There is currently a rather frequent need to build multi-floor buildings for the tertiary sector, with each floor having a considerable surface area, in which the stair-wells/lift-units, which could serve as stiffening elements, are positioned either laterally or on the outside of the structure.

In general, prefabrication techniques for multi-floor frames involve the use of hinged structures, which exploit the stiff floor obtained by casting the co-operating cap in order to transmit all the horizontal actions to the resistant sections.

Amongst horizontal actions, of major importance are seismic actions, which, in the absence of bracing cores, in general induce displacements that exceed standard specifications, whereas, in the presence of bracing cores, these undergo high toppling actions, so requiring extensive and costly foundations. In addition, the considerably large surfaces, if reference is made to just one bracing core, cannot be interrupted by

construction joints, and consequently the frames undergo high stresses due to seasonal thermal variations so that, albeit having a stiffening block, also the individual pillars must be sized taking into account the stresses due to thermal variations.

The rigid floor is moreover made with a co- operating cast which cannot be cast, as occurs in traditional building techniques, floor by floor, but only when the structure is completely assembled. The reason for this is that assembly must be performed using a mobile crane, which has to position, for each grid, girders and floors at the various floors, before passing on to the next grid.

In such conditions, the assembly stage proves critical because the conventional actions that are to be expected according to current standards during assembly do not in general encounter stiffening cores nor, even if there were any, are the structural connections to these possible, hence imposing the need for the structure to be calculated as a hinged frame without bracings with considerable stresses at the foot of the pillars, due to the cantilever-like operation of the individual pillar, with inevitable problems of

instability and of second-order moments, and with consequent large dimensions of the pillars.

The general purpose of the present invention is to overcome the drawbacks of the known art referred to above, in an extremely simple, inexpensive and particularly functional way, i. e., providing a frame structure in the two directions <BR> <BR> (i. e. , not only in the direction of the girders, but also in the direction of the floors), which, exploiting a first-phase joint, provides fixed-end nodes in order to guarantee stability and containment of the strains in the assembly stage, and which, once assembly is completed, with the second-phase joint made with additional reinforcement in the integrative castings, will be able to withstand actions during use, with the result of having smaller dimensions of the pillars, reduced heights of the floor system, contained strains of the frame, and elimination of the bracing cores.

With a view to achieving the above purposes, according to the present invention, the intention has been to provide a prefabricated multi-floor frame structure, having the characteristics described in the annexed claims.

The structural and functional characteristics of the present invention and its advantages as compared to the known art will emerge even more clearly and evidently from an examination of the ensuing description, with reference to the attached drawings, which illustrate a prefabricated multi- floor frame structure made according to the present invention, and in which: - Figure 1 is a plan view of a prefabricated multi-floor frame structure according to the present invention; - Figure 2 is a cross-sectional view according to the trace II-II of Figure 1 of a frame structure according to the present invention; - Figure 3 is a cross-sectional view according to the trace III-III of Figure 1 of a frame structure according to the present invention; - Figure 4 is an enlarged partial perspective view of the pillar-capital-girder node of a frame structure according to the invention; - Figure 5 is a view similar to the one illustrated in Figure 4, enlarged and partially exploded ; - Figure 6 is a vertical cross section according to the trace VI-VI of Figure 7 of a box girder according to the invention;

- Figure 7 is a detail in plan view, illustrating a central capital and a box girder; - Figure 8 is an enlarged sectioned plan view illustrating the first-phase joint obtained by means of a pin and loops of harmonic wire between the capital and the girder; - Figure 9 is a sectioned elevation of the joint illustrated in Figure 8; and - Figure 10 is a perspective, partially cutaway and sectioned. view of the frame structure according to the invention.

With reference to the drawings, a prefabricated multi-floor frame structure is designated, as a whole, by 10, and, as illustrated in the example according to the present invention, comprises, in general, pillars 11, girders 12 and tiles 13, connected together in order to form a prefabricated structure with fixed-end nodes.

According to the invention, the pillars 11 are full-height pillars, having a shaft with constant cross section and with current reinforcement.

Internal points of lightening, where the axial load is reduced, and insertion of steel profiles in the bottom part, where the axial load is high, enable sizing of the shaft within small dimensions that are maintained constant throughout the entire

height. Fitted on the shaft are cross capitals 14, on which there is fixed a box girder 12.

The cross capital 14 of the central pillars can adapt its height and width to the height and width of the girder until it becomes, with displacement the separator on the formwork, a cantilever capital or a collar capital 21 of the side pillars 11.

The first-phase joint is made in the assembly stage, for example by inserting a pin 15 into two loops overlaid with harmonic wire 16, and by injecting into said connection a fast-hardening additivated concrete.

Hence, whenever the girder 12 is positioned on the pillar 11, and the tile 13 is positioned on the girder 12, there is obtained a fixed-end joint, the purpose for this being to obtain in all cases a frame structure with fixed-end nodes in the two directions as it is assembled so as to guarantee structural stability and containment of strains, and so that, in use, once the assembly is completed, with the second-phase reinforcements 18 inserted in the integrative castings, it may provide a frame structure with fixed-end nodes capable of withstanding, with limited strains, the

working loads and the horizontal actions of the wind or of an earthquake.

