Project: Enlarging and re-enforcing the existing columns and pouring new ones for an underground flood control basin, Bern, Switzerland
Contractor: Ramseier Bauunternehmung AG, Bern
Owner: City of Bern
MEVA Solution: Circo half shells mounted on carriages for manual transport, Special wooden formwork to pour the starters
Engineering and support: MEVA Formwork Systems, Seon (Switzerland) and Haiterbach (Germany)
The underground flood control basin in Bern‘s city centre was built over 40 years ago. Inside the 7 m high basin hall, 14 square columns carry the basin’s roof. As the high groundwater exerted more and more pressure against the basin’s base slab, there was risk of the slab being lifted and the columns punching through it. To prevent this from happening, the 60 cm square columns were re-enforced with concrete, turning them into circular columns with a diameter of 1.10 m. In addition to re-enforcing the columns, more earth and gravel will be put onto the roof to increase the load and act against the hydrostatic uplift. This in turn will increase the pressure on the existing columns at both ends, and re-enforcing them was the only way to stabilise the basin to allow further use.
High performance and low weight
As the poured concrete could not be compacted with vibrators, SCC concrete had to be used, although it develops a high fresh concrete pressure. In addtion, pouring had to be done from below, meaning that during the pour the concrete was constantly moving up to a height of 7 m with no chance to control the rate of pouring. All this left no other choice but to use a highperformance steel formwork capable of handling high concrete pressure. Another crucial parameter for the formwork selection was low weight. The complete formwork had to be moved manually, as no crane could be used to assemble, disassemble or move it. Nor was it possible to use an electrical jack or other device to move the formwork. No electrical equipment was permitted underground to avoid short circuits in case of sudden flooding.
“No other provider can offer such a light steel formwork for circular columns“, said the contractor’s deputy chief executive Remo Brunner when asked why he chose MEVA’s Circo circular column formwork for this underground job. The Circo steel formwork is not only light but also handles fresh concrete pressure loads of up to 120 kN/ m².
A mobile carriage ...
How to move the formwork manually? The MEVA engineers developed a set of two carriages. Circo half shells are firmly mounted to each carriage in full pouring height. When a column is complete and the concrete has set, the shells are opened and retracted, wheeled to the next column, positioned, precisely adjusted and closed again for the next pour. All work is done manually and the weight per carriage including formwork and accessories allows the units to be manually wheeled over the slightly inclined base slab.
... with 2 functions in 1
Equipped with spindles to lower and elevate the wheels, each carriage fulfils a double function: With the wheels on the floor, the carriage serves for transport. With the wheels in the air, each carriage sits firmly on the floor holding the formwork tight and transferring the high concrete pressure to the ground.
“A column per day, with only 2 workers instead of 3“
Remo Brunner and foreman Kay Boss are enthusiastic about the MEVA solution, which is so smooth that the project requires less staff than they had planned. They coated all 14 columns and poured two new circular columns using only one Circo unit and benefitting from the special carriage solution with time and labour savings.
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