EP0058851B1

EP0058851B1 - Building structure of prefabricated elements

Info

Publication number: EP0058851B1
Application number: EP82100763A
Authority: EP
Inventors: Nevio Soncini
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-02-13
Filing date: 1982-02-03
Publication date: 1985-08-21
Also published as: DE3265497D1; ES8301306A1; IT1135451B; ATE15090T1; GR75169B; IT8119713A0; EP0058851A1; ES509543A0

Abstract

Building structure of prefabricated elements, comprising a skeleton of prefabricated pillars and beams, mutually connected in correspondence of the junction points by a concrete casting; a narrow pillaring (3) projects upwardly from the top headpiece of each underlying pillar, for the support of a twin overlying pillar, said pillaring delimiting a space which deeply extends into a cavity (4) in the underlying pillar for housing connection reinforcing rods (9) projecting from the opposed headpiece (8) of the overlying pillar and overlapping the reinforcing rods (18) of the underlying pillar, at least by the minimum length foreseen by the rules on reinforced concrete buildings. Moreover, at least part of said pillaring is provided at the top with a support element (15) adjustable in height.

Description

The object of the present invention is a building structure of prefabricated elements, and particularly a structure consisting of prefabricated beams and pillars of reinforced concrete.
Nowadays, prefabricated constructions - particularly of beams and pillars - are increasingly spreading out in the building industry, since they offer undoubted and widely known practical advantages of stoutness and erection speed.
The critical point of any structure of this type - particularly if it is meant for buildings with several floors - is of course the junction between the various pillars, in correspondence of which are also fixed the horizontal beams.
The most widespread technique in performing these junctions provides for the prefabricated pillars to be formed with at least part of the reinforcing rods emerging from their ends. For the assembly, an overlying pillar is placed - by means of a crane - onto an already stabilized underlying pillar, up to approaching the respective emerging reinforcing parts, while leaving relatively spaced the opposed concrete end headpieces. While the overlying pillar is supported by the crane, the corresponding reinforcing rods are welded together. The free space between the two headpieces of the pillars is used for supporting and fixing the headpieces of the horizontal beams and for a subsequent concrete casting, designed to act as binder and make the junction perfectly stable.
Alternatively, in order to reduce the crane employment times, an equipment has been set up which is formed by two metal pieces of frusto- conical shape being spaced by a detachable hollow metal cylinder. The equipment is inserted into proper cavities obtained in the opposed headpieces of the pillars, between which it is interposed, so as to provide for the temporary support and spacing of said pillars. The removal of the spacing cylinder allows to recover the equipment once the reinforcement has been welded, before carrying out the concrete casting.
As can be easily realized, these techniques are rather complicated and delicate. The welding of the reinforcements has to be carried out by highly qualified workmen and it is complicated by the fact that seldom the opposed reinforcing rods are in a perfectly adjacent position, as is required in order to perform efficient weldings; furthermore, great ability and care are required to hold the pillar during the welding operation, so that it may keep:

- perfectly stable and plumb,
- in perfect alignment with the underlying pillar, and
- exactly spaced, in height, from this latter.

Moreover, as soon as the welding has been carried out, the pillar must still be supported vertically - for instance by means of the usual provisional wooden structures - up to setting of the concrete casting in correspondence of the junction. Equally, up to this moment, the pillar cannot be loaded with the overlying structure.
The problems are partly solved by a more recent type of prefabricated structure, wherein each pillar terminates, at the upper end, with an axial, projecting metal tube, or the like, acting as temporary support. The same pillars are provided, at the lower end, with an qually axial hole, apt to receive said tube. This engagement has first of all the advantage of holding the overlying pillar in a position adjusted in height, since the top level of the tube and, respectively, the bottom level of the opposed axial hole, are exactly determined during prefabrication. Alternatively, the tube can be threaded and provided with a bushing, apt to be screwed on the same, which adjust- ably supports the upper pillar (see AU-B-30476/ 67). But the said engagement performs a scarce binding function between the two pillars. For this purpose, there are in fact provided one or more cavities surrounding said axial tube, which are designed to house reinforcing rods emerging from the bottom end of the overlying pillar. Such cavities are then filled with a concrete casting which binds the junction between the pillars and the horizontal beams.
This type of structure - though having the advantage of automatically and exactly determining the level of the pillars - still suffers however from some drawbacks:

- on one hand, in fact, the engagement of the tube into the axial hole is not - nor can be - so precise as to keep the overlying pillar perfectly plumb; thus, the usual provisional wooden structures are still required for supporting the pillar up to setting of the concrete casting into the junction;
- on the other hand, the junction has not turned out to be so resisting to bending and tensile stresses, as would have been indispensable, for instance in the case of aseismatic structures.

