NL8100332A - RIGID PROFESSIONAL IN CABLE CONSTRUCTION AND METHOD FOR MANUFACTURE AND USE THEREOF. - Google Patents

Description

NO 29.780 - 1 -

Rigid truss girder in cable construction and method for its manufacture and application

The invention relates to a rigid, flat lattice girder with at least two fields, consisting of a top and a bottom rail, cross connections between and diagonal connections in the fields, with at least four anchoring points, two of which are at each end , wherein the anchor points are in the plane of the beam and the load engages in the plane of the beam and substantially perpendicular to the span and wherein the anchor points besides the operating load also have 10 tensile forces in the direction of the beam directly or indirectly can take.

Rigid, flat lattice girders are generally supported on supports at their ends, while they may also be clamped there. In both cases, a relatively large number of bars will be subjected to pressure in the lattice girder. The others are taxed on tension. With varying loading conditions, such as can occur due to wind load, loads can occur in a number of bars which can vary between pressure and tension.

All bars that have ever been subjected to pressure must be sufficiently kink-resistant and in practice bars with a cross section are used for this purpose, in order to provide a sufficient inertia radius against kinking. Known safety margins are of course taken into account, but when a buckling rod would collapse and also when a tension-loaded rod would collapse, the entire lattice girder collapses and neighboring girders can be dragged out of the plane by overload and loading.

The object of the invention is to provide a simpler and, under many circumstances, safer lattice girder, which is largely built up of non-rigid cables. Nevertheless, in its plane, a rigid lattice girder is provided. The lattice girder according to the invention is now characterized in that the top and bottom rail of the girder and the 55 diagonal braces each consist of one or more cables, which - with the exception of the anchoring points - are rigid 8 1 00 33 2 4 '.

- 2 - compression rods placed as cross braces between the top and bottom rail at those corresponding points of angle change where diagonal dressing cables connect to the top and bottom rails.

5 It will be clear that, where non-rigid cables cannot absorb a pressure load, all cables in the lattice girder must be pretensioned in such a way that under all occurring operating conditions a tensile stress in each cable is always maintained, with the exception of 10 so-called zero cables. To this end, the truss beam according to the invention requires at least four anchoring points, two of which at each end, which anchoring points lie in the plane of the beam. In addition to the operating load, the anchoring points must be able to absorb the necessary tensile forces in the direction of the beam. It is outside the invention in which manner said tensile forces are transmitted directly or indirectly from the anchoring points to the ground.

Of the lattice girder according to the invention, only the cross-ties between the top and bottom rail are designed as kink-rigid compression bars. The aforementioned compression rods are included in those places in the lattice girder, where diagonal connection cables connect to the top and bottom rails in points of angle change. As crossbeams, the compression bars divide the truss beam into a number of fields. The number of fields of a lattice girder according to the invention will generally be even, but an odd number is also possible.

According to a preferred embodiment, the interconnecting anchor points continuously follow continuous cables as main cables at least once the path of a diagonal connection cable. Thanks to the continuous running of the main cables between the anchoring points, unnecessary connections between cables are avoided. This is very cost effective and considerably simplifies the construction. With longer spans with multiple fields, multiple cables in the bottom rail and top rail can thus run parallel to each other. This number can vary from field to field, while diagonal-40 connections can also consist of several parallel cables.

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Because the main cables are at angular change points. at least once following the trajectory of a diagonal dressing cable, each main cable contributes to the stiffening of the beam.

5 From the calculations of the expected loads as a result of own weight, roof construction, snow and wind load, thermal influences inside and outside the building or shadow and sun side, the necessary preloads for each cable can be determined such that in each cable t 10 tensile stresses are maintained under all operating conditions. From these calculations also follow the pressure loads to which the rigid compression bars acting as cross-connections are subjected.

In the points of angular change, ie at the ends of all the pressure bars, all passing cables continue. Only in order to keep the push rods in place and in the correct position with certainty, according to a preferred embodiment it is provided that in all points of angular change the rod ends are fixedly adhered to the cables passing there, for instance with a hardening and somewhat elastic permanent synthetic resin.

