Background of the Invention

Field of the Invention

This invention relates to a nonlinear spring bracing device, and more particularly to a supplementary variable stiffness device used in a bracing system for seismic protection in structures.

Description of Related Arts

Systems and devices having variable stiffness are devised to dissipate energy and mitigate damages caused by wind and earthquake in structures such as bridges and buildings. These protective systems and devices include shear wall, rigid frame, base isolation, active control and passive control systems such as bracing system.

US 5,036,633 discloses a variable damping device having a variable coefficient of damping for controlling the vibration of a structure by estimating the resonance property and the damping property. The optimal coefficient of damping corresponding to an external force is determined by a computer based on the earthquake information obtained from sensors. Since electricity and electrical sensors are required for the operation, the control of the structural response can be delayed.

US 5,845,438 discloses a brace apparatus for bracing a building structure. The brace apparatus includes a brace member attached to the structure, a slider means mounted on the structure and connected to the brace member, and a damper means connected to the slider means for damping and restricting sliding movement of the slider means relative to the structure. The brace apparatus minimises the seismic disturbance by applying linear damping forces to the structure. The linear action of the brace apparatus indicates a constant stiffness when resisting an increasing displacement. In this case, the performance of the linear action is restricted in the occurrence of large displacement.

US 5,819.484 discloses a friction spring energy dissipating unit for bracing a building structure. The principal components of the dissipating unit comprise a plurality of spring friction rings stacked with axial alignment within a housing. In operation, the spring friction rings experience a compression force as bracing members imposing a compression force or a tension force to the stack ends through a thrust rod. However, this dissipating unit necessitates complicated manufacturing process and maintenance procedure.

Accordingly, it can be seen in the prior arts that there exists a need to provide a bracing device for protecting a structure against seismic motions effectively. Summary of Invention

It is an objective of the present invention to provide a high performance bracing device which does not require any power supply to function.

It is also an objective of the present invention to provide a bracing device having a nonlinear action as adaptive system for protecting structure against large displacement.

It is yet another objective of the present invention to provide a bracing device having an easy-to-fabricate and simple maintenance design.

It is a further objective of the present invention to provide a bracing device having a simple installation feature to equip a bracing system.

Accordingly, these objectives may be achieved by following the teachings of the present invention. The present invention relates to a nonlinear spring bracing device for seismic protection of a braced structure, characterised by: a housing; a core positioned in a middle of the housing; a pair of interior mounts, each disposed adjacent to the core; a pair of nonlinear springs, each having a first end attached to one of the pair of interior mounts and a second end attached to a sidewall of the housing; a rod passing through the pair of interior mounts and the pair of nonlinear springs, the rod being coupled to the core; means for connecting the nonlinear spring bracing device to a brace; wherein a seismic load imposed to the braced structure being transferred to the nonlinear spring bracing device, displacing one of the pair of interior mounts and compressing one of the pair of nonlinear springs in a direction opposite to a direction of the seismic load to counteract a force of the seismic load.

Brief Description of the Drawings

The features of the invention will be more readily understood and appreciated from the following detailed description when read in conjunction with the accompanying drawings of the preferred embodiment of the present invention, in which:

Fig. 1 is a perspective view of a nonlinear spring bracing device.

Fig. 2 is a front view of the nonlinear spring bracing device.

Fig. 3 is a top view of the nonlinear spring bracing device.

Fig. 4 is figure showing an installation layout of the nonlinear spring bracing device in a structure.

Fig. 5a&5b are figures showing the performance of the nonlinear spring bracing device when a seismic load is laterally applied to the structure in different directions. Detailed Description of the Invention

As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting but merely as a basis for claims. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the scope of the present invention as defined by the appended claims. As used throughout this application, the word "may" is used in a permissive sense (i.e., meaning having the potential to), rather than the mandatory sense (i.e., meaning must). Similarly, the words "include," "including," and "includes" mean including, but not limited to. Further, the words "a" or "an" mean "at least one" and the word "plurality" means one or more, unless otherwise mentioned. Where the abbreviations or technical terms are used, these indicate the commonly accepted meanings as known in the technical field. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures. The present invention will now be described with reference to Figs. 1 -5b.

The present invention relates to a nonlinear spring bracing device (10) for seismic protection of a braced structure, characterised by:

a housing (1 1 );

a core (12) positioned in a middle of the housing (1 1 ); a pair of interior mounts (15), each disposed adjacent to the core

(12);

a pair of nonlinear springs, each having a first end attached to one of the pair of interior mounts (15) and a second end attached to a sidewall of the housing (1 1 );

a rod (14) passing through the pair of interior mounts (15) and the pair of nonlinear springs, the rod (14) being coupled to the core (12);

means for connecting the nonlinear spring bracing device (10) to a brace (17);

wherein a seismic load imposed to the braced structure being transferred to the nonlinear spring bracing device (10), displacing one of the pair of interior mounts (15) and compressing one of the pair of nonlinear springs in a direction opposite to a direction of the seismic load to counteract a force of the seismic load. In a preferred embodiment of the nonlinear spring bracing device (10), the device (10) further comprises a pair of exterior mounts (16), each disposed on the sidewall of the housing (1 1 ), for attaching the pair of nonlinear springs. In a preferred embodiment of the nonlinear spring bracing device (10), the pair of nonlinear springs are made of a rigid material.

