Prefabricated spatial structure

A prefabricated spatial structure includes rods which are rectilinear tubes having a circular section and closed at each end by a cap which is joined to the tube by means of an annular weld or any other convention system and which has a hole concentric with the axis of the rod. The circular head of a special bolt is housed in the interior part of the cap. The bolt includes two threaded bodies having different diameters and opposite threading directions, the threaded body closest to the head having a smaller diameter than the diameter of the hole of the cap. The other threaded body is situated at the end of the bolt and has threads identical to that of the holes made in a node. The difference in diameters of the bodies is determined by a step which forms a flat or truncated resting surface coaxial with the axis of the bolt. The bolt is provided with a threaded nut which is coupled to the threaded body having the greater diameter. Each node has a series of threaded holes, the axes of which meet at the geometric center of the node.

BACKGROUND AND SUMMARY OF THE INVENTION 
The field of application of the invention is that of spatial structures 
formed by the repetition and conjunction of many simple and geometrically 
similar elements. It is particularly applied to those spatial structures 
formed by rods and nodes, the arrangement of which is such that the rods 
are predominantly subjected to traction or compression strains. 
The object of this invention is to provide a joining system formed of nodes 
and rods which are economical to manufacture and simple to use, and which 
provide the desirable properties of: 
(A) The specific dimensions between the axes or centers of the nodes of the 
structure are determined at the time of manufacture, according to the 
particular project, without requiring adjustments or correction on site. 
(B) Any rod can be assembled or dismantled, even after the relative 
positions between adjacent nodes have been fixed. 
(C) The aforementioned property is fulfilled irrespective of the geometry 
of the structure. This property together with the former permit the 
assembly to be effected in any assembling order. 
(D) The system has versatility such that the rods can meet at the node in 
any direction of space, without any restriction other than the existence 
of a minimum angle between adjoining rods which prevents interference 
therebetween. 
(E) The system is resistant in all directions, a desirable property when 
the system is applied to various shapes differing from conventional mesh 
shapes. 
(F) All the resistant sections can be utilized for the optimum yield of the 
material. 
(G) The assembly of the node with the joining elements reproduces a 
behavior sufficiently close to that of a calculated hypothetical behavior 
of space lattices, that is to say to a pure joining with elevated axial 
rigidity and with reduced rigidity to bending found in the maximum 
proximity to the geometric center of the node. 
In the system to be described hereinafter, the nodes can have any geometric 
shape, provided that the shape adapts to the reception from different 
directions in which the rods can lead, although the original spherical 
shape provides a maximum degree of regularity in space and adapts more 
appropriately to any geometric structural shape, maintaining an equalness 
in the resistant capacity in all of them. To obtain a greater rigidity, 
the node is preferably a sphere, solid or hollow. To provide the node with 
accessibility from the exterior, the mechanical connections to the ends of 
the rods are left-hand threaded holes whose axes preferably meet at a 
point which shall be referred to as the geometric center of the node. The 
sphere presents, at the outer portion surrounding each hole, a plane 
perpendicular to the axis of the hole which shall be referred to as 
"seating surface", inasmuch as a corresponding part or surface of the rod 
rests thereon. 
The rod is formed by a tubular profile having a circular section, which is 
closed at the ends by means of caps or plugs having a slightly cylindrical 
or truncated shape. These caps have a cylindrical hole coaxially aligned 
with the axis of the rod and are joined to the tube by means of a 
butt-welded annular cord which encircles the entire thickness of the tube 
in order to transmit the strains which the resistant section thereof is 
capable of withstanding. Through the hole of the cap is introduced a 
special bolt provided with a cylindrical head and a stem having two 
threaded portions having different diameters and reverse or opposite 
threading directions. The diameter of the head is greater than that of the 
hole of the cap so that the head can rest on the inner surface of the cap. 
