INNOVATIVE TECHNIQUE TO CONSTRUCT A ROBUST DURABLE SEISMIC PROTECTIVE DEVICE

Abstract

The invention is an innovative technique to construct a robust durable protection device for structures against dynamic loadings such as earthquakes, wind, or mechanical vibrations. The technique utilizes friction between a sliding material such as PTFE and Cementitious Material (CM) (not metal) to protect structures. The invention controls the surface roughness of the CM by employing a designed mix with small size to no aggregates and cast it in molds with different roughness to produce a friction coefficient ranging from 0.3% to 40%. The CM mix preferably has a ultimate strength higher than 3,000 psi. The CM includes, but is not limited to, polymer concrete, high performance concrete, geopolymer and ultra-high-performance concrete. The resulting sliding material and the specially molded CM can be used in several forms to protect structures against dynamic loading such as dampers or base isolators.

Description

BACKGROUND OF THE INVENTION

The present invention relates to seismic protective devices and in particular to seismic isolation devices and damping devices for structures.

Dynamic forces, such as those result from earthquakes, winds, and mechanical vibrations, cause significant damage to unprotected structures. These structures include, but are not limited to, buildings, bridges, houses, hospitals, data centers, wharves, constructed facilities, nuclear plants, and critical infrastructure. The hazard is also extended to nonstructural components such as mechanical and electrical equipment, utilities, building contents, piping systems and architectural partitions. Among the most vulnerable structures are the substandard non-retrofitted ones. Such structures impose risks on human lives. Once structures are damaged, millions of dollars will be spent on either repairing, demolishing, or replacing them. Many lives will be affected or lost as a result. There is a human and economic cost to earthquakes and other natural disasters.

Seismic protective technologies such as base isolation, passive and semi-active damping devices, self-centering walls and frames, and other emerging technologies, help improve the damage-mitigation and post-earthquake functionality, predictably, resiliency and reliably. However, most of the prior-art patents for these technologies have been implemented on a limited scale in actual structures because of the prohibitive costs associated with their implementation. The implemented system in actual structures is often expensive and poses durability problems such as poor fire and corrosion resistance. Corrosion constitutes a major drawback since it significantly deteriorates the device's performance, and the structure becomes unprotected over time.

The current state of the art uses one of the following devices to protect the structures from earthquakes. These devices can be divided into two categories:

1) Base isolation:

• • a) Elastomeric-based such as Lead Rubber Bearings (LRBs);
  • b) Friction based such as friction pendulums, for example described in U.S. Pat. No. 8,371,075 and Published US Application No. 2006/0174555 for:
    • I) Single friction pendulums;
    • ii) Double friction pendulums; and
    • iii) Triple friction pendulums.2) Passive and semi active damping devices (for example in U.S. Pat. No. 7,774,966).

These devices use either friction or material damping to dissipate the energy exerted on a structure by seismic events, wind buffering or mechanical vibration. Frictional devices rely on the friction generated between sliding surfaces, one is made of metal such as stainless-steel, and one made of materials such as Polytetrafluoroethylene (PTFE) or Ultra-High Molecular Weight Polyethylene (UHMWPE) friction material. These devices are, however, expensive, complicated to manufacture and have durability issues as stated earlier. Devices which use material damping such as LRB, can only be used as base isolators and not necessarily as dampers. These also pose high fabrication cost while exhibiting the same durability issues. They are also vulnerable to fire and can be damaged quickly causing catastrophic failures of structures.

More than 90% of previous patents related to seismic protection isolators or dampers have not been put into practical use due to the substantial expense linked to their application. While many of these prior-art patents have demonstrated significant effectiveness in mitigating seismic forces on supported structures, their lack of cost-effectiveness and their durability problems have rendered them unused. A primary goal of the innovative method outlined below is to establish an economically viable, cost-effective, and durable earthquake protection system.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the above and other needs by providing a technique to construct a seismic protective device that addresses known problems. The present invention utilizes friction between a sliding material such as Polytetrafluoroethylene (PTFE) and non-metallic materials such as Cementitious Material (CM), not metal, to protect structures. The CM is a mix with small size to no aggregates and cast in special molds to produce a wide array of surface roughness that results in a wide array of friction coefficients ranging from 0.3% to 40%. The product is highly durable, fire resistant, low-cost and can be used in many configurations. The technique uses existing material in an innovative way to create a device, which utilizes friction to protect structures.

