SMART SELF-CENTERED SHEAR WALL SYSTEM

Abstract

A structural control system for civil infrastructures with recovery-based performance under extreme environmental loading is provided. The recovery-based structural control system may be utilized in both newly constructed and existing buildings as a retrofit to reduce the vulnerability to extreme environmental loading. The structural control system combines steel plate shear wall (SPSW) and the shape memory alloy (SMA) to provide extra recovery ability in a building's main element or supplemental structural control systems. The combination of SMA with SPSW, as a lateral resistive force system, develops a self-centering, energy absorber that provides a re-useable and affordable steel plate shear wall, called Smart Self-Centered Shear Wall (SSCSW) system. In the SSCSW system, pre-straining is applied to SMAs to eliminate the residual deformation that is known to appear in long-term use.

Description

RELATED APPLICATIONS

This application claims priority benefit of U.S. Provisional Application Ser. No. 63/534,625 filed on Aug. 25, 2023, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to structural engineering, and in particular a shear wall system that employs shape memory alloy to recover the structural shape of the underlying framing of a building in response to environmental events including extreme wind loads and seismic loading events.

BACKGROUND OF THE INVENTION

The growing world population and required living space and dwindling available land for settlement, as well as the general trend towards urbanization has led to vertical development of multi-level and high-rise structures. In addition, with increasing land values taller developments have become justified to cover land acquisition costs, as well as to fulfill people's desire to live in taller buildings with the accompanying status and views afforded by these structures. These factors have led to high-rise or multi-story commercial and housing developments in areas that are prone to earthquakes and that have generally not seen high-rise developments in the past.

Furthermore, civil infrastructures around the world, particularly buildings, are easily devastated by strong earthquakes, high winds, waves, and tsunamis. For example, the devasting earthquake in Turkey and Syria in 2023 killed over 50,000 people, and many more people were injured due to the collapse of buildings in which they were residing. Such devastating building collapses occur in part because the structural elements of such buildings fail when the applied loads exceed what the building is capable of withstanding and because of the buildings' limited energy dissipation.

Many studies have been conducted on designing buildings with expected structural behavior under many harsh environmental loading conditions. In most cases, the capability of structures to withstand extreme environmental loads is addressed by using extra construction materials to enhance the strength/stiffness of civil infrastructure. Based on the large size of many buildings, significant raw materials and energy are required to produce and transport these raw materials. For example, the incremental increase in construction materials of tall buildings creates adverse effects on the environment by consuming raw materials and producing greenhouse emissions. In addition, extra materials at a construction site take up more space and introduce additional labor costs. Many attempts have been made to balance structural demands and consumed construction materials to preserve natural resources, provide reliable homes for tenants, and reduce the carbon footprint.

Structural control systems (SCSs) have been designed and installed in many buildings including steel and concrete structures to preserve buildings exposed to lateral loads, like seismic loads experienced in modest to strong earthquakes. Structural control systems currently employed illustratively include passive tuned mass dampers, friction dampers, semi-active stiffness control devices, and active tendon systems.

FIG. 1A illustrates a typical structural steel frame 10 with a series of columns 12 and cross members or beams 14. The development of structural steel framing enabled modern high-rise construction in the 1890's and began the age of the modern skyscraper by eliminating the need for thick bearing walls on lower floors as the height of a structure increased. FIG. 2 illustrates a steel plate shear wall system (SPSWS), which is one of the most efficient and simple structural control systems that provides lateral force-resistance. The SPSW system is widely used in many countries, e.g., Canada, China, Japan, and the United States. As shown in FIG. 1B, a typical SPSW consists of a steel infill plate 16 that is surrounded by boundary column beams 12 and boundary cross member beams 14, and in some cases one or more of optional horizontal stiffeners or optional vertical stiffeners. FIG. 1C is a detailed sectional front view of the SPSW system shown in FIG. 1B in which the optional horizontal stiffeners 18 and optional vertical stiffeners 20 are included in the structure. However, due to weaknesses found in the conventional SPSW systems, such as permanent deformation of the steel infill plate and low energy dissipation capacity, this solution is suboptimal. The permanent deformation still contributes to costly repairs to the structure even though the building may survive the initial extreme loading event. Currently, conventional construction materials, such as steel and concrete, have a limited capacity to provide recovery in buildings. For example, the strain-stress response of steel-based components provides little recovery capability and energy absorption capacity is limited. Furthermore, there is currently an increased interest in recovery-based performance (e.g., Federal Emergency Management Agency (FEMA) report P-2090) of civil infrastructure that minimizes permanent deformation of civil infrastructure in response to adverse loading events.

