US20060150538A1

US20060150538A1 - Load-limiting device

Info

Publication number: US20060150538A1
Application number: US11/024,359
Authority: US
Inventors: Gareth Thomas
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-12-27
Filing date: 2004-12-27
Publication date: 2006-07-13

Abstract

A load-limiting device for using in a braced frame structure is provided. The load-limiting device may be placed in a braced frame and connected to the braces of the braced frame. The load-limiting device is able to limit the lateral loads induced in the structure during a dynamic event by plastic and ductile deformation. The load-limiting device, by limiting the dynamic loads in the braced frame, may protect other less ductile areas of the structure from the loads that might lead to extensive damage, member failure and/or structural collapse. The load-limiting device is positioned within a braced frame structure and may be easily removed after it has undergone plastic deformation and replaced with an undeformed load-limiting device. The load-limiting device exhibits elastic strength to survive, without deformation, minor load scenarios. The device is suitable for retrofitting in existing structures that are susceptible to dynamic activity and that have inadequate dynamic loading capacity.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention generally relates to the construction of dynamic load resistant building equipment. More particularly, the present invention relates to a device that dissipates energy during a major dynamic event. Further, the invention relates to a device that limits the loads being transmitted to the parts of the structures that are difficult to repair or replace. The invention relates to a device that may undergo plastic deformation to limit the loads levied on a structure during a dynamic event. The present invention may also be a load-limiting device that can be replaced and/or removed after plastic deformation.
2. Description of the Prior Art
The response of buildings to major seismic events is often of sufficient magnitude to induce inelastic behavior of many components within the building. The inelastic behavior and/or characteristics displayed by the building may take the form of local yielding, cracking, buckling and fracturing of structural members. Often, the damage done to a building during a dynamic event is so severe that it jeopardizes the integrity of the entire building and/or the building must be destroyed to insure public safety.
A direct consequence of the acceptance of inelastic response of a building during major earthquakes is the possibility of significant damage being incurred during the seismic event. The cost of repairing the damage then becomes a component in the life cycle cost of the building. A well-documented comparison in the response of two difference buildings to an earthquake in Managua in 1972 highlighted the costs of repairing the damage done during a seismic event. (1)
One of two buildings observed in the comparison utilized a concrete shear wall lateral load carrying system. The concrete shear wall lateral load carrying system was able to withstand the seismic loads with modest damage while an adjacent building used a moment-resistant frame to withstand the lateral loads induced during the earthquake. This was believed to be a ductile system that provided a reliable method for avoiding catastrophic building failure. The building in question did not fail catastrophically but suffered extensive damage associated with inelastic response that proved to be too extensive to be repaired economically. In fact the building using the moment-resistant frame to withstand the lateral loads had to be abandoned and destroyed.
A structural system that relies on beneficial inelastic action during seismic response was proposed by Popov et al. (2) In that case, a modification was applied to the traditional braced frame building system. The modification of the commonly used braced frame system consisted of installing cross-braces into the building frame with marked end offsets. This had the effect of inducing increased bending stresses in the beam and, ultimately, plastic hinges at the high stress locations. The presence of these hinges may provide a method for dissipating energy in a ductile way. However, the damage associated with the formation of plastic hinges in the beams of the building is very difficult and expensive to repair.
Another method that has been used to limit structural response during a seismic event adopts a hydraulic damper at strategic locations throughout the frame. (3) This provides a method for dissipating energy from a seismic event in a controlled and engineered way. The disadvantage of this method is that it is very difficult to incorporate energy dissipation similar in magnitude to plastic hinge mechanisms without major cost and inconvenience for older, established building structures. Moreover, incorporating the hydraulic damper has many packaging ramifications associated thereto. Still further, the need for periodic routine maintenance of these hydraulic damper systems in locations throughout the building is a serious disadvantage to this type of system as the routine maintenance may be difficult to perform and costly to complete.
U.S. Pat. No. 6,651,395 discloses a device that limits relative movement of two elements of a structure by absorbing the deformation energy. The device absorbs the energy by plastic deformation using a method by which the deformable material is restrained by a stronger and stiffer guiding material. The performance of the device is dependent on the precise shape of the guiding component in the device.

