Self-centering energy dissipative brace apparatus with tensioning elements

The present invention generally relates to a self-centering energy dissipative brace apparatus. A bracing system is often needed to stabilize, strengthen or stiffen structures such as buildings which are subjected to severe or extreme conditions. The brace apparatus may be installed in a structure to dissipate input energy and minimize residual deformations related to exceptional loading imposed on the structure by winds, earthquakes, impacts or explosions. The apparatus integrates self-centering properties and energy, dissipative capacities which help minimize structural damage.

FIELD OF THE INVENTION

The present invention generally relates to an energy dissipative brace apparatus with self-centering properties. More specifically, the present invention is concerned with a brace apparatus for installation in structures which may be subjected to extreme loading conditions.

BACKGROUND OF THE INVENTION

Although the design of structures under normal loading conditions aims at meeting serviceability and ultimate strength requirements by providing strength, stiffness and stability, it has been recognized recently that to effectively and safely resist extreme loading conditions such as earthquakes and blast loads, a fundamentally different approach must be used. It is economically unfeasible as well as being potentially unsafe to design structures for linear elastic response under such loading conditions, especially if, as a result of this design philosophy, no ductility capacity is provided in the system. This implies that the nonlinear behavior of yielding systems, which limits the seismic forces induced in structures, is a highly desirable feature.

For yielding systems, the energy dissipated per cycle through hysteretic yielding (inelastic deformations) is generally associated with structural damage. Such yielding systems are expected to sustain residual deformations which can greatly impair the structure and increase repair costs. This raises important questions which usually remain unanswered following extreme loading conditions: does a structure that has undergone a certain level of inelastic deformation still provide the same level of protection as before? Must all yielded elements be replaced? Must the state of the material at every location where yielding has taken place be assessed?

There also exists a strong belief, mainly from the public, that a structure designed according to the latest seismic codes, for example, would require little or no structural repair and would result in minimal disruption time following an earthquake. Current research efforts in earthquake engineering still embrace this philosophy of achieving stable hysteretic response of predetermined elements of the structure. Structural damage and residual deformations are therefore expected under design level earthquakes.

For example, traditional steel braced frames are designed primarily to assure life safety under a major earthquake. They are expected to sustain significant damage after an earthquake due to repeated cycles of brace tension yielding and brace compression buckling. Furthermore, as a direct consequence of the damage induced in these elements, the final state of the entire building is likely to be out of plumb. Similar response is also expected from the other conventional steel, reinforced concrete, masonry and timber structural systems (moment-resisting frames, walls, etc.). Poor structural performance also results in damage to operational and functional components of buildings, such as architectural components, building services or building contents. Both structural and non structural damage can impact on the safety and rescue of building occupants and can lead to interruption of building operations.

This reality has important consequences as to the costs of repair and the costs induced by disruption time following an important earthquake. Note that a structure that is found to be structurally sound after an earthquake may be condemned if the costs of straightening are elevated or if it appears unsafe to occupants. Increasingly, owners of structures in seismic prone areas that are faced with the expected state of their structure following a major earthquake often opt to directly implement higher performance systems. Furthermore, insurance companies are also increasingly basing their premiums on expected damage costs, and with this additional incentive, the number of owners that will adopt high performance systems for new or existing structures is likely to increase.

The current state-of-the-art for specialized dampers that are used to improve seismic performance mainly consists of either hysteretic (yielding), friction, viscously damped, viscoelastic systems or shape memory alloys. The hysteretic (yielding) systems consist of elements that are designed to undergo repeated inelastic deformations and that exhibit variable hysteretic responses.

A first family of such systems is referred to as yielding systems such as the buckling restrained braces or yielding steel plates. Yielding systems have been successfully implemented in numerous projects in Asia and North America. A second family of such systems is referred to as friction systems, of which one of the most popular is the Pall system. This system has been implemented in a very large number of structures in the past 15 years.

Note that none of these two families of systems exhibits self-centering properties, which can negatively impact on the overall performance of structures when subjected to earthquakes and other severe or extreme loads and may result in permanent deformations.

Viscous systems are specialized devices that exhibit a velocity dependent force and increase the damping of the structure thus reducing the response under seismic loading. Viscoelastic dampers also exhibit a velocity dependant force to increase damping while providing an additional elastic restoring force in parallel. Structures equipped with viscous and visco-elastic dampers require the main structural system to provide sufficient elastic stiffness and strength to resist the applied loads. These devices do not assure self-centering properties if the main structural elements undergo inelastic deformations.

A shape memory alloy is generally a metal that regains by itself its original geometrical configuration after being deformed or heated to a specific temperature. Shape memory alloys generally provide highly specialized production capability, but are generally expensive materials.