Thus, there exists a need for structural control systems for civil infrastructures that provides higher levels of energy dissipation and minimizes the amount of permanent deformation of the structures to improve the recovery-based performance of structures in order to preserve such structures when exposed to seismic and other adverse loads and maximize restoration of the underlying structure to its initial state after such events.

SUMMARY OF THE INVENTION

A smart self-centered shear wall (SSCSW) system is provided. The smart self-centered shear wall system includes a set of frame columns joined to a set of frame beams, a connection plate, a set of gussets, and a set of cables. The frame columns and frame beams define an area with at least three corners with a shear wall mounted within the area. An individual gusset plate of the set of gusset plates is affixed in each one of the at least three corners of the area. The set of cables are formed of shape memory alloy material (SMA) each having a first end and a second end, the first end of each of the SMA cables is attached to one of the gusset plates in one of the at least three corners, and the second end is connected to an attachment point on the connection plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter that is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1A is a perspective view of an existing structural steel frame of a building;

FIG. 1B is a perspective view of an existing structural steel frame reinforced with a steel plate shear wall (SPSW) system;

FIG. 1C is a detailed sectional front view of the SPSW system shown in FIG. 1B in which the optional horizontal stiffeners and optional vertical stiffeners are included in the structure.

FIG. 2 is a perspective view of a structural steel frame reinforced with a smart self-centered shear wall system (SSCSWS) in accordance with embodiments of the invention;

FIG. 3 is an exploded view of the smart self-centered shear wall system (SSCSWS) implemented in the structural steel frame of FIG. 2 in accordance with embodiments of the invention;

FIG. 4 is a schematic diagram of the smart self-centered shear wall system in accordance with embodiments of the invention;

FIG. 5A is a schematic diagram of a smart self-centered shear wall system according to embodiments of the present invention in an unloaded state;

FIG. 5B is a schematic diagram of the smart self-centered shear wall system of FIG. 5A after a lateral load applies force towards the left side;

FIG. 5C is a schematic diagram of the smart self-centered shear wall system of FIG. 5A after a lateral load applies force towards the right side;

FIG. 6A is a graph showing the ideal hysteresis response of superelastic effect of a shape memory alloy;

FIG. 6B is a graph showing the ideal hysteresis response of shape memory effect of a shape memory alloy;

FIG. 7 is a graph showing a schematic hysteresis response of a pre-strained SMA according to embodiments of the present invention before and after applied cyclic loads;

FIG. 8 is a graph showing a schematic hysteresis response of a conventional, prior art SMA before and after applied cyclic loads;

FIG. 9 is a graph showing the hysteresis responses of the 0% and 1.7% pre-strained specimen for 1000 cycles;

FIG. 10 is a graph showing energy dissipation capacity for 0% and 1.7% pre-strained specimen for 1000 cycles;

FIG. 11 illustrates a system for applying pre-stress on the SMA cable according to embodiments of the present disclosure; and

FIGS. 12A-12C are schematic diagrams showing the steps for applying pre-stress on SMA cables according to embodiments of the present disclosure.

DESCRIPTION OF THE INVENTION

The present invention has utility as a structural control system for civil infrastructures with recovery-based performance under extreme environmental loading. Embodiments of the inventive recovery-based structural control system may be utilized in both newly constructed and existing buildings as a retrofit to reduce the vulnerability to extreme environmental loading. The critical nature of recovery-based performance of civil structures is mentioned in Federal Emergency Management Agency (FEMA) report P-2090. Embodiments of the invention combine steel plate shear wall (SPSW) and the shape memory alloy (SMA) to provide the extra recovery ability in a buildings' main element or supplemental structural control systems.

Shape Memory Alloy (SMA) refers to a “memory” metallic alloy that can recover its original shape after undergoing large deformation (strain) up to 14% of the initial length. In addition, SMA can dissipate energy when it goes to the inelastic revisable phase. In embodiments of the invention, superelastic SMA is combined with SPSW, as a lateral resistive force system, to develop a novel self-centering, energy absorber, to provide a re-useable and affordable steel plate shear wall, called Smart Self-Centered Shear Wall (SSCSW) system. In embodiments of the inventive SSCSW system, pre-straining is applied to SMAs to eliminate the residual deformation that is known to appear in long-term use. With use of embodiments of the SSCSW, the lifespan of a building may remarkably improve under various loading conditions, particularly earthquakes, because of the recovery capability and energy dissipation capacity of SMAs.

