EP1113116A2

EP1113116A2 - A stud and an exterior wall

Info

Publication number: EP1113116A2
Application number: EP00128698A
Authority: EP
Inventors: Jan Strömberg
Original assignee: BPB Ltd; Plannja AB; BPB Gyproc Nordic East AB
Current assignee: Plannja AB; BPB Gyproc Nordic East AB
Priority date: 1999-12-30
Filing date: 2000-12-29
Publication date: 2001-07-04
Also published as: EP1113116A3; AU2719901A; NO20006721L; NO20006721D0; WO2001049952A9; NO316327B1; WO2001049952A1; EP1242697A1; SE9904864D0

Abstract

An insulated exterior wall of a building is made up of inner and outer boards (31,32 and 33,34) screwed to sheet steel studs (37-39) and there are insulation (40) in the spaces between the studs. The web (14-18) of each stud is retracted inwardly a distance that is between 1/3 and 2/3 of the of the width of the flanges, and the retracted portion (18) of the web has overlapping longitudinal slots (19) such that the transverse thermal transmission capability and the transverse bending stiffness of the stud are less than 1/3 of the corresponding values of a corresponding non-slotted web.

Description

Field of invention

This invention relates to a stud for exterior walls, made of bent sheet steel and comprising two parallel flanges and a slotted web between the flanges and a wall construction based on such studs.

Brief description of the state of the art

Exterior walls in buildings with high demands on thermal insulation, for instance apartments and offices in cold climates are increasingly often made up of inner and outer boards screwed to C-shaped steel studs and fully insulated with mineral wool. Typical wall thickness is 150- 300 mm. In these walls the studs form thermal bridges which reduces the heat insulation. In order to reduce thermal bridging the webs of the C-studs may be perforated with overlapping slots perpendicular to the thickness of the wall. That reduces the heat transfer typically 4 to 8 times. A disadvantage with this perforation is that the strength and stiffness of the web are reduced, typically to 10-30 % of that of an unperforated web. This causes difficulties when screwing the boards to the stud. It may even make it necessary to use a thicker gauge steel than otherwise necessary, which increases the cold bridging and the costs.

Object of invention

It is an object of the invention to provide a stud for exterior walls, which has good thermal properties and is sufficiently stiff during the erection of the wall. This is achieved principally by a stud in which, in at least half the distance between the flanges, the web is retracted inwardly a distance that is between 1/3 and 2/3 of the of the width of the flanges, and the retracted portion of the web has overlapping longitudinal slots such that the transverse thermal transmission capability and the transverse bending stiffness of the stud are less than 1/3 of the corresponding values of a corresponding non-slotted web. The invention is defined by the claims.
It is an advantage that an inventive stud is both considerably stronger and considerably stiffer than an ordinary C-stud with the same weight. Further, the inventive studs can be packed to a volume for transportation and storing that is almost only half of the volume for ordinary C-studs

Brief description of the drawings

Figure 1 is a section through a stud in accordance with the invention.
Figure 2 shows how the stud in figure 1 deforms when subjected to a force by the drilling point of a screw fastening a board to the stud.
Figures 3 and 4 correspond to figures 1 and 2 respectively, but show a modified design of the stud.
Figures 5 and 6 correspond to figures 1 and 2 respectively, but show the shape and behaviour of a conventional C-stud.
Figure 7 is a fragmentary view showing a slot pattern in the web of the stud shown in the preceding figures.
Figure 8 is a view corresponding to figure 7, but showing an alternative slot pattern.
Figure 9 is a transverse section taken along lines 9-9 in figure 7.
Figure 10 is a horizontal section through an exterior wall having studs of the kind shown in the preceding figures.
Figure 11 is an end view of two studs put together.
Figure 12 is an end wiew corresponding to figure 11 but showing the two studs when being put together.
Figure 13 shows a plurality of studs shown in figure 11 packed for transport.

Detailed description of the illustrated example of the invention.

