EP0340331A1 - Process for making identical elongated products on a pre-stressing bed - Google Patents

Abstract

In the making of elongated products of prestressed concrete - in particular turnout sleepers - in a prestressing bed, one additional, as a rule lost, concrete abutment element (7, 8) each is cast in the end areas (5, 6) of the formwork (l) at the start and end of the prestressing bed together with the planned products (2/1, 2/2...2/n). The length of the abutment elements (7, 8) is dimensioned in such a way that the friction force between concrete and prestressing-bed formwork can absorb the component prestressing force which acts on the products in the end position (2/1, 2/n) due to transposition of the prestressing force during setting of the concrete. <IMAGE>

Description

The invention relates to a process for the production of long prefabricated parts in the fitted bed, as described generically in the characterizing part of claim 1, and means for carrying out the method.

Preloaded long finished parts with a constant cross-section, as is the case, for example, with turnout sleepers, are preferably manufactured one after the other in long clamping beds. They are connected to one another during production with the full cross-section or at least with the tendons spanned from abutment to abutment and are separated from one another by separating cuts after the concrete has hardened.

During the manufacturing process, redistribution of the prestressing force occurs, which can lead to damage to the precast elements: When the concrete hardens in the formwork through which the prestressing tendons are applied, heat of hydration develops, which heats and lengthens the precast strand and the formwork equally, but does not change the length of the prestressed bed.

• 1. Hydratationserwärmung und Wärmedehnungen finden im vollständig weichen Beton statt, die Abkühlung in einem Beton mit vollständig entwickelter Haft­festigkeit. Die Vorspannung ist festgelegt durch ein ε_v = 5mm/m = 5 x 10⁻³, bezogen auf die Spanngliedlänge von 80 m. Eine Erwärmung von 20° durch Hydratation von
  ε_t+ = α_t+ x Δ t = 1,0 x 10⁻⁵ x 20 = 2 x 10⁻⁴
  Der Spannungsverlust beträgt in diesem Fall
  
  d.h. Δ6 ist ein vernachlässigbarer Wert.
• 2. Hydratationserwärmung und Wärmedehnung finden im bereits vollständig erstarrten Beton bei voll ausgebildeter Haftung statt. Die Spannkraft im Fertigteil verändert sich dann nicht. Die Län­genänderung des Fertigteilstrangs bewirkt eine entsprechende Verkürzung, d.h. Entspannung der nicht in Beton eingebetteten Endabschnitte der Spannglieder. Die Längenänderung des Fertigteil­strangs beträgt bei einem 80 m langen Spannbett:
  Δℓ₁ ≈ ℓ₁ x α_t x Δt = 80 x 10⁻⁵ x 20
  = 1600 x 10⁻⁵ = 1.610⁻² m
  Die Längenänderung aus Vorspannung in den Endabschnitt beträgt bei ℓ₂ = Länge eines Endabschnitts = 1,5 m:
  Δ ℓ₂ = 2 x ℓ₂ x ε_v = 2 x 1,5 m x 5 x 10⁻³ = 1,5 x 10⁻²,
  d.h. diese Längenänderung hat dieselbe Größenord­nung wie die Längenänderung des Stranges, d.h. an den Endflächen ist die Vorspannung null. Der Grenzfall 2 ist demnach der kritische Fall und ist gekennzeich­net durch das Verhältnis freie Spannglied-Endlängen zu Spannbettlänge.

The stress redistribution takes place between two borderline cases and is explained using the example of an 80 m long bed with 83 m abutment spacing:

• 1. Heating and expansion of hydration take place in completely soft concrete, cooling in a concrete with fully developed adhesive strength. The preload is determined by a ε _v = 5mm / m = 5 x 10⁻³, based on the tendon length of 80 m. A heating of 20 ° by hydration of
  ε _{t +} = α _{t +} x Δ t = 1.0 x 10⁻⁵ x 20 = 2 x 10⁻⁴
  The voltage loss in this case is
  
  ie Δ6 is a negligible value.
• 2. Heating and thermal expansion take place in the already fully solidified concrete with fully developed adhesion. The clamping force in the finished part does not change. The change in length of the prefabricated strand causes a corresponding shortening, ie relaxation of the end sections of the tendons not embedded in concrete. The length change of the prefabricated strand for an 80 m long bed is:
  Δℓ₁ ≈ ℓ₁ x α _t x Δt = 80 x 10⁻⁵ x 20
  = 1600 x 10⁻⁵ = 1.610⁻² m
  The change in length from prestressing in the end section is at ℓ₂ = length of an end section = 1.5 m:
  Δ ℓ₂ = 2 x ℓ₂ x ε _v = 2 x 1.5 mx 5 x 10⁻³ = 1.5 x 10⁻²,
  ie this change in length is of the same order of magnitude as the change in length of the strand, ie the prestress on the end faces is zero. Limit case 2 is therefore the critical case and is characterized by the ratio of the free tendon end lengths to the length of the prestressed bed.

