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Patent Searching and Data


Title:
FIRE RESISTANT FLOOR BEAM WITH FLANGES AND HEAT INSULATION
Document Type and Number:
WIPO Patent Application WO/2020/167190
Kind Code:
A1
Abstract:
A floor beam of steel having a section showing at least two in principal vertically oriented webs (1,1'), one to the webs upper part fixed horizontal top flange (2) and one to the webs lower part fixed horizontal bottom flange (3) extended outside the webs, acting as support for a floor (4) preferably of concrete elements. One extra horizontal flange (5) is fixed between the webs (1,1') at a distance above the bottom flange (3) at the same time as the space between the bottom flange (3) and the flange (5) containing a heat insulating material (6) against fire.

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Inventors:
THOR JÖRGEN (SE)
Application Number:
PCT/SE2020/000006
Publication Date:
August 20, 2020
Filing Date:
February 10, 2020
Export Citation:
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Assignee:
VÄSTSVENSKA STÅLKONSTRUKTIONER AB (SE)
International Classes:
E04B5/29; E04B1/94; E04C3/07; E04C3/293
Domestic Patent References:
WO1990012173A11990-10-18
WO2008119876A12008-10-09
Foreign References:
US20180291626A12018-10-11
SE457364B1988-12-19
NL1020608C22003-11-18
DE10259584A12004-07-15
Other References:
See also references of EP 3924567A4
Attorney, Agent or Firm:
NORÉNS PATENTBYRÅ AB (SE)
Download PDF:
Claims:
Claims

1. A floor beam of steel with a section showing at least two in principal vertically oriented webs (1,1'), one to the webs upper part fixed horizontal top flange (2), one to the webs lower parts fixed horizontal bottom flange (3) extended outside the webs, acting as support for a floor (4) preferably of concrete elements, characterized in that one extra horizontal flange (5) is fixed between the webs (1,1') at a distance above the bottom flange (3) at the same time as a space between the bottom flange (3) and the flange (5) contains a heat insulating material (6) against fire.

2. A floor beam of steel according to the claim 1 characterized by that the fire protective heat insulating material (6) is fixed inside the beam already when producing the same.

3. A floor beam of steel according to the claim 1 or 2, characterized by that the fire protective heat insulating material (6) consists of stone wool with a density of at least 150 kg/m3.

4. A floor beam of steel according to the claim 1,2 or 3, characterized by that the thickness of the beams bottom flange (3) and flange (5) are adjusted in relation to each other so that the cross section area of the flange (5) is at least 50 % larger than the area of the bottom flange (3) and the fire protective heat insulating material (6) is at least 20 m in thickness .

Description:
FIRE RESISTANT FLOOR BEAM WITH FLANGES AND HEAT

INSULATION

Since the -70's decade, a special technology has with a great success been developed in Sweden and the Scandinavian countries, namely, to build multi storey buildings with load bearing structures of steel in combination with precast floor elements of concrete. Included, and characteristic, for this technology are floor beams of steel with a cross-section similar to the one of a hat. This composed of two at a distance from each other vertical webs, a horizontal top flange attached to the upper part and between the webs and at the lower part a wider horizontal bottom flange extended out from the webs. This bottom flange acts as support for the concrete floor elements and ensures that the beams will be integrated within the floor depth. Only the underside and the edges of the bottom flange is visible under the floor elements. Beams of this type normally are called Hat Beams or HSQ beams .

An advantage with steel beams integrated within the floor depth is that the total depth of the floor being limited, which is of great importance due to the fact that the allowed building heights in Sweden, and also in the other Scandinavian countries, is limited in the town plans. Another advantage is that only the bottom flange can be exposed to fire whilst the other parts of the beam are protected by the surrounding concrete. This is important as the strength of the steel and hence the load bearing capacity of the beam is decreased by heat from fire. That effect normally implies that exposed parts of the steel must be provided with some suitable fire protection. By having only the bottom flange exposed, the area, and also the cost, of obtaining the necessary fire protection of the beam is decreased.

RECORD COPY TRANSLATION

(Rule 12.4) The most common way to protect these types of Hat Beams from fire is to cover the bottom flange with an intumescent fire protecting paint. The main advantage with this type of fire protection is that the paint is having a thickness of only some millimeter and hence do not increase the total thickness of the floor. A drawback is however the relatively high cost per square meter of painted area and that the aesthetic appearance is often being coarse or even similar to an elephant's skin, which at least many architects will find negative. Another drawback is that the paint cannot be exposed to water. Most intumescent paints are water based due to environmental reasons. The actual paint application procedure also requires that the humidity is limited, and that the temperature is kept above zero. This means that the painting application can only be done when the weather is meeting those requirements. This normally means that painting on the building site cannot be done until the steel-structure is protected enough against the outside weather conditions. To be forced to restrict the painting application according to above circumstances can be disturbing for the building process itself. The above also means that the fire resistance of the beams during the build process is limited, which means a potential risk if fire should occur during the building process. To paint the beams in advance in a factory is on the other hand normally not an alternative due to a high risk of damaging the sensitive paint during transport and erection.

