August_1966 — Page 78

Bollmora

project.

Heavy-duty tower crane is a feature of most building systems

SKARNE

HEAVY

AN

Nadvantage claimed for the heavy construction system de- veloped by Ohlsson & Škarne, of Stockholm, is that it offers the archi- tect a free choice of facades and so eliminates an over-uniform and cell- like appearance.

In the Skarne heavy system, as in light construction systems, the interior wall elements are load bearing and the external walls are merely cladding units. Hoisting machinery able to take loads of up to 12 tons is requir- ed. For multi-storey blocks tower on tracks are used, and for four-storey blocks, gantry cranes mobile cranes.

cranes

or

Another advantage of the heavy system is the reduction in the number of joints, since wall and floor slab ele- ments are of room-size. This allows simpler finishing operations as there are no visible joints in the room and no marks of joints left in the floor panels. The erection of large-sized elements takes no longer than small- er units and they can be manufactured to the same tolerances.

By the Skarne system the inner walls are mounted first, followed by the slabs. Thereafter the outer walls are set, usually by a special gang working independently of those mounting the concrete elements. From the ground beams to the roof all is prefabricated and there is no in situ casting.

Example

An example of the Skarne heavy system is the Bollmora project, near Stockholm, where 1,000 flats have

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been erected in eight and nine-storey blocks.

The element factory was а de- mountable steel construction, contain- ing the batch tower, one bay for the battery of wall moulds and another bay for the floor slabs. In this fac- tory the slabs were cast horizontally on concrete moulds. Nowadays ver- tical casting and steel moulds are normal.

The walls are cast in vertical steel moulds, transported vertically and of course mounted vertically too. They need no reinforcement, except for some transport devices.

In the same factory special ele- ments for garbage chute, sanitary channels and the like were produced. Battery casting makes steam-curing unnecessary. The day after casting. the mould is opened and the elements are moved into storage, where they remain for at least three weeks to cure.

Inner walls and floors were erected by tower cranes on tracks. The cranes had a capacity of 200 ton- meters, i.e. the crane could take a load of 12 tons at a radius of 15 metres.

External walls consist of a Siporex sandwich construction with two lay- ers of lightweight concrete and an in- termediary layer of polystyrene foam plastic. These outer wall elements were prefabricated in Siporex factor- ies and delivered fully treated to the site.

They are one-storey high and have a width of 50 cm.

The external walls could also have been constructed with room-sized timber studding, or insulated concrete elements having a prefinished exterior surface of exposed crushed marble. In

all these cases, the coefficient of heat transfer is extremely low, from 0.25 to 0.3 (Swedish standard) and they have a fully finished surface which needs no after treatment. Elements. 50 cm. wide are mounted with the aid of a small crane, capacity 2 ton-metres. This crane is put into operation when the floor elements above are placed on the load-bearing walls. Mov- ing the small crane is very simple the big crane takes it by the neck and places it at the required position.

Spray Plastering

A block is roofed as quickly as pos- sible and as soon as a storey has got its outer wall, the fully painted and glazed windows are set in order to as- sure full protection for the immediate start of the interior work.

The concrete surfaces are ideal for spray-plastering treatment. Walls to he papered need only an additional patching at air bubbles and joints, and walls to be painted are spray-plastered twice to give them a suitable surface for colour application by roller. Ceil- ings are treated with the same plaster in a textured structure.

After papering or painting, the per- manent fittings are screwed into posi- tion. Doors and door frames are fit- ted after the papering. Ready-painted skirtings and base boards are fitted at the same time as the kitchen joinery. The parquet floor is coated with thermo-setting plastic before delivery. Lacquered aluminium architraves are provided around the doors. Galvanis ed, forged balcony railings, external aluminium window sills, and other features that require little mainten-

Far East Architect & Builder August, 1966