ES1288129U - Combined steel-concrete box girder and flat slab comprising the same - Google Patents

Abstract

The invention discloses a combined steel-concrete box girder, likewise the flat slabs (30) incorporating the same, comprising: a first lower longitudinal metal sheet (12), a second upper longitudinal metal sheet (14), of a width smaller than that of the first metal sheet (12) and parallel thereto; and two vertical metal web plates parallel to each other, disposed at the distance necessary for their external sides to project slightly with regard to the edge of the upper metal sheet (14) in order to facilitate the welding thereof. The webs are cut in the shape of teeth separated by holes, in such a way that the teeth and holes have the same dimensions. The girders of the invention display an improved assembly in the slabs (30) whereof they will be part, with no need for stringers and enabling, through the holes in their vertical webs, the arrangement of transversal reinforcements, endowing the assembly with greater solidity and cohesion, where said slabs comprise a plurality of formwork or prefabricated elements (32) resting on the edges of the lower metal plates (12) of the box girders, and a pour of concrete (36) where said girder features a number of corrugated rebars welded to a number of metal positioning plates (38).

Description

BOX BEAM AND A MIXED STEEL-CONCRETE FLAT FLOOR WHICH

UNDERSTANDS

Technical field of the invention

The present invention belongs to the technical sector of construction, for example and without limitation, to the construction of industrial, commercial, residential buildings, etc.

More specifically, the invention refers to a box beam, for a flat-type mixed steel-concrete floor, called "slim-floor'Tshallow-floor", from the technical terminology derived from English, intended to be used in floors and roofs of multi-storey building constructions. This type of slab is characterized by the fact that the beams used are embedded in the edge of the slab itself, avoiding sagging. The invention also refers to the fact that said box girder has the particularity that the webs that make it up are formed on the basis of sheets cut in a saw tooth, forming lattices with gaps between the teeth, in such a way that the teeth and the gaps are one the negative of the others. This allows two cores to be obtained with each cut, optimizing the use of the material and eliminating sheet metal remains.

State of the art

In the construction of buildings, there is an increase in mixed steel-concrete construction by allowing the advantages of structural steel and concrete to be combined, not only in terms of resistance capacity but also in terms of construction, functional and aesthetic aspects. The mixed steel-concrete flat floors of the "slim-floor" type, formed by steel beams embedded in the edge of the floor, are used more and more as they combine advantages over conventional construction systems such as, for example, those formed by hanging beams. . Among other advantages, they allow the total depth of the slab to be reduced, the useful space between slabs to be increased and the installation of technical equipment below the slab to be facilitated, by achieving a smooth ceiling or one with ribs with minimal slack. Other advantages are the speed of construction, as it does not require formwork or propping, and the fire resistance inherent to the construction typology.

The flat steel-concrete “slim-floor” slabs, in addition to the steel beams, incorporate embedded elements that make up the slab, such as: reinforced or prestressed concrete slabs or slabs, prestressed hollow core slabs, reinforced or prestressed concrete joists prefabricated or executed "in situ", metal joists or collaborating steel sheets. Concrete is poured into the metal beam to form a composite beam. If the slab has a compression layer (concrete and/or reinforcement), the concreting is carried out together (box beam and compression layer), guaranteeing beam-box/slab monolithism, and continuity with the distribution and negative reinforcement, in your case.

There are various types of flat beams used in slabs of the "slim-floor" type that have been developed since the 70s of the last century. These beams are usually made based on commercial profiles with the disadvantages that this entails. One of them is the need to have connectors between the beams to form the floors. Another additional disadvantage of using commercial profiles is the lack of versatility of these beams to be able to adapt to the specific needs of the building or plant under construction.

The dimensioning of flat floor beams can be considered with the principles of the UNE-EN 1993-1-1 and UNE-EN 1994-1-1 standards. The UNE-EN 1993-1 -1:2013 standard presents the necessary procedures for checking the Ultimate Limit States ULS and Service Limit States ELS of said beams in the construction stage, before the hardening of the concrete.