If it follows from the strength calculations that it is desirable to subdivide one or more fields into shorter fields and / or if the load in certain sections of continuous main cables should become too high, the invention provides, according to a preferred embodiment, that one or more secondary cables are provided which, from a point of angular change on one line 30, cross at least once along a diagonal to a point of angular change on the other line, at least one end of the side cable being tensile connected to the main cable. This connection, for example with clamps, always takes place on a main cable, so that the rigid compression rods as cross braces are never loaded in a direction more or less perpendicular to their center line in the plane of the beam. This prevents any risk of unintentional displacement or displacement of the pressure rods.

It is further preferred that the rigid pressure 40 bars are positioned substantially perpendicular to the lines.

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The rigid lattice girder according to the invention allows great flexibility in the structural and architectural design. For example, the beam can be designed as a truss, whereby the bottom rail can also show an upward curve, as is often desired for psychological reasons. If several fields are used, it is also possible to design the top rail as a truss with a varying angle of inclination along its length and even with an opposite angle of inclination in certain fields. This may be desirable in view of the incidence of light, ventilation and rainwater drainage and the like.

Compared to the existing rigid lattice girders, built up from bars, the beam according to the invention has only a minimum of bars loaded under pressure, such as the cross-beams. Since the other "bars" consist of cables that are subjected to tensile stress, a minimum of material can be used. Compared to comparable known rigid lattice girders, built from rods, the girder according to the invention is in the majority of cases considerably lighter in weight and also cheaper, because a large number of the nodes consist of nothing but diverting into a point of angular change of one or more cables over the ends of the compression bars.

An additional great advantage of the beam according to the invention consists in that it is characterized by a high safety against failure. After all, if one of the cables is so heavily loaded by, for example, an overload that it stretches more than calculated and possibly even starts to flow, the tensile pretension in these and in other cables is automatically reduced as a result of angular changes. The latter tax reduction has a positive effect on the overloaded cable and relieves it. Although the truss girder will thereby change somewhat in shape and cracks may occur in the roof when a rigid roof is used, the intrinsic safety described above will prevent the construction from collapsing completely. This property also includes an opportunity to apply even lighter structures.

It will be clear that also composite constructions of the rigid, flat lattice girders according to the invention are possible, in that a number of at least three flat lattice girders are combined in such a way that the top rail of one at least partly coincides with a bottom rail of another, that spatial truss beams are created, such as beams with triangular or rectangular cross section.

A further important advantage of the lattice girder according to the invention consists of the simple factory-made manufacture and assembly at work and the intermediate transport. This is characterized by the following steps: - making each individual cable with end connections to length according to the drawing, - making the pressure rods, 15 - laying out in a flat plane, such as on a mounting floor, all cables and compression rods at the calculated location and according to the designed route, - attaching the cables to the ends of the compression rods, for example with an adhesive (for example, a hardening synthetic resin) and of the secondary cable (ends) to the main cables with, for example, clamps, everything according to drawing, - rolling up the lattice girder (like a rope ladder) on a reel, - unrolling, after transport, at the construction site of the lattice girder and anchoring it to the supporting construction in the anchoring points, - tensioning the anchors according to the calculated displacements.

As is the case with classic rigid lattice girders, where each rod is pre-machined, pre-drilled or welded to length, the various cables with their end connections are prepared in the factory to the length indicated in the drawing. On a flat installation floor, all cables and compression rods are now laid out straight at the calculated location 35 and according to the design route. In all points of angle change at the ends of the compression bars, the main and secondary cables are permanently secured with hardening elastic plastic. The ends of any secondary cables are also secured to the 40 main cables with clamps, for example. After curing, the whole can be rolled up on a reel as an 8 1 0 0 33 2 - 6 rope ladder, after which transport to the construction site is easy. Ultimately rigid lattice girders of many tens of meters in length can easily be transported in this way. At the construction site, the ends of all main cables are attached to the corresponding anchoring points, with the beam still unstressed. As a last action, the anchors are prestressed over the calculated displacements. The calculated pre-stresses are thus applied in all 10 cables and the lattice girder has become rigid and immediately loadable.

In many cases the lattice girder according to the invention will be attached to four anchoring points, but it is within the scope of the invention that a larger number of anchoring points can be used.

The invention will be explained in more detail with reference to the following figure description of exemplary embodiments.

Fig. 1 shows a rigid, flat truss beam according to the invention, designed as a truss with two fields.

Fig. 2 shows a straight, rigid, flat lattice girder according to the invention, constructed with six fields and constructed with secondary cables.

