Method of constructing structures with seismically-isolated base

Abstract

A seismically isolated structure and a method of constructing same provide a rigid diaphragm, a plurality of footings each positioned at least partially under the rigid diaphragm, and a plurality of base isolation devices each positioned between a footing and the rigid diaphragm, wherein the rigid diaphragm was constructed in situ above the footings generally below its final elevation. A barrier is positioned between the rigid diaphragm and at least the footings to prevent bonding between the rigid diaphragm and the footings. The barrier, which may be structural or chemical or a combination thereof, may also span between the footings if appropriate.

Description

FIELD OF INVENTION

[0001] This invention relates generally to a method of constructing structures with a seismically-isolated base, in particular, a method of constructing structures supported on base-isolation devices.

BACKGROUND OF INVENTION

[0002] The building codes used in the U.S. were based on one of three model codes: the Building Officials and Code Administrators International, Inc. (BOCA) National Building Code (NBC); the Southern Building Code Congress International, Inc. (SBCCI) Standard Building Code (SBC); and International Conference of Building Official's Uniform Building Code (ICBO's UBC). However, BOCA, ICBO and SBCCI recently formed the International Code Council.RTM. (ICC) and produced the International Building Code.RTM. (IBC), a single, unified family of building codes, for use throughout the U.S. The three model codes were merged into one in an effort to integrate the most current earthquake knowledge and seismic design technology into the building codes.

[0003] Scientists began studying earthquakes as early as 1880, but gathering meaningful and accurate seismic activity data proved difficult due to the irregularity of earthquake events and long intervals of inactivity therebetween. Only the more recent 1971 San Fernando earthquake and 1979 Imperial Valley earthquake helped develop a better understanding of building behavior and the effects of earthquakes on buildings.

[0004] It is now appreciated that it costs much less to prepare for earthquakes than it does to repair the damage afterward. According to research by National Earthquake Hazards Reduction Program (NEHRP), the costs of providing seismic-resistant features for the protection of life rarely exceed two percent of the construction costs for new buildings. However, the focus o n building safety measures has been more toward preventing fatalities than preventing structural damage. For example, Section 1626.1 of the 1997 UBC states that the purpose of the earthquake provisions is primarily to safeguard against major structural failures and loss of life, not to limit damage or maintain function. Similarly, the 1997 NEHRP indicates that its design earthquake ground motion levels could result in both nonstructural and structural damage. In fact, engineers recognize that new buildings could sustain so much damage in a severe earthquake that they may have to be demolished and rebuilt, yet still not collapse. While there is no question that there exist the necessary engineering expertise and technology to design and build highly earthquake-resistant structures, the cost would be prohibitive. As such, economic considerations have been balanced against minimum safety levels.

[0005] Base isolation devices ("BIDs") are known for their ability to isolate building and structures from seismic activity or ground vibrations caused by heavy equipment. Most BIDs also damp the movement. BIDs are not limited to any particular physical structure but incorporate a variety of different mechanisms and means to accomplish their isolation and damping functions. BIDs are generally anchored to a footing or foundation from which they support the base of a structure. A rigid diaphragm often serves as the base of a building and generally includes a framed concrete slab with inlaid reinforcing steel bars (often referred to as "reinforcing steel " or "rebars"), as shown in FIGS. 2a-2f. In a seismically-isolated structure or building, the rigid diaphragm is designed to span between the BIDs and withstand vertical loads.

[0006] BIDs can be installed either during construction of a new structure or in retrofitting of an existing structure. However, the use of BIDS has often been limited to "critical structures" such as hospitals and selected government facilities, leaving most single family homes, low rise apartments and condominiums, particularly those of light wood frame construction in the Western United States, vulnerable to earthquake damage. This problem is compounded by the fact that construction methods for light wood frame structures follow generally similar formats. Since construction budgets and schedules are often closely monitored, the construction industry disfavors disruptions or deviations from those methods that would increase cost or prolong construction schedules even if they render the structure safer and more earthquake-proof.

