COMPOSITE BEAM STRUCTURE

This invention relates to a composite structure, and in more detail a composite beam structure, used in the construction industry.

Background

A composite structure can be understood as almost any structure composed of two or more materials, such as e.g. a conventional reinforced concrete structure. Between different structural elements, composite operation is always created when the elements are continuous i.e. monolithic or connected with a shearing connection.

According to recent practice, a composite structure is generally understood as a combination of steel structures or sheet structures and concrete or reinforced concrete.

The most important and conventional way to connect two different construction materials is the use of concrete-steel composite structures, such as composite beams, in multi-storey residential, industrial and commercial buildings.

The operating principle of the steel-concrete composite structure is based on the almost perfect or partial co-operation between the steel part and the concrete part. The steel part can be of structural steel or sheet structural steel and the concrete part of common concrete, high- strength concrete or light concrete.

The basic type of a steel-concrete composite structure commonly used as an intermediate floor structure can be considered to be a single- span freely-supported composite beam on which a hollow-core slab / a closed composite slab or the like rests. For ensuring the co-operation between the steel part and the concrete part, most often are utilised dowels, dowel pins, welded on the upper flange of a steel profile, which are dimensioned as elastic connectors.

The ratio of steel and concrete should be optimal in the composite structures. Steel is liable for tensile stresses and concrete is liable for bearing stresses, then the best characteristics of each can be utilised. Also, the almost identical thermal expansion coefficients of concrete and steel and the protective effect of concrete in the corrosion of steel give extensive possibilities to the use of composite structures, such as composite beam structures. Concrete can also support the thin steel parts and prevent them from buckling and collapsing. Intermediate floors of the concrete composite structure are usually composed of steel beams and concrete slabs or reinforced concrete slabs. Slabs in the composite-structured intermediate floors rest either on the main beams or the secondary beams. The main beams convey loads coming from the slabbing in the connections of pillars. Composite-structured intermediate floors are usually utilised in multi-storey commercial, office and residential buildings.

In a composite beam constituted by concrete and steel (usually the concrete part is pressed and the steel part drawn in the composite beam structure), the co-operation between the parts is provided mechanically. The composite beams are installed on supports, after which hollow-core slabs or other slabs or the like are installed resting on them. After the installation of the slabs, the seams and the beam are filled with concrete.

Also, several different composite beam structures and arrangements are known.

From specification WO 2004/031507 Al, a composite beam structure is known which structure includes several dowel pieces for forming a connection between steel and concrete, and the dowel pieces are bar- like pieces circular of their cross-section which are fastened on the upper surface of the beam. On the upper end of the dowel pieces, there is a widened part, circular seen from the top, and the arrangement according

to the specification further utilises a support mesh in forming and improving the connection between concrete and steel.

Specification US 6807789 describes a composite structure in which the beam is formed of several pieces fastened to each other by welding and in which the upper part of the beam structure is narrower than the lower part, and in which concrete casting totally fills the inner part of the beam. Openings have been formed in a plate part being vertical in the middle of the beam structure.

Specification AT 301821 describes a composite structure in which folds have been made for support in a V-shaped piece fillable with concrete, manufactured by bending from a plate.

Known arrangements include disadvantages.

Known structures require relatively lot of processing, such as weldings, bendings etc., and this is extremely undesired, or known arrangements have not been able to implement the functioning of the connection, i.e. the co-operation between steel and concrete in the connection, in the best possible way such that the connection would operate almost perfectly (or perfectly which is the aim of the connection).

The object of this invention is to provide a novel type of a composite structure, or in more detail a composite beam structure, by means of which disadvantages of known arrangements can be minimised or eliminated, and thus by means of which is provided a functioning and extremely good composite beam arrangement of its costs and other characteristics i.e. technical qualities.

Known arrangements utilise several dowels arranged into connection with the beam. An advantage of the arrangement according to the invention compared to the known arrangements is that it requires less support pieces i.e. dowels than recent arrangements for connecting steel and concrete to each other and that, with the same or a smaller number

of dowels, a better composite effect is provided in the connection between concrete and steel.

