CA2352368A1 - Load-bearing structures - Google Patents
Load-bearing structures Download PDFInfo
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- CA2352368A1 CA2352368A1 CA002352368A CA2352368A CA2352368A1 CA 2352368 A1 CA2352368 A1 CA 2352368A1 CA 002352368 A CA002352368 A CA 002352368A CA 2352368 A CA2352368 A CA 2352368A CA 2352368 A1 CA2352368 A1 CA 2352368A1
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- Prior art keywords
- boards
- board
- scaffold
- load
- plank
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- E—FIXED CONSTRUCTIONS
- E04—BUILDING
- E04C—STRUCTURAL ELEMENTS; BUILDING MATERIALS
- E04C2/00—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels
- E04C2/02—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by specified materials
- E04C2/10—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by specified materials of wood, fibres, chips, vegetable stems, or the like; of plastics; of foamed products
- E04C2/20—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by specified materials of wood, fibres, chips, vegetable stems, or the like; of plastics; of foamed products of plastics
- E04C2/22—Building elements of relatively thin form for the construction of parts of buildings, e.g. sheet materials, slabs, or panels characterised by specified materials of wood, fibres, chips, vegetable stems, or the like; of plastics; of foamed products of plastics reinforced
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- Engineering & Computer Science (AREA)
- Architecture (AREA)
- Life Sciences & Earth Sciences (AREA)
- Wood Science & Technology (AREA)
- Civil Engineering (AREA)
- Structural Engineering (AREA)
- Laminated Bodies (AREA)
- Compositions Of Macromolecular Compounds (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
Abstract
A load bearing element is extruded from a thermoplastic plastics material which is preferably a recycled material such as printed packaging formed, preferably of biaxially oriented polypropylene and is compounded so that the element has a flexural modulus of 4000 MPa or above.
Description
WO 00!31356 PCT'/GB99/03880 This invention relates to static and dynamic load-bearing structures, in particular but not exclusively to structures for walking on or for retaining wet concrete. The invention relates in particular to scaffold boards, formwork beams and formwork panels.
Scaffold boards and formwork have traditionally been made of wood. Canventional wooden boards used in the construction industry have a gross weight in the range of from about 27 to 30 kg.- They are thus heavier than might be desired for handling by a single person and are themselves environmentally undesirable insofar as they represent use of only slowly renewable resources. Cheaper and more rapidly renewable forms of timber are generally unsuitable for reasons, inter alia, of strength. However, all wood boards, formwork panels and beams are subject to desgradation caused by entry of water. This leads to deterioration of mechanical character, warping and cracking. Particular problems in the tropics are exces.~ive warping because of elevated temperatures and that of attack by insects, for example termites. For this reason, timber boards utilised at outside locations tencL only to have a useful life of from about six months to about 15 months.
A further problem with wood scaffolding boards is that timber has a roughish surface in which water can accumulate. This can prove a significant problem under icy conditions when the existence of ice will be difficult to identify and can lead to accidents. Even under normal conditions, the coefficient of friction of wood surfaces is somewhat low and can make scaffold boards sl.ppery, especially when wet. Moreover, a common general problem at building sites is the theft, inter alia, of scaffold boards and formwork panels,.
The best that has been achieved hitherto with timber scaffold boards in countering their theft has been to apply a rough printing to the board by continuous rubber stamping or to paint the ends of the board using a characteristic colour combination: The first type of security measure may be difficult to observe and the second can be readily circumvented by a thief merely by sawing off the ends.
It is an object of the present invention to provide a low cost alternative to a wooden scaffold board or formwark screen panel of conventional type which, as much as possible, is free from the problems set out above.
According to one aspect of t~ze present invention, there is provided a load bearing structural element formed from a preferably recycled thermoplastic plastics material which is compounded so that the element has a flexural modulus of 4000 MPs or above.
Preferably, the flexural modulus is 5500 MPs or above.
A characteristic feature of t:he material used to form structural elements embodying the invention is flexural modulus, also known as flexural stiffness or elastic modulus. This can be precLicted by supporting the structural element across its recommended maximum span, applying a centred load and using the following equation:
F (2L3-Lb2+ (b3/4) E = _______________ 96yi where:
E = Elastic modulus (in Pascals) F = Load (in Newtons) i = 2nd moment of inertia of structural element s cross section (in m4) L = Span (in metres) WO 00/31356 PC'1'/GB99103880 _3~
b = Centred space of load d~.stribution (in metres) y = maximum deflection, absolute value (in metres) .
Similar results can. be obtained from a distributed load such as would be experience by formwork.
Thus, it is readily possible to establish whether a material will enable a structural element produced therefrom to possess a flexural modulus as required by the present invention.
For a narrow scaffold board :having an external maximum section of 230 x 45 mm and a length of 3900 mm, when:
F = 1500 I~
i _< 12 x 10-' in m4 L = 1.5 m b = 0.5 m y s 0.015 m, duration of load = 168 hours the flexural modulus will be greater than 5500 MPa.
The flexural modulus (elastics modulus) of a structural element embodying this invention can be calculated from the deflections. Rods made of the compositions and having a diameter of less than 35 mm are simply supported across a span greater than 340 mm.