Embodiments of the invention integrate SMAs to enhance a structure's dynamic behavior, e.g., reduction of the permanent deformations and drifts subjected to the applied lateral loads by providing enhanced energy dissipation capacity, damping, and re-centering of structures. Therefore, remarkably fewer construction materials are needed, and building codes are met. The SSCSWS, have the potential to save the lives of thousands of people and preserve buildings, which are located in seismically active zones. Under long-term load, the energy dissipation capacity, the re-centering ability, and the damping coefficient in SMAs in the SSCSW system decrease gradually.

It should be appreciated that the usage of SMA cables in the present invention and based on the configuration of the cables, affords dissipation of horizontal load forces, vertical load forces, or a combination thereof. According to certain inventive embodiments, a steel plate shear wall (SPSW) is integrated with a smart metallic alloy to pull the system back into the original position after experiencing a seismic load. According to embodiments, the alloy is capable of recovering the original state even after experiencing substantial elongation relative to the initial length. Accordingly, the present invention provides significantly enhanced structural behavior and preserves civil infrastructure over their lifespan. As a result, the present invention affords increased energy dissipation of external loads while also providing enhanced recovery phenomena in structures after removing the loads, compared to a conventional SPSW.

The present invention will now be described with reference to the following embodiments. As is apparent by these descriptions, this invention can be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, features illustrated with respect to one embodiment can be incorporated into other embodiments, and features illustrated with respect to a particular embodiment may be deleted from the embodiment. In addition, numerous variations and additions to the embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure, which do not depart from the instant invention. Hence, the following specification is intended to illustrate some particular embodiments of the invention, and not to exhaustively specify all permutations, combinations, and variations thereof.

It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range of from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

Unless indicated otherwise, explicitly or by context, the following terms are used herein as set forth below.

As used in the description of the invention and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Also as used herein, “and/or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

While the present invention is further detailed with respect to rectilinear/cuboidal embodiments defined by four corners in a base plane and eight corners overall, it is appreciated that present invention is also operative with triangular, pentagonal, hexagonal and higher order polygonal units, regardless of whether such polygons are regular or irregular.

Referring now to the figures, FIG. 2 is a perspective view of a structural steel frame 10″ reinforced with an embodiment of a smart self-centered shear wall system (SSCSWS) 30. As shown in greater detail in FIGS. 3 and 4. According to embodiments, the major components of the inventive smart self-centered shear wall system include a frame column 12, a frame beam 14, a steel plate shear wall 16, a horizontal side stiffener 18, a vertical side stiffener 20, connection plate 32, gusset plate moment connections 34, and SMA cables 36. In the embodiment shown, a set of four SMA cables 36 are attached to the corners of the rectilinear area or frame defined by the frame columns 12, a frame beams 14 by the gusset plates 34 positioned in the corners. In a specific embodiment each of the four distal ends of the SMA cables 36 attach to a connector 40, where each connector 40 is attached to a gusset plate 34 with a nut 38N and a bolt 38B. In an exemplary embodiment the nut 38N is a M5 hex nut, and the bolt 38B is a M5 hex bolt. The proximal ends of each of the four SMA cables 36 are attached to a separate corner of the connection plate 32 with an open jaw socket 42. A second set of nuts 44N and bolts 44B secure each of the open jaw sockets 42 to a corner of the connection plate 32. In an exemplary embodiment the nut 44N is a M10 hex nut, and the bolt 44B is a M10 hex bolt.

As readily seen in FIG. 4 the mounted SMA cables form an X-brace within the frame area in which the steel plate shear wall 16, the horizontal side stiffeners 18, and vertical side stiffener 20 are mounted.

It is appreciated that while four SMA cables are shown, alternative embodiments may use six, eight, or more cables to control deformation of the structure.

It is appreciated that the framing of the structure used with embodiments of the smart self-centered shear wall system may be reinforced concrete and the steel plate shear wall 16 is affixed within a rectilinear area defined by the reinforced concrete columns and reinforced concrete cross beams. The reinforced concrete may contain SMA bars.

