and pedestrians to cross to a footpath on the northern side of Coles Street. This wall was proposed to continue and reduce in height eastwards towards Steel Street, providing for a pedestrian footpath ramp down to a bus stop on Newcastle Road.
3.2 Detailed design
Several refinements were introduced as the detailed design was developed.
Given the highly visible nature of the structure, an onus was given to improving the aesthetics by replacing some of the more utilitarian features proposed in the concept design. Whilst adding cost in some areas (the balustrade), in other instances this resulted in cost savings by removing additional steelwork. To achieve this, the engineer and urban designer worked collaboratively with the TfNSW project team and the TfNSW Centre for Urban Design. What began as conceptual sketches from these sessions was refined, developed and detailed using 3D modelling to result in the final design.
Improving the safety of users and the maintainability of the structure were also factors that drove changes. Finally, confirmation of service locations also resulted in adjustments to the concept design
3.2.1 Main Span
The recent tied arch pedestrian bridges constructed by TfNSW proved a useful starting point for this structure, however the context of these structures is slightly different to that presented for the Shared Path Bridge at Jesmond.
At the time of this project, previous tied arch bridges constructed by TfNSW were all Sydney based. They were also located in more urbanised environments, close to larger generators of pedestrian traffic such as schools, train stations and shopping areas. These bridges also did not have room for extensive approach ramps, and therefore were not designed for cyclists. Consequently, recent bridges of this type have been constructed with stairs and lifts. The lift structures provided a strong vertical element at either end of the bridge. The elevated landings and main span connecting the two lift shafts have previously been fully enclosed with safety screens and a translucent roof. The provision of the continuous roof linked the two lift shafts, forming a horizontal rectangular element between the two.
Early in the concept design process it was decided that the shared path bridge site at Jesmond did not warrant lifts. This was partly due to the lower patronage, the predominance of cyclists and vandalism and maintenance concerns. Removing the lifts, removed the strong vertical visual element on either side of the main span.
The purpose of the roof was then also reviewed, and during the early stages of the detailed design it was decided that the roof was unnecessary. This was primarily because the path approaches for the bridge were uncovered. Removal of the roof eliminated risks associated with its maintenance (for gutters etc.) and public safety risks from unauthorized access. Removal of the roof also meant that a greater surface area of the structure would be exposed to the cleansing influence of rainwater, resulting in potentially improved durability outcomes.
Removal of the roof also meant that the steel framing which was used to support it and the safety screens on previous designs could also be eliminated. However, the safety screen still needed to be replaced with a feasible alternative. A lightweight stainless-steel netting was proposed for this. This material was selected so as not to detract from the main structural arch elements. The netting was used above handrail level only with the lower section of the balustrade constructed using perforated powder coated aluminum panels. This material was selected to articulate the solid barrier at the lower level, providing a visually semi-permeable element that enhanced safety and also provided visual re- assurance of the balustrade robustness for the end users. These refinements saved approximately 9 tonnes of steelwork and associated cladding. Figure 5 below shows a comparison of the main span cross section.
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Figure 5- Comparison of main span cross sections, concept design on left, final detailed design on right
After removal of the roof and steel framing, the arch hangers were extended above the top chord in order to support the safety screen to the required height. The lower balustrade panels and netting were then aligned with the inside faced of the top chord. This eliminated the risk of people climbing the top chord whilst still emphasizing this key structural element to path users. This is illustrated below in Figure 6.