A sustained load of 31 kilograms is applied to the centre of the rods so that the "ultimate elastic madulus" is considered to be reached when deflection remains unchanged for five days under a constant temperature of 45 °C. ' Preferably, a structural element in accordance with the present invention has a ratio of flexural modulus (in Megapascals) to density (kg/m3) of at least 2.5:1. Preferably, the ratio is at least 3:1, more preferably at least 4.2:1.
The density of a particular strucaural element can be easily determined and, using the equation above, the ratio can be easily calculated.
Thus, for a narrow scaffold board having an external maximum section of 230 x: 45 mm and a length of 3900 mm mentioned above, which has a density of less than 13 0 0 kg/m3 , the ratio of f le:~tural modulus to density will be 4.2:1.
Structural elements in accordance with the invention can have a stiffness which exceeds the deflection standards set out in European draft legislation EN12811, a creep which satisfies creep standards established by the European Health & Safety Executive over an ambient temperai~ure range of -20 to 50°C, an impact resistance in exceas of standards set by the European Health & Safety E:cecutive and as measured at a temperature of -20°C: arid which has twice the impact strength of dry timber at 20 °C.
Preferably, the element meets the specification for a timber scaffold board as described by BS2482:1971 In accordance with the present invention, there is provided a structural element which preferably comprises an extruded plastics composition which comprises 30-90 wt% of thermoplastic polymer, and 10-60 wt% of elastic modules increasing material.
Preferred amounts of the respective materials are 40-75 wt4, more preferably 50-65 wt%, of thermoplastic polymer,,and 25-50 wto, more preferably 30-45 wt%, of an elastic modules increasing material.
The thermoplastic polymer may be polyethylene, polypropylene, or polyethylene terephthalate. However, in general, polypropylene is better at resisting creep and is better able to resist lower temperatures, having an operating range generally of -20 -~ 45°C. The polypropylene is preferably bi-axially oriented ~5 polypropylene (BOPP?, which is a common material in packaging and has a low cost for recycling purposes, especially if contaminated with printing inks whose presence precludes most conventional processing techniques.
The elastic modulus increasing material may be glass beads, talcum powder, etc, but it is preferred if it is glass fibres. Such glass fibres are preferably recycled glass fibres because of cost considerations and it is even possible to use gl~~ss fibre "fluff". Tt is preferred if the glass fibres lave a length of greater than about 5mm, preferably in the range 8--12 mm, in order to provide the product with additional rigidity.
To enhance the elastic modulus further, the composition may additionally comps°ise a coupling agent, to enhance bonding between polymer and elastic modulus increasing material and/or a nucleating agent, the latter ensuring a uniform compact microcrystalline structure, in relatively low amounts, such as 1 to 3, preferably 2 wt%, and from 0.1 to 2 wt%, preferabl~r 0.5 wt%, respectively.
Polyr.:er materials employed in. the production of product, especially board structures, embodying the invention may have incorporated therein in particular, fire retardants, W stabilisers and friction increasers. In this way, there is readily obtained a material which is not easy to ignite according to BS476, pa=t 12 and having a low surface spread of flame when tested to BS 476, part 7. The materials utilised can be ccrpounded so as to ensure low emission of toxic fumes in a fire, low emission of smoke in a fire and absence c= molten droplets in a fire. Some of these requireme~s cannot be met by, or .are inappropriate for, wooden scaffold boards. Others are potential problems w~en using plastics materials, which problems are readily addressed by suitable; compounding.
Such materials are preferably present in an outer layer on the product or board which may have a thickness of up to 1 mm, preferably 0.5 mm.
Mention has already been made of problems of slipping on timber scaffold boards. This problem can readily be addressed in the practice of the present invention when, instead of producing the board material as a single extrusion, it is produced as a co-extrusion with an anti-slip surface being provided thereon. For this purpose a thermoplastic polyethylene or polyolefin material such as EPDN or TPO may :be provided. Such layer can also contain the other ;additives mentioned hereinabove as suitable for inclu;~ion in a co-extruded outer layer or be a separate layer. Such a material is however not suitable for use alonE= because of its inability to meet structural requirements.
A preferred composition of t:he outer layer comprises up to 80 wto, preferably about 52 wto, of thermoplastic olefin (TPO) and up to 20 wt o, preferably 10 wt%, of low density polyethylene (LDPE) which provide anti-slip propertie:~ on for example scaffold boards. Such layers, in addition, provides for easy release of concrete where; formwork boards and panels suc:~ layers also protecting the board or panel front abrasion and scuffing and weaknesses that may be caused by scratching or impact. I:n addition, the compositicn may have 25 wto of a brominated organic compound such as decabromodiphenyl oxide and 12.5 wto of Sb03 as flame retardants. A pi~~ment may be added to 0.5 wto, and a UV additive such as tinuvin to 0.5 wto.
The structural elements in accordance with the present invention can also be used for decking, system batons, access platforms; boardwalks, walkways, piers, jetties, staging, shuttering, lintels, shelving, telegraph doles, pallets, road humps, fencing, barriers, seating, benches etc. However, the invention will be described hereinafter primarily with reference to scaffold boards.
Such boards can readily be made by a continuous extrusion process and cut to length so as to be compatible with timber scaffold x>oards which generally are available in lengths of 3.9 ncetres, 3.0 metres and 2.4 metres, in each case ~ 20 mm and having a width of 225 mm ~ 2 mm and a thickness of 45.5 mm ~ 0.5 mm.
