EP0086993A1 - Truss girder - Google Patents

Abstract

1. A lattice girder having at least one upper boom (O) and at least one lower boom (U) connected to one another by individual struts (1) in a zig-zag or sawtooth arrangement, the end of one strut (1) being provided at a respective junction point with an extension (12) welded to the boom (O, or U, respectively) and following the axis of gravity (S) of said boom, while the end of the other strut (1) is received in abutment in the bend between said one strut and its extension (12), so that at each junction point (K) the axes of gravity (S) of the two joined struts and of the respective boom (O, or U, respectively) pass through a common point of intersection, said struts (1) being open-profiled rods the ends of which adjacent said junctions being deformed to a flat web section linearly extending said axes of gravity (S) of said struts, characterized in that in cross-section said struts (1) comprise an S- or Z-shaped open profile with its minimum axis (X) directed perpendicular to the main plane (T) of said girder and its axis of gravity (S) at the center of the profile height (h) as viewed perpendicular to said minimum axis (X), and in that the transition from this cross-section to said web section occurs gradually.

Description

The invention relates to a welded truss of the type mentioned.

In a known truss girder of this type (DE-OS 29 47 748), the strut bars have an open profile with a V-shaped cross section. The strut ends are deformed over a predetermined longitudinal section to form the flat strip cross section, which is perpendicular to the main beam plane and is used to form a welded node. At the node there is a common intersection between the lines of gravity of the two struts that meet and the respective belt. So that the strut ends deformed into a flat strip cross section extend exactly the center of gravity of the undeformed, open strut profile, it is necessary to flatten the cross-sectional profile of the struts and also to bend them until the center of gravity in the flattened extension area is flush with the center of gravity of the rest of the profile profile. The deformation of the strut ends is expensive and complex and must be carried out with great precision and using special tools. In practice, it has even proven to be more expedient to start from a flat strip material and to deform or emboss this strip material between the flat strut ends into the open strut profile. However, special tools are also required for this, so that the individual struts cannot be endlessly pre-produced. Another serious disadvantage of this known truss girder lies in the relatively low resistance to buckling or twisting of these individual struts, since the transition area lying outside the straps from the flat strip cross-section to the profile cross-section is unable to absorb high loads. In addition, an open V-profile has a pressure point outside the center of gravity, around which it is twisted or bent under higher loads. These last-mentioned disadvantages cannot be avoided simply by using thick-walled profile bars or increasing the profile cross section, since the weight plays a dominant role in relation to the load-bearing capacity in such lightweight trusses.

Furthermore, a proposal for the formation of a truss girder is known (FR-PS 900 974), in which the struts of the strut structure are formed from profiles with a tubular cross-section, the struts being flattened at their ends as an extension of the center line of the strut profile. Apart from the fact that this lattice girder does not meet modern requirements, since no common intersection points of all clashing lines of gravity are possible in the nodes, these struts have the disadvantage that they bend slightly in the exposed transition area from the full profile cross section to the flattened end cross section. Such closed profiles for struts of a truss are also not compatible with the requirements of lightweight construction, since they drive the weight of the truss too high in relation to the load-bearing capacity.

The invention has for its object to provide a welded truss girder of the type mentioned To create, which is characterized by particularly buckling and twist-resistant struts in the strut, the struts should be particularly easy and inexpensive to manufacture and process.