The threaded portion nearest to the head has a right-hand thread having an 
outer diameter smaller than that of the hole of the cap so that it can 
pass therethrough and turn freely in its interior. The other portion of 
the bolt, situated at the end opposite to the head, has a left-hand thread 
of the same size and type as the threaded holes of the node. The length of 
the other or outer threaded portion, which shall be referred to as 
"penetration length" since it is the dimension by which the bolt 
penetrates into the node, should be at least that necessary so that, 
depending on the type of bolt and on the quality of the material, the 
forces to which the rod is subjected can be transmitted to the nods. The 
two threaded portions of the bolt are coaxial and the difference between 
the diameters thereof is such that the diameter of the inner threaded 
portion is greater than the diameter of the outer threaded portion, the 
two portions being separated by a plane perpendicular to the axis of the 
bolt, which plane presents an annular surface which shall be referred to 
as "resting surface" and which, upon complete assembly of the rod, will 
rest precisely on the "seating surface" of the corresponding hole of the 
node. The assembly is completed with a right-hand threaded nut which is 
coupled to the threaded portion having a greater diameter of the bolt. The 
elements of the assembly are positioned such that the head of the bolt 
remains in the interior of the rod, with the stem passing through the cap 
toward the exterior and the nut threaded on the inner threaded portion 
which extends through the cap. In the final positioning for assembly, or 
at initiation of the assembly operation, the nut is at the most exterior 
or outer part of its threaded portion, so that between the nut and the 
exterior surface of the cap there is a length of thread, which length 
shall be referred to as "introduced length". This length of free thread 
constitutes the magnitude which the bolt will be withdrawn outwardly of 
the rod with respect to the final position of the assembly. The length of 
the right-hand or inner threaded portion of the bolt, prefectly defined at 
the time of manufacture, should be greater than the sum of the thicknesses 
of the nut and the cap, and in any case the introduced length shall be 
related to the penetration length, a condition which has the purpose of 
fulfilling property B above. 
Joining of the end of the rod to a node takes place as follows. Firstly, 
the end of the bolt is placed in front of or facing the corresponding hole 
of the node. Once the bolt is so positioned, the nut is acted upon by 
turning it while the outer end of the bolt is slightly pressed against the 
node to initiate threading therebetween, which later on progresses without 
the need of exerting the initial pressure. Due to the fact that the bolt 
has two reversely threading portions, a main feature of this invention is 
that the same turning direction, during driving of the bolt, can produce 
two different threading effects, that of the outer threaded portion of the 
bolt into the hole of the node and that of the nut onto the inner threaded 
portion of the bolt. The sequence of these two threading steps is 
independent of the will of the user carrying out the assembly. Before the 
two reach their respective end limits, both steps offer very limited 
resistance to threading rotation. However, the first threading effect to 
be produced is that which has the smaller resistance to its own threaded 
rotating advance. As a possible development of the complete process, in 
case the threading of the nut onto the bolt is that which shows the 
greater resistance, then when acting on the nut, the nut will make the 
bolt turn, which will penetrate into the node until the resting surface of 
the bolt abuts against the seating surface of the node. At that moment the 
resistance to turning of the bolt increases considerably and the nut, 
still rotated in the same direction, will be threaded onto the bolt in a 
direction approaching the head until the nut presses the cap at the end of 
the rod. Thereafter, further turning of the nut encounters resistance 
corresponding to the simultaneous tightenting of the nut against the cap 
and of the bolt into the node. On the other hand, if the rotation of the 
bolt is that which offers a greater resistance during the initial turning, 
then the process will take place in the opposite order, producing first 
the threading of the nut on the bolt until the nut and the head contact 
the cap. Then, further turning of the nut causes rotation of the bolt 
within the cap and threading of the bolt into the node until the bolt 
abuts therewith. 
After assembly and final tightening of the two ends of a rod to their 
respective adjacent nodes, the relative position between the centers of 
the nodes is perfectly determined since the distance between the centers 
of the nodes is the sum of the distances from the centers of the nodes to 
the corresponding seating surfaces; the distances from seating surfaces of 
the bolts to the respective seating planes of their heads; and the 
spacings between the inner resting surfaces of the caps at both ends of 
the rod. All these dimensions are determined during the manufacture of the 
elements, based on a given installation or project, none of them requiring 
any adjustment or correction on site. 
Dismantling of a rod is carried out by acting on the nuts in a direction 
reverse to that described above regarding tightening. The same driving 
direction of the nut, due to the two threads being of reverse direction, 
originates the two steps of the process, the first of which consists in 
that the nut, after initially rotating with respect to the bolt, frees the 
cap and is moved along the bolt until it establishes contact with the node 
at which moment it offers a resistance to the turning of the nut with 
respect to the bolt. Overcoming such resistance, which will be equal to 
that of tightening, the bolt is unlocked from the node and it starts to 
turn together with the nut until it leaves the node completely. Once this 
operation has been made at both ends, the rod can be withdrawn feely 
without modifying the position of the adjacent nodes, since the 
introduction of each bolt can be made in a length equal to or greater than 
that of penetration. 
