AU8231087A

AU8231087A - A beam and a method of producing the same

Info

Publication number: AU8231087A
Application number: AU82310/87A
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: DK358588D0; DK157205C; WO1988003211A1; DK358588A; EP0328544A1; WO1988003209A1; WO1988003210A1; AU8231187A; AU8231287A; DK157205B

Description

A BEAM AND A METHOD OF PRODUCING THE SAME

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 accommodated, with end portions or bent end regions, in recesses in the flanges. The invention also relates to a method of producing the beam, in which the flanges are provided with recesses and the beam web is formed to have rods which extend reciprocally between the flanges and which extend into the recesses and are anchored there.

BACKGROUND ART

A beam of the type mentioned by way of introduction is previously known from SE 7610600-4. The beam according to this publication has both of the beam flanges divided in two longitudinal wooden laths or battens, grooves arranged in V-shape formation in relation to one another being disposed preferably in one, but possibly in both of the laths, the grooves being intended for accommodating the bent portions of the beam web arranged in zigzag formation. In this instance, the grooves are of substantially the same form as the bent portions of the beam web. After placement of the bent portions of the beam web, i.e. their turns or elbows, in the V-shaped disposed grooves, the two laths which each constitute the beam flange, are glued together.

A beam of the above-outlined prior art type has but limited carrying capacity and, moreover, suffers from relatively large sagging before breakage. The cause of the problems inherent in the prior art beam is primarily to be found in the different strength properties in the wood material on the one hand, and in the steel material of the beam web on the other. Thus, with the above-described construction, it is impossible to avoid very severe point loadings from the steel material of the web against the wood material in the beam flanges. As a result, the wood material in the beam flanges will suffer from extreme deformations - and even breakage - before the the strength of the beam web has by any means been utilised to the full. SE 7901795-0 discloses a similar beam. According to this publication, attempts have been made to improve the inherent properties of the beam by the use of glue joints for anchoring the beam web in recesses in the beam flanges, in other words, the joint union is based on the employment of adhesion between the applied glue and adjacent wood material in the beam flanges.

The problem concerning the prior art beams resides primarily in the fact that the elasticity modulus of the steel included in the beam web is considerably greater than the elasticity modulus in the wood material used in the beam flanges, and the prior art constructions have not been designed in such a manner to take into account these different material properties. Furthermore, glued connections are generally difficult to realise int. al. because of the extreme requirements of cleanliness of the glued surfaces and the requirement of perfect fit between the glued surfaces, and, in addition, stringent requirements for complete filling-out with glue of gaps between wood and metal. Nor does the gluing by any means entail that these differences in material properties are compensated for; instead, despite the gluing, major local loading peaks occur which are disastrous for the glue joint proper and the softer material connected therewith.

PROBLEM STRUCTURE

The present invention has for its object to realise a beam of the type disclosed by way of introduction, the beam being designed in such a manner that it will possess large load carrying capacity and suffer from minor saggings before breakage. In particular, the present invention has for its object to propose a beam constructed in such a manner that the differences in material properties between the beam web and the flanges will have no negative effect. The invention further has for its object to realise a beam whose function may also be maintained without the adhesion effects which characterise glue joints, as regards the connection of the beam web to the beam flanges. Finally, the invention also has for its object to realise a beam which may be manufactured simply and economically in varying sizes and lengths. The present invention also has for its object to realise a method for the production of the beam indicated by way of introduction, the method being devised to permit the adequate taking into account of the different strength properties of the material types included in the beam. The present invention further has for its object to realise a method for producing a beam by means of which its manufacture will be simple, the resultant beam will possess good strength properties and but a slight degree of sagging before breakage, and, in addition, production of such a beam will be economical and rational.

SOLUTION

The object forming the basis of the present invention will be attained in respect of the beam proper if this is characterised in that the recesses are of a width transversely of the longitudinal direction of the flanges which is greater than the width of the rods; that the recesses have end walls which are approximately transversely directed or undercut in relation to the longitudinal direction of the flanges; and that there are provided, about the portions of the rods accommodated in the recesses, anchorage bodies produced of plastic material.

Further advantages will be achieved in respect of the beam, if this is also given one or more of the characterising features as set forth in claims 2-8.

