AU8231287A

AU8231287A - A beam

Info

Publication number: AU8231287A
Application number: AU82312/87A
Authority: AU
Inventors: Lars Stalin
Original assignee: STALIN KONSULTER AB
Current assignee: Stalin Konsulter AB
Priority date: 1986-10-30
Filing date: 1987-10-29
Publication date: 1988-05-25
Also published as: AU8231187A; EP0328544A1; DK157205C; WO1988003210A1; DK157205B; WO1988003209A1; DK358588D0; AU8231087A; DK358588A; WO1988003211A1

Description

A Beam

TECHNICAL FIELD

The present invention relates to a beam with flanges manufactured of wood and a beam web connected to the flanges and consisting of rods manufactured from metallic tube or rod material, the rods extending reciprocally between the flanges and being anchored in the flanges.

BACKGROUND ART

Beams of the type mentioned by way of introduction are known in a plurality of different variations, of which one is described in Swedish Printed Application No. 7610600-4. In the beam according to this publication, the web is produced from a continuous length of round or square iron extending in zigzag formation between the beam flanges. The bent portions of the web, i.e. its V-shaped bent elbows or hairpins are anchored in the beam flanges in recesses provided therein.

A beam of the above-described type possesses the advantages of light weight and low cost, but nevertheless suffers from a number of serious drawbacks, of which the primary is caused by the fact that the beam web is manufactured in one piece. In the manufacture of the prior art beam, practically the sole solution available is a beam web of a maximum of 8 mm round steel or corresponding box steel. The reason for this is that these material dimensions are the largest available on the market in hot dip production. To manufacture a beam web in larger dimensions and then hot dip the web before assembly of the beam is carried out is, for reasons of cost, quite unrealistic. When a beam of the above-considered type is placed under load, every second of the rods extending in zigzag formation between the beam flanges will be exposed to compressive loading, while every other will be exposed to tensile stress. If such a beam were to be loaded to failure point, the failure would, as a rule, be initiated in that one of the compressive-loaded rods is buckled out, its load-bearing capacity failing entirely. Since, furthermore, the compressive loading on the rods varies along the length of the beam, and if the beam is placed under anything like continuous loading, so that the rods located at the ends of the beam will be exposed to the greatest loading, it will readily be perceived that failure will, as a rule, be initiated at the ends of the beam long before the central region of the beam has reached any critical loading factors. Thus, a beam of this type is not particularly efficient when it comes to making optimum use of the materials in the beam.

PROBLEM STRUCTURE

The object of the present invention is to realise a beam of the type disclosed by way of introduction, the beam being designed in such a manner that it may simply and cheaply be manufactured in optional dimensions without any need to fear the occurrence of problems in the corrosion protection of the beam web. The present invention also has for its object to realise a beam which is designed in such a manner that it can be made of uniform strength throughout its entire length in the event of more or less continuous loading, in other words the beam possesses optimum strength properties.

SOLUTION

The objects forming the basis of the present invention will be attained if the beam according to the present invention is characterised in that at least certain of the rods are of cross-sectional configuration, of a cross-sectional area, or of a material which differs from those applying to remaining rods.

As a result of these constructional features, it is possible to dimension the beam web in such a manner that it will possess strength properties which may be expected to prevail locally within the beam under loading. Thus, it is possible to make the rods subjected to compressive loading more resistant to buckling than those rods which, in normal loading of the beam, are exposed to tensile stress. Furthermore, it is a simple matter to render the rods of the beam web thicker and thereby stronger, out towards the ends of the beam.

According to one preferred embodiment of the present invention, at least certain of the rods are suitably interconnected with one another and with the flanges by the intermediary of anchorage bodies which are produced from a rigidly settable plastic material and which are accommodated in corresponding recesses in the flanges.

