GB2150199A - A device for prestressing steel support constructions - Google Patents

Abstract

The working platform 1 of trestle bridge scaffolding is strengthened by two trussing members 2 demountably attached to the bridge, between which extends a tensioning member 3. Each trussing member 2 consists of rods 5, 6, 7, 9 arranged in a triangular configuration. <IMAGE>

Description

SPECIFICATION Adeviceforprestressing steel support constructions The invention relates to the prestressing of steel support constructions. It may be advantageously used with trestle bridges, whose working platforms are made from prefabricated components.

Scaffolding is known which comprises two support towers spaced from one another and a working platform which is supported on these support towers or may be adjusted in terms of height between these towers. Forthe purposes of rapid assembly, both the supporttowers and the working platforms are made from prefabricated components which are bolted together at the place of use. The components of the working platform are constituted bytwotubularframe girders each consisting of two tubular support memberswhich are disposed in parallel and are connected together by transverse rods. Head plates provided with bores are welded to the ends of thefourtubular support members and are designed to enable the components to be bolted together.

Scaffolding of thins type, which is known as trestle bridgework, is very economic compared with conventional flat scaffolding because trestle bridgework provides for both a lower use of steel and shorter assembly times. Theworking platforms may, however, only be used in limited lengths with a limited bearing capacity. If greater span widths or higher loads are required, the rods must be dimensioned so that they are stronger which not only leads to an uneconomically high use of steel but also to more difficult handling and may even make assembly impossible in some cases.

It is also known to increase the bearing capacity of steel support constructions by prestressing.

A so-called intermediate trestle technique provides a possibilityforthe application of prestressing forces.

In this respect, one or two posts are disposed symmetrically on the lowertubularsupportmembers of the support to be trussed, the stressing elements e.g. cables extendingfrom one end ofthe supportto be trussed via the lower end point of the posts to the other end ofthe support. However the polygonal course ofthetension members requires a high degree of accuracy during manufacture ofthe guide points which haveto bespeciallyshaped, leading to an increase in the cost of the operation. It has therefore already been proposed to arrange the tension mem bers solely between the posts and to connect the ends of the support members with the posts by tension bands.In the case of constructions, such as the working platforms of trestle bridges, which consist of two parallel main support members, each support would have to be individually pre-tensioned and provided forth is purpose with an intermediate trestle.

This requires, on one hand, a high degree of precision in the application of the pre-tensioning forces to the two supports and, on the other hand, increases the number of individual components used in an undesirable way. These are considerable drawbacks for use with scaffolding constructions which haveto be assembled and dismantled constantly.

With a view to overcoming these drawbacks the present invention provides a device for prestressing a demountable steel support construction which in cludes first and second spaced apart tubular support members extending in a common direction, said device comprising first and second trussing elements eachcomprisingaframoworkforbeing domountably attached to both of the support members at positions spaced apart in said common direction, and a tension memberfor being mounted in tension on and to extend between said elements at a location to one side of a plane containing the longitudinal axes of said support members.

The invention thus permits, forthe working platform of a trestle bridge an increase in the bearing capacity andtherefore a reduction in thetime and materials required for construction of the scaffolding.

Also it is possible to improve operating conditions in the case of wall or roof works.

The invention accordingly provides a solution which enables the prestressing of detachable working platforms in a simple manner, the prestressing construction consisting of few components enabling rapid assembly and dismantling.

In an embodiment of the invention two threedimensional trussing elements are detachably disposed on the lower flanges of the working platform and are connected together by a tensioning element.

Each three-dimensional trussing element consists in this respect of a stable triangular section having its point facing downwardly, which is formed from rods.

The rods which extend obliquely upwardly ofthe triangular section are adjacent to the loworflangos of the working platform, whilst two tension rods extend obliquely upwardlyand outwardlyfrom the lower corner of the triangular section and are connected by means of connection plates orthe like with the lower flanges of the working platform. Pressure plates may be disposed atthe ends of the oblique rods ofthe triangularsection.

In orderto facilitate assembly, it is advantageous to provide the triangular section with clamping devices.

In addition, a tensioning member mounting for fastening the tensioning member is disposed in the triangular section, which mounting advantageously comprises a tubular element. Reinforcements, which provide the three-dimensional trussing elements with further stability, are disposed between the rods of the triangular section and the tension rods.

The tensioning element may consist of individual or of several parallel individual rods orwires.

The invention is described in further detail by way of example with reference to the following embodiment shown in the drawings wherein: Fig.l is a view of a working platform with a prestressing device ofthe invention.

Fig. 2 is a section along the line A-A of Fig. 1.

Fig. 3 is a perspective view of a three-demensional trussing element.

