BACKGROUND OF THE INVENTION
[0001] The present invention relates to a load dissipating and limiting device for protecting,
recovering and making civil and industrial works, having a high strength against undesired
static, seismic, aeolian and dynamic effects.
[0002] As is known, in the civil and industrial construction field, as well as in the historical
monument field, it is necessary to provide structural protection against non frequent
but predictable events such as earthquakes, wind storms and any other dynamic effects
susceptible to cause vibrations.
[0003] The mentioned constructions must safely resist against the above mentioned loading
conditions, possibly without any structural damages.
[0004] Moreover, it is also necessary to consider all those phenomena, having a not dynamic
origin, subjecting the constructions to undesired deformations.
[0005] Also known is the fact that at present, near all the existing constructions, both
of historical and civil and economic interest, have not been designed and built for
resisting against the mentioned events and, actually, they have been found as unsatisfactory
from the strength and resistance standpoint.
SUMMARY OF THE INVENTION
[0006] Thus, the aim of the present invention is to overcome the above mentioned drawbacks,
by providing a load dissipating and limiting device, providing an improved stability
and increased damping of the vibrations, as well as the possibility of connecting
two or more constructional or structural elements which could be subjected to mutual
displacements, in order to dampen and limit said possible displacements.
[0007] Within the scope of the above mentioned aim, a main object of the present invention
is to provide a damping technique which can be easily applied owing to the use of
very compact and/or easily concealable devices, thereby overcoming any architectural
limitation imposed by the designer.
[0008] A further object is to provide a damping material having a very good resistance against
to the atmospheric agents.
[0009] Yet another object of the present invention is to provide such a device allowing
to limit the loading applied to the end portions thereof, as a strain or deformation
is imposed and which, moreover, is specifically designed for limiting a displacing
exceeding a maximum designed value, with the additional possibility of self-orienting
according to a direction required by the structure or construction, by means of anchoring
articulated connections and/or by exploiting its flexibility or elastic properties.
[0010] Another object of the present invention is to provide such a dissipating device which
is very stable in operation also under temperature variations and as the load application
frequency is changed.
[0011] Th above mentioned aim and objects, as well as yet other objects, which will become
more apparent hereinafter, are achieved by a load dissipating and limiting device
for protecting, recovering or making civil and industrial works, having a high strength
against undesired static effects, seismic effects, aeolian and dynamic effects in
general, characterized in that said device comprises a plurality of shape memory alloy
wires operating based on a super-elastic effect and being provided with end portions
interconnected to connecting elements for coupling to a construction to be protected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Further characteristics and advantages will become more apparent hereinafter from
the following detailed disclosure of a preferred, though not exclusive, embodiment
of a load dissipating and limiting device, which is illustrated, by way of an indicative
but not limitative example, with reference to the accompanying drawings, where:
Figure 1 is a schematic cross-sectional view illustrating the load dissipating device
according to the present invention;
Figure 2 is a graphic diagram illustrating the axial stress depending on the percentage
strain;
Figure 3 is further graphic diagram illustrating the force versus the displacement;
Figure 4 illustrates a load dissipating and limiting device provided with a fluid
holding bellow assembly;
Figures 5a, 5b and 5c illustrate characteristic curves as obtained by the inventive
device and by a further arrangement of the super-elastic effect S.M.A. wires; and
Figure 6 illustrates a pattern in which the wires, being pre-stretched, under any
mutual displacement applied to the anchoring end portions, are deformed under pulling
and react according to a characteristic curve as that shown in Figure 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] With reference to the above mentioned figures, the load dissipating and limiting
device, for protecting, recovering and making civil and industrial works, having a
high strength or resistance against undesired effects such as static effects, seismic
effects, aeolian effects and dynamic effects in general, according to the present
invention, which has been generally indicated in Figure 1 by the reference number
1, comprises a plurality of wires 2 made of a shape memory alloy (S.M.A.), exploiting
the super-elastic effect, which are arranged in an adjoining mutual relationship,
thereby the individual wires will operate in parallel to provide the designed reaction,
the length of said wires being set depending on the designed displacement
[0014] At their end portions, said wires 2 are coupled to locking elements, generally indicated
by the reference number 3, which are coupled to articulated coupling elements or connecting
elements 4, in order to apply them to the structures to be protected, possibly under
a stretched condition.
