GB2038393A

GB2038393A - Wooden Lattice Beam

Info

Publication number: GB2038393A
Application number: GB7850363A
Authority: GB
Original assignee: BAVEG
Current assignee: BAVEG
Priority date: 1978-12-29
Filing date: 1978-12-29
Publication date: 1980-07-23
Also published as: GB2038393B

Abstract

A wooden lattice beam has joints between angled struts 4' and 5 and the top chord 1 and the bottom chord 2 characterised by the strut ends and the chord in the region of its connection with the struts being interconnected with each other by means of wedge-shaped teeth 9 of like pitch and like profile and/or one or more plates 11. The teeth 9 are preferably between 7.5 and 20 mm long, and the joint formed in this case is then glued. The wedge teeth, formed on the chords may extend right along the chords. The plate or plates 11 may be glued and/or nailed in position, and may pass through or between tenons extending from the strut ends when teeth are not employed. The plates may be webs of preformed sections. <IMAGE>

Description

SPECIFICATION Wooden Support The invention relates to a wooden support having integral, transverse top and bottom chords and at least one assembly of successive struts extending therebetween to form a double-Tsupport, with the assembly of successive struts being composed of individual struts that extend at an angle relative to one another, the end faces of two struts which respectively meet at a junction being securely connected to an inside surface of the top chord, or, respectively, the bottom chord.

Wooden supports of the type mentioned have become known, in which the chords were, for connection of the struts to the chords, relatively greatly weakened by grooves. It was necessary for compensating this weakening to design the chords to have particularly thick walls, which led, however, to supports which were heavy and costly.

It is the object of the invention to provide a wooden support of the type mentioned at the outset, in which the chords are subjected to a comparatively much lower weakening for connection of the struts than has so far been considered necessary for supporting a certain load.

According to the invention, this object is accomplished in that the strut and the chord in the region of its strut connection surface engage into one another with wedge-shaped teeth of like pitch and like profile and are glued together.

Wedge-type tooth connections have been known for a long time, in which two boards or planks or beams inter-engage at their ends with wedge-shaped teeth of like pitch and like profile and are glued together.

A comparable problem concerning weakening as with the chords of wooden supports does not exist in the known wedge-type tooth connections between two wooden parts to be glued together.

This problem, however, is of particular significance in the evaluation of a wooden support having high supporting capacity and minimum chord cross-sections. It was the more surprising that this problem which had not been solved for a long time can be solved in a particularly simple manner by using the wedgetype tooth connections which also have been known for a long time. Hence, it is inventor's particular merit to have recognized in the present case that the use of the known wedge-type tooth connection first makes it possible to connect two angularly contacting strut ends to the inner side of a chord at comparatively low weakening of the chords.

The lengths of the teeth may be between about 7.5 mm and 30 mm, preferably between 7.5 mm and 20 mm. The shorter the tooth length, the greater the number of teeth across the width of the struts. The number of teeth also depends on the side angle that is chosen. Selection of the number of teeth and of the side angle of the teeth depends on the required strength of connection of the struts to the chords. The chords are weakened the less, the shorter the tooth length and the smaller the number of teeth. On the other hand, the strength of connection increases with increasing glueing surface between the strut teeth and the chord teeth. Hence, minor chord weakening require, for a sufficiently strong strut connection, many relatively short teeth and, thus, relatively wide struts.Major chord weakening when the teeth are longer allow for a smaller number of teeth and, thus, relatively more narrow struts. It will be understood that in this connection optimum conditions can be determined for the respective support on the basis of design and expenses, all of which have in common a relatively low weakening at comparable loads over against prior art.

The chords may be of the same width as the struts, preferably the chords are wider than the struts, so that the chords have non-weakened chord sections in the longitudinal support direction on both sides of their center connection surfaces.

