EP0678140A1

EP0678140A1 - Floor component and method of manufacture thereof

Info

Publication number: EP0678140A1
Application number: EP94903210A
Authority: EP
Inventors: Jörgen Thor
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-12-18
Filing date: 1993-12-17
Publication date: 1995-10-25
Also published as: WO1994015037A1; SE500785C2; SE9203816L; SE9203816D0; NO952430D0; NO301433B1; NO952430L

Abstract

The invention relates to a floor element (1) of concrete (2) intended to be prefabricated and which in its inner parts contains spare bodies (6) of considerably lighter material than concrete. The element (1) comprises one in the longitudinal direction, on the upper surface (3) and on the bottom surface (4), equal and upwards directed cumbering determined by a constant cumbering radius (10).

Description

Floor component and method of manufacture thereof

Floor structures to multy story buildings like offices, appartment houses etc are normally made of concrete eithe as on site cast floors or as prefabricated floor elements

Floor structures cast on site imply a not very rational construction method, a big labour force requirement, weather dependent and a long time for drying all moisture bound up during the casting.

Normally the casting is done in two steps. First the load bearing deck is casted. Later on when the building has go roof and walls a top casting is done which is needed as a base for the flooring. Sometimes the casting to a finishe surface can be done in one and the same casting (one step casting). This, however, put big requirements on planning workmanship and the weather conditions. A rain can com¬ pletely destroy the surface.

Building with elements implies a rational and faster way of construction. In Sweden and in many other countries th most common element type to floor is so called hollow cor elements. These consist of concrete elements of some lenght with longitudinal holes in the middle of the ele¬ ment height. The function of the holes is primarily to save material and limit the weight with a preserved total structural height and thereby keeping mainly the same loa bearing capacity and stiffness.

The hollow core concrete elements are produced very ra¬ tional in a longish continuous casting process where a wagon automatically is moved forwards on a casting bed. The wagon delivers concrete, forms the elements and creat es the holes. Afterwards a cutting to desired element lengths is done.

For elements with longer span prestressed reinforcements are used. This prestressing authomatically gives the elements a precumbering. For longer spans a precumbering also iε required as compensation for the deflection due t the dead weight and the load on the elements.

The precumbering through the prestressing however, often becomes rather uncontrolled. This can result in that two elements placed side by side get a different precumbering. Especially noticeable is this when an element is cut or when elements of different lenght are placed side by side. This often results in time consuming adjustment works as loading or alternatively propping of elements to get thes to the same level before casting of the joints between th elements can be done.

An other drawback with hollow core concrete elements is a on the whole less good measure accuracy. This together with the above mentioned problem with the precumbering results in the need of relatively thick layers of top con¬ crete to obtain the necessary smoothness and finishing as a base for the flooring. This takes away some of the in¬ tended advantages of element construction because the top concreting take times and again large amount of moisture is added.

In the same way as for on site casted floor the top con¬ creting often has to be done after that the building has got roof and walls. Filling the joints between the ele¬ ments with concrete however has to be done already during the erecting due to the fact that the floor normally is used for stabilizing the building. Before the elements have been joint this stabilizing capacity iε lacked. An other drawback with this element type is the difficul¬ ties to afterwards take up larger holes for instance to shafts or similar. This is due to the fact that the rein¬ forcement then is cut and thereby the load bearing capaci¬ ty is at risk.

Compared with a conventionally on site casted floor struc¬ ture it is also difficult to obtain the same toughness and continuity as will be obtained for the on site casted floor structure. Special join reinforcement or other ar¬ rangements are normally required to secure the building against progressive collaps.

Lately information also have been brought forward which indicate that the elements .in certain applications can get a large reduction of the shear force capacity with a reduced safety against shear collaps as a consequence.

The present invention consists of a prefabricated floor element of concrete with all the advantages of element construction but without the drawbacks pointed out above for hollow core elements. More over the design of the element and the joint procedure imply that the same tough¬ ness and continuity as for a conventionally on site casted floor can be obtained.

The invention will now be described in more detail with reference to the accompanying drawings, where

Fig. 1 shows a plane section, cross sections and a long¬ itudinal section of a finished element.

Fig. 2 shows the principle for the casting and the mould design, Fig. 3 shows the design of the longitudinal joints bet¬ ween two elements,

Fig. 4 shows the design of the end joint of the element

Fig. 5 shows how a static composite function with a steel beam can be obtained,

Fig. 6 shows a division of a long mould in parts.

Fig. 7 shows an example how the precumbering of the mould can be obtained,

Fig. 8 shows examples of the design of the mould sides,

Fig. 9 shows examples of the design of the end stop and

Fig. 10 describes the principle for the production of an element.

