[0001] The present patent application relates to a new kind of structural panel point for
mixed steel-concrete reticular trusses. At the state of the art there are known some
embodiments of panel points for mixed steel-concrete reticular structures, commonly
used in the building field for realizing structures in reinforced concrete.
[0002] They are generally structures constituted by one or more prefabricated metal reticular
trusses, which are assembled in a concrete casting realized in the building yard.
The placement of such structures is provided firstly by the positioning of the prefabricated
reticular truss and in the following by the realization of the concrete casting. Therefore,
two phases of the useful life of such structures, commonly called phase 1 and phase
2, can be distinguished.
[0003] The phase 1 is the phase in which the resistance is provided totally by the steel
lattice, which being self-supporting, has to resist to the floor and completing fluid
concrete weight, to the weight of the additional reinforcement prearranged before
the casting at the points stressed by negative moments and to accidental loads possible
during the phase 1. The steel lattice, being subjected to each above described action,
has to remain in an acceptable deformation field, which is expected and calculated
in the project phase. In phase 2, instead, the resistance is provided by the structure
formed by the steel lattice and by the concrete of the additional casting, which at
the end of the curing, has developed the mechanical properties expected in the project
phase. Since the additional casting of concrete is made on the entire deck, it is
able to make the entire structure integral, thus providing a continuous beam assembly.
[0004] During phase 1, according to constructive systems known at the state of the art and
commonly used in the building field, the prefabricated steel lattices coming from
the workshops are rested, by means of suitable cranes, on the heads of pillars, thus
realizing structures, statically schematizable as beams simply rested on the ends.
A schematization of the static model of phase 1 applied to the embodiment of the mixed
reticular trusses is shown in figure 1. As it can be noted, the kind of constrain
considered at the intersection between beam and pillar is a support (1). On the beam
a distributed vertical load (3) acts, which generates a not negligible maximum moment
(4) in the middle of the beam between two adjacent supports (1).
[0005] During phase 2, consequently to the concrete curing, the reference static model for
calculating stresses and deformations becomes that of a beam fixed to the ends, one
schematization of which applied to the embodiment of the mixed reticular trusses known
at the state of the art is shown in figure 2, where it can be noted how a support
at the intersection between beam and pillar is no more provided, but it is provided
a fixed end (2). Obviously, it is needed to provide structural continuity at the constraints,
yet in during phase 1. Generally, in fact, on one pillar (21) more beams (11, 12,
13, 14) are rest, which can be arranged according to various directions as it is shown
in figure 3. According to what is known at the state of the art, the structural continuity
at the constraints is made possible by using bars (31, 31) with better bond coefficient,
simply rested on the longitudinal reinforcements (111, 121, 131, 141) of the prefabricated
beams (11, 12, 13, 14), resting on the same pillar. Such bars, said also additional
bars, are positioned before the casting, and are normally bonded with binding wire
to the beams to be bonded. In this way, when the concrete casting comes to curing,
the reinforcements guarantee a continuity between the adjacent beams by means of known
resistant mechanisms due to the adherence between steel and concrete.
[0006] The embodiments known at the state of the art, commonly used in works in ordinary
reinforced concrete have many limits, mainly linked to the uncertainties inherent
to the building yard operations. The correct positioning of the bars (31, 32) and
the suitable anchorage of the same to the longitudinal reinforcements of the prefabricated
beams, which guarantee their position also during the casting, are in fact fundamental
requirements for the correct functioning of the structure. The work thus realized
has to correspond in fact to the structural model provided in the project phase, according
to which the resistance and deformation tests are carried out.
[0007] Yet referring to the uncertainties of the building yard operations, it is needed
that the concrete thickness covering the additional reinforcements complies with the
minimum dimensions provided by the regulations concerning the adopted calculating
models, so that the desired resistant mechanisms can be developed. This implies particular
attention during the concrete casting phase.
[0008] Moreover, as it is known, the adherence anchorage needs that a certain length percentage
of reinforcement called "anchorage length" to be summed up with the one really resistant,
is destined only to guarantee the starting of suitable resistant mechanisms. The calculating
modes of the anchorage lengths of the bars with better coefficient bond are defined
by the regulations on the basis of a series of project parameters. In the most recently
regulations, such for example the New technical regulations on construction (NTC 2008)
and the Eurocode 2, the trend is a substantial increase in the anchorage length. From
figure 3 it is clear that the additional reinforcements (31, 32) are provided with
a non negligible length.
