FIELD OF THE INVENTION
The present invention relates to a device for clamping, spherical ball joints
joining spaced-apart structural components in a space frame structure.
BACKGROUND OF THE INVENTION
A space frame is known and constitutes a 3D lightweight rigid Structure, which is
an assembly of linear elements that transfer forces in a 3D manner. A Space
frame Structure comprises a plurality of trusses joined together by a spherical
ball joint. In a Space frame, this connecting joint plays an important role. The
total weight of the joint is around 15% of that of the space frame structure.
Joints are known to have a decisive effect on the strength and stiffness of a
structure, and depend on the connecting techniques for example, bolting,
welding or special mechanical connectors. A joint is also affected by the shape of
the members (trusses) such as circular, square hollow section, rolled steel
section. Members are connected to a single joint. Members are located in a 3D
space and hence the force transfer mechanism is more complex.
Mero connection system is known in the art. Many patents are available in the
art for example, US Patent 4371279. The prior patents deal primarily with space
frame node connectors having fastener means for attaching the frame members
to each other. According to the prior art, space frame structure consists of
spherical node connector in which interlocking struts joined in a geometric
pattern by using bolts, end cone (mandrel), sleeves and connection nodes.
Important components of the space truss joint are as follows: Pipe, weld, end
cone (mandrel), sleeve, bolt and spherical node. Threaded holes are cut in the
sphere. The bolts are having threads to fix inside the mandrel forming a proper
joint system. Once a structure is erected, and suddenly collapses due to failure
of connection parts (like bending and buckling in the bolts causes to subsequent
failure) or design failure in the truss, then it is very costly as well as difficult to
reconstruct the space frame structure.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a device for clamping
spherical ball joints joining spaced-apart structural components in a space frame
structure.
Another object of the invention is to propose a device for clamping spherical ball
joints joining spaced-apart structural components in a space frame structure,
which acts as a parallel path to absorb axial loads.
A further object of the invention is to propose a device for clamping spherical ball
joints joining spaced-apart structural components in a space frame structure,
which increases safety of the spherical joints.
SUMMARY OF THE INVENTION
According to the invention, a clamping device is provided to support the erected
trusses. Each joint in top chord and bottom chord consists of a pair of O clamps,
tension bars and steel bolts. The main structural considerations in the design of
space truss elements are the buckling of compression chords and web bracing
members including design of the joints enabling effective and efficient
transmission of tension forces between the bars and nodes whilst minimizing
secondary bending effect. This clamping device strengthens the joint as well as
derives its strength from the inherent rigidity of the triangular frame.
Accordingly, the flexural loads transmitted in the form of tension and
compression loads along the length of each strut, will always be less. One each
clamping device has to be placed at each and every joint of the erected
structure. Figure 1 shows a typical space structural frame and a typical joint
configuration.
Clamping arrangement are made over existing spherical joint. Configuration of
clamping arrangement is like this-two Structural truss member, four Clamps, four
tension bars, four high tensile steel bolts, four Washers and four Nuts. This
clamping device is placed at each and every joint of the erected structure. The
device configuration is based on analytical and experimental results. The analysis
is carried out under certain assumptions, for example, O. clamp and truss
member are assumed integral in analysis.
Various types of joint configurations were analyzed, tested for maximum axial
loads to arrive at an optimum design, ease of fabrication and ease of
implementation. The details of analytical and experimental results are presented
below.
Experimental Studies and Analytical Results
The deflection and stress values of the device including the constituent
components are as shown in Tables 1 & 2. A detailed finite element analysis is
carried out. The joint modeled with 3D Finite elements and analyzed using NX
NASTRAN software for the required axial load of 200kN.
Evaluation of linear static analysis (Clamping Arrangement)
Load testing of the inventive clamping device
Tests were conducted on three samples:-
i) First one is with lesser clamp width 60mm and 6mm thick and 2nos. M24 bolts
and one tension bar of 6mm on each side of clamp.
ii) Second one is with clamps of 95mm wide and 4nos. of M16 Bolts and two
tension bars of 6mm on each side of clamp.
iii) A sample 3 of the proposed clamping arrangement was made Clamps of
95mm wide and 2nos. of M24 Bolts and 2tension bars of 12mm tested on each
side of clamp. M24 Bolts is to be designed to take care of the maximum bearing
stress with flat surfaces.