SUMMARY OF THE INVENTION

The present invention provides a dampening system for bracing the frame of a structure during a dynamic event. More particularly, the present invention relates to a load-limiting device for braced frames. Moreover, the present invention relates to a load-limiting device that may be placed in a braced frame that may have plastic deformation characteristics. Further, the present invention relates to a load-limiting device that may be placed in a braced frame that may plastically deform during a dynamic event and wherein the load-limiting device may preserve a structure from extensive and/or comprehensive damage to the structure after a dynamic event. Moreover, the present invention relates to a load-limiting device that may plastically deform in response to a dynamic event and that may be positioned within a braced frame structure. The load-limiting device may be easily removed and replaced after plastic deformation with another non-plastically deformed load-limiting device.
To this end, in an embodiment of the present invention, a load-limiting device for use in a braced frame is provided. The device for use in the braced frame has a braced frame structure having at least one beam and a first column and a second column. Moreover, the present invention has a load-limiting device releasably attached to a brace wherein the brace is attached to the braced frame structure. Further, the present invention has a connection means releasably attached to the load-limiting device. Additionally, the invention has a load-limiting device providing biaxial support for the braced frame wherein said load-limiting device is being able to dissipate energy in the braced frame structure.
In an embodiment, the load-limiting device is able to plastically deform in response to a load applied thereto.
In an embodiment, the load-limiting device is able to plastically deform in response to load wherein said load-limiting device has elasto-plastic properties to allow for formation of a plastic hinge mechanism.
In an embodiment, the load-limiting device can withstand small loads without plastic deformation based on elasto-plastic properties.
In an embodiment, the load-limiting device is constructed of a plastic material.
In an embodiment, the load-limiting device is constructed of a metal based elasto-plastic material.
In an embodiment, the load-limiting device is attached to said connection means wherein said connection means couples the load-limiting device and the brace in the braced frame structure.
In an embodiment, the load-limiting device has an opening thereon for attachment of the connection means to the brace.
In an embodiment, the load-limiting device has a plurality of connection points wherein said connection points are releasably attached to said connection means.
In an embodiment of the present invention, a dynamic load, load-limiting device system for a braced frame is provided. The system has a braced frame structure having at least one beam and a first column and a second column. The system further has a brace frame structure having at least one brace. Moreover, the system has a load-limiting device releasably attached to said brace wherein said brace attaches to said at least one beam and a connection means detachably coupled to said at least one brace and said load-limiting device. Moreover, the system has the load-limiting device in connection with said brace and said braced frame structure to dissipate energy when high lateral loads are placed on the braced frame structure.
In an embodiment, the load-limiting device may undergo plastic deformation when subjected to high lateral loads.
In an embodiment, the load limiting device is releasably attached to said brace wherein said brace is attached to said at least one beam.
In an embodiment, the load limiting device is releasably attached to said brace wherein said brace is attached to said two columns.
In an embodiment, the load-limiting device when subjected to a dynamic event may yield to form hinged mechanisms to dissipate energy from the braced frame structure during a dynamic event.
In an embodiment, the load-limiting device may be removed from the braced frame structure after a dynamic event wherein the load-limiting device has undergone plastic deformation and further wherein a new un-deformed load-limiting device may be inserted into the braced frame structure to replace a plastically deformed load-limiting device.
In an embodiment of the present invention, a method for using a load-limiting device system is provided. The system comprising the steps of: providing a braced frame having at least one beam and two side columns; integrating at least one brace into the braced frame; integrating a load-limiting device into the system; and providing a connection means to connect the load-limiting device to the braced frame wherein a connection means is releasably attached to said load-limiting device and said brace.
In an embodiment, the method further comprises the step of: placing the load-limiting device into an existing braced frame with a connection means.
In an embodiment, the method further comprises the step of: providing the device with an indicator means wherein said indicator means allows for assessment of plastic deformation of the load limiting device.
In an embodiment, the method further comprises the step of: periodically checking said load-limiting device for the existence of plastic deformation after dynamic activity.
In an embodiment, the method further comprises the step of: removing a plastically deformed load-limiting device from a braced frame after a dynamic event.
In an embodiment, the method further comprises the step of: replacing a plastically deformed load-limiting device from a braced frame with an un-deformed load-limiting device after a dynamic event.
It is, therefore, an object of the present invention to provide a load-limiting device, a system and a method of using the same.
