Abstract:
The invention relates to cross bracing for wooden structures, formed by vertical posts (21), horizontal beams (22) intersecting each other at junctions, braces (23, 24, 25) situated diagonally between two adjacent junctions, and gussets (35-40) which connect the braces to the beams and the posts. The braces comprise transverse grooves (41) near their ends, and the gussets comprise a heel (45) at least one of their ends which can engage in one of the grooves in the braces.

Description:
FIELD OF THE INVENTION 
     The present invention relates to cross bracing for wooden structures, and more particularly to structures used for atmospheric cooling apparatuses. Atmospheric cooling apparatuses are currently used in various industries and in the generation of electricity in order to recycle water which has been heated and has to be cooled, or to cool heated water before discharging it to the environment, or more generally for the cooling by ambient atmospheric air of water which is hotter than this air in order to use it in industrial processes. 
     BACKGROUND ART 
     The infrastructure of cooling apparatuses comprises an external infrastructure supporting the shell of the cooling apparatus, i.e, its outside walls and the roof which it may possess, and an internal framework supporting the lining of the cooling apparatus. 
     Numerous atmospheric cooling apparatuses have a wooden infrastructure, which may either be the external infrastructure, or the internal framework, or the system comprising the external infrastructure and the internal framework. 
     These wooden infrastructures are formed from wooden structures. These wooden structures essentially comprise posts (columns) and beams intersecting at junctions. In order to ensure the stability of this system of posts and beams, and in particular to ensure its resistance to winds and earth movements up to a certain limit, cross bracings are added to this system. These cross bracings obliquely connect the junctions. They are diagonal elements which increase the resistance of the structure to horizontal stresses, and together with the posts and beams they constitute the structural elements of the structure. 
     In general, posts and beams intersect at junctions and are continued on both sides of these junctions. Together with other posts and beams situated in the same approximate vertical plane, they form a grid. The structure comprises braces situated within this grid between two diagonally adjacent junctions, and by gussets which connect the braces to each other beyond the junctions and which connect them to the posts and beams. 
     The gussets are connecting plates which transmit the horizontal loads of the beams (forces, tensions, stresses) to the braces and to the posts. These loads essentially originate from the stresses due to the wind and due to earth movements, and from the loadings on the adjacent braces. 
     Hitherto, simple flat metal plates, which are relatively thick and which are drilled with a plurality of holes for the passage of bolts, have always been used as gussets. These metal plates are fixed to the braces by means of bolts, with the interposition of washers. These washers are flanged or serrated washers (claw washers) and penetrate the wood with their claws or flanges. They transmit the forces between the wood and the bolts by shear and compression. The bolts transmit the forces between the washers and the gussets by shear. When serrated washers are used, the claws, which end in a sharp point, are driven into the wood by force, for example by nailing or in a press. When flanged washers (shear washers) are used, a circular groove of the dimensions of the flange of the washer is previously cut in the wood and these washers are then embedded in the wood. 
     All the wooden components are cut, drilled, countersunk, etc. in a workshop specialising in woodwork, whilst the assembly is erected on site, where all the assembly hardware (gussets, washers, bolts, nuts, etc.) is delivered. These metal parts, which are subjected to stress, which are in a hot humid atmosphere and which are constantly wetted by water containing various dissolved salts, are made of stainless steel or of another relatively noble metal and are therefore expensive parts, particularly the bolts and washers, which are machined parts. When assembly is effected using serrated washers, embedding these washers in the wood is an operation which is costly on site. 
     The forces to which the braces are subjected are not the same for all the braces; they depend on the location of the brace in the structure. Moreover the load on a brace is greater the closer it is situated to the ground. Consequently, if one washer is sufficient to transmit the force from a brace to a gusset at the upper level of the tower, two of them are required, for example, at the intermediate level, and three are required at the lower level, or even more (for example two, four and six, respectively). 
     As a result, the assembly hardware will comprise various gussets of different lengths, depending on the number of holes which they must have in order to receive the requisite number of bolts supporting the special flanged or serrated washers. 
     In practice, when the claws or the flanges of the washers transmit forces to the wood by subjecting it to compression, of the order of 100 kg/cm 2 , these forces are transmitted to the bulk of the brace in order to be propagated along the length of the latter, in practice by shear, of the order of 10 kg/cm 2  and is thus ten times less. 
     The differences in length between the various gussets are relatively great. They are sufficiently great that there are cogent economic reasons for not making all gussets to a standard length equal to the greatest length necessary. 
     SUMMARY OF INVENTION 
     The object of the present invention is to provide a simplified cross bracing having a lower hardware cost and a shorter time of assembly. 
