WO1995016084A1

WO1995016084A1 - Composite beam to be filled with concrete

Info

Publication number: WO1995016084A1
Application number: PCT/FI1994/000557
Authority: WO
Inventors: Heikki HIRSIMÄKI
Original assignee: Ppth Teräs Oy
Priority date: 1993-12-09
Filing date: 1994-12-08
Publication date: 1995-06-15
Also published as: FI935531A0; FI94451B; FI94451C; AU1244195A

Abstract

A composite beam to be filled with concrete, intended for use for instance with concrete slab structures. The invention relates to a concrete-filled composite beam, comprising a lower plate (2) and an upper plate (3) and between them a structure of web plates (4a, 4b) inclining towards each other and comprising projections (5a-5n, 6a-6n). The projections (5a-5n, 6a-6n) are interlaced, whereupon the cross section of said composite beam (1) forms an x-shaped structure.

Description

Composite beam to be filled with concrete

The invention relates to a composite beam to be filled with concrete, intended for use for instance with concrete slab structures, comprising a lower plate, an upper plate, web plates connecting the upper and lower plate and equipped with projections, and planes extending outside the web plates. A conventional load-bearing structure in floors has been steel-concrete beams, installed to rest on separate columns. In order to make said steel-concrete beams rigid enough, they are produced with a considerable height. For different heat, water, electricity and ventilation installations the beams have to be perforated or the height of the floor structure has to be correspondingly increased. Therefore, said steel-concrete beam becomes highly impractical, since the height of the floor structure increases, simultaneously lowering the space into which the floor is made.

Steel beam solutions are also previously known, for example I-beams, where slabs are set on top of the steel beam so that the joint of the slabs is positioned on the steel beam. The space left between the slabs is filled with concrete or with other corresponding material to provide a solid slab construction. Different kinds of bonding elements can be placed in said space, whereupon the slabs adhere better to each other and correspondingly to the steel beam. The problem with said I-beams is in particular their fire resistance, since when an I-beam is used as a supporting beam it is conventionally placed under the slabs, whereupon a separate construction is needed to protect the beam from fire. For example the beam can be covered with a separate fire-resistant plate. Therefore, the construction will become very expensive and time- consuming.

So-called light steel beams are also known, which function during building as steel beams on top of which the slabs may be placed. Correspondingly, the light steel beams can be placed in the joint between the slabs, so that when concrete is being poured into the joint, the light steel beam is also filled with concrete, thus forming with the concrete a concrete- steel beam placed in the joint between the slabs. The mechanical strength of the light steel beams is achieved through the design of their structural elements. The basic idea is to design the web plates connecting the upper and lower surfaces in such a way that they form a solid unyielding entity in connection with the upper and lower plate.

Finnish Patent 84,847 discloses a frame construction of a composite beam, intended for use during building as a supporting beam to support the slabs to be joined. When the slabs are joined together by means of soldering concrete, the composite beam becomes an entity connecting the slabs to each other by means of the soldering concrete in the joint between the slabs. Said composite beam uses a beam with a basically I-shaped cross-section, a separate fire-resistant plate being connected to the lower part of the beam so that there remains a space between the beam with the I-shaped cross-section and the fire-resistant plate. The fire- resistant plate and the beam with the I-shaped cross- section are interconnected by means of bars so that supporting elements, triangular-shaped in the longitudinal direction, are formed on the side of the beam with the I-shaped cross-section, connecting the fire-resistant plate to the beam and simultaneously making the structure of the composite beam considerably more rigid. The slabs are set on the composite beam so that the fire-resistant plate supports the slabs on both sides of the beam with the I-shaped cross-section. After this the joint between the slabs is filled with soldering concrete and left to harden, whereupon the concrete sticks to the bars provided on the sides of the beam and correspondingly fills the space between the fire-resistant plate, the beam with the I-shaped cross- section and the slabs. However, the construction of said composite beam is very complicated, and therefore its manufacture comprises several different stages, and thus the manufacturing costs become high. Another problem is also how to concrete the beam, because when a joint is being filled between the slabs it is extremely difficult to control how well the soldering concrete has filled the space between the lower surface of the beam with the I-shaped cross-section and the fire-resistant plate. Therefore non-concreted areas easily remain in said space, and then the load-bearing capacity of said composite beam is no longer equivalent to that of a fully concreted beam. Neither does the fire resistance of said beams correspond to that of a fully concreted beam. In case of fire, the supporting structure is formed only by the beam with the I-shaped cross-section, since the fire-resistant plate located beneath it gets softer during a fire and cannot be relied on to then provide structural tenacity. Therefore the beam with the I-shaped cross-section has to be made very solid, with the result that it becomes weighty, and thus the entire composite beam is heavy and difficult to handle in building sites.

