New Zealand Engineering 1999 March

Construction

Cleared for Take-Off!

Business as usual
Structural engineering considerations
Building services considerations

The Wellington Airport Terminal redevelopment is close to completion and going through the final stages of its $90 million transformation into a world class airport. To keep the facility operational for its users throughout construction, the project team faced their share of challenges. Beca principals David Whittaker and Keith Paterson highlight some of the complexities of the job.

There may be some users of Wellington airport who will feel a touch of nostalgia when the demolition ball crashes through the old domestic passenger terminal. Many others, however, will look forward to a modern and convenient terminal with new and expanded facilities.

Wellington International Airport Ltd (WIAL) had a brief to redevelop terminal facilities to handle the growing passenger and aircraft numbers up to the year 2011. Over this period passenger numbers are expected to increase from 3� million per year to 6 million per year. Hardly any of the existing buildings or surrounding area will be left untouched, and the redevelopment features a new 20,000 m2 multi-user terminal, the first of its kind in Australasia, with commuter, national and international airlines sharing the facilities.

Departing passengers will check in on the first floor which is accessible from the new elevated roadway. Other facilities on Level 1 are ticketing, a range of retail outlets, extensive food and beverage services, and other lounge areas. Passengers arrive at Level 1 too, and can leave directly or drop to the ground level to reclaim baggage and then gain direct access to taxis, shuttles, etc.

In addition to the new main terminal building, extensive construction activity has taken place in the existing international passenger terminal and on the Southwest Pier where domestic gate lounges and club lounges have been built.

Optimal use of the plan area and volume of the new main terminal was essential to allow it to be constructed in one stage between the existing buildings. Strategies for expansion have been considered carefully for each aspect of the function of the building.

The redevelopment had its beginnings in 1995 when Beca Carter Hollings & Ferner Ltd and Airplan New Zealand Ltd, with assistance from Craig Craig Moller as architects and Rider Hunt as quantity surveyors, were commissioned to prepare a Terminal Area Development Concept Report, which formed the basis of the current redevelopment.

With commencement of construction in 1996, the past three years have seen a flurry of activity which has provided its share of challenges for all involved, in particular because the work had to be carried out amidst a fully operational airport.

This article outlines some of the engineering challenges faced by the design team.

Business as usual

From the outset, the overriding requirement for the project team was to maintain the terminal fully operational with minimum disruption to operations and the travelling public during the entire construction period. The construction activity, therefore, was planned with sufficient flexibility to handle changing requirements of airlines, government agencies, aviation security, retailers, and others operating at the airport.

The need for flexibility, multistaging and commercial risk control suggested a series of about 35 lump sum packages as the appropriate method of engaging contractors to construct the works. The detailed planning associated with the packaging of the work was driven primarily by the need to continue operations at the airport. This required extensive input from WIAL, the tenants, the designers and, in some cases, the contractors.

All building contracts have been awarded to Mainzeal and civil contracts to Higgins and Fulton Hogan. Separate direct contracts were awarded to Glidepath and Airport Engineering Ltd for baggage handling and airbridges.

Other drivers such as the need for civil works to be completed during summer, airline schedules and leasing obligations, meant that there was a further dimension to the considerations of the designers and planners.

Key decisions about the construction sequencing were made between WIAL’s project manager and the Beca led design team. As the puzzle unfolded, regular reviews of cost and extensive temporary works were required to ensure that the overall financial state of the project was in good health and the safety of the travelling public maintained.

Structural engineering considerations
The principal requirements of the structural engineering solutions were cost effectiveness, simplicity and ease of installation. Wherever possible, existing structure was retained or strengthened in order to minimise cost.

In respect of the structural concrete elements, a series of interactive meetings with the contractor during the design period enabled buildability considerations to be prominent in the design, yielding savings in time to construct and therefore cost.

For the major free-spanning room structure, the architect and Beca Buildings structural engineer David Whittaker chose a large column-free space for both check-in hall and the food and beverage area.

The seismic resisting system is a moment frame in one direction and a braced box supported on cantilever ground floor columns in the other direction. Craig Craig Moller made a feature of the steel bracing members in the large glazed walls on each side of the building.

The structural solution for the new Koru lounge for Air New Zealand on the Southwest Pier was to build over and around the existing operating building with new structure to create gate lounges and the club lounge above. The piecewise construction enabled Air New Zealand to continue to operate out of the Southwest Pier with minimal disruption to its passengers. The resulting views from the enlarged pier are spectacular.

The Main Terminal building structural component was finished six weeks ahead of a tight programme and this enabled advancement of other construction activities and an overall improvement to the completion date.

Building services considerations
The series of lump sum contract packages challenged the Beca Building Services team as to how the sitewide systems could be designed and specified for the entire campus, yet committed on a partial basis.

Little or no documentation of underground services and critical distribution systems throughout existing buildings meant that investigation was required before sensible building services strategies and outcomes could be developed.

To gain familiarity with the existing systems, several months were spent opening up and surveying these services to piece together a more complete picture. While this was a time consuming exercise, it has been of considerable value to both the designers and the contractors, and provided a higher level of certainty in planning and construction sequencing. The consequences of any unscheduled outage are too great to risk. A sub-strategy for the sitewide services packages was developed which involved documentation of complete sitewide services and calling tenders competitively for the complete package. As the smaller packages of construction work were designed in detail, portions of the preferred supplier for sitewide services systems were then redocumented into the individual construction packages. This strategy enabled a competitive tender for the entire scope of work to be obtained. A close liaison between specifying engineers and vendors enabled detailed planning for the new systems to operate progressively as the construction packages are completed.

Other technical design decisions were taken in close consultation with WIAL. Such things as the extent of systems backed up by emergency power, and the extent and performance of airconditioning systems, were tailored to suit the commercial imperatives of WIAL. In regard to airconditioning, transient spaces with minimal heat loads were not airconditioned at all, simply mechanically or naturally ventilated. The commuter lounge at the south end of the redevelopment is mechanically ventilated and heated, not airconditioned.

Central plant for airconditioning chillers and heating boilers have been located at the existing main plant room which served the original international terminal, in order to utilise as much of the existing infrastructure as possible.

In summary, the technical challenges are many but to date they have been overcome by the teamwork of WIAL, the contractors, consultants and airport stakeholders. When the project is complete, no part of the old terminal area will remain. The new terminal and all the associated facilities: new or enlarged and refurbished piers and aprons; new roading systems and carparks; will be there for all to enjoy. Of great significance to this project has been the contribution from client, stakeholders, designers and builders alike. There is high anticipation in Wellington for the completion of this landmark project.

David Whittaker and Keith Paterson are principals in Beca Buildings - a business line of Beca Carter Hollings & Ferner Ltd.