Obel Tower, Belfast The use of a crane-independent formwork solution helps the Karl Group to meet its tight construction schedule at Belfast’s tallest building. The construction team at the 28-floor Obel Tower at Donegall Quay in Belfast have to progress the build at the rate of one 600 m² floor fully cast per week of build time. According to the project team, meeting such a tight deadline is the single most important prerequisite for compliance with the tight construction schedule at the site. Lead contractor on the Obel Tower project is O´Hare & McGovern Ltd. Meanwhile, Fernwave Ireland Ltd, which is in charge of CIP concreting, has opted for a single-source formwork solution from Doka. Extraordinary in its architecture, the Obel Tower is also a challenging build in many ways on account of the difficult boundary conditions, according to the project team. Space is at a premium on the site, which is bordered by a six-lane urban motorway, an elevated railway and the Lagan River itself. Just one slewing tower crane can be accommodated at the site at a time and the solution for formwork lifts has to be totally crane-independent. Planning for the formwork on this build had to be detailed and trimmed for maximum efficiency, with every allowance made for the extremely limited crane capacity. As a result, Doka Ireland was commissioned to supply the complete formwork solution for all the CIP concreting. "We are using automatic climbers for the CIP core and the Table Lifting System TLS for crane-independent lifts of the Doka tables, so we can successfully deal with both those key challenges – limited craneage and the one-week cycle for the deck slabs," asserts Ronan McHugh, Fernwave’s Project Manager.

The central structure core is being climbed with 22 high-capability Doka SKE 50 automatic climbing brackets.

The Xclimb 60 protection shield ensures maximum safety at the top four floors.

The lead contractor has also opted to use the Xclimb 60 protection shield to maintain safety standards. As the building rises, the slab edges of the top four floors are constantly protected inside a full enclosure and everyone inside is shielded against the weather. The shield also has to be climbed as rapidly as possible as soon as forming work is completed, so the engineers from Doka Ireland allowed for a second platform level for the follow-on work on the CIP slabs.

Climbing 80 metres in a weekly cycle The central CIP core of the building is being climbed with 22 of the high-end, high-capability Doka SKE 50 automatic climbing brackets. To keep setup times short and help minimise the complexity of on-site logistics, the working platforms for the climbers and 250 m² of Doka beam formwork were delivered to site on a JIT rota. The potential of the automatic climbing formwork had to be exploited to the full right from the word go, so an experienced site foreman from Doka familiarised the people from Fernwave with the most efficient work routines and supervised final assembly. “The assistance we had from the Doka site foreman was extremely important in terms of enabling us to meet schedule on the weekly cycle for the CIP core. The standard height is 2.8 metres, and we are able to form up, set the reinforcement, and cast the concrete within two or three days with only two men,” explains Mr McHugh. The SKE 50 climbers are able to deal with changes in cross-section, so the two reductions in wall thickness between floors ten and twenty are easily handled without time-consuming modifications, he added. The shaft formwork has to be quick-lifted, so the top 50 panels are combined with Framax stripping corner I to form lift-out formwork boxes. The stripping corner I units enable each of the beam-formwork panel assemblies to be backed off quickly from the concrete, so the shaft formwork can be lifted up into position for the next pour without any further disassembly. The formwork for the lift shafts is climbing with SKE 50 plus automatic climbers fitted up with a central climber section. Seven SKE 50 automatic climbing formwork brackets are in use on the central stairwell shaft, carrying not only the wall formwork but also a concrete pump distributor up from floor to floor as progress on the high-rise continues. The floor slabs have a 600 m², sickle-shaped footprint and are being formed by the Fernwave site crew with 150 identical Dokaflex special tables. This approach ensures optimum adaptability of the floor-slab formwork to the unique floorplan with no need for the large adapter panels that would otherwise take a great deal of time to prepare. Crane capacity is extremely limited and ideally, floor-slab forming should be crane-independent, so the tables are being lifted from level to level with two TLS table lifting systems. “It’s very much on account of the fact that we are using these two TLS units that we’ve been able to maintain this tight weekly cycle right through this phase of the build. The TLS units keep our shifting times short and allow us to reap the benefit of continuous and speedy workflows,” Mr McHugh added.