The current regulations on composite structures UNE-EN 1994-1-1:2011 do not explicitly cover the dimensioning of “slim-floor” beams, nor does it cover the possibility of exploring the composite behavior of a beam without slip connectors. According to the previous rule, to consider a mixed behavior, there must necessarily be connectors between the steel and the concrete of the beam, but the scientific literature and the tests carried out prove the behavior in mixed section in this type of beams, without the need for said connectors, although, if desired, realizations of the mixed box-beam can also be carried out in accordance with the invention, also provided with connectors.

There are box girders with side stringers with holes (DE202015104628U1 and CN203429885U). Making holes to manufacture the lateral webs wastes a lot of material and increases the cost of these beams. In addition, the webs do not form a 90° angle with both the upper and lower plates to which they are welded (CN203429885U), having a worse mechanical behavior and a higher production cost. The upper plate also protrudes from the side of the web (CN203429885U) and even the sides have folding angles at their bases (WO03100185A1), which make them more prone to collapse in situations of vertical overstress. The lower resistance of the beams described in the state of the art to vertical force stresses is evident by presenting (CN203429885U) even holes in the upper plate. There are also box girders with sides with openings and reinforcements with steel bars useful in case of fire (EP1690999A2), but, again, the upper plate protrudes from the side walls and the union between the upper plate and the webs is made by coupling male-female between their respective notches and projections, in the form of complementary trapezoidal teeth, which makes it easier for them to collapse earlier, in the event of an increase in vertical forces, because this type of coupling offers less rigidity than that proposed by the present invention and, furthermore, the reinforcing bars made of fire-resistant material are arranged in a different way to that proposed in the invention, not welded, apart from needing joints between the box girders.

Other box girders described in the state of the art (NL8700070A), require that trapezoidal teeth be made in both upper and lower plates and that they be folded, which entails an extra cost, to be welded along the smaller edges of the teeth. trapezoidal. This type of beam has less resistance to vertical tension forces, as it does not have a wider lower plate and cannot be attached to the floors without connecting elements, for the same reason. This same problem, the absence of a wider lower plate that confers, on the one hand, greater resistance to the tensions of vertical forces and, on the other, serves as a support for the floor elements, without the need to provide the beam with elements of connection, also seen in RU2677188C1 The previous problems existing in the state of the art are solved with the box girder and the composite steel-concrete floor that comprises it, of the present invention.

Summary description of the invention

In order to address the aforementioned problems and disadvantages in the state of the art, the invention provides a box beam for mixed metal-concrete flat slabs comprising:

• a first lower, longitudinal metal sheet;

• a second upper longitudinal metal plate, smaller in width than the first plate and parallel to it; Y

• two vertical metal cores, parallel to each other, arranged at a distance in which their outer face protrudes slightly from the edge of the upper sheet, to facilitate welding. For the purposes of this description, it is understood that the two vertical webs protrude slightly with respect to the edge of the upper plate, in that it rests on part of the width or thickness of said webs, leaving the rest of said width or thickness partially uncovered. of the vertical souls. This implies that an angle is formed between both edges, that of the upper plate and those of the vertical webs, which is used to facilitate welding. The metallic welding fluid fills said angle or step between said edges. In addition, as the lower plate is wider, the webs are recessed from their edge, leaving enough space to support the elements of the floor. The souls are cut in the shape of teeth separated by alveoli, so that the teeth and the alveoli have the same dimensions.

By having a complementary profile, it is possible to obtain the two webs of a beam by cutting a single piece of sheet steel, without wasting any material. The cut can be made by any method known in the state of the art: laser, plasma, thermal lance, water jet, shearing, etc. This implies material savings, avoids the generation of waste and the beams produced have greater strength at lower material cost. The most suitable geometry to achieve these advantages is a trapezoidal sawtooth cut, but other geometric shapes may be equally appropriate (rectangular, truncated semicircular, etc...). It suffices that the alveolar elements have a continuous lower base suitable for being welded on the lower plate of the box-beam and that the alveolar elements have a substantially straight surface opposite the base, of sufficient length, to allow their Rigid and robust welding with the upper plate of the box-beam itself.