To date, self-centering behavior has mainly been achieved by specialized dampers comprised of complex inter-connected spring elements that require sophisticated fabrication processes and shape memory alloy materials that are prohibitive in most common structural projects because of elevated costs.

In U.S. Pat. No. 5,819,484 entitled “Building structure with friction based supplementary damping in its bracing system for dissipating seismic energy” (issued on Oct. 13, 1998), Kar teaches about a brace apparatus that provides re-centering capabilities through a friction spring energy dissipating unit, but which converts tension and compression applied to the apparatus into compression exerted on the stack between the two ends of the apparatus which are mountable to two portions of a building.

In U.S. Pat. No. 5,842,312 entitled “Hysteritic damping apparati and methods” (issued on Dec. 1st, 1998), Krumme et al. teach about damping apparatus using one or more tension elements fabricated from shape-memory alloy to provide energy dissipation. However, the apparatus of Krumme et al. which has two relatively moving bracing members linked together by the tension elements provides that some tension elements are involved during a force loading, but the self-centering behavior of the damping apparatus results from specific nonlinear material properties and do not involve mechanical interaction between elastic components.

The previous discussion leads to suggest that an optimal extreme load resistant system should:

i) incorporate the nonlinear characteristics of yielding structures to limit the forces imposed on the system by the severe or extreme loading, and dissipate input energy to control deformation;

ii) reduce the cost of repairs of the structure by encompassing re-centering properties allowing it to return to its original position after the extreme loading;

iii) further reduce the cost of repair by minimizing the occurrences of damages to the main structural elements.

Optimal resistance to severe or extreme loading increases the performance level of structures in the event of a major earthquake, hurricane or the like which sometimes occur in highly populated urban areas. Structures equipped with these high performance elements significantly offer better responses to such extreme loading with minimal damage, reduced repair costs and disruption time.

Furthermore, these systems may be very attractive to local, provincial and federal government facilities as well as to owners and managers of critical facilities that must remain functional during and immediately after major or catastrophic events.

OBJECTS OF THE INVENTION

An object of the present invention is therefore to provide an apparatus which encompasses the same architectural features as current technology and the same response characteristics under service loads, but offers a highly enhanced response under severe cyclic loading which minimizes structural damage and efficiently provides self-centering characteristics.

A further object of the present invention is to provide an apparatus which efficiently develops the aforementioned hysteresis and self centering capacities by combining simple and structural elements and readily available materials such as, for example, structural steel and high-strength tensioning elements.

SUMMARY OF THE INVENTION

More specifically, in accordance with the present invention, there is provided an apparatus designed in the form of a bracing system that achieves a hysteretic behavior and self-centering properties by combining specialized components that can be built using readily available construction materials. In addition the apparatus may be provided with energy dissipating systems such as, but not limited to, friction surfaces, yielding sacrificial members, visco-elastic materials, viscous fluid dampers or shape memory alloys to provide the desired level of energy dissipation.

There is therefore provided a brace apparatus to be mounted between two portions of a structure subjected to a loading force to limit movements due to the loading force, the brace apparatus including a fixed portion having a first end to be mounted to a portion of the structure, the first end defining a first abutting surface and a second end defining a second abutting surface, the brace apparatus further including a movable portion having a first end to be mounted to a portion of the structure, the first end defining a first abutting surface and a second end defining a second abutting surface, the brace apparatus further including a tensionable assembly mounting the movable portion to the fixed portion so that a) the first movable portion abutting surface is in proximity of the second fixed portion abutting surface, and b) the first fixed portion abutting surface is in proximity of the second movable portion abutting surface, the tensionable assembly including a first abutting element in the proximity of the first end of the fixed portion and a second abutting element in the proximity of the first end of the movable portion; the first and second abutting elements being interconnected by an adjustable tensioning element; wherein, i) when a loading force moves the movable portion away from the fixed portion, the first abutting element abuts the first fixed portion abutting surface and the second abutting element abuts the first movable element abutting surface to thereby limit the movement of the movable portion away from the fixed portion and ii) when a loading force moves the movable portion towards the fixed portion, the first abutting element abuts the second movable portion abutting surface and the second abutting element abuts the second fixed element abutting surface to thereby limit the movement of the movable portion towards the fixed portion.