     Another object of the invention is to provide greater standardization of the hardware, i.e. fewer different parts to be manufactured, stored and handled. 
     According to the invention the cross bracing is formed by braces comprising one or more transverse grooves near their ends, by gussets each comprising a heel at least one of their ends which can be engaged in one of the grooves in order to interlock the gussets with the wooden structure and to fix the gussets to the braces. 
     According to the invention, each gusset is one of three types, namely end gussets, extension gussets and inter-brace gussets. The end gussets have to fix the brace either to the anchorage sole piece or to a junction of the structure at the end of a beam. One end of this type of gusset is bent at an angle of about 90° to form a heel. The extension gussets, which are intended for reinforcing other types of gussets, each comprise a heel as well as an offset towards the middle of their length. The inter-brace gussets, which are intended for interlocking the braces on both sides of a junction, comprise a heel at each of their ends. The structure can thus be standardized and easily produced on site with a single type of brace and with these three types of gussets. 
     According to one advantageous embodiment of the invention, all the braces to be used in a cross bracing unit are identical. Preferably, they comprise a plurality of transverse grooves at their ends. 
     According to one preferred embodiment, the interlocking is achieved by a fixing means employing: 
     first bolts and corresponding nuts, which pass through the braces and the gussets and hold the gussets against the braces; 
     second bolts and corresponding nuts, which interlock the gussets, either with the structure of posts and beams at the junctions, or with the anchorage sole pieces of the posts. 
     In general, the first bolts can be smaller than the second bolts. 
     In addition, the fixing means advantageously comprise bushes to be used when a gusset is reinforced by an extension gusset. In this situation, the bush transmits the forces between adjacent gussets. Moreover, flat washers (backup rings) are used to hold the bushes in place. 
     These parts, i.e., the braces, three types of gussets, two types of bolts, the bushes and the washers, constitute all the parts necessary to produce a structure on site. 
     With the aim of facilitating assembly, the gussets will be provided with standard holes drilled in the factory. Thus, in one embodiment: 
     each end gusset has three holes: 
     a central hole for positioning the gusset against the brace; 
     a hole for fixing the gusset either to the anchorage sole piece or to a junction of the structure; 
     a hole for the possible installation of an extension gusset. 
     each inter-brace gusset has five holes: 
     two holes at the ends for the possible installation of an extension gusset; 
     a central hole for interlocking the gusset with a junction of the structure; 
     two holes on both sides of the central hole for positioning the gusset against the brace. 
     each extension gusset has two holes, for fixing the extension junction to another junction and to the brace. 
     In order to simplify manufacture in the factory, provision may be made for the distance between two adjacent holes to be the same for all the gussets. 
     Regarding length, the extension gussets are generally the shortest; the end gussets will have a length which will generally be slightly less than twice that of the extension gussets; the inter-brace gussets will have a length which will generally be slightly less than twice that of the end gussets. 
     The present invention also provides a kit of parts, comprising a plurality of and gussets, at least one extension gusset, and at least one inter-brace gusset. A preferred form of the kit also includes a plurality of braces. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings in which; 
     FIG. 1 is a schematic elevation of part of a structure; 
     FIGS. 2, 3 and 4 are enlarged illustrations of the three parts which are circled in FIG. 1; 
     FIGS. 2a, 3a and 4a are views along the arrows A--A of FIGS. 2, 3 and 4; 
     FIGS. 5, 6 and 7 are side views of three types of gussets; 
     FIGS. 5a, 6a and 7a are views along the arrows of FIGS. 5, 6 and 7, respectively; 
     FIGS. 8 and 8a are a side view of a bush and a view along the arrows A--A of FIG. 8, respectively; and 
     FIGS. 9 and 9a are a side view of a back-up ring and a view along the arrows A--A of FIG. 9, respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, this shows part of a wooden structure formed by four posts 21a, 21b, 21c and 21d, three beams 22a, 22b, and 22c and three braces denoted by reference numerals 23, 24 and 25, respectively. In the example the three braces form a complete line of the structure. 
     The brace 23 is fixed to the junction 31 formed by the post 21 a and the beam 22a by means of end gussets which are described in detail below with reference to FIGS. 2 and 2a. 
     The brace 24 is fixed firstly to the junction formed by the post 21b and the beam 22b by means of inter-brace gussets and secondly to the junction 32 formed by the post 21c and the beam 22c by means of another inter-brace gusset. The inter-brace gussets are described in detail below with reference to FIGS. 3 and 3a. 
     The brace 25 is fixed to the post 21d and to the anchorage sole piece 26 (junction 33) by means of end gussets illustrated in FIGS. 4 and 4a. 