[0007] Methods for raising structures, including buildings and houses are also known. Houses may be lifted for a number of reasons, including increasing crawl space, correcting for settling of soil below the house, elevating for flood protection and elevating for earthquake retrofitting. During the elevation process, most houses are separated from their foundations, raised on hydraulic jacks, and held by temporary supports while a new or extended foundation is constructed below. The size and number of jacks, as well as the number and layout of the temporary lifting beam or plate, depend on the size, shape and size of house being lifted. Thus, while elevating a structure, such as a single family home, low rise apartments and condominiums, is known, the process can be expensive and dangerous. Walls may crack during the move and detailed calculations of allowable bearing pressures should be made to ensure proper use of supporting beams or plates during the elevation process. Moreover, since a popular guideline allows for lifting a house no more than 1/16 inch per day, the process can also be extremely time-consuming. As such, lifting an older house or building or one after construction has been completed for purposes of earthquake retrofitting, even if the house or building is smaller, can be logistically and/or economically prohibitive for the owner.

[0008] Access to the BIDS for inspection post installation is desirable to ensure the integrity of the BIDS over the lifetime of the building and after any significant seismic event. As such, the construction of basement or subbasement has often precluded the use of BIDS in almost all by the most crucial of newly constructed buildings. While the installation of BIDS in a new construction having a basement is possible, there is usually a significant increase in construction time and expenses stemming from the additional excavation and construction materials, such as for a subbasement to provide space and continued access to the BIDS and falsework to provide temporary support to the basement floor during construction.

[0009] Accordingly, there is a desire for a method of constructing a structure or building that allows for the installation of BIDs between with minimal deviations from generally known and accepted grading, ground preparation and construction practices and procedures. The method should also avoid or at least minimize delays in construction of the structure above the base or foundation and minimize the risk of damage to the structure. Moreover, the method should facilitate use of known or readily available technology and means to accomplish the installation of BIDs so as to minimize labor, material, cost and time.

SUMMARY OF THE INVENTION

[0010] The present invention provides a seismically-isolated structure and a method of constructing same. The seismically-isolated structure has a rigid diaphragm, a plurality of footings each positioned at least partially under the rigid diaphragm, and a plurality of base-isolation devices each positioned between a footing and the rigid diaphragm, wherein the rigid diaphragm was constructed in situ above the footings generally below its final elevation. To that end, a barrier is positioned between the rigid diaphragm and at least the footings to prevent bonding between the rigid diaphragm and the footings. The barrier, which may be structural or chemical or a combination thereof, may also span between the footings if appropriate. In one embodiment, each footing is configured with a recessed formation that accommodates a lifting device, and a surface for mounting a base-isolation device. In another embodiment, whereas each footing has a surface for mounting a base-isolation device, it is the rigid diaphragm this is configured with recessed formations to accommodate the lifting devices. In either embodiment, there is access to the base isolation device after installation for inspection and maintenance purposes.

[0011] The method of constructing a seismically-isolated structure includes providing footings in the ground, positioning a barrier between footings and a rigid diaphragm, constructing the rigid diaphragm on the barrier, elevating the rigid diaphragm, and installing base isolation devices between the footings and the rigid diaphragm. The method includes pouring concrete of the rigid diaphragm on the barrier which may be structural, chemical or a combination thereof, to prevent bonding of the rigid diaphragm with at least the footings, if not also to prevent bonding with the ground spanning between the footings. The method also includes constructing above the rigid diaphragm before elevating the rigid diaphragm and providing recessed formations in either the footings or the rigid diaphragm to accommodate lifting devices used to lift the rigid diaphragm. Moreover, the footings are configured to support the base isolation devices that are mounted below the rigid diaphragm and to allow access to the base isolation devices for inspection and maintenance subsequent to construction of the structure.

[0012] The present invention also provides for a structure having a basement that is built on a rigid diaphragm supported on base isolation devices. Footings and a concrete slab spanning therebetween form a subbasement surface on which a barrier is placed and the rigid diaphragm is formed thereon.

[0013] The present invention offers many advantages, including general adherence to known construction methods, costs and timelines for structures of comparable size and complexity, but provides for a structure that incorporates base-isolation devices for better adaptation against earthquakes or other types of seismic activity or ground vibrations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

[0015] FIG. 1 is a cross section view of one embodiment of construction with a seismically-isolated base in accordance with the present invention;

[0016] FIG. 2a is a top plan view of a known rigid diaphragm of the prior art

[0017] FIG. 2b is a cross section view of one embodiment of the rigid diaphragm of FIG. 2a taken along line 2b-2b;

[0018] FIG. 2c is a detailed view of a portion of the cross section view of FIG. 2b.