Generally, such planks or boards embodying the invention will be hollow and to ensure that they satisfy the aforementioned physical parameters, they may be provided with internal walls extending longitudinally thereof.
Many advantages are attainable with boards embodying the invention. Firstly, there is a considerable weight reduction. A 3.9 metre Long board which is to bridge a 1.5 metre span may have a weight of 18.3 kg compared with 24 kg fo:r a wet timber board.
If only a 1.2 metre span has to be bridged, then such a board may be made sa as to have only a weight of only about 16.8 kg.
Mention has also been made hesrein of the restricted lifetime of timber boards. With recycled plastics material, it,is possible to produce boards having a life which is a minimum of three times that of timber. No preservative or treatment is required as there will be no susceptibility to fungicidal rot or termite attack. Warping or bowing will not occur and unless the board is severely misty°eated, there will be no splintering. The boards are a7.so resistant to acids, alkalis, solvents; detergents, greases and oils which degrade wooden scaffold boaz-ds. Resistance to chemicals in concrete is advantageous for formwork applications.
Boards embodying the invention will be free from _g_ hazardous metal plates as are generally used as end protection on wooden scaffold boards a:nd formwork girders. Extrusion methods make it possible to produce radiussed edges. In addition to the safe handling thus made possible, the ends of hollow scaf:~old boards can be closed off by tightly fitting injection moulded end caps knocked firmly into the open ends of the profile before it has fully cooled down after E=_xtrusion. These end caps can be manufactured fram unbreakable and resilient plastic material and in a co:Lour which may be indicative of the source of the plank. They can also be employed as water-tight connectors between formwork panels. Better security against theft can be achieved by providing a coloured bead co-extrude:d along the plank, or continuously embossing or hot, foil stamping the name of the owner along the plank possibly on both major faces. These cannot be removed without damaging the plank. Each owner may employ a characteristic colour or pattern. In addition, an embossed tread pattern may be applied to the major faces of the plank.
In addition to providing a co-extruded anti-slip surface, it is possible for an anti-slip surface texture to be embossed or moulded into one or both opposite surfaces of the plank, the surface texture being designed to satisfy or exceed appropriate coefficient of friction standards.
Extrusion of mixes of materials to be utilised in the production of the planks or boards may take place using a high efficiency venting screw such as a Ventus screw. Additionally, one can utilise a rotary channel pump according to w097/42019 for dosing into an extruder consistent quantities of particulate material such as recycled polymer material, in p<~rticular chopped film which may be printed film, ie. low grade material, but not liquid or powder. Such a dosing method avoids granulation of plastics m~~terial.
-In order to achieve a product with relatively long glass fibres in it, it is necessary to add these fibres after working by the extruder screw used in compounding the material for the board which would otherwise fragment glass fibres to too great an extent.
Dispensing of glass fibres and other solid material into matrix passing through the downstream portion of an extruder may be achieved using a flow pump according to EP-A-0467842 for transferring and compacting particulate solids. The glass fibres are also preferably oriented in planes parallel to a load bearing surface thereof by passage through a known minti-layer grid producing multi-:layering of glass fibres in the extrudate obtained. This ensures a maximum strength of product. It lzas also been found that the stiffness of the product is improved if the glass fibres are not of a uniform length.
For a better understanding of the invention and to show haw the same can be carried ~Lnto effect, reference will now be made by way of example only to the accompany'ng drawings wherein:
Figure 1 shows a set of boards embodying the invention, these being shown in cross-section and each board having an internal web thickness of 5 mm;
Figure 2 is a bar chart showing the results of impact tests on prior art scaffold planks and scaffold planks embodying the invention; amd Figure 3 is a graph of deflection against time for one board embodying this invention..
Referring to Figure 1, there is shown a series of extruded boards embodying the invention and having the following dimensions and weights.
a) plastics toe-board 150 mm x 25 mm in cross-section with 4 mm external wall thickness, the board having a length of 2.49 metres max: and a weight of 3.8 kg.
b) plastics plank 225 mm x 45 mm in cross-section with an external wall thickness of mm and a maximum length of 3.9 m, the plank to be supported at 1.2 m max. centres and having a weight of 14.9 kg.
c) plastics plank 225 mm :x 45 mm in cross-section with 7 mm wall thickness and 3.9 rn long, to be supported ~~t 1.5 mm max centres, the plank having a weight of 18.3 kg.
d) plastics plank 225 mm :~ 52 rnm in cross-section with 7 mm wall thickness and 3.9 m long, to be supported <~t 1.8 max centres.
The plank has a weight of :~9.8 kg.
e) plastics plank 300 mm ~~ 52 mm in cross-section with 7 mm wall thickness and 3.9 m long, to be supported ait 1.8 m max centres.
The plank has a weight of 24.8 kg.
f) plastics plank 225 mm ~: 65 mm in cross-section with 7 mm wall thickness and 2.4 m long to be supported at. 2.4 rn max centres.