Experimental evaluations were conducted to determine and regulate/control the surface roughness of the CM. By manipulating the surface roughness of the CM a desired Coefficient of Friction (COF) between the CM and various sliding materials, such as PTFE, UHMWPE, among others is obtained. The COF between the CM and these materials is important as it determines the level of friction/damping generated by earthquake protection devices.

The CM mixture incorporated no aggregates or aggregates of small to medium sizes and is cast in specialized molds having specified roughness, facilitating the creation of CM surfaces with diverse roughness levels. This diversity in surface textures yielded a broad spectrum of friction coefficients, ranging from 0.3% to 40%. Experimental tests utilized molds fabricated from materials including plastic, wood, steel (with varying finishes), stainless steel (also with varying finishes), and plexiglass. The surface roughness of these molds was quantitatively assessed using a commercially available surface roughness tester, before pouring the CM. Subsequently, the CM is poured into these molds to create pads. After the CM material hardened, the surface roughness of the CM pad is measured employing the same device used for the molds.

The resultant surface roughness of the CM closely matches that of the molds, with a variance of +/−10%. Certain molds exhibited exceptionally smooth surfaces, and the CM successfully replicated this level of smoothness. Achieving such smooth surfaces on CM enables its application in earthquake protection devices as a replacement for steel or stainless-steel plates traditionally used with sliding materials to create damping effects.

The present invention provides a method for manufacturing concrete with different surface roughness. Since COF between different materials is dependent on the surface roughness of such materials, thus, through precise control over the CM surface roughness, it is possible to regulate the COF between the CM and sliding materials. Consequently, this allows for the design and adjustment of the damping effect generated by the device. Utilizing different molds for casting the CM can result in varied surface roughness, thereby enabling the customization of the damping effect during seismic events.

By facilitating variable damping through the interaction between the CM and sliding materials, these devices can be tailored for specific applications. For instance, they can serve as seismic base isolation devices, whereby a building or structure is mounted onto them, effectively isolating it from ground movements. Additionally, these devices may be employed as dampers along a building's height, providing supplementary damping through controlled friction.

A comparative study was conducted to evaluate the anticipated COF between the finalized CM pad and various sliding materials. This study employed COF data from established materials like stainless steel and polished stainless steel, tested against a spectrum of sliding materials including Verigin PTFE, woven PTFE, and UHMWPE. Surface roughness served as the parameter for gauging the expected COF between the measured CM pads and the aforementioned range of sliding materials. The findings from these assessments are provided in Table 1.

TABLE 1
Expected COF based on the comparable study
	CM	Material
	Surface	Compared	Sliding	Expected
Molds	Roughness	to CM	Material	COF*
Stainless	0.4 μm	Stainless	Virgin PTFE	5% to 20%
Steel 2B		steel 2B	Woven PTFE	3% to 12%
Polished	0.08 μm	Polished	Virgin PTFE	3% to 8%
Stainless		Stainless	UHMWPE	1% to 1.5%
steel or		steel	Lubricated	0.3% to 1.5%
Plexiglass			PTFE or
			Lubricated
			UHMWPE
*A range is provided since COF depends on many factors such as axial stress applied and velocity.
A COF of 40% is expected to be achieved if the mold used is wood with very high surface roughness.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein:

FIG. 1 is a cross-sectional view showing a sliding puck and slider on a flat Cementitious Material (CM) pad on a flat concrete pad, according to the present invention.

FIG. 2 is a cross-sectional view showing how the sliding puck and slider slides on the CM pad when horizontal dynamic loads are applied.

FIG. 3A is a cross-sectional view showing the sliding puck and slider over a flat CM pad surface without stoppers, according to the present invention.

FIG. 3B is a cross-sectional view showing the sliding puck and slider over a flat CM/concrete pad surface with stoppers, according to the present invention.

FIG. 4A is a cross-sectional view showing the sliding puck and slider over a curved CM/concrete pad without stoppers, according to the present invention.