In a preferred embodiment of the nonlinear spring bracing device (10), the nonlinear spring comprises conical spring (13).

In a preferred embodiment of the nonlinear spring bracing device (10), the means for connecting the nonlinear spring bracing device (10) to the brace (17) is a hole provided at one end of the rod (14), the brace (17) passing through the hole for connecting the nonlinear spring bracing device (10) to the brace (17).

The term 'seismic load' as used herein refers to a load on a structure caused by any dynamic load such as earthquake, ground motion, wind, tsunami, sea wave, vehicle, machinery or similar source. Below is an example of bracing device from which the advantages of the present invention may be more readily understood. It is to be understood that the following example is for illustrative purpose only and should not be construed to limit the present invention in any way. Examples

Figure 4 illustrates a structure defined by two spaced columns (19) and an upper beam (20) extending between the columns (19). A brace (17), preferably a cross brace (17) is interposed in the structure. Another example of preferred brace type is inverted V brace. More preferably, each of the two columns (19) has a pulley (21 ) attached thereto and the brace (17) is made of a flexible material to engage with the pulley (21 ). Examples of brace (17) of flexible materials are rope, wire, and cable. The brace (17) passes through one pulley (21 ) and extends to another pulley (21 ), forming a cross brace (17) having a closed lower end. The pulleys (21 ) may be attached to a junction of the structure, which formed by the cross brace (17), by means of any types of pinned connection known in the art. A nonlinear spring bracing device (10) is applied to the structure by locating the device (10) at a position generally midway of the closed lower end of the cross brace (17). The device (10) may comprise a rod (14) with holes at both ends and the device (10) is connected to the brace (17) by passing the brace (17) through the holes of the rod (14). The device (10) may be installed on a bottom beam or foundation of the structure by fastening a housing (1 1 ) of the device (10) to a planar plate mounted on the bottom beam or the foundation using any fastening means known in the art.

Figures 5a and 5b illustrate performance of the structure incorporated with the device (10) in response to seismic vibration. The cross brace (17) includes two bracing members, 18a, 18b. Referring to Figure 5a, when a seismic load is imposed to the structure laterally from left to right, the structure is prompted to move to the right side. Thus, the bracing member 18a is compressed and buckled. The device (10) and the bracing member 18b are now receiving a tensile force transmitted through the pulley (21 ). The rod (14) of the device (10) is driven to move to the left. Referring to Figures 1 -3, a core (12) of the device (10) is coupled to the rod (14) while a pair of interior mounts (15) can move front and back in longitudinal direction along the rod (14). Preferably, the core (12) is equipped with two guides (22) at both sides, which allow and guide the core (12) to move along the rod (14). When the rod (14) moves to the left, the core (12) sandwiched between the pair of interior mounts (15) moves to the left and pushes the left interior mount (16) to the left. A left conical spring (13) attached to the left interior mount (16) is compressed. The force of compressing the left conical spring (13) resists against the movement of the rod (14), the bracing members (18a, 18b) and thus, the structure to the right. Accordingly, the movement of the structure is counteracted and the displacement of the structure is restricted by the device (10).

Conversely, when a seismic load is applied to the structure laterally from right to left (Figure 5b), compression force and tension force are transmitted to bracing member 18b and bracing member 18a, respectively. In this circumstance, the device (10) is driven to move to right and the displacement of the structure is restricted by the compression of the right conical spring (13). The conical spring (13) of the device (10) behaves as nonlinear spring in which the gradient of stiffness varies according to extend of displacement, that is, the stiffness of the conical springs (13) increases in nonlinear order when displacement is increasing. In contrast, linear spring provides constant stiffness when the displacement is increasing. Therefore, action of nonlinear spring is adaptive and shows better performance. The device (10) increases the lateral stiffness of the structure without scarifying the energy dissipation characteristics and ductility characteristic of moment resistance structure. For large vibration amplitudes, the device (10) acts to refrain unacceptably large storey drift. Accordingly, the braced structure can display ductile performance in dissipating seismic energy.

Although the present invention has been described with reference to specific embodiments, also shown in the appended figures, it will be apparent for those skilled in the art that many variations and modifications can be done within the scope of the invention as described in the specification and defined in the following claims.

Description of the reference numerals used in the accompanying drawings according to the present invention:

Reference

Description

Numerals

10 Nonlinear spring bracing device

1 1 Housing

12 Core

13 Conical spring

14 Rod

15 Interior mount

16 Exterior mount

17 Brace

18a, 18b Bracing member

19 Column

20 Beam

21 Pulley

22 Guide