Figure 6- Arch interaction with balustrade As noted above, elimination of the lifts and roof removed the solid vertical elements at the end of the main span. In addition, changes to the barrier visually de-cluttered the structure, improving transparency and emphasising the structural elements. The challenge remained to integrate the ends of the main span with the landings and ramps beyond. It was proposed that this be achieved by adjusting the hanger geometry. This was done by starting with a vertical hanger at midspan and rotating the remaining hangers / safety screen posts by increasing increments towards the piers. After some investigation, incremental rotations of two degrees away from vertical were adopted for each hanger. This resulted in a rotation of 16 degrees for the last hanger / safety screen post located at the main span support. Further refinement of the arch geometry included gradual reduction of the safety screen posts from minimum required height for the screen where the netting intersected the top chord,
Page 7 10h Australian Small Bridges Conference 2021 to a greater height at the piers. This contributed to a more dynamic aesthetic for the bridge when viewed in elevation. To complete the integration with the landings, triangular sections of netting were extended two to three balustrade posts from the end of the main span. This helped to visually connect the main span with the landings but also served the function of restricting unwanted access to the top flange of the top chord. Changes to the main span are illustrated in Figure 7 and Figure 8 below.
Figure 7- Main span elevation – concept design
Figure 8- Main span elevation – detailed design A sensitivity analysis of the structural performance was undertaken before adopting the proposed changes to the hanger rotation. Cases investigated included:
• Case 1 – The configuration with all hangers vertical and the original framing for the roof and safety screen in place. • Case 2 – The configuration with the hanger starting at vertical at mid-span and then rotating incrementally by two degrees for each bay towards the support (with a rotation of 16 degrees at each end). This also includes removal of additional internal framing for the safety screen and roof.
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Figure 9 below shows the models for both cases and summarises key axial forces, deflections and bending actions.
Figure 9- Comparison of arch results As can be seen in Figure 9, the change in design action, deflection and utilisation for Case 2 relative to Case 1 is negligible. Deflections for Case 2 actually decreased relative to Case1. Removal of the roof and screen framing dead load contributed to this. Consequently Case 2 was designed and detailed accordingly as the preferred solution. This included the relevant section capacity and buckling checks as well as dynamic assessment.
The main span is supported on laminated elastomeric bearings and restrained transversely for collision loading via a custom fabricated shear dowel assembly on each pier. Vertical restraint is also provided with tie down bolts through the bearing attachment plates at each pier. Movements are accommodated via slotted holes in the attachment plates and cover plates are provided at each end of the main span. The main span is detailed with path lighting, a traffic camera and with future provision for potential digital advertising signs.
Urban design advice initially suggested the use of weathering steel for the main arch steelwork. This was to reflect the industrial and steelmaking heritage of Newcastle. Early discussions with the TfNSW team ruled out the use of weathering steel for this bridge due to its relatively new application in Australia. Consequently, the steel work is painted a burnt orange colour (Dulux Hot Ginger) to emulate weathered steelwork. To provide contrast, the perforated aluminum panels are powder coated dark grey. Isolation of dissimilar metals is employed as appropriate to avoid potential bi- metallic corrosion.
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The main span piers remained as blade piers, with each pier supported on a pile cap with permanently cased bored cast in-situ concrete piles. Both piers were designed for road vehicle collision loading in accordance with AS5100.2 (4). Consideration was given to modifying the piers to have the central section cut out (when in elevation) with a parabolic profile to form a forked configuration with each of the fork tines supporting an elastomeric bearing. This was not pursued due to potential constructability challenges and collision load and lateral restraint requirements. As a compromise a parabolic rebate was provided in each face of the piers to help articulate the visual bulk of this element. Figure 10 below shows the finished pier in elevation.
Figure 10- Elevation view of blade pier
3.2.2 Ramps
The development of the approach ramp design was heavily influenced by existing services. Slit trenching of the existing communications on the northern side confirmed that they were further south than initially expected. This meant that the services either required relocation or the ramp needed to be modified to ensure clearances required by the utility authority were achieved. Due to the cost implications of relocation it was decided instead to modify the ramp support geometry. Rather than the central ramp support columns proposed by the concept, the design was revised to offset all columns towards Newcastle Road. Even with the offset columns, further mitigation was required to reduce the risk of potential damage to the optic fibre route.