The working mechanism of the inventive smart self-centered shear wall system (SSCSWS) 30 is shown in FIGS. 5A-5C. That is, FIG. 5A shows the smart SCSWS when no load is applied. While the lateral loads move the system toward the left side, as shown in FIG. 5B, the SMA identified by TL goes under tension load. The SMA cables also absorb the energy when it goes to the inelastic reversible phase. The diagonal SMA cables make the whole system recover the initial position when the load is removed. The system works in the same way if the system works oppositely and moves to the right with an applied lateral load, as shown in FIG. 5C.

Shape Memory alloy refers to a class of metallic alloys, that can recover their initial shape after experiencing large deformation from the original length. Exemplary of these materials are those detailed in Table 1 and Table 2. The shape memory effect (SME) and super elasticity (SE) are the main reasons SMAs exhibit this exceptional characteristic, as shown in FIGS. 6A and 6B. Recovery in SE happens when the external loads are removed, however in SME, heat internally or externally must be applied to the SMA to eliminate the permanent deformation (strains) and recover the initial state. SME and SE make SMAs ideal nominees for use in civil infrastructure to enhance the structural parameters, e.g., damping, the energy dissipation capacity, and particularly the recovery capability. In still other inventive embodiments, an SMA includes a plurality of separated conductors interfaced with a surface of SMA. A controller forms circuits between two or more specific conductors to control a path of current situated between those specific conductors to heat and activate those sections thereof. In the SMA-based system, SE is widely used over the SME. It is mainly due to the simplicity in use and its ability to recover without the need to have a source of heat.

Like other metallic alloys, the functionality of SMAs can differ from ideal assumptions because of degradation under dynamic loads. The schematic diagram of the behavior is presented in FIG. 7. Hence, the energy dissipation capacity and recovery ability can be reduced, as presented in FIGS. 9 and 10. According to embodiments, to avoid such degradation, the SMA is pre-stressed. As shown in FIG. 7 the pre-stressed SMA eliminates permanent deformation in the long-term use that would be observed without application of pre-stress to the SMA. Therefore, only reduction in energy dissipation should be considered, as shown in FIG. 8, schematically for conventional SMA material. The experimental results of the pre-strained SMA and change in the energy dissipation capacity are illustrated in FIGS. 9 and 10, respectively.

According to embodiments, the SMA cables are formed of any of the shape memory alloys listed in Tables 1 and 2.

TABLE 1
Alloys having shape memory effect.
		Transformation
	Transformation-temperature range	hysteresis
Alloy	Composition	° C.	° F.	Δ° C.	Δ° F.
Ag—Cd	44/49 at. % Cd	−190 to −50	−310 to −60	=15	=25
Au—Cd	46.5/50 at. % Cd	30 to 100	85 to 212	=15	=25
Cu—Al—Ni	14/14.5 wt % Al	−140 to 100	−220 to 212	=35	=65
	3/4.5 wt % Ni
Cu—Sn	=15 at. % Sn	−120 to 30	−185 to 85
Cu—Zn	38.5/41.5 wt % Zn	−180 to −10	−290 to 15	=10	=20
Cu—Zn—X	a few wt % of X	−180 to 200	−290 to 390	=10	=20
(X = Si, Sn, Al)
In—Ti	18/23 at. % Ti	60 to 100	140 to 212	=4	=7
Ni—Al	36/38 at. % Al	−180 to 100	−290 to 212	=10	=20
Ni—Ti	49/51 at. % Ni	−50 to 110	−60 to 230	=30	=55
Fe—Pt	=25 at. % Pt	=−130	=−200	=4	=7
Mn—Cu	5/35 at. % Cu	−250 to 180	−420 to 355	=25	=45
Fe—Mn—Si	32 wt % Mn, 6 wt % Si	−200 to 150	−330 to 300	=100	=180

TABLE 2
Mechanical properties of SMA materials*
	Alloy	εmax(%)	εs(%)	EA(MPa)	(Af ° C.)
	NiTi49.1	5	3.6	40.4	44.6
	NiTi49.5	5.7	4.6	45.3	53.0
	NiTi50	3.1	2.2	117.8	77.8
	NiTi	8.2	6.8	30.0	42.9
	NiTi45	6.8	6.0	62.5	−10.0
	NiTi44.1	6.5	5.5	39.7	0
	NiTi40Cu10	4.1	3.4	72.0	66.6
	NiTi41Cu10	4.1	3.1	91.5	50.0
	NiTi41.5Cu10	3.4	2.8	87.0	60.0
	NiTi25Cu25	10.0	2.5	14.3	73
	CuAlBe	3.0	2.4	32.0	−65
	FeMnAlNi	6.1	5.5	98.4	<−50
	FeNiCoAlTaB	15.0	13.5	46.9	−62.0
	*as detailed in Shahin Zareie et al., Structures 27 (2020) 1535-1550.

