[0001] As known, in the construction of prestressed reinforced concrete railway sleepers,
for the laying of tracks, the harmonic steel bars forming the reinforcement for the
sleepers (usually four pairs of bars, positioned by twos, side-by-side and superposed)
are anchored by means of plates comprising holes and seats, to which each single pair
of bars stays anchored by means of a head formed by cold upsetting at the end of each
bar. The bars are then tensioned to the desired extent, before casting is performed,
moving the plates by drawing with a bolt comprising a screw external to the plates,
which bolt crosses said plates through an appropriate central hole thereof and is
screwed to a nut internal to the plates and bearing thereon.
[0002] This known arrangement has several drawbacks.
[0003] First of all, the nuts of the bolts for drawing the plates and thus the reinforcement
bars of the sleeper, remain each time englobed into the casting and thus into the
sleepers when the forms are being dismantled, with a waste of material involving a
certain expense; furthermore, the anchor plates for the reinforcement bars are likely
to undergo, during drawing, even considerable wobbling which causes the bars to leave
their ideal position, away from the plane provided therefor, up to taking unacceptable
positions: this requires tools and inspections to check said position, involving considerable
costs and waste of time.
[0004] The present invention concerns a plate for the anchorage and tensioning of the reinforcement
bars for prestressed reinforced concrete railway sleepers, which allows to avoid these
drawbacks and which provides furthermore important improvements and advantages in
respect of known technique.
[0005] Said plate is substantially characterized in that it comprises, in a single piece
obtained by hot-pressing of standard steel, two pairs of holes and anchorage seats
for the harmonic steel bars positioned on one of the two reinforcement planes of the
sleepers, and a pair of threaded holes into which screw two tensioning screws for
the tensioning of said bars.
[0006] Said plate is suitably formed of two thicker elongated lateral portions housing said
holes and seats, which are centrally connected by an easily deformable staple of reduced
thickness.
[0007] The invention is now described in further detail, by mere way of example, with reference
to the accompanying drawing, which illustrates a practical embodiment thereof and
in which:
Fig. 1 is an external view of the plate according to the invention;
Fig. 2 is a lateral view of the same plate; and
Fig. 3 shows the plate from the inner side, opposite to that of figure 1.
[0008] As can be seen from the drawing, the plate according to the invention - obtained
in a single piece by pressing of standard steel - comprises two substantially oval
elongated lateral portions 1 and 2, centrally connected by a rectangular staple 3.
[0009] The lateral plate portions 1 and 2 house pairs of holes 4, meant to be crossed by
the ends of the reinforcement bars for the sleepers being constructed, said holes
4 forming seats 5 onto which bear the heads - formed by cold upsetting - of said
bars. Between the holes 4, said portions 1 and 2 comprise larger threaded holes 6
for the tensioning screws.
[0010] The lateral portions 1 and 2 are thicker than the connecting staple 3 and their central
part surrounding the holes 6 is even thicker.
[0011] In use, a plate as that illustrated allows to anchor and tension all four bars of
one of the two reinforcement planes of the sleeper to be cast, using a pair of tensioning
screws screwed into the threaded holes 6 and tensioned by means of two identical coupled
jacks.
[0012] It is evident that the remarkable width of said plate prevents any undesired wobbling
thereof (even when the form is being dismantled) and maintains a perfect lie (or anyhow
within very strict tolerance limits) of the reinforcement bars on their planes. The
plate according to the invention thus eliminates all the most serious drawbacks of
previous technique. It also guarantees an improved prestress diffusion in the concrete
at the heads of the sleeper. Furthermore, the absence of sharp edges in the geometrical
configuration of the sleeper prevents any undesired notching effects in the concrete.
[0013] Moreover the presence, in the structure of the plates, of the staple 3 of reduced
thickness - far more deformable than the rest of the structures - allows the permanent
absorption of any elongation differences in the reinforcement bars, which may always
arise during the tensioning operations (even if these are carried out with a strictly
uniform law, under an even pull of identical jacks). In practice, the plate takes
up a Z-configuration which helps to absorb the differences in behaviour of the bars,
allowing the two tensioning screws to obtain the same tensions in the four bars, independently
of any errors in the mounting, or differences in length, of the bars employed.
[0014] The construction of sleepers is thereby improved with obvious advantages.
[0015] The increased thickness of the plate in correspondence of the holes 6 finally allows
to dispose of quite a long threading, so as to guarantee the positive holding of the
screwing engagement between the tensioning screws and said plate even under highest
stress, though using for the plate low cost materials, as standard steel, and without
having to provide for any special treatments in correspondence of the actual threading.
[0016] Also from the economical point of view, the advantages which the use of the plates
according to the invention allows to obtain are thus quite evident.
1) Plate for the anchorage and tensioning of metal reinforcements in the construction
of prestressed reinforced concrete railway sleepers, characterized in that it comprises,
in a single piece obtained by hot-pressing of standard steel, two pairs of holes and
anchorage seats for the harmonic steel bars positioned on one of the two reinforcement
planes of the sleepers, and a pair of threaded holes into which screw two tensioning
screws for the tensioning of said bars.
2) Plate as in claim 1), formed of two thicker elongated lateral portions housing
said holes and seats, which are centrally connected by an easily deformable staple
of reduced thickness.
3) Plate as in claim 1) or 2), wherein the central part of said lateral portions,
housing the threaded hole for the tensioning screw, is of further increased thickness.
4) Plate as in claims 1) to 3), wherein said lateral portions have an oval shape.