There is therefore provided a brace apparatus mountable between two portions of a structure subjected to a loading force, the brace apparatus including a first bracing member having a first end mountable to one of the two portions and a second end, each having an abutting surface, a second bracing member having a third end and a fourth end mountable to another one of the two portions and each having an abutting surface, the first and second bracing members being movably operatable between a rest position and a transitional position such that i) the first end is in proximity of the third end so as to define a first proximity end pair and the second end is in proximity of the fourth end so as to define a second proximity end pair, ii) the first end is opposed to the fourth end so as to define a first opposed end pair and the second end is opposed to the third end so as to define a second opposed end pair, the brace apparatus further including a tensionable assembly including abutting elements in the proximity of the first and second proximity end pairs, the abutting elements being interconnected by a tensioning element; whereby the first and second bracing members are movable apart when the loading force applied to the first opposed end pairs i) tensions the apparatus such that respective abutting surfaces of the first opposed end pair abuts on respective abutting elements, ii) compresses the apparatus such that respective abutting surfaces of the second opposed end pair abuts on respective abutting elements; the tensioning element being tensionable under the loading force such as to alternatively move the first and second bracing members from the rest position to the transitional position.

DETAILED DESCRIPTION

The present invention relates to a brace apparatus provided for the dissipation of input energy applied to structure systems, such as for example beams, columns, braces, walls, wall partitions, subjected to severe, extreme and/or repetitive loading conditions. The brace apparatus is mountable to portions of the structure to restrain or oppose to the relative motion between the two portions. In doing so, the brace apparatus generally maintains minimal residual deformations, dissipates energy and includes self-centering capacities once the input energy changes or ceases to be applied to the structure. Typically, input energies are related to exceptional loadings caused by winds, earthquakes, impacts or explosions which are sometimes imposed on structures or architectural systems.

As shown in the illustrative embodiment ofFIG. 1, the apparatus30generally includes a first bracing member32, a second bracing member34, a tensionable assembly36, energy dissipative systems38and guiding elements39. The second bracing member34may be viewed as a fixed member and the first bracing member32may be viewed as a movable member of the apparatus30. Of course, one skilled in the art will understand that the movement between the members32and34is relative.

The bracing members32and34, shown inFIGS. 1 to 3and in more details inFIG. 4a, include ends40a,40b,40c,40dprovided with respective abutting surfaces42a,42b,42c,42dwhich are configured and sized as to abut with the tensionable assembly36. The bracing members32and34further include apertures45providing the space requirement for the installment of the energy dissipative systems38and for inspection of the apparatus30after operation, as will be further described hereinbelow.

For clarity purposes, the various ends40a,40b,40c,40dof the bracing members32and34will also be referred to as “end pairs” of the apparatus30in the following description. More specifically, the end40awhich is in proximity of the end40cdefine a first proximity end pair and the end40bwhich is in proximity of the end40ddefine a second proximity end pair. Similarly, the end40awhich is opposed to the end40ddefine a first opposed end pair and the end40bwhich is opposed to the end40cdefine a second opposed end pair.

In the illustrative embodiment ofFIGS. 1 to 4d, ends40a,40d(the first opposed end pair) are further provided with end connections44a,44dadapted for mounting the apparatus30on the external structure (not shown) subjected to input energy. The end connections44a,44dare plates or any other structural element fixedly attached (welds, bolted or joined assemblies) to the bracing members32and34. The end connections44a,44dare configured and sized so as to receive a loading force and as to transmit it to the apparatus30. Optionally, the end connections44a,44dare further designed to yield at a certain loading force level to protect the integrity of the apparatus30.

The bracing members32and34, are generally parallel, longitudinally extending and independently movable one with respect to the other when subjected to a certain level of loading force. In the illustrative embodiment, the first bracing member32is a tubular member located inside of and generally concentric to the second bracing member34.

As illustrated inFIGS. 1 to 3and in more details inFIG. 4b, the tensionable assembly36includes four adjustable tensioning elements46(only two shown inFIG. 4b), and two abutting elements48a,48binterconnected by the tensioning elements46. The tensioning elements46are generally pre-tensionable tendons, cables or rods which are mounted to the abutting elements48a,48bthrough various types of fastener assemblies, such as for example nuts49, clamping or attachment devices capable of providing tension adjustability to the tensioning elements46.

The tensioning elements46are generally symmetrically positioned with respect to the abutting elements48a,48bin order to provide for better load distribution within the tensionable assembly36. The number of tensioning elements46, their modulus of elasticity, their ultimate elongation capacity, their total area and their length are selected to achieve the desired strength, the post-elastic stiffness, the deformation capacity, and the self-centering capacity of the apparatus30.

The tensioning elements46are capable of deforming under a loading force applied to the apparatus30such as to allow a targeted elongation of the apparatus30resulting from relative movement between the two bracing members32and34, as will be further described hereinbelow. This deformation first generally occurs without yielding and with minimal loss of the pre-tensioning force in the tensioning elements46.

