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Doka formwork systems shape-up to the challenge of Y-columns, irregular floor plans and windy conditions on mixed-use development in the heart of Manchester.
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A combination of Doka’s Guided Climbing System, Dokaflex tables and custom-made, pre-assembled formwork is helping John Doyle Construction to make good progress on the first major development in the Greengate area of Manchester city centre.
Spectrum is a mixed-use development of residential, retail and office space by Isle of Man-based developer Dandara Ltd. The first phase includes the construction of four residential blocks, ranging from four to 13 storeys high and containing a total of 350 one- and two-bedroom apartments.
Block 1 has six floors, with up to 3942m2 of available space on each level. Blocks 3 and 5, the two main blocks, offer just over 5000m2 on the podium, rising to 5220m2 on level one and then 6338m2 on the remaining 10 storeys. Block 6 provides 1572m2 of residential space on each of its six storeys.
The buildings, which have podium-level courtyard gardens and full height glazing, are a standard core and post tensioned slab construction. There are, however, some challenging aspects for main contractor John Doyle Construction to deal with.
Block 1 has a triangular shaped floor plan, while a key feature at the entrances of Blocks 3 and 5 are four, Y-shaped, fair face concrete columns, each measuring three storeys tall.
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To achieve the irregular slab shapes, John Doyle Construction is using Dokaflex tables with modified tables at the corners of the building and standard Dokaflex for the infill areas. Dokaflex tables are quick to move and easy to adjust, making them ideal for large-scale decking jobs. To further speed up the operation and reduce crane requirements, John Doyle has also opted for Doka’s table hoist system. This enables the assembled table sections to be raised to the next level without the need for a crane. The modified tables provide additional safety.
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For the Y-columns, Doka designed special formwork shutters, which were preassembled and delivered to the site ready-to-use. Each column is 8m high, has a central stem measuring 800mm square, and an overall width of 5.5m. They are poured in two sections using self-compacting concrete.
“The self-compacting-concrete is ideal for complex shapes, fair-face work and applications where it is physically impossible to use vibrating equipment,” explains project manager Luca Amitrano.
“The basic mixture is the same as conventional concrete but there is a special admixture that increases the flow and prevents the fines and aggregates from segregating.”
“It comes out like normal concrete but then suddenly settles like tomato ketchup.”
He adds, “Pouring rates are the same as for conventional concrete, and are determined by the shutter pressure.
“At the start of each pour, a technician from the supplier did a spread check to ensure the viscosity was correct.
“Because of the highly fluid nature of the mixture, it is important to have tight joints on the formwork.”
“It is also essential to have a continuous supply of the concrete. If the duration between batches is too long, the top layer develops a film and this creates a visible joint between the batches and a possible weak point in the structure.”
C60 self-compacting-concrete can reach the same strength as conventional C60 concrete in about 7-10 days, reaching full strength of about 100 N/mm² in 28 days.
On Blocks 3 and 5, the main contractor has a combination of standard rectangular Dokaflex tables and Aluxo support towers up to 8m high.
The Aluxo system provides support for the 1300mm thick transfer slab on level 2 of Blocks 3 and 5. It is also used to support the pre-cast balconies that run the full length of both blocks and come in on level 2. Once the slab has been constructed and the balconies securely fixed, the Aluxo is replaced with Dokaflex tables. These are set on the balconies at this level to construct the level above. The table layout then remains the same for subsequent pours.
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The cores are being built simultaneously using Doka’s Guided Climbing System (GCS) and Framax panels. As with the table hoists, GCS reduces crane usage, making the project less reliant on weather conditions.
Suspension points along the completed section of the structure guide the external climbing platforms during lifting operations, enabling John Doyle Construction to reposition the entire formwork unit quickly and safely with a single crane lift. Work can also continue in wind speeds of up to 44 mph because the formwork remains anchored to the structure at all times.
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The core formwork includes Doka’s Framax stripping corners. These significantly speeds up the striking of formwork in shafts by eliminating the need to dismantle the formwork between each pour. A spindle mechanism, operated from the top of each corner, draws the corner in on itself, leaving a gap of about 60mm between the formwork panels and the poured concrete. The entire shaft formwork, including the internal shaft platform, is then lifted as a single unit, reducing considerably the number of crane lifts and labour costs compared to other systems.
On average, John Doyle Construction is achieving six-day cycles on cores and two weeks for the slabs, which is their required cycle time.
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“These systems allowed us to continue working when the weather conditions made it impossible to use the crane,” says project manager Luca Amitrano.
He adds, “GCS provides an extremely wide platform which allows safe and unhindered access to wall formwork.
“The service from Doka was very good. Technical support was excellent and there was good detail on the drawings. They also responded rapidly to design changes on the core walls and the Y-columns.”
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| The cores are being built simultaneously using Doka’s Guided Climbing System (GCS) and Framax panels. GCS reduces crane usage, making the project less reliant on weather conditions. |
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| Spectrum is a mixed-use development of residential, retail and office space by Isle of Man-based developer Dandara Ltd. A combination of Doka’s Guided Climbing System, Dokaflex tables and custom-made, pre-assembled formwork is helping John Doyle Construction to make good progress on the first major development in the Greengate area of Manchester city centre. |
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