The plank has a weight of 13.1 kg.
g) plastics system scaffold batten 375 mm x 65 mm in cross-section with 7 mm wall thickness and 2.4 m long, to be supported at 2.4 m max centres. The batten has a weight of 18.5 kg.
h) plastics system scaffold batten 320 mm x 85 mm in cross-section with 7 mm wall thickness and 3.0 m Long, to be supported at 3.0 m max centres, the batten having a weight of 23.8 kg, Boards were manufactured from mixtures having the following compositions:
- i~oards a), b) and boards the same as board b) except for a wail thickness of 7 mm I', Masterbatch 5 wt4 Biaxially oriented polypropylene (BOPP) 65 wt%
Glass fibre 30 wto - Boards the same as board b) but intended to be supported at 1.5 m centres, and such boards with a wall thickness of 7 mm:
Masterbatch 5 wto BOPP 53 wt%
Glass fibre 42 wt%
~-5 - Boards the same as board f ) exce:pt for a wall thickness of 6 mm, a length of 3.9 m and intended to be supported at 1.8 m centres; such boards with a wall thickness of 7 rnm; board g); boards the same as board g) except for a wall thickness of 6 mm:
Masterbatch 5 wt%
BOPP 55 wt%
Glass fibre 40 wto - Board f) and boards the same as hoard f) except for a wall thickness of 6 mm:
Masterbatch 5 wto BOPP 50 wto Glass fibre 45 wt%
In each of the above cases, the masterbatch comprises:
Polypropylene 2.8 parts by wt Coupling agent (malefic anhydride) 2 parts by wt WO 00/31356 PC'1'/GB99103880 nucleating agent (MDBS) 0.2 part by wt It will be appreciated that the amount of glass fibre in the composition is increased when increased stiffness is required, for example, when the boards are intended to be used across larger spans.
Each of the above boards was co-extruded with an 0.5mm thick outer layer which comprises the following:
Thermoplastic olefin (TPO) 51.5 wt%
LDPE 10 wta flame retardant (decabromodi:phenyl Oxide) 25 wt o flame retardant (Sb03) 12.5 wt%
pigment 0.5 wt%
UV additive 0:5 wt%
Tests have been carried out on boards embodying the invention as follows:-1. Impact test Testing to new standards prod>osed by the European Health & Safety Executive, a 50 kilogram dead weight of sand was dropped on to the centre of a plank supported at 1.3 metre centres and lightly restrained at each end. It was required that the board be able to withstand an impact energy of 600 joules. A total of 5 boards we=a employed. A wet timber scaffold board tailed at an impact energy of about 390 joules. Two different dry timber scaffold boards failed at about 590 joules although audible cracks were heard at about 490 joules. A first board embodying the invention did not fail until subject to an impact energy of about 780 joules while a second plastics board did not fail until subject to an impact energy of about 870 joules. The results a=a illustrated graphically in Figure 2.
2. Deflection Boards A board embodying the invention was tested to a new standard proposed under BS draft document EN12811 and HD1000. For this purpose, measurement was made of the deflection caused by a load ~~f 1.5 KN applied to wn area of 500 mm x 230 mm at the centre of the board, with the board supported between 1.5 metre centres. It is a requirement that deflection must not exceed 1% of the span (a maximum of 15 mm). DZeasurements were carried out daily after extrusion and cooling. The plank utilised is made of the plastic sample of the second plastics board utilised in the impact test.
Deflection values were measured d!.aily and axe shown in Figure 3 of the accompanying drawings for which it can 35 be seen that immediate application of the load achieved a deflection of 9.2 mm which increased by another 1 mm over one hour and levelled off at 11.2 mm over the next three days. Upon removal of the loading, a residual deflection of 2 mm was recorded.
Scaffold boards and formwork have traditionally been made of wood. Canventional wooden boards used in the construction industry have a gross weight in the range of from about 27 to 30 kg.- They are thus heavier than might be desired for handling by a single person and are themselves environmentally undesirable insofar as they represent use of only slowly renewable resources. Cheaper and more rapidly renewable forms of timber are generally unsuitable for reasons, inter alia, of strength. However, all wood boards, formwork panels and beams are subject to desgradation caused by entry of water. This leads to deterioration of mechanical character, warping and cracking. Particular problems in the tropics are exces.~ive warping because of elevated temperatures and that of attack by insects, for example termites. For this reason, timber boards utilised at outside locations tencL only to have a useful life of from about six months to about 15 months.
A further problem with wood scaffolding boards is that timber has a roughish surface in which water can accumulate. This can prove a significant problem under icy conditions when the existence of ice will be difficult to identify and can lead to accidents. Even under normal conditions, the coefficient of friction of wood surfaces is somewhat low and can make scaffold boards sl.ppery, especially when wet. Moreover, a common general problem at building sites is the theft, inter alia, of scaffold boards and formwork panels,.
The best that has been achieved hitherto with timber scaffold boards in countering their theft has been to apply a rough printing to the board by continuous rubber stamping or to paint the ends of the board using a characteristic colour combination: The first type of security measure may be difficult to observe and the second can be readily circumvented by a thief merely by sawing off the ends.
It is an object of the present invention to provide a low cost alternative to a wooden scaffold board or formwark screen panel of conventional type which, as much as possible, is free from the problems set out above.
According to one aspect of t~ze present invention, there is provided a load bearing structural element formed from a preferably recycled thermoplastic plastics material which is compounded so that the element has a flexural modulus of 4000 MPs or above.
Preferably, the flexural modulus is 5500 MPs or above.
