The present disclosure relates to an improved mechanism having the features of the preamble of claim 1.
Mechanisms of this type are well known. They are useful for the construction of space frames of any structural form, e.g. for buildings.
The main advantage of mechanisms of this type is that there are no openings through the walls of the structural components of the tubular framework members, e.g. relatively large openings through the walls of the conical end, for the insertion of the bolts, and longitudinal slotted holes through the walls of the sleeve, for the passing through of the pin and for the longitudinal movement of the bolt with the pin with respect to the sleeve, as is shown in
In addition to the aesthetic problems, the above mentioned openings through the walls of the structural components of the tubular framework members create structural safety problems, as will be illustrated hereinafter.
In practice, a relatively large opening is made on the pipe portion of the tubular framework member for the insertion of the bolts, which reduces both the ultimate tension and the ultimate compression resistance of the pipe. In the case of compression, it is possible to have failure of the pipe due to asymmetrical local elastic-plastic buckling of the walls of the pipe ("asymmetrical" because of the fact that only one opening is provided, although claim 2 of document
Furthermore, the longitudinal slotted holes through the walls of the sleeve, as in
In addition to the above mentioned strength problem of the sleeve, the longitudinal slotted holes through the walls of the sleeve expose the most highly stressed portion of the bolt to the environment; thus it is possible for dust and water to collect between the bolt and the walls of the sleeve. In this case, the presence of specific chemical compounds in the environment, e.g. aqueous electrolytes, particularly when containing H2S, may induce cracking of the bolt. This cracking (stress-corrosion cracking) may take the form of a relatively slow, stable crack extension or, as is often the case, an unpredictable catastrophic fracture. It is thus necessary to effectively protect the bolt with the pin against corrosion.
For many years, it has been the usual practice to protect the bolt with the pin against corrosion with electroplated coatings. Since, however, bolts are now made of high-strength steels, e.g. of property class 10.9, electroplating - including pickling for scale and rust removal - increases the probability for a hydrogen-induced fracture of the bolt (hydrogen embrittlement). Hydrogen embrittlement can cause dangerous and sometimes catastrophic failures, if it occurs in critical tubular framework members, particularly in wide-span roof structures. The probability of encountering hydrogen embrittlement can be reduced by using lower-strength steels, by limiting immersion times in acid or plating baths, and by in-process (intermediate) baking. According to International Standard ISO 4042:1999(E) "Fasteners - Electroplated coatings", page 3: "In cases of parts with high tensile strength or hardness or which have been surface hardened, which have absorbed hydrogen and are under tensile stress there is the risk of failure due to hydrogen embrittlement"; and, page 4: "Complete elimination of hydrogen embrittlement cannot be assured. If a reduced probability of encountering hydrogen embrittlement is desired, alternative procedures should be evaluated".
Document
Notwithstanding the many advantages of mechanisms of this type, the problem of the confirmation - that the bolt is completely screwed into the threaded hole of the node connector - still needs to be solved.
Incomplete (i.e. less than the required) length of engagement in the threaded assembly is likely to happen under the following possible conditions: when the length of the internal thread of the node connector has been manufactured to a length shorter than the required length of engagement, when there is a manufacturing error, or damage, in the internal thread of the node connector or in the external thread of the bolt, or when the erection worker has not fully screwed the bolt into the threaded hole of the node connector. If this occurs in the assembled space frame, the corresponding mechanism cannot carry tension; and, when the space frame is loaded, the redistribution of internal forces may overload neighboring tubular framework members.
If failure of the threaded assembly should occur, it is preferable for the bolt with the pin to break rather than to have either the external or internal thread stripped; and the length of engagement of mating threads should be sufficient to carry the full load necessary to break the bolt without the threads stripping. This length determines the required length of engagement to prevent stripping of either the external or internal thread in mechanisms of this type.
It is an object of the present invention to provide a solution to the problem of the confirmation that the bolt with the pin is completely screwed into the threaded hole of the node connector; and, as a consequence, that the corresponding mechanism in the assembled space frame can carry tension as well as compression.
Another object is to provide an improved mechanism which solves the connection problem of the pipe in a simple, economical and aesthetic manner; and this with a minimum number of different components.
Still another object is to provide an improved mechanism with increased structural reliability.
