Client: HF Development
One of Glasgow’s most prominent city centre projects in recent years has been HFD Property Group’s 122 Waterloo Street, a nine-storey commercial development pre-let to Morgan Stanley. The building forms the first phase of the Bothwell Exchange that will include a second building on the northern section of the site.
Located within Glasgow’s Central Business District, 122 Waterloo Street provides 13,900m2 of space over the basement, ground and the eight open-plan upper floors, all of which can extend to circa 1,700m2.
As with most high profile, modern and desirable commercial schemes, 122 Waterloo Street has long clear-free spans on all floors. The requirement for clear-spans was one of the main reasons for choosing a steel frame as the use of steelwork has aided in achieving the long, flexible spans with no internal columns, while the use of cellular beams has integrated the services within the structural floor zones, removing the need to increase the height of the building.
A series of 17.25m long UB sections, spaced at 6m centres, form the office floorplates. For the required efficiency and to accommodate the buildings services within the structural void. BHC fabricated service penetrations into these long-span beams. To further maximise the column-free office space, the structure’s three precast cores were offset along the north elevation, instead of being placed in a more traditional position towards the centre of the building.
Adding some extra useable space to the upper floors is a 1.5m wide cantilever along the main south elevation overlooking Waterloo Street that extends upwards from the second floor. Working in conjunction with the core, the cantilevering façade has portalised connections for added stability, forming a rigid frame along this entire elevation.
BHC erected the steelwork using the site’s two tower cranes, with the heaviest steel lift being two 9tonne columns that extend upwards from the basement to the first floor. Many of the loads from the building’s cantilever are directed down to the foundations via these two columns that are positioned either side of the cores.
In addition to the supply and fabrication of the structural steelwork, BHC also supplied and installed the precast elements for the cores together with the metal decking.
To help speed up the erection process and allow the other follow-on trades to get started as soon as possible, the project team devised a sequential construction programme. This has initially involved BHC erecting the steelwork for the entire building footprint up to the second splice level located at floor five. Once this level was reached the metal decking was immediately installed and the floor cast provided a safe working platform for the steel erection to continue for the uppermost levels.
BHC then commenced erecting the steel from level five, while below work was simultaneously ongoing to install the first-floor slab. Once complete, the first-floor slab acted as a crash deck allowing work to be completed on the basement and ground floors, as work also simultaneously progressed above on the second, third and fourth floors.
Creating an architectural top to the building, the roof level is surrounded by what the team would describe as “crown detail”. Formed by a series of columns spaced at 6m centres this steelwork is not connected to the main steel frame but is instead bolted to the concrete upstands as this provides better waterproofing. The 4m-high columns are all connected by secondary members and support a black powered coated aluminium cladding system.