SE506073C2 - Prefabricated building facade elements - Google Patents

Abstract

The present element invention relates to a prefabricated facade element (1) for buildings comprising a thermal insulation (3) accommodated internally within the element enclosed by an inner leaf (5) facing inwards towards the interior of an intended building and an outer leaf (6) facing outwards from the interior of said building. The inner leaf (5), which consists of light clinker concrete, is securely attached to a border (8) of light clinker material extending around the insulation (3) and is provided with internal reinforcement (9) extending into the border (8). The surface leaf (6) with the reinforcement (10) applied to it is so arranged as to be secured by the aforementioned inner leaf (5) with its associated border (8) in such a way that it is capable of absorbing the forces which give rise to periodic movements.

Description

506 10:73 For example, the temperature can be specified as a function of time t according to Temp = M + A x sin (2 x pi x t / T) Attenuation, phase shift.

If the sun shines on an outside of an outer wall, the outer part of the wall will of course vary greatly in temperature as the solar intensity varies. Some distance into the wall, the effect is less, it is said that the oscillation is damped.

It can be assumed that when the sun shines most intensely, it will also be the warmest on the outside, say at 12 on the day. A number of hours later, there will be a certain rise in temperature on the inside. The time shift is usually called phase shift. j It can thus be said that the climatic factors affect a building component in a way that can provide both attenuation and phase shift.

From a practical point of view, it therefore applies that a façade layer is affected by phase shift and damping to a small degree, while the inner parts of an outer wall are affected in a more damped manner. This has the consequence that differences in movements and displacements will arise between e.g. the facade layer of a wall and the underlying structure.

Free and resistance shrinkage If a part of a building shrinks (swells) and if it is assumed that this shrinkage can take place without any resistance, no stresses arise and thus no problems in general.

There is usually a difference between free shrinkage and different degrees of resistance shrinkage. Especially when comparing different mixing recipes and the like, a comparison is made according to the principle of free shrinkage. In general, it can be said that mixing recipes that provide little shrinkage should be sought.

Determination of free shrinkage must take place in a way that allows the material to move almost freely during the shrinkage process. 506 073 The free shrinkage can be significantly greater than the resistance shrinkage. It can be assumed that the first part of the free shrinkage is not formed at all in experiments with resistance shrinkage due to the fact that the material can take up the shrinkage as plastic deformations.

SE, B, 335217 refers to a facade element which is built up of different materials and with connecting rods therein to hold the different material layers together. A frame formed by U-beams is enclosed in recesses in the insulating material. The frame made in this case is connected to an outer plate with the material in the various layers consisting of concrete and that reinforcement is missing in the rim. However, this facade element does not allow free shrinkage and is also complicated.

Tensions, invisible cracks.

One problem is that steel is a very unambiguous material, while plaster is more indeterminate and variable. This means that e.g. The e-module can vary within quite wide limits for plastering.

Since plaster, like other cement-based materials, has a small tensile strength in relation to the compressive strength, it can be stated that the calculated stress is large.

The conclusion from this is probably that there is not infrequently a fine structure of cracks even in well-functioning and durable plaster layers.

Visible cracks.

Fine cracks can occur in almost all plaster layers and these are not normally harmful.

The question then becomes why there are sometimes wide cracks in plaster. a) If the plaster carrier, for example masonry, cracks, or has cracks, it is obvious that a plaster layer on such a plaster carrier will also crack. b) Assume that a plaster layer is applied to a masonry. Due to the plaster layer being subjected to relatively large shrinkage, 506,073 split stresses arise between the masonry and the plaster. If the adhesion is not sufficient, so-called boom can occur and the shrinkage that is formed over the area with the boom can accumulate in a relatively wide and visible crack. c) Plaster layer on solid or resilient surface: The first variant has been described above. The second variant corresponds in its most pure form to plaster on soft mineral wool and that the plaster's own weight is transferred to an underlying frame via easily displaceable attachments. In such a case, the plaster cake can shrink and swell without the need for any stresses in the plaster which can give rise to cracks. However, if the design fails so that unintentional holding occurs, occasional wide cracks may form. This is because shrinkage over a large plaster field can accumulate in a single wide crack.

Stress concentrations, reinforcement.

It is obvious that a plaster field begins to crack in the areas of the field where the stress is greatest.

You can see voltage in a material as a flow (voltage flow). In the event of a reduction in area, the flow must be concentrated.

In e.g. window corners create extra high voltage. This is because the voltage lines there must be curved and thereby become constricted in the "curve". Should a crack occur in a facade field, it will probably occur at a window corner. Reinforcement of plaster can take place to varying degrees. A first step may be to add reinforcement where special stress concentrations can be expected.