The construction of frames with fixed-end nodes in the two directions requires that: - the primary elements (girders) and secondary elements (floors) should have a current cross section capable of withstanding both positive and negative moments; - design of the primary and secondary elements should be possible with a minimal rise that remains stable over time ; - the moment of the secondary elements (floors) should be transferred onto the pillar 11 via a high torsional inertia of the primary elements (girders) ; and - the secondary elements, which can be set at a distance from one another, should be torsionally rigid in order to prevent transverse flexibility of the floor.

The above requirements may be obtained via a particular hollow box girder 12 which can be produced using the same techniques and same equipment used for making the hollow floor.

The box girder is characterized by an internal hole of fixed width, with two ribs having a

thickness that can vary according to the shear and a pre-compression designed in such a way that the strains are small and above all stable over time so that, under dead loads, there do not occur viscous rotations on the supports with burdensome transfer of moments from positive to negative over time. The girder is characterized by: - high torsional inertia so as to transfer the negative moments of the floor onto the pillar; - extensive possibility of perforation for passage of wiring or water systems or the like in a position corresponding to the pillar; - a first-phase joint which, at the moment of assembly provides a fixed-end joint, said first- phase joint being sized for making a frame structure resistant to the vertical and horizontal actions expected in the assembly stage ; - a second-phase joint for absorbing high fixed-end moments, in use, this being obtained with steel bars integrated with the reinforcement of the first-phase joint, which are positioned on the integrative casting in positions corresponding to the ribs; - possibility of perforating the top slab for making an integrative casting, which will increase the compressed area, increase resistance to

shearing actions, and contain the integrative reinforcements possibly occurring at the bottom edge in the girder-pillar and tile-girder connection; - possibility of replacing a floor element with the box girder that rests in the thickness of floor system, girder upon girder, in order to provide openings, to carry locally greater loads, or to increase the stiffness of the floor, it being possible also to hypothesize that the girder, in its smaller dimensions of thickness of the ribs, irrespective of its length, which may in all cases be 2.50 m, may produce the secondary structure (floor) ; - construction of floor systems without cantilevers in view, of minimal encumbrance and with plane intrados ; - high resistance to fire due to the presence of the plane intrados ; and - possibility of conveniently making the girder edge 22 by obtaining two L-shaped girders from the central box girder 12.

There is thus obtained a prefabricated structure with fixed-end nodes starting right from assembly, with the pillar shaft having constant cross section and current reinforcement, with cross

capital having a width equal to that of the box girder, on which the latter is fixed with a top and bottom first-phase and second-phase connection that is obtained as described above.

The same first-phase joint and second-phase joint that is made between the pillar and the girder is obtained at the top edge, between the tile 13 and the girder 12, whilst at the bottom edge it is generally preferable to ensure connection for possible fixed-joint positive moments between the tile 13 and the girder 12 using an anchor bolt, such as the one designated by 19.

In general, the bottom first-phase joint is made immediately after laying of the element, by forming a hinge-like constraint, whilst the top joint can also be made when assembly of the individual grid is completed.

In this way the bottom edge, which is subjected to compressive stress by the action of the weights of the cap and of the accidental loads reduces or annuls the tensile stresses due to the positive moments, in use, which arise from the horizontal actions.

The top joint, which is already stressed by the added dead loads requires an increase in the reinforcement 18, which is sized according to the

maximum negative moments and is inserted in a co- operating cap 20.

The loop 16 of the top first-phase joint, which both for the girder 12 and for the floor elements is made with harmonic wire, is stressed by the permanent loads at the moment of assembly and by the horizontal actions, which, during assembly, are imposed by standards.

The harmonic wire is hence able to respond to the increase in additional stresses of the overloadings, which are simultaneously absorbed also by the reinforcements 24 inserted in the second-phase co-operating cap 20, thus possibly constituting a sort of pre-stressing of the harmonic wire for its complete exploitation.

The harmonic wire, which is pre-stressed by the dead loads, is thus able to co-operate also for the maximum live loads together with the additional reinforcements.

The frame structure with fixed-end nodes requires that the stair wells and lift shafts should not be stiffening structures, and could hence be prefabricated elements mounted on top of one another with interposition of a neoprene support in a position corresponding to the newel

posts so as to prevent the well or shaft from presenting excessive stiffness.

From what has been described above with reference to the figures, it appears evident how a prefabricated multi-floor frame structure with fixed-end nodes according to the invention provides structural stability during assembly, enables reduction in the dimensions of the pillars and in the thickness of the floor system, contains the strains of the frame, and does not require bracing cores. The purpose mentioned in the preamble of the description is therefore achieved.

Of course, the modalities for obtaining the first-phase joints in the prefabricated multi-floor frame structure according to the invention may differ from the ones illustrated purely by way of non-limiting example in the drawings, as may likewise differ the materials employed.

The field of protection of the invention is consequently delimited by the annexed claims.