Precast concrete

Published by Basilio on

Precast concrete systems are the greatest exponent of mechanization in the construction sector. The prefabrication allows the setting of the mortar in optimal conditions and the reduction of the construction time of the building. This allows you to expand the range of options to create spaces in the Architecture.

Total concrete precast systems

These systems have the characteristic that they decompose the structure into prefabricated pieces at the factory using prestressed concrete, and later they are assembled on site. Its main advantage lies in the speed of assembly on site. And in the quality of the material, since the pieces set in a factory under controlled conditions. They are joined with tongue and groove and bolts so that work is simplified on site.

Unidirectional structural systems are generally used. Since although there are also bidirectional systems, these are more expensive and more complex. Although in favor of bidirectional systems, it should be noted that they need fewer pillars.

Bidirectional system Unidirectional system

Precast prestressed concrete systems.

In prefabrication, prestressed systems are usually used, which consist of the tensioning of the reinforcement before the application of the concrete. Since when it sets, the reinforcement will tend to recover its original length by introducing axial forces in the piece. This compensates for the tensile stresses when the armature is loaded.

Allowing therefore greater spans in the beams using the same material that would be used in the traditional reinforcement. Prestressing is widely used in precast, since having to set the pieces in a factory can control the process.

1 State of beam loads

2 Beam deformation

3 Prestressed

4 Axiles caused by prestressing

5 Deformation caused by prestressing

6 Axles of the prestressing counteract the shear of the state of loads in the beam.

Post-tensioned precast concrete systems

Post-tensioned or post-tensioned concrete is called concrete that is subjected, after pouring and setting, to compression forces by means of active reinforcements (steel cables) mounted within sheaths. Unlike prestressed concrete, in which the reinforcements are tensioned before concreting, in post-tensioning the reinforcements are tensioned once the concrete has acquired its characteristic strength.

As in prestressed concrete, the advantage of post-tensioning consists in compressing the concrete before it is put into service, so that the tractions that appear when bending the piece translate into a loss of the previous compression, avoiding more or less As the concrete works in tension, stress for which it is not a suitable material.

Prefabrication with concrete panels.

The precast concrete panels allow the building to be constructed without beams or pillars. Following the construction system of load-bearing walls. They allow to build with great speed, economy and cleanliness by means of tongue and groove and bolts that join the panels and the forged pieces.

They also improve insulation and allow the facade to be load-bearing. Therefore, buildings are more resistant to torsion and resist earthquakes better.

There are three prefabrication systems with panels:

  • The transversal ones, placing the panels in the transversal direction.
  • Herringbone, Placing the panels in the longitudinal direction placing parallel transverse panels in the core.
  • And the mixed one, which is a mixture of both.
prefabricacion con paneles de hormigón

Example of a mixed system with a non-bearing façade. In this case, the weight of the slab is distributed over the interior panels, allowing the façade not to support weight.

Cellular systems.

edificio prefabricado hormigón capsulas

These systems consist of the decomposition of the building into interchangeable modules supported by an independent structure. In cellular systems, panels lack structural function. One of the most famous examples is the "Nakagin Capsule Center”, Modular building, with 14 levels high and 140 individual capsules, which are used as housing and offices. Work of the Japanese architect Kisho Kurokawa, in the 70s. Each unit (or capsule) was 2.5 × 4m.

The modules must be able to be transported by a large articulated truck. From there, all combinations of transportable pieces are possible, obtaining an almost infinite number of possibilities and sizes of spaces for these homes, both on one floor and in several

Kurokawa tower

The system consisted of a reinforced concrete structure with communication cores to which the containers were anchored at 4 points, allowing the possibility of periodically reconfiguring the tower, depending on the needs of the moment. The 2.3 x 3.8 x 2.1 m modules were prefabricated in a workshop, with a light steel enclosure, and then assembled on site in the tower. They had furniture and amenities of the time (such as television and telephone) and could be grouped to accommodate entire families.

Portal structures

The porches are made up of pillars and beams, and they are distributed in parallel to configure the building. They are generally used in unidirectional structures, although they are not exclusive to these. There are arcaded systems with rigid knots and articulated knots.

deformacion porticos estructura

Rigid knot structures

Rigid node structures have monolithic joints at the nodes formed by welding, bolting, or concreting. It is little used due to the problem of transportation and joints.

Rigid node structures have monolithic joints at the nodes formed by welding, bolting, or concreting. It is little used due to the problem of transportation and joints.

It is indicated for buildings of 3 to 5 heights and non-seismic areas.

nudos articulados estructura

Articulated knot structures

Articulated knot structures have joints supported by knots. They are used in constructions of a maximum height of 12 m, and from 1 to 3 heights.

The horizontal actions are distributed among all the supports due to the diaphragm effect of the slab.

Intraslational structures

Intraslational systems introduce a stiffening element in the structure to establish an intraslational system. They are generally elevator or stairwells. Walls are also used. This improves the torsional strength of the building, allowing a greater height (more than 5 floors). The walls can be prefabricated, cast-in-place or masonry. Support connection to foundation

Pillar anchors

Boxed

It is usually used on good soils. Recess surfaces can be smooth or rough

Pods

Anchor conduits must be generously dimensioned, both for subsequent backfilling and to compensate for errors

Bolts

It is used to embed in elements cast in situ. The prefabricated part is screwed by means of a plate to the base element.

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