WO1992003623A1

WO1992003623A1 - Meshed beam

Info

Publication number: WO1992003623A1
Application number: PCT/FI1991/000259
Authority: WO
Inventors: Seppo RYYNÄNEN
Original assignee: Gesertek Oy
Priority date: 1990-08-21
Filing date: 1991-08-21
Publication date: 1992-03-05
Also published as: FI89400B; FI89400C; AU8314491A; FI913483A0; FI913483A

Abstract

The invention relates to a beam structure, generally comprising two flange sections and at least one web section fitted therebetween. The web section is made of diagonal steel wires or bars which are welded crosswise to each other to form a diagonal wire or bar mesh (86, 86b, 86c, 86e). The web forming wires or bars are positioned at least in three layers and oriented such that the wires or bars (86b) in the outer layers are substantially parallel to each other, and the wires or bars (86c) in the intermediate layer are crosswise to the wires or bars (86b) in the outer layers.

Description

Meshed beam

The present invention relates to a beam structure, generally comprising two flange sections and at least one web section fitted therebetween.

The Applicant's earlier Patent application FI 904137 discloses a composite beam structure, comprising a light web section made of a diagonal meshed sheet. Prior known are also several beams with web sections made of metal trusses.

A drawback in the prior art beams is e.g. that a web section takes up a lot of expensive steel material. In a trussed web, the long diagonal stringers must be made dimensionally stable to prevent buckling. One of the drawbacks in a sheet-webbed beam is the inconve¬ nience of installing equipment extending through the web. In addition, a possible concrete layer has a poor adherence to a smooth surface. In order to pre¬ vent the buckling of a sheet-webbed beam, it is gener¬ ally necessary to use unnecessarily thick sheet metal.

An object of this invention is to alleviate the above drawbacks. It is accomplished by means of a beam struc¬ ture of the invention in a manner that the web section is made of diagonal steel bars which are welded cross¬ wise to each other for a diagonal wire or bar mesh.

The invention can be practiced in a great deal of dif¬ ferent applications. The accompanying drawings are only intended to serve as examples and to illustrate the way the invention is put to practice. The posi¬ tions of various structural elements can be selected arbitrarily. For the sake of clarity, the following descriptions of drawings include e.g. terms like top and bottom sections, although this may also relate to different lateral directions.

Fig. 1 is a side view of a section of a beam of the invention, showing a diagonal bar mesh.

Fig. 2 is a perspective view of a section of a beam of the invention.

Fig. 3 shows in principle the directions of tensile and compressive forces in the bars.

Fig. 4 shows a perspective view of a twin-webbed beam of the invention.

Fig. 5 shows a horizontal section of a web portion of the invention, provided with a profiled sheet as a keep-off element between two diagonal bar meshes.

Fig. 6 shows another horizontal section with both diagonal meshes carrying three superimposed bar layers.

Fig. 7 shows a visualization, wherein the keep-off elements comprise diagonal steel sheet mem¬ bers welded to diagonal steel bars.

Fig. 8 shows a visualization of a beam of the inven¬ tion having its top flange made of a rectan¬ gular reinforcement bar resh.

Fig. 9 shows a principle of assembling a flange from rectangular sections of a reinforcement bar mesh. Fig. 10 shows a longitudinal section of a beam of the invention with a bottom flange which is made of a rectangular reinforcement bar mesh extend¬ ing in the longitudinal direction of the beam.

Fig. 11 shows a longitudinal section of two beams of the invention which are superimposed for to be used together.

Fig. 12 shows a principle having a small-meshed sheet screen secured behind a strong and large-meshed diagonal bar mesh.

Fig. 13 shows a cross-section of a beam of the inven¬ tion during the course of shotcreting.

Fig. 14 shows a visualization of an assembly of the invention with a corrugated sheet mesh fitted between two diagonal bar meshes as a keep-off element.

