GB2338252A

GB2338252A - Fire-resisting wall

Info

Publication number: GB2338252A
Application number: GB9913329A
Authority: GB
Inventors: Paul V Howard
Original assignee: BPB Ltd
Current assignee: BPB Ltd
Priority date: 1998-06-08
Filing date: 1999-06-08
Publication date: 1999-12-15
Anticipated expiration: 2019-06-08
Also published as: GB9812326D0; DK1007803T3; DE69920378D1; AU4278499A; GB9913329D0; EP1007803A1; GB2338252B; DE69920378T2; EP1007803B1; WO1999064690A1

Abstract

A fire resisting wall structure, offering prolonged fire resistance at considerable heights, comprises two rows of spaced vertical supports or studs (10, 14), in which the rows of studs are separated by a central layer of fire resisting building board (11-13) to which the studs of both rows are secured, while the opposite outer faces of the studs are covered by respective facing layers of fire resisting building board (16-17) secured to the studs. The thickness of the central layer should be greater than that of either of the facing layers.

Description

2338252 - 1 Fire-Resisting Wall This invention relates to fire resisting

partition walling constructed from spaced vertical supports or studs, secured at top and bottom and having a covering of building board.

I- Fire resisting walls have been designed to survive a fire duration with no loss of integrity or insulation performance. This has led to a design where a wall consists of metal studs with boards attached to each side and occasionally insulation in the cavity. As the fire test progresses the layers of boards fall way until finally the wall fails either by heat transfer or through loss of integrity.

Particularly useful in this connection are boards made in accordance with our Patent GBB-2 053 779, which consist of a set cementitious (usually gypsum) core, preferably reinforced with chopped inorganic fibre, and a surface layer on at least one face comprising an inorganic fibre sheet embedded in the gypsum surface so that the material of the core extends in a continuous film over the web outer surface of the sheet. This board affords good resistance to spread of flame, owing to its wholly inorganic surface, but also has a high degree of inherent fire resistance arising from the behaviour of the core materials when the board is exposed to fire.

When a gypsum surface is exposed to fire, the combined water of crystallisation is gradually released in the form of water vapour in two stages, both of which are specs/3) 9 8 15.99 1 1 1 endothermic, while a covering of calcined gypsum remains strongly adherent to the uncalcined material, retarding the dehydration process, which becomes progressively slower as the thickness of the calcined layer increases. While this continues, the temperature behind the plane of calcination remains only slightly above 100'C so that, until all the water of crystallisation in the board has been expelled, the temperature of materials in contact with or adjacent to the unexposed side of the board should not exceed 1000C. This is well below the ignition temperature of most materials that are either used in building or stored in buildings.

Once the gypsum content of the board is completely calcined, the residue (Calcium sulphate) continues to act as an insulating barrier for as long as it remains intact. Inorganic fibre webs and core fibre reinforcement help to ensure the integrity of the board and to maintain a barrier to the fire for some considerable time after calcination.

With this design of partition the metal framework of the wall is at temperature of around 1000C at the point of failure for the wall, as all the boards on the exposed face have fallen away. This presents a problem when a wall of extended height is required, as at elevated temperatures steel suffers loss of strength. This strength loss means that the wall will not remain stable and consequently will not support the boards on the unexposed face of the metal.

To make matters worse, when steel is heated differentially it undergoes thermal bowing which means that the weight of the wall itself is acting eccentrically. For this reason, fire resistant partitions of considerable height, for example up to 20m, have only been achieved by the use of specs/39815.99 load-bearing structural frameworks, which enable the partition to be subdivided into smaller areas affording the desired resistance.

It is an object of the present invention to provide an easilyerected partition wall structure which can offer four hour fire resistance at considerable heights, for example up to 20m, without the use of a load-bearing structural framework.

11-1 1 1.

1 1 - In accordance with this invention, such a fire resisting wall structure comprises two rows of spaced vertical supports or studs of fire resistant material, preferably of metal such as steel, in which the rows of studs are separated by a central layer or core of fire resisting building board to which the studs of both rows are secured, and the opposite outer faces of the studs are covered by respective facing layers of fire resisting building board secured to the studs, the thickness of the central layer being greater than that of either of the facing layers, as illustrated by the example described herein. The preferred board is inorganic fibre reinforced gypsum board, for example of the kind discussed above.

The invention achieves its object by providing support to the boards for the duration required. Of the two metal frames separated by the board core, the frame closest to the fire is sacrificial whilst the second frame remains cool and consequently has the strength to keep the wall standing for the required duration. The thick-er core continues to be supported by the surviving frame.

specs/39815.99 4 - To attain greater fire resistance, each layer of board is preferably made up of several thicknesses of board. The desired thickness of the central layer can be obtained by employing at least two thicknesses of board while the facing layers may consist of fewer thicknesses of board.