Another object of the present invention is to provide a load-limiting device and a method for using the same, for use in structural applications.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be integrated into a structural frame.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be integrated into a structural frame having an X- or K-brace.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein a frame incorporating the load-limiting device may withstand lateral seismic loads.
Yet another object of the present invention is to provide a load limiting device and a method for using the same wherein the load limiting device may withstand high dynamic loads.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be compressed.
Yet another object of the present invention is to provide a loading limiting device and a method for using the same wherein the load-limiting device may withstand high seismic stress.
Another object of the present invention is to provide a load limiting device and a method for using the same wherein the load-limiting device may not undergo plastic deformation during low dynamic loads.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may have a plurality of connection points to connect to a typical braced frame.
An object of the present invention is to provide a unique load-limiting device and a method for using the same wherein the load-limiting device may have a plurality of connection points and an opening therein.
A further object of the present invention is to provide a load-limiting device and a method for using the same wherein at low load levels the device will experience stresses within the linear elastic range for the material used in the load-limiting device wherein the load limiting device will not undergo plastic deformation.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be comprised of metal.
Yet another object of the present invention is to provide a loading limiting device and a method for using the same wherein the device may be comprised of a high strength material.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be comprised of any material capable of undergoing plastic deformation.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may have a design that avoids local stress risers that may prematurely yield or fatigue with normal loads on a structure.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may use materials that have elasto-plastic stress strain properties.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may have elasto-plastic stress strain properties similar to low-carbon steels.
A further object of the present invention is to provide a load-limiting device and a method for using the same wherein the performance of the load-limiting device may not be impaired by strain-hardening of the material in the active part of the device.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same that as deflections in the structure are increased, yielding of the device avoids a significant increase in internal loads in the building structure itself.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may form a plastic hinge mechanism when subject to loads.
An object of the present invention is to provide a unique load-limiting device and a method for using the same wherein the device may have a plastic hinge mechanism that may be induced during plastic deformation of the load-limiting device.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may have a plastic hinge mechanism wherein the plastic hinge mechanism may deform in response to a dynamic event.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be used in buildings, vehicles, aircraft, furniture, roller-coasters and other structures.
An object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be used for bridges, office or industrial buildings, homes, heavy lifting equipment and/or any structure that experiences severe dynamic loads and/or any structure prone to seismic events.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be able to dissipate energy during a dynamic and/or seismic event.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be able to dissipate energy during a dynamic event by further yielding of the material in the plastic hinges of the load-limiting device.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the plastic moment of a section of the device may be proportional to the plastic section modulus and the yield strength of the material used.
A further object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be able to dissipate energy during many load reversal cycles without premature failure due to cracking and/or buckling.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may undergo reverse yielding and allow for a plastic hinge mechanism to be compressed.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be manufactured with a plurality of load capacities depending on the strength requirements of the load-limiting device.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device strength may vary from story to story in the structure in which it is placed.
An object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be able to maintain ductility during severe load-limiting cycles.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be checked after an earthquake of moderate to severe intensity.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be easily removed from the structure if plastic deformation of the device is found.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be easily removed from the structure of a building after a seismic event if plastic deformation of the device is detected.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be removed from the structure after a dynamic event if plastic deformation of the device is detected and further wherein a new load-limiting device may be inserted into the place of the plastically deformed load-limiting device.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device may be configured with a variety of variations depending on the type of structure for which the device is to be fitted.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the device is interchangeable with new load-limiting devices.