Fig. 15 shows a cross-section of a beam of the inven¬ tion with two -web sections made of a bar mesh and with an intermediate space therebetween filled with concrete.

Fig. 16 shows one possibility of assembling a diagonal bar mesh from steel bar loops .

Fig. 17 is a view of assembling the web of a beam from steel bar loops.

Fig. 18 shows one possibility of fabricating a diagonal steel bar mesh by diagonally cutting a rectan¬ gular steel bar mesh into sections. Fig. 19 shows a visualization of a 3-layer steel bar mesh.

Fig. 20 shows a cross-section of a triangular box beam of the invention.

Fig. 21 shows a cross-section of a triangular box beam having its bottom flange reinforced with concrete casting.

An essential object of this invention is to provide a light and inexpensive beam. An effort is made to ex¬ ploit steel as effectively as possible by dividing it into a bar mesh, wherein the length section of an in¬ dividual strip will be small between welded nodes. Thus, buckling is prevented even with a small amount of steel. The reinforcement bars, secured together by welding and arranged in various layers, provide a rigid structure also in lateral direction. The in¬ vention is capable of providing structures having a great flexural rigidity. Thus, even with long spans, it is possible to avoid supports during construction work. Beams of the invention can also be temporarily laid on top of each other to serve together in critic¬ al installations.

Fig. 1 illustrates a section of an elongated steel beam, wherein the web comprises diaggonal steel bars 86 in the form of a steel-bar mesh. The diverging, crosswise disposed steel bars 86 are welded securely to each ot¬ her at all nodes 94. Thus, the buckling-sensitive free ar section only remains within the section between two nodes 94. The welding job required by a bar mesh can be reliably carried out e.g. by automatic welding mach¬ ines. The beam carries a top flange 52 which generally serves as a member taking up compression stresses. The beam carries also a bottom flange 57 which generally serves as a member taking up tensile stresses. The diagonal position of steel-bar mesh 86 is ideal in terms of transmission of forces. The web comprises a lot of voids or openings to make the structure lighter and to facilitate the passages of various equipment. The web consists primarily or solely of diagonal steel bars 86.

Fig. 2 illustrates a perspective view of a beam of the invention. In this case, said flanges 52 and 57 are made of steel sheet, to which the diagonal bar strips 86 of a web are securely welded. In this case, the diagonal steel-bar mesh 86 consists of crosswise bars 86 laid in three layers. The crosswise steel bars 86 are welded to each other at all nodes 94. In many instances, it is preferable that the bar mesh has at least three layers of diagonal bars 86 with two bars serving parallel to each other as a pair and having a crosswise bar therebetween. Thus, for example, compressed diagonals 86 can be provided with two bars to further reduce the possibility of buckling. In fig. 19 the case is illustrated in more detail. The diagonal bars serving as a pair brace or rigidify the entire web in lateral direction. Fig. 2 only illustrates flanges 52, 57 and a web 86, 94 included in the beam. In reality, the beam is generally provided e.g. with upright struts at the ends of a beam and possibly also in the mid-sections of a beam.

Fig. 3 illustrates how various diagonal bars 86b and 86c included in a meshed web 86 receive various forces. At mesh-bar nodes 94, for example, the diagonal bars 86c extending in one direction take up tensile stresses and the diagonal bars 86b extending in the other direction take up compression stresses. Hence, the tensile and compression stresses run into each other at a node. A tensile stress always tends to keep the bar or mesh straight, i.e. to prevent buckling. In directions under a compression stress, in particular, it is preferable to increase the number of bars, as shown also in fig. 19.

In fig. 4, the web section of a beam is made of two parallel disposed diagonal bar meshes 86, each including two crosswise bar layers. Thus, the forces can be distributed over a larger area in flanges for an improved function of flanges 52, 57. In fig. 4, said diagonal bar meshes are set at a distance from each other. Hence, the intermediate space can be filled with a desired material.