These objects are achieved by an improved mechanism having the features of the characterizing part of claim 1.
By rotating the sleeve, a torque is transmitted to the bolt through the pin, thus screwing the bolt into the node connector. When the bolt is fully screwed, the sleeve is in contact with both the node connector and the conical end. By applying an appropriate torque to the sleeve, the bolt with the pin tightens the node connector and the conical end on the sleeve, the bolt head being in contact with the rear bearing surface of the conical end. Next, the socket set screw is fully screwed. If the rear end of the socket set screw is at least flush with the outermost peripheral surface of the sleeve, this confirms that the bolt with the pin is completely screwed into the threaded hole of the node connector. In the assembled three-dimensional structure, tension from the pipe to the node connector, and conversely, is transmitted through the bolt; compression is transmitted through the sleeve.
Some advantages of the present invention are:
The invention will be further described, by way of example only, with reference to the accompanying drawings wherein like elements are numbered alike in the several Figures:
Hereinafter, the best mode for carrying out the present invention is described in detail.
The structure according to
The three-dimensional structure according to
The node connectors 1 are spherical, with partial flat bearing surfaces 11, distributed on their outer surface, having radial threaded holes 10.
Each tubular framework member 30 comprises one metal pipe 9 and two improved mechanisms 12, fixed to the ends of the metal pipe 9, which connect the ends of the metal pipe 9 to the node connectors 1.
Each improved mechanism 12 comprises a bolt 8, a pin 4, a sleeve 3, a socket set screw 2 and a conical end 7.
The bolt 8 has a hole for the passing through of the pin 4 and a radial groove 18, preferably cylindrical with a bottom which has the form of a spherical cap. The axis 5 of the radial groove 18 is perpendicular to the longitudinal axis 15 of the bolt 8; and is in the same plane with the longitudinal axis 15 of the bolt 8.
The sleeve 3 has a front bearing surface 23, a rear bearing surface 13, a longitudinal hole for the passing through of the bolt 8, two opposite longitudinal grooves 14, on the walls of the longitudinal hole, where the ends of the pin 4 move, and a radial threaded hole 20 of small diameter, which has the same circumferential position with either one of the two opposite longitudinal grooves 14, the axis 6 of which is approximately perpendicular to the longitudinal axis 15 of the bolt 8 and is in the same plane with the longitudinal axis 15 of the bolt 8. The small diameter radial threaded hole 20 is very close to the rear bearing surface 13 of the sleeve 3.
The socket set screw 2 is screwed through the radial threaded hole 20.
The conical end 7 has a longitudinal hole 17 for the passing through of the bolt 8 and is welded to the pipe 9 with a circumferential weld 16 which has preferably been ground.
The bolt 8, the sleeve 3, the conical end 7 and the pipe 9 have a common longitudinal axis 15. This common longitudinal axis 15 is the longitudinal axis of the tubular framework member 30.
The axis 5 of the radial groove 18 and the axis 6 of the radial threaded hole 20 are configured to have the same circumferential position, and the same longitudinal position exactly when the bolt 8 is fully screwed and the bolt head 19 is in contact with the rear bearing surface 29 of the conical end 7, as is shown in
When the bolt 8 is at the rearmost position, as shown in
Just before the bolt 8 reaches the most forward position of its relative movement with respect to the conical end 7, as is shown in
If the rear end 24 of the socket set screw 2, after it has been fully screwed, projects outwardly from the outermost peripheral surface 25 of the sleeve3, as is shown in the longitudinal section and in the section B-B of
The maximum relative displacement of the bolt 8 of the improved mechanism 12, with respect to the conical end 7, is restrained by the contact of the pin 4 on the front bearing surface 28 of the conical end 7, when the socket set screw 2 does not project into the longitudinal groove 14 of the sleeve 3, as shown in the longitudinal section and in the section B-B of
Towards the opposite direction, as is shown in
In areas with low temperatures and when it is possible for water to collect within the tubular framework member 30 (e.g. during temporary storage before erection), repeated freezing can lead to rupture of the wall of the pipe 9 through successive expansion and contraction until the elongation limit is reached. In order to prevent this phenomenon, the small opening 26 at the end of the pipe 9 is placed at the lowest relative elevation during the assembly of the space frame and is sealed using a plug 27 after the construction of the roof cladding.
The improved mechanism of
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