A still further type of prefabricated structure, which tends to eliminate the aforementioned drawbacks, makes use of essentially hollow pillars, which are employed as follows. (See FR-A-1380023.) Onto an underlying pillar - on which the slab has already been placed and completed, and from the top of which project connection reinforcing rods - is mounted a new hollow pillar, taking care to arrange said reinforcing rods into its cavity. Said pillar is rested onto the slab and is held plumb by means of the usual provisional wooden structures; then the pillar itself is filled with concrete casting, starting from the top and taking care to previously introduce therein also a metal reinforcement for subsequent connection to a further overlying pillar.
Also this system, however, is not free from drawbacks:

-to start with, already in the prefabrication stage, the construction of a hollow pillar, with square or rectangular section, can be realized only by means of very special equipment and taking particular care, whereby the costs involved are relatively high;
-furthermore, also the installation presents difficulties, and this both for what concerns the plumbing with the usual provisional structures- taking also into account the requirement of perfect stability for the subsequent casting - and for what concerns the leveling which, being obtained by direct bearing of the pillar onto the slab, can show even considerable level differences between one point and the other of the slab.

All these drawbacks are now solved by a building structure of prefabricated elements, comprising a skeleton of prefabricated pillars and beams, mutually connected in correspondence of the junction points by a concrete casting, posts projecting upwardly from the top headpiece of each underlying pillar for the support of an identical overlying pillar and delimiting a space which extends into a cavity in the underlying pillar, said space and cavity being apt to house connection reinforcing rods, characterized in that at least part of said posts are provided at the top with a support element adjustable in height; in that said connection reinforcing rods project from the lower headpiece of the overlying pillar into said cavity, to lie adjacent to the reinforcing rods buried in the underlying pillar at least by the minimum length foreseen by the rules on reinforced concrete buildings; in that said cavity is just deep enough to house the rods projecting from the overlying pillar, the inner walls of said cavity being provided with a set of horizontal grooves to improve the bond of the concrete casting; and in that further reinforcing rods are provided, projecting from said lower headpiece of the overlying pillar and from the bottom of said cavity to form connection means for an element of mutual anchorage between the two superposed pillars,
Preferably, said posts are in a number of four and are positioned in correspondence of each of the four corners of the pillar, three of such posts being provided with said support elements adjustable in height.
Finally, to allow a faster concrete filling and without any blowholes, the lower headpiece of the pillar is shaped preferably like a pyramid with downward apex and it is furthermore provided with a hole leading into a feed and vent pipe, which lets onto one of the side walls of the pillar, in proximity to said headpiece.
Further characteristics and advantages of the present invention will anyhow result evident from the following description of a preferred embodiment thereof, illustrated by way of example in the accompanying drawings, in which:

Figure 1 is a perspective view, with disjoined parts, of the junction of pillars and beams according to the present invention;
Figure 2 is a section view of a pair of superposed pillars, showing the reinforcing rods and the anchorage element; and
Figure 3 is a schematic plan and elevational view of a foundation element.