The real hardening process lies between the two borderline cases. The prestressing loss in the end sections of the tendons is between 4 and 100%, in the practical case of the example around 25%.

The 25% loss of tension acts as a prestress on the end faces of the two finished parts in the end position and must be absorbed by the concrete at an early stage of hardening. This prestress is large enough to exceed the adhesive strength to the tendon and the splitting tensile strength in the entry area of the force in the young concrete and to cause damage in the end anchoring sections of the tendon.

The object of the invention is to avoid damage to finished parts arranged in the end position when producing finished parts in the fitted bed.

The object is achieved by a method as described in the characterizing part of claim 1.

Claim 2 specifies an abutment element for carrying out the method according to the invention, which fulfills the requirements of claim 1 for concrete with normal hardening behavior.

In claim 3, means are proposed with which the friction between the abutment element and formwork can be increased and the length and thus at the same time the costs for the abutment element can be reduced.

To further increase the economics of the process, efforts will be made to design the abutment elements so that they can be used economically.

• Fig. 1 + 2: ein Spannbett für die Herstellung langer Fertigteile, z.B. Weichenschwellen.
  Fig. 1 in Aufsicht, Fig. 2 im Längsschnitt;
• Fig. 3 : einen Längsschnitt durch ein Widerlagerelemen nach Anspruch 3 mit erfindungsgemäßer die Reibung verstärkender Vorrichtung;
• Fig. 4 + 5: das Beispiel einer Vorrichtung nach Anspruch 3.
  Fig. 4 im Teilquerschnitt, Fig. 5 in Teilaufsicht.

The invention is explained with an example in FIGS. 1 to 5. Show it:

• Fig. 1 + 2: a fitted bed for the production of long finished parts, eg turnout sleepers.
  Figure 1 in supervision, Figure 2 in longitudinal section.
• 3 shows a longitudinal section through an abutment element according to claim 3 with the device which increases the friction according to the invention;
• 4 + 5: the example of a device according to claim 3.
  Fig. 4 in partial cross-section, Fig. 5 in partial supervision.

For a device for the production of long pre-stressed prefabricated parts 2/1, 2/2 ... 2 / n - for example turnout sleepers - the prefabricated parts 2 in a formwork 1 between abutments 3, against which tendons 4 are anchored and prestressed, one behind the other poured. The abutment elements 7, 8 according to the invention are arranged in the end regions 5, 6 of the formwork 1. The individual finished parts 2/1, 2/2 ... 2 / n manufactured one after the other in a fitted bed are limited by the head scales 10 of the separating devices 9 forming the finished parts 2.

The length of the abutment element 8 is determined by the friction between the formwork and the abutment element. The abutment element 7 has a device 11 which increases the friction. It consists of two parts 12, 13, of which part 12 is firmly connected to the side wall of the formwork 1 and tapers upwards in a wedge shape, while part 13 has at least the thickness of part 12 - in the example it has a greater thickness and encompasses part 12 from three sides - the part 12 downwards accordingly opens overlapping and has means 14 with which it can be pulled up out of the formwork 1.

Claims (3)

1.Procedure for the production of long pre-fabricated parts from prestressed concrete - primarily turnout sleepers - in the prestressed bed, whereby the precast elements are manufactured one after the other between face formwork panels in a prestressed bed traversed by prestressed tendons and the prestressed tendons anchored in independently founded abutments are relaxed after sufficient hardening of the concrete and between the Face formwork panels of successive prefabricated parts are severed, characterized in that
that together with the planned prefabricated parts (2/1, 2/2 ... 2 / n) in the end areas (5, 6) of the formwork (1) at the beginning and at the end of the prestressing bed, an additional, usually lost abutment element ( 7,8) is poured from concrete, and that the length of the abutment elements (7,8) is dimensioned such that the frictional force between the concrete and the prestressed bed formwork is at least as large as the partial tensioning force that occurs before the tendons (4) are released. from the abutment (3) during the hardening process of the concrete to the end faces of the abutment elements (7, 8) facing the abutments (3). 2. abutment elements made of concrete for performing the method according to claim 1 ,
that the length of the element measures 1-1.5 m at a partial clamping force of 25% of the planned preload. 3. abutment element according to claim 2, characterized in
. that on the side panels of the formwork (1) of the prestressing bed in the area of the contact surfaces of the side panels with the abutment element (7,8) at least one protruding into the clearance of the prestressing bed, increasing the friction between the formwork (1) and the abutment element (7,8) Device (11) is arranged,
. that these devices consist of two parts (12, 13), of which one part (12) tapers upwards in a wedge shape and is firmly connected to the formwork side wall, while the other part (13) of at least the same thickness forms the first part (12) overlapping opens downwards in a wedge shape and can be removed upwards and
. that the free space created by pulling the releasable part (13) between the side panels of the formwork of the tensioning bed and the abutment element (7,8) in the longitudinal axis of the tensioning bed is at least so long that it allows the abutment element (7,8) to slide along with the relaxing tendons (4) in the prestressed bed after releasing the anchoring on the tendon abutment (3).

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