The level of pre-tension in the tensioning elements46generally ranges from no pre-tension at all to some fraction, typically between 20% and 60% of the maximum allowed deformation of the tensioning element46. The level of pre-tensioning determines the force level at which the relative movement starts between the bracing members32and34, determines the initiation of energy dissipation in the energy dissipative mechanisms38and determines the change in the stiffness of the tensioning elements46ranging from the initial elastic stiffness to the post-elastic stiffness. The level of pre-tension also provides the re-centering capability of the apparatus30, as will be further explained hereinbelow. If the level of pre-tension is not sufficient to overcome the force required to activate the energy dissipation mechanisms38, the apparatus generally does not display a full re-centering capacity, but the tensioning elements46generally provide additional post-elastic stiffness to the apparatus30.

The abutting elements48a,48bare plates or any other suitable structural elements that are positioned in the proximity of the first and second proximity end pairs40a,40cand40b,40d. The abutting elements48a,48bare configured and sized so as to cooperate with the abutting surfaces42a,42b,42c,42dof the ends40a,40b,40c,40dwhen the bracing members32and34are moving with respect to one another under a loading force, as will be further explained hereinbelow.

In the illustrative embodiment ofFIGS. 1 and 4b, the abutting element48aincludes a passage (not shown) extending therethrough and into which the end connection44ais slidably received. The other abutting element48bis slidably received within the end connection44d.

Turning back toFIGS. 1 and 3, the guiding elements39are shown in the form of plates, blocks, or other suitable structural elements which are provided between the bracing members32and34to allow, guide or impose the relative movement of the bracing members32and34, while still helping to maintain their relative alignment. Guiding elements39may also be used to connect or mount the tensionable assembly36along the length of the bracing members32and34, to enhance the buckling capacity of members32and34. The guiding elements39may further include absorbing materials such as for example rubber, Teflon® or elastomeric materials which are used to mitigate impact between the bracing members32and34.

Energy dissipative systems38, which are schematically illustrated inFIGS. 1 to 5and10ato13d, include friction50, yielding52, viscous54and/or visco-elastic56mechanisms or other components such as for example shape-memory alloys57that are mobilized or involved to dissipate energy when relative movement develops between the bracing members32and34. These mechanisms may be used individually or in combination such that the properties of the energy dissipative system38can be tuned to achieve any desired response under specific types of loading force. The energy dissipative system38is generally chosen to sustain minimal damage under severe loading and/or to be easily replaceable. Further, the energy dissipative system38is generally designed to allow quick inspection and replacement within the apparatus30, with minimized disruption time following any extreme loading situation.

The friction mechanisms50illustrated inFIGS. 1 and 2each includes two support members60a,60b, two friction interfaces62a,62band an extending member64. In the illustrative embodiment, the support members60a,60bare fixedly mounted on the bracing member34, and each includes a slot66. The extending member64is fixedly mounted on the bracing member32and extends toward the support members60a,60bsuch that fasteners68fixedly mounted through the extending member64engage the slots66to hold the friction mechanism50in a clamping arrangement.

The friction interfaces62a,62bare located in the clamping arrangement between the support members60a,60band the extending member64are so configured and sized as to provide friction between the two bracing members32and34. Depending on where friction sliding occurs in the friction mechanism50, the friction interfaces62aand62bmay or may not include slots that correspond to the slots66of the support members60a,60b.

The clamping arrangement provides that a normal force generates friction between the friction interfaces62a,62bwhen there is relative motion between the bracing members32and34. In the illustrative embodiment ofFIGS. 1 and 2, the slot66and fastener68are mounted in a sliding arrangement to first allow a relative movement between the bracing members32and34. The sliding arrangement provides a restrained movement capacity of the extending member64attached to the fastener68, which is guided by the slot66along the direction of movement of the bracing members32and34.

Optionally, the friction interfaces62a,62bmay be removed from the friction mechanism50if support members60a,60b, and extending element64exhibit the required frictional characteristics. In this case, the friction is achieved by directly clamping together the support members60a,60band the extending member64. Further optionally, the slot66may be positioned directly on the extending member64.

The friction mechanism50generally displays stable hysteretic characteristics under dynamic loading, with minimal uncertainty on initial and long-term friction properties. Specialized, non-metallic friction interfaces (not shown), or treated metallic surfaces (not shown) may also be used to provide specific hysteretic characteristics to the friction dissipative mechanism.

The yielding mechanisms52, which are schematically shownFIG. 5, may further be used as part of the energy dissipative system38to provide energy dissipative capacity when the two bracing members32and34are relatively moving. The yielding mechanism52includes metallic elements (not shown) inserted between and mounted to the two movable bracing members32and34. The metallic elements (not shown) are generally selected to yield under axial, shear or flexural deformations, or a combination thereof.

The viscous mechanisms54and the visco-elastic mechanisms56, which are schematically shown inFIG. 5, may also further be used as part of the energy dissipative system38to provide energy dissipative capacity when the two bracing members32and34are relatively moving. The viscous mechanism54includes viscous devices (not shown) containing viscous fluids (not shown) inserted between and mounted to the two movable bracing members32and34. The viscous mechanism54includes visco-elastic materials (not shown) connected to plates inserted between and mounted to the two movable bracing members32and34.

