Prestressed Beam Lines

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Casting Beds

 

Casting beds are made of a supporting structure with different drill holes positions for different pieces width upon which are placed the fast-locking systems for attaching the lateral moulds.

It’s available as well the hydraulical version of the bed, where in the internal part of the bed are placed the hydraulical cylinders that open and close the lateral sides against the bottom. A fast-locking system guarantees the perfect closure of the side against the bottom, resisting in this way to the force of the concrete during casting.

On top of this support structure the different bed bottoms are placed, depending of the size of the piece there will be different sets of bottoms. The bottom is made by a first quality casting plate of thickness 6 or 8mm, and can be conceived in 2 different ways in relation to the different customer requirements

  • One bottom for every dimension of the beam base, and lateral sides closed against the lower part of the bottom.
  • One “universal” bottom of bigger width, and lateral sides leaning over the bottom itself. This solution is more suitable for wide variety of beam base dimensions.

 

Pre-Stressing Heads

 

Group of steel beams for strands anchoring, studied for a pre-determined Prestressed load at a certain centre of gravity, composed of an active and a passive stressing head:

  • active stressing head. Steel structure anchored inside the floor of the customer site, into pre-determined reinforced abutments; 1 or 2 perforated beams, fixed or adjustable in height, with with drill holes designed according to client´s requirement to fit the different type of pieces to manufacture; slacking cylinders to release the stressed cables during demoulding, in order to handle the cables safely. During tensioning of cables and all casting and curing phases, cable force is kept by some steel spacers, that are removed at demoulding either by hand of by an hydraulical device. Stressing head can be equipped by small crane for handling the strand stressing jacks.
  • Passive stressing head. It incorporates the same steel structure anchored inside the floor as the active head, as well as the same perforated beams, without the slacking cylinders.

 

Self-Reacting Structure

As an alternative to Pre-Stressing Heads, for customer who don’t want to face huge civil works for the abutments of pre-stressing-heads, is a Self-Resisting structure, that better fits to shorter prestressing lines.

Self-reacting structure can be external to the casting bed or can be incorporated underneath the bed supporting structure. According to customer needs, it can lead to minimum or even zero civil works.

In the system it’s always present the perforated beam both in the active and passive side of the structure, with the presence of slacking single effect detensioning cylinders with their steel spacers.
 

Hydraulical Unit for tensioning and detensioning of cables

Essential equipments in a prestressing lines are the hydraulical units and jacks that allows the tensioning of each single strand, and the detensioning of all the line in a single stroke. All Bianchi range of these machines is available at this link

Mould sides for Prestressed beam/girders

 

The lateral sides are placed on the casting bed using a fast locking system to fasten them to the support structure, fast lock and changeover system for the tightening of the top of the mould. Sides are equipped with a platform in case of big elements height in order to help people that need to operate on the mould.

According to the different element to be produced, the sides can be modular in different ways, in length and in height, in order to reach the maximum flexibility for the customer with the minimum set of sides elements supplied.

The most common type of sides that can be manufactured are

  • Mould sides for beam or girder type I o double T, used mainly in industrial buildings and public works, as rail beam for overhead crane, floor slab element, or structural element for small bridges
  • Mould sides for main beam or girder TI/TL or R (rectangular)
  • Mould sides for prestressed delta beam or girder, used for the construction of roofs
  • Mould sides for beam or girder type Y or ‘ipsilon’
  • Mould sides for bridge beam or girder

 

Any coupling between movable parts of the mould in contact with concrete is equipped with rubber gasket  in order to avoid concrete leakage. Gasket can be placed underneath the casting surface (with metal chamfer welded on the plate), or welded on the shuttering, with special shape (GF type) that guarantees the presence of the chamfer in the rubber itself.

Mould sides can include a vibration system consisting of a series of vibrators that can be electric or pneumatic. The vibration compacts the concrete by removing air and increases its mechanical strength after curing. Furthermore, vibration allows using concrete with less moisture and accelerates the curing process, in order to increase productivity.

The heating system of the prestressed lines also increases productivity by accelerating the curing process. This system consists of a series of finned pipes positioned either inside the side walls or underneath the base frame, where hot water or industrial steam flows at the pressure that can arrive up to 4-5 bar. The external part of the lateral sides is covered by isolation canvas or plastic panels.