FI86326B - BRANDMOTSTAONDSKRAFTIG, FOERTILLVERKAD BJAELKLAGSBALK AV STAOL. - Google Patents

Abstract

The fire resistant, pre-stressed structural flooring carrying beam of steel includes two vertical webs (2) and a bearing plate (4) along the bottom of the beam extending outside the webs (2) for bearing the floor structure, the upper side of which is above the upper side of the steel beam after finished concrete pouring. The webs (2) are those of two channels (1) fixed to the bearing plate (4) with their toes in opposing, mutual, spaced relationship. The upper flanges (5) of the channels are provided with projecting means (6, 6 min ) fixed at pre-determined mutual spacing along the beam. An open space between the channels (1) is thus provided between the toes of the channels for filling with concrete (10) when concrete is poured, such as to achieve static co-action between the steel beam and concrete via the means (6).

Description

1 86326

The present invention relates to a fire-resistant, prefabricated midsole steel beam for supporting a beam between a support beam which cooperates with concrete and comprises two vertical webs. -10 The top of the base after finished casting is located above the top of the steel beam. The beam, with a horizontal support flange projecting out in both directions at the bottom, is shaped so that it is mainly located inside the beam thickness and so that the static interaction between the steel beam and the concrete casting is maintained; said casting is preferably carried out on site in conjunction with the casting normally performed on the beam element. Due to the special design, the beam has a high rigidity with respect to the weight of the steel and the height of the structure, and in addition, good fire resistance is maintained.

Steel beams are becoming more common in multi-storey buildings supported by beams. Depending on the number of storeys and the activity carried out in the building, a bracket and beam are usually subjected to a fire resistance requirement of one or two hours.

The conventional method is to use I- or H-shaped rolled beams and place the beam on their upper 30 flanges. The disadvantage of this method is that the total thickness of the beam increases. Downward beams also make it difficult to install air conditioning and piping. In addition, the beams must be fire-protected to provide the required fire resistance. This most often needs to be done by lining-.35 rack beams completely, for example with drywall.

One way to reduce the above disadvantages is to place the beam elements on the lower flange of the beams. This reduces the overall height of the beam 2 86326 and facilitates the installation of air conditioning and piping. Fire protection is also facilitated because only the lower flange is exposed to fire at the same time as the inner parts of the beam remain cool due to the surrounding concrete, even during the long-term effect of the fire. The fire protection normally required is achieved by painting the lower flanges of the beams with refractory paint. The disadvantage of this method is that the thickness of the beam limits the structural height of the beams. In certain cases, this may cause difficulties in creating sufficient rigidity with longer spans. However, the biggest drawback is the difficulty of installing the beam elements, as the ends of the elements have to be placed between the flanges of the support.

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To avoid the latter problem, beams with a closed hollow profile and protruding lower flanges have been developed. These are made by welding four plates together with continuous welds. The disadvantage of such beams is that they are more expensive to manufacture than rolled I or H beams of the same weight or load-bearing capacity, inter alia because of the need for expensive special welding equipment. A further developed model of the latter beam is described in the Swedish publication SE 448 897. Said beam is manufactured by welding the upper flange and the lower flange to the four flange edges of the H-profile. The flanges of the H-profile thus form the vertical column of the new hollow beam, and the vertical column of the H-profile forms the central flange. The beam can be manufactured using ordinary welding machines, and therefore it is less expensive to manufacture than the above-mentioned beam having a common hollow profile. On the other hand, material costs increase because relatively thick vertical columns and a center flange are not statically ideal ... 35 from an ideal point of view. The weight of the beam to achieve a certain stiffness or load-bearing capacity also increases in general. The fire resistance is slightly better than ordinary hollow beams due to the fact that at the points where the heat rise during the fire 3 86326 is limited, the relatively thick vertical columns correspond for the most part to the load-bearing capacity. On the other hand, however, the lower part of the beam must be painted with fire protection if a fire resistance time of one hour is to be achieved, or alternatively the 5 beams are not used statically up to the permitted values, which in turn reduces material costs.

