DESIGNING FOR CONSTRUCTION IN A THIRD-WORLD NATION – KOOKABURRA STREET VIADUCT, PAPUA NEW GUINEA

CHARANJIT SINGH1, MOUSTAFA AL-ANI1, PETER WILES1

1 Opus International Consultants Ltd

SUMMARY The design and construction of the ~600 m long Kookaburra Street viaduct in Port Moresby, Papua New Guinea is presented in this paper. Some of the challenges faced during design are presented, with a design for construction philosophy identified as key to successful and timely delivery of the project. INTRODUCTION Papua New Guinea is a nation of 7 million people occupying the eastern half of the island of New Guinea, as well as its offshore islands in Melanesia, located north of Australia. Despite the extreme poverty in which the majority of the population live, Papua New Guinea boasts the sixth fastest-growing economy in the world due to an abundance of natural resources. The vast majority of the Papua New Guinea population lives in agricultural environments, with only 18% living in urban centres. Port Moresby is not only the largest urban centre but also the capital. Despite an abundance of cultural and natural diversity, Papua New Guinea is recognised as a third-world nation and was only recently removed from the United Nation’s ‘least-developed countries’ list. Decades of under-investment and poor management had led to a stagnant economy and poor infrastructure. However, the recent increase in export of natural resources has driven the nation’s economy to become the sixth-fastest growing in the world, which was highlighted by the decision to host the 2015 Pacific Games in Port Moresby. The infrastructure in Port Moresby, as it is throughout the rest of Papua New Guinea, is ill-equipped to accommodate the anticipated growth in traffic during the Pacific Games. The Pacific Games will comprise 21 nations competing across 28 sporting events over a two-week period, attracting over 4500 athletes and officials and thousands of tourists to the city.

Figure 1: Papua New Guinea location

Preparations for the Games included significant infrastructure upgrades and other construction works. A major component of the infrastructure works is the upgrade of Kookaburra Street in Port Moresby. The objective of the project is to provide a direct link between Jacksons International Airport and Waigani, where the PNG government offices are situated. The project was put out to tender by the owner, National Capital District Commission (NCDC), as a Design & Build. Hawkins were awarded the contract for design and construction of the project and engaged Opus to carry out design of the viaduct and approaches. CONCEPT & DETAILED DESIGN This viaduct is part of the Kookaburra Street Upgrade in Port Moresby, Papua New Guinea. The concept design, and subsequent detailed design, of the viaduct was based on the specimen design provided by Bloxam, Burnett & Olliver Ltd. Design of the viaduct was carried out using a combination of Australian and New Zealand design codes, with seismic demand determined based on local design guidance (Department of Works 1985). Design codes used throughout the structural design included:

AS 5100 – 2004: Bridge Design Standard (Standards Australia 2004)

AS 3600 – 2009: Concrete Structures (Standards Australia 2009)

NZS 3101 – 2006: New Zealand Concrete Structures Standard (Standards New

Zealand 2006)

NAASRA bridge design specifications 1976, section 2: design loads (NAASRA 1976)

NZTA Bridge Manual 3rd Edition (for seismic design and detailing) (NZTA 2013)

Earthquake Engineering for Bridges in Papua New Guinea – 1985

Location The site is located in Port Moresby between the Godwit Street / John Guise Drive / Independence Drive Roundabout and the airport roundabout, as shown in Figure 2, and includes the upgrade of John Guise Drive and Kookaburra Street within this area. The viaduct is part of the road improvement project providing direct access between Jacksons International Airport and Godwit Street / John Guise Drive / Independence Drive Roundabout.

The viaduct starts north of Kookaburra Street/Jabiru drive junction and ends just south of Boroko Creek Bridge with a total length of 594 m. The viaduct will provide direct access from Waigani to Jacksons International Airport avoiding five junctions/roundabouts, Port Moresby city centre, and Hubert-Murray Highway.

Figure 2: Project location

Constraints

Major constraints identified during preliminary and detailed design included:

compressed design and delivery period,

long lead times for most items,

security concerns for valuable elements,

lack of available skilled resources,

road intersections, roundabouts and creek crossing,

maintaining access from at-grade Kookaburra street, and

underground services.

Standardising the design to reduce the number of bespoke elements allowed for reduced design requirements, a shorter design duration, and facilitated faster construction through repetition and economies of scale. Due to the project location, the compressed design and

Extent of Works

Proposed Viaduct

delivery period was further compounded by long lead times for most materials. A combination of security concerns and lack of available skilled resources limited the potential for implementation of accelerated construction techniques. The location-related constraints resulting from existing services, intersection and waterway crossings, and alignment of Kookaburra Street below the viaduct dictated the span and column arrangements to some extent. Where long lead items, such as precast beam moulds, large diameter grade 500E reinforcement bars, elastomeric bearings and expansion joints, were identified as critical during the design process, Hawkins were informed early to allow the items to be ordered well in advance of construction.

The existing bridge between Hubert Murray Road and the airport roundabout over Boroko Creek will remain place and will not be upgraded. As a result, the viaduct abutment location was constrained by the ability to provide at-grade road access to the viaduct. Based on the identified constraints, the chosen alignment, shown in Figure 3, consisted of 19 spans ranging in length from 27.5 m to 33 m and a total viaduct length of 594 m.