[0015] The locking elements comprise a conic locking wedge 10, which is engaged in a sleeve
11 having an inner conic surface, and therebetween the end portions of said wires
2 are arranged; the wedge and sleeve or jacket are made of a material having a surface
hardness less than that of said wires, thereby the inner conic wedge, having a less
hardness, is forcibly engaged in its seat thereby locking said wires.
[0016] A glass element 12 is moreover provided for holding therein said sleeve or jacket
and wedge, said element 12 being coupled to the connecting or coupling elements which,
for example, can comprise a latching stem.
[0017] If it is required to provide resistance against very high frequencies, then the wires
2 are introduced into a liquid, a fat material or gel material, having high thermally
conductive characteristics and, in particular, having a thermal transmission equal
to or better than that of ethylenglycol.
[0018] To that end, a liquid or fluid holding bellows 20 for holding therein a liquid or
fluid 21 is provided.
[0019] The operation or performance of the device will depend on the thermomechanical characteristics
of the shape memory alloy as used and installed under a wire form.
[0020] Figure 2 illustrates a graphic diagram related to the mechanical characteristics
of the used wires and clearly illustrating the obtained super-elastic effect by subjecting
to an axial deformation or strain a wire sample.
[0021] The material, which at the start was in an austenitic phase, presents now an elastic
phase, to which a proportional relationship between the applied stress and obtained
strain would correspond.
[0022] Upon achieving a critical strain ε
A, the austenite starts to transform to martensite, to which would correspond a nearly
constant stress up to the end of the transformation occurring at a critical strain
or deformation ε
M.
[0023] This deformation or strain range ε
A - ε
M, in which the phase transformation occurs, can be used for the intended purposes.
[0024] In fact, in the mentioned characteristic range, as the applied load is removed, the
material will tend to return to its unstrained or unstrained condition, thereby providing
an elastic recovering due to the martensite-austenite transformation as shown by the
bottom curve of the pseudo-hysteretical cycle shown in Figure 2.
[0025] More specifically, the cycle of Figure 2 shows the energy dissipated for unit of
volume by the used material, and can be easily transformed into the characteristic
curve of the full limiting device, if the number, diameter and length of the used
wires are known, as clearly shown in Figure 3.
[0026] The subject device will be conventionally designed to operate in a displacement range
S
A ÷ S
M, at a force level within the range of F
1 ÷ F
2.
[0027] Moreover, the device can be pre-stretched to a designing force level by applying
a displacement S* corresponding to a preset strain or deformation ε* in the range
ε
A ÷ ε
M.
[0028] The above mentioned pre-stretching will allow to immediately actuate the operating
dissipating effect of the device, according to the characteristic curve of Figure
3, for any displacement applied to the structure.
[0029] If the strain or deformation of the wires would exceed the value ε
M, than the wire, in a full martensitic phase, would display an immediate stiffening
up to a deformation corresponding to the martensite yielding point ε
Y, with a subsequent plasticizing and work hardening of the material to a breaking
point ε
R.
[0030] The stress corresponding to the deformation or strain ε
Y, much greater than the austenite-martensite transformation stress, will provide a
safety factor, of a comparatively very high value, both on the yielding and on the
breaking point.
[0031] The progressive stiffening effect, corresponding to strains greater than ε
M, can be used for limiting the displacement of the structure the dissipating device
is applied to, thereby preventing any undesired deformations of the structures from
occurring.
[0032] As mentioned, in the case of a vibration having a frequency greater than or equal
to 1 Hertz, it would be suitable to immerge the shape memory material wires into a
fluid (fat or gel) such as ethylenglycol, operating to dispose of the generated heat
to the outside.
[0033] The invention, as disclosed, is susceptible to several modifications and variations,
all of which will come within the scope of the inventive idea.
[0034] Moreover, all of the details can be replaced by other technically equivalent elements.
[0035] Thus, for example, even if a conic wedge has been used in the locking elements, it
would be possible, based on the same principle, to use a prismatic wedge configuration.
[0036] A further SMA super-elastic wire arrangement can provide a characteristic curve of
the subject device among them shown in Figure 5 (Figures 5a, 5b and 5c).
[0037] In fact, according to this arrangement (see Figure 6), the wire, which are pre-stretched
to a strain or deformation level of ε*, with 0≤ε*<ε
M, for any mutual displacement imposed to the anchoring ends thereof, will be always
strained under a pulling force and will react according to the characteristic curve
already shown in Figure 2.