The wedge-type teeth, or, respectively, the wedge-type grooves of the chords may be limited to the respective connection surfaces for the struts, but they may also extend over the entire length of the chords. In this manner, the points of connection of the struts to the chords can be freely selected. This means that chords having wedge-type teeth or, respectively, wedge-type grooves on their surfaces facing the struts, which teeth or grooves extend over their entire length, may be used for wooden supports having different spacings between the strut connection surfaces.

The strength of connection already achieved of the struts connected by wedge-type teeth with the chords can still be substantially increased according to the invention, at comparatively little further weakening of the chords, by using at least one plate-configured connecting member made of sheet metal, plastic, wooden material or plywood.

In this case, the plate-shaped connection member in part engages like an auxiliary tenon into a chord slot parallel to the chord teeth, and in part into two strut slots which are in alignment and are parallel to the strut teeth. The strut slots as well as also the chord slot are substantially deeper than the length of the teeth. It also is of particular advantage when the connecting member in the slots extends in vertical direction substantially beyond the tooth length on both sides of the connection surface. Finally, it may be essential that the longitudinal extent of the connection member be substantially greater than the connection surface of a chord.

The plate-shaped connection member located in the slots is glued and/or nailed to the chord and in the associated strut. It is of particular advantage in that regard that the slot in the chord and the slots in the two associated strut ends be relatively narrow, thus only slightly weakening above all the support, but also the strut ends, while the composite construction completely within the range of a juncture can be substantially increased on account of the comparatively large surface area of the connection member. Metal sheets, in particular, may be thin and, accordingly, the thicknesses also of the slots, into which a metal sheet is to be inserted, are low.

The combination according to the invention of the wedge-type tooth connection between the struts and the chords with a connection surface each of at least one plate-shaped connecting member may be of particular advantage because a strut connection to the chords selected to be relatively weak with a view to minimum chord weakening leads already by one plate-shaped connecting member per juncture to a substantial improvement in the strength of connection in that connection: the belt weakenings caused by the slots for the plate-shaped connecting members are in no proportion to the increase in connection strengths achieved by the plate-shaped connecting members.Therefore, a tooth connection of the strut ends to the chords with relatively short tooth lengths selected with a view to as low as possible a weakening of the chords can be substantially improved already by inserting one plate-shaped metal sheet, without having to put up with any substantial additional weakening of the chords.

The problem mentioned above is also solved according to the invention in a wooden support of the type mentioned at the outset in that for connection oftwo strut ends to the top chord, or, respectively, to the bottom chord at least one plate-shaped connecting member of sheet metal, plastic, wooden material or plywood is provided, which engages part into a chord slot extending in longitudinal support direction, and in part into two strut slots in the strut ends, which slots are in alignment with one another and extend in longitudinal support direction, with the connecting member being glued and/or nailed, on the one hand, to the strut ends and, on the other hand, to the chord.

It was found according to the invention that the connection of two struts to a chord can also already be achieved by at least one flat, plateshaped connecting element alone, without any additional tooth-connection being required.

On the other hand, it may be of advantage if, in addition to at least one connection plate, the strut ends and the chord engage into one another in the region of the strut connection surface by parallel tenons of like pitch and like profile and are glued together, with the depth of the strut slots as well as also the depth of the chord slots substantially exceeding the tenon length.

The parallel tenons differ from the above mentioned wedge-type teeth in that the tenons are defined by parallel sides and engage into grooves having corresponding parallel walls, while the wedge-type teeth and the associated wedge-type grooves are of conical, more or less tapering cross-section.

The connection of the struts to the chords by the parallel tenons results in a relatively extensive weakening of the chords because the strut tenons extend relatively deeply into the chord and frequently beyond the substantial depth of said chord. This connection by a relatively deeply extending tenon contrasts with the fact that frequently only two relatively narrow tenons are present at a juncture, as opposed to the above described connections of the struts with the chords by a plurality of teeth.

In order to maintain weakening of the belts as low as possible in this case also, the tenon thicknesses are maintained as low as possible.