As a result of these constructional features, extremely simple manufacture of the beam will be made possible, a reliable anchorage of the beam web in the beam flanges being also achieved. Further advantages will be attained according to the present invention if the beam is also given one or more of the characterising features as set forth in claims 3 to 7.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The nature of the present invention and its aspects will be more readily understood from the following brief description of the accompanying Drawings, and discussion relating thereto. In the accompanying Drawings:

Fig. 1 is a plan view of a beam according to the present invention;

Fig. 2 is an end elevation of the beam of Fig. 1; Fig. 3 is a detailed view of one of the flanges included in the beam at an anchorage region for the beam web;

Fig. 4 is a section taken along the line A-A in Fig. 3; Fig. 5 is a detailed view of one of the beam flanges in one of the anchorage regions for the beam web, this embodiment being slightly modified; Fig. 6 is a section taken along the line B-B in Fig. 5; Fig. 7 shows a detail of a beam flange at an anchorage region for the beam web in a further modified embodiment;

Fig. 8 is a section taken along the line C-C in Fig. 7; Fig. 9 is a section similar to the section of Fig. 8, but with a modified embodiment of the beam web; and

Fig. 10 is a corresponding section with yet a further embodiment of the beam web.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the Drawings, it will be apparent from Fig. 1 that a beam according to the present invention has two beam flanges 1 and 2, and a beam web 3 extending therebetween. The beam flanges are manufactured of wood, while the beam web is manufactured of metal, preferably steel.

Suitably, the beam web 3 is manufactured of tube or rod material and may, along certain portions of the beam, be bent in one piece from a longer continuous length of this material, while the web may, along other sections of the beam, be manufactured of separate rods 4, so that there will thereby be formed a beam web between the beam flanges 1 and 2 which has reciprocally extending rods 4. At those portions of the beam web 3 which are manufactured by bending of a long continuous length, closely adjacent rods 4 will have bent conjunction regions which may be V-shaped, U-shaped or bent in any other suitable configuration. As is apparent from Fig. 1, these bent conjunction regions between closely adjacent rods 4 are accommodated interiorly in recesses in the two beam flanges 1 and 2. For those portions of the beam web 3 which are manufactured of separate rods 4, their design will be described in greater detail below, but it may already be assumed that the end portions of these rods 4 are accommodated in recesses in the beam flanges 1 and 2.

In Fig. 1, the rods forming the beam web 3 have been shown as straight rods which run in zigzag formation at an angle of approximately 60° in relation to the longitudinal direction of the beam flanges. Naturally, the rods 4 need not be arranged in this manner, but the angle between the rods and the beam flanges may vary within broad limits. In practice, a range of between 45° and 60° has proved to be usable, in which instance 45° provides the best transfer of forces between the flanges and the rods. This entails that if the rods are viewed as rigid, an optimum strength will be obtained for this angle. However, employing this angle, the rods placed under compressive loading will have a relatively large free buckling length, for which reason relatively high demands will, naturally, be placed on the material dimensions in the rods.

According to the invention, it may be appropriate to arrange such rods 4 as, on loading of the beam, will be exposed to compressive loading at a greater angle to the flanges of the beam than is the case with such rods 4 as are exposed to tensile stress.

In Fig. 2, the beam flanges 1 and 2 are shown as being approximately square in cross-section, but, of course, this is not a critical requirement according to the present invention, instead the cross-sectional configuration of the beam flanges may be completely different and may, for instance, be rectangular or be of any other form which proves to be practical in view of the use to which the beam is put or in view of the manner of its manufacture. Figs. 3 to 8 show how web rods 4 of one piece manufacture are arranged in recesses 5 of different designs provided in the beam flanges 1 and 2. If it is assumed, in Figs. 3 to 8, that the illustrated beam flange is the lower beam flange 2, Figs. 3, 5 and 7 will show a section of this beam flange 2 seen straight from above. According to the present invention, recesses 5 are provided in the beam flanges 1 and 2, the recesses being, according to Figs. 3, 4, and 7, 8, respectively, defined by end walls 6 and a bottom wall 7, while those shown according to Figs. 5 and 6 are defined by outer end walls 16, inner end walls 17, outer bottom walls 18 and an inner bottom wall 19, such that the recess will have an outer portion 14 and an inner portion 15. It will be apparent from the Drawings that the end walls 6, and 16 and 17, respectively, are approximately at right angles to the longitudinal direction of the beam flange 2, or at least transversely directed in relation thereto. Furthermore, the bottom walls 7, and 18 and 19 in the recess, are approximately parallel to the lower defining surface 8 of the beam flange 2. For anchoring the rods 4 in the beam flange 2, use is made of an anchorage body 9 which is formed of a plastic composition with a thermosetting plastic and a suitable filler. As thermosetting plastic, use may, for example, be made of polyesters, epoxy or vinyl and the proportion of filler in the plastic composition should be at least 50%. In the manufacture of the beam, the plastic composition is poured as a liquid or viscous paste into each recess 5 completely around the portions of the rods 4 accommodated in the recesses, so that the recesses will be completely filled with the plastic composition. Once this has set, the result will be a form permanent stable anchorage body which is firmly connected to the rods (by surrounding them) and which is of the same form as the recess 5.