A characteristic feature of t:he material used to form structural elements embodying the invention is flexural modulus, also known as flexural stiffness or elastic modulus. This can be precLicted by supporting the structural element across its recommended maximum span, applying a centred load and using the following equation:
F (2L3-Lb2+ (b3/4) E = _______________ 96yi where:
E = Elastic modulus (in Pascals) F = Load (in Newtons) i = 2nd moment of inertia of structural element s cross section (in m4) L = Span (in metres) WO 00/31356 PC'1'/GB99103880 _3~
b = Centred space of load d~.stribution (in metres) y = maximum deflection, absolute value (in metres) .
Similar results can. be obtained from a distributed load such as would be experience by formwork.
Thus, it is readily possible to establish whether a material will enable a structural element produced therefrom to possess a flexural modulus as required by the present invention.
For a narrow scaffold board :having an external maximum section of 230 x 45 mm and a length of 3900 mm, when:
F = 1500 I~
i _< 12 x 10-' in m4 L = 1.5 m b = 0.5 m y s 0.015 m, duration of load = 168 hours the flexural modulus will be greater than 5500 MPa.
The flexural modulus (elastics modulus) of a structural element embodying this invention can be calculated from the deflections. Rods made of the compositions and having a diameter of less than 35 mm are simply supported across a span greater than 340 mm.
A sustained load of 31 kilograms is applied to the centre of the rods so that the "ultimate elastic madulus" is considered to be reached when deflection remains unchanged for five days under a constant temperature of 45 °C. ' Preferably, a structural element in accordance with the present invention has a ratio of flexural modulus (in Megapascals) to density (kg/m3) of at least 2.5:1. Preferably, the ratio is at least 3:1, more preferably at least 4.2:1.
The density of a particular strucaural element can be easily determined and, using the equation above, the ratio can be easily calculated.
Thus, for a narrow scaffold board having an external maximum section of 230 x: 45 mm and a length of 3900 mm mentioned above, which has a density of less than 13 0 0 kg/m3 , the ratio of f le:~tural modulus to density will be 4.2:1.
Structural elements in accordance with the invention can have a stiffness which exceeds the deflection standards set out in European draft legislation EN12811, a creep which satisfies creep standards established by the European Health & Safety Executive over an ambient temperai~ure range of -20 to 50°C, an impact resistance in exceas of standards set by the European Health & Safety E:cecutive and as measured at a temperature of -20°C: arid which has twice the impact strength of dry timber at 20 °C.
Preferably, the element meets the specification for a timber scaffold board as described by BS2482:1971 In accordance with the present invention, there is provided a structural element which preferably comprises an extruded plastics composition which comprises 30-90 wt% of thermoplastic polymer, and 10-60 wt% of elastic modules increasing material.
Preferred amounts of the respective materials are 40-75 wt4, more preferably 50-65 wt%, of thermoplastic polymer,,and 25-50 wto, more preferably 30-45 wt%, of an elastic modules increasing material.
The thermoplastic polymer may be polyethylene, polypropylene, or polyethylene terephthalate. However, in general, polypropylene is better at resisting creep and is better able to resist lower temperatures, having an operating range generally of -20 -~ 45°C. The polypropylene is preferably bi-axially oriented ~5 polypropylene (BOPP?, which is a common material in packaging and has a low cost for recycling purposes, especially if contaminated with printing inks whose presence precludes most conventional processing techniques.
The elastic modulus increasing material may be glass beads, talcum powder, etc, but it is preferred if it is glass fibres. Such glass fibres are preferably recycled glass fibres because of cost considerations and it is even possible to use gl~~ss fibre "fluff". Tt is preferred if the glass fibres lave a length of greater than about 5mm, preferably in the range 8--12 mm, in order to provide the product with additional rigidity.
To enhance the elastic modulus further, the composition may additionally comps°ise a coupling agent, to enhance bonding between polymer and elastic modulus increasing material and/or a nucleating agent, the latter ensuring a uniform compact microcrystalline structure, in relatively low amounts, such as 1 to 3, preferably 2 wt%, and from 0.1 to 2 wt%, preferabl~r 0.5 wt%, respectively.
Polyr.:er materials employed in. the production of product, especially board structures, embodying the invention may have incorporated therein in particular, fire retardants, W stabilisers and friction increasers. In this way, there is readily obtained a material which is not easy to ignite according to BS476, pa=t 12 and having a low surface spread of flame when tested to BS 476, part 7. The materials utilised can be ccrpounded so as to ensure low emission of toxic fumes in a fire, low emission of smoke in a fire and absence c= molten droplets in a fire. Some of these requireme~s cannot be met by, or .are inappropriate for, wooden scaffold boards. Others are potential problems w~en using plastics materials, which problems are readily addressed by suitable; compounding.
Such materials are preferably present in an outer layer on the product or board which may have a thickness of up to 1 mm, preferably 0.5 mm.
Mention has already been made of problems of slipping on timber scaffold boards. This problem can readily be addressed in the practice of the present invention when, instead of producing the board material as a single extrusion, it is produced as a co-extrusion with an anti-slip surface being provided thereon. For this purpose a thermoplastic polyethylene or polyolefin material such as EPDN or TPO may :be provided. Such layer can also contain the other ;additives mentioned hereinabove as suitable for inclu;~ion in a co-extruded outer layer or be a separate layer. Such a material is however not suitable for use alonE= because of its inability to meet structural requirements.
