GB2480109A

GB2480109A - An open-ended and hollow prism particularly for use as a lint l

Info

Publication number: GB2480109A
Application number: GB1007722A
Authority: GB
Inventors: James Murphy
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-05-08
Filing date: 2010-05-08
Publication date: 2011-11-09
Also published as: GB201007722D0

Abstract

The prism 1 comprises no more than six planar walls 2 enclosing a central cavity, wherein at least two of the walls are parallel with one another and include formations 3 on their inner facing surfaces that are suitable for locating a plurality of strips between the at least two walls such that the strips are oriented perpendicular to, and bridge between, the at least two walls. The prism may be constructed from pultruded glass fibre reinforced polymers and comprise four side walls arranged in a square or rectangular cross section. The formations may comprise rectangular ribs arranged in pairs equally spaced across the inner facing surfaces to form grooves 5, the ribs of one of the inner facing surfaces being directly opposite the ribs on the other of the inner facing surfaces. The prism may be used as a lintel or window sill that reduces cold bridging.

Description

1 IMPROVED HIGH LOAD BEARING GRP BOX SECTION 2 (TYPE) LINTEL 3 THE AREA OF THE INVENTION 4 The invention concerns the improvement of the load bearing properties of Pultruded glass fibre reinforced polymer box section (type) lintels and enabling said properties 6 to be adjusted on site for the load bearing and gap spanning distance requirements of 7 individual building tasks.

8 BACKGROUND TO AREA OF THE INVENTION

9 Post and lintel constructions have been used to support loads above an opening in a wall for centuries, ranging from the stone circles at Stonehenge to 11 present day windows and doorways in commercial and residential buildings. Lintels 12 are horizontally disposed architectural members that are employed to span an opening 13 in a building such as windows and doors to carry the load of the building above that 14 opening. They have been fabricated from a wide range of materials including, stone, timber, concrete and steel. Of these concrete and steel are commonly used due to their 16 durability and inexpensiveness 17 A box cavity lintel consists of opposed upper and lower walls and opposed 18 side walls to form a box section, and may possess up to two wings. One of the wings * ..* * 19 extends laterally away from each side of the box section. The box section is situated S.....

in the cavity of a cavity wall when in use, and the two wings are built into an inside * : 21 and outside wall of the cavity wall respectively. I..

22 The primary requirement of a lintel is its load bearing capacity but resistance S...

23 to weathering, corrosion and consequent reduction in its load bearing capacity are *.....

* 24 equally important. Clearly, because of their size, they also need to be readily transportable and manipulated on building Sites. The construction industry has tried I to satisfy these needs by developing steel lintels (US 4020612, US 4409764, US 2 4757656 and US 6367209). However, a problem with steel lintels is there high 3 thermal conductivity relative to the traditional concrete material of construction which 4 gives rise to the phenomena of "cold bridging".

Cold bridging occurs when heat is transferred by conduction through any 6 material that bridges the inside wall to the outside wall through the cavity of a 7 "cavity" wall, thereby creating cold spots, and subsequently increased condensation 8 on the inside, warmer side, of the wall. Cold bridging can occur through the lintel 9 itself, if the lintel is made of a material of high thermal conductivity such as steel.

Existing steel lintels are known to conduct heat, and it is an aim of some 11 embodiments of the present invention to provide a lintel that does not significantly 12 conduct heat in order to reduce cold bridging. A further disadvantage of known steel 13 lintels is that they need to be protected from corrosion by galvanisation and where 14 exposed to the weather subsequently painted regularly. A similar need to protect from the effects of weathering arises with the use of wooden lintels and it is an aim of some 16 embodiments of the present invention to provide a maintenance-free lintel.

17 To avoid the problems of "cold bridging" and corrosion GB 2410508(2005), 18 GB 2435057 & GB2435057 teach the use of glass reinforced plastic which possesses 19 low heat conductivity together with a pultrusion manufacturing technique to maximise *..S * : * 20 the load bearing capacity of a relatively light weight box section lintel. Fibreglass .: :* 21 Pultrusion is well known as a manufacturing technique for lineal profiles to maximise 22 the structural strength of Pultruded glass reinforced polymer.