The method according to the present invention will be attained in that the flanges and beam web are aligned in relation to one another, in that opposingly directed sides of two rods mutually meeting in each recess are brought into contact with guide edges in or at the recesses; that the flanges are tensioned towards one another so as to form, together with the beam web, a unit; that a thermosetting plastic composition is introduced into the recesses of the flanges so to form therein anchorage bodies, that the plastic composition is allowed to cure and set, whereafter the tension of the flanges towards one another is caused to cease.

Further advantages will be attained in respect of the method of producing the beam according to the present invention if the method is also given anyone or more of the characterising features as set forth in claims 10-16.

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 invention; Fig. 2 is an end elevation of the beam of Fig. 1; Fig. 3 is a detail view of one of the flanges included in the beam in 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 detail view of one of the beam flanges in one of the anchorage regions of the beam web, the 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; and Fig. 9 shows the tension distribution in the anchorage body in the embodiments according to Figs. 5 and 6.

DESCRIPTION OF PREFERRED EMBODIMENT

Referring to the Drawings, it is 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 1, 2 are manufactured of wood, while the beam web is manufactured of metal, preferably steel. In this Figure, the beam flanges are shown as being parallel and of uniform thickness, but of course the flanges may make an angle with one another so that the beam may have greater height at its one end. In such a case, the beam flanges may be of thicker cross-section at that end of the beam which is highest.

Suitably, the beam web 3 is manufactured of tube or rod material and may be bent in one piece from a longer continuous length of this material, or be composed of shorter pieces, so that there will thereby be formed, between the beam flanges 1 and 2, reciprocally extending rods 4. In that preferably the beam web 3 is produced by bending of long continuous length, closely adjacent rods 4 will have bent conjunction regions which may be V-shaped, U-shaped or be bent in any other suitable manner. As will be apparent from Fig. 1, these bent conjunction regions between closely adjacent rods 4 are interiorly accommodated in recesses in the two 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 65° 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. On the other hand, a larger angle will give poorer transfer of forces, but it should be set against this factor the very fact that the free buckling length of the rods reduces when the angle increases, for which reason, and given that the rods cannot be prefectly rigid, it is probable that the optimum will be reached with an angle which is slightly greater than 45°. Further according to the invention, neither do the rods 4 need be arranged in a regular pattern, but, for example, every other rod may be at right angles to the longitudinal direction of the beam flanges, while every second rod is obliquely inclined. As an important compromise measure, the rods 4 exposed to compressive loading when the beam is placed under load may be at a larger angle to the beam flanges 1 and 2 than those exposed to tensile stress (see further below). A further alternative may reside in the fact that the rods 4 are reciprocally bent in wave formation between the beam flanges, for example following the form of a sine curve or the like. 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. As was intimated above, the cross-section may also vary along the length of the beam. Figs. 3 and 4 show a first embodiment of the invention and, more closely, a detail view of one of the beam flanges 1 and 2 and the manner in which the rods 4 included in the beam web 3 are fixed in the flange. If it is assumed, in Figs. 3 and 4, that the illustrated beam flange is the lower beam flange 2, Fig. 3 will show a section of this beam flange 2 seen straight from above.

According to the invention, there are provided, in the beam flanges 1 and 2, recesses which are defined by end walls 6 and a bottom wall 7. In the illustrated embodiment, the recess 5 has a contour which is approximately rectangular viewed in a plane parallel to the plane of extent of the beam web 3. This entails that the two end walls 6 are approximately at right angles to the longitudinal direction of the beam flange 2 or are at least transversely directed in relation thereto. Furthermore, the bottom wall 7 in the recess is 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 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, a form-permanent anchorage body will be formed which is well connected to the rods, by surrounding them, and which has the same form as the recess 5.

