Tensioning bundles comprising a plurality of tensioning members such as stranded wires, rods or single wires

Tensioning bundle includes tensioning members running parallel to one another such as stranded wires or single wires. According to the invention the tensioning bundle as a whole is covered with at least one synthetic resin in an extruder. For tensioning such bundles the tensioning members may be tensioned individually or jointly.

The invention also relates to a process for tensioning such tensioning 
bundles. 
Up to now it was conventional regarding the manufacture of such bundles to 
provide the stranded wires or wires individually with a synthetic resin 
covering, e.g. made of polyethylene, a grease coating or a galvanic 
coating and to then bundle several of such stranded wires or wires. It is 
further known to galvanically coat or grease the stranded wires or wires 
prior to covering them with synthetic resin. Such stranded wires or wires 
can move within the synthetic resin covering. The disadvantage of the 
bundling of the stranded wires or wires coated with synthetic resin lies 
in the fact that a relatively thick bundle is obtained. 
Furthermore tensioning members consisting of rods, wires or stranded wires, 
Individual or bundled, were carried in enveloping pipes of sheet metal or 
synthetic resin the filling of the cavity between the tensioning members 
and the enveloping pipe being effected by means of cement or so-called 
permanently plastic substances by pressing in the filling material before 
the tensioning of the tensioning members or thereafter. 
At their ends the tensioning members were provided with anchoring means and 
were tensioned. They can be accommodated inside or outside a supporting 
structure; in the latter case the enveloping pipe itself must also be made 
of corrosion-resistant material. 
The disadvantages of the known processes were often the corrosion 
protection for which an operating process of its own was necessary 
resulting in high time consumption and expenditures. Also, the risk of 
faults in protecting the tension members was not inconsiderable. 
Disadvantages arising from the rods, wires or stranded wires touching at 
deflecting regions of the tensioning members which resulted in increased 
friction during pretensioning and thus losses of pretensioning forces as 
well as reduction of strength, in particular fatigue strength, must also 
be mentioned. 
OBJECTS AND THE INVENTION AND GENERAL DESCRIPTION 
It is the object of the invention to provide measures by which, whilst 
avoiding this disadvantage, the space requirements for the tensioning 
bundle are minimized and the latter can furthermore be manufactured in a 
more labour saving way than previously. 
To attain this object the invention proposes that the tensioning members in 
the bundle run parallel to one another and are jointly covered by a 
synthetic resin. 
In the case of cables for electrical installations it is indeed known to 
envelope several insulated wires with a joint synthetic resin covering. 
Apart from the fact that these cables are not intended for reinforcing 
concrete, the wires Inside them do not run parallel but are joined in a 
plait. 
According to a further feature of the invention, the stranded wires or 
wires are provided, preferably in an extruder, with a corrosion-protecting 
and/or lubricating material, e.g. grease and/or a galvanic coating and/or 
a thin coating of hard synthetic resin prior to the covering being 
applied. 
When applying the synthetic resin, the stranded wires or wires often lie in 
such a way that the synthetic resin can also penetrate between the 
stranded wires or wires whereupon the bundle is compressed in order to 
attain the desired small diameter. In this context it may happen that the 
covering does not adopt the exact desired surface outlines. In order to 
avoid this risk, the invention proposes the application of a second 
covering of synthetic resin. This covering can bond homogeneously with the 
first covering so that an integral covering is formed. 
According to a further feature of the invention it is also possible to 
manufacture the second covering in a synthetic resin different from the 
first covering. 
With such bundles difficulties may also arise with regard to the 
characteristics during bending or rolling up. By using harder synthetic 
resin, respectively a thicker layer of soft resin in applications where a 
stronger protection of the stranded wires by the covering is required, an 
excessive load may result in the case of excessive bending and resultant 
damage to the covering, or the bundle cannot be rolled to sufficiently 
small dimensions as required e.g. for transport purposes. 
It is therefore an additional object of the invention to provide measures 
by which the tensioning bundles are provided with sufficiently protecting 
coverings which can be rolled to sufficiently small dimensions. 
In order to solve this problem a further feature according to the invention 
proposes that the stranded wires or wires are provided with an inner 
covering made of soft synthetic resin and an outer covering of a harder 
synthetic resin. 
Within the scope of the invention the stranded wires or wires can be 
provided with a plurality of concentric coverings of synthetic resin a 
lubricating layer being provided between at least two coverings, 
permitting the bundle with the inner covering to move during tensioning 
thereof in relation to the outer covering. 
The coverings and optionally also the lubricating layer are applied by 
successive extruders. 
In the case of buildings where several stranded wires have to be laid next 
to one another, it is advisable to combine the stranded wires with the 
preferably soft synthetic resin into a tape. 
Finally it is the object of the invention to eliminate the above mentioned 
disadvantages of the known processes. This object is attained by the 
tensioning bundle according to the invention, the rods, wires or stranded 
wires being tensioned individually or jointly. 