The sheet steel stud shown in cross section in Figure 1 is a wall stud for exterior walls. It is made of sheet steel with a thickness in the range of 0,75 to 2 mm. It has two flanges 12, 13 and an intermediate web 14-18. The web consists of two portions 14, 15 perpendicular to the flanges, two inclined portions 16, 17, and a central portion 18. The central portion 18 of the web has a great number of overlapping slots 19, as best appears from figure 7 which show slots that are cut without removal of material. Figure 8 shows an alternative design with slots 19 in the form of punched elongated holes. The slots reduce the heat transfer through the web by a factor 3 to 10 depending of the size and distance of the but in the same time they make the web both softer and weaker by bending also by a factor around 3 to 10; weaker the more the heat transfer is reduced. The flanges 12, 13 have folded back edges 20, 21. The edge 20 of the flange 12 is folded perpendicularly to the flange, whereas the edge 21 of the flange 13 is folded back. The folding of the edges and the fact that the flange 12 is somewhat wider than the flange 13 makes it possible to put the studs two together in pairs as shown in figures 11 and 12. Such studs put together in pairs can then be piled into a transport package as seen in figure 13. The central portion 18 of the web lies roughly on a line between the middle points of the flanges 12, 13, which is advantageous but not necessary which will be explained later. The flange 13 lies within two normals that can be drawn from flange 12 at the corners of flange 12.
Figure 2 shows the situation when a board 23 is screwed with a piercing or self-drilling screw 22 pressing against the flange 13. The shear centre 24 of the profile is close to the web 18 and close to the plane of the direction of the screw force. It means that there is almost no twisting of the profile and that the bending moment in the weakened web 18 is causing only minor deformations.
Figures 3 and 4 show the same as figure 1 and 2. The difference is that the flange 25 is turned the other way. The shear centre 27 is also then close to the web. The behaviour when screwing the board is the same as for the stud in figure 1.
Figure 5 shows a common C-stud with, through perforations, a weakened web 28. The sheet steel thickness must be 1 mm or more due to the weak web and the difficulties to screw boards on such a profile. Figure 6 shows the same stud when a board 23 is being screwed to it. Its shear centre 29 is located some centimetres outside the web. When the force of the drilling point of the screw 22 acts on the flange 30 the eccentricity of the force causes the profile to rotate away and the web to bend extensively. The drilling is difficult since the flange is not normal to the drilling point. Furthermore, there is a gap between the board and the flange at the drilling point and it is a risk that the gap is never closed. Increased sheet metal thickness reduces these difficulties but it also increases the cold bridge and makes the drilling process slower. The movements when using a stud according to the invention are much smaller and the flange moves almost parallel to the board so that the disadvantages with the deformations mainly caused by the weak web is eliminated. This is a main advantage with the invention, but there are also other advantages as will be shown later. The advantage is at its peak when the web is retracted to the middle of the width of the profile and the retraction cover most of the height of the profile as in figure 1. However the advantages starts to appear at less retraction and remains with even greater retraction. A reasonable limit is that the web 14-18 at at least half of the distance between the flanges shall be retracted inwardly a distance which is between 1/3 and 2/3 of the width of the flanges.
When bending a stud of thin gauge steel in its stiff direction perpendicular to the flanges, the compressed parts tend to buckle if they are wide enough. The overall stiffness and strength of the stud in a wall is depending of the areas of the unbuckled parts of the flanges and of the nearby web. The part of the web in the stud in figure 6 that does not buckle is a little portiont close to the corner, whereas for the studs in figure 1 and 3 the parts 14 and 16 (or 15 and 17 when bending in the other direction) are normally not buckling at all. An accurate calculation for one size of studs has shown that the stud in figure 1 is 18 % stronger for bending out of the wall plane (that is in the direction of the web) than a common C-stud according to figure 5 with the same weight.
Figures 11 and 12 show how studs can be put together in pairs. One necessary condition is that one flange is at least two sheet thicknesses wider than the other. Figure 12 shows two studs when being put together and explains why it is an advantage to fold the end stiffener of the narrower flange inwards. Also C-studs can be piled in the same way. The difference appears in figure 12, where the studs are packed for stocking and transportation. Through the shape of the studs they can be packed twice as dense as C-studs can be.
If the web portions 18 are pulled past the middle, these web portions will collide at attempts to put the profiles together according to Fig 11. If the web portions 18 are not extended to the middle of the profile, a distance between the web portions will appear when putting the profiles together according to Fig 11, which means that they will not be as compactly piled as is shown in Fig 13. This means that the portion 18 should be within a few mm, for example within 5 mm, from this line between the middle points of the flanges but not pass this line. It also appears from Fig 12 that the combined lengths of the web portions 14 and 15 shall not surpass the length of the web portion 18.
Figure 10 shows in a horizontal section an exterior wall in which double layers of wallboards, for example gypsum wallboards 31, 32, are attached to the flanges 12 of the studs by means of non-illustrated screws and double layers of wallboard 33,34 are attached to the flanges 13 in the same way.
The studs are vertical but they can also be used horizontally if they are fixed to brackets on pillars.
The webs perforated as in figures 7-9 are typically reducing the heat transfer 4-6 times and are typically 5-8 times softer for bending than an unperforated web. The invention makes it possible to increase the perforations even more, to make the web up to 10 times softer, which may reduce the heat transfer down to 1/10 of the heat transfer of the unperforated web.
Within the concept of the invention there are many alternatives to be considered. The flange stiffeners 20-21 may be folded in other angels than described. The parts of the web adjacent to the flange 14-15 may be inclined and may even be eliminated so the inclined part 16-17 starts directly from the corner of the flange. The flat middle part of the web 18 may be inclined for instance when the flanges are directed in different directions as in figure 3. It may also have unslotted areas and/or be stiffened by additional folds in the sheet steel with only minor influence on the heat transfer. The invention is not limited to the shapes in figure 1 and 3 but covers also the above described alternative shapes.