With reference to fig. 1 iε shown how the finished elemen

1 is built up of concrete 2 with a top surface 3, bottom surface 4 and two side surfaces 5 and in the concrete placed spare bodies 6 of considerably lighter material than concrete, for instance cellur plastic.

The element is not produced aε a hollow core element in a continuous casting process but is casted according to fig.

2 up and down in a fix and upwards open mould 7. The casting in a fix mould gives a considerably greater mea¬ sure accuracy. The bottom 8 in this mould as well as the upper edges 9 of the longitudinal sides have a downwards directed bending in form of a constant radius 10 in the order of 200-300 m. The downwards directed bending with a conεtant radius implies that the finished element 1 gets precumbering the size of which is a function or the ele- B

ments length or span. The precumbering as a function of the span for a radius of 250 m can be seen in the table

The choice of radius is adapted so that the shown precumbering roughly corresponds to the estimated deflection for the span in question due to the dead load of the elements. This results in that the ele¬ ments after erection become mainly plane.

The advantage with a precumbering in the form of a constant radius also is that the same precumbering always will be obtained for the one and same element length irrespectively where in a long mould the ele¬ ment is produced. The result is, that the problem with different levels between elements placed side by side which where mentioned concerning the hollow core ele¬ ments, will normally not arise even if two elements placed side by side would have different lenghts.

If in special cases εtill a certain difference in level would arise between two elements the longitu¬ dinal joint 11 between the elements is designed in such a way that a simple adjustment possibility exists in the form of hoops 12 caεt into the joint. By for instance providing the hoops with threads and use a steeel plate 13 with holes corresponding to the hoops the elements easily can be adjusted to the same level with aid of nuts 14 which are screwed on the hoops 12.

The described adjustment arrangement is simple to obtain when producing the elements by casting in a fix mould but impossible or very difficult to obtain by the continuously hollow core element production. The arrangement can also be used to fix the elements to each other before the casting of the joints is done. This results in the elements, in contrary to hollow core elements, will act as a stabilizing slab even without the joints being casted. The casting of the joints thereby can be done in a later stage if wished.

With reference to fig. 1, fig. 2 and fig. 3 another very big advantage which can be mentioned is that the constant precumbering 10 together with a sufficient smooth upper surface obtained already when casting the element by casting the upper surface 3 downwards ag¬ ainst a smooth mould bottom 8, results in that no top concreting on site is needed. Only the longitudinal joints 11 between the elements and the joints at the end of the elements have to be filled with mortar or concrete. Thereby the adding of a lot of water is avoided which a later top concreting will require.

The design of the joints in the end 15 of the element can be seen in fig. 4. The design implies that a bare reinforcement mesh 16 which is ancored in the element will be covered in concrete when casting the joints. This makes it possible to easily obtain a continuity with negative momentε and thereby an increased load bearing capacity and stiffneεs by adding a rein- forcement 17 above the support which is covered in concrete together with the bare mesh. Thereby an effi¬ cient ancoring to the elements is obtained. For hollow core elements this possibility to obtain a continuity over the support is lacking.

As is shown in fig. 5 the design of the end joints also implies that a very efficient static composite function easily can be obtained if the support is a composite beam by the element end joints 15 and the reinforcement mesh 16 and the reinforcement 17 respec¬ tively being efficiently casted together.

In order to give the floor element a larger stiffness and load bearing capacity also for longer spans a sufficient structural height is needed. For the pre¬ sent element a structural height of 300 mm has been chosen for the normal case. Light spare bodies 6 (fig. 1) have been put into the middle of the element so that the element shall not be too heavy. This results in that the element weight, with maintained loadbear- ing capacity and stiffness, will only be a little more that half of the weight of a homogenous concrete floor with the same height.

The spare bodies are arranged in such a way that a "cross beam system" is created (beams as well along as across the element). This gives the element a very high stiffneεε and more in general it is true that the high stiffnesε in relation to the weight compared with a homogenous floor with the same weight gives the ele¬ ment a very good sound insulation quality. Not at least the transverse beams 18 add to an increased stiffness across the element which is of value espe¬ cially for the impact sound insolation. The longitudinal beams 19 also have a pure static function by transferring shear forces from the tensile reinforcement in the bottom to the compressed plate in the top. To be able to transfer these shear forces a hoope reinforcement, or similar is needed in the lon¬ gitudinal beams.

If the element joints (longitudinal and end joints) are casted in a later stage, which as pointed out is possible, the "check pattern" created by the joints can be used for putting in cables and smaller pipes.

Between the beams of the element, where the spare bodies are situated, holes can easily be taken up for shaft etc without the loadbearing capacity being at risk.