Certain aspects of design and execution should be born in mind to avoid a 
disadvantage which could otherwise be produced during the previously 
described assembly process. If, through a greater resistance of the 
threading of the bolt into the node, the nut advances on the bolt, it can 
occur that from the moment at which the nut contacts the cap and the cap 
contacts the head of the bolt, the pressure exerted between the nut and 
the head presses the cap, thereby creating friction sufficient to prevent 
the torsional rotation of the bolt-nut assembly, i.e. rotation of the bolt 
within the cap. In this position the bolt cannot be screwed into the node 
unless the complete rod turns on its axis, which is not possible if the 
opposite end has been previously assembled. This phenomenon has the 
probability of being producing when the friction, originated by the 
pressure between the nut and the head of the bolt against the respective 
outer and inner surfaces of the cap, equals the tightening torque which 
gives rise to the force generated by such pressure. Such situation 
therefore depends on the helix angle of the threads and on the roughness 
of the contacting surfaces. 
In normal bolts and nuts having a single thread and materials having 
ordinary surface finishes, the previously mentioned difficulty can be 
produced and a way of preventing it would be on the basis of a greater 
helix angle (the thread having a varied inlet of special design) or highly 
polished and greased contacting surfaces. However, there are other 
alternative solutions which can be applied if the former is economically 
disadvantageous and which, by means of providing resistance to the advance 
of the nut on the bolt, guarantee that the step of advance of the bolt and 
tightening of the node is produced before the tightening of the nut to the 
head of the bolt by means of the cap. Without considering them as sole 
solutions, the following can be considered exemplary: 
(A) A circumferential recess may be provided in the inner threaded portion 
on which is housed an incomplete or diametrically cut washer, so that 
after preventing the nut from approaching the head of the bolt during the 
first threading step until tightening of the bolt to the node, the washer 
can be withdrawn at will to allow tightening of the nut toward the head of 
the bolt. 
(B) A diametral hole may be provided in the inner threaded portion, and a 
recess may be provided in the nut. The nut insures rotation of the bolt by 
means of a pin which is introduced through the nut into the hole, thus 
preventing relative rotation between the bolt and the nut. After 
tightening the bolt into the node, the pin is withdrawn to be able to 
effect tightening of the nut. 
(C) Two nuts instead of one may be placed on the inner threaded portion so 
that rotation of the outer nut causes the outer nut to abut the inner or 
counter-nut, thus causing the bolt to turn until it is tightened into the 
node. The inner nut is then turned in the same direction until it is 
tightened to the head of the bolt, and then the outer nut is finally 
tightened onto the inner nut. 
(D) The inner threaded portion may be provided with two or more parallel 
bevels or cut-outs so that a wrench may be applied thereto to directly 
rotate the bolt until it is tightened into the node. Then the nut is 
tightened toward the head of the bolt. 
The system of this invention has all the previously mentioned properties. 
The relative position between the centers of the nodes are perfectly 
determined by the manufacturing dimensions of the nodes and rods. The 
introduced distance will be related to the penetration distance so that it 
is possible to assemble and dismantle any rod even after the positions of 
the adjacent nodes have been fixed. The accesses to the nodes through the 
exterior of the same permit the former property to be carried out for any 
geometrical structural design. 
Departing from a spheric shape for the node, obtained by casting, forging 
or mechanical working, the adaptation of a rod in one direction is only a 
question of the formation of the corresponding threaded hole. This can be 
done in any direction of space, obtaining furthermore the same resistant 
characteristics in all of the rods. Provided that the welding of the 
tubular profile to the cap is made under correct conditions, the resistant 
capacity thereof can be completely utilized, since the complete section 
thereof is maintained throughout the length of the rod. 
The most flexible pieces of which the joining system is comprised only 
function under axial forces, which makes it possible to obtain a 
remarkable axial rigidity and a low number of fitting in operations, such 
that the actual behavior or performance does not depart from the 
hypothetical calculated behavior of a space lattice. 
Naturally, the invention is not limited to the specific details of this 
specification, but also encompasses those arrangements which could be 
susceptible to change, with the principle of two threads having reverse 
directions permitting two tightening operations to be made in the same 
rotational direction. Among other various embodiments which are to be 
included within the scope of the invention are, for example: 
(A) The nodes need not be spheric but may be polyhedric, hollow or solid, 
formed by one or plural pieces and made by casting, by shaping and by 
welding or by complete mechanical working processes. 
(B) The rods may be of hollow or filled profiles and have a circular or 
polygonal section, particularly square or rectangular. 
(C) The portion of the bolt having a smaller diameter and which penetrates 
into the node may have right-hand threads, the other portion of the bolt 
together with the nut may have left-hand threads. 
(D) The seating and resting surfaces may, instead of being flat, adopt 
other shapes, particularly truncated which offers certain mechanical 
advantages. 
(E) The caps may be plates with outer truncated surfaces for rods having a 
circular profile or truncopyramidic surfaces for rods having a polygonal 
profile, and with an inner flat, truncated or truncopyramidic surface, 
depending on the needs due to the reduction in weight or length of the 
bolt. 