Yet another object of the present invention is to provide a load-limiting device and a method of using the same wherein the device may be connected to the X-brace of a building by a connection means.
Another object of the present invention is to provide a load-limiting device and a method of using the same wherein the load-limiting device may be connected to the bracing of the building by a connection means where the connection means may be a mechanical connection using high strength fasteners.
Yet another object of the present invention is to provide a load-limiting device and a method of using the same wherein the load-limiting device may be connected to the beam and/or column of a structure by a connection means wherein the connection means may be any means of connecting the load-limiting device to the braced frame structure.
A further object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be rectangular in shape.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be square in shape.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be oval in shape.
An object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be circular in shape.
Still another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be connected to the existing brace of constructed building to stabilize and dissipate energy from a dynamic event.
Yet another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be applied externally to brace a building frame.
Another object of the present invention is to provide a load-limiting device and a method for using the same wherein the load-limiting device may be used on internally braced structures.
Still another object of the present invention is to provide a load-limiting device and a method of using the same wherein the device may be connected to the brace of a structure using a connection means wherein the connection means may be any mechanism to connect the device to the beam of the structure.
These and other objects of the invention will become more clear when one reads the following specification, taken together with the drawings that are attached hereto. The scope of protection sought by the inventors may be gleaned from a fair reading of the Claims that conclude this specification.
Additional features and objects of the present invention are described in, and will be apparent from, the detailed description of the presently preferred embodiments and from the drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a load-limiting device attached to the frame of a structure in an embodiment of the invention;
FIG. 2 is a schematic representation of the prior art braced frame of a building which does not include a load-limiting device;
FIG. 3 a is a close-up schematic representation of the prior art braced frame of a structure which does not include a load-limiting device;
FIG. 3 b is a close-up schematic representation of a braced frame having a load-limiting device in an embodiment of the present invention;
FIG. 4 is a schematic illustrating a structure and the stresses involved during a dynamic event wherein the load-limiting device is illustrated in a previous state before dynamic activity and during a dynamic state;
FIG. 5 illustrates the plastic deformation undergone by the load-limiting device in an embodiment of the present invention;
FIG. 6 is an illustration of the load deflection sequence for the load-limiting device during a dynamic event in an embodiment of the present invention;
FIG. 7 is an illustrative view of a plurality of different load-limiting device geometries for various bracing configurations in an embodiment of the present invention;
FIG. 8 is an illustrative view of potential geometries for the load-limiting device in an embodiment of the present invention; and
FIG. 9 is a schematic of the external surface of a structure having external load-limiting devices in an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings wherein elements are identified by numbers and like elements are identified by like numbers throughout the 10 figures, the invention is depicted in FIG. 1 and shows a load-limiting device 1 for dissipating energy during a dynamic and/or seismic event. In a preferred embodiment of the present invention, the load-limiting device 1 may have a first side 3, a second side 5, a third side 7 and a fourth side 9. It should be understood that although a preferred embodiment of the present invention illustrates a four sided object, the invention is in no way limited to a load-limiting device 1 having four sides. On the contrary, the invention includes inter alia, load-limiting devices as illustrated in FIG. 8 that may be manufactured and used in a plurality of different shapes and sizes to accommodate various structural applications. In a preferred embodiment, the structural application is for a building. The load-limiting device 1 in a preferred embodiment may have a first connection point 11, a second connection point 13, a third connection point 15 and a fourth connection point 17.
As illustrated in FIG. 1, the load-limiting device may have a connection means 19 that may attach the load-limiting device 1 to a brace 21 means that may attach to the frame (not shown) of the structure. The connection means 19 may attach to an opening 23 on the load-limiting device 1 that may allow for connection means 19 to be attached through opening 23 and ultimately connected to the frame of the building by brace 21. The connection means 19 may be any means of connecting the load-limiting device 1 to the frame of the building and/or structure. The connection means 19 may be releasably attached to the load-limiting device 1 and/or it may be an external portion that may be attached to the load-limiting device 1. The connection means may be a high strength bolt that passes through the opening 23 of the load-limiting device 1 that allows the brace to be clamped to the load-limiting device 1. The connection means 19 may also be a weld, adhesive bonding, clevis, shackle and/or any other means for connecting the load-limiting device 1 to the brace 21 of the structure 27.