This was achieved with the use of permanent casings for the bored piles. Permanent casings reduced the risk of damage whilst augering and did not require excessive vibration for casing extraction which could have damaged the services. Whilst the offset columns and permanent casings were only required for services on the northern side, they were also replicated on the southern side for consistency. Figure 11 below shows a three-dimensional view from the Revit model with the service locations shown.
In addition to changes to the elevated ramp, the location of services also required adjustment to the abutment ramp. At the locations of the abutment ramp, the optic fibre route deviated to the north, however it was still close enough to warrant revision. Consequently, the plan width of the abutment ramp was reduced to be less than the required path width. Small corbels supported the full width of the path and kerbs at the higher level. Again, this was replicated on both sides.
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Figure 11- Proximity of communications route to structure Changing the supports of the elevated ramp to offset columns also proved a catalyst for revisiting the geometry of the columns and the ramp cross section. Firstly, the columns were revised to a tapered rectangular shape, rather than the circular column proposed at concept. This was because the rectangular section allowed alignment of the outside face of the column with the outside face of the elevated ramp. A curved fillet transition between the column and the ramp was adopted after consideration of an angular chamfer alternative. The ramp cross section was also changed to a rectangular section with the soffit formed by two slightly inclined planes culminating in a vertex at the centreline of the cross section. This change allowed the ramp deck element to better integrate with the offset columns. Ramp columns where spaced at approximately 12 m centres to coincide with landings required by the mobility and access requirements.
Following consultation with TfNSW, supports for the approach ramps were designed for a reduced collision load of 500 kN. This was because their increased distance from Newcastle Road placed them outside the clear zone. For the northern side, the proximity of Coles Street was considered, however it was agreed with TfNSW to adopt a collision load of 500 kN due to this being a 40 km/hr shared zone for local traffic only.
To complement the changes in the ramp concrete geometry, the ramp balustrades were also revised from proprietary modular railing to a custom balustrade. The custom balustrade was fixed to the side of the ramp and comprised posts cut from UC sections with perforated aluminum panels spanning between the posts. The perforated panels extended below the bottom corner edge of the ramp and slightly above the top of the post to hide the varying ramp and handrail profile which was required for landings in accordance with the mobility and access standard AS 1428 (2). This also helped to hide construction joints at the column locations. Posts were painted and panels powder coated dark grey to match the main span balustrade. Cradles for stainless steel handrails and cyclist rub rails were supported from the balustrade posts. Light posts and a privacy screen for nearby residents at the northern ramp were also incorporated with the balustrade. Similar to the main span, isolation was provided between dissimilar metals to avoid bi-metallic corrosion. Figure 12 below illustrates the change between the elevated ramp cross section from the concept design to the detailed design. Figure 13 also shows the completed balustrade on the southern ramp.
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Figure 12- Comparison of ramp cross sections, concept design on left, final detailed design on right
Figure 13- Finished balustrade on southern ramp
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The changes to the ramp column arrangement impacted the supports for the elevated structure at the abutment ramp. The concept design proposed that the elevated ramp be supported on two laminated elastomeric bearings at the abutment ramp. At all other locations it was proposed to be integral with the central ramp columns and the blade piers. Offsetting the columns resulted in a rotation of the elevated ramp with downwards deflections at the free end of the cantilever. This also resulted in the columns deflecting horizontally towards the free end of the cantilever. At the abutment ramp this meant the that the elastomeric bearing which had been proposed on the same side as the columns, experienced negligible compression loading under dead weight and uplift for some live load cases. In addition, movement of the ramp horizontally towards the free end of the cantilever also caused horizontal shear on the bearings in the transverse direction. To address the uplift and the horizontal loading, the bearing which was previously proposed to be located on the same side as the column supports was replaced with an uplift / lateral restraint bracket.