Combinations of more than one of the above mentioned mechanism50,52,54,56,57may then be used to optimize and diversify the hysteretic characteristics of the apparatus30. With the addition of the tensionable assembly36, the apparatus30is therefore able to exhibit a “Flag-Shaped Hysteresis” behavior, which combines energy dissipative and self-centering capabilities.

FIG. 6shows the individual contributions of the friction, yielding, viscous (at high and low velocity) and visco-elastic (at high and low velocity) mechanisms in terms of their force/deformation behavior.FIG. 7illustrates some combinations of those mechanisms.

Even if only two different dissipative elements are shown inFIG. 7, a combination of more than two dissipative systems of the same type, or combinations of more than two types of dissipative mechanisms may also be used. Other combinations may also exist, such as for example, three different dissipative systems or more than one energy dissipative mechanism of the same type used in combination with another different energy dissipative mechanism. The overall hysteretic response of the apparatus30is generally obtained by summing the contributions from the various components described herein.

FIG. 8shows a force displacement curve of a typical linear elastic system andFIG. 9illustrates a typical self-centering system, both systems representing a yielding structure of equal initial stiffness and mass. In these Figures, the shaded area represents the energy dissipated per cycle through hysteretic yielding, which is generally associated with structural damage to a structure under loading and which can significantly impair a structure and increase its repair costs. The self-centering capacity incorporated in the apparatus30offers a hysteretic behavior which is optimized (diagrammatically shown inFIG. 9) having regards to the response and the residual deformation.

The apparatus30in operation is shown inFIGS. 4cand4dand schematically illustrated inFIGS. 10ato13d. These Figures illustrate the behavior of the brace apparatus30, at the moment where input energy applied to the structure where the apparatus30is mounted to, is transmitted to the apparatus as loading forces, such as for example compression or tension forces. As stated hereinabove, the brace apparatus30is mountable to such structures via end connections44a,44dof the first opposed end pair40a,40d. The apparatus30is therefore able to receive the loading force such that its configuration changes from a rest position (FIG. 1) to a transitional position where input energy is dissipated by relative motion between the two structural bracing members32and34(FIGS. 4c,4d).

As shown inFIG. 4cwhen under a certain level of tension loading force, the brace apparatus30allows for a relative movement of the bracing members32and34. First the pre-tensioning of the tension elements46has to be overcome, which then results in the elongation of the tensioning elements46and the initiation of relative movement between the bracing members32and34. In the process, the tensioning elements46are further tensioned since abutting surface42apushes on abutting element48aand since abutting surface42dpushes on abutting element48b. When under a compression force, as illustrated inFIG. 4d, the tensioning elements46of the tensionable assembly36are also further tensioned in the process, since abutting surface42cpushes on abutting element48aand since abutting surface42bpushes on abutting element48b.

By elongating, an additional tension force gradually builds-in the tensioning elements46such as to provide the self-centering properties of the brace apparatus30. For instance, if the loading force was to cease at that time, the apparatus30is generally brought back to its rest position (seeFIG. 1) by the additional tension force developed in the tensioning element46. As stated previously, if the level of pre-tension is not sufficient to overcome the force required to activate the energy dissipation mechanisms38, the apparatus generally does not display a full re-centering capacity, but the tensioning elements46generally provide additional post-elastic stiffness to the apparatus30.

As soon as relative motion between the bracing members32and34starts to occur under the loading force, the energy dissipative system38(only friction mechanism50shown inFIGS. 4c,4d) are activated, opposing to the relative motion of the bracing members32and34. For instance, when tension is applied to the apparatus30as inFIG. 4c, and once the initial force and resistance of the tensioning elements46are overcome, the apparatus30elongates while energy is dissipated through the dissipative system38. As discussed previously, the illustrative embodiment ofFIG. 4cshows that the fasteners68in a sliding arrangement with the slot66generally move along the relative direction of movement of the bracing members32and34.

At that time, depending on the selected tensioning elements46with respect to the resistance and configuration of the selected combination of energy dissipative systems38, the additional tension force developed in the further extended tensioning elements46generally provides to the apparatus30the capacity of heading back to its initial position (FIG. 1) when the loading force ceases or changes from tension to compression.

Another example highlighting the hysteretic behavior of the apparatus30while in operation is schematically illustrated inFIGS. 10ato13d. More specifically,FIGS. 10ato11dillustrate the hysteretic behavior of a brace apparatus30submitted to tension and compression and equipped with a friction mechanism50or with a yielding mechanism52. InFIGS. 12ato13dillustrate the hysteretic behavior of the apparatus30submitted to tension and compression and equipped with velocity dependant viscous mechanism54or visco-elastic mechanism56.

