Azerbaijan's Flame Towers - complex cores in a single casting

The skyline of Azerbaijan's capital, the oil-rich Baku, will be changed dramatically by the striking HOK-designed Flame Towers development. When complete their dramatic shape and fiery orange facades will dominate the Bay of Baku and the historic city centre.

With a design inspired by Azerbaijan’s tradition of fire worship, the Flame Towers, a DIA Holding project, is being constructed on a 28000 m² site on a common podium, which when complete will accommodate a three-level parking garage and shopping mall.

Each tower will have a different role; one will be a residential high-rise, one an office tower, and the third a hotel.

The signature tower is the 165 m-high, 39 storey apartment building, which is located at the southern end of the complex with breathtaking views of the Caspian Sea. The northern-most tower, the 143 m-high hotel tower, will have 228 hotel rooms and 61 suites, while the 150 m-high western tower will have more than 35000 m² of office area.

The geometries involved are exceptional. Constantly changing floor heights, up to 8 m, and added structural strength thanks to a large number of bottom joists cast alongside the floor slabs, combine with a slender core for an extremely challenging project.

The cores contain a large number of lift shafts, some extremely narrow, and all of which have to be concreted in a single cast. This is because the reinforcing is exceptionally closely spaced, making it uneconomical to install rebar connections for a second-fix casting for the walls.

Another problem was the areas unpredictable winds, which gust in off the Caspian Sea, and extremely limited crane capacity.

Core cross-section

To complete the cores formwork manufacturer Doka's engineers are using a total of 182 SKE 50 and 8 SKE 100 automatic climbing systems to carry about 4000 m² of Top 50 beam formwork.

Densely packed reinforcing makes it difficult to place the suspension cones, which is where the SKE 50 "really comes into its own", according to a DIA spokesman, because it needs only one suspension cone per section.

Another factor to the SKE 50's success has been use of its 50 kN per cylinder load-bearing capacity in the narrow shafts. According to Doka, climbing systems beefed up to a higher rating would be off-scale on this build and uneconomical on account of the higher price.

The individual climbing brackets are set up as standing scaffolds with suspended formwork (a gallows-type configuration). This means that over the entire core of the building the highest platform level is a completely planked and fully accessible floor area.

Another advantage is that the platform means the rebar to be set for the next section serves as a set-down for material that is then climbed along with the rest of the gear. Once the entire core cross-section has been concreted, the formwork climbs hydraulically to the next concreting section, taking 5 minutes for each metre climbed.

One hydraulic unit can move as many as 20 rams, so multiple platform units are climbed simultaneously. All of which helps keep progress on schedule because there is just one crane per tower and all three are in constant use moving materials.

Baku's fiercely gusting winds mean the system's crane independence pays off in two ways. The climbing formwork is anchored to the structure at all times and can be moved safely and quickly even when the wind is gusting at 72 km per hour.

Fast and strong

Doka also supplied its steel d2 load-bearing scaffold for propping the floor slabs and heavy bottom joists.

In the office tower it is being used to prop a foyer with a ceiling height of 25 m. Speedy setup and straightforward height adjustment in a 300 mm grid make the job fast and cost effective.

The frame system is also strong and stable, making it suitable to withstand horizontal forces, such as the loads from the tearing winds off the Caspian Sea.