     As shown in FIG. 1, the end gusset fixed to the junction 31 does not comprise an extension gusset, and the end gusset fixed to the junction 33 comprises two extension gussets. 
     This becomes clear if the force exerted on the braces is considered. 
     If P is a lateral force exerted on the part of the structure considered, and if, in this example, it is assumed that this force is constant over the height, i.e. is identical for the three beams, the thrust P in beam 22a produces a force &#34;D&#34; in brace 23, which is transmitted to brace 24, where it is added to the force transmitted to this brace by beam 22b. Brace 24 transmits a force &#34;2D&#34;  to brace 25, which again receives a force D from beam 22c. The force in brace 25 is thus &#34;3D&#34; in this example. 
     Brace 23 is attached to junction 31 of the part of the structure considered by two end gussets (one on each side face), whilst its lower end connects it to the structure and to brace 24 via two inter-brace gussets. For this brace 23, which is subjected to the least stress, the sizing of the elements present is such that no extension gusset is necessary if an end gusset absorbs a force &#34;0.5D&#34;. 
     In contrast, brace 24, which is acted upon by a force &#34;2D&#34;, has two extension gussets at each of its ends, one for each side face of the brace; each extension absorbs a force &#34;0.5D&#34;. 
     Finally, brace 25 receives three gussets for each side face, two of which are extension gussets. At the upper end of the brace the latter are connected to an inter-brace gusset, whilst at the lower end they are connected to an end gusset. There are therefore six gussets at each end, each transmitting a force &#34;0.5D&#34;, the addition of which just corresponds to the force &#34;3D&#34; of the brace. 
     FIGS. 2 and 2a show, on a larger scale, the junction 31 formed by the post 21a, the beam 22a and the brace 23. Brace 23 has three transverse grooves or notches 41 at its end, on two opposite faces. These grooves 41 are produced in the joinery shop. They are equidistant from each other and are formed over the entire width of the brace. For reasons of standardization of manufacture and of interchangeability on the construction site, the number of cuts in each brace is preferably equal to the maximum number which the most heavily loaded brace must have. In the example, each brace has twelve cuts (in three places on two opposite faces at each end). 
     Junction 31 is interlocked (on its two opposite faces) by means of end gusset 35. This gusset is a metal plate cut to form a rectangle, which is bent at one end to form the heel 45 and which is drilled with holes for the passage of bushes and bolts. In the example the gusset has three holes (FIG. 5). 
     FIGS. 3 and 3a show the junction 32 formed by post 21c, beam 22c and braces 24 and 25. The junction is interlocked (on its two opposite faces) by means of an inter-brace gusset 36, and is reinforced at the end of brace 24 by an extension gusset 37 and at the end of brace 25 by two extension gussets 38. Each inter-brace gusset 36 has a heel 45 at each end and is drilled with five holes (FIG. 6). 
     Each extension gusset (37-38) comprises a heel 45 at one end, an offset 42 towards the middle of its length, and two holes, one on each side of the offset (FIG. 7). 
     FIGS. 4 and 4a show the junction 33 formed by post 21d, anchorage sole piece 26 and brace 25. The junction is interlocked (on its two opposite faces) by means of an end gusset 39 and two extension gussets 40. 
     FIGS. 5, 6 and 7 show an example of each type of gusset in detail. By way of example, these parts may have the following dimensions. Thus the thickness of the base metal plate is 4 mm, the height of the heel is 15 mm and the width of the gussets is 80 mm, the latter value being equal to the smallest width of the side face of the brace which receives gussets. A brace may be wider than the gusset, but in principle the gussets should never protrude beyond the braces. 
     The holes in the gussets have diameters of 22 mm when they have to be able to receive bushes 51, the outside diameter of which is then also 22 mm, the tolerances on these diameters being such that the bushes can be introduced manually, without looseness, into pairs of gussets. This is the case for the end holes 44 of the gussets. The other holes 43 have a diameter of 14 mm in order to be able to receive either bolts of 12 mm diameter, namely those of the junctions and anchorages of the structure, or bolts of 8 mm diameter intended for holding parts. The inside diameter of the bushes 51 is then 10 mm if the same diametric clearance is desired as for the 12 mm bolts (FIG. 8). 
     The large washers 52 (FIG. 9) have an inside diameter equal to the inside diameter of the bushes 51 and an outside diameter of 25 mm, which is substantially greater than that of the bushes, so that they can be clamped against the gussets and can thus hold the bushes in place, the thickness of the bushes being equal to that of two gussets, or 8 mm. 
     The offset 42 of the extension gusset is 4 mm thick, corresponding to the thickness of the sheet metal of the gussets. 
     The thickness of the large washers is not critical. It may be equal to that of the gussets (2 mm) or thinner. 