The object is achieved according to the invention by the features specified in the characterizing part of the main claim. Such a profile of the struts is characterized in that the pressure point lies in the center of gravity, that is to say that the kink or twist resistance of the strut is significantly higher than in the case of other, open profiles. In addition, both the center of gravity and the pressure point remain unchanged regardless of the symmetrical deformation of the erofil cross section to the flat or flat band cross section, so that it is not difficult to find the center of gravity and the line on which the pressure point lies, right up to the point of intersection with the Continuing the center of gravity of the belt or the other strut. Another particularly important aspect is the simple and inexpensive manufacture of this profile. Such struts can be produced as endless rolled profiles, in which case it is sufficient to cut the individual struts, for example with a flat or impact shear, since in this cutting process the strut end is deformed down to a flat strip cross section, as required for the further processing of the struts in the truss is. The individual struts that carry the extension section need only be rolled flat over the length of the extension section and bent accordingly, which is also quick and inexpensive to carry out with a simple tool. Another advantage of this strut design is that despite a significantly increased buckling, pressure and torsion resistance of the struts a favorable support weight in relation to the load capacity. In addition to the increased structural strength and thus improved load-bearing capacity of the light-weight carrier, the salient advantages of the profile cross-section are its simple deformation. Regardless of whether a rolled continuous profile with an S- or Z-shaped cross-section is assumed, which is flattened to form the flat strip cross-section, or whether a flat strip material is assumed that is rolled into the cross-sectional shape, the transition range from. Belt cross section on the S or Z cross section a straight-line continuation of the center of gravity. No special care needs to be taken when deforming, since the profile height decrease or increase in any case runs symmetrically, i.e. in the height direction from the center of gravity.

An expedient embodiment of the subject matter of the invention is further evident from claim 2. This design measure takes into account the requirement that an expediently straight intersection edge between the two struts abutting each other is required only at the common intersection of all the heavy lines. On the other hand, this has the significant advantage that the strut profile gradually decreases in profile height up to the point of intersection of the lines of gravity, so that there is no abrupt transition between the full profile height and the flat strip cross-section, at which point there is a particular risk of kinking or an extremely critical danger point in the static connection of the girder, namely twice at each node.

Another preferred embodiment of a truss according to the invention, in which the deformation of each strut end with a gradual transition and in the profile height symmetrical to the center of gravity up to the flat band cross section is accomplished in a predetermined longitudinal section, as is known for example from FR-PS 900 974 , explains claim 3. Because the actual flat belt cross-section is only at the common intersection of the lines of gravity, the gradual transition area from the full profile cross-section with the full profile height to the flat belt cross-section is moved into the belt where the profile side edges are welded to the belt. As a result, each end area of the strut, critical of itself against kinking or twisting, in which the profile height gradually decreases, is stably supported within the belt.

The measure highlighted in claim 4 is expedient. Despite their low weight, open or closed hollow profiles have high structural strength due to the profiling. They also desirably enter into an extraordinarily stable bond with the struts. Since the strut ends have diverging profile side edges due to the gradual deformation, the inner walls of the hollow profiles of the belt have to compensate or absorb this divergence, so that these divergent profile side edges do not need to be straightened or eliminated by additional and expensive measures during the production of the struts. Most conveniently, this is done by the oblique sections of the inner walls of the hollow profiles, which compensate for this divergence.

In practice, an embodiment of a carrier has now proven to be particularly useful with regard to the relationship between the carrier weight and the load-bearing capacity, as can be inferred from claim 5. The ∑-shaped cross-section of the hollow profiles leads, in addition to the advantage of compensating for the divergence of the profile side edges of the longitudinal struts in the node, to the fact that the kinked inner wall of the hollow profile is significantly more resistant to buckling and kinking than an inner wall of comparable height with a comparable hollow profile with a flat inner wall .

A further, important idea of the invention is also evident from claim 6, according to which a general stiffening of the support can be achieved in a particularly simple and effective manner. Buckles through welded cross plates are known per se. However, the extension sections welded here between the hollow profiles of the belts each have an interplay with the profile shape of the hollow profiles of the belt, since they are welded to the center lines of the belt, with these hollow profiles the center line running at the level of the fold line of their inner walls. These kink lines in the inner wall of each hollow profile in turn stiffen the buckling and kink resistance of the hollow profiles that are used to form the belt. Particularly in the case of larger girders, where the height of the hollow profiles forming the belts is considerable, a particularly effective fastening results from the interaction of the design-fixed extension sections of the struts and the hollow profiles of the belts which are reinforced with regard to the resistance to buckling and buckling by the buckling of the inner walls.

Below, the subject of the invention is based on the Drawings explained.