[0038] In the latter case, the wires (Figure 6 - elements of type 1) are wound in the assembling
step on spools (Figure 6 - elements of type 2) which will be threaded on respective
pin elements (Figure 6 - elements of type 3).
[0039] The assembling of the spools, the axial distance of which will be advantageously
equal or less than that of the respective pin elements, on said pin elements, can
be carried out exclusively by stretching the wires and, accordingly, by deforming
them to increase their axial distance to the distance existing between the pin elements.
[0040] To this size difference of the inter-axes will correspond a deformation or strain
ε* of the wires.
[0041] If desired, the pin-spool system can also comprise a single monolithic element, in
order to allow a simple assembling to be easily performed.
[0042] The anchoring hardware (Figure 6 - elements of the type 4 and 5) must be suitably
perforated, by elongated holes, to provide both an abutment of a pin element and an
entraining displacement as imposed by the other pin.
[0043] This would allow the wires to be stressed always under a pulling stress, for any
mutual displacement applied to the end portions of the device.
[0044] This system, as the first, can provide, for operating at a frequency greater than
1 Hz, to immerge the wires in a suitable medium (Figure 6 - element of type 6).
[0045] Moreover, the anchoring of the wires shown in Figure 6 can be replaced by the other
above disclosed type using the wedge locking system.
[0046] The details of the system for anchoring the device to the structure can be designed
depending on the contingent requirements, to better fit the considered type of construction.
[0047] The main feature of the latter system is that, differently from the first, it would
not require to be prestretched on the field or as it is applied to the structure,
since the wires are actually prestretched during the assembling thereof.
[0048] It should be apparent that the device does not apply to the structure any stresses,
since it is self balanced in its inside.
[0049] In particular, the device will provide a reaction exclusively as a mutual displacement
occurs.
1. A load dissipating and limiting device for protecting, recovering or making civil
and industrial works, having a high strength against undesired static effects, seismic
effects, aeolian and dynamic effects in general, characterized in that said device
comprises a plurality of shape memory alloy wires operating based on a super-elastic
effect and being provided with end portions interconnected to connecting elements
for coupling to a construction to be protected.
2. A load dissipating and limiting device, according to the preceding Claim, characterized
in that said device comprises, at the end portions of said wires, locking elements
for coupling to said connecting or coupling elements.
3. A load dissipating and limiting device, according to the preceding claims, characterized
in that said locking elements comprise a locking conical wedge arranged in a sleeve
having a conical inner surface, said wedge and sleeve being made of a material having
a surface hardness less than that of said wires.
4. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said device comprises a glass element for holding therein
said sleeve and wedge, said glass element being coupled to said connecting or coupling
elements.
5. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said device comprises a space defined about said wires
for holding herein a fluid, a fat or a gel having thermal transmission characteristics
equal to or greater than those of ethylenglycol, for operating at a frequency greater
than or equal to 1 Hertz.
6. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said device comprises a bellows coupled, to the end
portions thereof, to said locking elements and holding said fluid therein.
7. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said wires are wound, during an assembling operation
thereof, on spools threaded on respective pin elements.
8. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said device is provided with a plurality of spools having
an inter-axis equal to or less than that of said respective pin elements, said spools
being assembled on said pin elements by stretching said wires and thereby straining
said wires to increase said inter-axis to the spacing of said pin elements.
9. A load dissipating and limiting device, according to Claim 8, characterized in that
said size difference of said inter-axes corresponds to a straining of said wires.
10. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that the pin element-spool system can also comprise a single
monolithic element.
11. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said device comprises anchoring means provided with
elongated holes to allow both a mechanical abutment on a pin element and an entraining
displacement as applied to the other pin element.
12. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said wires are stressed by a pulling force for any mutual
displacement applied to the end portions of said device.
13. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that, for operating at a frequency greater than 1 Hz, said
device provides to immerge said wires into a suitable medium.
14. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said wires are anchored by a wedge anchoring system.
15. A load dissipating and limiting device, according to one or more of the preceding
claims, characterized in that said device is so designed that said wires are pre-stretched
during the assembling thereof and wherein said device does not apply any stress to
said structure, since it is innerly self-balanced, to react exclusively as a mutual
displacement is applied.
16. A load dissipating and limiting device for protecting, recovering and making civil
and industrial works, having a high strength against undesired static, seismic, aeolian
and dynamic effects, according to the preceding claims, and as substantially disclosed
and illustrated and for the intended aim and objects.