Finnish Patent 85,745 discloses a fire- resistant steel beam. The steel beam is made of two web parts, inclining towards each other and situated at a certain distance from each other, an upper plate connecting their upper parts, and a lower plate connecting their lower parts. Moreover, there is a projection attached to the lower part of the web parts outside them, the slab structures resting on said projection. Furthermore, a fire-retardant part, for example fire-retarding wool or the like, is applied to the lower surface of the beam. Holes are formed in the web plates, the edges of the holes being pressed into the space between the web plates to increase the surface to which the soldering concrete can stick. When the slabs are joined together by means of concrete, the space between the web plates and the upper and lower plate of the beam is also meant to be filled with the same soldering concrete. The problem is that the inside of the beam cannot be completely emptied of air. Therefore an air space that the concrete cannot enter easily remains in the upper part of the beam. Thus, the structural strength of said beam when filled with concrete is questionable and this has to be taken into consideration in designing the beam and checked in the construction site. Furthermore, the manufacturing of said steel beam is extremely complicated, because even though when the web plates are connected to the upper plate the welding is easy to perform, when the lower plate is joined to the web plates the beam blank has to be turned around and the welding has to be performed from the other side. The manufacture of the steel beam calls for several stages, thus increasing the manufacturing costs. Correspondingly, it is very difficult to place a fire-retarding material on the lower surface of the lower plate so that it would not be damaged during transportation and building.

Finnish Patent 86,326 discloses a fire- resistant prefabricated steel beam for floors. The steel beam is made of two vertical columns and a horizontal support flange attached to the lower part of the columns to support the slabs. Correspondingly, there is also a horizontal support in the upper part of the beams to support the vertical beams. The problem with said beam is its relatively straight surfaces, because when the joint between the slabs is filled with soldering concrete, there are not enough surfaces in said steel beam to which the concrete can stick. Since the vertical columns of said beam are made of channel beams, the entire construction becomes very heavy and difficult to handle. When the joint between the slabs is filled with soldering concrete, it must be specifically ensured in the building site that the concrete fills the steel beam completely, which however is very difficult, since the steel beams are closed structures and it is not easy to observe the degree to which they are filled. Therefore the space between two channel beams positioned against each other is seldom completely filled with soldering concrete, but there remain non-concreted areas and therefore said steel beam has to be designed using a great margin of safety.

German Auslegeschrift 1,267,405 discloses a composite beam, where vertical parts connected to each other from their upper surfaces are installed on top of the lower plate. The lower parts of the vertical part are bent alternately outwards and inwards, whereupon the lower parts of the vertical parts form a construction with a V-shaped cross-section, which supports the vertical parts when connected to the lower plates. The problem with said beam is how to fill it with soldering concrete, however, because it is not easy to empty air out of the upper part of the vertical parts. Therefore non-concreted areas easily remain in the upper part of the beam's vertical parts. Furthermore, it is difficult to secure the lower part of the beam's vertical parts to the centre of the lower plate, and therefore it takes time to manufacture the beam. Moreover, the manufacturing of the web plates has several stages, which increases also the manufacturing costs of the beam.

The object of the present invention is to provide a composite beam intended for use for instance with concrete slab structures, eliminating above problems and creating a very large bonding surface for the soldering concrete.

This invention is characterized in that the web plates and the projections are formed in such a way that the web plates can be interlaced in an inclined position so that the composite beam forms a structure with a substantially X-shaped cross-section.