FIG. 4B is a cross-sectional view showing the sliding puck and slider over a curved CM/concrete pad with stoppers, according to the present invention.

FIG. 5A is a cross-sectional view showing the sliding puck and slider over double curved CM/concrete pad without stoppers, according to the present invention.

FIG. 5B is a cross-sectional view showing the sliding puck and slider over double curved CM/concrete pad with stoppers, according to the present invention.

FIG. 6A is a cross-sectional view showing the sliding puck and slider over double curved CM/concrete pads without stoppers like FIG. 5A but with more rotational capacity, according to the present invention.

FIG. 6B is a cross-sectional view showing the sliding puck and slider over double curved CM/concrete pads with stoppers like FIG. 5B but with more rotational capacity, according to the present invention.

FIG. 7A is a side view showing a diagonal configuration of damping devices used within a structural system of a building to produce damping and absorb the energy from dynamic loading like earthquakes, according to the present invention.

FIG. 7B is a top view of the damping device, according to the present invention.

FIG. 7C is a cross-sectional view of the damping device taken along line 7C-7C of FIG. 7B, according to the present invention.

FIG. 8A is an elevation and cross-sectional views showing a horizontal configuration of the damping device of a horizontal slider within a structural system of a building to produce damping and absorb the energy from dynamic loading like earthquakes, according to the present invention.

FIG. 8B is a top view of the damping device of the horizontal slider, according to the present invention.

FIG. 8C is a cross-sectional view of the damping device of the horizontal slider taken along line 8C-8C of FIG. 8B, according to the present invention.

FIG. 9 shows actual test results for roughness coefficients for eight specimens using different molds (steel, stainless steel, plexiglass, plastic, and others).

Corresponding reference characters indicate corresponding components throughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims.

Where the terms “about” or “generally” are associated with an element of the invention, it is intended to describe a feature's appearance to the human eye or human perception, and not a precise measurement, or typically within 10 percent of a stated value.

The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense but is made merely for the purpose of describing one or more preferred embodiments of the invention. The scope of the invention should be determined with reference to the claims.

The present invention is a seismic protective device and an innovative technique to construct a robust durable protective device. The technique uses existing material in an innovative way to create the protective device, which utilizes friction to protect structures. As described in FIG. 1, the device consists of a sliding puck 10 supporting a protected structure 11, a slider 14, and a pad 12 made of a designed Cementitious Material (CM) mix. The sliding puck 10 and the slider 14 slides on the pad 12. The slider 14 is preferably made up of material such as Polytetrafluoroethylene (PTFE) or Ultra-High Molecular Weight Polyethylene (UHMWPE). The pad 12 may, for example, be flat, spherical, cylindrical, or a concave surface made of CM instead of metal. Because minimizing the friction was a key performance factor for prior protective devices, the pad 12 was usually made of metal in the prior art. The present invention utilizes the pad 12 made from CM not metal.

This modification has two major advantages:

• • 1) significantly increases device durability and fire resistance; and
  • 2) reduces the cost of fabrication since it eliminates the cost of machining, welding, and painting the metallic surfaces. The technique controls the surface roughness of the CM, which is a fundamental characteristic of the device, by employing a designed CM mix with small size to no aggregates and cast in special molds to produce a wide array of surface roughness that results in a wide array of friction coefficients ranging from 0.3% to 40%. The CM mix preferably has ultimate strength higher than 3,000 psi to be able to withstand the weights of the structures. The CM includes, but is not limited to, polymer concrete, high performance concrete, geopolymer and ultra-high-performance concrete.

The resulting device can be used as either a damper or a base isolator to protect structures by dissipating the energy exerted on them by seismic events, wind buffering or mechanical vibrations, or by isolating the structure from the ground. It can be used in different configurations and in different locations in the structure as illustrated in FIGS. 3A to 6B.

FIG. 3A shows the sliding puck 10 and the slider 14 sliding over a flat surface 13a of a CM pad 12 and FIG. 3B shows the sliding puck 10 and the slider 14 sliding over the flat surface 13a of the CM pad 12 with stoppers 16.