RESULTS
i) The clamps of Sample 1 started yielding after reaching a load of 13Tonnes
and experiment was carried out till a load of 19.2 Tonnes is reached.
ii) As seen from the experimental results of sample 2, the clamp withstood the
maximum applied load of 225kN.
iii) A sample 3 of the proposed clamping arrangement was made and the same
was tested, by applying a maximum load of 22.96Tonnes (225kN), result was
similar to sample 2.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figures 1,2,3,4 each shows the existing spherical joint connection system of prior
art, in which:
Figure 1 is an existing spherical joint connection system which shows typical
connection detail of the system.
Figure 2 shows solid 3d Isometric front and back view of existing spherical joint
connection system.
Figure 3 shows an exploded view of the component of existing spherical joint
connection system.
i) Spherical Node (P) ii) Hexagonal Sleeve (Q) iii) Mandrel or Cone (R) iv) Bolt
(S)
Figure 4 In space frame structure (8 tubular members-4 horizontal and 4 inclined
members- connected to Mero node)
Figure 5 shows the typical placement of a clamping device at the existing
spherical joint.
Figure 6 shows tubular members of the device out of which four connecting
members are horizontal (a) and four connecting members are inclined (b)
according to the invention.
Figure 7 is an assembled perspective view of a clamping device for spherical joint
according to the invention.
Figure 8 is an exploded isometric view showing a process for disassembly of a
preferred embodiment of the invention.
Figure 9 is a detailed view showing a space frame using an inventive clamping
device in the joint.
Preferred embodiments of the present invention will be further described in detail
hereinafter.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE
INVENTION
A clamping device of prior art is shown in figure 1.
Referring to figure 2 & 3, a prior art spherical joint connection system has mainly
six components (i) Spherical Node 'P' (ii) Hexagonal Sleeve 'Q' (iii) Mandrel or
Cone 'R' (iv) Bolt 'S' (v) Key (Keyway 'T' shown in figure 2.) (vi) Pin (Pinhole 'U'
shown in figure 2).
Exploded view of a Mero connection system is shown in figure 3 (prior art US
Patent 4371279). Use of a Hexagonal sleeve or socket 'Q' the entire bending
moment is taken by socket 'Q' instead of bolt 'S' thereby reducing the risk of bolt
failure. The sphere 'P' is flattened with a minimum surface diameter of 1.8d
around the bolt hole such that the connecting member fully rests on surface and
any buckling load is transferred to the spherical ball 'P' directly without stressing
the bolt by the hexagonal sleeve. If the ball is in perfect spherical shape, the flat
end of the connecting Hexagonal sleeve (sometimes called as Force Limiting
Device) makes a line contact instead of a surface contact. This may lead to a
sway in the connecting tube about the bolt fixed on the sphere. Furthermore, the
connecting joint is in perfect spherical shape and hexagonal sleeve can rotate on
spherical surface, thus causing bending in the bolt and leading to subsequent
failure.
A spherical joint 'P' with a series of flat facets for a space frame having
connecting members or nodes and tubular structural member is provided in
which the shank of a connecting bolt'S', whose head is located within the hollow
end portion of the tube, extends through an aperture in the tube end for
engagement with a threaded opening in the node. The tube shank has a
longitudinally extending keyway 'T' formed therein in which a key is slidably
received. A sleeve having an unthreaded inner bore receives the bolt shank 'S'
and has an internal keyway T' which receives a portion of the key to rotatably
lock the nut and bolt together so that the nut may be rotated to rotate the bolt
and engage its shank in the threaded opening of the connecting member. In this
system, hollow tubular structural members are connected to node points or
connecting elements by the use of bolts mounted in the ends of the tubes. The
bolt'S' should form a fixed connection with the mandrel that is to be welded to
the tubular truss member. Proper torque and axial force for mild steel pieces
tightened together by means of hexagon socket head cap screw. The bolts 'S'
are slidably mounted in the tube ends and are held from inadvertently falling into
the tool end by a spanner sleeve pinned to the bolt. In the illustrated
embodiment of the invention, structural elements are hollow tubular members
whose ends are closed by mandrel 'R'. These tube ends are connected by the
bolt and nut assemblies to the nodes. Bolt'S' and sleeve 'Q' assembly is mounted
on the mandrel 'R' of the tube. The assembly includes a bolt having a head and a
shank which extends from the head to a free end. The bolt is slidably received in
an unthreaded aperture or opening formed mandrel. The bolt is assembled in the
mandrel 'R' before the mandrel 'R' is welded to the open end of the tube. To
prevent complete retraction of the bolt into tube the bolt is provided with a
longitudinal keyway formed in its threaded shank. To prevent removal of sleeve
from shank, the sleeve is pinned to key by a pin. Sleeve is rotated by any
convenient wrench and rotation is continued until a tight connection is formed
between the tube and the node. To disassemble the space frame, the structural
joint of the present invention is readily disassembled by reverse rotation of nut.