The main technical drawback of intumescent paints will however be that the function of these paints is to expand by heat, resulting in a protective insulating layer against the fire with a thickness of 40-50 mm. This means that connecting installation and building parts, for example inner walls and so on, which could prevent the expansion of the paint, is not allowed . Due to the above-mentioned problems with intumescent paints,

Hat Beams in the form of composite steel and concrete beams have been developed. This resulting in that the bottom flanges do not need to be fire protected. Such a beam is for example known by the Swedish patent 437 364. The hollow space in the Hat Beam between the webs and the flanges is filled with concrete. In the lower part of the concrete a number of longitudinal reinforcement bars are fixed. When the bottom flange is heated and weakened by fire, the reinforced bars which are protected by the concrete will take over the bottom flange load bearing function. In order that the steel and concrete shall act together as a composite statically and not become deformed, some form of closely spaced to the steel fixed devices are required which transfer the forces between the steel and the reinforced concrete. In case the concreting is done first on the building site the same is true as for the beams protected by intumescent paint, meaning that the fire resistance during the building process is limited.

A composite beam of steel and concrete according to above is naturally more expensive to produce compared with a Hat Beam made of steel only. However, the higher production cost can in many cases be justified due to the fact that the cost of the intumescent paint is left out and the drawbacks of the painting is eliminated. Lately concrete has been questioned more generally within the building industry due to environ mental reasons.

Furthermore, a tendency in the communities is that the requirements concerning fire protection of structures are increasing. At least this is that valid regarding larger and higher buildings where the use of Hat Beams are most frequent. This can among other things be noticed in a proposal of "Boverket" to EKS 11, which will replace EKS 10. In the EKS documents the requirements of the load bearing capacity for different structures in case of fire is given. In the type of buildings where the above-mentioned beams normally are used, the proposal according to EKS 11 is that the former requirements of a fire resistance during 60 minutes or R 60, in many cases will increase to 90 minutes or R 90. Furthermore, in other cases where the requirements were R 60 or R 90 requirements these may be increased to 120 minutes or R 120.

An increase in the requirements of fire resistance will increase the costs for ordinary Hat Beams as well as for composite Hat Beams. For ordinary Hat Beams a larger amount of intumescent paint are required. Such a high requirement as R 120 can in many cases be difficult to fulfill with intumescent paints. For the composite beams a larger amount of rein forcement bars will be required resulting in increased costs.

The present invention solves the above-mentioned problems and shows a Hat Beam out of steel, which fulfills the increased requirements of fire resistance without the corresponding increased costs, and where there is no need for intumescent paint or a composite structure such as the ones being reinforced by concrete. The beam according to the present invention also have a built in fire protection, already from the factory, which means that fire during the building process can be taken care of.

The present invention is described with reference to the drawing enclosed, where

Fig. 1 shows a cross section of the beam according to the pre sent invention. With reference to figure 1 it is shown how a Hat Beam section of steel is composed in a way known per se by two in principal vertical webs 1,1', one horizontal to the webs upper part fixed top flange 2 and one horizontal to the webs lower parts extending bottom flange 3 acting as a support for a floor 4 preferably of precast concrete elements. At a distance above the bottom flange 3 there is a horizontal extra flange 5 fixed between and to respective web 1,1'. Between the flange 3 and the flange 5 there is a fire protective material 6. This material can preferably consist of an approximately 20 m thick stone wool insulation having heigh density.

An at high temperatures stable heat insulated material 6 under the flange 5 in combination with said outside of the webs 1,1' and above the top flange 2 located concrete 4 with a high heat absorbing effect, generating a strong heat radiation from the flange 5 within the void of the beam to the webs 1,1', which are cooled by the concrete and top flange 2 respectively implying that the increase in temperature of the extra flange 5 in case of fire is limited. By that, the flange 5 can be designed as having a full load bearing capacity even for a very long fire exposure under the beam and compensate for the by fire exposed, and hence weakened, bottom flange 3.

The thickness of the beams bottom flange 3, top flange 2 and the flange 5 can be adjusted in relation to each other and to the heat resistance of the insulation 6, to ensure that an optimal load bearing capacity will be obtained for the steel section as well in normal design against collapse as in the design for fire.