The loss of strength of connection of the struts to the chords suffered in this respect can be balanced out already by one plate-shaped connecting member. In that connection, the effect of a plate-shaped connecting member is particularly advantageous in this case also if its extent in longitudinal direction is substantially greater than the extent in longitudinal direction of the connection surface to a chord, and in this case also the particular advantage is attained-that the narrow slots in the chords for engagement of the plate-shaped connection members only constitute a comparatively very low chord weakening.

Hence, it will be understood that the combination of at least one plate-shaped connecting member with a parallel tenon connection of two struts to a chord can be of particular advantage.

In this respect, the slots for engagement by the plate-shaped connecting members in the strut ends may be located outside of the strut tenons and/or within the strut tenons and/or at least in part outside the strut tenons. Correspondingly, the slots for engagement by the plate-shaped connecting members in the chords may be located within the chord tenons and/or outside of the chord tenons and/or at least in part outside of the chord tenons.

If at least two plate-shaped connecting members of sheet metal or plastic are used per connecting point, it may be of advantage to connect these members with one another by a transverse web, which comes to lie on the outer chord side. This of course also applies for the plate-shaped connecting members in conjunction with a wedge-type tooth connection, or alone.

The invention is also based on a process for producing wooden supports according to the invention, in which the struts are connected to the chords by wedge-type teeth or by parallel tenons, .with at least one plate-shaped connecting member being additionally inserted. The process consists in that, after the grooves have been produced in the chords and in the blanks of two struts each contacting at a juncture under a selected angle, along with production of the wedge-type or parallel teeth of the struts which enter into engagement in the grooves as well as production of the slots in the chords and struts for engagement by plate-shaped connecting members, glueing of at least one juncture occurs under a pressure applied from outside onto the juncture, and in that this external pressure is maintained until the connecting member or members have been nailed to the chord and the two struts by a minimum number of nails which fully receive the internal juncture stresses caused by the outer pressure, in which respect the inner juncture stress is substantially received by the glue, or, respectively, the glued surfaces after the glue has completely set.

The process is of particular advantage in a wedge-type tooth connection of the struts to the chords because it is particularly in this case that considerable pressures influence the junctures of a support structure, which pressures according to the invention need not be maintained until the glue has fully set but, rather, only until the respective, plate-shaped connecting members have been connected by nails.

The invention will be described below without limitation reverting to the embodiments shown in the drawings, which in no way limit the invention.

The drawings show in Fig. 1 and 1 a two embodiments respectively in vertical section in longitudinal support direction; Fig. 2 and 2a cross-sections perpendicularly to the longitudinal support direction through two embodiments; Fig. 3 and 3a two different chord sections in perspective view; Fig. 4 a vertical section in longitudinal support direction through a further embodiment; Fig. 5 and 6 a horizontal section and a crosssection according to figure 4 and Fig. 7-13 cross-sections transversely to the longitudinal support direction through further embodiments.

Figure 1 shows a wooden support according to the invention shown with broken-away top and bottom chords 1 and 2 as well as two struts 4 and 5 located adjacent the top chord under an angle and two struts 5 and 4' adjacent the bottom chord. The strut ends are provided with relatively short wedge-type teeth 9 that engage into corresponding wedge-type grooves 10 in the chords. As has been described above, the number of wedge-type teeth may be lower, but may also be greater than the number shown. According to figure 1 a, a relatively thin plate-configured connecting element 11 is provided at each juncture in the center in longitudinal support direction, which element like an auxiliary tenon engages into a corresponding narrow slot 1 3 in the top or, respectively, bottom chord and into corresponding narrow slots 14 and 1 5 in the strut ends.It will be understood that two or more parallel connecting elements may be provided instead of one connecting element, which connecting elements substantially or completely penetrate the chords and may additionally be united in U- or T-shaped manner outside of the chords by means of transverse ledges.

The plate-shaped connecting elements 11 are nailed and/or glued to chords and to the struts.

Instead of only one plate-shaped connecting element 11, there may also be two or more connecting elements extending parallel to one another. The connecting elements may consist of sheet metal, plastic, wooden material or plywood.