• Fig. 1 übereinander angeordnete Schnitte entlang einem bestimmten Längsabschnitt einer Strebe eines Fachwerkträgers, indem das Profil der Strebe allmählich bis zu einem ebenen Bandquerschnitt abgeflacht ist,
• Fig. 2 einen Längsschnitt durch einen Knotenpunkt eines Leichtbau-Fachwerkträgers gemäß der Erfindung,
• Fig. 3 den Knotenpunkt von Fig. 2 in einer perspektivischen und schematischen Darstellung,
• Fig. 4 eine Querschnittansicht des Knotenpunktes von Fig. 2 in der Ebene IV-IV, und
• Fig. 5 einen schematischen Detailschnitt in der Ebene V-V von Fig. 2.

Show it

• 1 shows sections arranged one above the other along a certain longitudinal section of a strut of a truss, in that the profile of the strut is gradually flattened to a flat strip cross section,
• 2 shows a longitudinal section through a node of a lightweight truss according to the invention,
• 3 is a perspective and schematic representation of the node of FIG. 2,
• Fig. 4 is a cross-sectional view of the node of Fig. 2 in the plane IV-IV, and
• 5 shows a schematic detail section in the plane VV of FIG. 2.

3, a node K is shown in perspective of a lightweight truss, this node being provided here, for example, in a lower flange U of the truss. At the node K, two struts 1 of a strut work arranged in a zigzag arrangement, not shown, come together, whereby it can be seen that the strut 1 coming from the top right in FIG , which is indicated here in dashed lines, is bent and follows this line of gravity. The lower chord U is formed by two open hollow sections 11, 24 which are arranged in parallel and at a distance from one another and have a Σ-shaped cross section. The strut 1 coming from top left in FIG. 3 is butted into the bend of the other strut and welded to it. Furthermore, they are inner half of the lower flange of the profile side edges of the struts welded to the lower flange. The struts 1 have an S-shaped cross-sectional profile, which is gradually flattened in the area of extension of the struts to a flat band cross-section, with which the struts extend into the lower flange U.

Figures 1 and 2 show the profile course and the formation of the node K in detail.

1, the struts have a cross section that approximately corresponds to an open S. A middle, essentially straight web 2 merges into arc sections 3 and 4 running in opposite directions, to which end sections 5 and 6 approximately parallel to one another are connected. One longitudinal edge of the profile is designated 7, while the other is designated 8. In the lowest representation of the profile cross section in FIG. 1, the profile width of profile side edges 9 and 10 is determined and designated bA. The profile width b _A is measured in the direction of the so-called minimal axis X, which minimal axis is the axis of the minimum moment of inertia passing through the center of gravity S of the cross-sectional area or the profile. The maximum axis Y, that is the axis of the maximum moment of inertia, is perpendicular to this axis X. It also passes through the center of gravity S. In this rotationally symmetrical profile cross-sectional shape, the so-called pressure point D also coincides with the center of gravity S. The profile height h _A is measured in the direction of the maximum axis Y.

The struts 1 with the cross-sectional shape according to FIG. 1, bottom illustration, run between the straps of the carrier and form the strut mechanism. In each case in the area in which the struts 1 lead into the straps are, they are deformed in their cross-section to a flat strip cross-section (Fig. 1, representation C). This means that the profile height h _A is gradually reduced to h _C , at the same time the profile width b _{A increases} to the value b _C. The profile side edges 9, 10 inevitably diverge in the area between A and C (see also FIG. 1), and approximately with a straight course, as the line drawn between points A1 through B1 to C1 in FIG. 1 shows. In the range D, the profile height of _A h has decreased to h _B, while the _P r _ofile has increased br _{G E} b of _A to _B b. During the deformation between sections A and C, however, the profile height h has decreased symmetrically with respect to the minimum axis or center of gravity (is the same as the line of center of gravity S). In other words, despite the change in cross section from the full profile height to the profile height of the strip cross section, the center of gravity has been continued in a straight line. This desirable effect is due to the selected profile shape.