In both Figs. 1 and 2, the truss girder with two, 25 and six fields, respectively, is fixed in four anchoring points. These points are named Lp and Lq on the left in the drawing and Rp and Rq on the right in the drawing. The anchoring points are shown schematically as points in, for example, a concrete wall. However, the points can also form part of, for example, a steel construction. In all cases, the supporting wall or steel structure L and R will have to absorb the own weight and the roof load transferred by the beam at the anchoring points. However, the clamping forces for the cables need not be transmitted to the ground through supports L and R; they can, for example, be routed via individual cables to individual anchoring blocks in the ground. The constructions L and R then mainly have a load-bearing function and can be made much lighter, because they do not have to pass through any or only a small bending moment.

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In the figures all cables from left to right, so all main cables, are indicated with numbers 1,2, 3 and so on. The fields are indicated with a, b, c and so on, while for each cable, for the part that goes through a 3 route in a certain field, the field designation is added to the cable name: 2c indicates that part of cable 2 that passes through the field c is running. In the figures, the rigid compression bars forming the cross-ties are indicated by a combination of two letters, for example bc, 10, which means that this compression bar bc lies on the boundary between the fields b and c. The ends of the cross braces all lie on the top line or the bottom line and are therefore indicated by the two letters of the pressure rod concerned, plus p and q respectively, originating from the top and bottom anchoring point and the top and bottom line running therebetween.

The optional side cables, as shown in Fig. 2, carry codings according to the same system as the main cables and their connection points with main cables are indicated with the letters r, s, t and u (fig. 2). Whether a particular cable belongs to a main cable or a secondary cable can only be concluded from the figure and cannot be read from the coding used.

In both Figs. 1 and 2 an even number of fields are shown, so that in the middle of each lattice girder a symmetry line S-S can be indicated, on which line a pressure rod is also placed. It will be clear that an odd number of fields in one beam is also possible. Nor do the left and right anchoring points 1p and 1q, rp and rq, respectively, have to be at equal distances, while application of more than two anchoring points per end of the lattice girder is also possible.

In the figures, only the cross braces ab to ef are designed as rigid compression bars. All other connections consist of non-rigid cables.

To illustrate that the rigid and flat lattice girders according to the invention need not only have straight continuous 40 bottom and top rails, Fig. 1 shows a truss girder as an 81 00 33 2 - 8 example, with the point abp higher at the top the anchoring points Lp and Rp. The pressure bar ab is longer than the distance between the anchor points Lp to Lq and Rp to 5 Rq, respectively, so that the lower end abq of the pressure bar ab is less high above the connection line Lq-Rq. In Fig. 1 nevertheless point abq is higher than said connecting line, in order to obtain the often desired optical effect under the span, whereby the impression is avoided, as the span would sag downwards.

As can be seen from the codings of both figures, all main cables run at least once through the path of a diagonal connection cable, which means that the main cables make an essential contribution to the stiffening of the lattice girder and to the carrying capacity of the beam. Nevertheless, under certain circumstances cables may run straight without making an angular change at any point of angle change. In general, the side cables, such as 6c and 6d in Fig. 2, will also pass through an angle change, namely at cdq, but also near their ends s and t, where the side cable from 6b to 6c makes an angle change along the point bcp , respectively cable 6d to 6th over the point dep. As mentioned earlier, side cables transfer their forces to main cables. In points s and t (fig. 2) the secondary cable 6 is connected tensile to the main cable 3. The same applies to secondary cable 5, which is connected tensile to the main cable 1 in points r and u. With the exception of the situation in any reaction points of the beam, 30 none of the cables in any end of a push rod are tensively connected to them. The cables run on either side of these ends of the compression bars. For a number of passing cables, these ends form the aforementioned angular change points, while for straight cables these end points are not angular change points in their trajectory. However, for the purpose of manufacture and assembly on the construction site, it is preferable to fix all passing cables in the ends of the compression bars to each other and to the compression bars firmly but elastically, for example by using a hardening but 8 1 00 33 2% - 9 - slightly elastic plastic. This avoids the danger that pressure rods may shift slightly in the plane of the beam, especially during assembly.