[0019] FIG. 2d is a cross section view of an alternative embodiment of the rigid diaphragm of FIG. 2a;

[0020] FIG. 2e is a detailed view of a portion of the cross-section view of FIG. 2d;

[0021] FIG. 2f is a perspective view of the rigid diaphragm of FIG. 2d;

[0022] FIG. 3a is a top plan view of the construction of FIG. 1;

[0023] FIG. 3b is a detailed view of a portion of FIG. 3, showing a rigid diaphragm and a barrier, each with a recessed formation, above a footing;

[0024] FIG. 4 is a cross section view of the construction of FIG. 1 before elevation of the rigid diaphragm, using a sheet barrier spanning the surface on which the rigid diaphragm is formed;

[0025] FIG. 5 is a cross section view of the construction of FIG. 1, before elevation of the rigid diaphragm, using a granular barrier spanning the surface on which the rigid diaphragm is formed;

[0026] FIG. 6 is a cross section view of the construction of FIG. 1, before elevation of the rigid diaphragm, using a combination of a chemical barrier and a granular barrier below the rigid diaphragm.

[0027] FIG. 7a is a cross section view of a footing of FIG. 3a, configured with a step, during construction of the rigid diaphragm;

[0028] FIG. 7b is a cross section view of the footing of FIG. 7a, showing the installation of a lifting device following removal of a filler element and an exposed barrier portion;

[0029] FIG. 7c is a cross section view of the footing of FIG. 7b, showing elevation of the rigid diaphragm and installation of a BID;

[0030] FIG. 8a is a cross section view of a another footing of FIG. 3a, that is below a recessed formation formed in the rigid diaphragm, showing installation of a lifting device;

[0031] FIG. 8b is a cross section view of the footing of FIG. 8a, showing elevation of the rigid diaphragm, removal of the barrier and installation of a BID; and

[0032] FIG. 9a. is a cross section view of another embodiment of construction with a seismically-isolated basement in accordance with the present invention;

[0033] FIG. 9b is a cross section view of the construction of FIG. 9a before elevation of the rigid diaphragm; and

[0034] FIG. 10 is a top plan view of the construction of FIG. 9a.

DETAILED DESCRIPTION OF THE INVENTION

[0035] Shown in FIG. 1 is a construction site with a structure S constructed in accordance with the present invention. The structure S has a rigid diaphragm 12 that is supported on a plurality of base isolation devices (BIDs) 14, which in turn are supported on footings 16 positioned in ground 18. As such, the structure S is generally isolated from seismic activity or vibration that occurs in the ground 18 surrounding the footings 16.

[0036] As understood by one of ordinary skill in the art, the rigid diaphragm 12 is a structure that is rigid in its own plane. As illustrated in FIGS. 2a-2e, rigid diaphragms 12 of the prior art are generally rectangular and constructed of concrete 20 with reinforcing steel 22. FIGS. 2b and 2c show one embodiment and FIGS. 2d and 2e show another embodiment. It is understood by one of ordinary skill in the art that the rigid diaphragm may be configured differently and be reinforced with different materials. For example, another suitable construction of a rigid diaphragm may be a post-tensioned concrete slab where post-tensioning is a method of reinforcing concrete, masonry, and other structural elements by prestressing during their construction phase for the purpose of counteracting the anticipated external loads that they will encounter. Regardless of the embodiment, the rigid diaphragm is designed to carry a dead load (weight of rigid diaphragm itself and structure(s) thereon) and live loads (people and their property on the rigid diaphragm and structure), as well as horizontal loads from wind or seismic forces applied to the structure A nonlimiting example of a suitable embodiment of a rigid diaphragm for use as a floor or base of the structure S is illustrated in FIG. 2f.

[0037] Referring to back to FIG. 1, the ground 18 and rough grading thereof at the construction site generally around and below the structure S are prepared using conventional engineering and construction methods. The footings 16 are constructed using conventional engineering and construction methods. The footings have a size, configuration and strength (including load bearing ability) adapted for the subsequent installation and use of BIDs 14 and lifting devices. The footings 16 of this disclosed embodiment have a generally rectangular cross section and are discontinuous from each other in block form. Referring also to FIG. 3a, a footing 16 is positioned generally under each corner 30 of the rigid diaphragm 12 and along edge 31 of the rigid diaphragm. In more general terms, the footings can be described as being positioned within the "field" of the rigid diaphragm, such as where there is sufficient overlap between the rigid diaphragm and each of the footings for each footing to simultaneously accommodate at least a lifting device and a BID, as discussed below in further detail. As understood by one of ordinary skill in the art, the footing 16 may have a different cross-section, for example, a circular cross-section, and they may also be continuous and extend along below opposing edges of the rigid diaphragm. For example, in FIG. 3a, the footings 16a and 16f may be connected and footings 16c and 16d may be connected. Moreover, the footings may be positioned anywhere underneath the rigid diaphragm so long as they remain accessible for installation and removal of the lifting devices and BIDs as discussed further below. In accordance with conventional construction methods, the width of the footing may be substantially greater than the width of vertical walls 32 above it (see FIG. 1).