Preferably the beam is made of steel, specifically S-355 JR steel plate. Steel is the metal normally used in the construction of buildings, but other metallic materials can also be used without departing from the scope of protection of the present invention.

The welding of the lateral webs at their upper and lower edges to the respective upper and lower plates can be carried out by methods known in the steel industry. For example: electric arc welding, laser welding, electron beam welding, ultrasonic welding, friction welding, fusion welding, etc.

The alveolar webs are placed in such a way that both equal and complementary profiles are welded to the upper plate, that is, to the narrower plate, on the smaller side of the trapezoidal teeth. This produces a beam with greater resistance, because the wider plate is placed in the lower part of the beam structure and the part of the web that presents a continuous profile would be welded at its lower base, on said wider plate, offering greater resistance to bending and traction due to vertical loads. In addition, this geometry facilitates the filling of the concrete in the entire volume of the box-beam and the placement of transverse bars through the alveoli, guaranteeing the behavior of a composite beam.

Preferably, the lateral webs are arranged in such a way that they present an offset or phase shift between the alveoli of both webs, that is, those of one web with respect to those of the other. That is, when the beams are seen from the side, the alveoli of one web coincide with the teeth of the other web and vice versa. In this way, a more homogeneous distribution of stresses and deformations is achieved along the beam, and the concrete is poured to adequately fill the interior of the box. Without However, the souls can be placed in such a way that the alveoli of one coincide transversely with the alveoli of the other soul, leaving diaphanous spaces between the trapezoidal teeth, on both sides.

Another embodiment of the invention is the one in which the alveolar side webs are welded in opposite directions. One of the lateral webs, with the smaller sides of the teeth, in one example, as a trapezoidal shape, welded to the lower plate and the other parallel alveolar lateral web, welded in the opposite direction, with the smaller sides of the teeth, in this same example, also with a trapezoidal shape, although it could be any other shape, welded on the upper plate. In this other embodiment, the webs can also be staggered or blunt.

Another aspect of the invention provides a beam according to the invention and a concrete core located between the first and second plates and the webs. The pouring of the concrete is done in such a way that it protrudes from the box beam.

Another aspect of the invention provides a flat slab comprising a plurality of beams according to the invention, different types of formwork, or prefabricated elements supported on the edges of the lower plates of the beams, and a concrete pouring that joins the whole, including the interior of the box girder. The beams of the invention support 15-60 cm thick slabs on their lower plate. Once the slab elements have been placed, the concrete is poured, completely covering and filling the box girder. In the event that the slab has a compression layer, the concreting of this layer and that of the beam are done simultaneously.

The box girder can include longitudinally arranged corrugated bar steel to meet additional needs in case of fire. These corrugated bars are preferably welded to plates arranged inside the box, which have recesses or housings of suitable dimensions for the correct housing and welding of the bars, to fix their positions. Taking advantage of the alveoli of the lateral webs, whatever their arrangement (parallel or alternate), a transverse reinforcement can be arranged using corrugated bars, preferably, which improve the mixed behavior, steel-concrete, of the structure. section.

Lastly, in another embodiment of the invention, the box girders can have symmetrical openings in their upper and lower plates, to which hollow tubular structures are welded, arranged parallel to the alveolar webs. These tubular structures allow all kinds of installations to be arranged within them, such as wiring, pipes, etc... The corrugated bars that improve the fire resistance of the box-beams of the present invention can also be welded on the sides of these vertical tubular structures.

Brief description of the figures

An embodiment of the invention is described below, by way of example and without the intention of constituting any limitation to the scope of protection of the present invention. Reference is made in the description to the following figures, in which:

Figure 1 shows a perspective view of a metal beam according to an embodiment of the present invention.

Figure 2 shows a cross-sectional view of the metal beam shown in Figure 1.

Figure 3 shows an elevation view of the metal beam shown in Figure 1.

Figure 4 shows a detail of the complementary cut profile of the webs of the beam in Figure 1 obtained from a single piece of sheet metal 300 mm wide.