The calculated loading on this bracket was relatively small. The bracket comprised two opposite handed stiffened fabricated steel angle brackets. One housed a standard size hole for a M24 bolt. The other had a long-slotted hole in the direction of longitudinal movement. A stainless-steel surface was provided on the inside face of one bracket and an Ultra High Molecular Weight Polyethylene (UMWPE) surface on the inside face of the other bracket to allow for lateral restraint and sliding movements. Pre-camber (albeit small) was also applied to the columns to account for the deflection under dead load. The uplift / lateral restraint bracket is shown below in Figure 14 and Figure 15
Figure 14- Three-dimensional model of uplift / Figure 15- Installed uplift / lateral restraint bracket lateral restraint bracket
Further changes were made to the abutment ramps during the detailed design. During the concept stage they were proposed to be earth filled U-shaped structures with the shared path concrete founded on the infill material with no connection to the walls. Cost and constructability investigations during the detailed design found it preferable to design the abutment ramp as a voided structure with the path forming a structural element which connected the two walls to create a box. After review with the client this change was implemented for the detailed design. In addition, the outer faces of the abutment ramps were treated with a form liner to provide a textured finish. This is discussed further in Section 3.2.3 below.
Finally, during the detailed design, adjustments to the ramp and stair layouts were made to improve user safety. These included widening the landing either side of the main span to provide a refuge at the top of the stairs, avoiding the risk of pedestrians with limited sight distance stepping in front of cyclists. A holding rail was also provided in these locations to reduce the risk of cyclists going down the stairs and to further aid separation at the stair conflict point. Similarly, the flighting arrangement for the stair access on the southern side of Newcastle Road was revised to provide increased sight distance for pedestrians before they needed to step into the on grade shared path which runs parallel to Newcastle Road.
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3.2.3 Retaining walls
As noted above, the concept design proposed an L-shaped cast in-situ concrete retaining wall between Newcastle Road and Coles Street. This wall retained a level paved area that allowed the ramp users to connect to Coles Street (which is a shared zone for cyclists) and the local path network. The maximum wall height is approximately four metres. The eastern section of the wall reduces in height as it retains a footpath that grades down to existing bus stops on Newcastle Road. Urban design input during the detailed design led to treatment of the outer face of the wall with a textured form liner. The proximity of the wall to the existing road meant that it could not be screened with landscape planting and consequently this treatment helped to visually recede the wall and to discourage graffiti.
West of the proposed concrete retaining wall there was an existing concrete block wall which supported the existing ramp from Coles Street to the signalised mid-block crossing. During the concept design the block wall was proposed to be demolished and reinstated with a batter and small toe wall. However, during detailed design it was agreed to construct a sandstone block retaining wall instead at this location. The sandstone block wall was designed as a gravity wall reliant on multiple courses of sandstone blocks at the base. The wall extents were increased to flatten the existing steep vegetated batter adjacent to Newcastle Road, improving maintenance access.
3.2.4 Road design
Urban design improvements were made during the detailed design, replacing many bollards and an extensive paved area along the southern side of Coles Street (near the top of the retaining wall) with a re-directive Elsholz kerb and planting beds. Standard kerb and gutter previously proposed along Newcastle Road during the concept design was also changed to re-directive Elsholz kerb to offer protection for existing electricity poles.
4 DIGITAL ENGINEERING
Recent developments in digital engineering were used throughout the delivery of the project and these proved particularly useful in addressing and communicating complex geometry issues associated with the structure. This helped to achieve a high level of collaboration across the team and to communicate the proposed design to stakeholders and the community.
The bridge was modelled completely in 3D using Autodesk Revit during the concept and detailed design stages. This model served as a basis for interactive visualisation tools, both computer based and immersive virtual reality. This included conventional virtual reality (comprising a headset and handheld controls) and a cyclist virtual reality interface that has been developed by Aurecon. The cyclist interface comprises a stationary instrumented bicycle that users can ride whilst wearing a virtual reality headset. Both were used by stakeholders to interact with the proposed design and provide feedback. The visualisation model was also used. A screen shot from the visualisation model and a photo of the bicycle virtual reality interface are shown below in Figure 16 and Figure 17 respectively.