5 All cables and compression bars can be accurately calculated in terms of effective length, load, strain, etc. The cable characteristics are known from information supplied by the cable manufacturer and from any additional measurements. In contrast to single steel wires, which follow Hooke's law in terms of their force-stretching characteristics, stranded and / or braided steel cables at low loads first exhibit a pre-stretch M path in their characteristics, before adopting Hooke's law. to follow. By taking this into account when determining the ultimate length of the cable in the designed truss under the operating loads, the mounting load and thus the unstretched stretched manufacturing length can be accurately determined. In addition to the. compression rods can thus all the cables be accurately manufactured to length beforehand and laid out stretched on a flat mounting floor according to the designed route and at the calculated location. After all passing cables have subsequently been attached to the ends of the compression bars, the lattice girder is ready for mounting by means of pre-tensioning the cables ending in the anchor points. However, the pre-assembled beam is not yet rigid and can be rolled up on a reel like a rope ladder and transported in that shape. A beam of many tens of meters in length can thus be transported in a simple manner and unrolled at the final construction site. After fastening the lattice girder to the anchoring points, in an unstressed state, only each anchoring point needs to be tensioned over the pre-calculated length in order to obtain the desired pretension in all cables of the lattice girder, whereby it has not only become rigid, but in addition, able to bear the calculated taxes. Apart from applied safety margins, at least a low tensile stress will be maintained in all cables under all load conditions. The beam 40 thus remains rigid.

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In Fig. 2, all pressure bars ab to ef are shown equally long. Moreover, their length is equal to the distance between the anchoring points Lp and Lq, Rp and Rq, respectively. However, this is not necessary. For example, by choosing different lengths and also positions for the compression bars ab to ef, the lattice girder can take a truss shape with successively viewed from the center, different angles of inclination from the top and bottom rail. In principle, even opposite angles of inclination are possible. It will be clear that the beam can also be designed as a concave, convex or concave-convex arc-shaped beam.

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Claims (8)

1. A rigid, flat truss with at least two fields, consisting of a top and a bottom rail, cross braces between and diagonal braces in the fields, with at least four anchoring points, two of which at each end, with the anchoring points in the plane of the beam and the load engages in the plane of the beam and substantially perpendicular to the span and where the anchoring points can also directly or indirectly absorb 10 tensile forces in the direction of the beam, in addition to the operating load, characterized in that of the beam the top and bottom rail and the diagonal braces each consist of one or more cables, which - with the exclusion of the anchoring points - rigid compression rods are placed as cross-braces between the top and bottom bar on those corresponding points-of-angle change where diagonal connect bandage cables to the top and bottom rails. Truss beam according to claim 1, characterized in that the anchoring points between opposite continuous cables (main cables) follow at least once the path of a diagonal connection cable. Truss beam according to one or more of the preceding claims, characterized in that one or more auxiliary cables are provided, which cross at least once along a diagonal from one point of angular change on one line to a point of angular change on the other rule, wherein at least one end of the secondary cable, for example with clamps, is tensile connected to a main cable. Truss beam according to one or more of the preceding claims, characterized in that, in a truss with multiple fields, various cable elements consist of more than one parallel cable. Truss beam according to one or more of the preceding claims, characterized in that the rigid compression bars are placed substantially perpendicular to the rails. 81 00 33 2 f. - 12 - Η Truss beam according to one or more of the preceding claims, characterized in that in the skirting of angle change at each end of each rigid thrust rod, the cables passing there are firmly adhered to the rod ends, for instance with a hardening plastic. 7. Composite construction of rigid, flat lattice girders s, characterized in that a number of lattice girders according to one or more of the preceding claims are combined in such a way that the top rail of one coincides at least in part with a bottom rail of another, which spatial truss beams are created, such as beams with a triangular or rectangular cross section. 8. Method for the manufacture and assembly of a box girder according to one or more of the preceding claims, characterized by the following steps: - the preparation of each individual cable with end connections according to the drawing, - the preparation of the compression bars, 20. stretched laying in a flat plane, such as on a mounting floor, of all cables and compression bars at the calculated location and according to the designed route, - attaching the cables to the ends of the compression bars, for example with an adhesive (for example a Curing plastic) and of the secondary cable (ends) to the main cables with, for example, clamps, all according to the drawing, - rolling up the lattice girder (like a rope ladder) on a reel, - unrolling it, after transport, at the construction site of the box-30 work beam and anchoring to the supporting structure in the anchoring point and, - tensioning of the anchors according to the calculated displacements. 8100332