[0038] As shown in FIG. 1, each footing 16 is constructed with sufficient strength or load bearing ability at the placement of a BID 14 so that it can bear horizontal and verticals loads, the latter including at least the vertical load of the BID, as well as the respective vertical load of the structure S borne by the BID. To that end, each footing is formed with a generally flat upper surface 34 on which a BID can be mounted to the underside of the rigid diaphragm 12 at a corner 30 or an edge 31.

[0039] It is understood by one of ordinary skill in the art that the BIDs are not limited to any particular type or structure since a variety of devices that provide seismic isolation and damping are known. Known BIDs and the like include those disclosed in U.S. Pat. Nos. 6,324,795, 6,318,031, 5,970,666, 4,942,703 and/or 4,644,714, the entire contents of which are incorporated by reference herein.

[0040] As shown in FIG. 3a, the rigid diaphragm 12 of the structure S is well supported from below by a plurality of BIDs each of which is generally centrally supported on a footing. Each footing has a portion that is directly below the rigid diaphragm. As described below in further detail, the rigid diaphragm is formed in situ at an elevation near is its final elevation so as to minimize the construction labor, time and cost involved in rendering the structure S less susceptible to earthquake damage.

[0041] In accordance with the present invention, a method of construction of the structure S begins with preparation of the ground 18, including rough grading to a selected height h, as shown in FIG. 1. Excavations 36 and other preparations are made in the ground for the formation or placement of the footings 16. Generally, concrete is poured into framed excavations to form the footings 16, although it is understood that the footings 16 may be formed elsewhere and transported to the excavations 36. The flat surfaces 34 of the footings 16 are formed to be generally level with the ground 18 at height h such that the ground 18 and the flat surfaces 34 form a generally flat supporting surface 38 for the formation of the rigid diaphragm 12, as described further below. However, it is understood by one of ordinary skill in the art that the surfaces 34 of the footings may also be above or below the grade 18 as desired or appropriate.

[0042] When the footings 16 have sufficiently cured or are otherwise at a stage where they have reached a sufficient strength or load bearing ability, the rigid diaphragm 12 may be formed above it. In accordance with the present invention, a barrier or bond breaker 40 is placed on at least the flat surfaces 34 of the footings 16. The barrier may be structural or chemical in nature, or a combination thereof, and depending on factors including the type of barrier used and the type of ground spanning between the footings, the barrier may cover not only the flat surfaces 34 but the generally flat supporting surface 38 defined by the both the flat surfaces 34 of the footings and the ground 18 spanning therebetween.

[0043] Because the rigid diaphragm 12 is formed on the supporting surface 38, the barrier 40 serves to separate the rigid diaphragm 12 from at least the footing 16, if not also the ground 18 when appropriate, and prevents formation of bonds therebetween. Where the ground spanning between the footings has dirt or debris or is otherwise of a nature that does not bond significantly with concrete, the barrier need not cover the ground.

[0044] In particular, where the rigid diaphragm 12 is formed from concrete poured in situ (that is, poured on site onto the barrier 40, above the footings 16 and the ground 18), the barrier 40 prevents adhesion between the rigid diaphragm 12 and the footing 18 and/or the ground 18 while the concrete cures. The barrier 40 may be a tarp 40' (FIG. 4), for example, a 2-3 mm thick polyethylene sheet, sheets of plywood or steel plates 40a and 40b (FIG. 3), sand, gravel or other granular particles 40'' (FIG. 5), chemical coating (e.g., a bond-breaker) or sealant 40''' that is brushed, poured, sprayed, spread and/or otherwise applied to the surface 38 of the footings 16, and/or combinations of the foregoing (FIG. 6), that can prevent adhesion of the concrete of the rigid diaphragm 12 to the footing 16 and the ground 18 but still provide the generally flat support surface 38. It is understood by one of ordinary skill in the art that multiple plywood, plates or tarps may be adjoining or nonadjoining depending on the nature of the support surface 38. It may also be preferable for the barrier 40 spanning the surface 38 to have a generally uniform thickness, or provide a generally a flat surface 38.