The bolt, the Force limiting device, the mandrel and the connecting tube should
behave as a perfect single system for proper transmission/distribution of forces
in the space structure.
Figure 4 shows a prior art spherical joint connection system in space frame
structure having eight tubular members in which four horizontal truss members
and remaining four are inclined members, these are connected to flattened end
of Spherical node.
The embodiment in Figure 5 shows the clamping device in very simple manner
and can be easily understood. The figure illustrates the fundamental constructive
principle of the space frame according to the present invention. To construct a
space frame, two horizontal tubular members (a) are joined at spherical joint
with clamping arrangement (refer figure 6). 4 Nos. Horizontal tubular members
(a) and 4 Nos. inclined members (b) form an upended pyramid shape.
Figure 7 shows an assembly of this invention, in which all the components put in
single unit and presented in perspective way. In the embodiment shown in figure
7, the manner in which the various component parts are attached to the holes in
this arrangement. Clamping is done over existing spherical joint connection
system for strengthening the already erected space frame structure. Clamping
arrangement consists of mainly clamps (2) and tension bars (3). Clamps (2) and
tension bars (3) make a right angle to the structural truss member (1).
Each joint on the top chord and also at bottom chord are strengthened. The
transverse space frame pipes are joined together at the space ball joint with
clamps (2) and tension bar (3) on both sides O-clamp - a clamp in the shape of
the letter C. C-clamp is a type of clamping device typically used to hold a wood
or metal work piece, and are often used in, but are not limited to, carpentry and
welding. These clamps are called "O"clamps because of their C shaped frame,
but are otherwise often called G-clamps or G-cramps.
The clamps (2) are bolted over the required pipe with bolts (4) made up of high
grade tensile steel on both sides of the clamp. Tack welding is done for proper
mating between clamps (2) and structural truss members (1). In addition to the
above, the clamp has to be fully welded to the pipe on one side and tack welded
on the other side with a minimum thickness fillet weld. Tack welding is used to
weld two pieces together in order to form a basic right-angle joint. Tack Welding
refers to a temporary weld used to create the initial joint between two pieces
being welded together. The welds should be fundamentally sound, considering
they provide the foundation for the entire joint. Additional benefits of tack
welding include ease of removal in order to correct improper alignment with
components welding together, stabilizes the overall alignment of components
welding together, reduces movement and distortion during the welding process
and offers temporary joint strength if an object needs to be moved or
repositioned.
After tack welding between clamps (2) and structural members (1), two tension
bars of standard thickness plates are bolted over structural members (1) side by
side. Bolt (4) is inserted into the hole of assembly (7) of clamps (2) and tension
bars (3), locked by washer and lock nut. Bolt is tightened by wrench. Washer is
used here to distribute the load of a threaded fastener, such as a screw or nut.
High quality bolted joints require hardened steel washers. Nut meant for locking
mechanisms keep bolted joints from coming loose. It also resists loosening under
loading and torque. This arrangement has to be placed at each and every joint of
the erected structure at site. It is important that the quality of material of
clamps, tension bars and bolts and proper weld quality to be ensured with
quality control measurements, as the final safety of structure depends on this.
The clamping arrangement involving O clamps and bolts is a parallel path for
taking axial loads (along with bolts and spheres). The design is made for the
extreme contingency of having to support entire axial load (if spherical joint
fails). Hence quality check from considerations is very important.