On loading of a beam designed according to the present invention, and in particular according to Fig. 1 (it is here presupposed thus that the beam flanges 1 and 2 are approximately parallel and that the rods 4 have the same angle to the beam flanges), every other rod 4 will be exposed to tensile stress, while every second rod will be exposed to compressive loading. In the embodiment according to Fig. 1, these loadings will be of equal magnitude, for which reason there is formed a resultant force H (see Fig. 9) directed along the flanges. In this case, there will be no vertical resultant, since the vertical components of the rod loadings will be equal but counter-directed. On. the other hand, a torque will be exercised against the anchorage body 9, such that this will have a tendency, under the action of the loading forces of the beam, to twist about an imaginary axis 20 which is approximately at right angles to the plane of the beam web 3 and which extends somewhere through the anchorage body 9 or which, depending upon the geometric conditions which apply and the loading conditions which prevail, may even be located outside (in Figs. 4, 6 and 8 over) the anchorage body. 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 above-mentioned axis 20. As a result of the shape of the recess 5 and because the anchorage body is form permanent, such a torque cannot take effect unless either the material in the beam flange 2 or in the anchorage body 9, or possibly in both, be considerably deformed. Thus, there prevails form- permanent engagement between the anchorage body 9 and the recess 5. It should be emphasised that, to prevent the rods 4 from being detached from the beam flanges, no adhesion between the material in the anchorage body 9 and the material in the beam flanges is necessary; instead anchorage of the rods is effected in that the anchorage body is form-permanently locked in its recess by the applied loading. Naturally, a manifest adhesion may further improve the retention of the anchorage body in the beam flange under load, but this adhesion is, as mentioned, not a critical requirement.

The twist-impeding effect against the anchorage body 9 may also be described such that the horizontal composant H strives to urge the anchorge body 9 against the right-hand end surface 6, in Fig. 4, of the recess 5, so that friction there occurs between the end surface 6 and the anchorage body 9. As long as this friction is sufficiently great, no sliding can take place between these surfaces, for which reason the anchorage body 9 cannot be twisted about the axis 20.

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, material, the particle size of the filler employed and, naturally, also the type of plastic material per se and 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 (material properties) and particle structure of the filler.

One method of realising a more or less 'continuous' transition, in terms of strength, between the different material properties resides in the fact that the anchorage body is given, in its central regions, an elasticity modulus which approaches that of steel, while, in its peripheral parts, which come into contact with the wood material in the beam flanges, it is given a considerably lower elasticity modulus, in that the outer regions of the anchorage body are not permitted to set and cure to such an extent as the more centrally located regions. Such a varying degree of of setting and curing in the anchorage body may simply be realised according to the present invention by varying the moisture content of the wood material which is used in the beam flanges. Other chemical influences which reduce the degree of setting and curing in the plastic material may be employed, for example by coating the wood material with a suitable agent. On influence by the moisture content in the wood, this takes effect such that the higher the moisture content, the lower will be the degree of setting and curing for the plastic material, and consequently also the elasticity modulus. A further method for locally varying the elasticity modulus in the plastic composition resides in effecting modifications to the pouring and casting process proper or to the viscosity of the poured plastic composition. As a result, it will hereby be possible to achieve a certain sinkage of the filler, so that the total content, or the content of fractions of different particle sizes varies vertically in the cast anchorage body 9. In this context, it should also be emphasised that the effect of modifications in the elasticity modulus will be greatest in those parts of the anchorage bodies 9 which are of greatest length in the longitudinal direction of the beam flanges. In order, despite the use of anchorage bodies 9, to reduce the risk of point loadings on the wood material, the form and dimensions of the recesses 5 in relation to the form and dimensions of the rods 4 are of decisive importance. Hence, it is apparent from Fig. 3 that the end walls of the recesses 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 6 and the bottom wall 7, are rounded with a radius which is of approximately the same order of magnitude as the diameter of the rods 4. Furthermore, the bottom wall 7 itself may also suitably be curved with approximately the same radius as the diameter of the rods 4.

The width which the recesses 5 must have (at right angles to the plane of the Drawing in Fig. 4) is critical in at least two respects. First, the width must, by a suitable margin, exceed the diameter or transverse dimension of the rods 4 of the beam web 3. A factor of two may here be a suitable point of departure. Secondly, the total end surface 6 (see further below with reference to Figs. 6 and 8) of the recess 5 must be of such an area that the normal tension caused by the resultant H and acting via the anchorage body on the wood material will not be beyond the capacity of the wood material to absorb.

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. A further improvement of the strength properties will be achieved if there are cast, in the anchorage body 9, one or more transverse metal pins which extend into the beam flange 2 in approximately the same manner as the above-mentioned channels 10. These pins (this also applies to the channels 10) should be placed in spaced apart relationship, preferably as far as possible, from the axis 20 about which the moment of torque acts on loading of the beam. Such pins are necessary in those cases when the friction caused by the horizontal resultant between the anchorage body 9 and the pressure loaded end surface 6 of the recess is incapable of fully counteracting the moment of torque about the axis 20.

