[0001] The present patent application relates to a steel lattice, of the non-self-supporting
kind, to be used in the realization of mixed steel-concrete reticular systems. In
these systems, the non-self-supporting steel lattices can be used when it is not needed
that the beams are self-supporting in phase 1. With phase 1 it is intended the placement
phase of the mixed steel-concrete structure in which the concrete resistance cannot
be relied on because the casting has not yet been provided or in the first phases
of the casting, in which it is not yet cured.
[0002] For the placement of mixed reticular structures with non-self-supporting lattices
it is needed to arrange supporting shoring of the metal structures and respective
formworks; to position the single core lattices as shown in fig. 1 with suitable spacers;
to position the stirrups and the additional bars and in the following to carry out
the concrete casting. When concrete curing is ended, the beams and the orientations
have become supporting to all the loads of the working phase and the form removal
can be provided.
[0003] With reference to the technological aspects, what currently distinguishes the ordinary
concrete structures from the mixed reticular ones with non-self-supporting lattices
is the provision of shear reinforcements which arrive in the building yard in the
form of single core lattices, pre-welded in bar couples, two upper bars and two lower
bars, with the function of upper and lower longitudinal reinforcement respectively,
as it is shown in figure 2 and figure 3.
[0004] This feature is a considerable advantage in the placement phase as firstly it reduces
the time significantly, which is a fundamental aspect from the technical point of
view, and it reduces the possibilities of error in the reinforcement positioning phase.
As for the structural computing, the non-self-supporting lattices are to be tested
in the whole mixed steel-concrete structure, obviously referring to the continuous
beam model. The models of the non-self-supporting metal lattices known at the state
of the art have some drawbacks linked to the placement phase. In fact, as said, the
lattices arrive as singles pieces in the building yard, where then they have to be
correctly positioned on the formworks and constrained by means of bindings to the
stirrups so that during the casting they maintain their original position. This implies
that, even if the longitudinal reinforcements are yet pre-welded to the lattices,
a series of expensive and uncertain operations continue to be needed.
[0005] From the point of the view of the structural behavior, according to the current constructive
modes, the steel lattices have to resist when the concrete casting is cured and so
they have to interact substantially therewith. Given the morphology of the entire
structure and the natural vocation of the steel to resist to traction and of the concrete
to resist to compression, the compressed steel bars can reasonably, and with suitable
constructive measures, be eliminated from the lattice, thus allowing material to be
spared and lighter structures to be obtained which are to be maneuvered in the placement
phase.
[0006] There are also other drawbacks relating to the structural behavior of the currently
used models, linked in particular to the lack of transversal holding reinforcements
along the development of the beam, which are needed to allow the balance of the lower
transversal thrusts, generating at the concrete connecting rod. The lack of transversal
reinforcements, as for example stirrups, along the whole development of the beam,
which is also prescribed by the national and international rules, exposes the structural
element to the risk of flaw and of structural behaviors, which are not easily predictable
in the projecting phase.
[0007] Aim of the lattice object of the present invention is therefore to provide a non-self-supporting
metal lattice to be used in the realization of mixed steel-concrete reticular structures,
which solves the drawbacks linked to the embodiments known at the state of the art,
and allows a faster and more correct placement, a material sparing and a better predictability
in the projecting phase of the structural behavior.
[0008] The detailed description of the invention will refer to the appended drawings 1 to
10.
Figures 1 and 2 show views of the non-self-supporting lattice according to an embodiment
known at the state of the art,
Figures 3, 4 and 5 show views, respectively side axial and section views, of the lattice
known at the state of the art,
Figures 6 and 7 show views of a preferred embodiment of the non-self-supporting lattice
according to the present invention,
Figures 8, 9 and 10 show views, respectively side, axial and section views, of a preferred
embodiment of the non-self-supporting lattice according to the present invention.