Further objects and embodiments according to the invention are evident from 
the following description in which examples of tensioning bundles 
according to the invention are explained in more detail with reference to 
drawings.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
In this context FIGS. 1 to 3 and 5 to 9 show only one of the stranded wires 
whereas the remaining stranded wires are indicated in a simplified manner 
by a circle only. 
FIG. 1 shows a known stranded wire bundle. This comprises individual 
stranded wires 1 which are each individually provided with a synthetic 
resin covering 2. In the example shown, six such stranded wires 1 are 
arranged around a central stranded wire 1' parallel to one another. Such a 
stranded wire bundle has to occupy relatively much space when used as a 
pretensioned stranded wire bundle due to the covering 2 separately applied 
onto each stranded wire 1, respectively 1'. 
The bundle shown in cross section in FIG. 2 has stranded wires running 
parallel to one another, as provided according to the invention and has 
been injection coated as a whole with preferably soft synthetic resin, 
e.g. polyethylene, by means of an extruder causing the synthetic resin 3 
to form a coating as well as penetrating into the spaces between the 
stranded wires 1. Before applying the covering of soft synthetic resin, 
the stranded wires may be dry, they can however, as illustrated, also 
receive a coating 4 serving as corrosion protection, composed of grease, a 
hard synthetic resin or applied by galvanic alloy. This coating, in 
particular if it consists of grease, may also fill out the inner spaces 
between the tensioning members. 
FIG. 2 shows a wrap of stranded wires arranged around a central stranded 
wire. It is, however, also possible to superimpose any number of wraps 
over one another. 
In FIG. 3 the bundle of parallel stranded wires 1 is enveloped by a 
double-layered covering, respectively by two concentrical coverings 3, 5. 
The covering is preferably effected in two stages by means of two 
extruders. In this context it is advisable to first fill the space between 
the stranded wires 1 and in such a way that the distance of the stranded 
wires is greater than in the final stage, whereby the synthetic resin also 
penetrates into the space between the inner stranded wire, and the 
stranded wires surrounding it, whereupon the stranded wires are compressed 
to attain the smallest possible diameter of the covered bundle. 
In a second stage the outer synthetic resin covering 5 is applied so that a 
round covered bundle arises. 
The two synthetic resins may be selected optionally according to the 
desired characteristics of the covered bundle. Thus it is possible to make 
both coverings of the same synthetic resin or the inner covering 3 of a 
synthetic resin softer than the outer covering 5. This process is 
preferably effected by successive extrusions of two extruders set up in 
series. It stands to reason that within the scope of the invention the 
inner covering may be made of a synthetic resin harder than the outer 
covering. 
According to a further feature of the invention a lubricant may be included 
between the two coverings 3 and 5, or rather between the outer covering 5 
and a further concentric covering, making it possible during tensioning of 
the bundle for the bundle with the inner covering to move relative to the 
outer covering. This kind of covering may also be applied in an extrusion 
process. 
Often it is necessary, however, to accommodate several stranded wires next 
to one another. In this case the stranded wires 1 may be enveloped by the 
envelope 4 and be united to a tape next to one another by the synthetic 
resin 3. In FIG. 4 the tape consists of two and in FIGS. 5 and 6 of four 
stranded wires, FIG. 6 showing a tape with a covering different from that 
of FIG. 5. In the embodiments according to FIGS. 4 to 6 the stranded wires 
1 are separated from one another by longitudinal webs 7 of the covering. 
It is, however, also possible to arrange the stranded wires closely 
touching one another so that the webs 7 become inapplicable. 
It is left to the designer to arrange the stranded wires parallel to one 
another, into other cross sectional configurations of the stranded wire 
bundles, as is shown for example in FIGS. 7 to 9. 
Within the scope of the invention the number and the cross sectional shape 
of the superimposed coverings as well as the number of coatings of 
lubricants between each two coverings are not limited. 
This permits the outer shapes of the bundles to be optionally designed and 
to be accommodated in a very space-saving manner both within a building 
structure as well as along its outer wall. 
Instead of stranded wires single wires may also be combined to a bundle 
within the scope of the invention, and such single wires may, prior to the 
application of the covering with the soft synthetic resin, be provided 
with a galvanic coating or a coating of grease or thin hard synthetic 
resin. For anchoring purposes the ends of the bundles so obtained are 
stripped of the synthetic resin covering, the surfaces of the stranded 
wires being cleaned so that they can then be bonded by concreting, casting 
or clamping. 
For anchoring the stranded wires, the end of the bundle may be split open 
as shown in FIG. 10, and each end of the stranded wire, respectively the 
tensioning member is provided with its own anchoring means 8. Naturally it 
is also possible to anchor both ends in a joint anchoring plate. Although 
in the present case a bundle of only two stranded wires is shown, in the 
same way bundles consisting of more than two tensioning members, may 
likewise be separated into individual members. 
The bundles according to the invention are used for example for the 
pretensioning of supporting structures with external or internal 
accommodation of the bundles, for ground anchors or as diagonal cables, 
e.g. in the case of suspended bridges. Inter alia they also have the 
advantage that they can adapt to any desired course.