The selection of the material also depends upon the manner in which and the means by which the connecting element is securely connected to the chord and to the struts. Thin plywood plates are particularly advantageous for glueing, but they do not exhibit the strength of metal sheets, which on their part can well be connected by means of nails. However, no problems that cannot be solved are encountered either in glueing metal sheets or plastic plates to wood. The struts 4, 5 or 5, 4' are supported on a chord substantially only at the end faces of their wedge-shaped teeth 9. In this way, the wedge-type teeth of the struts have a maximum length of engagement into the associated wedge-type grooves of chords 1 and 2.

Figure 2 shows a cross-section taken along lines Il-Il of Figure 1 a. It can clearly be recognizedttherefrom that the slot 13 for engagement of the plate-shaped connecting element 11 completely penetrates the chord 1.

Hence, the connecting element 11 can also be inserted into the belt from the top. Figure 2a shows a similar cross-section through a juncture, in which the slot 1 3 merely does not completely penetrate the chord, so that the connecting element 11 can only be inserted into the chord from below.

Figure 3 shows a perspective view of a chord section according to the invention, in which the wedge-shaped grooves 10 extend over the entire chord length, so that the points of connection of the struts to the chord may in advantageous manner be freely selected. Figure 3a is a perspective view of a further chord section according to the invention, in which the wedgeshaped grooves are present only in the regions of connection of the struts.

Figures 4, 5 and 6 show in embodiments the strut connection to a chord by means of two parallel tenons 9', which engage into corresponding parallel grooves 10' in chord 1. A continuous slot 13 is additionally provided in the chord 1, and slots 14 and 1 5 are provided in the strut ends, which slots are outside of the tenons.

A plate-shaped connection element 11 engages into the slots. It will be understood that the invention is not to be limited to the design with two tenons.

Figure 7 shows a cross-section of an embodiment, in which there are two additional connecting elements 11, 11 in addition to the plate-shaped connecting element 11 for further strengthening-the connection, which connecting element engages into the chord and the struts outside of the tenons. Figure 1 3, finally, shows a strut connection according to the invention, in which two strut ends are fastened to the chord without connection by a tenon or connection by teeth, and in which the connection preferably occurs by a plurality of parallel, plate-shaped connecting elements 11 alone in longitudinal support direction, which elements engage into slots in the chord and in the two struts. It will be understood that more than two connecting elements according to Figures 10 or 11 may be connected with one another.Individual connecting elements, preferably of sheet metal or plastic, may also be angled in L-shaped manner outside of the chord slot in order to increase the strength of connection of a connecting element in the chord, as correspondingly is the case in the embodiments according Figures 10 or 11. It will be understood that these additional means for increasing the strength of connection may correspondingly be used with the most varying embodiments.It will furthermore be understood that the plate-shaped connecting elements may also be glued and/or nailed to the chords and the struts with or without a connection of the struts by tenons, and that the selection of the means for connection is in this case also dependent on the respective conditions; in this respect-as in the embodiments described at the outset-the objective pursued primarily is to as far as possible increase the supporting capacity of a chord at like cross-section of the chord in order to obtain lighter-weight and, consequently, less expensive wooden supports, in which the precious material wood is far better utilized than is the case still with the known comparable wooden supports. It is to be understood, moreover, that the embodiments can be combined in a variety of ways, and that these provide the skilled worker with suggestions as to t4 design which are based on the inventive iaea and are within the scope of the invention. For example, two parallel assemblies of successive struts may also extend between the chords instead of one assembly of successive struts. In that connection, one or more connecting elements in the struts of one assembly of successive struts may also be connected in Tor U-shaped manner with one or more connecting elements of an adjacent assembly of successive struts outside of the chords.

Claims

1. A wooden support having integral, transverse top chords and bottom chords and at least one assembly of successive struts extending therebetween in order to form a double-Tsupport, with the assembly of successive struts being composed of individual struts extending at an angle relative to one another, of which the end surfaces of two struts which respectively meet at a juncture are securely connected to an inside surface of the top chord or, respectively, bottom chord, characterized in that the strut ends and the chord in the region of its connection surface with the struts engage into one another with wedgeshaped teeth of like pitch and like profile and are glued together.