Fig. 5 illustrates two 2-layer diagonal bar meshes 86b, 86c, between which is secured e.g. by welding a profiled thin sheet 1 as a keep-off element to provide the meshes with a mutual spacing. At the same time, the profiled thin sheet braces diagonal bar meshes 86b, 86c in lateral direction for an anti-buckling effect.

In fig. 6, a profiled sheet 1 is fitted on both sides with 3-layer diagonal steel-bar meshes 86b, 86c, 86b. The parallel steel bars 86b, 86b is here preferably disposed to extend in the direction of compression stresses.

In fig. 7, between parallel diagonal bars 86 are welded crosswise diagonals 86e of sheet material in an effort to keep the edge-located bars 86 off of each other. The crosswise diagonal strips 86e provide the web with lateral stability. The diagonal bar members 86, 86e create a rigid structure. On the outside of outermost bars 86 it is still possible to weld yet other diagonal bar layers in a crosswise pattern.

In fig. 8, the top flange 52 of a beam is made of a rectangular bar πesh, comprising steel members 50a which take up stresses and extend in the longitudinal direc¬ tion of the beam. The longitudinal steel members 50a are interconnected by means of transverse steel members 50b. In terms of providing a functional flange, said longitudinal and transverse steel members 50a, 50b are preferably welded together at nodes. A flange as shown e.g. in fig. 8 can be reinforced e.g. with concrete, which is preferable in many cases for taking up com- pressive forces. If necessary, the bottom flange 57 can also be designed the same way. The concreting can be effected at a subsequent stage by only carrying the light frame of a beam to an installation site. The heavy and firm concrete layer need not be added until at a later stage, if desired. In view of concreting, it is preferable to use ribbed bars 50a, 50b.

Fig. 9 illustrates halves 50a, 50b of a rectangular welded flange mesh. Those can be inserted from oppo¬ site sides of a web mesh 86b, 86c to lie against each other in contact with a web. Bars 50b coming from opposite sides are laid parallel to each other in a flange in transverse direction and, thus, can be readily joined together e.g. at a construction site. Bars 50b can be inserted e.g. through the voids of a diagonal bar mesh to provide a natural link in a web.

In fig. 10, the bottom flange is made of reinforcement bars 50a, 50b by applying the principle shown in fig. 9. The ends of 86d of diagonal bars are bent to extend parallel to the flange to facilitate welding or to bind an eventual concrete layer. In fig. 11, two beams of the invention are laid on top of each other temporarily for an imporved bearing capac¬ ity during installation work. The bottom beam can e.g. be cast inside concrete 6. The bearing of uncured con¬ crete mass requires a larger amount of steel than what is needed at the final stage when concrete carries part of the load and adds particularly to the compression strength in the upper portion of a beam. This situation requires an upper auxiliary beam which is fastened to the bottom beam e.g. by means of fastening screws 82. Between the beams can be fitted elevation members 25 for a subsequent detachment of the beams from each other. If desired, fasten^'ing screws 25 can be used to give the bottom beam a pre-elevation in view of the final situa¬ tion. In terms of stress during a subsequent working phase, the temporary upper beam is preferably turned upside down in a manner that a strong bottom flange 57 serves on top as a compression flange. A compression flange 52 of the lower, stationary beam can be primari¬ ly formed by using e.g. cast concrete 6. After the lower beam has hardened and attained a sufficient strength, the temporary upper beam can be detached e.g. by loosening said screws 82. Thus, the concrete layer 6 in the upper portion of the beam receives compress¬ ion stresses. If desired, the structure can be sort of pretensioned in its upper portion since, upon loosen¬ ing said screws 82, the beam is slightly depressed over its mid-section while the ends are supported. The re¬ moved upper beam can be utilized at another construc¬ tion site after turning the beam to its proper position.