The next step is to reinforce the whole thing, but still apply reinforced reinforcement where stress concentrations can be expected.

For the reinforcement to be effective, it must be sufficient in quantity. It can be said that there is a threshold below which one should not go, because below the threshold you probably do not get any significant effect from the reinforcement.

Plaster reinforcement should generally have the purpose of being crack-distributing.

The condition for crack-distributing effect can be formulated: In order for a reinforcement to become crack-distributing = 5 S06 073, the tensile force present in the plaster cake must be able to be absorbed by the reinforcement just before cracking. You can thus formulate the requirement for crack reinforcement according to: A xf P ctk yk p Ap area cross section, plaster As area cross section, steel (reinforcement) dp thickness plaster Eck characteristic value of E-module, concrete fctk characteristic value of tensile strength, concrete (t stands for tensile) Fyk characteristic value of the yield strength of steel (characteristic value is actually a statistical quantity used to indicate strength values, this means, for example, that the stated value is exceeded by a probability of 5%) c is distance between reinforcement wires (center distance) Ac concrete area, index c stands for concrete It can be said that the reinforcement ratio (As / Ap) of the cross section must be greater than the ratio (fctk / fyk). The need for reinforcement thus increases with the thickness of the plaster layer and with the tensile strength of the plaster.

The main object of the present invention is thus primarily to provide a prefabricated building facade element which effectively and simply solves said problems with crack formation along the outside of the element.

Said object is achieved by means of an element according to the present invention which is mainly characterized in that the surface plate and the inner plate are arranged connected to each other via stainless steel reinforcement ladders, that the inner plate, which is formed of lightweight clinker concrete, is fixedly connected. provided with internal reinforcement extending into the rim, wherein the surface plate with applied reinforcement and external surface layer is arranged held by the said inner plate with associated rim in order to be able to absorb the forces which give rise to periodic movements.

The invention is described below as preferred embodiments, reference being made to the accompanying drawings in which Fig. 1 shows the building facade elements according to the invention in the operative position of a depicted building, Fig. 2 shows a horizontal section along two joined elements, Fig. 3 shows a vertical section Fig. 4 shows a cross section of an element according to the invention, Fig. 5 shows examples of prior art with previously applied free-shrinking method of a wall outer layer, and Fig. 6 shows a further example according to the invention. .

The building facade element according to the present invention is constructed by the following sub-characteristics: A) that the surface plate 6 and the inner plate 5 are arranged connected to each other via stainless steel reinforcement ladders 9, B) that the inner plate 5, which is formed of lightweight clinker concrete, is fixedly connected to the insulation 3 itself stretching rim 8 of lightweight clinker material and C) is provided with internal reinforcement 9 extending into the rim 8 D), the surface plate 6 with applied reinforcement 10 and outer surface layer 11 being arranged to hold the said inner plate 5 with associated rim 8 for to be able to absorb the forces that give rise to periodic movements.

This allows free shrinkage of said formed building elements which are simple both in terms of manufacture as construction and use.

A so-called prefabricated building facade element 1, which is formed by a thermal insulation 3 received internally in a space 2 of the element 1, which is surrounded by an inner plate 5 facing an interior 4 of an intended building and a surface plate 6 facing away from the interior 4 of said building, which is thus intended to face the free 7, according to the present invention the inner plate 5, and the surface plate 6 are securely held to each other. More specifically, the inner plate 5, which is formed of lightweight clinker concrete, is fixedly connected to a rim 8 extending around the insulation 3, which also consists of lightweight clinker material, and which inner plate 5 is provided with internal reinforcement 9 and which extends into sargen 8.

In this case, the surface plate 6 with reinforcement 10 applied at some stage and an outer surface layer 11 is arranged to hold the said inner plate 5 with associated rim 8 in order to be able to absorb the forces which give rise to periodic movements, i.e. shrinkage or swelling of said elements 1.

This effectively solves the problem of emerging stresses and reducing the risk of cracking in the outer surface facade layer 11 of plaster that is applied to the element 1, in the place when the element 1 is erected and mounted in the intended desired location.

More specifically, the element 1 can consist of an inner disc 5 whose strength is adapted to the loads which the element 1 is intended to carry and with a thickness A which varies from, for example, 100 to 120 mm.

The thermal insulation is preferably selected from cellular plastic with a suitable thickness B of, for example, 120 to 150 mm.

The surface plate 6 preferably also consists of lightweight clinker material whose strength class is K5, and with a thickness C which varies between about 50 and 80 mm.