FIG. 4A shows the sliding puck 10 and the slider 14 sliding over a concave surface 13b of the CM pad 12b and FIG. 4B shows the sliding puck 10 and the slider 14 sliding over the concave surface 13b the CM pad 12b with stoppers 16.

FIG. 5A shows the sliding puck 10 and slider 14 sliding over a double curved CM surfaces 12a and 12b having concave surfaces 13a and 13b. Depending on the mold type, material and cast technique, the surface 13a could have the same roughness as the surface 13b or the surface roughness can be different. Having higher roughness values for surface 13b will produce more damping and limit the deformations during strong earthquakes.

FIG. 5B adds stoppers 16 to limit the movement of the sliding puck 10 and slider 14 and is otherwise similar to FIG. 5A.

FIG. 6A shows the sliding puck 10 and a curved upper sliding puck 10b, and sliders 14, 14b, and 14c. The sliding puck 10 and slider 14 slide on the lower curved cementitious material surface 13b. A curved upper sliding puck 10b and sliders 14b and 14c slide between a curved top surface 15 of the sliding puck 10 and the upper concave surface 13a. The concept is the same as FIG. 5A but with more rotational capacity by including more sliding surfaces for the sliding puck in between surface 13a and surface 13b.

FIG. 6B adds the stoppers 16 to limit the movement of the sliding pucks 10 and 10b and sliders 14, 14b and 14c and is otherwise similar to FIG. 6A.

FIG. 7A is an elevation view showing a diagonal configuration of the present invention showing damping devices 40 used within a structural system 50 comprised of beams 30, diagonal braces 32, columns 34, and CM damping devices 40 of a building to produce damping and absorb the energy from dynamic loading like earthquakes, FIG. 7B is a top view of a damping device 40, according to the present invention, and FIG. 7C is a cross-sectional view of the damping device 40 taken along line 7C-7C of FIG. 7B, according to the present invention.

The CM damping device 40 is comprised of the CM pad 12, the slider 14, and the sliding puck 10. The slider 14 is fixed to the sliding puck 10 and the CM pad 12 slides over the slider 14 and the sliding puck 10. The slider 14 material may be PTFE or UHMWPE or other material.

FIG. 8A shows a horizontal configuration of the damping device 40 that may be used within the structural system 50 of a building to produce damping and absorb the energy from dynamic loading like earthquakes. The structural system 50 is comprised of beams 30, braces 32, columns 34. The CM damping device 40 is shown in FIG. 8B and a cross-sectional view of the damping device 40 taken along line 8C-8C of FIG. 8B is shown in FIG. 8C. The CM/Concrete damping device 40 is comprised of CM pad 12, the slider 14, and the sliding puck 10. The slider 14 is fixed to the sliding puck 10, and CM pad 12 sliding over the slider 14. The slider 14 material may be PTFE or UHMWPE or other material.

FIG. 11 shows actual test results for roughness coefficients for eight specimens using different molds (steel, stainless steel, plexiglass, plastic, and others).

The innovative technique produces a protective device. Below is a summary of the key characteristics and advantages over other solutions:

1) The slider 14, the sliding puck, and the CM/Pad 12 can be used in different configurations:

• • a) The slider 10 and pad 12 can be used as base isolators in a manner similar to metallic friction pendulums without the inherent problems of the metallic friction pendulums, as mentioned herein above (problems with durability, corrosion, fire, and high cost).
  • b) The slider 10 and CM pad 12 can be used as dampers in a manner similar to metallic friction dampers without the inherent problems of the metallic friction dampers, as mentioned herein above (problems with durability, corrosion, fire, and high cost).

2) The CM pad 12 is cast using CM instead of metal thus reducing manufacturing and life cycle costs while improving its durability and fire resistance.

3) Surface roughness can be controlled to accommodate different levels of damping and lateral displacements. Thus, the slider 10 and CM pad 12 are applicable to resist a spectrum of dynamic loads such as weak to moderate to strong earthquakes. Surface roughness is achieved by changing the mold type and material and cast technique.

4) The slider 10 and CM pad 12 can be formed in different shapes, such as flat or curved to serve different functions and applications.