According to embodiments, the SMA is pre-stressed using a novel system using a customized nut, as provided in FIG. 11. According to embodiments, the pre-stressing system using a customized nut is implemented into the smart SCSWS. FIGS. 12A-12C show the steps for pre-stressing the SMA cables according to embodiments of the present invention. In pre-stressed materials such as concrete, SMA bars are provided in some inventive embodiments. As a result, such pre-stressed materials exhibit reduced crack propagation and improvements in material fatigue resistance are noted when used in the context of an inventive SCSWS.

According to embodiments, the smart SCSWS is configured to be integrated with different types of steel, concrete, and timber buildings, particularly high-rise ones, to provide their stability and serviceability under ground movements having different intensities, frequency contents, and magnitudes. The systems are easily installed in the frames of already constructed buildings without changing the structural elements to retrofit them as well as in new construction buildings. By using the inventive smart system, the life expectancy of new and existing buildings can be extended due to meeting new requirements and safety codes determined by updated regulations and buildings codes. An additional benefit of the inventive smart FPS is its optimization of construction materials.

Patent documents and publications mentioned in the specification are indicative of the levels of those skilled in the art to which the invention pertains. These documents and publications are incorporated herein by reference to the same extent as if each individual document or publication was specifically and individually incorporated herein by reference.

The foregoing description is illustrative of particular embodiments of the invention but is not meant to be a limitation upon the practice thereof. The following claims, including all equivalents thereof, are intended to define the scope of the invention.

Claims

1. A smart self-centered shear wall (SSCSW) system comprising:

a set of frame columns joined to a set of frame beams that define an area with at least three corners;

a shear wall mounted within the area;

a gusset plate affixed in each one of the at least three corners of the area;

a connection plate with at least three attachment points;

a set of cables formed of shape memory alloy material (SMA) each having a first end and a second end, the first end of each of the SMA cables is attached to one of the gusset plates in one of the at least three corners, and the second end is connected to one of the attachment points on the connection plate.

2. The system of claim 1 further comprising a set of horizontal side stiffeners and a set of vertical side stiffeners.

3. The system of claim 1 wherein each of the SMA cable first ends are attached to a connector, the connector configured for attachment to one of the gusset plates.

4. The system of claim 1 wherein each of the SMA cable second ends are attached to an open jaw socket, the open jaw socket configured for attachment to the connection plate.

5. The system of claim 1 further comprising a first set of nuts and corresponding bolts to secure each of the connectors to the gusset plates.

6. The system of claim 5 wherein the first set of nuts and corresponding bolts have M5 threads.

7. The system of claim 1 further comprising a second set of nuts and corresponding bolts to secure each of the open jaw sockets to the connection plate.

8. The system of claim 7 wherein the second set of nuts and corresponding bolts have M10 threads.

9. The system of claim 1 wherein the set of SMA cables are arranged in a X shape.

10. The system of claim 1 wherein each of the SMA cables are configured to deform and subsequently recover their initial shape.

11. The system of claim 1 wherein each of the SMA cables are configured to recover their shape after experiencing deformation up to 14% of its original length.

12. The system of claim 1 wherein each of the SMA cables is pre-stressed.

13. The system of claim 1 wherein the first end of each of the set of SMA cables is attached to the gusset plate by a pre-stressing nut.

14. The system of claim 1 wherein the second end of each of the SMA cables is attached to the connection plate by a pre-stressing nut.

15. The system of claim 1 wherein at least one of the SMA cables is pre-stressed.

16. The system of claim 1 wherein the set of frame columns joined to the set of frame beams are formed of steel.

17. The system of claim 1 wherein the set of frame columns joined to the set of frame beams are formed of reinforced concrete.

18. The system of claim 17 wherein the reinforced concrete contains SMA bars.

19. The system of claim 1 wherein the area is rectilinear and the at least three corners is four corners.