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CLASSIFICATION OF INDUSTRIALISED CONSTRUCTION

By Barry Long,2014-01-04 18:32
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CLASSIFICATION OF INDUSTRIALISED CONSTRUCTION

FIGURE 9. Arrangement of tie beams.

    Earthquake: South-east Europe, the Balkans, Turkey, Cyprus and the Kafkas region are on an earthquake belt and very frequently experience earthquake disasters. Thus it is very important that the construction systems are safe in respect to earthquakes. Earthquakes are graded with numbers up to 12. Earthquakes with 5 6 forces may cause minor defects

    on buildings. However 7 9 forces may cause complete destruction

    depending on the strength of the buildings. The destruction lessens as the distance to the centre of the earthquake increases.

    Earthquake precautions should be considered not only on the buildings themselves but also on the areas around buildings. Street width, distance between the buildings and the green areas should also be considered from the point of earthquake security.

    If the building plan is too complex it may be divided into simpler forms by earthquake joints (Figure 8). Actually, not only the building plan but also the section, structure and the mass should be solved regularly without excessive openings, cavities or overhangs in earthquake areas.

    In skeleton building systems the lower parts of the columns above the foundations should be connected to each other with tie beams (Figure 9). Special care should be given to the connection systems of prefabricated columns, beams, floor and wall components.

    In load bearing building systems there should be cross walls whose spans do not exceed the levels given by the “Earthquake Guide”. There should not be any opening less than 1.5 m distance to the corners of the building.

    It is necessary to define the terms “building material”, “building component” and “building element” here. Building materials are

    shapeless materials like cement, sand, steel, timber etc. When a building

material is formed as a distinct unit with a shape, it is called “building

    component”. Thus a brick, a steel profile or a door is a building component. Building components can be of three types; “profile building

    component”, “unit building component” and “composite building

    component”. Each part of a building with special function like wall, floor, roof, foundation is called “building element”.

CLASSIFICATION OF INDUSTRIALISED CONSTRUCTION

    Industrialised construction systems can be classified according to various characteristics. One of the classifications depends on whether the elements cast in situ or of prefabricated units.

    A) Wet Systems: Wet systems are those which are produced by

    casting the elements to the moulds on building.

    B) Dry Systems: Dry systems are those which are produced by the

    assembly of prefabricated units without the use of any liquid type

    jointing material.

    The second classification depends on the degree of industrialisation. A) Developed Traditional Construction Systems: In these systems

     industrialisation principles are applied to traditional construction

     systems. Like tunnel formwork, sliding formwork, slab lifting etc. B) Semi Industrialised Construction Systems: The elements are

     produced on site or at temporary workshops.

    C) Fully Industrialised Construction Systems: In these systems all

     the units are produced at the factory and assembled on site.

    A third classification depends on the weights of the building components and elements.

    A) Heavy Industrialised Construction Systems: In these systems

    units are heavy and large like floor or wall panels.

    B) Light Industrialised Construction Systems: In these systems

     components are made of small and light units.

    A fourth classification depends on whether the building components are interchangeable or not.

    A) Closed Industrialised Construction Systems: In these systems all

     the components of a particular system are produced by one

     company.

    B) Open Industrialised Construction Systems: In these systems the

    components of a particular system are obtained from different

    companies which utilise the same joint design and which have

    dimensional coordination between each other.

    Another classification is made according to the structural systems of the building. There are also sub systems of this classification (SEY & TAPAN, 1987).

    A) Skeleton Systems: In which the columns and beams carry the

     building load.

     A1) Column-Beam-Floor Systems: In which the building loads are

     conveyed from floor to beam and from there to the columns.

     A2) Frame Systems: In which the structure of the building is composed

     of frames and the floors.

     A3) Column-floor Systems: In which the loads are conveyed directly

     from the floor to the columns.

B) Load Bearing Panel Systems: In these systems wall and floor

     panels carry the building load.

     B1) Large Panel Systems: The sizes of the panels are as large as the

     size of the space they enclose.

     B2) Small Panel Systems: The vertical and the horizontal building

     elements of a space are composed of more then one panel. C) Cellular Systems: In which the building is composed of cell units

     produced at the factory and assembled on site.

     C1) Block Type Cellular Systems:

     C2) Panel Block Type Cellular Systems:

     C3) Skeleton Block Type Cellular Systems:

     Cellular systems can also classified as Open Cellular and Closed

    Cellular Systems. In open cellular construction systems one space is made of more then one cell. In closed cellular construction systems one space is made of one cell only.

TUNNEL FORMWORK CONSTRUCTION SYSTEM

    In tunnel formwork construction system, reinforced concrete is used as the structural building material. The system provides the casting of both the load-bearing walls and the floor under a single process. This is a developed traditional system and it is a wet construction technique (FIG 10). It is a very fast construction technique and it is very suitable for medium high-rise buildings.

    In this system special steel formworks are used. Once the formwork for a storey is set, the reinforced concrete walls and the floor are cast continuously. Thus a building which is monolithic in nature is obtained and it is very durable against horizontal stresses. The system has two variations depending on the type of the tunnel formwork used.

A) Semi-tunnel formwork,

    B) Full tunnel formwork.