[0009] The construction modes set by the kinds of beams now available on the market impose
to calculate the stresses in a differentiated way in phase 1 and phase 2, applying
then the principle of effects overlapping, in the hypothesis that the deformation
in first and second phase are maintained in the elastic range. In particular, the
calculation is carried out considering the metal structure in phase 2, pre-stressed
by the loads of phase 1. Therefore, for the Ultimate limit state tests, the effects
deriving from the phase 1 are considered as permanent actions (structural) in the
load combinations of the phase 2. Such effects refer to the stresses and to the respective
deformations. To carry out the calculations according to these hypotheses implies
a significant computational load with, in addition, the need for the operators to
carry out a double structural test for the two phases, changing each time the structural
model and the reference loads.
[0010] In particular in the calculations of the stresses the structural model of the beam
with simple supports at the ends in phase 1, shown in figure 1, implies that in the
middle of the beam relevant stresses (4) are reached (maximum positive moment), on
the basis of which the dimensioning of the lower plate (112, 122) of the prefabricated
lattice is carried out. Such lower plate (112, 122) in phase 2, when the beam has
the end constraints similar to fixed joints (2), whose rigidity is defined each time,
results over-dimensioned.
[0011] Moreover, at the moment, the upper longitudinal reinforcements (111, 121) of the
lattice (11, 12), which have to resist to compression during the phase 1, are practically
inactive during phase 2 at the critical area of the beam. This means that the upper
stringers of the lattice which have to resist to compression in phase 1 and to remain
almost inactive to traction in the area interested in phase 2 are not optimally exploited.
In synthesis, the current constructive modes force to over-dimensioning the metal
reinforcements with respect to the loads to be effectively resisted in working phase.
[0012] Aim of the present invention is therefore to provide a structural steel panel point
to be used in realizing mixed steel-concrete reticular structures, which while improving
the constrain conditions of the structures in phase 1 allows not to over-dimension
the metal reinforcements with respect to the loads to be supported in the working
phase. Consequently, there results an important economical advantage, linked to cost
reduction for purchasing, working and transporting the metal reinforcements.
[0013] Moreover there result other advantages linked to the elimination of the building
yard uncertainties which impose to over-dimension the additional reinforcements, and
to less computational load in testing the structure in phase 1 and phase 2.
[0014] These and other advantages will be highlighted in the following detailed description
of the present invention, which refers to the appended drawings 1 to 8.
Figure 1 shows a scheme of the static model of the loads acting during the phase 1
on a mixed reticular structure realized according to techniques known at the state
of the art.
Figure 2 shows a scheme of the static model of the loads acting during the phase 2
on a mixed reticular structure realized according to techniques known at the state
of the art.
Figure 3 shows a structural panel point realized according to embodiments known at
the state of the art.
Figure 4 shows a view of a preferred embodiment of the structural steel panel point
according to the present invention, in which it is shown the assembly of lower bars.
Figure 5 shows a view of a preferred embodiment of the structural steel panel point
according to the present invention, in which it is shown the assembly of upper bars.
Figure 6 shows two constrained beams with the structural panel point according to
the present invention.
Figure 7 shows four cross-constrained beams with the structural panel point according
to the present invention.
[0015] As yet said, the steel lattice (11, 12, 13, 14) arrive in the building yard according
to the current constructive modes. After their positioning on the heads of the pillars
(21), first the additional reinforcement (31, 32) are arranged and next the concrete
casting is carried out.
[0016] As it is shown in figure 4 and figure 5, on the lattices comprising the steel panel
point according to the present invention there are provided sections (40, 41) constrained
to the metal lattices (11, 14) at the constraint of the same pillar (21). The sections
(40, 41) are preferably in steel, and the constraint of these lattices (11, 14) occurs
preferably by welding. In this way, the constraint of the section (40, 41) to the
lattice (11, 14) can be carried out in the workshop and not in the building yard.
The sections (401, 402, 411, 412) are arranged so that, once the two beams (11, 14)
are arranged in their assembly position, through the sections (401, 402, 411, 412)
of the two adjacent beams one or more threaded bars (50) can be introduced, which
function as additional reinforcements. According to an assembly scheme particularly
common in the building field, the threaded bars (50) can be arranged in parallel to
the main axis of the lattice (11, 14), as shown in figures 4 and 5.
[0017] The constraint of the beams (11, 14) by using the structural panel point according
to the present invention occurs, after the positioning of the same, by introducing
the threaded bars (50) inside the sections (401, 402, 411, 412) constrained to the
two beams (11, 14) and which are aligned when the same are in assembly position. On
each threaded bar (50), before or after introducing the sections therein, a couple
of nuts (51) are screwed for each section crossed by the bar (50).