Fig. 11 only illustrates a part of quite a long struc¬ ture capable of crossing long spans. The applications may include e.g. bridges and floors of buildings and other such structures. As a vertical structure it is possible to design e.g. various walls. The structure is light without the weight of concrete. By the ad¬ dition of concrete to the structure it is possible to create a composite structure capable of withstanding major stresses.

Fig. 12 illustrates how a diagonal and large-void reinforcement mesh 86 is fitted with a small-loop mesh 10 for an increased rigidity and to prevent the pass¬ age of an eventual concrete layer. The small-loop mesh can be provided with stiffening corrugations 49 for increasing structural rigidity.

In fig. 13, a beam is designed in a manner that the web section is made of a diagonal reinforcement mesh 86, which is well capable of taking up shearing forces if it is e.g. welded to a bottom flange 57 and to a top flange 52. In the longitudinal direction of the beam, said web section can be straight or it can be corrugated. The reinforcement mesh can be accompanied by a small- void mesh 10 for preventing the passage of concrete. The web section of the beam is reinforced with a con¬ crete layer 6, which also serves as an anti-corrosion layer. The frame element of the beam is light prior to the addition of concrete and, thus, it can be readily carried around at a construction site e.g. to serve as a frame element for larger structures. The high strength is attained by not spraying concrete 6 until at a final or nearly a final stage.

Fig. 14 illustrates how between two diagonal bar meshes 86 is fitted a meshed sheet 86a, the latter being cor¬ rugated to serve as a keep-off element. The steel-bar meshes 86 can be fastened e.g. by welding to meshed sheet 86a for improved lateral stability in the web of a beam. This way, the diagonal bar meshes 86 can be linked together.

Fig. 15 illustrates one twin-webbed beam of the inven¬ tion, the space between webs 86 being filled with con¬ crete 6. In order to prevent the lateral escape of con¬ crete, the diagonal bar meshes are fitted with a fine- meshed screen 10. Webs 86 and fine-meshed screens 10 can be bound to each other e.g. as shown in fig. 14. If desired, the concrete core 6 of the beam can be further reinforced with additional steel members 50 which can be e.g. prestressed steel members. The top flange 52 can be provided with an opening for carrying out concrete casting.

Fig. 16 illustrates diagonal wire loops 86b and 86c, wherein the ends 86d of a loop are designed to be parallel to the flange of a beam. The diagonal wire members 86b and 86c can be set to extend in various directions.

Fig. 17 illustrates how the wire loops of fig. 16 are laid on top of and crosswise with each other. At nodes 94, the crosswise wires 86b and 86c are welded to each other. The loop ends 86d are set to be parallel to subsequent flanges for easier fastening.

Fig. 18 shows a principle for cutting a rectangular, welded wire mesh 86 along inclined lines 75 into sec¬ tions of a diagonal wire mesh. The uncut ends of such sections can be joined together to produce even long diagonal wire meshes for long beams.

Fig. 19 illustrates a three-layer diagonal wire mesh. The parallel superimposed wires 86b serve as pairs and are well capable of taking up compression forces. Between wires 86b extend crosswise wires 86c. All three wire layers are welded on top of each other at nodes 94. The pairs-forming wires 86b stabilize the entire mesh structure. Thus, the web of a beam is also provided with excellent lateral rigidity.

Fig. 20 illustrates a cross-section of one triangular beam. In this case, a top flange 52 is made of e.g. stee bar or tube. If desired, bottom flanges 57 can be made o the same materials. The laterally mounted webs 86 are made of diagonal steel wires, which are crosswise welded to each other to form a diagonal wire mesh. If desired, the beam cross-section can be designed as an equilateral triangle, whereby all sides and all apexes 52, 57 can be designed mutually identical. Thus, also the side extending between bottom flanges 57, 57 is made of a diagonal steel-wire mesh 86. Thus, the position of a bea will bear no significance. For example, the box beams included in bridges can be set side by side in a manner that, with two adjacent beams, the apex of one points upwards and that of the other points downwards. A desired number of adjacent beams can be fastened to each other e.g. by welding. If desired, a triangular beam can also be set in upright position to serve e.g. as a mast. In¬ side the triangle will remain a void 92 which can be utilized in the final structure. If the sides 86 of a triangular beam are lined with a fine-meshed screen 10, as shown in fig. 12, the surface of the triangle can be reinforced e.g. by means of shotcreting.