2. A wooden support according to claim 1, characterized in that the relation 7.5 mm s1 < 30 mm substantially applies for the tooth length 1.

3. A wooden support according to claim 1 or 2, characterized in that the chords have nonweakened sections on both of their connection surfaces.

4. A wooden support according to one of the claims 1-3, characterized in that, for strengthening the connection of one or two strut ends to the top, or, respectively, bottom chord, at least one plate-shaped connecting member of sheet metal, plastic, wooden material or plywood is provided, which in part engages into a chord slot parallel to the chord teeth and in part engages into two strut slots in the ends of the struts, the slots being in alignment with one another and being parallel to the strut teeth, with the depth of the strut slots as well as also the depth of the chord slots substantially extending beyond the tooth length, and with the connecting member being glued and/or nailed, on the one hand, with the strut ends and, on the other hand, with the chord.

5. A wooden support according to claim 4, characterized in that the longitudinal extent of the plate-shaped connecting member is substantially greater than the longitudinal extent of the connecting surface to a chord.

6. A wooden support according to one of claims 1-3, characterized in that the wedgeshaped teeth or, respectively, wedge-shaped grooves of the chords extend over the entire length of the chords.

7. A wooden support having integral, transverse top and bottom chords and at least one assembly of successive struts extending therebetween and respectively consisting of individual struts extending at an angle relative to one another to form a double-T-support, of which the end surfaces of two struts respectively meeting at a juncture are securely connected to an inside surface of the top, or, respectively, bottom chord, characterized in that, for connection of two strut ends to the top or, respectively, bottom chord, at least one plateconfigured connecting member of sheet metal, plastic, wooden material or plywood is provided, which in part engages in a chord slot extending in longitudinal support direction and in part engages in two strut slots in the end of the struts, which slots are in alignment with one another and extend in longitudinal support direction, with the connecting member being glued and/or nailed, on the one hand, with the strut ends and, on the other hand, with the chord.

8. A wooden support according to claim 1, characterized in that, in addition to the plateshaped connecting member, the strut ends and the chord in the region of its strut connection surface interengage with parallel tenons of like pitch and like profile and are glued together, with the depth of the strut slots as well as also the depth of the chord slot substantially exceeding the tenon length.

9. A wooden support according to claim 8, characterized in that the longitudinal extent of the plate-shaped connecting member is substantially greater than the longitudinal extent of the connecting surface to a chord.

10. A wooden support according to claim 7, 8 or 9, characterized in that for engagement of one or more plate-shaped connecting members one or more pairs of slots that are parallel to the tenons extend in the strut ends outside the strut tenons and in the chord within a chord tenon and/or in the strut ends within the strut tenons and in the chord outside of one or more chord tenons and/or in the strut ends at least partially outside of the strut tenons and in the chord at least partially outside of one or more chord tenons.

1 A wooden support according to one of claims 4--10, characterized in that at least two plate-shaped connecting members of metal or plastic are connected with one another in the form of a yoke outside of the chord.

12. Process of producing a wooden support according to one of claims 2-11, characterized in that, after the grooves have been produced in the chords and the blanks of two struts each contacting at a juncture under a selected angle, and after production of the wedge-shaped or parallel teeth of the struts which engage into the grooves as well as after production of the slots in the chords and struts for engagement by plateshaped connecting members, at least one juncture is glued under a pressure applied from outside to the juncture, and in that this external pressure is maintained until the connecting member or members have been nailed with the chord and the two struts with a minimum number of nails that fully receive the internal stresses at the juncture caused by the external pressure, with the internal juncture stress being substantially received, after the glue has completely set, by the glue or, respectively, by the glued surfaces.

13. A wooden support substantially as described with reference to Figures 1 to 3, or Figures 1 a to 3a, or Figures 4 to 6, or any of Figures 7 to 13, of the accompanying drawings.