FIG. 2 illustrates the prior art braced frame system 25 often employed in a structures 27 that is prone to dynamic and/or seismic activity. The braced frame system 25 consists of attaching a brace 21 to the building frame beams 29 with little or no joint eccentricity. As illustrated in FIG. 3 a, the building frame may have a first beam 31 and a second beam 33 and a first column 35 and a second column 37 that may be connected to a brace 21 which extends from a first beam 31 to a second beam 33. The braced frame system 25 tends to be a reliable method of dissipating energy during a dynamic event without being subject to member yielding. A problem with the braced frame system 25 is that during a severe dynamic event, high stresses may be imposed in the frame beams 29 and if the stresses are high enough, they can cause serious or irreparable damage to the structure. The mechanism associated with the damage may be brittle in nature and lead to catastrophic failure.
FIG. 3 a further illustrates the prior art typical bay in the braced frame systems 25 used in the construction of a structure 27 in an attempt to accommodate lateral loads when a structure 27 is subjected to a dynamic load. As FIG. 3 a illustrates, the brace 21 is attached to the first beam 31 and the second beam 33 of the structure 27 and when subjected to a dynamic load, the brace 21 may stretch to accommodate these loads. However, if the loads imposed on the brace 21 are too great, severe damage may be caused to the structure 27 and extensive repairs must be made to repair and/or reconstruct the structure 27.
FIG. 3 b illustrates the same braced frame system 25 that may include the load-limiting device 1 contained therein. The braced frame system 25 consists of a first beam 31 connected to both a first column 35 and a second column 37. The first column 35 and the second column 37 are connected to a second beam 33 that is parallel to the first beam 31. A brace 21 may be connected to the frame structure within the interconnected beams 31, 33 and columns 35, 37. The brace 21 may be connected to a first beam 31 and extend to the second beam 33. In another embodiment, the brace 21 may extend from a first column 35 of the braced frame system 25 to a second column 37 of the braced frame system 25. The load-limiting device 1 illustrated in this embodiment is rectangular in shape. However, any shape and/or size of load-limiting device 1 may be contemplated. The load-limiting device 1 may be placed at a point on the brace 21 that may be connected to the beams 31,33 and/or the columns 35,37 of the structure 27. In a preferred embodiment, the load-limiting device 1 may be positioned centrally between a plurality of braces 21 in the structure 27. Moreover, the load-limiting device 1 may be located centrally between the interconnected beams 31, 33 and columns 35, 37. The load-limiting device 1 may be connected to the brace 21 by a connection means 19. The load-limiting device 1, during dynamic loading of the braced frame structure 27 may undergo plastic deformation to dissipate and/or absorb dynamic energy. Moreover, after a dynamic load has been placed on a load-limiting device 1 and the load-limiting device 1 has undergone plastic deformation, the load-limiting device 1 may be removed from the structure 27 by disengaging the connection means 19, removing the load-limiting device 1 and replacing the used, elasto-plastically deformed load-limiting device 1 with a new load-limiting device that has not undergone plastic deformation.
FIG. 4 illustrates a schematic of the deformation process of the modified braced frame system that shows the brace forces 41 acting on the load-limiting device 1. FIG. 4 further illustrates the inertia force 43 placed on a structure 27 and more specifically on the beam 31,33 and braces 21 of the structure 27 during a dynamic event. If and when a structure 27 is exposed to a dynamic event, the inertia force 43 induced by the dynamic event would act on the braces 21, the beams 31,33, the columns 35,37 and the load-limiting device 1. FIG. 4 further illustrates the inertia forces 43 induced by the dynamic event causing the braces 21 and the load-limiting device 1 to move in relation to the inertia forces 43 placed on the structure 27. The deformed geometry of FIG. 4 illustrates that plastic hinges 45 have formed at the corners of the load-limiting device 1. In the plastically deformed configuration, the loads carried by the load-limiting device 1 and the associated braces 21 may not be increased appreciably. The shear force being carried by the braced bay may not increase even when the bay inter-story sway increases. This behavior limits the magnitude of the loads acting on other parts of the frame including the beams 31, 33 and the columns 35, 37, avoiding the possibility of fracture of other less ductile components in the braced frame system 25.
FIG. 5 illustrates the load-limiting device 1 during a severe loading event in which parts of the load-limiting device 1 have plastically deformed. The regions that have deformed plastically are generally referred to as a plastic hinge 45, because of the change in angle from one side of the plastic hinge 45 to the other side. The plastic hinge 45 is bounded on one side by a connection portion 44 which is designed to be strong enough to preclude plastic deformation. The plastic hinge 45 is bounded on a second side by an elastic portion 48 which takes up most of the length of the bottom cord of the load-limiting device 1. Within the elastic portion 48, the stresses are low enough that the load-limiting device 1 material remains elastic.