Figure 5 shows a flat floor detail according to an embodiment of the present invention. 5A with compression layer (40) and 5B, without compression layer.

Detailed description of the invention

Figure 1 shows a perspective view of a metal beam (10) according to an embodiment of the present invention. Beam 10 is made from S355-JR sheet steel cut and welded to form a box girder for composite flat floors. steelconcrete. The beam (10) comprises a lower longitudinal steel plate (12) 600 mm wide and 12 mm thick and 4.6 m long, an upper longitudinal steel plate (14) 314 mm wide, 10-15 mm thickness and 4.6 m in length, parallel to the plate (12) (see Figure 2). The beam (10) comprises two lateral alveolar webs (16, 18), parallel, 220-365 mm high, 6-10 mm thick and 4.6 m long. The alveolar webs are welded on both sides (upper, with trapezoidal teeth and lower, continuous base) to both plates, so that the external faces of the lateral webs protrude slightly from the edges of the upper plate, facilitating welding (Figure 2 ). The two webs are parallel to each other and perpendicular to the upper and lower plates, to which they are welded, so that the lateral edges (20) of the lower plate (12) protrude from the lateral webs (16, 18) to give support to the floor or prefabricated elements, in use (See Figure 5) and the lateral edges of the upper plate (14) are slightly set back from the lateral ends of the webs (16, 18). As can be seen in Figure 3, the alveolar side webs (16, 18) have a complementary profile (22, 24) to one another, in the form of trapezoidal teeth (26). In this way, the sheet metal used to manufacture the cores is used to the maximum.

In Figure 3 it can be seen that the webs (16, 18) have been welded in such a way that the cut profile (22, 24) of the webs (16, 18) is welded by the edges of the teeth (26) with the upper plate (14), so that there is an offset between the teeth of each web (16, 18), that is, when viewed from the side, the teeth (26) of a lateral web coincide with the gap between the teeth (26) of the lateral core of the opposite side and vice versa. In this way, on the one hand, full use of the sheet used to manufacture the webs is produced and, on the other, when the lateral webs are offset, a better distribution of resistance to vertical forces is achieved. The offset of the webs also makes it easier for the concrete to completely fill the interior of the box, because there is always an outlet for the trapped air during concreting.

Figure 4 shows the geometry of the trapezoidal teeth (26) of a particular embodiment of the invention, which have a height of 220 mm from the edge of the sheet metal, have an upper edge 100 mm wide, the The sides of the teeth have a width of 80 mm and the continuous base of the webs has a height of 80 mm to the base of the trapezoidal tooth, with a width of the base of the tooth of 160 mm, with which these souls can be manufactured from a 300 mm wide plate, without wasting material. This is due to the fact that the webs have geometrically equal and complementary profiles.

Figure 5A shows a flat floor (30) using the metal beams of the invention described above, with a compression layer (40). The beam is placed with the widest plate (12) at the bottom, so that the edges of the widest bottom plate (12) support the precast concrete slabs (32). Once all the beams and slabs have been placed, HA-25-F/12/I concrete is poured over the entire assembly, to create a concrete layer (36), which extends continuously through the gaps in the souls inside the beams, forming mixed box beams with steel reinforcement and a concrete core (36). A cross brace (42) is disposed across the sockets. The longitudinal reinforcement (34) necessary in case of fire is shown inside the box. Said longitudinal reinforcement is made up of corrugated bars of different diameters (34) supported and welded on sleepers (38) that have notches with dimensions adapted to the profiles of the bars (34). In addition, transverse bars (42) are also shown that cross the box girder through the notches of the alveolar webs, both in the case of parallel disposition of the notches of the webs, and when said webs are counterbalanced and the notches of the alveoli, decaled.

Figure 5B shows a flat slab (30) without a compression layer.

It is worth mentioning that for the embodiments of the box girder, according to the present invention, described above, the calculation checks of the resistances required by the regulations in force have been carried out, that is, the Technical Building Code / Structural Safety / Actions in Construction (CTE-SE-AE), Technical Building Code/ Structural Safety/ Steel (CTE-SE-A), Structural Steel Instruction (EAE) and Structural Concrete Instruction (EHE-08).