In all these figures, the elongation of the apparatus30under the loading force F is expressed as δ, while δ′ illustrates the deformation in the mechanisms50,52,54,56mounted to the two bracing members32and34. InFIGS. 12ato13d, both a low velocity and high velocity response are illustrated since this energy dissipative system displays a velocity dependent hysteresis. The high velocity response is generally expected during the extreme loading, while the low velocity response (which generally provides the self-centering property) characterizes the expected response following the extreme loading.

For concision purposes, the relative movements involved during operation of the brace apparatus30subjected to loading forces will be further explained with reference toFIGS. 10ato11donly, but the same principles apply to other combinations of different energy dissipative system (FIGS. 12ato13d) as described hereinabove.

FIG. 10aschematically illustrates the brace apparatus30equipped with a friction mechanism50or yielding mechanism52mounted to the bracing members32and34and subjected to a tension loading force, but before the applied tension loading force is large enough to overcome the initial pre-tensioning of the tensioning element46.

Up to a certain level, a force F tensions the apparatus30such that the tensioning element46and the dissipative mechanism50,52opposes to the relative motion of the bracing members32and34. At that stage, the apparatus30generally starts to linearly deform as schematically illustrated inFIG. 10b.

If the loading Force F reaches a certain level which is larger than the force required for overcoming the initial pre-tensioning of the tensioning element46, the force F reaches the tension separation level (70inFIGS. 10band10d). At that time, the members32and34start moving in opposite directions by a distance δ, as schematically illustrated inFIG. 10c. The stiffness then changes from the elastic to the post-elastic stiffness. The tensioning element46mounted to both members32and34is therefore elongated by a generally similar displacement and may deform under such loading. The dissipative mechanism50,52generally also deforms by a displacement δ′.

Once the loading force changes its direction such as it usually does in an oscillatory earthquake loading, the opposite compression force F shown inFIG. 11amoves the bracing members32and34toward their original position, which generally corresponds to an opposite and equal displacement δ. At this stage, the two bracing members32and34are generally aligned and the dissipative mechanism50,52generally put back to its initial configuration. If no compression force F is provided after the tension loading F, the additional tension force built in the tensioning element46generally repositions the bracing members32and34to the configuration shown inFIG. 11a. As explained hereinbefore, this phenomenon may be explained by the pre-tensioned and further stretched condition of the tensioning element46.

As seen inFIG. 11b, the corresponding hysteretic response of the dissipative mechanism50,52moves from the tensioned side of the force F toward the compression side of the force F by passing generally near the zero force-displacement point in the diagram. In the case where no opposite compressive force F is provided, the additional tension force of the tensioning element46returns the system to the rest position, generally corresponding to the zero force-displacement point in the diagram.

When the opposite force F reaches a compression separation level72required for overcoming the initial pre-tensioning of the tensioning element46, as illustrated inFIG. 11d, the dissipative mechanism50,52and the tensioning element46are overcome such that the bracing members32and34start moving in opposite directions by a distance δ. The dissipative mechanisms50,52then generally deform by a corresponding displacement δ′.

Generally speaking, the relative movements of the various components of the apparatus30described hereinabove may alternate as long as the deformation imposed on the apparatus30remains within the maximum deformation for which the apparatus30has been sized for. As described hereinbelow in other illustrative embodiments, the bracing members32and34may include specially designed end connections44aand44d, or an additional structural element generally mounted in series to the apparatus30, that may be designed to yield or slip with friction prior to attaining the ultimate deformation capacity of the tensioning elements46, and thus minimizes the possibilities of the tensioning elements46failing in the event of unexpectedly higher deformations caused by energy input level higher than anticipated and thus protect the integrity of the apparatus30.

The bracing members32and34are typically made out of any material generally used for rigid structures or architectural constructions, such as, for example, steel, aluminum or fiber reinforced polymers (FRP). The material of the members32and34is generally chosen to prevent or minimize the buckling or yielding occurrences and, thereby, to significantly reduce damages to the portions of the structure to where the members32and34are mounted. The tensioning elements46may also further be made from various types of materials such as for example tendons bars or cables which may be made of, but not limited to, high strength steel tendons, rods, bars or of composite FRP tendons or bars including, for example Aramid, Carbon, Glass or the like. The tensioning elements46may further be provided with a UV or fire protective layer.

The apparatus30which as been described herein may therefore be used by being mounted on, connected to or integrated in various types of structures74, such as for example in, multi-storey structures, buildings, towers, bridges, offshore platforms, storage tanks, etc., some being shown inFIGS. 14ato14j.