An advantage of the invention is its economy in the quantity of building board required for a given degree of fire resistence. This follows from the location of the majority of the boards, that is, the greater amount of fire resistant material, in the centre layer, where it is protected by the sacrificial outer layers. This centre-weighted or symmetrical design enables thinner facing layers to be used than if each facing layer itself had to constitute the main defence against the transmission of fire, which might attack either side. The facing layers, or at least the layer on that face exposed to a known fire risk, preferably incorporates a material of high fire resistance and integrity, for example a metal (e.g. steel) sheet; this can be used to maximise the potential of the air cavity or may serve to reduce the number of thicknesses of board employed in the outer layers.

This wall is designed to maintain 4 hours fire resistance at extended heights and consequently when tested at 3m height achieves 5 hours fire resistance. However, the traditional failure criteria do not apply, and the critical factor is the temperature of the cold metal frame at 4 hours duration. The cold metal frame has a temperature of approx. 1OCC with a small temperature differential over the stud at the four hour duration, which allows the. design to be used at extended heights.

specs/39815.99 Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing which is a horizontal section through a wall in accordance with the invention.

In erecting the partition shown in the drawing, a first framework includes a metal head channel and base channel which are fixed at 60Omm centres to the adjacent floor and ceiling surfaces respectively. Strips of inorganic fibre reinforced gypsum board 72mm wide and 25mm thick are interposed between the channels and the surfaces to which they are fixed. metal studs 10 are then positioned at 60Omm centres between the head and base channels. The end studs at the sides of the partition are fixed to the adjacent wall at 60Omm centres through another strip of inorganic fibre reinforced gypsum board.

Three thicknesses of inorganic fibre reinforced gypsum board, arranged in abutting vertical lengths, are fixed by screws to the faces of the studs 10 which are to constitute the inner face in the finished partition. A first layer 11 of 15mm board is fixed by 25mm screws at 30Omm centres to all metal framing, a second layer -12 of 25mm board by 42mm screws at 30Omm centres and the third layer 13 of 15mm board by 75mm screws at similar spacing. The joints between the boards are staggered with respect to adjacent layers, with a full board at the fixed edge.

A second similar metal stud framework (but using 50mm thick strips of board at the head, base and sides) is constructed alongside and in contact with the three layers of board.

The studs 14 in the second framework are staggered by 30Omm with respect to the studs 10 in the first framework, and the specs/39815.99 second framework is fixed to the three layers of board 11-13 using 75mm screws.

1-, 11 The external face of each framework is then lined with 0.7mm steel sheet 15 fixed at 30Omm centres with 13mm wafer head screws. A layer of 25mm board 16 is fixed to the steel sheet using 25mm screws at 150mm centres round the perimeter and down the centre of the boards, and an outer layer of 15mm board 17 is fixed through to the steel sheet at 30Omm centres using 42mm screws round the perimeter and down the centre of the boards. The vertical joints between the boards in the outer layers are positioned such that no joint is in alignment with the position of a stud. All joints are taped and filled, and screwheads spotted, with a conventional joint filler.

In a typical example, the channels and studs are of cold formed hot dipped galvanised steel in accordance with BS 2989 (EN 10142), and the boards are glass fibre reinforced gypsum board in accordance with UK Patent GB-B-2 053 779, preferably as sold under the designation 'Glasroc S'.

In a test conducted on a partition 3m high and 3m wide, constructed in a concrete lined steel restraint frame having an opening of this size, the partition demonstrated fire resistance of five hours when tested in accordance with BS476: Part 22: 1987.

specs/39815.99

Claims

CLAIMS il-1 1. A fire resisting wall structure comprising two rows of

spaced vertical supports or studs, in which the rows of studs are separated by a central layer of fire resisting building board to which the studs of both rows are secured, and the opposite outer faces of the studs are covered by respective facing layers of fire resisting building board secured to the studs, the thickness of the central layer being greater than that of either of the facing layers.
2. A wall structure according to claim 1 in which the central layer of building board comprises at least two thicknesses of inorganic fibre reinforced gypsum board.
3. A wall structure according to claim 1 or 2 in which the facing layers each comprise two thicknesses of board and the central layer comprises at least three thicknesses of board.

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4. A wall structure according to claim 1, 2 or 3 in which at least one outer facing layer includes a layer of sheet steel.
5. A wall structure according to claim 4 in which the steel sheet is the innermost layer at the outer face and is secured directly to the underlying stud.

specs/39815.99