GIRDER OF LATTICE TYPE

Abstract: Girder of lattice type having an upper and a lower chord (11, 12, 112, 113) and inclined struts (13, 114) therebetween, which are connected to the chords by joints. According to the invention the struts enter recesses in the chords and are fastened in the recesses by a hardening and binding medium as polyurethane, epoxy glue or similar.

Description: GIRDER OF LATTICE TYPE • | The present invention relates to a girder of lattice type, comprising an upper and a lower chord and between the chords inclined struts fastened to the chords in a zig zag pattern. The chords are : often made of wood and the struts of metal and the invention aims specifically to problems that arise in connection with this type of girder. In earlier girders of this type the struts are attached to the chords by clamping means or by other fastening means which are adapted to enter into the ood material as screws or nails. These fastening means have certain disadvantages, one of them being that the joint between the straits and chords of wood becomes weakened when the wood dries and shrinks-. In -case of varying loads there is furthermore the risk that a play arises in the joints. These disadvantages are serious in that the strength of the girder may become substantially lower than calculated, the result being unex¬ pected failures. The invention aims at a solution of these problems in that the struts enter into recesses in the chords and are faste— ned in these recesses by a hardening and adhering material which fills out the space around the struts within the re¬ cesses. By this is firstly achieved that the weakening of the chords by the recesses for connecting the struts is compensated by the filling material. Secondly is achieved a fixing of the joint between the struts and the chords, so that the . . i strength- of the joint is not lessened in course of time by drying of the wood and no play is allowed to be initiated because the joint is subjected only to resilient deforma- tions. As joining material can be used a hardening material which also. should adhefe both to the wood in the chords and the metal in the struts. The strength of the material itself and of the joints therebetween and the components must of course be sufficient for resisting occurring forces. This- eans that in general the joining material must have the same c pressive and tensile strength as the material in the chor and in the struts. As suitable adhering materials can be mentioned polyurethane plastic and epoxy glue. Closer details of the invention appear from the following specification with appended drawings showing: Fig. 1 , a side view of a girder according to the inventio Fig. 2, a perspective view of a separate chord according the invention. Fig. 3 » a detail in perspective of a joint for the struts Fig. h , the same detail as in Fig. 3 but with joining mat rial in the joint. Fig. 5 > a side view of the joint. Fig. 6, a second embodiment of the joint. Fig. 7 » a side view of a girder with joints according to third embodiment of the invention. Fig. 8, a section on a larger scale on the line 8 - 8 in Fig. 7 showing the chord without the struts. Fig. 9 > a section on the line 9 - 9 in Fig. 8. Fig. 10, the same section as in Fig. 8 showing both the chord and the struts. Fig. 11, a section on the line 11 - 11 in Fig. 10. In Fig. 1 is shown a side view of a girder 10 according t the invention comprising chords or flanges 11 and 12 of wood and a web in the form of inclined struts 13 of metal suitably steel. The struts can be tubular or solid and they can form a continuous zig zag shaped bar as shown in Fig. 1. Possible joints in this bar are placed at the places where the web is countersunk into the chords. lig. 2 shows a separate chord 12 with recesses 15 for the struts 13. Fig. 3 shows in perspective a detail of how th bent portion 16 between two struts in a continuous zig za bar 13 is inserted in a recess 15. Fig. shows the same view as Fig. 3 but with the joint filled with binding mat O IP rial 1 7 . Fig. 5 shows in a side view how the curved intermediate portion 16 between two struts in a continuous zigzag bar is placed at a certain depth below the upper surface of the upper chord 12, so that the binding material 17 covers the portion 16 which firstly improves the strength and secondly improves the heat insulation between the struts and the upper side of the girder. The said is of course also valid for the joints in the lower chord 11 in relation to the lower side thereof. Fig. 6 shows another embodiment 20 of the recesses 15 where the top 21 of the recess lies below the upper surface of the chord 12. The recess 20 can suitably be machined with a shank-end mill,- which ca have a. plane end or a_ rounded end depending on what shape the bottom of the recess 20 is supposed to have. The shape can suitably be the same as the shape of the strut, for instance a rounded bottom for a strut having a round section. Also the recess 1 can be made with a shaik-end mill but can alternatively be made with a straight saw. Figs. 7 to 11 show a further embodiment of the invention. The view in Fig. 7 is similar to the one in Fig. 1 but the sections in Figs. 8 to 11 are different. The reference num¬ bers are also different. The girder 110 comprises a zigzag bent bar 11 forming inclined struts 114 between two chords, one upper chord 112 and one lower chord 113. The bar 111 is bent in zigzag form from a bar, a strip or similar and com¬ prises straight portions 114, which form struts in the gir¬ der, and bent portions 115 which enter into recesses 116 in the chords. Fig. 8 shows the upper chord 112 i cross section on the line 8 - 8 in Fig. 7 with the bar 111 removed, and Fig. 9 shows . the same portion in longitudinal section on the line 9 - 9 in Fig. 8. In Figs. 8 and the bar 111 has been removed in order to illustrate the recess 116 more clearly. The web or strut bar 111 is attached to the chords 112 and 113 by inserting the curved portions 115 into the recesses 116 and filling the space between the bar 111 and the' re¬ cess 116 with a binding substance 117. The joint is illust rated in Figs. 10 and 11 where the recess 116 is shown fil with the fastening substance which surrounds the curved po tion and fills the recess 116 up to level with the inside 118 of the chord 112, and correspondingly for the lower chord 113. The fastening material is also in this case a suitable hardening and binding substance, for instance po-JL urethane plastic (resin) or epoxy glue. In.the embodiment in Figs. 7 to 11 the recesses 116 are op only towards the inside of the chords and form a slit in the inside surface. The advantages from this are that as little as possible is removed from the wood in the chords, the pocket formed by the recess gives a firm fastening of- the glue joint and said pocket also forms a seat for the portion 115 which facilitates the assembling of the com¬ ponents before applying the glue 117. O P Λ, WIP

Claims: Claims 1. Girder of lattice type comprising an upper and a lower chord and- between them inclined struts, characterized in that the struts (I3 » 1l4) are countersunk into recesses (1-5,20,116) in the chords (11,12,112,113) and are fastened therein by a hardening and binding substance (17,117). 2. Girder as defined in claim 1 , characterized in that the struts are formed by a continuous bar, plate or similar (13 » 111) bent to zigzag orm- with straight portions (13 » 114) forming the struts and bent portions (16,115) therebetween, the bent portions being countersunk into the recesses (15, 116) in the chords. 3. Girder as defined in any of the preceding claims, charac¬ terized in that the recesses (1 * 5,116) in the chords (11,12, 112,113) are open only on the inside of the chords. 4. Girder as defined in any of the preceding claims, charac¬ terized in that the hardening and binding substance is poly- urethane (17,117). 5. Girder as defined in any of the preceding claims, charac¬ terized in that the chords (11 ,12,112,113) are of wood and the struts (13,111 ,114) of metal.

Inventors: ERICSSON A
Applicants: ERICSSON A, FRELENA AB
Application year: 1979
Main classification: E04C3
IPC codes: E04C3