It will be apparent from Fig. 4 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 6 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 Fig. 4 that there is a space 13 between the top portion 12 of the meeting rods 4 and the bottom wall 7 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 and can be given an elasticity modulus which gradually reduces from one level in the proximity of the elasticity modulus of the steel adjacent the top portion 12, to a level which is considerably lower and which approaches the level of the wood material in the bottom wall 7.

The above-considered beam is suitably manufactured in such a manner that the beam flanges 1 and 2 are produced possibly by finger jointing of timber, so that defects in the timber may thereby be sifted out and the quality of the flanges is guaranteed. Thereafter, the recesses 5 are milled at suitable spacing using a ball-nosed or rounded milling tool, such that both the end walls 6 and the bottom wall 7 will thereby have the requisite arching, as well as the transition regions between the end walls and the bottom wall. Furthermore, the beam web 3 is bent out from a continuous length of rod or tube material, whereafter the bending regions with the top portions 12 are passed into corresponding recesses 5 in the one beam flange. Thereafter, the other beam flange is placed on the opposing top portions of the beam web, so that these will also be accommodated in the recesses in this beam flange. In this position, the rods 4 will be guided towards the edge regions 11 and the entire unit may be held together in a simple manner in that the beam flanges 1 and 2 are drawn towards one another by means of very simple clamping tools, jigs or the like. The thus formed unit is suitably placed with the beam web vertical, whereafter the plastic composition is poured into each one of the recesses 5 in the lower beam flange. Naturally, the tightening tension of the two beam flanges towards each other is maintained throughout. Thereafter the plastic composition in the recesses of the lower beam flange is at least allowed to gel, and possibly to set at least partially, whereupon the beam is inverted and the plastic composition is also poured into the other beam flange, this being followed by at least gelling, but preferably also partial curing and setting of the plastic material, before the beam flanges 1 and 2 are released from the clamping tools employed.

In such embodiments where use is made of channels from the side edges of the beam flanges, these may, naturally, also be used for pouring of the plastic composition, in which event the openings of the recesses 5 facing the beam web 3 are suitably plugged or closed by appropriate means.

Theoretical calculations have established (relating to one embodiment which will be described below with reference to Figs. 5 and 6) the pattern of the tension distribution in the anchorage body 9 on loading of the beam. In most practical situations, forces are transferred between plastic and wood in such a manner that the adhesion between the materials is of major importance. This said, the adhesion between plastic and wood is difficult to document and quantify in terms of 'strength properties', for which reason the calculations which have been conducted are made without regard to the adhesion forces which may also occur. As a result, the strength values which have been calculated hereby are on the safe side and demonstrate unambiguously that adhesion forces are not required for the function of the beam. Hence, the load carrying capacity will be fully sufficient even without any adhesion between the anchorage bodies and adjacent wood material.

Fig. 9 shows the appearance of the tension distribution in the anchorage body 9 on loading of the beam in the embodiment according to Figs. 5 and 6. It should be observed that the loading direction for the rods 4 of the beam web is shown opposite to that which applies in the remaining Figures.

The prerequisites on which the calculations are based are: that the anchorage body 9, is influenced by normal forces from the web rods 4 and that there is no vertical loading at the interstice 21. The interstice 21, which is the point of intersection of the centre lines of the web rods 4 will, therefore, only be influenced by a horizontal force H, that the anchorage body 9, on breakage, moves as a rigid body in relation to the wood about the twist axis 20, that there occurs, in the surfaces exposed to compressive loading, a normal tension which, in the examined state, immediately prior to breakage, will assume the value of ol parallel with the fibres and o2 at right angles to the fibres, that, because of friction forces, shearing stresses (t1, t2 and t3) will occur in those surfaces which are exposed to compressive loading, and that the friction force reduces in those surfaces where the relationship between vertical and horizontal movements is less than the coefficient of friction. On the basis of the measured values of geometric quantities, the stresses and tensions in the abutment surfaces of the anchorage body 9 against the wood, may be calculated using equilibrium equations, in that the position of the twist axis 20 is first determined. Once the position of this axis has been determined, the different stresses may be calculated, and it proves that the shearing stress (t1, t2, or t3) will be dimensioned, since timber of the strength class in question here, for example T 24, will only be capable of withstanding a stress transversely of the fibres of 2 Mpa. On the other hand, the stress along the fibres may be as much as 9 Mpa. A benchmark calculation of the loads which the beam can withstand before the contemplated stresses are exceeded shows that the carrying capacity of the beam is more than sufficient under normal loadiig, even though the calculation of the carrying capacity of the beam did not include the increase which may be expected because of adhesion forces between the anchorage body and the wood material.