A convenient way to produce the elements is in a elon¬ gated mould 40-80 m with a bottom of steel on a vib¬ rator table. The length is devided into a number of parts, where each part contains the before mentioned bending radius of 200-300 m (fig. 6). To take out the bending on the whole lenght of the mould would create too big differences in levels between the lowest and highest point. A convenient lenght of one part can be 20-30 m. This gives a difference in level of about 200 and 450 mm respectively.

The bending can for instance be obtained by making the legs 20, which support the mould bottom 8, with dif¬ ferent heights corresponding to the bending radius (fig. 7).

A suitably normal element width is 1200 mm and the height 300 mm. The mould sides can be made of steel profileε 21 composed according to fig. 8. In the mould sides holes 22 are made for casting the previous men¬ tioned adjustment bars 12 into the element.

The end stops can be made up of steel profiles 23 according to fig. 9.

With reference to fig. 10 the very production can suitably be done as follows. The given measures etc shall be seen as examples and can vary within certain limits.

a) In the mould end stops 23 are arranged corre¬ sponding to the element length and spare forms 24 are placed in order to make the reinforcement mesh 16 bare in the element endε.

b) Reinforcement meεh 16, reinforcement hoopes 25 and hoope bars 12 for the adjustment of the ele¬ ments are arranged in the mould. Further spare forms 26 in order to make the reinforcement mesh bare in the element ends are put on top of the mesh.

c) A first about 70 mm thick concrete layer 27 is casted in the mould and vibrated.

d) Cellur plastic blocks 6 about 180 x 1500 mm are put into the mould on top of the recently casted first concrete layer 27.

e) Reinforcement mesh 28 is put above the cell plas¬ tic blocks 6 and the remaining concrete 28 is casted. The upper surface (the finished elements bottom surface) is drawn to the desired smooth¬ ness. If possible the elements are heated for a quicker hardening. f) The elements are taken out from the mould 7 by lift hokes 30 in the end stops 23.

In fig. 11 a simplified alternative to conventionally shearforce reinforcement is shown in the form of rein¬ forcement hoopes (compare 25 in fig. 10b). Instead the reinforcement mesh 16 is being made wider and bent up along its longitudinal sides whereafter the reinforce¬ ment mesh 28 is connected to the bent mesh 16. In fig. 11 a is shown the proceedings at casting and in fig. 11 b the finished element in the turned right way.

Claims

1. Floor element (1) of concrete (2) intended to be prefabricated, in its inner parts containing spare bodies (6) of considerably lighter material than con¬ crete, characterized in that the element (1) comprises one in the longitudinal direction, on the upper sur¬ face (3) and on the bottom surface (4) equal and up¬ wards directed precumbering determined by a constant cumbering radius (10).

2. Floor element (1) aε claimed in claim 1, charac¬ terized in that the cumbering radius (10) is betwen 200 and 300 .

3. Floor element (1) as claimed in any one of the preceding claims, characterized in that the top sur¬ face (3) is so smooth that no top concreting or level¬ ing is needed but a flooring can be directly put on to the elements after the casting of the joints.

4. Floor element (1) as claimed in any one of the preceding claims, characterized in that in the lon¬ gitudinal joint (11) special hoope bars (12) are cast¬ ed which together with a steel plate (13) and nuts (14) makes it possible to easily adjust two side by side placed elements to level in height.

5. Floor element (1) as claimed in any one of the preceding claims, characterized in that the design of longitudinal joint (11) with hoope bars (12), steel plate (13) and nuts (14) resultε in that the elements act as a stabilizing slab even before casting of the jointε.

6. Floor element (1) as claimed in any one of the preceding claims, characterized in that the element ends have spares (15) and a bare reinforcement mesh (16) which makes it possible for the element to effi¬ ciently, statically cooperate with a composite beam by the on site placed reinforcement (17) being efficient¬ ly casted together with the beam and the reinforcement mesh (16) .

7. Floor element (1) as clamied in any one of the preceding claims, characterized in that the required shear force reinforcement for transferring shear forc¬ es from the tensile to the compression side is achie¬ ved by that the longitudinal εides of reinforcement mesh (16) are bent and the ends are connected to the reinforcement mesh (28).

8. Method for producing of a floor element (1) of concrete (2) containing spare bodies (6) of concidera- bly lighter material than concrete, characterized in that the element (1) is casted up and down in an up¬ wards open mould (7), the bottom (8) and εides (9) of which comprise an equal and in the longitudinal direc¬ tion downwards directed cumbering determined by a con¬ stant cumbering radius (10).

9. Method for producing of a floor element (1) as claimed in claim 8, characterized in that the cumb¬ ering radius (10) of the mould (7) iε between 200 and 300 m.