The three-dimensional model of the bridge and visualisations helped identify and resolve several issues. One example was checking site lines in easterly and westerly directions for the traffic camera that was mounted on the main span. Another was resolving the interfaces between the balustrades on the bridge approach ramps with the main span. The three-dimensional model was provided for information to the contractor and fabricator and provide a useful starting resource for developing fabrication models.
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Figure 16- Screen shot from interactive visualization Figure 17- Virtual reality bicycle interface model
5 CONSTRUCTION
Daracon Group were awarded the contract for construction of the bridge and work commenced in late 2019. JC Butko Engineering were engaged by Daracon Group for steel fabrication for the project. Bridge construction continued through 2020 with the main span being installed in September 2020. The main span was completely fabricated in a workshop before being transported to site and erected with a 400-tonne mobile crane during a night road occupancy. The concrete deck was cast afterwards during normal construction hours. Figure 18 below shows the main span installation being undertaken. The bridge was opened to pedestrian traffic in December 2020. Minor finishing civil works remain, and the project will be complete in early 2021.
Figure 18- Main span installation Minor adjustments were made to the design during construction. Bridge and structure related changes are discussed further below. Other changes were primarily related to utility relocation works. For the watermain relocation works, unforeseen conditions (regarding valve locations etc.) led to minor adjustments to the design. For the electrical relocation works, modifications to the design were made in response to an update of health and safety standards from the utility authority.
5.1 Steelwork
During the design phase, options were provided for constructing the main span top and bottom chords using either standard Rectangular Hollow Sections and Square Hollow Sections or by using sections
Page 15 10h Australian Small Bridges Conference 2021 fabricated out of steel plate. This was based on experience from previous bridges of this nature where the required order size was insufficient for rolling hollow sections to a curve.
For this project the contractor and fabricator opted to fabricate both the top and bottom chord from plate, rather than using standard hollow sections. This approach also helped facilitate the fabrication of the top to bottom chord node connection. During construction the fabricator was concerned distortion may occur during fabrication and subsequently introduced additional internal stiffeners to help control this risk. Additional changes to the top to bottom chord connection were also made to simplify fabrication. Figure 19 below shows the arch in the fabrication workshop.
Figure 19- Arch fabrication Both the contractor and fabricator had three-dimensional modelling capabilities, and this proved extremely beneficial for producing shop drawings and assessing changes, for the main span and particularly for the balustrade which is discussed further below.
5.2 Balustrade
Balustrade posts were proposed to be fixed to the concrete approach ramps using cast-in ferrules. During construction the contractor identified a requirement for greater tolerance for balustrade fixings to assist with constructability. The contractor and design team worked collaboratively to introduce minor adjustments to the panel widths, post and panel hole sizes, and washer and packing configurations. As noted above the use of three-dimensional modelling by the contractor aided in communicating and refining the proposed modifications.
During construction there were some concerns raised regarding the robustness of the perorated aluminium panels, particularly due to potential damage from vandals. Whilst these load cases had been assessed during design, consideration was given to providing a stiffening bend at the top of the perforated panel. To resolve this before placing the bulk panel order, it was agreed that the fabricator would construct a mock-up of one bay of balustrade in the workshop and assess the robustness of the panels. Deflections and robustness of this mocked up balustrade proved acceptable and the construction progressed as per the original design.
A lesson learnt from this process is to include a hold point for prototypes of custom balustrades in the tender documentation for future projects. This provides a contractual mechanism to review and validate the design assumptions prior to material supply and fabrication
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5.3 Retaining walls
During construction the contractor proposed modifications to the sandstone block wall to result in time and cost savings. The maximum wall height was two metres and to achieve the required factor of safety for the critical seismic load case, a base width of two metres was also required. This wall was originally proposed to be constructed as a mass of interlocking sandstone blocks with a typical block size of 500 mm by 500 mm square by two metres long. This proved expensive and it was revised to a no fines mass concrete block with one layer of sandstone blocks for the facing. For the revised configuration stainless steel tie rods were drilled and fixed to the blocks and then cast into the no fines concrete.