(F) The tube may be butt-welded to the plate, which may be more favourable 
by way of resistance or angle which can offer manufacturing advantages.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 is a perspective exploded view illustrating a spherical node 1 which 
is shown sectioned along a horizontal plane on which are located the axes 
of four threaded holes 3 each of which has surrounding the entrance 
thereof a bevel 2 which constitutes a seating surface for a step 8 of a 
bolt. The number of threaded holes 3 correspond to the number of rods 12 
to be joined to the node, only the lower half of which is illustrated. The 
ends of two rods are illustrated meeting at the node in the plane of the 
section in an assembled position, the end of one rod being shown in the 
same section as through the node. Also shown is another rod to enter the 
node from below, this rod and the joining structure thereof being 
illustrated as exploded. The rods 12 have a circular section and are 
closed at their ends by caps 11 to which they are joined by means of 
welding 13. A head 10 of the bolt 6 is housed in the interior of the rod 
behind the cap 11. Bolt 6 has two threaded portions 7 and 9 which have 
opposite threads and which are separated by the step 8. A nut 4 is 
threaded by its thread 5 onto the inner threaded portion 9 of the bolt 6. 
After assembly of the rod and of the attachment elements, they cannot be 
separated from interiorly of the rod, since the head 10 of the bolt 6 is 
always situated in the inner part of the tube whose end is closed by the 
cap 11. 
FIGS. 2, 3, 4 and 5 represent a possible arrangement of the successive 
steps of the assembly of an end of a rod to a node. 
FIG. 2 represents a node and an end of a rod facing the same, in a position 
for initiating the assembly. The nut 4 is partially threaded onto the 
portion 9 of the bolt so that the same can be extended into the interior 
of the rod, allowing the end of the rod to be located at a distance from 
the node equal to or smaller than the distance which will remain after 
assembly. 
FIG. 3 represents a first moment of the assembly after having started 
threading of the portion 7 of the bolt into the node. The nut is activated 
by means of a wrench (activation which is represented in the figures by 
means of continuous arrows) the drawing corresponding to the phase in 
which rotation of the nut causes longitudinal movement or advancement of 
the bolt into the node (which advancement is represented by discontinuous 
arrows). 
FIG. 4 represents a more advanced step, after the moment at which the bolt 
has reached its final position with respect to the node. The nut, 
activated by a wrench, rotates along threaded portion 9 and approaches the 
head of the bolt. 
FIG. 5 represents the final position at which the nut has contacted the cap 
and has caused the cap to be against the head of the bolt. After 
establishing these contacts, due to the reverse threading directions of 
portions 7 and 9, continued activation of the nut simultaneously produces 
tightening of the nut to the head of the bolt and of the bolt to the node, 
if this second tightening had not been sufficiently produced previously. 
FIGS. 6, 7, 8 and 9 are perspective views representing four modifications 
to the arrangement represented in FIG. 1, with respect to the movable 
parts of the end of the rod, and specifically to insure rotation of the 
bolt with the nut to thread the bolt into the node. 
FIG. 6 shows an incomplete washer 15 which, when inserted into a 
cylindrical recess 14 in the threaded portion 9 prevents the nut from 
approaching the head of the bolt. Thus, when the nut is rotated, if the 
nut tends to rotate on threaded portion 9 of the screw, when the nut 
establishes contact with the washer, it cannot continue with its advance 
and it will cause the bolt to rotate, which will insure the threaded 
portion 7 is threaded into the node until tightened therein, at which 
moment the washer is withdrawn to continue with the assembly operations of 
FIGS. 4 and 5. 
FIG. 7 shows a bolt with a hole 16 in its threaded portion 9 and a nut 17 
whose rotation with respect to the screw is prevented by a pin 18 which 
passes through the nut into the hole 16 in the bolt. After tightening of 
the bolt to the node, the pin is withdrawn and the assembly operations of 
FIGS. 4 and 5 are continued. Both hole 16 and recess 14 illustrated in 
FIG. 6 will preferably be formed in the zone of portion 9 which is finally 
covered by the nut. 
FIG. 8 shows a screw with two nuts which, in place of the nut 4 illustrated 
in FIG. 1, can each have individually a smaller thickness than nut 4. In 
the first part of the process, the outer nut 19 is rotated and, on 
contacting the inner nut 20 in the form of a counter-nut, will cause the 
bolt to turn until it is tightened into the node. Then, the inner nut 20 
is rotated to move the same against the cap, which also has pressed 
thereagainst the head of the bolt. 
FIG. 9 shows a bolt which there are formed two bevels or cut-out portions 
21 which permit the bolt to be rotated directly by a wrench until it is 
tight in the node, whereafter the nut is rotated until it presses against 
the cap with the head of the bolt also pressed against the cap.