As can be seen in FIG. 2, due to the deformation of the profile of the struts 1 there is an offset between the profile side edges 9 and 10, which is of no further importance. In the area of these mutually offset side edges 9 and 10, the two struts butting against one another are welded to the belt (upper belt or lower belt), as is indicated by the weld seams 13, 14, 15 and 16. This welding is of course carried out with two hollow profiles 11, 24, on their inner walls 30. The center of gravity S of the two struts 1 meet with the center of gravity S of the lower flange at a common point. The center of gravity S. lies at a distance H from the upper side of the belt designated by 34. The strut on the left in FIG. 2 shows the ver bent at the node K in the direction of the center of gravity S of the belt Extension section 12, in which the flat band cross section is maintained. This extension section 12 is also welded to the inner walls 30 of the hollow profiles 11 and 24 and form a so-called buckle with them. For structural reasons, a corrugation of the extension section 12 is expedient, at least in the area in which the weld seams 19, 20 end with the inner walls 30. In solid lines, a corrugation 21 is indicated, which leads to a tongue 22 via a rounded transition 23 which avoids a notch effect. The corrugation 21 creates a rounded bend in the area of the transition 23 to improve the resistance to buckling or buckling in this area. It is conceivable, as was indicated in dashed lines, that the extension section 12 is corrugated over a larger part of its longitudinal extent, which would contribute to improving the effect of the buckle. The band-shaped cross-section of the strut 1 coming from the top right comes into the bend between the extension section 12 and the strut on the left in FIG. 2 in a blunt joint Sidewalls 30 in the other welds.

From FIG. 2 it can also be seen how the profile side edges indicated in FIG. the points A1, B1 and C1 located there are gradually rotated into the plane of the drawing by the gradual twisting of the profile side edges inf _d ge of the deformation to form the flat band cross section, so that the struts ultimately lie snugly with the profile side edges against the inner walls 30 of the hollow profiles 11, 24.

FIG. 4 shows the node K from FIGS. 3 and 2 in a view of the section plane IV-IV from FIG. 2. In particular, the diverging profile side edges 7, 8 or the profile side edges 9, 10 which are highlighted can be seen. The lines S of the struts 1 lead to the center of gravity S of the belt, which in FIG. 4 runs perpendicular to the plane of the drawing. The hollow profile 11, which is designed here with a Σ-shaped cross-sectional configuration, can be seen in solid lines from the lower flange in FIG. 4. The hollow profile 11 will of course be combined in the belt with a hollow profile 24 of the same cross-sectional shape arranged in a mirror image. In Fig. 4, however, other possibilities of hollow profile shapes in dashed or dash-dotted lines are indicated on the side opposite the hollow profile 11. For example, a U-profile 31 which is inclined in accordance with the divergence of the profile side edges could be used to form the lower flange, the lower leg of this U-profile then also being able to be placed horizontally, as indicated at 32, for later placement of the carrier on a bearing. Furthermore, a completely closed box section 33 could also be used to form the lower flange, which, however, would also have to be inclined due to the divergence of the side edges of the section. The hollow profile 11 on the right in FIG. 4 could also be designed as a closed box profile or have an additional end plate (which can be borrowed with the one indicated at 33).

The hollow profile 11 with its Σ-shaped cross section has two mutually parallel legs 27 which are provided with bends 25 and 26 which improve the structural strength. The two legs 27 are connected to each other by the profile inner wall 30, which profile inner wall consists of two symmetrically obliquely inwardly bent wall sections 30a and 30b, which meet in a continuous crease line 29. The kink line 29 lies at the level of the heavy line S of the lower chord. The inclination of at least the Waml section 30a is so matched to the divergence of the profile side edges of the struts 1 that the minimum axis designated X1 of the hollow profile 11 is parallel to the main plane labeled T, and that the upper side 34 or the legs 27 are perpendicular thereto Main plane T of the carrier lie. The cross-sectional shape of the hollow profile 11 not only compensates for the divergence of the profile side edges as a result of the deformation of the profile of the struts from the S shape to the flat strip cross-section, but also brings about a significantly improved buckling resistance or kink resistance of the hollow profile 11. If the welding of the extension section 12 to the wall 30 of FIG. 2 is considered, it can be seen that, according to FIG. 4, an extraordinarily stable fastening between the hollow profiles 11 and 24 (FIG. 3) of the respective belt is achieved when the edges of the extension section 12 are welded to the inner walls in the area of the kink lines 29. In addition to the higher buckling strength of the hollow profiles, this results in an improved absorption of the shear forces and moments in the belts transmitted by the buckle or the welded-in extension section. This can be easily recognized when considering FIG. 2. If the hollow profile 11 shown experiences a tensile load to the right parallel to the plane of the drawing, while the hollow profile 24 of the same belt lying in front of the plane of the drawing has to absorb a tensile load directed parallel to the plane of the drawing, the welded longitudinal section 12 is rotated perpendicular to the plane of the drawing and thereby the Indent inner walls 30 on which he is supported. However, since these are significantly more buckled than flat inner walls due to the buckling, significantly higher loads can be absorbed in the directions explained above than with equally strong straps in belts with hollow profiles with flat inner walls. This improvement in effectiveness is based on the interplay between the struts with their special profiling and the deformation area of the profile, which is shifted into the height region of the belt, on the strip cross section with the special cross section of the hollow profiles forming the belts.