Referring to exploded view in figure 8, the entire components are disassembled
in very elegant manner. For showing the components, different numerals are
used. The upper O clamp 2 numbers '2i' and lower O clamp 2 number '2j' are
fastened to the truss member T by upper tension bar '3i' and lower tension bar
'3j'. Tension bar '3i' and '3j' and clamp '2i', '2j' are connected by bolts '4',
washers '5', nuts '6' which are inserted centrally into located drilled holes '7' of
the member. Truss member 'I' and O Clamp '2i' and '2j' both are tack welded to
each other. The upper O clamp '2i' and lower O clamp '2j' are similar in every
respect. Upper tension bar 3i' and lower tension bar '3j' are also similar in every
respect. The nut '6' is used for locking to the clamp and tension bar. The circular
drilled hole V in tension bar '3i' and '3j' and clamp '2i' and '2j' are for receiving a
bolt. A washer '5' is used along with the nut '6' to ensure that the tension bar '3i'
and '3j' and clamp '2i' and '2j are securely fastened. In order to fasten the
members to the tension bar '3i' and '3j' and clamp '2i' and '2j', the bolts '4' with
the washers '5' t hereon are screwed part way into the threaded holes. The
heads of the bolts '4' and washers '5' are then inserted. The bolts are then
tightened against the junction of joint. Welding provides a rigid joint between
clamp and pipe. Crossing members, truss member 'I' and clamp '2i' and '2j' are
joined by tack welding. This welded joint section has enough reliable strength.
This increases buckling strength. It is inexpensive and light in weight. This
welding is to be done in situ at a height. Only one side of the clamp it will be
accessible. Hence welding must be properly done with extreme care. Quality
must ensure this. Some tack welding on the other side, if possible must be done.
If O clamps have relative movement with respect to pipes, the joint would be
totally ineffective. Forming in the diameter of O clamps must confirm to the
outer diameter of corresponding pipe.
The quality of bolts is ensured and lock nut is provided to ensure that bolts do
not became loose under loading conditions. Height and width of the O clamps is
the most crucial dimension. The intermediate crane columns which are to be
used to vertical support, a proper downward contact has to be properly checked.
This has to be done on every individual column depending upon local
requirement. Overall quality of fabrication must be maintained.
After implementing this clamping arrangement to the joint, all members perform
equally well in the tension and compression. The structure has excellent
structural efficiency and stability.
In figure 9, a front view as well as a side view is shown to illustrate the
invention. This is projected view in which front view gives length and height
dimension while in side view we can get height and width dimension of the
whole assembly.
WE CLAIM :
1. A clamping device disposable over a spherical ball joint joining spaced-
apart components in a space frame structure, the device comprising a
plurality of, O - shape clamps welded over two horizontal tubular
members of the spherical ball joint, and further jointed to a plurality of
tension bars by means of bolts, lock nut, spring washer, each joint on the
top chord and at bottom chord is strengthened, wherein a plurality of
transverse space frame pipes are joined together at the space ball joint
with the clamps and tension bar on both sides.
2. A clamping device as claimed in claim 1 wherein said transverse space
frame pipes comprises at least four horizontal and four inclined tubular
members.
3. The clamping device as claimed in claim 1 wherein at least four clamps
are provided.
4. A clamping device as claimed in claim 1 wherein at least four tension bars
are provided.
5. The clamping device as claimed in claim 1 wherein four each hexagonal
bolts are used for connecting clamps and tension bars.
6. The clamping device as claimed in claim 1 wherein at least four holes are
provided to each clamp and each tension bar.
7. A clamping device as claimed in claim 1, comprising at least four spring
washers.
8. A clamping device as claimed in claim 1, comprising at least four nuts.

ABSTRACT
The invention relates to a clamping device disposable over a spherical ball
joint joining spaced-apart components in a space frame structure, the
device comprising a plurality of, Ω - shape clamps welded over two
horizontal tubular members of the spherical ball joint, and further jointed
to a plurality of tension bars by means of bolts, lock nut, spring washer,
each joint on the top chord and at bottom chord is strengthened, wherein
a plurality of transverse space frame pipes are joined together at the
space ball joint with the clamps and tension bar on both sides.