5) The slider 10 and CM pad 12 can have more than one friction surface to protect structures against different load intensities.

6) The slider 10 and CM pad 12 are easy to manufacture and do not require specialized equipment such as Computer Numeric Control (CNC) machines.

7) The slider 10 and CM pad 12 are inexpensive and can be mass-produced without significant investment. This will allow developing countries with significant seismic hazard to protect their buildings and lives at an affordable cost. The device claimed herein is also affordable for typical residential construction. This is particularly advantageous since many homeowners and developers elect not to seismically protect their structures due to the high cost of current protective devices.

8) The slider 10 and CM pad 12 offers high durability, low maintenance, extended service life, decreased life-cycle cost, not prone to corrosion, and high fire resistance.

The invention is tested and verified using different molds such as steel, stainless steel, plexiglass, plastic, and others. The final surface roughness of the CM varied significantly depending on the molds used (see FIG. 9). For example, the CM pads casted in smooth molds such as stainless steel or plexiglass showed low roughness coefficients (Ra=around 0.1 μm). While other molds such as steel or rough plastic gave higher roughness coefficients (Ra=0.5 to 2.7 μm). Therefore, by controlling the mold and the mix, different damping levels and displacements can be accommodated.

While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.

Claims

1. A seismic protection device comprising: a pad made of Cementitious Material (CM);a sliding puck supporting a protected structure; anda slider made of sliding material between the sliding puck and the pad.

2. A seismic protection device of claim 1, wherein the CM is polymer concrete.

3. A seismic protection device of claim 1, wherein the CM is a high performance concrete.

4. A seismic protection device of claim 1, wherein the CM is geopolymer and ultra-high-performance concrete.

5. A seismic protection device of claim 1, wherein the coefficient of friction between the pad and the slider ranges from 0.3% to 40%.

6. A seismic protection device of claim 1, wherein the pad has an ultimate strength higher than 3,000 psi.

7. A seismic protection device of claim 1, wherein the slider is made of Polytetrafluoroethylene (PTFE).

8. A seismic protection device of claim 1, wherein the slider is made of Ultra-High Molecular Weight Polyethylene (UHMWPE).

9. A method of constructing a seismic protection device, the method comprising the steps of: preparing a mix of cementitious material (CM) to produce a desired surface roughness;casting a pad using the CM mix;positioning a sliding puck supporting a protected structure on the pad; anda sliding material attached to the sliding puck resides between the sliding puck and the pad.

10. A method of constructing a seismic protection device of claim 9, wherein the CM mix is comprised of small size aggregate to no aggregate.

11. A method of constructing a seismic protection device of claim 9, wherein the CM mix is cast in molds with varying roughness to provide coefficient of friction from 0.3% to 40% between the pad and sliding puck.

12. A method of constructing a seismic protection device of claim 9, wherein the CM mix is comprised of polymer concrete.

13. A method of constructing a seismic protection device of claim 9, wherein the CM mix is comprised of high performance concrete.

14. A method of constructing a seismic protection device of claim 9, wherein the CM mix is comprised of geopolymer and ultra-high-performance concrete.

15. A method of constructing a seismic protection device of claim 9, wherein the CM mix is designed to have an ultimate strength higher than 3,000 psi.

16. A method of constructing a seismic protection device of claim 9, wherein the pad surface has a range of coefficient of friction from 0.3% to 40%.

17. A method of constructing a seismic protection device of claim 9, wherein the sliding material is made of Polytetrafluoroethylene (PTFE).

18. A method of constructing a seismic protection device of claim 9, wherein the sliding material is made of Ultra-High Molecular Weight Polyethylene (UHMWPE).

19. A method of constructing a seismic protection device, the method comprising the steps of: preparing a mix of cementitious material (CM) to produce a desired surface roughness;casting a pad using the CM mix; andpositioning a slider fixed to a sliding puck against the pad within a seismic damper system.

20. A method of constructing a seismic protection device of claim 19, wherein: the CM is either polymer concrete, high performance concrete, geopolymer, or ultra-high-performance concrete;the CM has a coefficient of friction ranges from 0.3% to 40%; andthe pad has an ultimate strength higher than 3,000 psi.