Claims

A stud for exterior walls, made of bent sheet steel and comprising two parallel flanges (12,13) and a slotted web (14-18) between the flanges, characterised in that,
at at least half the distance between the flanges, the web 14-18) is retracted inwardly a distance that is between 1/3 and 2/3 of the width of the flanges, and that the retracted portion of the web (18) has overlapping longitudinal slots (19) lengthways the stud such that the transverse thermal transmission capability and the transverse bending stiffness of the web both are less than 1/3 of the corresponding values of a corresponding non-slotted web.
A stud according to claim 1, characterised in that the web (14-18) comprises flat end portions (14,15) against the flanges (12,13) and inclined flat portions (16,17) between the end portions and said retracted portion(18) which is substantially flat.
A stud according to claim 2, characterised in that the flat end portions (14,15) are at substantially right angles to adjacent flanges (12,13) and have widths between 10 and 30 mm.
A stud according to claim 2, characterised in that said flat retracted portion (18) of the web between the inclined portions (16,17) is at right angle to the flanges (12,13) and located within 5 mm from a plane through the middle points of the flanges.
A stud according to any one of claims 1-4, characterised in that the slots (19) extends over a width of at least 1/3 of the distance between the flanges
A stud according to any one of claims 1-5, characterised in that the flanges (12,13) are between 30 mm and 70 mm wide.
A stud according to any one of claims 1-6, characterised in that the flanges (12,13) are bent in the same direction
A stud according to any one of claims 1-6, characterised in that the flanges (12,13)are oppositely directed
A stud according to any one of claims 1-8, characterised in that one flange (12) is somewhat wider than the other and that the narrower flange (13) is situated between two parallel normals that can be drawn from the wider flange at the corners thereof.
A stud according to any one of the preceding claims, characterised in that the slots (19) are such that the thermal transmission capability of the web is between 1/4 and 1/8 of the thermal capability of an corresponding web without slots and that the the transverse bending stiffness of the stud is less than 1/5 of the stiffness of a web with an corresponding web without slots.
A stud according to any one of the preceding claims, characterised in that the sheet steel thickness is between 0.75 and 2 mm.
An insulated exterior wall of a building, comprising inner and outer boards (31,32 and 33,34) screwed to sheet steel studs (37-39) and insulation (40) in the spaces between the studs, characterised in that the web of each stud, at at least half the distance between the flanges, is retracted inwardly a distance that is between 1/3 and 2/3 of the of the width of the flanges, and that the retracted portion of the web has overlapping longitudinal slots (19) such that the transverse thermal transmission capability and the transverse bending stiffness of the web are less than 1/3 of the corresponding values of a corresponding non-slotted web.