An essential idea of the invention is that the upper and lower plate are connected by means of the web plates, the projections of which are interlaced in an inclined position, thus forming a web structure with an X-shaped cross-section. An essential idea of a preferred embodiment is that when the upper plates are attached to the interlacing web plates, the upper plate is positioned in such a way that the projections form a bonding surface for the soldering concrete also above the upper plate. Furthermore, it is essential that the components of said composite beam can be joined together in a very simple manner by welding from the same side, and thus the welding may be performed by a robot or other corresponding automatic apparatus. Correspond¬ ingly, the adhesion between the concrete and the beam is great due to the structure of the web plates of the beam. Furthermore, the height of the beam can be adjusted by placing the web plates at a desired angle to each other, whereupon the distance between the upper and lower plate can either be increased or decreased. Correspondingly, it is easy to camber said structure during the manufacturing, thus improving the load- bearing properties of the composite beam. An essential benefit of the invention is that said projection-type web construction provides a very great adhesion between the concrete and the beam. Another essential benefit is that the beam does not form separate enclosed chambers, but the soldering concrete fills the beam structure completely from the lower plate to the upper plate, and correspondingly the spaces between the slabs in the lateral direction. This can be taken into consideration when the beam is being designed, because the soldering concrete fills entirely the space between the slabs and the upper and lower plate of the beam. A further essential benefit is that due to the web structure, the beam requires less building material and therefore the manufacturing costs will be lower. It must also be noted that by means of similar web plates, composite beams of different height can be manufactured by changing the angle between the web plates. Moreover, an essential benefit is that separate bonding bars can be installed between the projections of the web plates to further ensure that the soldering concrete will stick to the beam, and to increase the adhesion between the beam and the concrete. The invention will be described in greater detail in the following drawings, in which

Figure 1 is a perspective side view of a composite beam according to the invention,

Figure 2 is a cross-sectional side view of a composite beam,

Figure 3a is an end view of a beam according to the invention without an end flange, Figure 3b is an end view of another embodiment of the beam, and

Figure 3c is a representation of still another embodimen . Figure 1 is a perspective side view of a composite beam 1. The composite beam comprises a lower plate 2 and an upper plate 3, and web plates 4a and 4b connecting the lower and upper plate together to form a web structure. The web plates 4a and 4b are made of a single plate by flame cutting so that a cutting line similar to a rectangular wave is cut into the plate, whereupon projections 5a - 5n and 6a - 6n are formed simultaneously in both web plates 4a and 4b. Therefore, material of suitable width yields web plates 4a and 4b in the desired form by means of simultaneous cutting. In particular, if flame cutting is used, a narrow opening is formed between the projections 5a - 5n and 6a - 6n, and thus the web plates 4a and 4b can be placed in an interlacing position so that the projections 5a - 5n can be set between the projections 6a - 6n. A construction which is X-shaped when viewed from the end of the web plates is achieved, and the angle 7 between the web plates can be either decreased or increased to provide a composite beam 1 of desired height. The web plates 4a and 4b are attached from their lower parts 8a and 8b to the lower plate 2 by welding, after which the composite beam structure can be cambered by bending the composite beam blank upwards at the middle of its longitudinal axis, and thereafter by positioning the upper plate 3 in place in the space between the projections 5a - 5n and 6a - 6n of the web plates 4a and 4b, and by welding the upper plate to the projections 5a - 5n and 6a - 6n. The beam construction may also be cambered by means of special equipment so that the lower plate 2 and the upper plate 3 are simultaneously welded to the web plates 4a and 4b. The lower plate 2 of the composite beam 1 comprises planes 9a and 9b outside the web plates 4a and 4b, the function of the planes being to support the slabs before the joint between the slabs is filled with soldering concrete. Since there is a space left in the web plates 4a and 4b between the projections 5a - 5n and 6a - 6n, the soldering concrete can fill the structure of the composite beam 1 entirely, and simultaneously it can stick very well to the projections 5a - 5n and 6a -6n of the web plates 4a and 4b. If desired, the adhesion between the composite beam 1 and the concrete can be ensured by positioning separate additional bonding elements, for example reinforcing iron, between the projections 5a - 5n and 6a - 6n, all through the composite beam 1, so that when the joint between the slabs is filled with soldering concrete, the concrete will also stick to the reinforcing bars.

Figure 1 shows further the ends 10a and 10b of the composite beam 1, which also support the X-shaped cross-sectional construction of the composite beam 1. Said composite beam 1 can be prestressed by tightening the ends 10a and 10b by means of a wire rope passed between the web plates 4a and 4b, and the lower plate 2 or the upper plate 3, the wire rope being anchored first to one end 10a and tightened after that against the other end 10b by passing the wire rope through the end 10b, whereupon the composite beam 1 can be stressed higher from its middle than from the ends. The wire rope is locked into the tightened position at the other end 10b by means of, for example, a sleeve-type lock.

