• Client: Gatwick Airport Limited
• Photography: Webb Yates Engineers
• Completion: 2020
• Value: Confidential
• Size: 700 m²
• Expertise: Structures

As part of the ongoing development of the terminal, Gatwick Airport Limited (GAL) proposed to create an additional 700m2 of retail space by extending an existing mezzanine within the International Departures Lounge (IDL), and we were appointed as engineer.

The proposed location was within an extension to the North Terminal, constructed in 2000. While the existing structure is relatively simple, steel framed with composite slabs on metal decking, aspects of the building are significantly more complicated. In addition to the building spanning over an airside road providing access to the baggage hall, part of the building is also supported by columns from an earlier part-demolished building. At IDL level an open concourse was framed by retail units on two sides with a mezzanine level above. It was proposed to extend the mezzanine above the concourse to form the new retail space.

The greatest challenge posed by the project was constructing the new mezzanine within a live airport environment. GAL had been clear from the start that the concourse needed to remain open throughout construction, not only because it provided access to a large number of gates but also because of the number of retail units which would be affected were it to be closed. We worked closely with Balfour Beatty throughout the design process to ensure that this would be possible. The solution proposed was a collaborative design which incorporated modifications that would simplify the construction without compromising the structural integrity.

One of the most difficult aspects was bringing the structural members to site and getting them into position (spanning 28m across the concourse) without impacting the movement of passengers. In order to achieve this the cellular beams were spliced into three, with a secondary beam spanning between them at third points. A section of cladding was removed, and a special scaffold was constructed so that these 9m lengths of steel could be brought to site on the back of lorry and lifted directly from the lorry up to the terminal adjacent to site. During the day a relatively small area within the concourse was hoarded off to provide an area within which to store materials, whereas at night the site could be extended to allow for erection of the steels. The secondary beams at third points were supported on scaffold towers designed to distribute loads to the strongest points on the existing structure below allowing the 9m steels to be wheeled across the terminal and lifted into position using A frames. This meant that during a night shift 2 or 3 steels could be erected before returning the concourse to full use, with passengers passing underneath during the day.

Due to the limited floor zone the deflection of the new structure needed to be limited as far as possible. As the cellular beams were spliced precambering the beams would have been difficult and therefore the splices were designed with some tolerance to allow the structure to be jacked up once in place. The connections were then tightened fully so that the system was erected high, allowing for dead load deflection.