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Contractors World 2010 Volume 1 Issue 4
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[United Kingdom - Innovative Solutions to Overcome Challenges at Nuclear Facility . . .cont]
No cranage for formwork system
Caption: Close up of DOKA Climbing Shuttering System SKE 50
So evaluation of an alternative solution was carried out and, for this particular project, the Doka self-climbing formwork system is being used. Normally such systems are only used for high-rise applications, but it is proving very successful in this unusual situation where cranage is not a viable option.
The Doka SKE 50 plus self-climbing system features a suspended platform with maximum bracket load of 50 kN lifting capacity. The formwork shutting is made up of Doka Top 50, H20 timber beams and WS10 walings. It is designed for a maximum full hydrostatic concrete pressure of 106 kN/m².
A feature of the Doka self-climbing system is the ability to climb at a rate of 5 minutes per meter regardless of the number of platforms being raised at the same time.
Apart from the formwork climbing system meeting construction requirements; another reason for selecting the Austrian company Doka was because of their customer support services.
They are providing all of the design as well as training in Austria for 6 supervisors and making available on-site supervision as required.
Each pour is planned independently of the others. There are 14 platforms on one face, 16 on another and 19 on the third.
The fourth face is left open to provide access for installing various modules at a later date.
With the material handling and lifting solution in place, the challenges did not get any easier. As Beth Willoughby explained,
“The formwork is very complicated as there are many cast-in items – up to 200 or more - some of which required an intermediary pour to create a necessary plinth. “ Typical cast-in items are steel inserts and steel boxes.
Four week formwork cycle time
There will be a total of seven 4m lifts during the construction and cycle time is approximately 4 weeks. With the shuttering system jacked into position, there is a two-three day safety inspection to ensure the integrity of the system and safety of workers.
It takes anything up to three weeks to install the reinforcing steel and cast-in items. The reinforcing cages have to be built in-situ, there being insufficient space or crane capacity to be able to pre-assemble these as would usually be the case.
Two teams of steel fixers worked around the clock – eighteen during the day and ten at night when only one crane is used. The walls are heavily reinforced. So tight are the restrictions for the wall construction that the steel wall boxes are installed to tolerances of ±2 mm.
With the steel work and in-sets in place, there is another week to secure the shuttering, which then also has to be thoroughly inspected. Only once approved can the typical pour of 250 m³ take place. Concrete is being produced on site and Putzmeister M42 concrete pumps are hired in from UK concrete pump hirer, Pochin, who have a depot at Egremont, 8 km from the site.
The Putzmeister M42, mounted on an 8-wheel Mercedes truck, has an output of up to 140 m³/hour and delivery pressures up to 112 bar. These 4 folding arm type pumps are capable of 41.9 m height and 38 m gross horizontal reach. Conventional concrete is used together with plastisizers anti-cracking and anti-corrosive additives.
The finished surface has to be to F2 quality although there will be little exposed concrete. The inside walls are lined in part with stainless steel into which massive processing modules will be installed when the main structural works are completed. The outside walls will be virtually covered by the network of pipes.
Beth Willoughby said that, after the concrete has cured, the shuttering is retracted by 1 m giving easy access for steel fixers when jacked up. This is significantly more space than with conventional systems.
Caption: Aerial view of Evaporator D taken from the cab of the Self Erecting Tower Crane,
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Publisher: Roger Lindley
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