[0045] Regardless of the type(s) of barrier used, the present invention allows the rigid diaphragm 12 to be advantageously formed in situ. That is, the rigid diaphragm 12 is formed above the footing 16 and a relatively minimal distance below its final elevation in the completed structure, where the ground 18 and the footing 16 advantageously serve as the supporting surface 38 for the rigid diaphragm 12 during its formation and curing. As such, the rigid diaphragm need not be transported from a remote location nor is temporary falsework needed to support the rigid diaphragm while it cures, which minimizes disruption to construction schedules and limits additional construction costs.

[0046] Many variables affect the length of time a concrete slab needs to cure and the length of time during which curing can be expected. Some of the more common variables include cement--water mix ratio, cement-sand ratio, particle size distribution, presence of accelerators, curing compounds, environmental conditions, location of vapor membrane, and exposure to water during curing. Notwithstanding these numerous factors, a typical period for the concrete to cure may be a minimum of 28 days under normal conditions. However, in accordance with the present invention, construction of the structure S on the rigid diaphragm 12 can begin as soon as about one day after pouring of the concrete of the rigid diaphragm 12 so long as the concrete of the rigid diaphragm has reached sufficient strength to support the load of such construction.

[0047] In keeping with the present invention, construction of the structure S on the rigid diaphragm 12 can begin before the rigid diaphragm has reached its designated or allowable strength (which includes not only the strength to support the load of such construction and other vertical and horizontal loads, but to withstand carrying such loads "on points", that is to be supported at localized areas only, for example, only by its corners and edge regions). With conventional rigid diaphragms such as those that are formed at another location, such rigid diaphragms are generally not transported until they can withstand at least the stress and strain of being lifted and moved. Moreover, such rigid diaphragms are typically not placed on "points" until well into their curing period.

[0048] In contrast, the rigid diaphragm 12 of the present invention need not be transported from a remote location (and therefore avoids the delay in waiting for the concrete to cure sufficiently to be able to endure such transport), and construction of the structure S can begin well before the rigid diaphragm 12 reaches its designated or allowable strength. Accordingly, construction of the vertical walls 32 or other structures above the rigid diaphragm may begin generally after about one day after pouring of the concrete of the rigid diaphragm 12, so long as the concrete has cured to sufficient strength to carry the load of such construction. Moreover, construction of the structure S may continue on the rigid diaphragm 12 while the rigid diaphragm 12 cures to its designed or allowable strength, which may take about 28 days or more. In accordance with the present invention, the surface 38 supporting the rigid diaphragm enables such early construction.

[0049] After the rigid diaphragm 12 has reached its designed or allowable strength, for example, about 28 days or so, but typically before construction of the structure S is completed, lifting devices 42 are used to elevate (elevate, raise and lift, used interchangeably herein) the rigid diaphragm for installation of the BIDs 14 between the footings 16 and the rigid diaphragm 12. Hydraulic or mechanical lifting devices are known, particularly those used to lift structures and buildings. Suitable systems, including the Synchronous Lifting Systems 4-to-64 Point, are available from Enerpac Hydraulic Technology (Milwaukee, Wis.). Use of the barrier 40 between at least the rigid diaphragm 12 and the footing 16 allows the rigid diaphragm 12 to be readily separated from the footings 16 and lifted by such hydraulic or mechanical lifting devices.

[0050] To lift the rigid diaphragm, the lifting devices 42 are placed under the rigid diaphragm 12 generally around its corner and edge regions 30 and 31, as shown in FIG. 3a. Recessed formations 60 and 61 are formed in either the footings or the rigid diaphragm to accommodate the lifting devices. For example, a step 60c (FIGS. 7a, 7b and 7c) can be provided in footing 16c to provide a cavity 63c between the footing 16c and the rigid diaphragm 12 to receive a lifting device 42c. The recessed formation is created by any suitable means, as understood by one of ordinary skill in the art, when the footing is formed. As shown in FIG. 3a, the step 60c has a width that is less than half of the coextensive dimension of the footing, and a length that extends at least beyond the edge 31 of the rigid diaphragm, if not completely to the outer edge of the footing. This configuration allows the cavity to be readily accessible from the perimeter of the rigid diaphragm.