Figure 2 is a cross-sectional side view of the composite beam. The reference numerals are similar to those in Figure 1. The projections 5a - 5n and 6a - 6n of the web plates 4a and 4b can also be designed in such a way that the end parts 11a - lln and 12a - 12n of the projections 5a - 5n and 6a - 6n extend a certain distance above the surface level of the upper plate 3. This increases the adhesion between the soldering concrete and the composite beam 1. Furthermore, it is very easy to equip said end parts 11a - lln and 12a - 12n with additional bonding elements, for example reinforcing bars, by means of steel wire to facilitate considerably the work of the steel fixer. Said end parts 11a - lln and 12a - 12n form together with the composite beam 1 filled with soldering concrete a very strong entity, which sustains extremely heavy loading and use.

Figure 3a shows the composite beam of Figure

2 viewed from the end and without the end flange 10a, to illustrate the structure of the beam. The web plates 4a and 4b are fixed to the lower plate 2 and the upper plate 3. Correspondingly, the projections 5a - 5n and 6a - 6n of the web plates are interlaced in an inclined position, thus forming a composite beam with an X-shaped cross-section. Furthermore, the end parts 11a - lln and 12a - 12n shown in Figure 3a extend above the level of the upper plate 3. It must be noted, however, that the composite beam 1 can also be realized in such a way that the projections 5a - 5n and 6a - 6n extend only to the level of the upper plate 3, to which they are attached by welding. Moreover, Figure 3a shows supporting bars 13a to 13f which improve fire safety. The supporting bars 13a to 13f are positioned in Figure 3a by way of example in the triangular space formed by the web plates 4a and 4b and the lower plate 2, substantially from one end 10a to the other 10b in the longitudinal direction of the composite beam 1. Correspondingly, the supporting bars can be evenly positioned in the space with a triangular cross-section formed by the upper plate 3 of the composite beam 1 and the web plates 4a and 4b. In case of fire, the function of the supporting bars 13a to 13f is to replace the lower plate 2, which loses its structural strength either partly or completely when it warms up. Since the composite beam 1 is filled with soldering concrete, the supporting bars 13a to 13f are also surrounded by concrete, which due to its low conductivity of heat protects the supporting bars 13a to 13f, and thus the composite beam 1 maintains its load-bearing capacity also in case of fire. Correspondingly, supporting bars 13a to 13f can be placed outside the web plates 4a and 4b, for example on the planes 9a and 9b of the lower plate 2, or in the space above the planes 9a and 9b. The supporting bars 13a to 13f are most preferably installed in the composite beam while it is being assembled, since then it is easy to place them in the triangular spaces formed by the web plates 4a and 4b, and the lower plate 2 and the upper plate 3. For example reinforcing steel or flat iron can be used as supporting bars. In some cases the flat iron can replace the lower plate 2 or the upper plate 3 either completely or partly.

