U.S. patent application number 11/322590 was filed with the patent office on 2007-07-05 for method of constructing structures with seismically-isolated base.
Invention is credited to Boake Paugh.
Application Number | 20070151173 11/322590 |
Document ID | / |
Family ID | 38222883 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070151173 |
Kind Code |
A1 |
Paugh; Boake |
July 5, 2007 |
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.
Inventors: |
Paugh; Boake; (Rancho
Cucamonga, CA) |
Correspondence
Address: |
CHRISTIE, PARKER & HALE, LLP
PO BOX 7068
PASADENA
CA
91109-7068
US
|
Family ID: |
38222883 |
Appl. No.: |
11/322590 |
Filed: |
December 30, 2005 |
Current U.S.
Class: |
52/169.9 |
Current CPC
Class: |
E02D 27/34 20130101 |
Class at
Publication: |
052/169.9 |
International
Class: |
E02D 27/00 20060101
E02D027/00 |
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.
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.
* * * * *