[0051] Before the barrier 40 is placed on the footing 16c and construction of the rigid diaphragm 12, the cavity 63c may be occupied by a filler element 70c (e.g., a wooden, styrofoam or plywood block) to support the barrier and the rigid diaphragm and/or to act as a barrier (if its material is suitably nonadhesive to concrete) and prevent concrete from the rigid diaphragm from entering or settling in the cavity. If the barrier 40 is plywood or a steel plate that is sufficiently rigid to support the rigid diaphragm, the filler element 70c may be unnecessary. But if the barrier is nonrigid, such as a tarp, the filler element 70c should be placed inside the cavity 63c to occupy it and to support the barrier and the rigid diaphragm.

[0052] As shown in FIG. 7b, when it comes time to elevate the rigid diaphragm, the filler element 70c is first removed from the cavity 63c. Because the step 60c in the illustrated embodiment extends to the outer edge of the footing 16c, this is accomplished easily by sliding the filler element 70c outwardly from the cavity until the filler element clears the perimeters of the rigid diaphragm 12 and the barrier 40. Any portion of the barrier 40 under the rigid diaphragm that is exposed in the cavity 63c can be removed (e.g., by cutting, sawing, tearing, dissolving, etc.) to expose the underside of the rigid diaphragm. The lifting device 42c is then placed on the step 60c of the footing 12c under the rigid diaphragm 12 and actuated to raise the rigid diaphragm 12 to at least its final elevation or higher, as shown in FIG. 7b. A BID 14c is installed between the rigid diaphragm 12 and the surface 34c of the footing 16c and the lifting device 42c is removed from the cavity. In view of the foregoing, it is understood by one of ordinary skill in the art that the step 60c is sized to allow removal of the filler element and the barrier from the cavity and to allow installation, operation and removal of the lifting device 42c.

[0053] As an alternative to the recessed formations 60 in the footings, FIG. 8a illustrates a recessed formation 61, such as a pocket 61a, formed in the edge 31 of the rigid diaphragm 12. A bridge member 68, e.g., a reaction beam 69a, traverses the pocket 61a and provides a location under which the lifting device 42a is positioned to raise the rigid diaphragm 12. The reaction beam 69a is anchored (temporarily or permanently) to the rigid diaphragm 12 at generally opposing locations across the pocket 60a. The lifting device 42a is then actuated to raise the rigid diaphragm 12 to at least its final elevation or higher, as shown in FIG. 8b, at which time the barrier 40 is freed for removal. It is understood that the recessed formation may also be a hole 61' in the rigid diaphragm 12, as shown in broken lines in FIG. 3b.

[0054] As shown in FIG. 3b, the barrier 40 in this embodiment can be configured with its own pocket to follow the outline of the pocket 61 of the rigid diaphragm 12 so that the upper surface 34 of the footing 16 is exposed. Accordingly, the barrier 40 is not pinned under the lifting device 42 after the rigid diaphragm 12 is lifted, allowing the barrier 40 to be removed. A BID 14 is installed between the rigid diaphragm and the surface 34 of the footing 16.

[0055] When the BIDs 14 have been properly installed such that the rigid diaphragm 12 is supported on points by the BIDs as shown in FIG. 1, the lifting devices 42 are removed. A crawl space 48 of height H spanning at least the height of the BIDs is formed between the ground 18 and the rigid diaphragm 12. Additional foundations 52 near the footings 16 and the edge of the rigid diaphragm 12 can be provided as desired or appropriate, along with flashings 80 to cover any seismic gap between the structure and the grading and foundation.

[0056] Accordingly, the construction of FIG. 1 has the structure S supported on the rigid diaphragm 12 that is generally isolated from seismic activity or vibration in the ground 18. During an earthquake, the BIDs 14 isolate the rigid diaphragm 12 and the structure S from seismic forces in the ground 18. After a seismic activity, the BIDs 14 may be inspected via the crawl space 48.