[0018] The dimensions of the sections (401, 402, 411, 412), the nuts (51) and the threaded
bars (50) have to be chosen so that the nuts (51) thread on the threaded bars (50)
and the free space of the sections (401, 402, 411, 412) is such that the passage of
the threaded bar (50) is possible, but not the one of the nut (51) screwed on the
same. In this way, as it is shown in figure 6, the nuts (51) constrain the respective
position of the threaded bars (50) with respect to the beams (11, 14) and, so, of
the same beams the one to the other.
[0019] A feature of the sections (401, 402, 411, 412) is therefore to be hollow metal sections,
preferably obtained by extrusion. As it can be noted by the comparison of the elements
(401, 402) and (411, 412) in figure 4, their length can be strongly variable, and
it can be convenient chosen by the engineer according to the load features of the
projected work. Moreover, the shape of the sections can be preferably rectangular
or square, as it is shown in figure 4, but other shapes are not excluded from the
objects of the present invention, as for example the cylindrical one.
[0020] The unique obligation is that the arrangement of the sections (401, 402, 411, 412)
with respect to the beams (11, 14) and their dimension are such that the assembly
of the structural panel point is possible according to what above described. Moreover,
the use of the threaded bars (50) allows to respect scrupulously the distances between
the beams (11, 14) defined in the project phase, in addition to control the stress
imposed to the reinforcement and to the structural elements by the constraint. In
fact, it is sufficient to tighten the nuts (51) by means of a dynamometric key, in
order to comply with the prescriptions about the tightening torque defined in project
phase.
[0021] A plurality of sections (40, 41) can be constrained to the metal lattices (11, 14)
to realize the structural panel point without departing from the scope of the present
invention. According to a preferred embodiment, shown in figure 6, some sections are
provided at the upper (111, 141) and lower reinforcements (112, 142) of the metal
lattices (11, 14), but this aspect does not limit the possibility to arrange a different
number of sections in positions different from what is shown. Similarly, the kind
of lattice shown is to be intended only as a way of example and non limiting the aims
of the present invention, which can be usefully applied on metal reinforcements of
different shape or structure.
[0022] According to a preferred embodiment, shown in figures 4 and 5, the sections (411,
412) arranged at the lower reinforcements (112, 142) of the lattices (11, 14) can
be positioned so that they project axially with respect to the same lattices, and
they are usefully used as supports for a suitable positioning of the lattices (11,
14) on the heads of the pillar (21).
[0023] The use of the structural panel point according to the present invention allows to
solve the limits of the structural panel points known at the state of the art, linked
as said to the uncertainties during the phases of placement of the additional reinforcements.
In fact, the upper (111, 121, 131, 141) and lower reinforcements (112, 122, 132, 142)
of the beams (11, 12, 13, 14) realized to be constrained to the structural panel point
according to the present invention are provided with well defined housings, constituted
by the sections (401, 402, 411, 412), inside which the additional reinforcements (50),
in this case by the threaded bars, are to be introduced and bolted.
[0024] Moreover the provision of the bolts (51), in addition to their possible controlled
tightening, guarantees that during the casting phases the position of the beams (11,
12, 13, 14) and of the additional reinforcements (50) remains unchanged thus allowing
to reproduce exactly in the building yard the structural model expected in calculating
phase.
[0025] Moreover the threaded reinforcements (50) are active along their whole net length,
calculated from the first to the last threaded bolt (51) thereon. This aspect allows
to adopt shorter reinforcements, which are simply transportable and controllable,
in addition to be cheaper with respect to what is known at the state of the art. It
is not needed in fact, as occurs according to embodiments known at the state of the
art, to over-dimension the length of the additional reinforcements (31, 32) to guarantee
the adherence with the concrete.
[0026] Another advantage of the structural panel point according to the present invention
is that it allows to use a continuous beam model in the calculating phase since the
phase 1. Thanks to the threaded reinforcements (50) placed and bolted immediately
after the positioning of the lattices (11, 12, 13, 14) on the pillars (21) and before
the positioning of the floors and the concrete casting, it can be used in fact a calculating
schematization with more rigid constraints then a simple support at the pillars. This
allows to reduce the maximum moment (4) in the middle of the lattices (11, 12, 13,
14) and as a consequence to dimension in a more contained way the reinforcements of
the same lattice. At the same time, on the pillar (21) a bending stress is generated
which can be simply managed.
[0027] Moreover, as yet said, having since the phase 1 a continuous beam allows to carry
out the calculation on a unique structural model with pre-stressed reinforcements,
simplifying the calculations and diminishing the computational loads.