In Fig. 5 it is finally schematically emphasized how the extension section 12 welded between the hollow profiles 11 and 24 forms the buckle in the upper chord or lower chord (U, 0), where it is welded to the two hollow profiles 11, 24 along the buckling lines 29 .

Claims (7)

1. Truss girder with at least one upper (0) and at least one lower flange (U), which are connected to one another by zig-zag or sawtooth-shaped individual struts (1), of which the end of one strut (K) in the respective node (K) 1) is provided with an extension section (12) welded to the belt (0 or U) and following the center line (S) of the belt, while the end of the other strut (1) is butted into the bend between the one strut and its extension section ( 12), such that the lines of gravity (S) of the two close at each node (K) struts (1) and the respective belt (0 or U) that meet each other at a common point of intersection, the struts (1) being openly profiled bars, the ends of which in the knot area each form a flat and the centroid lines (S) of the struts ( 1) straight continuous strip cross-section are deformed, characterized in that the struts (1) have an S- or Z-shaped open profile in cross-section up to the strip cross-section with a minimal axis (X) directed perpendicular to the main plane (T) of the carrier and in the middle the center of gravity (S) lying perpendicular to the minimum axis (X) profile height (h). 2. Truss according to claim 1, characterized in that in each node. (K) the flat band cross-section (C) in the one, the bent extension section (12) having strut (1) only immediately before the turn and in the extension section (12 ) and the other strut (1) is only in the bend area in the bend. 3. truss according to claims 1 and 2, wherein the deformation of each strut end (5 or 6) is accomplished with a gradual transition and in profile height symmetrical to the center of gravity (S) up to the flat strip cross section in a predetermined longitudinal section (AC), thereby characterized in that the longitudinal section (AC) has a length which, taking into account the slope with which the strut (1) is guided in the belt (U, 0), at least that perpendicular to the belt and in the main plane (T) of the carrier seen distance (H) between the center of gravity (S) of the belt and that upper side (34) of the belt from which the struts to the node (K) are led into the belt. 4. truss according to claims 1 to 3, characterized in that the struts (1) in the longitudinal section (AC) along the diverging profile side edges (7, 8, 9, 10) are welded with a belt (welds 13, 14, 15, 16), which consists of two open or closed hollow profiles (11, 24; 31, 32, 33) opposite one another with an intermediate distance that allows the struts (1) to penetrate, with internal walls (30) between the upper side (34) and the height of the belt heavy line (5) following the divergence of the profile side edges of the struts (1) have inclined sections (30a) throughout. 5. truss according to claim 4, characterized in that the hollow profiles (11, 24) have an approximately -shaped cross-section with a buckling in the inner wall (30) leading to a fold line (29) at the height of the center line (S), wherein the portion (30a) of the inner wall (30) extending between the upper side (34) and the fold line (29) is adapted with its incline to the divergence of the profile side edges (7-10). 6. Truss girder according to claims 4 or 5, characterized in that the extension section (12) of the one strut (1) is welded to form a strap with two inner walls (30) along the fold lines (29). 7. truss according to claims 1 to 6, characterized in that the two struts (1) which meet at a node (K) are of identical design and are arranged in reverse relationship to one another, such that the with their One end butt into the bend of the other strut butting at the other end has an extension section (12) for a further node (K).

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