    Two semi-tunnel formworks are connected to each other side by side to form a complete tunnel formwork. Both the semi and full tunnel formworks can be connected on ends to form tunnel formworks for deeper rooms (Figures 11 A, B, C, D, E, F). Tunnel formworks are made of 34 mm thick sheet steel, have adjustable and wheeled elements. Tunnel formworks constitute moulds both for the wall and the floor of a building. Additional steel formworks for the side ends of the building and balconies or for working platforms are also used. After assembling the formwork; reinforcement, electrical and the other service pipes are positioned and the concrete is cast. The openings like doors, windows and chimneys are provided by the use of reservation moulds. Generally a curing method is applied for the fast setting of the concrete. Then the formworks are taken out of their position, cleaned, oiled, and positioned for an upper floor.

    The length of the tunnel formworks are 62.5, 125 and 250 cm. By jointing these formworks up to 1250 cm total length can be obtained depending on the lifting capacity of the crane. The widths of the formworks are 105, 135, 165, 195, 225, 255, 285 cm. The widths up to 570 cm can be obtained with the different combinations of these seven sizes. These combinations can provide many different room sizes. The heights of the formworks are between 230 to 300 cm. The average weights of the

    ;formworks are 70 kg per m. A faster construction rate can be achieved

    with the full tunnel formworks. However, cranes with higher load bearing capacity are needed and the cost of the formworks is also high. The cost of formworks is relatively lower of semi-tunnel formworks and more flexible plan types can be used, but assembling and disassembling takes more time.

    Tunnel formworks can be used many times, and it is possible to obtain smooth concrete surfaces each time. Thus, although the initial cost is high it is an economical formwork. It is necessary to provide a place at the site for the assembly of the formworks. Before the assembly the formworks should be cleaned and oiled with a suitable solution.

    No beams are used in this system; instead floor slabs thicker than 12 cm conventional reinforced concrete slabs are used. Generally the floor slab thickness is selected as 1520 cm. Depending on the span width the floor

    plates of the formworks are adjusted to have somewhat curved upward surface. When the formworks are taken out after the setting of the concrete, the slabs become horizontal due to their own loads. The maximum height of the curve from horizontal is 2 mm for 390 cm span, 4 mm for 570 cm span, and 820 mm for spans larger than 570 cm. A

    separate mould is used just above load bearing walls, which is 10 cm in height to form a master for the positioning of the formwork of the above floor (Figure 12).

    The load bearing walls are cast with the floors and have 20 cm thickness. This also provides a good sound insulation. Thermal insulation materials can be inserted to external load bearing walls. Various building components can be used for the other partition walls and for the external walls on the ends of the tunnel. They may be of prefabricated components or may be built on site depending on the construction flow chart. They are built after the removal of a floor’s formworks. Plastering is not needed for the internal surfaces. Since the smooth surfaced steel formworks are used the surfaces can be painted or covered with wallpapers. A thin coat of ready made rendering may be applied to increase the rainwater retarding features of the external surfaces.

    The stairs are generally built by prefabricated reinforced concrete elements either cast on temporary shops at site or at factories.

    In Turkey on the first and second degree earthquake areas up to 12 storeys, on the third degree earthquake areas up to 15 17 storeys and on

fourth degree earthquake areas up to 20 24 storeys of tunnel formwork

    buildings can be constructed.

    Another problem in tunnel formwork construction is the planning of the cranes. The lifting capacity of the crane is selected according to the maximum amount of weight it will lift. Thus for the full tunnel construction systems cranes with higher capacities are needed. Another factor in selection is the height of the building. Up to 5 floors mobile cranes, above this height tower cranes should be used. Tower cranes move on railways and in this case, the site layout should be appropriate to serve all the buildings once the railway for the crane is laid.

     2Normally for a 100 m flat the number of workers necessary are thus; 4 workers for the assembly of the formworks, 3 workers for dismantling of the formworks, 5 workers for setting up of the working platforms, 2 workers for laying the service pipes. Casting of concrete for a flat takes 34 hours. It is possible to complete coarse construction of one flat per day.

Curing:

    Curing is the heating of the formworks so that the concrete sets quickly. The tunnel formworks can be taken out of their position in 24 hours if the curing is done well. Sudden or slow heating gives different results. Sudden heating may result in cracks on the surface of the concrete. During the first 1.5 2.0 hours the temperature must not rise above 50 C,

    and it must not rise above 100 C during the next 5 6 hours. Thus the

    temperature rise per hour should not exceed 15 C. In Turkey curing is

    done mostly by water vapour. In some formworks there are pipes attached for this purpose. Sometimes the cast concrete is covered with a plastic cover and the water vapour is given under it. Yet another method is to cover the ends of the tunnel formworks with plastic curtains and the whole formwork is heated with a suitable heat source. Thus in winter moths 7 hour, and in summer months 4 hours of curing in average is needed.

Design Considerations:

    . Organisation of the space should be done according to the sizes of the

     formworks.

    . Vertical load bearing tunnel walls should be at the same span width

     throughout the building length.

    . The boundaries of the space should preferably, though not necessarily,

     intersect each other in right angles.

    . The main load bearing walls should be parallel to the narrow side of the

     building, and there should be cross load bearing walls as well. . Too much complex building plan effects the rational use of the

     construction system.

    . In site layout the movement of the cranes and the removal of the

     formworks should also be considered. One crane should be able to

     service at least two buildings at a time.

    . The maximum economical span width is 570 cm. It may be extended to

     630 cm with additional formworks.

    . Space heights should be the same for the whole building. . It is preferable to have all the doors at the same sizes. . The flow of the works and the use of the cranes should be carefully

     planned in order to achieve a fast and economical construction.

FIGURE 10. Tunnel formwork construction system.

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