As FIG. 5 further illustrates, the load-limiting device 1 may have an opening 47 thereon wherein the opening may allow for connection to a connecting means 19 that may attach the load-limiting device 1 to the braces 21 of the structure 27. During high loads, the load-limiting device 1 may undergo plastic deformation as shown in FIG. 5. The areas of the load-limiting device 1 that deform plastically versus elastically are a function of the geometry of the load-limiting device 1 and the orientation of the braces 21. FIG. 5 illustrates plastic hinging 45 in the horizontal portion of the load-limiting device 1. In another embodiment of the present invention, the plastic hinging may occur in the vertical portion of the load-limiting device 1. Moreover, plastic hinging may occur in both the horizontal portion and the vertical portion of the load-limiting device 1.
The load-limiting device 1 is able to dissipate energy by further yielding of the material enclosed in the plastic hinges 45 as further deformation is imposed. The amount of energy dissipated may be dependent on the geometry of the braced frame system 25, the geometry of the load-limiting device 1 and the plastic moment capacities of the relevant load-limiting device 1 cross-sections. The plastic moment of a section may be proportional to the plastic section modulus and the yield strength of the materials used. The design of the load-limiting device 1 may account for all these variables so that an optimum load-limiting device 1 may be manufactured that would have adequate elastic strength to survive design wind loads. Moreover, the design would allow for dissipation of energy during many load cycles without premature failure due to cracking and/or buckling during severe seismic events.
FIG. 6 illustrates the load-deflection sequence for the load-limiting device 1 during a dynamic event when the load-limiting device 1 is subjected to diagonally oriented loads as illustrated in FIG. 4. The area enclosed by the load-deflection plot during a load cycle is a direct measure of the energy dissipated by the load-limiting device 1 during one cycle of the dynamic event. The peak ordinate of the plot is proportional to the plastic moment of the device cross-section. The peak abscissa is related to the maximum shear and/or plastic deformation experienced by the load-limiting device. FIG. 6 illustrates the elastic loading 47 portion of the load-limiting device 1 in relation to the elastic unloading 49 portion and the elastic re-loading 51 portion of the load-limiting device 1.
FIG. 7 illustrates different device geometries for various braced frame systems 25 having different configurations. The basic prior art braced frame systems 25 are typically of the X-brace 53 or K-brace 55 type. The X-brace 53 or K-brace 55 type of configuration has braces 21 that attach to the beams 31,33 in a plurality of different formats. Changing the shape of the load-limiting device 1 could accommodate several other bracing configurations. When a different type of brace system 25 is employed, the load-limiting device 1 geometry and shape may be changed to accommodate the differently braced system 25. However, the load-limiting device 1 geometry and/or shape may be changed to accommodate connection features, manufacturing techniques, materials, architectural detail, and other variables in structural design and purpose. As FIG. 8 illustrates, there is very little limitation in the shape of the load-limiting device 1. The load-limiting device may be constructed in a plurality of geometries and/or shapes provided that a plastic hinge mechanism 45 can be supported when the device is severely loaded. A suitable load-limiting device 1 may exhibit the same plastic hinging mechanism 45 when the load is reversed.
FIG. 9 illustrates a further innovative application of the load-limiting device 1. FIG. 9 illustrates the use of a load-limiting device 1 in conjunction with externally mounted braces 21. In some situations, the structure 25 and/or building will use a brace system mounted on the outside of the structure 25 that may cover-several stories of the structure 25. The load-limiting device 1 may be used in this type of external bracing system in a similar fashion as the internal bracing systems. The dimension of the load-limiting device 1 may be greatly expanded to be adapted for external applications but may be used, none the less.
The load-limiting device 1 may need to be checked after a dynamic event of moderate to severe intensity. In the case of a moderate event it is possible that the load-limiting device may not have suffered any yielding and therefore can be left in place. Some damage may be expected for a major dynamic event and may be apparent by visual inspection of the structure. A “kinked” configuration of the type shown in FIG. 5 may be noticed during inspection of the load-limiting device 1. However, it is possible that yielding may not be obvious during the post dynamic event inspection. Therefore, in an embodiment of the present invention as illustrated in FIG. 1, an indicator means 55 may be used to indicate whether plastic deformation has begun on a load-limiting device 1. In an embodiment, the indicator means 55 may be a brittle coat of material that may be applied to the load-limiting device 1 in order to accentuate the presence of yielding and hence make detection of plastic deformation much more simplistic. A colored brittle coat may be used to assist in detection of plastic deformation and/or yielding. In another embodiment of the present invention, the indicator means 55 may be a mechanical device (not shown) to illustrate plastic deformation. In another embodiment, an electronic sensor (not shown) may be used as an indicator means 55 to confirm plastic deformation. However, it should be understood that any indicator means may be used that may indicate the presence of plastic hinging and/or plastic deformation.
While the invention has been described with reference to a particular embodiment thereof, those skilled in the art will be able to make various modifications to the described embodiment of the invention without departing from the true spirit and scope thereof. It is intended that all combinations of elements and steps which perform substantially the same function in substantially the same way to achieve substantially the same result are within the scope of this invention.