A preferred composition of t:he outer layer comprises up to 80 wto, preferably about 52 wto, of thermoplastic olefin (TPO) and up to 20 wt o, preferably 10 wt%, of low density polyethylene (LDPE) which provide anti-slip propertie:~ on for example scaffold boards. Such layers, in addition, provides for easy release of concrete where; formwork boards and panels suc:~ layers also protecting the board or panel front abrasion and scuffing and weaknesses that may be caused by scratching or impact. I:n addition, the compositicn may have 25 wto of a brominated organic compound such as decabromodiphenyl oxide and 12.5 wto of Sb03 as flame retardants. A pi~~ment may be added to 0.5 wto, and a UV additive such as tinuvin to 0.5 wto.
The structural elements in accordance with the present invention can also be used for decking, system batons, access platforms; boardwalks, walkways, piers, jetties, staging, shuttering, lintels, shelving, telegraph doles, pallets, road humps, fencing, barriers, seating, benches etc. However, the invention will be described hereinafter primarily with reference to scaffold boards.
Such boards can readily be made by a continuous extrusion process and cut to length so as to be compatible with timber scaffold x>oards which generally are available in lengths of 3.9 ncetres, 3.0 metres and 2.4 metres, in each case ~ 20 mm and having a width of 225 mm ~ 2 mm and a thickness of 45.5 mm ~ 0.5 mm.
Generally, such planks or boards embodying the invention will be hollow and to ensure that they satisfy the aforementioned physical parameters, they may be provided with internal walls extending longitudinally thereof.
Many advantages are attainable with boards embodying the invention. Firstly, there is a considerable weight reduction. A 3.9 metre Long board which is to bridge a 1.5 metre span may have a weight of 18.3 kg compared with 24 kg fo:r a wet timber board.
If only a 1.2 metre span has to be bridged, then such a board may be made sa as to have only a weight of only about 16.8 kg.
Mention has also been made hesrein of the restricted lifetime of timber boards. With recycled plastics material, it,is possible to produce boards having a life which is a minimum of three times that of timber. No preservative or treatment is required as there will be no susceptibility to fungicidal rot or termite attack. Warping or bowing will not occur and unless the board is severely misty°eated, there will be no splintering. The boards are a7.so resistant to acids, alkalis, solvents; detergents, greases and oils which degrade wooden scaffold boaz-ds. Resistance to chemicals in concrete is advantageous for formwork applications.
Boards embodying the invention will be free from _g_ hazardous metal plates as are generally used as end protection on wooden scaffold boards a:nd formwork girders. Extrusion methods make it possible to produce radiussed edges. In addition to the safe handling thus made possible, the ends of hollow scaf:~old boards can be closed off by tightly fitting injection moulded end caps knocked firmly into the open ends of the profile before it has fully cooled down after E=_xtrusion. These end caps can be manufactured fram unbreakable and resilient plastic material and in a co:Lour which may be indicative of the source of the plank. They can also be employed as water-tight connectors between formwork panels. Better security against theft can be achieved by providing a coloured bead co-extrude:d along the plank, or continuously embossing or hot, foil stamping the name of the owner along the plank possibly on both major faces. These cannot be removed without damaging the plank. Each owner may employ a characteristic colour or pattern. In addition, an embossed tread pattern may be applied to the major faces of the plank.
In addition to providing a co-extruded anti-slip surface, it is possible for an anti-slip surface texture to be embossed or moulded into one or both opposite surfaces of the plank, the surface texture being designed to satisfy or exceed appropriate coefficient of friction standards.
Extrusion of mixes of materials to be utilised in the production of the planks or boards may take place using a high efficiency venting screw such as a Ventus screw. Additionally, one can utilise a rotary channel pump according to w097/42019 for dosing into an extruder consistent quantities of particulate material such as recycled polymer material, in p<~rticular chopped film which may be printed film, ie. low grade material, but not liquid or powder. Such a dosing method avoids granulation of plastics m~~terial.
-In order to achieve a product with relatively long glass fibres in it, it is necessary to add these fibres after working by the extruder screw used in compounding the material for the board which would otherwise fragment glass fibres to too great an extent.
Dispensing of glass fibres and other solid material into matrix passing through the downstream portion of an extruder may be achieved using a flow pump according to EP-A-0467842 for transferring and compacting particulate solids. The glass fibres are also preferably oriented in planes parallel to a load bearing surface thereof by passage through a known minti-layer grid producing multi-:layering of glass fibres in the extrudate obtained. This ensures a maximum strength of product. It lzas also been found that the stiffness of the product is improved if the glass fibres are not of a uniform length.
For a better understanding of the invention and to show haw the same can be carried ~Lnto effect, reference will now be made by way of example only to the accompany'ng drawings wherein:
Figure 1 shows a set of boards embodying the invention, these being shown in cross-section and each board having an internal web thickness of 5 mm;
Figure 2 is a bar chart showing the results of impact tests on prior art scaffold planks and scaffold planks embodying the invention; amd Figure 3 is a graph of deflection against time for one board embodying this invention..