6 CONCLUSION
Whilst all projects inevitably develop throughout the various phases of delivery, the arc followed by this project has proven particularly rewarding for those involved. Part of this is because although the refinements that have been made are relatively small and in response to specific issues, they have made real improvements to the outcome, resulting in a new landmark structure for the area.
A willingness to challenge the concept together with a collaborative mindset from the client, design and construction teams has resulted in this outcome. This has also been supported using digital engineering throughout to communicate issues and ideas to delivery partners, stakeholders and the community. The usefulness of this is illustrated by Figure 20 and Figure 21 below. The left shows a photomontage of the proposed bridge, released to the community in 2019. The right shows the actual construction progress nearing completion in late January 2021.
Figure 20- Photomontage of proposed bridge Figure 21- Construction nearing completion in produced in 2019 January 2021
7 REFERENCES
• Ref1 – Australian Standard AS 5100.1:2017, Bridge design Part 1: Scope and general principles, Standards Australia, Sydney, 2017 • Ref2 – Australian Standard AS 1428.1-2009, Design for access and mobility Part 1: General requirements for access – New building work • Ref3 – Guide to Road Design Part 6A: Paths for Walking and Cycling, AGRD06A-17, Austroads, Sydney, 2017 • Ref4 – Australian Standard AS 5100.2:2017, Bridge design Part 2: Design loads, Standards Australia, Sydney, 2017, Standards Australia, Sydney, 2009
8 ACKNOWLEDGEMENTS
The authors wish to express their gratitude to Transport for NSW for granting permission to publish this paper. The authors also would also like to thank and acknowledge the TfNSW project team, Daracon Group and JC Butko Engineering for their respective roles in the delivery of this project.
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9 AUTHOR BIOGRAPHIES
Nathan Roberts is a Technical Director with Aurecon. He is also the Aurecon Newcastle Office Leader. Nathan holds a Bachelor of Civil Engineering with honours and has over 15 years’ experience in the design and construction of bridges and civil infrastructure. This also includes bridge assessment, rehabilitation and maintenance projects such as the ANZAC Bridge Maintenance Upgrade. Nathan's design background is supplemented with construction experience as a temporary works coordinator on large rail infrastructure projects in the UK. Nathan was the Aurecon Project Manager and Design Manager for this project. Dave Mockett is an Associate with Aurecon. He is a Chartered Professional Engineer who has 15 years’ experience in the design and construction of bridges in New Zealand, Australia, and Asia. Dave returned to New Zealand in 2019 after 4 years working in Hong Kong and Bangkok. Dave was responsible for leading the Shared Path Bridge structural design. Other notable projects include Auckland City Rail Link, Northconnex, Westconnex, and Moorebank Intermodal Freight. Dave is also a past presenter of the conference. Chutiwat Poolsilapa is a Bridge Engineer with Aurecon. Chutiwat holds a Bachelor of Civil Engineering with honours and has over 4 years’ experience in bridge analysis, design and construction. Chutiwat has been involved in many aspects of bridge and civil structures design, including concept to completion of bridge designs, load ratings, strengthening of existing structures and proof engineering. Miguel Wustemann (KI Studio) Miguel has over 32 years of experience as an architect and city and regional planner who specialises in urban design, master planning, and architecture. His multi- disciplinary skills and broad experience on a variety of projects internationally ranging from strategic planning, high rise construction, heritage conservation, transport and urban regeneration provides a thorough understanding of the complex issues regarding urban environments, their interfaces and functional integration. Miguel has worked on numerous large-scale urban development, regeneration and infrastructure projects in Australia, Germany, China and USA. His experience in collaborating with Government authorities on complex multimillion development and transport projects underpins his expertise in helping set new visions for urban environments. He has been practicing in Australia since 2000 as director of Infranet and then KI Studio. Miguel has a strong passion in design and believes: “vibrant urban spaces are rich and layered; engaging designs contribute to this outcome”.
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