Figure 3b shows another embodiment of the composite beam 1, where a jointless supporting unit 14 formed by the web plates 4a and 4b and the upper plate 3 is connected to the lower plate 2. Grooves of desired length are then cut into the edges of a straight plate at intervals equalling the width of the projections, perpendicular to the longitudinal direction of the plate, and in the middle of the plate there remains an uncut area, which in said beam forms the upper plate 3. Correspondingly, the projections can be bent in such a way that every other projection is bent at an angle of more than 90° in relation to the surface of the plate, and every other projection can be bent at a desired angle with respect to the upper plate 3, and thus the web plates 4a and 4b, cut out of a jointless plate, are formed by bending them in such a way that they cross each other. Figure 3b does not show those projections, which are not bent at an angle of more than 90° in relation to the upper plate 3. However, it is clear that the projections can be bent so that they reach the lower plate 2 and form together with the upper plate 3 a solid structure with the cross-sectional shape of a rhombus. Moreover, if desired, said composite beam structure can also be realized so that the lower plate 2 is grooved, and after that every other projection formed in the plate is bent so that it crosses a projection of the opposite side and together they form a structure which is X-shaped when viewed from one end. Figure 3c shows still another embodiment of the composite beam, where one web plate 4a is formed of the same plate with the upper plate 3 by cutting grooves into the plate and by bending the projections at an angle of more than 90° from the surface of the plate, and by placing the other web plate 4b diagonally in relation to the web plate 4a, in which case the second web plate 4b is manufactured for instance during the same cutting process as the upper plate 3 and the web plate 4a. The invention and the description related thereto are only meant to illustrate the idea of the invention. The details of the composite beam according to the invention can vary within the scope of the claims. Therefore, it is possible to place separate elevating supports for the slabs for example on the planes 9a and 9b of the lower plate 2, whereupon the slabs can be positioned to the desired height in relation to the lower plate 2 of the composite beam 1. Furthermore, it is possible to attach a stiffening bar to the surface of the upper plate 3 also in the longitudinal direction of the beam. It is also very easy to turn the composite beam 1 into a frame rail or an edge beam of a slab structure, with one side of the beam being closed by means of, for example, a separate steel plate or a mould, and then filling the beam with soldering concrete, whereupon the composite beam is able to support the edge of the slab. The lower plate 2 and the upper plate 3 can be either of the same or different width depending on the use of the beam. The web plates 4a and 4b can also be joined to the edges of the lower plate 2, if the lower plate 2 does not comprise the planes 9a and 9b. Moreover, it is clear that a composite beam according to the invention can also be installed in a vertical position and thus used as a column.

Claims

1. A composite beam to be filled with concrete, intended for use for instance with concrete slab structures, comprising a lower plate (2), an upper plate (3), and web plates (4a, 4b) connecting the upper and lower plate and equipped with projections (5a - 5n, 6a - 6n), c h a r a c t e r i z e d in that the web plates (4a, 4b) and the projections (5a - 5n, 6a - 6n) are formed in such a way that the web plates (4a, 4b) can be interlaced in an inclined position so that the composite beam ( 1 ) forms a structure with a substantially X-shaped cross-section.

2. A composite beam according to claim 1, c h a r a c t e r i z e d in that the web plates (4a,

4b) and the upper plate (3) are made of a jointless plate by cutting projections (5a - 5n, 6a - 6n) into both edges of the plate, so that the projections (5a - 5n, 6a - 6n) can be bent in an interlacing position to provide a structure with an X-shaped cross-section.

3. A composite beam according to claim 1, c h a r a c t e r i z e d in that the upper plate (3) and at least one web plate (4a) are made of the same plate.

4. A composite beam according to claims 1 and

3, c h a r a c t e r i z e d in that the web plate (4a, 4b) of the web construction is made of a jointless lower part (8a, 8b), that projections (5a - 5n, 6a - 6n) are connected to the lower part (8a, 8b) so that together the lower part (8a, 8b) and the projections (5a - 5n, 6a - 6n) form a jointless unit.

5. A composite beam according to any one of the preceding claims 1 to 4, c h a r a c t e r i z e d in that supporting bars (13a to 13f) are placed in the spaces with a triangular cross-section formed by the web plates (4a, 4b) and the lower plate (2) and the upper plate (3) , to increase the structural strength of the composite beam ( 1 ) .

6. A composite beam according to any one of the preceding claims 1 to 5, c h a r a c t e r i z e d in that there are planes (9a, 9b) in the lower plate (2) extending beyond the web plates (4a, 4b).

7. A composite beam according to claim 6, c h a r a c t e r i z e d in that there are elevating means on top of the planes (9a, 9b) to position a slab to a desired height in relation to the lower plate (2) of the composite beam ( 1 ) .

8. A composite beam according to any one of the preceding claims 1 to 7, c h a r a c t e r i z e d in that a tightening element is anchored to the ends (10a, 10b) of the composite beam (1), so that by tightening the ends (10a, 10b) towards each other in the longitudinal direction by means of the tightening element, the composite beam (1) can be prestressed.

9. A composite beam according to any one of the claims 1, 4, 5, 6, 7 or 8, c h a r a c t e r i z e d in that the projections (5a - 5n, 6a - 6n) of the web plates (4a, 4b) are connected to the upper plate (3) in such a way that the projections (5a - 5n, 6a - 6n) extend beyond the level of the upper plate (3).