In those cases where all rods 4 do not make equally large angles with the flanges 1 and 2, or when the beam tapers, a vertical resultant may also occur in addition to the horizontal resultant H. Such a vertical resultant also occurs at the outermost anchorage body at the ends of the beam. However, these vertical resultants have but marginal effect on the above-obtained calculations.

DESCRIPTION OF ALTERNATIVE EMBODIMENTS

Figs. 5 and 6 show a modified embodiment of the beam according to the invention, in which it is primarily the recesses 5 in the beam flanges 1 and 2 which have been given a different form. It will thus be apparent from the Drawing that the recesses 5 are composed of two recesses, an outer recess 14 and an inner recess 15 in association therewith. These two recesses have outer end walls 16 and inner end walls 17 which are transversely directed, at right angles, or possibly slightly undercut, in relation to the longitudinal direction of the beam flange. Moreover, the recesses 5 in this embodiment have outer and inner bottom walls 18 and 19, respectively, which are, suitably, approximately parallel to the longitudinal direction of the beam flange. Also in this embodiment, the transitional regions between the different end walls and the bottom walls are gently rounded, while the inner end walls 17 are in guiding cooperation, at the edge regions 11, with the rods 4. In accordance with that described above, both the end walls 16 and 17 and the bottom walls 18 and 19 are suitably arched, so that, thereby, sharp corners and loading concentrations are avoided. Furthermore, in accordance with that described above, the width of the recesses 5 is approximately twice the diameter of the rods 4. The beam according to Figs. 5 and 6 is manufactured in the same manner as that described for the beam according to Figs. 3 and 4.

Figs. 7 and 8 illustrate a further modified embodiment of the present invention, which should primarily be seen as a modification of the embodiment according to Figs. 3 and 4. The difference in relation to this embodiment is primarily that the end walls 6 of the the recesses 5 are not approximately at right angles to or transverse of the longitudinal direction of the beam flanges, but are obliquely directed in such a manner that the recess is, at its opening, shorter in the longitudinal direction of the flange than is the case for portions of the recess located further in. As a result, the recess will be undercut, which may also be said of the end walls 6.

A lightly modified embodiment of the variation according to Figs. 7 and 8 may readily be manufactured if the beam flanges 1 and 2 are held stationary during the milling operation which produces the recesses 5. In this instance, the milling tool is in the form of a uniform end mill with a rounded or ball nose tip which is mounted on a relatively long spindle capable of executing a pendulum motion in the longitudinal direction of the beam flange, whereby the bottom of the recess will have a certain curvature with a radius of curvature coinciding with the length of the spindle (including the end mill).The recesses will thus be deeper in the central region than in the proximity of the end walls 6.

In the embodiment illustrated in Figs. 7 and 8, it is of particular importance that the transitional region between the end walls 6 and the bottom wall 7 is gently rounded. That mentioned above concerning the alignment of the end walls 6 with reference to Figs. 7 and 8 may naturally also be applied to the embodiment according to Figs. 5 and 6, to the effect that both the outer end walls 16 and the inner end walls 17 may be obliquely inclined in the same manner as the end walls according to Fig. 8. In the embodiment according to Figs. 5 and 6, it is also possible to elect to make only either one of the outer or inner end walls obliquely inclined in the manner apparent from Fig. 8.

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. Transverse metal pins of the type touched upon in conjunction with the embodiment according to Figs. 3 and 4 may also be employed in the remaining embodiments.

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 degree in the plastic materialand 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. By such modifications in the elasticity modulus, any local stress peaks which initiate breakage can be avoided or reduced.

Finally, the elasticity modulus may also be varied locally in addition to using the above-discussed methods by using two different composite plastic compositions (same basic plastic but with different filler properties) in one and the same anchorage body. The invention should not be considered as restricted to that described above and shown on the Drawings, modifications being conceivable within the spirit and scope of the appended Claims.