The working platform 1 of the trestle bridge spanning two scaffolding towers (not shown) is prestressed by means of two three-dimensional trussing elements 2 and a tensioning member 3 disposed between the trussing elements 2. The working platform consists of two girders horizontally spaced apart and each bounded by a pair of tubular support members,the lowermost ones ofwhich are referenced 16. The members 16 extend in a common direction and lie with the longitudinal axes in a common plane. Thetensioning member extends in the common direction to one side ofthe plane, between the members 16, so as to strengthen the platform by prestressing. The tensioning member3 is formed in the embodiment as a round steel rod. Use could also be madeforthis purposeoftensioning ropes.Each ofthetrussing elements2hasatriangular section which is inherently stable and is formed from tubular rods 4,5 and 6 and two obliquely upwardly and outwardly extending tension rods7, 8which are connected with the lower apex of the triangular section. Reinforcements 9,10 are disposed between the tubular rods 5,6 and the tension rods 7, 8, which reinforcements provide the trussing element 2 with additional stability. The connection between the tubular rods 5,6 and thetension rods 7, 8takes place by means of the connection plates 5', 6' which are connected together by a tension member mounting 11 formed as a tube.The tension member mounting 11 is also designed to receive and anchorthetension member 3. Atthe upper ends ofthetubular rods 5,6 there is disposed in each case a pressure plate 12,13 on whose extension there is disposed a clamp device 14,15. The free ends of the tension rods 7, 8 are provided with connection plates 7', 8'. Bores are disposed in the connection plates 7', 8', which bores correspond to those of head plates 17 disposed on the lowertubularspanning members 16 of the working platform 1.

The three-dimensional trussing elements 2 enable the prestressing oftheworking platform 1 comprising two tubularconstruction supports connected together and made from prefabricated components. Forth is purpose it is simply necessaryto screwthe connection plates 7', 8' to the head plates 17 of the working platform and to connectthe clamp devices 14, 15 disposed on the extensions ofthe pressure plates 12, 13to the lowertubularflanges 16. The pressure plates 12,13 are thereby located accurately below a lower node of the tubular construction of the working platform 1.

The tension member 3 is then passed through the tension member mounting 11 of the trussing elements 2 located on both sides of the working platform 1 and isfastened and tensioned. The resulting prestressing forces are applied via the tension rods 7,8 and the connection plates 7', 8'to thetubularflange 16 of the working platform 1. The transmission ofthe effective pressure forces takes place via the tubular rods 5,6 of the triangular section and the associated pressure plates 1 2,1 3. The clamp devices 1 4,1 5 do not transmit any significantforces as they are simply designed to facilitate mounting.

Thethree-dimensional trussing element provides a three-dimensional intermediate trestle which may be simply assembled and dismantled and may be arranged atany point ofthesupport construction to prestressed.

The inventior. may be used very advantageously with trestle bridges whose working platforms are made from prefabricated components. It enables the working platforms to be prestressed without the need to modify the scaffold elements presentforthis purpose. Working platforms with or without prestressing may therefore be constructed, in accordance with requirements, from the elements used.

As a result of the arrangement ofthe prestressing device it is possible to construct trestle bridges or similarsupportconstructionswith higher load-bearing capacities or greater span widths, which results in substantial savings in materials and manufacturing time in addition to an increase in the possibilities for use.

Claims (15)

1. A device for prestressing a demountable steel support constructions which includes first and second spaced aparttubularsupport members extending in a common direction, said device comprising first and second trussing elements each comprising a framework for being demountably attached to both of the support members at positions spaced apart in said common direction, and atension memberfor being mounted in tension on and to extend between said elements at a location to one side of a plane containing the longitudinal axes of said support members.

2. A device according to claim 1 wherein each said trussing element includes a mount four said tension memberfirst and second pairs of rods wherein for each said pairthe rodsthereof are each connected at one endthereofto said mount and have at the other endsthereof respective means for attachmentto said tubular support members.

3. Adevice accordingto claim 2 including further rods connected to said rod pairs such that each said pair is included in a triangular rod configuration with the mountatan apex thereof.

4. A device according to claim 2 or 3 wherein the rods of the first pair are arranged for extending substantially normallyfrom the support members and the rods of the second pair are arranged for extending obliquely ofthe support rods and undertension.

5. A device according to claim 4 including pressure plates on the ends ofthe rods of the first pair, for transmitting compression forces to said tubularsup- port members.

6. A device according to claim 5 including clamp devices on the pressure plates, for clamping the plates to thetubularsupport members.

7. A device according to any one of claims 2 to 6 wherein said tension member mount comprises a tubular memberwelded to plates defining a triangular cross section, said rod pairs being attached to the plates.

8. A device according to any one of claims 2to 7 wherein reinforcing rods extend between rods of said first and second rod pairs respectively.

9. Adevice according to any preceding claim wherein the tension member comprises several individual rods or ropes disposed in parallel.

10. A device according to any preceding claim and mounted on said support members.

11. A device according to claim 10 wherein said support members each comprise part of a respective girder.

12. A device according to claim 11 wherein said girders form a working platform of a trestle bridge.

13. Adeviceaccording to claim 12whereinthe trestle bridge spans two scaffolding towers.

14. A support construction substantially as herein described with reference to the accompanying drawing.

15. Adeviceforthe prestressing of steel support constructions, preferablyforthe working platforms of trestle bridges, characterised by two three-dimensional trussing elements disposed detachably on the lower flanges of the working platform and connected together by a tension member, each three-dimensional trussing element comprising an inherently stable triangular section formed from rods with its apex pointing downwardly, whose obliquely upwardly extending rods are adjacent to the lower flanges and from whose lower corner there extend upwardly and outwardly two tension rods which are connected with the lower flanges of the working platformbyconnec- tion plates ofthe like.