As shown in figures 1 and 2, the pillar 1 terminates, on its upper headpiece 2, with four posts 3, arranged at the four corners of the pillar.
The posts 3 delimit a space which extends into a cavity 4 in the upper headpiece of the pillar 1.
The posts 3 and the cavity 4 delimit, on the upper headpiece, support surfaces 5 onto which fit exactly the end cogs 6 of the horizontal beams 7.
The lower headpiece 8 of the pillar 1 has a very open pyramid shape, from which project connection reinforcing rods 9, as well as a reinforcing rod in the form of a half-ring or eyelet 10. A similar half-ring or eyelet 11 is provided at the bottom of the cavity 4.
One of the four posts indicated by 3' in figure 2, is slightly higher than the others and terminates with a slight swell 13; whereas the remaining posts 3 each have, at the top, a support element 15 adjustable in height.
In figure 2, said support element 15 is simply formed by a round-headed bolt, apt to be screwed into a threaded bush 16, buried into the upper end part of each post 3. It is evident however that any other support element, adjustable in height, may be used to perform this function, since elements of this type are widely spread on the market.
Always with reference to the embodiment shown in figure 2, one notes that, in correspondence of the support element 15, there are provided suitable metal seats 17 buried into the lower headpiece 8, onto which acts the round head of the bolt. This arrangement is particularly suited for preventing cracks and splinters in the concrete during bolt adjustment.
The cavity 4 which - as better described hereinafter - is designed to house the concrete casting for connecting two superposed pillars, is formed with a set of deep grooves onto its surfaces, which are apt to improve the bond of the concrete casting, thereby preventing any possible slipping out thereof, even in the event of particularly heavy stresses. The cavity 4 is just deep enough to house the connection reinforcing rods 9 projecting from the overlying pillar.
For the assembly of this structure one proceeds as follows. After the bottom pillar has been fixed and stabilized into its seat (later on we shall see in detail the fixing system of the base pillar), the pillar 1 is carried over its top and is slowly let down by means of the crane, making sure that the lower headpiece 8 of the overlying pillar mates exactly with the upper headpiece 2 of the underlying pillar.
The heads of the support elements 15 and the respective seats 17, provided in correspondence of the posts 3, allow an easy and accurate centering of the pillar itself.
At this point, the connection reinforcing rods 9 will have penetrated inside the cavity 4 up to reaching the bottom thereof, up to lie adjacent to the reinforcing rods 18, buried within the headpiece 2, by a length complying with the present rules on reinforced concrete buildings.
For safety's sake, the rods 9 have surfaces with an improved bond coefficient.
The non-adjustable end of the post 3' defines the exact level at which the overlying pillar should be positioned. Since the pillars are prefabricated at the workshop, the exactness of said level is no doubt the best that can be obtained in buildings.
The support elements 15 of the other posts 3 are instead adjusted, with the overlying pillar already bearing thereon by means of a spanner or like - up to positioning the pillar itself perfectly plumb.
At this point, the pillar is perfectly stable on its support and, in normal conditions, it can already be released by the crane.
In order to anchor the overlying pillar onto the underlying pillar, one provides first of all to introduce into the cavity 4- by operating through the openings left free between the posts 3 - a stay 19, of the double screw type with hook couplings, well known per se, which is hooked at the bottom onto the eyelet 11 and, at the top, onto the eyelet 10. Said stay is tightened, by screwing, so as to form a safe anchorage of the two superposed pillars.
Of course, if operating in unfavourable weather conditions - whereby it could happen that a sudden gust of wind might knock down the overlying pillar before it has been anchored - it will be necessary to hook and tighten the stay 19 before the pillar itself has been released by the crane.
Once the two pillars have been mutually anchored, taking up the position shown in figure 2, one provides to insert the horizontal beams 7 which get fixed - as already said - with their end cogs 6 into the support surfaces 5. The beams 7 may be simply rested thereon, or else they may in turn be provided with projecting rods, apt to intersect with rods projecting from the opposed beam and, respectively, with the rods of the two pillars. Moreover, the beams 7 comprise median longitudinal notches 20, apt to allow the laying of transversal connection reinforcing rods and thereby enabling a continuity in said rods even on the lower side of the beam. This last characteristic turns out to be particularly important when there is a turnover in the curve of the bending moments, for instance due to moving loads or in circumstances of seismic quakes.
The beams 7, as shown in figure 1, are meant for the inner part of the building. The longitudinal ribs 21, provided on both sides of said beams, are in fact designed to support the tile forming the slab, and the beams themselves get completely covered by the concrete casting.
The peripheral beams (not shown) have a slightly different conformation; they in fact do not have one of the ribs 21 and they have instead a raised upper rim, apt to contain - with no need for any further forms - the casting designed to make up the slab.
When providing to introduce the concrete casting for connecting the two superposed pillars and the respective confluent beams, it will be sufficient to close the spaces lying between the posts 3, which are not occupied by means (for instance, for the peripheral pillars), with a slight form.
The slightly flaring shape of the lower headpiece 8 and the feed and vent pipe 22 provided between said headpiece and one of the side walls of the pillar, allow a perfect filling, preventing the formation of blowholes which would compromise its bond.
The system for laying the first pillar, or base pillar, will now be described with reference to figure 3.
The foundation element 23 consists of a metal trestle substantially formed by four appropriately connected angle bars, provided at the top with adjustable support elements 24, similar to the already seen elements 15, but far longer.
The transversal dimensions of the foundation element 23 are identical to those of the overlying base pillar, so that the support elements 24 fit perfectly into the respective seats provided in said pillar.
When starting the building, the different foundation elements are positioned and nailed onto a foundation layer 25, and they are set with a first casting up to the level indicated by F. At this point, one operates a perfect horizontal alignment of only one of the support elements 24, for each foundation element 23, which will then be blocked and considered fixed; any possible level differences of the foundation layer 25 and/or any inexactitudes in the planting will thereby be recovered, forming the fixed datum plane for the whole building.
It should be noted that the trestlework of the foundation element 23 allows,to introduce it, without any problem, into any type of foundation reinforcement (plinth, bed, face beam, back beam), which may in fact be easily crossed.
An alternative solution - even if quite equivalent from the functional point of view - would be to replace the posts 3 with metal elements welded to the reinforcing rods and buried into the pillar during prefabrication.
As can easily be understood, the advantages provided by the system according to the present invention, compared to known technique, are quite considerable:

- to start with, the times required for fixing a pillar are reduced to a minimum;
- no particularly skilled labour is required for performing very critical welds, nor is it necessary to hold up the crane for long lengths of time;
- the positioning of the pillar at an exact level is practically automatic and its plumbing is extremely easy;
- the mutual anchorage of the reinforcements of the two pillars is guaranteed, even independently from the binding function of the concrete;
--:the superposed pillar can start to be loaded practically just after its fixing, even without waiting for the concrete to set in the junction;
-the usual provisional wooden structures are no longer required for supporting the overlying pillar up to setting of the concrete; in fact said structures, as well as preventing the formation of a complete casting, also represent a great obstacle to the circulation of the workmen and of the machines engaged in forming the slab;
- there is even no longer need - except to a very slight extent and for the peripheral pillars - for the forms containing the casting, in correspondence of the pillar junction.

Claims

1. Building structure of prefabricated elements, comprising a skeleton of prefabricated pillars (1) and beams (7), mutually connected in correspondence of the junction points by a concrete casting, posts (3) projecting upwardly from the top headpiece of each underlying pillar (2) for the support of an identical overlying pillar and delimiting a space which extends into a cavity (4) in the underlying pillar, said space and cavity (4) being apt to house connection reinforcing rods (9), characterized in that at least part of said posts (3) are provided at the top with a support element (15) adjustable in height; in that said connection reinforcing rods (9) project from the lower headpiece (8) of the overlying pillar into said cavity (4), to lie adjacent to the reinforcing rods (18) buried in the underlying pillar at least by the minimum length foreseen by the rules on reinforced concrete buildings; in that said cavity (4) is just deep enough to house the rods (9) projecting from the overlying pillar, the inner walls of said cavity (4) being provided with a set of horizontal grooves to improve the bond of the concrete casting; and in that further reinforcing rods (10, 11) are provided, projecting from said lower headpiece (8) of the overlying pillar and from the bottom of said cavity (4) to form connection means for an element (19) of mutual anchorage between the two superposed pillars.

2. Building structure as in claim 1, wherein said posts (3) are in a number of four and are positioned in correspondence of the four corners of the pillar (1), three of the said posts (3) being provided with said support elements (15) adjustable in height.

3. Building structure as in claim 1, wherein said support elements (15) adjustable in height consist of round-headed bolts cooperating with opposed metal seats (17) buried in the lower headpiece (8) of the pillar.

4. Building structure as in claim 1, wherein the lower headpiece (8) of the pillar is provided with a seat for housing the top (13) of the post (3) of the corresponding underlying pillar, which is not provided with the support element (15) adjustable in height.

5. Building structure as in claim 1, wherein the lower headpiece (8) of the pillars is shaped like a pyramid with downward apex.

6. Building structure as in claim 1, wherein said connection reinforcing rods (9) have surfaces with an improved bond coefficient.

7. Building structure as in claim 1, wherein said further reinforcing rods (10, 11) forming connection means are curved into an eyelet and said element of anchorage (19) of the pillars is in the form of a double-screw stay with hook coupling.

8. Building structure as in claim 1, wherein said prefabricated beams (7), having a substantially rectangular section, are provided on their lower part with a longitudinal rib (21) for supporting the slab and with end cogs (6) for the bearing and fixing of said beams onto the pillar (1), and they comprise moreover at the end a wide median notch (20), apt to allow the laying of transversal rods for connecting the beams (7), said rods being arranged on the lower side of said beams and crossing the pillar.

9. Building structure as in claim 1, wherein a feed and vent pipe (22) is provided to fill said cavity (4) with a concrete casting binding the pillar (1) and the beams (7), said pipe connecting the surface of the lower headpiece (8) of the pillar with one of the side walls of said pillar, in proximity to such headpiece.

10. Building structure as in claim 1, comprising furthermore a foundation element (23) forming the supporting seat for the first pillar, said foundation element consisting of a metal trestle, having a transversal section equal to that of the pillar and being provided on the upper part with support elements (24) adjustable in height and with connection means for an element of anchorage to the overlying pillar.

11. Building structure as in claim 10, wherein said support elements (24) adjustable in height consist of four long round-headed bolts.