Referring to Figure 1, there is shown a series of extruded boards embodying the invention and having the following dimensions and weights.
a) plastics toe-board 150 mm x 25 mm in cross-section with 4 mm external wall thickness, the board having a length of 2.49 metres max: and a weight of 3.8 kg.
b) plastics plank 225 mm x 45 mm in cross-section with an external wall thickness of mm and a maximum length of 3.9 m, the plank to be supported at 1.2 m max. centres and having a weight of 14.9 kg.
c) plastics plank 225 mm :x 45 mm in cross-section with 7 mm wall thickness and 3.9 rn long, to be supported ~~t 1.5 mm max centres, the plank having a weight of 18.3 kg.
d) plastics plank 225 mm :~ 52 rnm in cross-section with 7 mm wall thickness and 3.9 m long, to be supported <~t 1.8 max centres.
The plank has a weight of :~9.8 kg.
e) plastics plank 300 mm ~~ 52 mm in cross-section with 7 mm wall thickness and 3.9 m long, to be supported ait 1.8 m max centres.
The plank has a weight of 24.8 kg.
f) plastics plank 225 mm ~: 65 mm in cross-section with 7 mm wall thickness and 2.4 m long to be supported at. 2.4 rn max centres.
The plank has a weight of 13.1 kg.
g) plastics system scaffold batten 375 mm x 65 mm in cross-section with 7 mm wall thickness and 2.4 m long, to be supported at 2.4 m max centres. The batten has a weight of 18.5 kg.
h) plastics system scaffold batten 320 mm x 85 mm in cross-section with 7 mm wall thickness and 3.0 m Long, to be supported at 3.0 m max centres, the batten having a weight of 23.8 kg, Boards were manufactured from mixtures having the following compositions:
- i~oards a), b) and boards the same as board b) except for a wail thickness of 7 mm I', Masterbatch 5 wt4 Biaxially oriented polypropylene (BOPP) 65 wt%
Glass fibre 30 wto - Boards the same as board b) but intended to be supported at 1.5 m centres, and such boards with a wall thickness of 7 mm:
Masterbatch 5 wto BOPP 53 wt%
Glass fibre 42 wt%
~-5 - Boards the same as board f ) exce:pt for a wall thickness of 6 mm, a length of 3.9 m and intended to be supported at 1.8 m centres; such boards with a wall thickness of 7 rnm; board g); boards the same as board g) except for a wall thickness of 6 mm:
Masterbatch 5 wt%
BOPP 55 wt%
Glass fibre 40 wto - Board f) and boards the same as hoard f) except for a wall thickness of 6 mm:
Masterbatch 5 wto BOPP 50 wto Glass fibre 45 wt%
In each of the above cases, the masterbatch comprises:
Polypropylene 2.8 parts by wt Coupling agent (malefic anhydride) 2 parts by wt WO 00/31356 PC'1'/GB99103880 nucleating agent (MDBS) 0.2 part by wt It will be appreciated that the amount of glass fibre in the composition is increased when increased stiffness is required, for example, when the boards are intended to be used across larger spans.
Each of the above boards was co-extruded with an 0.5mm thick outer layer which comprises the following:
Thermoplastic olefin (TPO) 51.5 wt%
LDPE 10 wta flame retardant (decabromodi:phenyl Oxide) 25 wt o flame retardant (Sb03) 12.5 wt%
pigment 0.5 wt%
UV additive 0:5 wt%
Tests have been carried out on boards embodying the invention as follows:-1. Impact test Testing to new standards prod>osed by the European Health & Safety Executive, a 50 kilogram dead weight of sand was dropped on to the centre of a plank supported at 1.3 metre centres and lightly restrained at each end. It was required that the board be able to withstand an impact energy of 600 joules. A total of 5 boards we=a employed. A wet timber scaffold board tailed at an impact energy of about 390 joules. Two different dry timber scaffold boards failed at about 590 joules although audible cracks were heard at about 490 joules. A first board embodying the invention did not fail until subject to an impact energy of about 780 joules while a second plastics board did not fail until subject to an impact energy of about 870 joules. The results a=a illustrated graphically in Figure 2.
2. Deflection Boards A board embodying the invention was tested to a new standard proposed under BS draft document EN12811 and HD1000. For this purpose, measurement was made of the deflection caused by a load ~~f 1.5 KN applied to wn area of 500 mm x 230 mm at the centre of the board, with the board supported between 1.5 metre centres. It is a requirement that deflection must not exceed 1% of the span (a maximum of 15 mm). DZeasurements were carried out daily after extrusion and cooling. The plank utilised is made of the plastic sample of the second plastics board utilised in the impact test.
Deflection values were measured d!.aily and axe shown in Figure 3 of the accompanying drawings for which it can 35 be seen that immediate application of the load achieved a deflection of 9.2 mm which increased by another 1 mm over one hour and levelled off at 11.2 mm over the next three days. Upon removal of the loading, a residual deflection of 2 mm was recorded.
3. Strength Test The superior high temperaturE~ strength of plastic boards embodying this invention i:; demonstrated by results of a test specified by draft European standard EN12811, conducted by. the Health ~~ Safety Laboratory.
The test involved a sample spanning 1.5m in an environment maintained at 40°C, undergoing a centred static load evenly distributed over 0.5m.
A load pf 594kg broke a stanf.ard timber board. A
load of 10I5kg did not break a plastic board.
The test involved a sample spanning 1.5m in an environment maintained at 40°C, undergoing a centred static load evenly distributed over 0.5m.
A load pf 594kg broke a stanf.ard timber board. A
load of 10I5kg did not break a plastic board.