[0057] An alternative embodiment of a structure S' built in accordance with the present invention is shown in FIG. 9a. The foregoing description generally applies for elements with similar reference numerals. The structure includes a subbasement SB below ground level with subterranean retaining vertical walls 100, and footings 116 and concrete ground slabs 118 therebetween to line the subbasement. In accordance with a feature of the present invention, upper surface 134 of the footings 116 and the concrete slabs 118 form a generally flat surface 138 on which a rigid diaphragm 112 can be formed. As shown in FIG. 9b, a barrier 140 is placed on top of the generally flat surface 134 to prevent adhesion between the surface 138 and the rigid diaphragm 112 and concrete is poured on the barrier to form the rigid diaphragm. As described hereinabove, construction above the rigid diaphragm 112 (e.g., vertical walls 132) may begin as soon as about one day after pouring of the concrete and well before the rigid diaphragm is elevated., provided the rigid diaphragm has cured to a strength sufficient to support the construction. When the rigid diaphragm has reached is designed strength or when it can support the vertical and horizontal loads placed on it the rigid diaphragm can be lifted in the aforementioned manner by lifting devices 142 that are accommodated by recessed formations including either steps 160 in the footings or pockets 161 in the rigid diaphragm for the removal of the barrier 140 and the installation of the BIDs 114 (see FIG. 10) As such, the structure S', inclusive of its basement, is isolated from seismic activity or vibration in the ground. A crawl space 148 allows inspection of the BIDs.

[0058] The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes to the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention. Moreover, the drawings may not be to scale. Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support for the following claims which are to have their fullest and fairest scope.

Claims

1. A method of constructing a seismically-isolated structure having a rigid diaphragm supported on base isolation devices, comprising: providing at least a footing in ground; positioning a barrier between footings and rigid diaphragm; Constructing the rigid diaphragm on the barrier; elevating the rigid diaphragm; and installing the base isolation devices between the footing and the rigid diaphragm.

2. A method of construction according to claim 1, wherein construction above the rigid diaphragm begins before raising the rigid diaphragm.

3. A method of construction according to claim 1, wherein the footing is positioned within a field of the rigid diaphragm.

4. A method of construction according to claim 1, wherein the barrier includes a tarp.

5. A method of construction according to claim 1, wherein the barrier includes sheets of plywood.

6. A method of construction according to claim 1, wherein the barrier includes a layer of sand.

7. A method of construction according to claim 1, wherein the barrier is chemical.

8. A method of construction according to claim 1, wherein the footing is constructed from concrete.

9. A method of construction according to claim 1, wherein the footing has a recessed formation that receives a lifting device.

10. A method of construction according to claim 1, wherein the rigid diaphragm has a recessed formation that receives a lifting device.

11. A method of construction according to claim 10, wherein the barrier has its recessed formation for the recessed formation of the rigid diaphragm.

12. A method of construction according to claim 1, wherein the rigid diaphragm is formed from concrete.

13. A method of construction according to claim 1, wherein the rigid diaphragm is reinforced with steel.

14. A method of construction according to claim 1, wherein the construction above the rigid diaphragm begins before raising of the rigid diaphragm.

15. A method of constructing a seismically-isolated structure, comprising: providing concrete footings in ground; laying a barrier above footings; constructing a concrete rigid diaphragm above the barrier; elevating the rigid diaphragm to its final elevation; constructing above the rigid diaphragm before raising the rigid diaphragm to its final elevation; and installing base isolation devices between footings and rigid diaphragm.

16. A method of construction according to claim 15, wherein construction above the rigid diaphragm comprises light wood frame construction.

17. A method of construction according to claim 15, wherein the footings are in block form.

18. A method of construction according to claim 15, wherein an upper surface of each footing and ground spanning between the footings form a generally flat surface on which the rigid diaphragm is formed.

19. A method of construction according to claim 15, wherein an upper surface of each footing and ground spanning between the footings form a generally flat surface on which the rigid diaphragm is supported before being raised to its final elevation.

20. A construction, comprising: a structure having a rigid diaphragm; a plurality of footings each positioned at least partially under the rigid diaphragm; a plurality of base-isolation devices each positioned between the rigid diaphragm and a footing; wherein the rigid diaphragm was constructed above the footings below its final elevation

21. A construction of claim 20, further comprising a barrier positioned between the rigid diaphragm and the footings during construction of the rigid diaphragm.

22. A construction of claim 21, wherein the barrier extends between the footings.

23. A method of constructing a rigid diaphragm for use in a seismically-isolated structure: providing footings; providing a barrier on the footings; and constructing the rigid diaphragm on the barrier.

24. A method of constructing of claim 23, further comprising: forming a generally flat surface on each footings to serve as a supporting surface for the rigid diaphragm as it cures.

25. A method of constructing of claim 23, wherein the barrier is rigid.

26. A method of constructing of claim 23, wherein the barrier is chemical.

27. A method of constructing of claim 23, wherein the barrier is granular.