When a beam designed according to the present invention is placed under loading, every other rod 4 will be exposed to tensile stress, while every second rod will be exposed to compressive loading. This entails that the anchorage body 9 will have a tendency, under the action of the loading forces of the beam, to twist about an imaginary axis 22 which is approximately at right angles to the plane of the beam web 3 and which as a rule extends somewhere through the anchorage body 9. If, in Fig. 4, the right-hand rod 4 is exposed to tensile stress, as intimated by the arrow, while the left-hand rod is exposed to compressive loading, this would have as a consequence that a moment of torque would be generated on the anchorage body 9 counter-clockwise about the axis 22. As a result of the shape of the recess 5 and because the anchorage body is configurationally stable, such a torque cannot take effect unless either the material in the beam web 3 or in the anchorage body - or possibly in both - is considerably deformed. Thus, to prevent the rods 4 from being detached from the beam flanges, no direct adhesion between the material in the anchorage body 9 and the material in the beam flanges is necessary; instead the anchorage of the rods is effected in that the anchorage body is form-permanently locked in its recess by the applied loading.

Those forces which the rods 4 exercise against the anchorage body 9 give rise to a horizontal resultant along the beam flange 2. This resultant prevents, by friction at the end surfaces 6 of the anchorage bodies 9, the twisting tendency about the axis 22 considered above.

One of the major problems inherent in prior art technology resides in the fact that the material properties in the steel material of the rods 4 and the wood material in the beam flanges 1 and 2 differ greatly from one another. According to the present invention, it therefore applies that the anchorage body 9 must be given material properties which, as far as is possible, approach the properties of both the steel and of the wood material. In this context, it might well be mentioned that the elasticity modulus in the wood material may vary between the order of magnitude of 10 000 and twice that level, depending upon the type of wood employed. The elasticity modulus for steel lies beyond 20 000, for which reason considerable differences may. be present in the size of the deformations which the different materials undergo on being placed under load. As regards the plastic material in the anchorage body, the material properties may be varied in a plurality of different manners, int. al. by varying the content of filler, the particle size of the filler employed and, of course, also the type of plastic material used, as well as the degree of setting and curing of the plastic material. Further parameters which may be employed for modifying the elasticity modulus of the plastic composition are the strength properties (materials properties) and the structure of the filler.

One method of realising a more or less 'continuous' transition, in terms of strength properties, between the different material properties resides in the fact that the anchorage body is given, in its central regions, an elasticity modulus which approximates that of steel, while, in its peripheral areas which come into contact with the wood material in the beam flanges, it may be given a considerably lower elasticity modulus, in that the outer portions of the anchorage body are not permitted to set and cure to as great an extent as the more centrally located portions.