In the embodiments described above, it is difficult to achieve a higher degree of static interaction between the ball and the concrete casting because the interaction is very limited around the beam. Static co-operation should be able to increase fire resistance as well as load-bearing capacity and rigidity. The latter feature is very important, because it is the rigidity that can become a problem for beams that are placed inside the beam thickness due to the limited construction height available.

It is an object of the present invention to provide a prefabricated steel beam as mentioned in the introduction which overcomes the problems described above. The beam according to the invention is characterized in that the webs consist of webs of two U-profiles attached to the support flange with their open sides facing each other and the flange edges of both U-profiles spaced apart, and that the U-profiles are spaced apart. the upper edges of the profiles have protruding members attached to them at predetermined distances from each other along the beam, said spacing 30 between the flange edges of the U-profiles providing an open space between the U-profiles for filling the beam with concrete during concrete casting and static interaction between the concrete.

-.35 The present invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 is a cross-sectional view of a prefabricated beam according to the present invention.

4 86326 Fig. 2 is a side view of the beam of Fig. 1, Fig. 3 is a cross-sectional view of the beam of Figs. 1 and 2 when the beam is installed on a construction site and supports two beam elements, Fig. 4 is a cross-section of another beam element supporting Fig. 5 is a cross-sectional view of a third beam 10 supporting two beam elements according to the present invention, Fig. 6 is a schematic longitudinal cross-section of a fourth beam embodiment according to the present invention, and Fig. 7 is a partially cross-sectional end view of the beam shown in Fig. 6.

Figure 1 illustrates a beam according to the present invention in cross section. The beam has two rolled U-profiles 1, which are placed side by side with the open ends facing each other so that a gap is formed between the respective end edges of the profile 1. The web or vertical column 2 of the U-profile 1 forms a vertical column of the new beam profile, and in terms of material costs this is more advantageous compared to the beam described in SE 448 897, because the vertical column of the U-profile 1 is thinner than the flanges of the H-profiles. The U-profiles 1 are welded from their lower flanges 2 to a sheet metal support flange 4. The upper flanges 5 of the U-profiles 1 and perpendicular to the longitudinal direction of the U-profiles 1 are welded with spacers 6 at a predetermined distance from each other to the sliding transmission to achieve synergies. The spacers 6 can, for example, be made of angled steel profiles or reinforced steel. The distance between the pieces is determined according to the respective loads. Alternatively, the spacers 6 can be made with outwardly extending screws 6 'welded to the flanges 5 or to a slightly extending area, so-called with pins shown schematically

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5 86326 shown in broken line in Figure 2. An end plate 7 is welded to the ends of the beam, which transfers the load of the beam to the base of the column, for example. The beam according to the present invention can be manufactured very simply, because conventional welding machines can be used in its manufacture. Unlike the above-mentioned beams such as hollow beams, only two longitudinal weld seams are required here instead of four. Only 10 short small welds are needed to weld the spacers 6 to the upper flange 5. The beams can be fabricated in advance in the workshop and installed in place on the construction site. After the installation of the beam support elements 8 (Fig. 3), a concrete casting is cast on the beam support flange 4 against the beam support flange 4. At the same time, the cavity of the beam and the space between the beam element 8 and the beam are filled with concrete. The spacers 6, 6 'maintain an effective static interaction between the steel beam and the concrete casting, which considerably increases the load-bearing capacity and rigidity of the structure compared to beams similar to those described in the introduction, which are similar in steel weight or height.

The design of the beam according to the present invention is also favorable for the fire effect. A substantial part of the carrying capacity is provided by the lower flanges 3 of the U-profiles. These are located under the protection of the support flange 4. Although the steel has a higher thermal conductivity, the support flange 4 forms a direct radiation shield U-profile 1 for the flanges 3; this, together with the concrete casting with a high heat capacity, causes the heat rise in the U-flanges 3 to be slower than in the case of conventional beams such as hollow beams. Due to this fact and the fact that the concrete casting during a fire corresponds to an increasing part of the load-bearing capacity, the fire resistance of the beam is substantially high without the fire insulation of the support flange 4.

