By the year 2040, travellers to Wellington International Airport Limited (WIAL) are expected to double from six million today to 12 million. To prepare for the increase in activity in and around its facilities, WIAL implemented a major redevelopment plan including a new 10-storey car park building and a new hotel, connected to the airport by a network of ramps and elevated road structures – known as the concourse.
We were commissioned to provide structural engineering services for this project. Wellington International Airport is situated on 110 hectares, an extremely small site in comparison to other international airports, which posed challenges to ensuring continuity of services during construction. Other key considerations for the project included a strong seismic focus due to Wellington lying on a major fault line and also the airport’s location which is buffered by strong winds carrying corrosive salt.
OUR APPROACH
We collaborated closely with the project architect to develop a shared vision and strong working relationships to support the project’s success. Our team was tasked with finding a solution that could withstand seismic and environmental forces. While structural steel was the most logical solution, salt exposure from strong winds posed long-term maintenance issues for exposed structure. We proposed an innovative approach that used a hybrid solution and resulted in several New Zealand-first implementations.
OUR SOLUTION
Carpark Building and Concourse
This solution incorporated precast concrete frames and replaceable steel buckling-restrained braces (BRBs) - the combination of lateral systems, a New Zealand first. It solved the issues of high maintenance costs associated with coating systems on steel frames, for both corrosion and fire protection, as well as the identified constraints with using concrete frames in a high seismic area. This was achieved by optimising the solution to accomplish a high level of seismic resilience while minimising maintenance cost at the same time as reducing initial construction costs.
We assessed the ground conditions and concluded that the raft slab foundation with its inherent resilience to liquefaction, coupled with cost effective implementation by avoiding a deep piled solution, was the preferred option. The use of fly ash for the foundation was environmentally friendly, cost effective and assisted with heat of hydration thereby minimising the risk and extent of cracking in the raft slab. We used Building Information Modelling (BIM) to model every pre-cast and in-situ building element to understand the stages of construction at design time, which helped minimize site queries in the building process. This design meant that offsite construction for the carpark building, and concourse was optimised, allowing the construction to be staged appropriately.
The staging of construction was important to managing operational continuity of airport facilities within the extremely constrained site. Customer disruption, which would result in lost revenue in carpark fees, was minimised by restricting significant concrete pours to weekly 11-hour periods during a relatively quiet time at the airport.
Hotel
The hotel site is in a critical position in the Airport site, obstructing loading dock deliveries and rubbish collection services, which are key operational services for the airport. Significant buried services which are critical to the operation of the airport also pass through or close to this part of the site.
Working closely with the client and design team, we developed solutions which minimised disruption. This included ensuring a safe passage on the first floor of the hotel, more discreet foundations given the high number of underground services on site, and screw piles to share seismic loads of the building. It was important that constructability considered the proximity of the site to airside operations, so we developed a structural steelwork solution where off-site fabrication was maximised. We worked closely with the contractor to support off site fabrication and installation of elements of the hotel fit out.
OUTCOME/CLIENT BENEFITS
WIAL is on track to achieving its 2040 masterplan. The project delivered resilient, low maintenance infrastructure with minimal disruption to airport users, ensuring Wellington International Airport continued to operate as a thriving hub amidst the major redevelopment.