*:::: 23 DE 10335692 teaches increasing the load bearing capacity of light weight box * : * 24 section lintel beams formed by Pultrusion from glass fibre reinforced plastic by the insertion along the length of the box section of an inverted "V"-shaped strengthener I the edges of which engage with the sides of the bottom surface and the tip rests 2 against the middle of the top surface. Given the increase in the load bearing capacity 3 of the box section lintel described in DE 10335692 there is a limit on the load bearing 4 strength that can be achieved without increasing the sectional size of the box lintel, the wall thickness of the box lintel, or the "V" shaped strengthener insert.

6 It will be appreciated that, for at least some aspects of the invention, the advantageous 7 performance properties of the current invention reside in the appreciation that the 8 aforementioned problems exist and that further increases in load bearing capacity of 9 light weight, maintenance free, box section lintels possessing minimal thermal conductivity would be advantageous to the building trade.

12 SUMMARY OF THE INVENTION

13 According to a first aspect of the invention, there is provided a box section 14 (type) lintel comprising a substantially empty and open ended polygon prism possessing no more than six straight enclosing walls with a plurality of substantially 16 rectangular protuberances running along the length of the inner surfaces of two 17 parallel sides (the top and the bottom inside surfaces of the prism) with the top and 18 bottom wall protuberances directly opposite each other. Separate rectangular bridging * : 19 strips designed to enter the box section perpendicular to the top and bottom walls, * :: 20 being guided and securely located by the channels effectively formed by the 21 substantially rectangular protuberances running along the length of the top and bottom 22 inside surfaces of the otherwise empty prism to bridge the space between top and *:::. 23 bottom inner walls, and effectively increase the load bearing capacity of the box 24 section lintel. A plurality of such bridging strips may be inserted into the prism in this manner.

1 The substantially empty and open ended polygon prism with its plurality of 2 substantially rectangular protuberances running along the length of the top and bottom 3 inside surfaces is readily manufactured by the Pultrusion process from suitable low 4 thermal conductivity materials such as glass reinforced polymer.

The rectangular bridging strips do not significantly contribute to the overall thermal 6 conductivity of the box section (type) lintel and may be formed from any suitable 7 material including the glass reinforced polymer or other polymeric material used to 8 form the substantially empty and open ended polygon prism.

9 In use the light weight box section lintel is cut to a suitable length spanning the gap to be built over and the required number of bridging strip lengths are cut to 11 equivalent length and threaded through the substantially empty and open ended 12 polygon prism, box section type lintel, between the retaining protuberances on the 13 inner surfaces of it's top and bottom walls. The load bearing properties of the box 14 section type lintel are controllable by increasing the number of bridging strips (strengtheners) inserted before the lintel is end capped. This invention eliminates most 16 of the previously enumerated disadvantages associated with the use of conventional 17 lintels.

19 BACKGROUND SCIENCE *..a

* 20 Without wishing to be bound by theory the following explanation will indicate why 21 the invention confers superior load bearing strength to box section I intels than has 22 been achieved previously.

*: : : 23 A comparison of two box section beam sections having the same cross- * : * 24 sectional area and one with a larger area was conducted, according to the procedure given in "An Introduction to Mechanical Engineering" by Hodder,( ISBN 978-0-340- 1 93995-6) page32, to determine the relative resistance to bending. The resistance to 2 bending is measured as the principal moments of inertia about the centroid of the 3 section its units being mm4. The value which gives the resistance to vertical bending 4 of the section is ly The method used to find the moment of inertia was the same in each case and 6 involved making a two dimensional drawing of each cross-section and then using the 7 built-in functions of the "Solid Works" 3D CAD draughting software.

8 The sections used are shown in detail in diagrams 1 to 3, below, and are designated as 9 parts A, B & C. All parts were drawn using the same outer box section. Parts A and C IC) have an internal section of the same area, whilst part B has an additional internal 11 section.

13 Part A (diagram 1) has two vertical sections within the outer box: 14 The total area is 2013 mm2.

The moment of inertia is 2283206 mm4.

17 Part B (diagram 2) has an additional vertical section within the outer box 18 (three in total): 19 Thetotalareais2569mm2. ***U

The moment of inertia is 2653652 mm4.