An application of the present invention to further increase the load-bearing capacity and fire resistance is to place one or more reinforcing steels 11 in the cavity of the beam 6 86326, as can be seen in Figure 4. The reinforcing steels 11 are attached to the beam before the spacers 6 are welded and preferably also attached.

The reinforcing steels 11 are placed so far apart from the bottom of the beam that they remain sufficiently cool for the required fire resistance time, while the distance to the top of the beam is chosen large enough to create an effective inner lever. Reinforcing steel 12 can also be placed close to the upper flanges 5 of the U-profiles 1 in order to increase the steel area, thus even in the upper parts of the beam.

Another embodiment of a beam according to the present invention can be seen in Figure 5; it can be used to achieve 15 very short fire resistance times. A thin thermal insulation layer 13 is placed between the support flange 4 and the lower flanges 3 of the U-profiles 1. Despite the fact that said insulation is thin, together with the high heat capacity of the concrete casting, it very much slows down the temperature rise in the lower flanges 3 of the U-profiles 1 during the fire, which is of great importance for the load-bearing capacity and also the fire resistance.

Another embodiment -25 of the beam according to the present invention can be seen in Figures 6 and 7; in this application, the reinforcement 11 is utilized in beam prestressing, which provides a further increase in the beam. For example, the tension can be adjusted to compensate for the deflection caused by the beam structure's own weight. For example, the tension can be provided by making the reinforcing steel 11 slightly longer than the distance between the two end plates 7 of the beam and by having the reinforcing steels 11 in their end portions through which the nuts 14 can cooperate with the reinforcing steel and fasten the reinforcing steel 11 between the end plates 7. In order to simply place the reinforcing steels 11 between the end plates 7, they can be provided with longitudinal grooves 15.

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Claims (9)

1. Fireproof, prefabricated beam floor beam in conjunction with concrete and comprising two vertical lifts (2) and a projecting horizontal support flange (4) projecting on the underside outside the web (2), the upper surface of which after finishing is located above the frame beam upper side, characterized in that the bodies (2) constitute life in two U-profiles (1), which are fixed to the support flange (4) with their open sides facing each other and with a distance between the flange edges of both U-profiles (1) and That at the upper flanges (5) of the U-profiles (1), these projecting means (6, 6 ') are fixed at predetermined distances from one another along the beam, whereby an open space between the U-profiles between the two U-profiles is provided. profiles (1) for filling the beam 35 with concrete (10) during concrete casting and for achieving a static interaction through the members (6, 6 ') between the frame beam and the beam Tong. IN; 9 86326 2. A beam according to claim 1, characterized in that at least one reinforcing iron (12) is fastened just below the upper flanges (5) of the U-profiles (1). 3. A beam according to claim 1 or 2, characterized in that at least one longitudinal reinforcing iron (11) is attachable in the space between the U-profiles (1) above the support flange (4) but below the center of gravity of the composite profile. 4. A beam according to any one of the preceding claims, characterized in that the beam comprises a thin thermal insulation layer (13) between the support flange (4) and the lower flanges (3) of the U-profiles (1). 5. A beam according to any of the preceding claims, characterized in that the reinforcing iron (11) is extended a distance, its total length being somewhat greater than the distance between the end plates (7), whereby it can be biased between the end plates (7) by nuts. (14) towards the outside 20 of the end plates (7) which cooperate with threads formed in the end portions of the reinforcing iron (11). 6. A beam according to any of the preceding claims, characterized in that an elongated bar (15) is provided in the end plates 25 (7) for facilitating the insertion of the reinforcing iron for prestressing the beam by the end plates (7). 7. Beam according to claim 1, characterized in that the projecting means (6) projecting from the upper flanges (5) preferably connect perpendicular to the longitudinal direction of the beam at predetermined distance and / or are formed from the upper flanges (5) or the area adjacent to them. protruding screws (6 ') ·