Modular prefabricated element used in building construction

A building construction element is used to form cast concrete interspaces in a concrete slab. The element has a bowl shaped portion which has a concave upper surface forming substantially a catenary as seen in vertical section. Supports are connected with the bowl shaped portion and extend downward relative to the bowl shaped portion.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a modular prefabricated element used in
 building construction, particularly used for making floors and related
 slabs with cast concrete interspaces.
 2. State of the Prior Art
 It has been known for a long time to provide aerated hollow spaces, also
 called interspaces, under the floors of residential and commercial
 buildings for the purposes of eliminating gases and humidity which can
 damage both people and the building structures.
 A modern and rational solution to the problem of eliminating the humidity
 and gases is described in Italian patent specification 1,253,374 and in
 Italian design application no. PN93 0 000012, both of the present
 applicant. The solution of these documents is a modular element that is
 preferably molded out of a plastic material in the shape of a spherical
 cap. It is provided with four supports that are connected to each other by
 four arches. The side edges of the arches are shaped so as to enable
 contiguous elements to be joined to each other, due to respective edges
 being able to overlap and snap-fit together. The contiguous elements can
 then form a solid and continuous surface.
 The prior art element described above, however, needs to be provided with
 reinforcing, i.e. stiffening ribs, in particular under the cap, so as to
 ensure that the surface is able to carry and withstand, without any
 problem, both the weight of the workers as the prior art element is
 installed, and the weight of the subsequent concrete casting. The prior
 art structural element is thus subject to both compressive and flexural
 stresses.
 As a result, construction of the mold that is used to manufacture the prior
 art element is complicated, with a corresponding high cost. Furthermore,
 the prior art element itself, when made of molded plastic material, tends
 to be insufficiently resistant and unstable as a whole.
 SUMMARY OF THE INVENTION
 Accordingly, it is a primary object of the present invention to provide a
 modular element for forming aerated hollow spaces, or interspaces, in
 building construction applications which not only ensures unaltered
 functional properties, but also allows for a lower material usage and a
 simpler and more rational molding process than the prior art element. It
 is a further object of the present invention to provide such an element
 that is capable of being easily adapted, with respect to both its shape
 and size, to a particular user application requirement.
 The objects of the present invention are achieved by the provision of the
 modular prefabricated element which has a bowl shape structure with an
 upper surface that is concave, symmetrical and substantially a catenary in
 vertical section. Resting supports are connected with the bowl shaped
 structure. Further, a frusto-conically shaped lateral surface forms a
 circular junction with the bowl shaped structure, the circular junction
 lying in a horizontal plane. The resting supports are connected with the
 frusto-conically shaped lateral surface so that the upper surface has a
 smaller radius than the resting supports. Upon the application of a
 vertical load to the upper surface, the upper surface is only subjected to
 radial tensile stresses.
 The bowl shaped portion, the frusto-conically shaped surface and the
 resting supports are preferably molded in one piece and thus unitary. The
 supports are essentially formed by extending the frusto-conically shaped
 surface downward from the bowl shaped portion at a plurality of points
 circumferentially spaced along the bowl shaped portion. The supports end
 in horizontal feet, and are essentially defined by arched spaces
 therebetween. Bent edges along the arched spaces along vertical planes are
 capable of overlapping and fitting together with like bent edges.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 A prefabricated modular element according to the present invention is
 formed with a cap-like structure having supports enabling the structure to
 rest on the floor. Referring to FIG. 2, the element itself includes a cap
 portion or bowl shaped structure 10 having an upper surface 12 that is
 concave and symmetrical. As seen in vertical section, noting for example
 the dashed line in FIG. 2, the upper surface is substantially a catenary.
 The outer edge of the surface of the cap portion is circular and lies on a
 horizontal plane.
 The prefabricated modular element according the present invention will
 support loads that bear down on the element, for example due to the weight
 of a worker during installation of the element itself, and the mass of
 concrete that is cast to form the slab. In FIG. 1, these loads are
 indicated by P, and are considered as being ideally applied to the center
 of the surface 12.
 The particular conformation of the cap portion 10 converts these loads into
 tensile stresses T that develop radially, tangentially to the surface 12.
 These stresses are exactly balanced where the surface 12 is circular and
 horizontal. This allows for the amount of material that is needed to
 manufacture the modular prefabricated element to be reduced, because the
 element itself does not work flexurally. That is, it does not undergo
 flexural stresses, but rather behaves like a membrane, and is only
 subjected to tensile stress.
 The surface 12 intersects a lateral surface 14 that is preferably in the
 shape of the frustum of a cone. The lateral surface 14 extends downwards
 with supports 16 as shown in FIGS. 2-6 in order for the element to rest on
 the floor. With respect to the frustum of a cone formed by the lateral
 surface 14, the surface 12 forms the smaller base thereof. This
 arrangement allows for a greater capability of the modular prefabricated
 elements to be piled in stacks. This also enables the height of the cap
 portion 10 to be reduced, enabling the free height of the hollow space, or
 interspace, to be correspondingly increased.
 At the intersection or junction point of the surfaces 12 and 14, the
 tensile stresses T breakdown into two forces as shown in FIG. 2. A force A
 is directed according the generatrix of the cone, i.e. according the
 lateral surface 14, and the force B is directed toward the center of the
 cap portion and lies on the horizontal plane containing the contour. The
 forces A resolve onto the resting plane or surface of the modular
 prefabricated element through the supports 16. The forces B tend to
 compress the contour, which is therefore practically only subject to
 compressive stress.
 FIGS. 3 to 6 illustrate various specific embodiments of the modular
 prefabricated element according the present invention. Each of these
 embodiments has supports 16 mutually connected through side arches that
 create through flow or passage apertures for discharging gases and
 humidity. They could also possibly be for the passages of cables and
 conduits therethrough. The supports 16 have a cross section that is
 inclined according to the conical shape of the lateral surface 14 of the
 modular prefabricated element. This allows the plurality of the elements
 to be superimposed or stacked in an optimum manner, allowing their volume
 to be reduced during storage and transport.
 The supports 16 are provided with feet 18 through which they actually rest
 on the floor. The connecting arches have bent edges 20 extending along
 substantially vertical planes. The bent edges 20 allow for contiguous
 elements to be joined to each other by overlapping and snap-fitting the
 bent edges 20 together. The feet 18 preferably have a triangular shape so
 that the feet of four contiguous elements are able to form a complete and
 solid square base.
 Accordingly, when concrete is poured over a surface of appropriately joined
 modular prefabricated elements as described above, the concrete is able to
 percolate along the shaped supports 16. By solidifying, the concrete forms
 actual pillars between the shaped supports 16 of different elements.
 Compared with prior art arrangements, the present invention allows for a
 smaller amount of concrete to be used for forming the floor or slab for
 the same useful height of the interspace or hollow cavity.
 Furthermore, with the modular prefabricated element according to the
 present invention, no reinforcing ribs are required to be provided. This
 allows the modular prefabricated elements to be more inexpensive and
 simpler to mold.
 Those with skill in the art will appreciate that the modular prefabricated
 element according to the present invention can be subject to a number of
 possible modifications and variations from the above-described embodiments
 without departing from the scope of the invention as defined by the
 appended claims.