* .. 21 * . S S.. * 22 Part C (diagram 3) has an inverted V' section within the outer box: 23 Thetotalareais20l3mm2.

24 The moment of inertia is 2238607 mm4.

S..... * .

I The conclusions from this calculated comparison are:- 3 Part A has the same cross-sectional area as part C, but gives a slightly increased 4 vertical bending resistance with reduced horizontal resistance. The vertical bending resistance will always be higher for a vertical section than that of an angled section 6 with the same area. The vertical reinforcements in section A can easily be added to in 7 order to increase the vertical bending resistance. The vertical reinforcement sections 8 can be made of any suitable material. The rectangular box and the vertical 9 reinforcements are the only items required to give a wide range of bending resistance. l0

11 Part B shows how the vertical bending resistance may be increased by the addition of 12 a single extra vertical reinforcement section. The number of vertical sections that may 13 be added would be limited only by the thickness and spacing of these parts.

Part C has an internal inverted V' section which reinforces the rectangular outer box- 16 section. The inverted V gives reinforcement to both the horizontal & vertical bending 17 resistance. To change the bending resistance of this design a V' made from thicker or 18 different material would be needed. To provide a wide range of bending resistance 19 multiple components would be required. e : 20 * *

21 THE INVENTION IS EXEMPLIFIED BY DRAWII'GS 1 TO 3 ** 22 DRAWING 1 23 Drawing 1 shows an isometric projection of a substantially empty and open ended * : * 24 rectangular prism (1) and shows a plurality of substantially rectangular pairs of protuberances (3) running along the length of the top and bouom inside surfaces of 1 the prism. The top inside surface substantially rectangular protuberances and bottom 2 inside surface substantially rectangular protuberances are positioned opposite each 3 other to create a mirror image, equally spaced across the surfaces separated. Each 4 protuberance of each pair of protuberances is spaced from 3 mm to5 mm apart preferably 3.5 mm to 4.5mm most preferably 3.9 mm to 4.2 mm from its nearest 6 neighbour. This effectively forms a plurality of opposed channels (5) capable of 7 acting as "runners" running along the length of the open ended and substantially 8 empty prism. The substantially empty and open ended rectangular prism is suitable for 9 efficient fabrication by the Pultrusion process using fibre-glass or basalt rovings and matting impregnated with fire-retardant polyester or polyurethane resins. A 11 particularly useful thermo-polymer for the process is a brominated isophthalic based 12 polyester thermoplastic containing catalysts but no accelerators, "Microdal" filler, 13 appropriate pigments and fire retardant resins.

14 The dimensions of the substantially empty and open ended rectangular prism (1), together with the thickness of the wall (2), determine the load-bearing capacity of the 16 substantially empty and open ended rectangular prism (1) or box section. The 17 Pultrusion process facilitates the fabrication of substantially empty and open ended 18 polygon prisms (drawing 1 shows a rectangular example) such as this in the (external) 19 size range 90mm to 215 mm, preferably 95 mm to 210 mm, most preferably 100 mm S...

by 204mm and in wall thicknesses of from 2mm to 6 mm preferably 2.5 mm to 5.5 21 mm, most preferably from 3 mm to 5 mm. The substantially empty and open ended :. 22 rectangular prism (1) or box section may be of any length in the range 2,000 mm to *:::: 15,000mm preferably 3,000 mm to 10,000 mm most preferably 4,000 mm to 8,000.

I.e... * *

DRAWL1G 2 1 Drawing 2 shows an isometric projection of a bridging strip (4) prior to insertion into 2 the substantially empty and open ended polygon prism (1). The bridging strip is 3 designed to slide smoothly between opposite pairs of protuberances (3) on the inside 4 surfaces of the top and bottom walls of the substantially empty and open ended polygon prism. It may be fabricated from the same material as the substantially empty 6 and open ended polygon prism or any other material such as steel, wood, etc the 7 nature of which does not influence the cold bridge inhibition properties of a box 8 section type lintel made in this manner. The thickness of the bridging strip is such as 9 to enable it to run smoothly between the channels (5). The width of the bridging strip must be in the range 80 mm to 220 mm such that it fills the space between the bases 11 of the opposed channels (5).

