WELLINGTON INTERNATIONAL AIRPORT MULTI-LEVEL CARPARK – SUPERSTRUCTURE CONSTRUCTION

STANLEY CHUNG, ANDREW DAVIDSON, CARL ASHBY

WSP Opus SUMMARY WSP-Opus designed the structure for the new 10 storey car parking building at Wellington International Airport for which the construction has been recently completed (August 2018). The Fletcher Construction Company (Fletcher) was responsible for the construction of this project. Included is a 10 storey concrete hybrid moment frame structure with buckling restrained braces (BRB’s) founded on a raft slab and an adjoining elevated road structure and concourse. The scope of this paper is to summarise the key design aspects of the construction of the superstructure including phasing, methodology and management of site constraints. Further information on the project can be found in the following conference papers:

• NZCS Conference 2016: Wellington International Car Parking Building

• NZCS Conference 2017: Wellington International Airport Multi-Level Carpark – Concrete Raft Slab Construction

Figure 1: Construction of Car Park Building

INTRODUCTION Wellington International Airport Limited (WIAL) is implementing a major re-development plan for the airport which includes the new parking building that will provide an additional 1090 carparks along with a transport and bus hub within the building. The site for the new car parking building is located to the North East of the existing terminal and has a network of ramps and elevated road structures (known as the concourse) which will connect the carpark to the new hotel and existing terminal, concourse and car parking building. WSP-Opus were engaged by WIAL to provide the structural engineering services for the car parking building, concourse and hotel. Fletcher have been contracted by WIAL for the construction of the car parking building and the adjoining concourse structures. BUILDING DESCRIPTION The car parking building is 10 storeys including a mezzanine level between ground and the first floor. Overall dimensions of this building are 78m x 51m x 28m high with a gross floor area of approximately 35,000m2, which will provide parking for up to 1090 cars. The concrete frames are largely precast cruciforms with precast double tee floor units. The super structure is supported on a raft slab that is between 1.0m and 1.5m deep. The concourse structure is a single level structure with a gross area of approximately 4400m2 including ramps. The concourse consists of four seismically separate structures; entry ramp, exit ramp, northern and western concourse sections. The concrete frames consist of in-situ columns and a combination of precast and in-situ beam units with precast double tee floor units. The foundations consist of shallow foundations. Elements were placed in consideration of the traffic lanes at ground level and also staging of works. SUPERSTRUCTURE DESIGN BACKGROUND Carpark Building The car parking building was originally proposed to be a steel braced frame structure with 30 metre deep bored pile foundations. It was the client’s request that the concrete option be considered due to the close proximity to the coastline, creating a durability issue resulting in high maintenance costs for WIAL associated with exposed steelwork. The fire protection for the steelwork was also a substantial cost. With the open sight lines within the building being a key aspect of the design a conventional shear wall system was not considered suitable. Both concrete frame with supplemental braces and the steel braced frame systems were presented as options during the preliminary design stage and cost estimates were prepared for both options. Without taking into account the ongoing maintenance of the building, the concrete option was still evaluated being cost effective. The concrete moment frame with supplemental BRB braces option was selected as the preferred structural form. This was due to concrete being durable and easier to maintain under exposure to adverse coastal frontage environmental conditions at the Airport compared to steel. There were also advantages in terms of fire treatment that would have been required and also the deep foundations that would have been required for the steel option. This option also satisfied architectural aesthetic considerations and limitations on sightlines and frame sizes that could be used within the space.

Concourse The concourse is an elevated roading structure which provides circulation routes from the terminal drop off area and allows and access to the carpark building and adjacent structures. The concourse structure is a single level structure constructed principally of reinforced concrete with a combined system of cantilever columns and moment frame structure and is in general been constructed with shallow foundations. The Northern portion of the Airport over which the concourse is located has a very complex, challenging and constrained traffic system with traffic functions critical to nearly all Airport operations converging in this area. The traffic routes that needed to be planned for and accommodated in the design and construction staging included;

• Main northbound traffic terminal drop-off circulation route • Northbound car parking / rental car circulation • Rapid bus transport terminal and bus circulation • Loading docks and waste servicing for airport commercial hub operations • Hotel (being built) arrivals / departure • Main taxi pick up (arrivals) northbound exit • Premium parking access and exit • Access to main fire panels and manifolds for emergency services • Premium rental car pick up departure • Cycle parking and pedestrian access to hotel, car parking, and bus transport hub and

northern pedestrian exit to city. • Large vehicle access / escape route • Underground services routes (including a rising sewer main to Moa Point treatment

plant for the entire Miramar peninsular, 20,000+ houses, to be relocated) • Changes in level an transition between the domestic arrivals terminal, existing carpark,

and the significant height difference of the new carpark (which accommodates a rapid bus transport hub)

The convergence of traffic routes at the ground level and critical horizontal infrastructure for the Airport and community was a significant constraint on where columns could be placed and construction staging also contributed to a challenging placement of elements. The key goal to achieving the required outcomes was to provide the western concourse with a clear construction line to work in with the existing exit lane for the concourse. This section of the concourse had to be constructed and in operation before the existing northbound exit ramp critical for maintaining circulation of the airport traffic (but limited options for ground level traffic flows and construction of the western concourse and hotel) could be demolished and the rest of the western concourse could be constructed.