Said calculation checks carried out are the service limit state of deflections under permanent loads, service limit state of deflections under total loads, service limit state of stresses in concrete, service limit state of stresses in steel, ultimate limit state bending in mixed section, state Ultimate shear limit in mixed section and fire situation with R90. In all the checks, the appropriate safety coefficients have been used for the materials and for the loads. After carrying out the checks, it can be concluded that both realizations of beams meet the strength and safety criteria required by current regulations and therefore are a viable solution for the construction of flat floors in multi-storey buildings.

With the tested steel box girders according to the invention (N20+5 and N30+10), permanent load deflections ranging between 7.91-12.14 mm are obtained, with the box girder without concrete filling and 4.08- 5.77 mm with the HA-25-F/12/I concrete-filled box girder. Camber (slight, convex curvature that is made in a beam or truss to compensate for any anticipated sag when supporting weight) can be given to the metal beam at the time of manufacture. Likewise, depending on the type of beam used, the critical stresses in the upper plate range between 160-170 N/mm2

Claims (12)

1. A box girder (10) for mixed metal-concrete flat floors comprising: • a first lower longitudinal metal plate (12); • a second upper longitudinal metal plate (14), of smaller width than the lower plate (12) and parallel to it; Y • two alveolar metal lateral webs (16, 18), parallel to each other, where the distance between their outer faces is slightly greater than the width of the upper plate (14), welded at their upper and lower edges, perpendicularly to both upper (14) and lower (12) metal plates, so that the lateral edges (20) of the lower plate (12) protrude from the lateral webs (16, 18) to support the slab (30), in use , and characterized in that the lateral edges of the upper plate (14) are slightly recessed with the outer face of the lateral souls (16, 18), where the upper plate (14) rests on part of the width or thickness of said lateral souls (16, 18), partially leaving the rest of said width or thickness of the lateral webs (16, 18) uncovered; in which said alveolar lateral webs (16, 18) have a continuous and straight side and the other side are profiles with teeth (26), separated by alveoli, so that the teeth and alveoli are geometrically the same, complementary ( 22, 24) and have the same dimensions. 2. A beam according to claim 1 characterized in that it is made of steel. 3. A beam according to any preceding claim, characterized in that the lateral webs (16, 18) are arranged in such a way that they present an offset or phase shift between the alveoli of both webs. 4. A beam according to claims 1 or 2, characterized in that the lateral webs are symmetrical, without offsets, leaving diaphanous gaps facing each other on both sides, between the teeth (26) that delimit the alveoli. 5. A beam according to any one of the preceding claims characterized for having welded corrugated bars (34) to improve fire resistance longitudinally and parallel to the direction of the box beam itself. 6. A beam according to claim 5, characterized in that the bars are arranged inside the box-beam welded to positioning metal plates (38). 7. A beam according to any of the preceding claims, characterized by having a transverse reinforcement (42), perpendicular to the longitudinal direction of the box girder, passing through the lateral webs, through their alveoli, in any arrangement of said webs, parallel or offset. 8. A beam according to any of the preceding claims, characterized in that the alveolar side webs (16, 18) are manufactured by cutting a single sheet of sufficient size, following a saw tooth profile (26) with a trapezoidal configuration, in the form that 2 symmetrical alveolar cores are obtained from a single piece. 9. A composite beam according to any of the preceding claims, characterized by comprising a concrete core (36) inside. 10. A composite beam according to claim 9, characterized in that the concrete covers and fills both the interior and exterior of the box beam. 11. A flat slab (30) characterized by comprising a set of two or more box girders (10), according to any of the preceding claims, a plurality of formwork, or prefabricated elements (32) supported on the edges (20) of the lower plates (12) of the box girders (10) and a concrete pouring (36) that joins the entire assembly, both outside and inside the box girder (10). 12. A flat slab (30) according to the preceding claim, further comprising a compression layer (40).