The apparatus30may further be used for new constructions which are built with traditional lateral load resisting systems (conventional braced frames, moment-resisting frames, shear walls, etc.) or with added dampers that do not exhibit the self-centering property. Structures may further be built with the apparatus30to enhance their seismic performance level, such structures including, for example, machine parts, buildings, bridges, towers, offshore marine structures, bridges or other structural applications (towers, chimneys. These structures may be subject to any type of loading, including acoustical, seismic, blast, impact wave and wind loading.

The apparatus30may still further be used with existing constructions which need to be strengthened or rehabilitated to meet more recent (generally more stringent) seismic code provisions or higher performance criteria. Rehabilitation of these structures could be done by using the proposed apparatus30for enhanced response under severe or extreme seismic or wind loading conditions. The apparatus30may also further be used in important structures which need to be protected from extreme blast loads. Furthermore, the apparatus30may also be used in other applications, such as for example, in mechanical engineering for vehicles subjected to impact, equipment or machinery that can be subjected to overloading or unanticipated loading conditions, etc.

The apparatus30is generally installed as a brace element between framing members in a structure, at an angle, vertically or horizontally at the base of structures, or generally in parallel with any movement within the structure that may necessitate control.

The fabrication of the apparatus30, its inter-connections and its connections to existing structures generally involve steps which may be made by regular construction workers. The apparatus30is generally entirely self-contained. Once assembled in the production factory, the apparatus30is then generally readily attachable or mountable to the structures in a similar way as traditional bracing elements are generally attached, by bolting or welding of the end connections (44a,44dinFIG. 4a) to the main structure needing bracing.

The apparatus generally includes inspection provisions, such as for example in the form of holes (not shown) in the bracing members to provide for inspection of the energy dissipative mechanisms that undergo deformations and dissipate input energy under extreme or repetitive loading conditions. If needed, the energy dissipative mechanisms may be individually replaceable from the inspection provisions following an extreme loading event.

A person skilled in the art will also easily understand that the number and the physical properties of tensioning elements may vary, and that the size, the shape, and numbers of bracing members may also vary. For instance, the bracing members may be made of circular, square or rectangular steel tubes or any combinations thereof. Other shapes can be used such as interconnected plates, I-shapes, C-shapes, etc. Further, other configurations and other types of energy dissipation systems may be used. More specifically, the friction mechanisms described may be located in a single location or in two or more locations, at any position along the length of the brace apparatus.

A brace apparatus130according to a second embodiment of the invention is illustrated inFIGS. 15 to 22. For concision purposes, only the differences between the brace apparatus130and the brace apparatus30illustrated inFIGS. 1 to 14jwill be described hereinbelow. For simplification purposes, end connections (44a,44d) will not be represented onFIGS. 15 to 22.

In this second illustrative embodiment, the brace apparatus130includes a first bracing member132, a second bracing member134, a tensionable assembly136and an energy dissipative system138.

The energy dissipative system138includes two friction mechanisms150a,150bprovided in proximity of the ends140a,140b,140c,140d. These friction mechanisms150a,150beach includes support members160a,160b,160c,160dmounted on the second bracing member134and extending members164a,164bmounted on the first bracing member132. In this illustrative embodiment, the support members160c,160dand the extending member164afurther act as end connections for mounting the apparatus130on external structures and transmitting the loading force to the apparatus130.

The extending members164a,164beach include slots166a,166b,166c,166dwhere fasteners168are received in, such as to clamp the extending members164a164bwith the support members160a,160b,160c,160d. The slots166a,166b,166c,166dand fasteners168are mounted in a sliding arrangement to allow a restrained relative under friction movement between the bracing members132,134.

A person skilled in the art will easily understand that the energy dissipative mechanism illustrated in this embodiment may be replaced by another hereinabove presented energy dissipative mechanism, such as, for example, a yielding, viscous, visco-elastic, or hysteritic mechanism.

A brace apparatus230according to a third embodiment of the invention is illustrated inFIG. 23. For concision purposes, only the differences between the brace apparatus230and the brace apparatus30illustrated inFIGS. 1 to 14jwill be described hereinbelow.

In this illustrative embodiment, the brace apparatus230includes an inner bracing member232, and two outer bracing members234,235that are located on each side of the inner bracing member232, a tensionable assembly236, an energy dissipative system238and guiding elements239.

The inner and outer bracing members232,234,235have ends240a,240b,240c,240d,240e,240fprovided with respective abutting surfaces242a,242b,242c,242d,242e,242f. Ends240a,240dand240fare further provided with end connections244a,244d,244f, which in this embodiment include a threaded portion245a,245d,245f.