Claims
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9825958.3 | 1998-11-26 | ||
| GBGB9825958.3A GB9825958D0 (en) | 1998-11-26 | 1998-11-26 | Load-bearing structures |
| PCT/GB1999/003880 WO2000031356A1 (en) | 1998-11-26 | 1999-11-19 | Load-bearing structures |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2352368A1 true CA2352368A1 (en) | 2000-06-02 |
Family
ID=10843122
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002352368A Abandoned CA2352368A1 (en) | 1998-11-26 | 1999-11-19 | Load-bearing structures |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP1135564B1 (en) |
| AR (1) | AR022111A1 (en) |
| AT (1) | ATE335890T1 (en) |
| AU (1) | AU747714B2 (en) |
| CA (1) | CA2352368A1 (en) |
| DE (1) | DE69932735D1 (en) |
| GB (1) | GB9825958D0 (en) |
| TW (1) | TW469319B (en) |
| WO (1) | WO2000031356A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ATE366418T1 (en) | 1996-04-25 | 2007-07-15 | Bioarray Solutions Ltd | LIGHT-REGULATED, ELECTROKINETIC COMPOSITION OF PARTICLES ON SURFACES |
| US9709559B2 (en) | 2000-06-21 | 2017-07-18 | Bioarray Solutions, Ltd. | Multianalyte molecular analysis using application-specific random particle arrays |
| AU7299301A (en) | 2000-06-21 | 2002-01-02 | Bioarray Solutions Ltd | Multianalyte molecular analysis using application-specific random particle arrays |
| US7262063B2 (en) | 2001-06-21 | 2007-08-28 | Bio Array Solutions, Ltd. | Directed assembly of functional heterostructures |
| JP4377689B2 (en) | 2001-10-15 | 2009-12-02 | バイオアレイ ソリューションズ リミテッド | Combined analysis of polymorphic loci with simultaneous interrogation and enzyme-mediated detection |
| WO2004047007A1 (en) | 2002-11-15 | 2004-06-03 | Bioarray Solutions, Ltd. | Analysis, secure access to, and transmission of array images |
| EP1664722B1 (en) | 2003-09-22 | 2011-11-02 | Bioarray Solutions Ltd | Surface immobilized polyelectrolyte with multiple functional groups capable of covalently bonding to biomolecules |
| US7563569B2 (en) | 2003-10-28 | 2009-07-21 | Michael Seul | Optimization of gene expression analysis using immobilized capture probes |
| US7848889B2 (en) | 2004-08-02 | 2010-12-07 | Bioarray Solutions, Ltd. | Automated analysis of multiplexed probe-target interaction patterns: pattern matching and allele identification |
| NL1034570C2 (en) * | 2007-10-23 | 2009-04-27 | Inxtru Bv | Method for manufacturing an endless, fiber-reinforced plastic element, as well as such an element. |
| WO2010068971A1 (en) * | 2008-12-18 | 2010-06-24 | Dymon Pallets Pty Ltd | Biaxially oriented polyethylene terephthalate (pet) pallet |
| WO2013117196A1 (en) * | 2012-02-06 | 2013-08-15 | Nordic Platform P/S | Deck for scaffolding and method for its adaptation |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1391622A (en) * | 1969-06-23 | 1975-04-23 | Tba Industrial Products Ltd | Reinforcement of thermoplastic polymers |
| EP0320745A1 (en) * | 1987-12-11 | 1989-06-21 | The B.F. Goodrich Company | Modular building structure and prefabricated components therefor and related methods |
| CA2232203A1 (en) * | 1993-05-28 | 1994-11-29 | Royal Building Systems (Cdn) Limited | Thermoplastic structural components and structures formed therefrom |
| US5783286A (en) * | 1996-04-04 | 1998-07-21 | Dinicola; James L. | Hollow-core plastic structural lumber alternative |
-
1998
- 1998-11-26 GB GBGB9825958.3A patent/GB9825958D0/en not_active Ceased
-
1999
- 1999-11-19 EP EP99956172A patent/EP1135564B1/en not_active Expired - Lifetime
- 1999-11-19 AU AU12823/00A patent/AU747714B2/en not_active Ceased
- 1999-11-19 AT AT99956172T patent/ATE335890T1/en not_active IP Right Cessation
- 1999-11-19 DE DE69932735T patent/DE69932735D1/en not_active Expired - Lifetime
- 1999-11-19 CA CA002352368A patent/CA2352368A1/en not_active Abandoned
- 1999-11-19 WO PCT/GB1999/003880 patent/WO2000031356A1/en active IP Right Grant
- 1999-11-23 TW TW088120427A patent/TW469319B/en active
- 1999-11-26 AR ARP990106027A patent/AR022111A1/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| GB9825958D0 (en) | 1999-01-20 |
| TW469319B (en) | 2001-12-21 |
| AR022111A1 (en) | 2002-09-04 |
| EP1135564A1 (en) | 2001-09-26 |
| AU747714B2 (en) | 2002-05-23 |
| EP1135564B1 (en) | 2006-08-09 |
| AU1282300A (en) | 2000-06-13 |
| WO2000031356A1 (en) | 2000-06-02 |
| DE69932735D1 (en) | 2006-09-21 |
| ATE335890T1 (en) | 2006-09-15 |
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| EEER | Examination request | ||
| FZDE | Discontinued |