HISTORY

The composite building elements firstly appeared in the 1920s in Japan, where bolted lattice girders and bolted columns of angular cross-sections were encased into concrete. In Europe, the use of composite girders began in Germany in late 1940s, during a steel deficiency period.

The first relevant regulation, DIN 4239, «Composite Beams in Buildings», was issued in 1956 and it was based on the Theory of Elasticity and the Allowable Stress Design Method. However, the rise in the use of composite elements in buildings has been booming especially in the 1980s, with Britain owning a prominent place and accounting for 60% of the building market. Respectively, in Japan it was 64%, in the US 50%, while in the rest of Europe about 33%.

Today, the European Committee for Standardization (C.E.N) has issued the Eurocode 4, which deals exclusively with composite structures and contains the rules for the design and execution of constructions with composite elements. This Regulation incorporates the knowledge and experience of technicians and scientists who have been involved in such constructions, the last few decades.

In Greece, composite structures are not so widespread, mainly because there has been no previous knowledge and experience in this field so far. However, due to the functionality, speed of erection and the low cost of the composite structures, this type of construction will soon gain the acceptance it has in the world.

FOUNDATION

The foundation, the floor and the ground floor are made of reinforced concrete with durability according to the static study. The specially nested metal anchorages of the wearer are placed before the foundation is concreted.

MAIN STRUCTURE

The supporting body of the structure consists of columns of either hollow or open section (IPE, HEA or HEB), open cross sections (IPE, HEA or HEB) and concrete slabs. The cross section of the columns for standard buildings is uniform per height without interruption at the levels of the slabs, the dimensions of which result from the static study based on the EC3 and EC4 Eurocodes.
All metal components, after being cut and before placement, are sandblasted and painted with epoxy paint and an anti-corrosion protection layer. All joints made at the factory are bolted to minimize work on site (welding, etc.).

SLABS

In the first stages of a composite concrete floor construction, this profile assumes the role of the formwork and finally – together with the hardened concrete – creates a composite floor slab with many advantages. As a result, its behavior must also be checked within the overall cross-section of the slab.

The operation of a composite slab is mainly based on the creation of a mechanical connection between the steel sheet and the hardened concrete, which must prevent any movement of the two materials. This is achieved mainly by its own form, since there are specially shaped ribs.

The operation of the steel sheet as a tensile element is not as critical as is its resistance to bearing dead loads of the slab. As a result, the tensile reinforcement of the slab – meaning the steel profile – is usually more than enough.

Therefore it is important that the composite slab be tested as a single cross-section both in terms of failure and functionality.

The remaining metal-type acts as a shuttering in the concreting stage, after which the reinforced concrete can accept loads of slab. The thickness of the slabs for standard openings in residential buildings is estimated to be approximately 15 cm. The absolute connection between the two materials composing a composite slab – the steel sheet and the reinforced concrete – is also achieved by the use of special shear joins, the cross section of which results from the static study.

MASONRY

The masonry (interior and exterior) can be constructed of various materials, and gives the possibility of flexibility in the architectural study. Specifically, it may consist of 3D panels, YTONG, and cement boards in the external walls and plasterboard on the internal walls.

The 3D panel construction consists of:

A) A three-dimensional industrial structural element composed of two parallel grids consisting of horizontal and vertical reinforcing bars Φ.3.0 or Φ.3.6 / S.500 welded together every 6.25 cm to all directions. The two grids are held parallel to each other by welded double-diagonal galvanized bars (64 pieces per m2 grid) of reinforcement Φ.3,6 / S.500.

In the gap between the grids and parallel to them, there is a built-in, expanded polystyrene slab of density of 18-20 kg / m3, with thickness of between 5cm to 25 cm, which is perforated by the two-corner bars and is securely held parallel to the grids at a controlled distance.

Primarily, the three-dimensional industrial building blocks are connected together with the continuous grids. Secondarily, are connected to the slabs, beams, and columns with special F8 cross-sectional linear fittings and P-shaped 50 cm lengths, which are electrically welded onto the metallic components.

Also, at the top of the openings, an internal and external additional grid is placed to handle the second class cracks in the masonry.

B) Two pieces of C20/25 fine aggregates concrete of 5 centimeters each on every side of the three-dimensional structural element.

The YTONG masonry construction follows the rules of the material manufacturer, except that no reinforced concrete zones are constructed, but these are replaced by MURFOR reinforcement of horizontal joins while, at the edges of the wall, a corner mesh is placed to achieve better coherence between both the columns and the girders.

HYDRAULIC – ELECTRICAL INSTALLATIONS

The water pipes are copper coated with a protective spiral. Sewage pipes are plastic heavy type.

The routes of both the hydraulic and the electrical installation are mounted on the 3D panels.

As noted above, the remaining stages of construction are the same as in conventional constructions, following the architectural proposal.