Figure 3: Viaduct alignment and span arrangement

DESIGN FOR CONSTRUCTION

Figure 4: Final viaduct design

Constructability

The evolution of the superstructure design was strongly influenced by construction considerations. The fabrication of two new Super T moulds on site for the project necessitated the use of a single Super T depth and profile for all spans, with some variation in flange widths. The Super T profile adopted in detailed design, shown in Figure 5, was 1525 mm in depth with a standard flange width of 2745 mm. This profile represented a change from the 1225 mm deep Super T assumed during the concept design stage, with the deeper section allowing for increased spans and a reduction from 21 to 19 total spans. The final superstructure design, shown in Figure 6, consisted of 7 beams per span, a reduction from the concept design of 1 beam per span or 19 beams in total. The reduction in the number of beams provided significant savings in construction cost and time, alleviating some of the construction programme pressure imposed by the availability of only two Super T moulds for the project.

Figure 5: Typical Super T profile used

Figure 6: Typical superstructure cross-section

The 200 mm thick deck slab was designed to be continuous for 3-4 span segments, with expansion joints provided at locations of deck discontinuity. The choice of superstructure and deck articulation, shown in Figure 7, not only reduced the number of expansion joints required, but also provided a form of longitudinal seismic restraint through the link slabs (discussed further below). The limited use of expansion joints also improved ride quality and reduced maintenance costs. The link slabs were de-bonded for 1.8 m either side of the piers to reduce the stresses induced due to rotation of the superstructure, with increased

reinforcement provided to allow for both differential shrinkage and longitudinal seismic restraint. The use of rectangular piercap beams was ruled out due to the excessive beam depth required to accommodate the almost 16.8 m column-to-column span at some piers, which would result in excessive overall structural depth. To remedy these issues, inverted-T piercap beams were adopted. The size of the piercap beams was kept constant throughout the viaduct to improve construction efficiency. The Super T beams are seated on elastomeric bearings supported on the flanges of the piercap beams. Two shear keys are provided per side of piercap to restrain transverse movement of the superstructure span.

Figure 7: Superstructure support detail

Three typical pier arrangements, shown in Figure 8, were used along the viaduct to avoid existing roads and services.

Figure 8: Pier arrangement

Crash barriers are formed using precast concrete panels bolted to the outer edges of the deck as permanent formwork for F-type TL4 barriers connected to the reinforced concrete deck. A pattern was applied to the face of the precast panels to integrate the urban design of the viaduct with the surrounding environment. Reinforced Earth (RE) walls were designed to be independent of the abutments at both ends of the viaduct structure, as shown in Figure 9, to allow for independent construction of the two elements. A minimum gap of 500 mm is maintained between abutments and the RE

walls, with the settlement slabs used to provide continuity and designed to carry live loads between the RE walls and abutments.

Figure 9: RE wall and viaduct structure interface

Design/construct interface The short time frame for design and construction required close collaboration between the design and construction teams. Precast beam mould requirements were finalised early in the design process so that the contractor could order and fabricate the beam mould as soon as possible. Design of piles and columns was influenced by the moulds available locally to the contractor. Reinforcement details for various items were provided to the construction team regularly so that they could order reinforcement according to these, and in some cases the reinforcement details were modified to suit availability of reinforcement and ease of placement for items like pier cap beams. The main emphasis of this process was to identify and address all design and construction issues as early as possible so that the tight schedule set for design and construction could be met while maintaining the integrity of the design and ease of construction. Security issues Due to prevalent security issues structural elements which are small and costly (PT bars, Reidbar threaded reinforcing system etc.) were not used in structural design. Conventional reinforcement was used where possible. Site tolerances A significant component of the ‘design for construction’ philosophy was the emphasis on appropriate site tolerances. The scarcity of skilled labour in Papua New Guinea heightened the necessity of designing for increased tolerances to provide greater flexibility during construction. The pile-to-column interface, column-piercap joint, Super-T to piercap gap, and barrier detailing were all specifically designed and detailed with increased tolerances. A prime example of the ‘design for construction’ philosophy was the use of non-lapped splices at the pile-to-column interface; this choice was deemed worthwhile, despite the slight increase in rebar length required, as it allowed for greater flexibility in column placement relative to the as-built location of the piles. Overall, the ‘design for construction’ approach was achieved through increased design effort, close collaboration with the construction team, and a negligible increase in construction cost but resulted in a design solution which avoided compound construction tolerance issues and minimised remedial work. Staged deliverables Due to the long lead times for many of the elements and in order to meet the construction programme the contractor required the design to be delivered in the following stages:

1. Reinforcement Quantities As only grade 300 or 500N reinforcement is available within PNG all reinforcement had to be procured and shipped from steel mills in Australia/China. These mills did not carry large stocks of Grade 500E and a specific run was required. When combined with shipping times, the contractor had to order the steel during the preliminary design stage.

2. Foundation design

The construction of the piles is critical path for the project. In order to provide some float the contractor required the piles to be delivered as an early package, 6 weeks before the final design deliverable.

