GB2308564A

GB2308564A - Box section girders

Info

Publication number: GB2308564A
Application number: GB9626818A
Authority: GB
Inventors: Hans Allgeier; Frank Conrad; Theo Munker; Walter Stowasser
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1995-12-28
Filing date: 1996-12-23
Publication date: 1997-07-02
Anticipated expiration: 2016-12-23
Also published as: DE19549268C1; GB2308564B; GB9626818D0

Description

2308564 1 A BOX-SECTION GIRDER The invention relates to a box-section

girder for use in particular as a crane jib or telescopic jib.

A box-section girder is known from French Patent 2316013. It consists of a first shell formed of thin-walled sheet metal sections and open on one side, and a second shell likewise open on one side, which are pushed into one another edgewise in overlapping manner and are welded together by means of exterior fillet welds on both sides. Both shells, as viewed in cross-section, have in their central region an inwardly extending recess, so that in the final assembled state virtually a double-T girder profile is produced. This profile is unsuitable for telescopic jibs, and furthermore is at great risk of bulging.

It is an object of the invention to provide a box-section girder which is highly suitable for telescopic jibs and can transfer large loads without the risk of bulging. Furthermore, its production should be less expensive than comparable designs.

A box-section girder in accordance with the invention comprises a thinwalled sheet metal U-shaped lower shell open at the top and a thin-walled sheet metal U-shaped upper shell which is open at the bottom, the shells being pushed into one another in overlapping manner and welded together by means of external fillet welds on both sides, wherein the lower shell and/or the upper shell has elongate holes, the shells being additionally welded by a plurality of plug welds.

The girder, which is particularly suitable to serve as a crane jib or as a telescopic jib, is shaped or welded together from thin-walled sheet metal material. The lower 2 shell which is pre-bent or welded-together and is open at the top and the upper shell which is pre-bent or weldedtogether and is open at the bottom, are pushed into one another in overlapping manner and the shells are welded together using a plurality of plug welds and fillet welds on both sides.

It is furthermore advantageous for the lower and/or upper shell to have openings to reduce weight without any loss of strength.

For reasons of strength, it may furthermore be appropriate for the lower and upper shells to have different sheet thicknesses. This does not interfere with the application of the weld seams.

For special loads, provision may be made for the lower and/or upper shell to have reinforcement plates or reinforcement rails on selected surfaces.

The invention also provides a method for the production of a box-shaped girder which is distinguished in that a first sheet metal section of predetermined length is prebent or sections are welded together into a lower shell which is open at the top, a second sheet metal section is prebent or sections welded together into an upper shell which is open at the bottom, and the lower shell and upper shell are then pushed into one another in overlapping manner and are welded. The result is a saving in reinforcement strips, in weld pool backing, and in weld seam preparation as required for the known V-weld as well as a saving in the external shaping device. It is also not-necessary to cut the sheet metal arms into lengths af ter edging. Furthermore, a significant advantage is obtained through lesser welding distortion. Viewed overall, therefore, the production time is shorter and the costs lower.

3 For certain applications, it is advantageous for the first sheet metal section to be bent into approximately a U-shape and the second sheet metal section likewise to be bent into approximately a U-shape.

The weld join is furthermore produced more quickly and more cheaply if elongate holes are cut into the lower shell and/or into the upper shell and the welding is effected by plug welds.

Advantageously the upper shell overlaps the lower shell and is additionally welded by means of one or more fillet welds.

The overlapping of the lower shell and upper shell can be effected accurately by placing the lower shell and upper shell on an internal core device so they are fixed at a height. The shells are then welded.

For girders of particularly large dimensions, it is advantageous for the fillet weld and the plug weld to be welded by welding robots.

The invention will now be further described by way of example only with reference to the accompanying drawings in which:- Fig. 1 is a partial side view of a box-section girder; Fig. 2 is a front view of the girder, and Fig. 3 shows a detail A of the overlap region of Fig. 2 on an enlarged scale and in section.

The box-section girder 1 which serves e.g. as a crane jib or as a telescopic jib, is shaped (edged) from sheet metal 4 sections la and 1b cut to size to form a thinwalled cross-section and then welded.

To this end, a first sheet metal section la is pre-bent by edging into a lower shell 2 which is open at the top or is welded together from flat parts. A second sheet metal section 1b is pre-bent by edging into an upper shell 3 which is open at the bottom or is welded together from flat parts. The lower shell 2 and the upper shell 3 are pushed into one another in overlapping manner and are welded in a fixed position, see Fig. 1.

As shown in Fig. 2, the first sheet metal section la and the second sheet metal section 1b are pre-bent or edged in approximately a U-shape.

As shown in Fig. 3, the lower shell 2 and/or the upper shell 3 have cut elongate holes 4, and the welding is effected by plug welds 5. The upper shell 3 which is pushed on to the lower shell 2 is additionally welded by means of one or more fillet welds 6. The fillet welds 6 and the plug welds 5 may be welded by welding robots.

Openings 7 for reducing weight or for internal assembly work may be made in the lower and/or upper shell 2, 3.

The thickness 8 of the sheets may be, as shown, identical or alternatively different. This depends on the required load-bearing ability of the girder 1 and is geared to the weld seams.

The cross-sectional shape of Fig. 2 need not be restricted to -the illustrated basic rectangular shape. Other polygonal cross-sections, such as triangular and the like may also be used.

Claims

1. A box-section girder comprising a thin-walled sheet metal U-shaped lower shell open at the top and a thinwalled sheet metal U-shaped upper shell which is open at the bottom, the shells being pushed into one another in overlapping manner and welded together by means of external fillet welds on both sides, wherein the lower shell and/or the upper shell has elongate holes, the shells being additionally welded by a plurality of plug welds.

2. A box-section girder as claimed in Claim 1 wherein the lower and/or upper shell has openings in order to reduce the weight.

3. A girder as claimed in either Claim 1 or Claim 2 wherein the lower and upper shell have different sheet thicknesses.

A girder as claimed in any preceding Claim wherein the lower and/or upper shell is provided with reinforcement plates or reinforcement rails on selected surfaces.

5. A method for the production of a box-shaped girder comprising forming a U-shaped lower shell which is open at the top and a U-shaped upper shell which is open at the bottom from thin-walled sheet metal material, cutting holes into the lower shell and/or the upper shell, pushing the shells into one another in overlapping manner, welding the shells together by means of external fillet welds on both-s des and by means of plug welds.

6. A method as claimed in Claim 5 wherein the upper shell overlaps the lower shell and is additionally welded thereto by means of an internal fillet weld.

6 6. A method as claimed in Claim 5 wherein the upper shell overlaps the lower shell and is additionally welded thereto by means of an internal fillet weld.

7. A method as claimed in either Claim 5 or Claim 6 wherein the lower shell and upper shell are placed on an internal core device to fix their position and are then welded.

8. A method as claimed in any one of Claims 5 to 7 wherein the fillet welds and the plug welds are produced by welding robots.

9. A box-section girder substantially as hereinbefore described and illustrated in the accompanying drawings.

10. A method for the production of a box-section girder substantially as hereinbefore described and illustrated in the accompanying drawings.