An advantage of the arrangement according to the invention compared to the known arrangements is that it provides a better connection between steel and concrete than known arrangements, which connection fulfils the demands of rigidity and endures loads and stresses directed at it better than known arrangements i.e. the connection is able to receive vertical and horizontal forces in the structure (occurring at its different points).

When using circular (dowel) pins, a large number of them is required in the longitudinal direction of the beam, and the dowel pieces which are the shape of a rectangular prism, such as e.g. quadratic, lack a projection surface receiving/conveying vertical forces.

An advantage of the arrangement according to the invention is also that awkward bendings or other laborious processing measures can be avoided in it.

A further advantage of the arrangement according to the invention is that, with the composite beam structure according to the invention, the consumption of steel required in the composite beam structure can be decreased and then a considerable economic benefit is provided.

The invention is characterised by what is stated in the appended claims and especially by what is stated in the characterising part of claim 1.

Next, the invention is described in more detail by referring to the accompanying drawings in which

Fig. Ia shows a cross-section of a simplified composite beam arrangement according to the invention seen from the end of the beam.

Fig. Ib shows an arrangement according to the invention seen from the side of the beam.

Fig. Ic shows a top view of dowel pieces, fastened inclined in the beam.

Figs. 2a-2f show a front view of the different shapes of the dowel piece.

In accordance with what is shown in Fig. Ia, in a beam 3 is arranged a slab-like piece 2, such as e.g. a hollow-core slab. The height of the slab- like piece is, according to the figure, almost equal to the height of the beam 3 but the slab can also be considerably lower than the height of the beam. On top of the slab, a casting 1 is formed which is advantageously concrete casting, and one or more dowel pieces 4 remaining inside the casting, which dowel pieces are fastened on the upper surface of the beam by welding at a desired point.

With a projection (projection surface) of the dowel piece 4, vertical and longitudinal forces are transferred.

The height of the casting can vary considerably depending on different targets of application, but typically the height of the casting is between 40 mm-200 mm.

The length of the dowel pieces is at least threefold in relation to the width of the upper surface of the dowel pieces. In an advantageous case, the length of the dowel pieces is at least about fivefold in relation to the width of the upper surface of the dowel pieces. The width of the upper surface of the dowel pieces is typically between 20 mm-70 mm, but it can also be wider or narrower, depending on the load of the beam or on the amount of composite effect required.

The length of the dowel pieces can vary, but it is typically at least 30% of the width of the upper surface of the beam. The dowel pieces can also extend over the width of the upper surface of the beam.

The dowel pieces are fastened in the beam in a perpendicular angle or inclined seen from the top as shown in Fig. Ic.

Because Fig. 1 is shown only to illustrate a composite beam structure according to the invention, it does not implicate steel profiles, composite plates or auxiliary reinforcements etc. remaining partially or totally inside the casting.

The arrangement according to the invention can utilise all already known beams and beam types, such as an I beam, a T beam, a WQ beam, a box beam etc.

According to Fig. 2, the dowel pieces can be the shape of a parallelogram or a trapezium, triangular, or the dowel pieces can include one or more bevels, such as e.g. shown in Fig. 2f. The dowel pieces can be substantially of the shape of T or I or L The dowel pieces can also include one or more roundings. It is also essential that the dowel pieces thus have at least one inclined surface or one curved surface or two straight surfaces or combinations of the above surfaces.

The dowel pieces can be hollow or perforated and support bars, such as e.g. round steel bars or the like, can have been arranged inside the dowel pieces, the task of which bars is to improve the composite effect by increasing the gripping surface. Round steel bars can also be utilised in anchoring the slab/slabbings on the beam and a mesh can be set at the base of the dowels to improve the composite effect. The mesh can be manufactured e.g. of steel.

It is well known by those skilled in the art that the invention is not limited to the embodiments described above, but it may vary within the scope of the enclosed patent claims.

According to the inventive idea, used arrangements may be varied quite widely. It is also possible to consider e.g. such an arrangement in which already known dowel pieces and/or sections (section arrangements)

increasing the grip of steel and concrete are combined with the dowel pieces described here to be used together in order to provide a composite effect as good as possible in the connection between steel and concrete.