The tensionable assembly236includes abutting elements248a,248binterconnected by tensioning elements246. The abutting elements248a,248bare in proximity of the ends240a,240b,240c,240d,240e,240fand the tensioning elements246are symmetrically positioned with respect to the inner and outer members232,234,235such as to favor a generally evenly distributed loading force in the tensionable assembly236and allow a generally uniform deformation of the apparatus230in operation. In this illustrative embodiment, the tensioning elements246are positioned outward of the outer members234,235.

The energy dissipative system238includes two friction mechanisms250that are each fixedly mounted to the inner bracing member232, and which extend in a frictional connection with the outer bracing members234,235.

The guiding elements239are fixedly mounted to the each of the tensioning members248a,248band mounted in a guiding cooperation with the ends240b,240c,240eof the bracing members232,234,235which are not provided with an end connection244a,244d,244f. The guiding elements239generally slidably restrain and guide the relative movement of the bracing members232,234,235. Optionally, the guiding elements239are mountable outside of the bracing members232,234and235.

The brace apparatus230operates in a similar way as described in the first embodiment. However, the loading force applied to the outer bracing members234,235is half the force applied to the inner bracing member232, but the effective apparatus230elongation is the same since two outer bracing members234,235participate in elongating the apparatus230.

A person skilled in the art will easily understand that the energy dissipative mechanism illustrated and described in this embodiment may be replaced by another hereinabove presented energy dissipative mechanism, such as, for example, a yielding, viscous, visco-elastic, or hysteritic mechanism.

A brace apparatus330according to a fourth embodiment of the invention is illustrated inFIG. 24. For concision purposes, only the differences between the brace apparatus330and the brace apparatus230illustrated inFIG. 23will be described hereinbelow.

In this illustrative embodiment, the tensioning elements346of the tensionable assembly336are located inside the inner bracing member332and inward with respect to the outer bracing members334,335. Optionally, the tensioning elements346may be located inside the outer bracing members334,335.

A person skilled in the art will easily understand that the energy dissipative mechanism illustrated in this embodiment may be replaced by another hereinabove presented energy dissipative mechanism, such as, for example, a yielding, viscous, visco-elastic, or hysteritic mechanism.

A brace apparatus430according to a fifth embodiment of the invention is illustrated inFIGS. 25 and 26. For concision purposes, only the differences between the brace apparatus430and both the brace apparatus30illustrated inFIGS. 1 to 14jand the brace apparatus130illustrated inFIGS. 15 to 22will be described hereinbelow.

The brace apparatus430is mounted to an external structure431at an attachment portion431a. The brace apparatus430includes a first bracing member432, a second bracing member434, a tensionable assembly436, a fuse system437and an energy dissipative system438.

The energy dissipation system438includes a friction mechanism450which includes an extending member464with an end portion465protruding from the apparatus430such as to be mountable to the attachment portion431aand thereby receive and transmit the loading force to the apparatus430. In the illustrative embodiment, the end portion465includes four slots467a,467b,467c,467dconfigured and sized as to cooperate with the fuse system437.

The fuse system437includes a slipping member469provided with a plurality of fasteners471. The slipping member469includes connectors473so configured and sized as to cooperate with the attachment portion431a.

The fasteners471are mounted in a sliding arrangement with the slots467a,467b,467c,467dto allow a restrained relative and under friction movement, which generally occurs at a predetermined load, between the apparatus430and the attachment portion431a.

For instance, the slip load of the slipping member469with respect to the slipping portion465is adjustable to occur at a value corresponding to an acceptable maximum deformation value of the apparatus430, such that once the slip of the slipping member469occurs, any additional deformation in the apparatus430occurs between the slipping member469and the slipping portion465. At that time, no additional deformation is imposed on the tensioning elements446.

To further provide that the deformation occurs between the slipping member469and the slipping portion465while minimizing the probability of overloading and damaging the apparatus430, the deformation capacity of the energy dissipative system438may be limited to a pre-determined value preventing further relative movement to develop between the bracing members432and434.

For instance, for a friction mechanism450as illustrated in this embodiment, the length of the slots466a,466bare adjustable such that when the acceptable deformation value is reached in the apparatus430, the fasteners468of the friction mechanism450start bearing on the edges of the slots466a,466bthus opposing to any more relative deformation in the apparatus430and consequently, in the tensioning elements446. It is generally at that time that any additional deformation occurs between the slipping member469and the slipping portion465, as described hereinabove.

A person skilled in the art will easily understand that the fuse system437described in this embodiment may also be used by replacing the friction mechanism by another energy dissipative mechanism or other blocking systems to protect the apparatus in case of excessive deformation demand such as, for example, a yielding mechanism. Further, the fuse system described in this embodiment may further be used with any of the previously described embodiments and that the number of slots, the type and number of fasteners and connectors may vary according to the design requirements of the brace apparatus.