In order, despite the use of anchorage bodies, to reduce the risk of point loadings on the wood material, the form and dimensions of the recess 5 in relation to the form and dimensions of the rods 4 may be of decisive importance. Hence, it is apparent from Figs. 3, 5 and 7 that the end walls of the recess 5 are arched with a radius of curvature which approximately corresponds to the diameter of the rods 4. Furthermore, the transitional regions between the end walls and the bottom wall, and the bottom walls, respectively, are rounded with a radius which is of approximately the same order of magnitude as the diameter of the rods 4. Finally, the bottom wall itself may also suitably be curved with approximately the same radius as the diameter of the rods 4.

It will be apparent from Figs. 3 and 4 that there may be provided, transversely of, or approximately at right angles to the plane of the beam web 3, one or more channels 10 from the side surface of the beam flange 2 in to the recess 5, through the recess and a further distance into the opposing side of the beam flange. These channels may be employed for introduction of the plastic composition which is to form the anchorage body, if the plastic composition is not introduced in the recess from above, that is to say from that side which is turned to face towards the beam web 3. Once the anchorage body 9 has set, the channels 10 will be filled with plastic material so that, thereby, the anchorage body will be even more reliably form-permanently fixed in the beam flanges 1 and 2. Concerning the overall strength of the beam, the use of such plugs on the anchorage body as are formed in the channels 10 will have as a consequence that failure safety increases, but that the flexural rigidity of the beam will decrease somewhat. The same type of channels 10 and plastic plugs extending into the beam flanges may also be employed in other embodiments.

As has been mentioned above, the anchorage body 9 will, on loading of the beam, show a tendency to twist in the recess 5 about the axis 22. In order to reduce the risk that such occurs, in other words to increase the retention of the anchorage body 9 in the beam flange, a transverse metal pin or other type of plug of good strength properties may be embedded in the anchorage body, these pins being located a distance from the axis 22 (approximately as one or more of the channels 10) and extending into corresponding bores in the beam flanges. These pins are necessary in such cases when the above-mentioned friction between the anchorage body 9 and the end surfaces of the recess 5 is insufficient. It will be apparent from Figs. 4, 6 and 8 that both of the rods 4, on their sides facing away from one another, abut against edge regions 11 on the ends of the end walls turned to face the beam web 3. Hereby, the beam web 3 will, on production of the beam, be guided in relation to the beam flanges, and vice versa, whereby complicated jigs and the like may be dispensed with.

It will further be apparent from Figs. 4, 6 and 8 that there is a space 13 between the top portion 12 of the meeting rods 4 and the bottom wall in the recess 5, this space being, in the finished state of the beam, filled with a part of the anchorage body 9. This space is essential, partly as regards guiding of the beam web 3 in relation to the beam flanges 1 and 2 with the assistance of the edge regions 11, and partly as regards the overall strength and 'continuity' in the joint between the rods 4 and the flanges 1 and 2. By employing the space 13, a part of the anchorage body 9 will lie between the top portion 12 and the bottom wall 7 of the recess 5, and this interjacent portion of the anchorage body will prevent point loadings on the wood material. Moreover, the space 13 serves an important function as regards realising a joint between separate web. rods 4 interiorly in the anchorage body, as will be more clearly apparent with reference to Figs. 9 and 10.

The description presented above has substantially related to such portions of the beam web 3 as are manufactured from a continuous length of rod or tube material. For such portions as are subjected to heavy loading, or if, for example, the dimensions of the beam are increased above a certain limit, the rods 4 included in the beam web 3 will be of relatively great length, for which reason their resistance to buckling rapidly reduces. This implies that if no special measures are adopted to stabilise the rods 4 subjected to compressive loading, the risk of buckling in the rods will rapidly increase to an unacceptable level.

According to the present invention, it is, as was intimated by way of introduction, possible to produce a beam of considerable dimensions in which, for example, a central region of the beam web 3 is produced in a continuous length, while the end portions of the beam web are produced in such a manner that each rod 4 will be of separate manufacture. In order to make possible fixed retention of the separate beam rods in the beam flanges 1 and 2 in a manner as described above, both of the rods are provided, at their ends, with angled hook portions 20 whose bending angle approximately corres- ponds to the angle between the above-discussed rods 4 in the embodiment according to Figs. 3 and 4.