CONSTRUCTION Carpark Building The construction of the superstructure of the car parking building was predominantly precast concrete construction. This form of construction was chosen for the cost effective construction considering speed of erection, quality of concrete finish and minimising site works compared to in-situ construction. The columns between the ground floor to the underside of level 2 were constructed in-situ due to the varying floor level on the first floor making precast only cost effective for beams.

Figure 2: Typical Cross Section of Building

The upper levels utilised precast concrete elements in a form of large single or double cruciform in both directions. This meant that the in-situ joints were placed typically near the mid span of the beams, and the beam-column joints with the BRB gusset connections were cast in a controlled environment at the precast yard. Transportable size and weight including cranage reach were also factors in determining the location of the in-situ joints

Figure 3: Cruciform Units in Construction

The BRB connections were constructed in two different manners based on location. The lower gussets were split into two sections. The vertical section was cast into the column at the precast yard. At the same time drossbachs were placed in the beam section so that the beam plate could be lowered and offered into place. Finally the two plates were welded on site to complete the connection. For the upper gussets, these connections were lifted into place. These connections were into precast units or a combination of precast and in-situ stitch. Where these were cast into precast units drossbachs were placed to allow these to fit and where these were placed in in-situ stitches, reinforcement was placed around the bars and these were poured in with the stitch.

Precast Cruciform Units with In-Situ Joints

In-Situ Columns with Precast Beams

Figure 4: Precast Double Cruciform and Typical Details

Figure 5:Upper Gusset Construction

Following the installation of the gussets BRB units were offered into place. The BRB units were various sized units depending on location with a maximum weight of 6 tonne and were lifted in place using mobile cranes. Connection at the top consisted of a pin which goes through the BRB and gusset. At the bottom the BRB was welded in place with on-site welding.

Figure 6:BRB Units and Gussets

Construction of the carpark building was done in three sections as per the figure below. This was due to limitations in lifting the precast concrete units in place with cranes that are available within New Zealand. On site a 400 tonne Liebherr Crawler Crane with Fly Gib was utilised and was on site for most of the duration of the construction of the car park. The maximum cruciform weight was limited to 24 tonnes for this construction methodology and crane size. The crane was also utilised to lift ramp elements, precast flooring and steel elements. For zones B and C of the construction the central area (3) lagged behind areas 1 and 2. This is to allow for the crawler crane to back out through the site and to allow sections of intra-zonal construction (ie. areas 1 and 2 of zone B were in construction at the same time as zone A).

Figure 7: Construction Sequence of Car Park

1

2

2

2

1B

1

3

3

Zone C Zone A Zone B

Figure 8: Construction of Zone B of Car Park

The ramp structure is also precast concrete with an in-situ concrete stich through the centre of this. These elements were also optimised to allow for the largest sizes that could be transportable and craned into place with cranage available in New Zealand. The precast units were supported on beams allowing for the gap between precast units to act as a seismic movement joint at mid-height of the storey.

Figure 9: Typical Cross Section of Ramp

Figure 10: Ramp Construction

Concourse The construction of the single storey concourse consists of in-situ columns with precast concrete beams connected with in situ stitches. This construction is similar to what has been done for the carpark building. Again the use of precast was done for speed of erection, quality of concrete finish and minimising site works compared to in-situ construction. Due to the varying slope of the concourse construction columns were in-situ elements.

Figure 11: Typical Concourse Cross Section

Sequencing of the construction of the concourse was an important aspect for the client as commercial transportation routes and public vehicle access had to be maintained throughout the construction. This directly affected the construction of the western section of the concourse as this overlapped with the existing exit ramp. This area was broken up into several sections with the construction of the area adjacent to the carpark initially. Once construction of this area was complete it enabled the changeover of traffic, on the ground and first floor, to the new section of concourse. This also allowed the existing exit ramp to be demolished and contractor’s access to this area to complete construction of the western section of the concourse.

Figure 12: Construction Staging for Northern Concourse

The project was completed in Revit with a full federated BIM modelling approach and execution plan being implemented down to the level of modelling that included every building precast element and insitu concrete stitch. (This was approximately L.O.D 350) The BIM modelling was utilised to inform and develop the construction and staging methodology along with all other discipline inputs. The process of model federation and critical staging review was led by the project Architect, Archaus Architects Ltd.

Figure 13: Construction of Western Concourse

The northern concourse section was also constructed in stages. This was primarily due to the space required to allow for the crawler crane to operate and complete section 3 of the car parking building. This area was split into two sections before finally being connected through the centre.

Figure 14:Construction of Northern Concourse

CONCLUSION The construction of the new reinforced concrete 10 storey car parking building and concourse structures at Wellington International Airport has recently been completed. The use of reinforced concrete was driven by the client need for a robust and easily maintained infrastructure in a challenging environment.

The layout, form and methodology for the Precast construction was chosen to provide cost effective construction, speed of erection, quality of concrete finish and the ability to minimise site works in a challenging and constrained site that had to remain operational while in construction. Significant early contractor involvement and collaboration with Fletcher Construction and the design team (WSP-Opus, Archaus, Traffic Design Group, Beca Civil) resulted in these key construction methodologies implanted into the overall design. The overall result was an outstanding outcome for the Wellington Airport with robust, durable, and easily maintained infrastructure asset, critical for the long term future Wellington Airport expansion plans provided with the least disruption to existing operations.