REFERENCES

(1) Wyllie, L. A., et. al., “Effects on Structures of the Managua Earthquake of Dec. 23, 1972”, Bulletin of the Seismological Society of America, Vol. 64, No. 4, August, 1974.
(2) Popov, Egor P., Amin, Navin R., Louie, Jason J. C., and Stephen, Roy M., “Cyclic Behavior of Large Beam-Column Assemblies,” Earthquake Spectra, Earthquake Engineering Research Institute, vol. 1, No. 2, pp. 9-23, 1985.
(3) Taylor, Douglas P., “Seismic isolator and method for strengthening structures against damage from seismic forces”, U.S. Pat. No. 5,462,141, Oct. 31, 1995.

Claims

1. A load-limiting device for use in a braced frame, comprising:

a braced frame structure having at least one beam rigidly interconnected to a first column and a second column;

a load-limiting device releasably attached to a brace wherein said brace is attached to said braced frame structure;

a connection means releasably attached to said load-limiting device; and

said load-limiting device providing biaxial support for the braced frame wherein said load-limiting device is able to dissipate energy in the braced frame structure.

2. The load-limiting device as described in claim 1, further comprising:

said load-limiting device being able to plastically deform in response to a load applied thereto.

3. The load-limiting device as described in claim 1, further comprising:

said load-limiting device plastically deforming in response to load wherein said load-limiting device has elasto-plastic properties to allow for formation of a plastic hinge mechanism.

4. The load limiting device as described in claim 1, further comprising:

said load limiting device which can withstand small loads without plastic deformation based on its elasto-plastic properties.

5. The load-limiting device described in claim 1 wherein said load-limiting device is constructed of a plastic material.

6. The load-limiting device described in claim 1 wherein said load-limiting device is constructed of a metal based elasto-plastic material.

7. The load-limiting device as described in claim 1, further comprising:

said load-limiting device attaching to said connection means wherein said connection means couples the load-limiting device and the brace in the braced frame structure.

8. The load-limiting device as described in claim 1, further comprising:

said load-limiting device having an opening thereon for attachment of the connection means to the brace.

9. The load-limiting device as described in claim 1, further comprising:

said load-limiting device having a plurality of connection points wherein said connection points are releasably attached to said connection means.

10. A dynamic load, load-limiting device for braced frames comprising:

a braced frame structure having at least one beam rigidly connected to a first column and a second column;

said brace frame structure having at least one brace;

a load-limiting device releasably attached to said brace wherein said brace attaches to said at least one beam;

a connection means detachably coupled to said at least one brace and said load-limiting device; and

said load-limiting device in connection with said brace and said braced frame structure to dissipate energy when high lateral loads are placed on the braced frame structure.

11. The dynamic load, load-limiting device as described in claim 10 further comprising:

said load-limiting device undergoing plastic deformation when subjected to high lateral loads.

12. The dynamic load, load-limiting device described in claim 10 wherein said load limiting device is releasably attached to said brace wherein said brace is attached to said at least one beam.

13. The dynamic load, load limiting device described in claim 10 wherein said load limiting device is releasably attached to said brace wherein said brace is attached to said two columns.

14. The dynamic load, load-limiting device described in claim 10 wherein said load-limiting device when subjected to a dynamic event yields to form a hinged mechanism to dissipate energy in the braced frame structure during a dynamic event.

15. The dynamic load, load-limiting device described in claim 10 wherein said load-limiting device may be removed from the braced frame structure after a dynamic event wherein the load-limiting device has undergone plastic deformation and further wherein a new un-deformed load-limiting device may be inserted into the braced frame structure to replace a plastically deformed load-limiting device.

16. A method for using a load-limiting device system, said method comprising the steps of:

providing braced frame having at least one beam and two side columns;

integrating at least one brace into the braced frame;

integrating a load-limiting device into the system; and

providing a connection means to connect the load-limiting device to the braced frame wherein a connection means is releasably attached to said load-limiting device and said brace.

17. The method of claim 16, further comprising the step of:

placing the load-limiting device into an existing braced frame with a connection means.

18. The method of claim 16, further comprising the step of:

providing the device with an indicator means wherein said indicator means allows for assessment of plastic deformation of the load limiting device.

19. The method of claim 16, further comprising the step of:

periodically checking said load-limiting device for the existence of plastic deformation after dynamic activity.

20. The method of claim 16, further comprising the step of:

removing a plastically deformed load-limiting device from a braced frame after a dynamic event.

21. The method of claim 16, further comprising the step of:

replacing a plastically deformed load-limiting device from a braced frame with an un-deformed load-limiting device after a dynamic event.