Fig. 9 shows an embodiment of the present invention in which a slighter or slimmer rod 4 is, as intimated by the arrow, subjected to tensile stress, while a more robust, or thicker rod 4 is subjected to compressive loading. The two hook-like portions 20 are nested in one another such that the ends of the rods are in mutual contact and, in addition, the hook portion of the thicker rod is laid interiorly in the hook portion of the slimmer rod. Hereby, both tensile stresses and compressive loadings may be transferred between the rods directly metal-to-metal.

Assembly and mounting of the rods according to Fig. 9 are realised in the same manner as described above, and the sole conjunction of the rods which is actually required in the beam is realised by means of the form-permanent anchorage which the anchorage body 9 affords as a result of its configurational stability. In this context, it should be emphasised that the ends of the rods 4 should be wholly enclosed in the anchorage body 9, as a result of which there will be formed, as mentioned above, the space 13 to the bottom surface of the recess 5. To facilitate mounting of the beam, in other words before and during pouring of the anchorage body 9, it is conceivable to employ a simple welding process such that, thereby, the rods 4 will be positionally fixed in relation to one another a sufficient degree to withstand handling. Alternatively, use may also be made of different types of clamps or unions of plastic or metal which, during the handling of the rods, hold the rods in the correct position in relation to one another. Naturally, it is also possible according to the present invention to employ jigs or fixtures in which the rods are placed and fixedly retained during the pouring and setting of the anchorage bodies. As was mentioned above, the beam intimated in Fig. 9 may have its central portion produced of rods 4 of the slimmer type and, furthermore, the rods placed in the end portions of the beam and subject to tensile stresses may also be of the same relatively slight material dimension. On the other hand, the rods placed under compressive loading, primarily in the end regions of the beam, should be designed with a thicker material cross-section, be of a superior material quality or be of tubular cross-section so that the resistance to buckling will thereby be sufficient. According to the present invention, it is also possible to design a beam in such a manner that all rods are produced separately from one another, in which event, for example, all rods exposed to compression are thicker than the rods exposed to tension. Possibly, several different material dimensions or cross-sectional configurations may be employed in one and the same beam, so that the overall strength will thereby be at the fully optimum level.

In the embodiment according to Fig. 9, the recess 5 for the anchorage body 9 must, naturally, be slightly wider than is the case in the embodiment according to Figs. 3 and 4, so that sufficient space may thereby be made available on both sides of the thicker rod 4.

Fig. 10 illustrates yet a further embodiment of the present invention which permits separate production of each individual rod 4. Also in this embodiment, the rods are provided with angled hook portions 20, but, as opposed to the embodiment according to Fig. 9, these hook portions are solely laid side-by-side interiorly in the anchorage body 9.

Neither in this embodiment is any other conjunction of the two rods 4 required above and beyond that which may be attained by the anchorage body 9, but to facilitate handling of the rods during construction of the beam, and during pouring and setting of the anchorage bodies, the same aids as were proposed above with reference to Fig. 9 are also conceivable here. Naturally, in the embodiment according to Fig. 10, the width of the recess 5 for the anchorage body 9 must be enlarged in relation to the embodiments according to Figs. 3, 4 and 9. This also implies that the width of the two beam flanges 1 and 2 is suitably greater than in the remaining embodiments. It might possibly be conceivable to provide a recess 5 which consists of two part recesses which are offset somewhat in relation to one another in the longitudinal direction of the beam flanges, so that the end regions of the composite recess will be narrower, such that dimensioning of these end regions corresponds to that disclosed above with reference to Figs. 3 and 4. The central region of the composite recess, in other words that part of the composite recess where both of the part recesses overlap and are in communication with one another, will, by this arrangement, obtain greater width, in which event the width here corresponds approximately to the sum total of the widths of the two part recesses. The defining limits of the wider central portion of the composite recess are shown in Fig. 10 by means of broken lines 21. This design of the recess 5 will entail a reduction of consumption of the plastic composition in the anchorage body 9, and, in addition, the form-permanent retention of the anchorage body 9, and its cooperation with the beam flanges may be further improved.