[0028] The provision of the reinforcements (40, 41) welded to the upper longitudinal reinforcements
(111, 121, 131, 141) of the lattices (11, 12, 13, 14) allows to activate to traction
said longitudinal bars, thus allowing the length of the additional reinforcements
to be reduced at minimum.
[0029] Moreover, the configuration of the panel point in its different elements, allows
to carry out easily the project following the local hierarchy principle of the resistances,
allowing to carry out a correct dimensioning of the different elements according to
the peculiarities of the structure used each time. Finally, the proposed solution,
as it is clear in figure 7, solves the problem of the interaction between the upper
(501, 502) and lower bars (503, 504) in case four beams coincide in the panel point.
The use of the rectangular sections (401) allows to mount easily the bars of the primary
beams (501, 503) and those of the secondary beams (502, 504) at different heights.
[0030] It is clear that what described can be realized with the most convenient material,
for example carpentry steel or reinforced concrete steel.
1. Apparatus for positioning and constraining metal beams to be used in mixed steel-concrete
structures, comprising:
- constraint means (401, 402, 411, 412) integral with the beam to be constrained (11,
12, 13, 14),
- at least an additional reinforcement (50, 501, 502, 503, 504)
- connecting means (51) to constrain said constraint means (401, 402, 411, 412) to
said additional reinforcement (50, 501, 502, 503, 504) characterized in that
said constraint means (401, 402, 411, 412) and said additional reinforcement (50,
501, 502, 503, 504) are configured so that they are constrained by means of said connecting
means (51).
2. Apparatus for positioning and constraining metal beams to be used in reticular mixed
steel-concrete structures according to claim 1, characterized in that said constraint means (401, 402, 411, 412) comprise at least a hollow section metal
bar, welded to the beam, and positioned so that the axis of the bar is parallel to
the axis of the beam.
3. Apparatus for positioning and constraining metal beams to be used in mixed steel-concrete
structures according to claim 1 or 2, characterized in that said additional reinforcement (50, 501, 502, 503, 504) comprises at least a threaded
bar and said connecting means (51) comprise nuts of such dimensions that they can
be screwed on said threaded bar.
4. Apparatus for positioning and constraining metal beams to be used in mixed steel-concrete
structures according to claim 3, characterized in that the dimensions of said threaded bar (50) and said hollow section metal bar (401,
402, 411, 412) are configured such that the threaded bar (50) can pass through the
hollow section (401, 402, 411, 412), but the nuts (51) threaded on the threaded bar
are greater than the opening of the section (401, 402, 411, 412).
5. Apparatus for positioning and constraining metal beams to be used in mixed steel-concrete
structures according to any one of the preceding claims, characterized in that said constraint means (401, 402) integral with the beam to be constrained allow said
additional reinforcement (50) to be positioned at different heights with respect to
the same beam.
6. Metal beam (11, 12, 13, 14) to be used in the reticular mixed steel-concrete structures
comprising the apparatus for positioning and constraining the metal beams according
to any one of the preceding claims.
7. Metal beam according to claim 6, characterized in that the beam is configured such that when said beam (11) in positioned on the same assembly
line of a second metal beam (14) according to claim 6, each of said constraint means
(401, 411) is positioned so that it can be connected, by means of an additional reinforcement
(50) constrained by means of said connecting means (51), to a corresponding constraint
means (402, 412) integral with the second beam (14) to be constrained.
8. Metal beam according to claim 6, comprising at least two constraint means (401, 411)
integral with the beam, positioned so that the additional reinforcements (50) constrained
to said constraint means integral to the beam, are positioned at the upper reinforcements
(111) and/or the lower reinforcements (112) of the beam (11).
9. Metal beam according to claim 7, characterized in that said constraint means (411) at the lower reinforcements (112) of the beam (11) project
axially with respect to the same beam (11).
10. Method for realizing a structural panel point comprising at least two metal beams
(11,14) according to any one of claims 5 to 8 to be constrained to a pillar (21),
comprising the steps of:
- positioning the beams (11, 14) in their assembly position with respect to the pillar
(21), possibly using as support said metal sections (411, 412) projecting from each
beam at the lower reinforcements (112, 142),
- introducing one or more threaded bars (50) through each couple of sections (401,
402) (411, 412) which is in corresponding position to the two beams (11, 14) to be
connected,
- constraining the threaded bars (50) to the metal sections (401, 402, 411, 412) by
means of a couple of nuts (51) threaded on each threaded bar (50) at each section
(401, 402, 411, 412),
- possible tightening of said nuts (51) by means of a dynamometric key so to guarantee
a controlled traction stretch to the threaded bar.