Fig. 21 illustrates how a beam as shown in fig. 20 is placed in a concrete-casting mould 69 by one of its sides. If desired, the side placed in the casting mould can be provided with steel members 50a parallel to bottom flange 57 for tensile stresses. After the hardening of cast concrete 99, the result will be a beam suitable for several applications. The other sides of a triangle can also be cast in concrete one by one the same way. This serves to create a sturdy, steel-reinforced structure.

The steel wires or bars used in the invention can be of an arbitrary type. The wires can have a cross- section which is e.g. circular, rectangular, flat or tubular. The wire surface can be smooth, profiled in longitudinal direction or provided with grips e.g. for concrete.

One application of a beam can be e.g. a bridge in a manner that a bridge-bearing system is constructed from beam structures of the invention. In addition to minor pedestrian bridges, such bridges may include heavily loaded bridges.

The diagonal, securely welded steel wires 86, 86a, 86b, 86c, 86d, 86e included in the web section of a beam can also be fastened to a flange by the application of friction after providing the flange with fastening mechanisms e.g. for clamp fitting.

A wire mesh asemployed in a solution of the invention is much more rigid than a cut-off mesh.

Claims

1. A beam structure, generally comprising two flange sections and at least one web section fitted therebetween, the web section being made of diagonal steel wires or bars which are welded crosswise to each other to form a diagonal wire mesh or bar mesh (86, 86b, 86c, 86e) , c h a r a c t e r i z e d in that the web forming wires or bars are positioned at least in three layers and oriented such that the wires or bars (86b) in the outer layers are substantially parallel to each other, and the wires or bars (86c) in the intermediate layer are crosswise to the wires or bars (86b) in the outer layers.

2. A beam as set forth in claim 1, c h a r a c t e r ¬ i z e d in that crosswise wires (86, 86b, 86c, 86e) in¬ cluded in the diagonal wire mesh of a web are welded to each other at every crossing or node (94) of said wires.

3. A beam as set forth in claim 1 or 2, c h a r a c ¬ t e r i z e d in that said diagonal wires (86, 86b, 86c, 86d, 86e) of a web are welded securely to a bottom flange (57) or a top flange (52).

4. A beam as set forth in claim 1 or 2 , c h a r a c ¬ t e r i z e d in that said diagonal wires (86, 86b, 86c, 86d, 86e) of a web are fastened to either flange (52, 57) by means of friction.

5. A beam as set forth in claim 1 or 2, c h a r a c ¬ t e r i z e d in that a web section is fastened to either flange (52, 57) by means of concrete (6, 99).

6. A beam as set forth in any of claims 1 - 5, c h a r a c t e r i z e d in that said diagonal steel-- wire mesh (86, 86b, 86c, 86e) is fitted with a fine-meshed screen (10) .

7. A beam as set forth in any of claims 1 - 6, c h a r a c t e r i z e d in that two side-by-side diagonal steel-wire meshes (86, 86b, 86c, 86e) are fixed to each other by means of some keep-off element (86a).

8. A beam as set forth in any of claims 1 - 7, c h a r a c t e r i z e d in that two beams are temporarily laid on top of each other.

9. A beam as set forth in any of claims 1 - 8, c h a r a c t e r i z e d in that the beam has a triangular cross-section, and at least one flank of the triangle has said diagonal mesh of wires or bars in three layers.

10. A beam as set forth in any of claims 1 - 9, c h a r a c t e r i z e d in that the beam structure is reinforced with concrete or some other similar re¬ inforcement material (6, 99).