More specifically, the surface plate 6 has internal reinforcement, so-called crack reinforcement 10 to divide any emerging cracks of the surface plate 6 and its waterproof plaster layer 11 of lightweight clinker concrete material to become more and finer cracks than before. Said reinforcement 10, 9 in the surface plate 6 and also in the inner plate 5, which suitably consists of a centrally placed reinforcement net with, for example, ø5cc 200mm, is fixedly connected to the rim 8. Otherwise, the reinforcement 9 in the inner plate 5 is adapted to the needs. to cope with carrying capacity. The reinforcement in each vertical section is constant, which means that the amount of reinforcement is increased around windows and other openings through the element 1.

Between said surface plate 6 and inner plate 5, reinforcement ladders 9 are arranged so that said plates 6, 5 are connected to each other via these reinforcement ladders. They are suitably designed in stainless steel Q 4.5 mm vertically oriented with cc 1000 and cast in the respective plate 6, 5.

The said building facade element 1, which can have a <506,673 height of up to about 2.7 m and be about 6 m long and is used for buildings is produced by casting. First, the inner plate 5 is cast, which is provided with a rim 8 around windows etc. and at vertical element joints 12. In the said rim 8 a reinforcement ladder 9 is laid, after which thermal insulation 3 is placed between the reinforcement ladders.

The said reinforcement ladders 9 protrude a piece whereby the surface plate 6, when casting the same, is connected to the interior of the element 1.

The said surface plate 6 is thus fixedly connected to the inner plate by vertical joints 12.

The elements 1 thus have an externally finished façade, brushed or smooth concrete or alternatively they consist of lightweight clinkers as a base for plastering on the site after installation, whereby a joint-free façade is obtained.

As a surface layer 11 of the elements 1 along the facade 13 of the building, a reinforced thick plaster has been used. The plaster layer then consists of clogging and surface plaster, with a total thickness of about 20 mm.

The reinforcement 10 for the surface plate 6 can consist of a galvanized plaster net with a mesh size of, for example, 20 mm and with a wire diameter of 1 mm.

The behavior of a building construction thus achieved from a building physics point of view can be described as follows: Climate: The outer part of an outer wall is exposed to a strong climate impact. This applies to both temperature and humidity. Towards the inside of the wall, the influence decreases. This means that the inner board, both thermally and moisture-wise, will almost certainly be in an indoor climate. Relative to the outer plate, it can be said that the inner plate is rather in a constant climate.

All materials, including lightweight concrete and plaster, shrink and swell.

The first non-periodic shrinkage is common to all cementitious materials. This shrinkage is rapid in the beginning, and additional shrinkage during the second year is only a few percent of the value for the first year. It can be said that most things happen during the first months. h kb 506 073 Depending on climate variations (over days and years), the different layers in an outer wall will alternately shrink and swell. Such movements are usually called periodic.

From what has been said, it can be concluded that a construction that is unsuitable from a movement point of view has a high probability of rupturing already during the first year cycle.

Movements and stresses.

If both the inner discs 5 and the surface discs 6 are completely followed in their movements, there will be no stresses.

The question is what happens if the inner plate 5 is immobile and the surface plate 6 shrinks, as the surface plate 6 is firmly connected to the inner plate 5 via the frames 8 at windows and vertical joints 12. When the plate 6 shrinks more, the shrinkage is prevented due to holding. The result is that a tensile stress in the surface plate 6 occurs. When fully held, the stress becomes = E X6.

Expected shrinkage depends on the climate in which the structure is located. Thus, for certain materials shrinkage in indoor climates is stated to be 0.7 to 1.0 per mille, and for outdoor climates 0.4 to 0.6 per mille. Higher U-value gives slightly less shrinkage.

The specified shrinkage values are so large that it cannot be expected that they will be able to be absorbed in the form of stresses in the lightweight clinker concrete.

With a density ro = 1200 (kg / m3) is obtained approximately: fCtk = 0.6 (MPa) and Eck = 9.2 (GPa) = 9200 (MPa) A shrinkage of, for example, 0.25 per mille would give a stress when prevented shrinkage 0.00025 x 9200 = 2.3 (MPa), i.e. far above fctk. Already a very insignificant shrinkage means that the tensile strength is exceeded. The shrinkage that must be overcome is not only the non-periodic but also the shrinkage (swelling) that periodic influences give. Thus, this is solved by the disc 6 being crack-reinforced 10 in order to distribute unavoidable cracks so that they become several and thus fine. The inner plate 5 is dimensioned with regard to load or given mini-reinforcement 9.

In order for a reinforcement 10 to become crack-distributing z sne 673, the tensile force present in the surface plate 6 just before cracking 10 must be able to be absorbed by the reinforcement 10. The requirement for crack reinforcement can thus be formulated according to ctk k Assume K5 and fctk approximately 5/6 = 0.83 (MPa) 0.05 x 0.83 <(1000/200) x (pi x 0.005 x 0.005 / 4) x 500 0.04 <0.05 which it should be For the steel has been assumed fy = 500 (MPa) k In estimation calculations, characteristic Ac xf <As x phytic values are used here because the purpose is to study the construction from a material point of view.