     Referring again to FIG. 5, it will be observed that the end gusset 35 comprises a heel 45, two large diameter holes 44 and one small diameter hole 43, these three holes being aligned along the centre line of the gusset. The hole 44 at the opposite end to the heel 45 is intended for fixing to the junction 31 by means of a large bolt. 
     In the case of the end gusset 39, the hole 44 at the opposite end to the heel 45 is intended for fixing to the anchorage sole piece 26. A bush 51 and a small bolt are used for this purpose. 
     The central hole 43 is intended for the passage of a small bolt for positioning gusset 35 against brace 23 or gusset 39 against brace 25, respectively. 
     The large diameter hole 44 near the heel 45 will receive a bush 51 if an extension gusset is used (as in the case of the end gusset 39 with two extension gussets 40); a small bolt will be passed through it. Even in the case where an extension gusset is not used (as is the case for gusset 35), a small bolt will also be used because the forces between the brace and the gusset are transmitted by the heel and not by the bolt, which merely serves to immobilize and interlock the elements present. 
     As shown in FIG. 6, an inter-brace gusset has a heel at each end and is drilled with five holes. 
     Two large holes 44 will be observed at the ends for receiving bushes 51 when extension gussets are required, as is the case for the inter-brace gusset 36 and the extension gussets 37 and 38. Small bolts pass through these holes; these bolts are simply intended for positioning the gussets against the braces. 
     In addition, gusset 36 comprises three small diameter holes 43, the central hole of which receives a large bolt which transmits the forces between the gusset 36 and the structure of posts and beams; the holes adjacent to the central hole receive small bolts for positioning the system and for reducing the buckling stress on the gusset. 
     FIG. 7 shows the extension gusset 37 (38 or 40). It has a single heel 45 at one end and a shoulder (or offset) 42 towards the middle of its length. 
     This offset 42 is intended to overlap another gusset (either an end gusset, or an inter-brace gusset, or another extension gusset). The height of the offset is equal to the thickness of the gusset. The part of the gusset between the heel and the offset is applied to the wood of the brace via one of its faces. The other face of this part of the gusset is either not in contact with anything when this gusset terminates a series of gussets (as opposed to the end of a brace) or receives the shoulder of another extension gusset. These extension gussets are only provided with two holes, each of large diameter, the hole in the shoulder receiving a bush for the transmission of force to another gusset, and the hole adjacent to the heel receiving a bush when this extension gusset is connected there to another extension gusset. The bolts which pass through the holes of these gussets are small bolts only, because they never transmit the forces of the brace but simply serve to apply the gussets against the braces and to hold the bushes in place (with the aid of their flat washers 52 and their bolts). 
     If the gusset terminates a series of gussets, the hole on the heel side may be smaller, but it would then have two types of extension gusset, which would make maintenance, storage and assembly more onerous without any benefit. 
     FIG. 8 shows a bush 51, the axial thickness of which is equal to twice the thickness of the gussets. The wall of the bush is relatively thick, so that it is able to transmit, by shear, the force between the two gussets connected by the bush. The outside diameter of the bush corresponds to the diameter of the large holes (44) in the gussets so that it can be accommodated therein without looseness. The inside diameter of the bush is dimensioned in order to receive the small bolts. A bush connects an extension gusset to another gusset comprising one or other of the three types of gusset. 
     FIG. 9 shows a flat washer 52, which completes the connection at the bushes 51. These washers are placed between the nut or the head of the bolt and the gusset; they are parts with an inside diameter corresponding to a small bolt (with a clearance), and with an outside diameter which is larger than the outside diameter of the bushes 51, so that they can be applied to the gusset and can thus clamp the pair of gussets against the brace and hold the gussets and braces in place. 
     It is clear that the invention is not restricted to the example described above, and that variants can be found for the design of the parts. 
     The advantages of using a gusset with a heel are apparent when it is realized that the heel of a gusset absorbs almost the force of three large bolts of a classical structure. It therefore reduces the labour cost and the materials cost. In practice, three bolts with flanged washers or serrated washers are distinctly more expensive than is the production of a heel. 
     The holes and cuts in the braces according to the invention are rapidly produced in succession in the joinery shop (which does not receive the assembly hardware) on the same machine without gripping and re-gripping the braces, whilst serrated washers of the prior art have to be laboriously driven into the braces on site, which is a much more laborious operation than the simple placement on site of the heels in the grooves (notches) which have previously been cut in the joinery shop. 
     Moreover, compared with the classical system with serrated washers, the invention also has the advantage of causing less damage to the wood and of providing cleaner surfaces for contact with the metal parts to which the forces are transmitted.