13 DRAWING 3 14 Drawing 3 shows in cross section the substantially empty and open ended rectangular prism (1) shown in drawing 1 with two (drawing 3a) and five (drawing 3b) bridging 16 strips (4) inserted into the substantially empty and open ended rectangular prism.

18 Bending Evaluation 5**S s. 19 In conducting work to determine the load bearing capacity of the invention over a * 20 range of spans (shown in mm in diagram 4 and diagram 5 below) and at two 21 uniformly distributed (over the gap) loads (load 1 being 10 kN and load 2 being 5 * 22 kN), the results shown in diagrams 4 and 5 were obtained. These show the effect of *: 23 increasing the number of vertical ribs (bridging strips), with 2, 3, 4 and 5 ribs being : 24 used. As the number of ribs is increased the vertical deflection under load (shown in mm) is reduced and as the load is reduced the vertical deflection also reduces. The I minimum span used in each case was 400 mm and the maximum span shown is 2000 2 mm.

3 Also shown in diagrams 4 and S is a comparison with a box section of similar 4 dimensions with an internal V section (see diagram 3) as described in DE 10335692.

It will be observed that the deflection versus span curve of the internal V section is 6 indistinguishable from the innovative lintel with two internal bridging strips.

8 DETAILED DESCRIPTION OF THE INVENTION

9 In a first embodiment the invention is used as a low thermal conductivity, light-weight, variable and readily adjustable load bearing capacity lintel of the box section 11 type where the aforesaid combination of properties are uniquely advantageous to the 12 building industry. This description of the invention will refer to a rectangular prism 13 and initially to drawing 1, which shows it in an isometric projection.

14 Drawing 1 shows a substantially empty and open ended rectangular prism (1) with external dimensions of from 90 mm to 215 mm, a wall thickness of from 2 mm to 6 16 mm and a length of from 2,000 mm to 15,000 mm. Protuberances, substantially 17 rectangular in profile, are evenly spaced across the inner surfaces of the top and 18 bottom walls and run the length of the prism. The free sides of the protuberances rise ..* 19 perpendicular to the inner surfaces of the top and bottom walls, spaced in the range of * 20 from 2 mm to 22 mni apart from its nearest neighbour and extend into the otherwise 21 empty open-ended rectangular prism by from 5% to 25% of the distance between the 22 inner surfaces of the top and bottom walls. The channels (5) formed by the * : 23 protuberances directly opposite each other on the inner top and inner bottom surfaces * : * 24 of the substantially empty and open ended rectangular prism facilitate the sliding into position, bridging between the top and bottom walls of the empty rectangular prism, I and securely locating one or more bridging strips (4) (drawing 2) along the length of 2 the prism and perpendicular to the top and bottom walls (see drawing 3).

3 In use the open-ended prism is cut to the required length and the appropriate 4 number of bridging strips, depending on the load bearing capacity required (the greater the number of bridging strips inserted the greater the load bearing capacity), 6 inserted and cut to the same length as the prism. The open-ended prism is then 7 capped at either end by methods well known in the art to finally fix the bridging strips 8 into position securely to produce a lintel.

9 The advantages of a lintel created using this embodiment of the invention over conventional lintels are many: light-weight and readily handled/installed by a single 11 operative; quickly customised for size and load-bearing capacity on site using hand 12 tools; eliminates the "cold-bridging" effect known to exist with conventional lintels, 13 and; may be manufactured in a wide range of appearances and require no 14 maintenance.

In a second embodiment the invention may be used as a sill at the base of a hole built 16 into a wall to accommodate, for example, a window frame. In this use the invention 17 may take the form of an open ended substantially empty pentagonal prism for 18 aesthetic reasons. It will be understood that the plurality of bridging strips need not 19 be symmetrically disposed across the entire width of the sill provided they that they * : ** 20 are across the area where parallel top and bottom inner wall surfaces exist.

21 In use the open-ended prism is cut to the required length and the appropriate number *:. 22 of bridging strips, depending on the load bearing capacity required inserted and cut to 23 the same length as the prism. The open-ended prism is then securely capped at either * : * 24 end by any known method to fix the bridging strips into position.