If the above condition is met, small fine cracks are prevented from continuing to widen because the yield strength of the reinforcement 10 is not reached. If the elongation continues, there will instead be a new crack some distance from the first. In order for it to work in the manner described, the forces present must be transferred between the outer reinforcement 10 and the inner plate 5.

The rim 8 can absorb the forces that shrinkage (or swelling) can give. From a static point of view, it will function as a short console.

Fig. 5 shows examples of how a disc, which is arranged free lumbar, changes (becomes shorter) due to free shrinkage.

The preferred embodiment shown in the drawings in Fig. 6 has the rim 8 arranged to extend only along the circumference of the said formed element. The surface plate 6 and the inner plate are then arranged connected to each other only via a central reinforcement 9, preferably indicated ladders, and which on the sides are surrounded by the thermal insulation 3. Thus, there is no rim in this preferred embodiment of the prefabricated building element 1. .

Putsen.

Traditionally, bricks or other masonry have been plastered. This can be characterized as plaster on a solid surface. Techniques that make it possible to apply plaster layers to, for example, mineral wool are also known. This can be described as plaster on a resilient surface. Decisive for whether it should be a question of ä H sne 073 one or the other principle is how the relationship between the plaster and the firmness of the substrate is shaped.

A plaster on the surface plate 6 will here work according to the principle of plastering on a solid surface. This means that the risk of cracks between element joints and otherwise is small. A prerequisite for this, however, is that the previously mentioned crack-distributing reinforcement exists. It should also be taken into account here that a good crack-distributing function of the reinforcement presupposes that stress concentrations around window holes etc. to a reasonable extent meet with reinforced reinforcement.

When plastering on solid surfaces, it can of course not be ruled out that a pattern of barely visible cracks (micro-cracks) arises. Such cracks cannot normally be considered harmful.

Frame relative to facade layers Of particular importance here is the question of how the current construction differs from facade layers consisting of bricks. A shell wall as a façade layer on a multi-storey façade is normally placed on a plinth wall or on a bracket. Such a facade layer will move in relation to the underlying frame in proportion to the total height of the shell wall.

For e.g. height 5 storeys, the upper edge of the wall will have movements from the entire height, i.e. about 14 m. Such a façade wall must be connected to the underlying frame in a way that allows the façade layer to be displaced almost freely. This can be fulfilled by using custom-made staples.

The current construction instead has a function meaning that the façade elements 1 can be considered to operate mainly separately.

In general, it can therefore be said that there can be no cracks in element joints if the facade element and the frame shrink to the same degree.

However, the invention is not limited to the embodiments of building facade elements described above and shown in the drawings, but can be varied within the scope of the patent claims without departing from the spirit of the invention.

Claims (8)

12 506 673 P a t e n t k r a v 1. l. Prefabricated building facade element (1), formed by a thermal insulation (3) received inside the element, which is surrounded by an inner plate (5) facing an interior of a intended building (4) and an interior of an said building ( 4) facing surface plate (6), characterized in that the surface plate (6) and the inner plate (5) are arranged connected to each other via stainless steel reinforcement ladders (9), that the inner plate (5), which is formed of lightweight clinker concrete, is firmly connected to a round the insulation (3) extending frame (8) of lightweight clinker material and is provided with internal reinforcement (9) extending into the frame (8), the surface plate (6) with applied reinforcement (10) and outer surface layer (II) being arranged to be held by the said inner disc (5) with associated rim (8) in order to be able to absorb the forces which give rise to periodic movements. Element according to Claim 1, characterized in that the surface plate (6) has an internal reinforcement (10) in the form of a galvanized plaster mesh, which is fixedly connected to the rim (8). Element according to one of the preceding claims, characterized in that the surface plate (6) comprises a waterproof plaster surface layer (II) of lightweight clinker concrete. Element according to one of the preceding claims, characterized in that the said surface plate (6) comprises crack reinforcement, so that any emerging cracks are divided into becoming more numerous and finer than before. Element according to one of the preceding claims, characterized in that the surface plate (6) is fixedly connected to the inner plate (5) via vertical joints (12). Element according to one of the preceding claims, characterized in that a rim (8) extends around windows and at vertical element joints (12). Element according to claim 6, characterized in that in the rim (8) a number of reinforcing ladders are inserted with a foam sheet (3) received between said reinforcing ladders (9). Element according to any one of the preceding claims, characterized in that in the rim (8) it extends only along The circumference of the said element, wherein the surface plate (6) and the inner plate (5) are arranged connected to each other only via the reinforcement (9) surrounded by the insulation (3) (Fig. 6).