[0009] Fundamental feature of the metal non-self-supporting lattice is the provision of
the sole rods (21) which, in a standard uniformly distributed load configuration,
are stretched.
[0010] This is clear from the comparison of figures 2 and 7. In figure 2, where it is shown
a lattice (1) according to an embodiment known at the state of the art, there are
provided rods (11, 12), which in uniformly distributed load configuration are both
stretched and compressed. In the lattice according to the present invention (2), shown
in figure 6 and more detailed in figure 7, there are instead provided only rods (21),
which in uniformly distributed load configuration are stretched. As it is well visible
in section view of figure 8, they are diagonal rods constrained to the upper reinforcement
in the closest end to the support (23) of the lattice (2) on the pillar (3), and to
the lower reinforcement in the closest end (212) to the middle (24) of the lattice
(2). This choice comes from the fact that in the working phase the concrete connecting
rods, with suitable constructive measures, are able to face by themselves the compression
stresses generating along the shear paths.
[0011] As it is clear from figure 8, the structure of the beam is symmetrical with respect
to a vertical axis passing through the middle. By analyzing the load path relative
to a load concentrated in the middle, it is to be noticed how the diagonal rods are
positioned at the traction stressed areas, since the steel reinforcement has to react
to the tractive efforts.
[0012] The lattice according to the present invention (2) comprises also closed stirrups
(25) at the lower knots of the core reinforcement, such that the balance of the transversal
thrusts is guaranteed, which generate at the concrete connecting rods at the soffit
of the beam (2).
[0013] Such stirrups (25) can be suitably comprised in the computing of the whole shear
resistance of the structural element, thus providing another resistant resource. Moreover
the introduction of the stirrups (25) allows to conform to what prescribed by the
national and international rules for similar structures.
[0014] Another advantage of the lattice (2) according to the present invention is that two
or more lattices (2) and the respective stirrups (25) can arrive in the building yard
yet welded according to the different constructive needs. In this manner, the placement
operations are reduced to the simple positioning of the pre-assembled lattice and
to the following casting. This allows not only to speed significantly the building
yard operations, but also to reduce the possibilities of error while positioning the
reinforcement before and during the casting.
[0015] What described represents a preferred embodiment of the metal lattice defined in
the following claims.
1. Metal non-self-supporting lattice for the realization of mixed steel-concrete reticular
structures comprising:
- at least a couple of upper longitudinal reinforcements (26) and at least a couple
of lower longitudinal reinforcements (27),
- connecting rods (21) of said upper and lower longitudinal reinforcements
characterized in that
said rods (21) are configured such that they are stressed only by tractive efforts
in conditions of downwards vertical load, uniformly distributed on the lattice (2).
2. Metal non-self-supporting lattice for the realization of mixed steel-concrete reticular
structures according to claim 1, characterized in that said rods (21) are constrained diagonally in a vertical plane to said upper (26)
and lower (27) longitudinal reinforcements, with the closest end (211) to the end
portion (23) of the lattice (2) constrained to the upper longitudinal reinforcements
(26), and the other end (212) constrained to the lower longitudinal reinforcements.
3. Metal non-self-supporting lattice according to claim 2, characterized in that the inclination of said rods (21) with respect to the vertical is between 30° and
60°.
4. Metal non-self-supporting lattice for the realization of mixed steel-concrete reticular
structures according to any one of claims 1 to 3, further comprising closed stirrups
(25) constrained to said supper and lower reinforcements.
5. Metal non-self-supporting lattice for the realization of mixed steel-concrete reticular
structures according to claim 4, characterized in that said closed stirrups (25) are positioned along the whole length of the lattice (2)
at the lower ends (212) of said rods (21).
6. Metal non-self-supporting lattice for the realization of mixed steel-concrete reticular
structures according to claim 5, characterized in that said closed stirrups (25) are positioned at close axial distance in the end portions
of the lattice.
7. Mixed steel-concrete reticular structure comprising a metal lattice according to any
one of the preceding claims.