Claims

1. A beam with flanges (1, 2) manufactured of wood, and a beam web (3) connected to the flanges and essentially comprising rods (4) manufactured of metallic tube or rod material, the rods extending reciprocally between the flanges and being, with end portions or bent portions (12), accommodated in recesses (5) in the flanges, characterised in that the recesses (5) are of a width transversely of the longitudinal direction of the flanges (1, 2) which is greater than the width of the rods (4), that the recesses have end walls (6, 16, 17) which are approximately transversely directed or undercut in relation to the longitudinal direction of the flanges; and that anchorage bodies (9) produced of plastic material are disposed about the portions of the rods accommodated in the recesses.

2. The beam as claimed in claim 1, characterised in that the transitional regions between end walls (6, 16, 17) and bottom walls (7, 18, 19) in the recesses (5) are rounded.

3. The beam as claimed in claim 1 or 2, characterised in that the plastic material in the anchorage bodies (9), or at least in their superficially located portions has substantially the same elasticity modulus as the wood material in the flanges (1, 2).

4. The beam as claimed in claim 3, characterised in that the plastic material has, in inner portions of the anchorage bodies (9), greater elasticity modulus than in superficially disposed portions thereof.

5. The beam as claimed in anyone of claims 1 to 4, and in which two rods (4) extend approximately V- or U-shaped into a recess (5), characterised in that the rods (4) are, on their sides facing away from one another, in abutment with the end edges (11) of the end walls (6, 17) which are turned to face the opening of the recess (5).

6. The beam as claimed in anyone of claims 1 to 5, characterised in that the portions of the rods (4) located in the recesses (5) are spaced from the bottom walls (7, 19) of the recesses.

7. The beam as claimed in anyone of claims 1 to 6, characterised in that the recesses (5) are, parallel to a plane through the plane of extent of the beam web (3), of an approximately rectangular contour, in which one longitudinal side of the contour is formed by a bottom surface (7) in the recess.

8. The beam as claimed in anyone of claims 1 to 6, characterised in that the recesses (5) are, parallel to a plane through the plane of extent of the beam web (3), of a contour which is composed of an inner, approximately rectangular portion (15) and an outer, approximately rectangular portion (14) in association therewith and being of greater length in the longitudinal direction of the beam than the inner portion.

9. A method of producing a beam with flanges (1, 2) manufactured of wood, and a beam web (3) of metallic tube or rod material, the flanges being provided with recesses (5) and the beam web being formed to have rods (4) reciprocally extending between the flanges, the rods extending into the recesses and being fixedly secured therein, characterised in that the flanges (1, 2) and the beam web (3) are aligned in relation to one another in that opposingly facing sides of two rods (4) mutually meeting in each recess (5) are brought into contact with guide edges (11) in or at the recesses (5); that the flanges (1, 2) are tensioned towards one another so as to form a unit together with the beam web (3); that a thermosetting plastic composition is introduced in the recesses of the flanges in order to form therein anchorage bodies (9); and that the plastic composition is allowed to set and cure whereafter the tension of the flanges towards one another is caused to cease.

10. The method as claimed in claim 9, characterised in that the plastic composition is first introduced into the recesses (5) of the one flange (1) and is allowed to at least partially cure and set therein, and then into the recesses (5) of the other flange, the tensioning of the flanges (1, 2) towards one another being maintained until the plastic composition in the recesses of the second flange has at least partially cured and set.

11. The method as claimed in claim 9 or 10, characterised in that the unit is turned with that flange downwards into whose recesses (5) the plastic composition is to be introduced.

12. The method as claimed in anyone of claims 9-11, characterised in that the plastic composition is introduced into the recesses (5) via the openings thereof facing the beam web (3).

13. The method as claimed in anyone of claims 9-11, characterised in that the plastic composition is introduced into the recesses (5) via channels (10) which have been provided in the flanges (1, 2) and which have been transversely directed in relation to a plane of extent of the beam web (3).

14. The method as claimed in anyone of claims 9-13, characterised in that the elasticity modulus, at least in an outer portion of the anchorage bodies (9) is given a value which roughly agrees with the elasticity modulus in the wood material of the flanges (1, 2) in that the moisture content therein is adapted to influence the degree of curing and setting in the plastic composition.

15. The method as claimed in anyone of claims 9-13, characterised in that the elasticity modulus is caused to vary locally in the anchorage body (9) in that a part of the filler material is allowed to sink before the plastic composition has cured and set.

16. The method as claimed in anyone of claims 9-15, characterised in that use is made, as guide edges (11), of end edges of end surfaces (6, 17), the end edges facing the beam web (3)and the end surfaces defining the recesses (5) or parts (15) thereof.