3. Beams Stage 1

The super-tee beams are being cast in PNG using moulds shipped in from Australia. The contractor only had two moulds available and given the number of beams required this placed them on the critical path for the project. As such a staged delivery of the beams enabled the project to be de-risked. The first stage covered the generic beam sizes of 33 m and 27.5 m and was delivered 4 weeks before the final design deliverable.

4. Beams Stage 2 The second beam package completed the beam deliverable and included the bespoke beams which required individual design and amendments to the mould.

5. Full design The final deliverable was the full detailed design package.

The approach to staged delivery was accommodated within the design fees by careful consideration as to the packages that could be made available and ensuring that the staging mirrored the design process to maintain efficiencies. The approach has helped to de-risk the project delivery with orders for all long lead items placed in a timely manner. CONSTRUCTION PHASE Interface between sub-consultants While Hawkins were awarded the contract for the project, the majority of the structural physical works was carried out by a combination of sub-contractors engaged by Hawkins. CivilPNG were engaged for piling works, while Smithbridge constructed the columns, piercaps and superstructure. Therefore the design team’s interactions were primarily with CivilPNG and Smithbridge, with Hawkins managing all communications.

Figure 10: Pile and column construction

Piles The viaduct piles were bored, with a temporary steel casing removed following the concrete pour. A number of issues were encountered during construction of the piles, constituting a mix of location and material related issues. Location-related issues for piling included deviation from design location, by up to 300 mm, and a clash with a water main which required re-location of a pile by 500 mm. Both issues required re-design of the pier cap beams as well as structural checks of the modified demands on the piles and columns. The adopted design philosophy of enhanced tolerances led to minimal physical works being required for the corrective action and allowed the project to proceed on programme. A number of issues were encountered during pouring of the concrete piles. A combination of poor workability of the concrete mix and substandard practice led to issues such as pulling out of the reinforcement cages and the concrete setting before completion of the pile. Several piles required remedial action, for which a variety of solutions were implemented. Beams One of the main challenges faced during the construction phase of the project was achieving the quality required in an environment in which prestressed concrete has seldom been used. The issues relating to construction of the Super T beams were manifested in a number of ways. A local concrete batch plant was set up by Hawkins specifically for the project. Imported aggregate and admixtures were required to achieve the specified concrete performance. Despite the specially-built batch plant, poor concrete workability and compaction, as shown in Figure 11, resulted in some defects during casting.

Figure 11: Poor concrete compaction and workability in Super T

The latest edition of the NZTA Bridge Manual (3rd Edition) includes a requirement for positive connectivity between the superstructure and substructure to guard against unseating, and associated catastrophic failure, of the superstructure during a major earthquake. This positive connectivity is usually provided through the bearing detail. Due to the relatively low seismic demand for the viaduct, a departure from the NZTA Bridge Manual requirements was approved by the client to waive the requirement for positive connectivity being provided by the bearings. Instead connectivity was provided through a combination of linkage bars at piers with expansion joints and the link slabs at all other piers.

Column/cap The column-piercap joint represented an important challenge of the design-construct interface. Prefabrication of the piercap reinforcement cage allowed for significant efficiency gains, and was identified as highly preferred, but required careful detailing. This included the use of Ancon couplers in lieu of column starter bars in the piercap, and careful consideration of the cage fabrication and joint construction process. Deck re-design The concept design for the bridge deck slab was based on the provisions of AS 5100.5, which relies on classic bending theory. However, a departure to NZTA Bridge Manual provisions at the detailed design phase was approved by NCDC. The NZTA Bridge Manual refers to the provisions of NZS 3101:2006 which allow for membrane action. The change to NZTA Bridge Manual resulted in savings of 100 tonne of rebar without a significant effect on performance. CONCLUSION The design and construction of the Kookaburra Street viaduct in Port Moresby, Papua New Guinea was presented in this paper, with a focus on the unique challenges encountered and addressed throughout the project. The key challenges were:

Staged deliverables and early identification of key parameters to enable fabrication of Super T moulds and allow for long lead times for procurement,

Achieving simplicity of design to allow for scarcity of skilled resources,

Close collaboration with construction team and client to deliver a best for project solution, including agreement on departures where appropriate,

Enhanced site tolerances and a design for construction approach to minimise the risk of programme delays and ensure timely delivery to tight deadlines

These challenges were well met by the design and construction teams to deliver a best for project design with very good client satisfaction. ACKNOWLEDGEMENTS The authors would like to thank members of the design team (Opus), construction team (Hawkins, Smithbridge, CivilPNG), and NCDC and their agent. REFERENCES Department of Works, (1985), “Earthquake Engineering for Bridges in Papua New Guinea”. NAASRA, (1976), “National Association of Australian State Road Authorities Bridge Design Specifications”. NZTA, (2013), “New Zealand Transport Authority Bridge Manual, 3rd Edition”. Standards Australia, (2004), “AS 5100 – 2004: Bridge Design Standard”. Standards Australia, (2009), “AS 3600 – 2009: Concrete Structures”. Standards New Zealand, (2006), “New Zealand Concrete Structures Standard”.