It should be emphasised that the embodiment according to Figs. 9 and 10 permits certain parts of the beam web to be produced in one continuous piece as described with reference to Figs. 3 and 4, while other parts of the beam web are produced by separate individual rods, such that adaptation of the strength properties of the rods may thereby be made to meet the loading which can be expected to prevail locally in the beam. By the division of the rods into separate units, it is also possible to employ different types of cross- sectional configurations in the different rods, as well as varying material qualities in different rods.

In those cases where the rods 4 are produced of tubular material, the rods may have compressed planar end portions which are bent and conjointed in full analogy with the hook portions 20 according to Fig. 9.

It could also be possible to place these planar portions against one another so that their plane will lie approximately parallei to the beam web 3, and to pass a transverse pin through apertures therein and into the material of the beam flange 2. In both of the immediately preceding alternatives, it should be underlined that the joint region between the rods 4 is enclosed within the anchorage body 9, for which reason this will realise a load- -transferring cohesion, first between the rods 4 themselves and secondly between the rods and the beam flange. In addition, the anchorage body provides a corrosion protection for those parts of the rods which are enclosed and which may be damaged by such operations as machining or welding.

All embodiments of the present invention allow for the employment of one or more channels 10, or for their exclusion. But if channels 10 are to be employed, these must be placed in the neutral line of the beam flanges, that is to say in that line where the tension on loading of the beam is, in principle, zero. As was mentioned above, the elasticity modulus in the anchorage body may vary depending upon position. This is realised by a variation of the setting and final curing degree in the plastic material, and this variation may be realised by adaptation of the moisture content in the wood material used, such that, for example a moisture content of the order of magnitude of 15% will result in poor setting and final curing of the plastic material and a consequentially low elasticity modulus, while a lower moisture content, down towards 8%, will result in a considerably improved setting and final curing of the plastic material (at least in the surface interface with the wood material), such that the elasticity modulus will also be considerably greater in this surface layer.

Finally, the elasticity modulus may also be varied locally - in addition to using the above-discussed methods - by using two different composite plastic compositions (the same basic plastic but with different filler properties) in one and the same anchorage body.

The present invention should not be considered as restricted to that described above and shown on the Drawings, many modifications being conceivable without departing from the spirit and scope of the appended Claims.

Claims

1. A beam with flanges (1, 2) produced of wood and a web (3) connected to the flanges and comprising rods (4) produced of metallic tube or rod material, the rods extending reciprocally between the flanges and being fixed in the flanges, characterised in that at least certain of the rods (4) are of a cross-sectional configuration, cross-sectional area or of a material which differs from that which applies for the remaining rods.

2. The beam as claimed in claim 1, characterised in that at least certain of the rods (4) are interconnected with one another and with the flanges (1, 2) by the intermediary of anchorage bodies (9) which are produced from a settable plastic composition and which are accommodated in corresponding recesses (5) in the flanges (1, 2).

3. The beam as claimed in claim 2, characterised in that the rods (4) are provided, in their ends accommodated in the anchorage bodies (9), with angled portions (20) which overlap one another.

4. The beam as claimed in claim 2, characterised in that the rods (4) are provided, in their ends accommodated in the anchorage bodies (9), with angled portions (20) where one such angled portion is located interiorly in another.

5. The beam as claimed in anyone of claims 1-4, characterised in that the rods (4) are, in a central region of the beam, produced from a tube or rod material of slighter cross-sectional area than the tube or rod material in the rods in the end portions of the beam.

6. The beam as claimed in anyone of claims 1-5, characterised in that those rods (4) which, on loading of the beam, are exposed to compressive loading, are produced from a tube or rod material of greater cross-sectional area than the tube or rod material in the remaining rods.

7. The beam as claimed in anyone of claims 4-6, characterised in that the angled portion (20) on a rod (4) produced from a thicker tube or rod material is located interiorly in the angled portion of a rod produced from a slighter tube or rod material.