Note: Descriptions are shown in the official language in which they were submitted.
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DAMAGE RESISTANT GLASS PANEL
[O1] The subject matter of this application was made with support of the
National
Science Foundation under Grant No. 9983896. The Government may have certain
rights in
the invention.
Field of the Invention
[02] The present invention relates to architectural glass panels suitable for
use in a
wide variety of architectural glass and building wall system framing
combinations. In
particular, the present invention relates to architectural glass panels having
a modified
geometry to improve their resistance to damage during earthquakes andlor other
movement
of the glass panels within their frames.
B ack~round
[03] In light of recent earthquakes in the United States, Japan and elsewhere,
considerable attention is now directed toward developing buildings that resist
damage during
earthquakes. Although the seismic performance of load bearing structures in
buildings has
improved, "non-structural" or architectural building elements have proved to
be vulnerable to
earthquake-induced damage. For example, curtain walls (a curtain wall is any
exterior
building wall comprised of any material, which carrzes no superimposed
vertical loads and is
"hung" on the building structural frame) and storefront wall systems have
shown the
vulnerability of architectural glass and related glazing components to damage
during
earthquakes. This damage includes serviceability failures (e.g., glazing
gasket dislodging,
sealant damage, glass edge damage and glass cracking), which require expensive
building
repairs and could ultimately lead to failures in the form of glass fallout,
which present a life
safety hazard. Earthquake-induced architectural glass glazing system failures
lead to costly
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repairs and can impose liabilities to building designers, building
contractors, building owners
and insurers.
[04] In response to concerns about nonstructural damage during earthquakes,
recent model building codes, e.g., International Building Code (IBC), 2000
(ICC 2000), now
require nonstructural components, such as architectural glass panels, to
accommodate the
maximum allowed building story drifts. According to, IBC 2000, exterior
nonstructural wall
panels or elements that are attached to or enclose the structure shall be
designed to resist the
forces prescribed by an equation presented in the model building code and
shall
accommodate movements of the structure resulting from response to design basis
ground
motions. In general, seismic codes require wall systems to accommodate drift
without much
guidance on how to achieve "acceptable" seismic performance for various wall
system types.
However, as noted by Behr and Wulfert (2001), new seismic design provisions
for
architectural glass published in the 2000 lVEHRP Provisions (National
Earthquake Hazard
Reduction Program 2001) are slated for adoption in the 2003 edition of the
IBC. The new
NEHRP seismic design provisions for architectural glass are based on a
combination of
design experience and laboratory test data., Moreover, these provisions now
reference
AA MA (American Architectural Manufacturers Association) test procedures (AAMA
2001 )
for determining the serviceability and glass fallout resistance of curtain
wall and storefront
wall system mock-ups. Although the AAMA. standard test procedures do not cover
wall
system types other than curtain walls and storefronts, these two wall system
types are
prevalent in modern building practice.
[OS] Aside from those glass configurations specifically exempted from-mock up-
=---
testing in the NEHRP design provisions, selection of appropriate architectural
glazing
configurations for seismic resistance can be a challenging and iterative
process. Fortunately,
a series of laboratory studies and some post-earthquake reconnaissance surveys
conducted
during the last twenty years have generated a significant database on the
expected seismic
performance of various combinations of architectural glass and wall system
framing types
(Memari et al. 2002a, SERI 2001, Behr 1998, Behr and Belarbi 1996, Behr et al.
I99Sa,
Behr et al. 199Sb, EERI I99S, Pantelides and Behr 1994, Lingnell 1994, Culp
and Behr
1993, Wang 1992, King and Thurston 1992, Thurston 1992, Deschenes et al. 1991,
Lim and
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King 1991, EERI 1990, Wright 1989, Evans et al. 1988, Sakamoto et al. 1984,
Sakamoto
1978). Additional studies have been directed toward the development of seismic
isolation
methods for new wall system installations and techniques to predict and
mitigate glass
damage and glass fallout in existing wall systems (Memari et al. 2002b, Memari
and Kremer
2001, Brueggeman et al. 2000, Memari et al. 2000, Zharghamee 1996).
[06] Several methods are available to mitigate architectural glass damage
caused
by earthquakes, but there is an ongoing need to improve both the glass
cracking resistance
and the glass fallout resistance in earthquake prone regions and elsewhere.
[07] One method of improving the earthquake resistance of architectural glass
is to
use laminated glass, which usually consists of two glass plies bonded together
with a
transparent polymeric interlayer such as polyvinyl butyral (PVB). Specialty
laminated glass
configurations are also available as glass-plastic Laminates and laminates
with multiple layers
of glass and/or plastic, and all-plastic laminates. Laminated glass,
particularly when the glass
plies are made of either annealed glass or heat-strengthened glass, is highly
resistant to glass
fallout because any broken glass fragments remain adhered to the PVB
interlayer and resist
falling dangerously from the wall system glazed opening. However, individual
glass plies in
a laminated glass unit are still vulnerable to cracking at drift levels
comparable to monolithic
glass panels with square-edged corners of the same nominal thickness as the
laminated glass
unit. Furthermore, a cracked laminated glass unit would still need to be
replaced at a
significant cost. Hence, the use of laminated glass can improve resistance to
glass fallout,
but not the resistance to glass cracking.
[08] Another earthquake-resistant glazing method is to apply a polymeric film
such
as polyethylene terephthalate (PET) over the entire glass surface and to use
an appropriate
anchoring technique to secure the film edges to the wall system framing. This
method, like
the use of laminated glass, can resist glass fallout effectively, but does not
necessarily resist
glass cracking. Although anchored films are used widely to retrofit in-service
glass panels,
application of anchored films is labor intensive, and often require a high
degree of
workmanship in the film application and the film anchorage installation that
is a challenge to
achieve properly in the field. Unanchored films, sometimes applied as a
seismic retrofit
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measure, are not completely effective in preventing glass fallout due to
earthquake-induced
building motions (Behr 1995).
[09] For some wall system designs it is possible to use deeper glazing pockets
for
frame members that hold the glass, thereby providing larger glass-to-frame
clearances in an
attempt to avoid glass-to-frame contact during racking displacements in an
earthquake. This
method presumes that the glass panel will have more freedom to translate and
rotate within
the glazing pocket, thus avoiding early glass failure under racking
conditions. This solution,
however, is costly in terms of the volume of wall system materials utilized,
and is not always
preferred architecturally because it requires the use of wide mullions to
provide the required
glass-to-frame clearances needed to avoid contact. Moreover, if the glass
panel is shifted too
far laterally in a particular direction due to in-service conditions or faulty
installation, the
weather seal of the framing system can be compromised and the glass itself
could be more
vulnerable to cracking under subsequent wall system racking movements.
[IOJ Finally, seismically isolated wall systems using unitized framing, or the
recently developed "Earthquake Isolated Curtain Wall System" (EICWS) are also
available.
Typically, isolated wall systems are designed to accommodate in-plane racking
movements,
but the EICWS can accommodate movements in'any direction because it permits
the
multidirectional sliding of the curtain wall in one story relative to adjacent
stories. Although
the EICWS solution is capable of providing a high level of earthquake
resistance to virtually
any type of architectural glass and any type of glazing system, the EICWS is
designed
primarily for new building construction, and, like other seismically isolated
wall systems,
could impose additional building design and construction costs. - - -
[11] Although methods such as seismically isolated wall systems, glass with
anchored safety films, laminated glass, and larger glass-to-frame clearances
(i.e., wide
mullion designs) can be used to mitigate earthquake-induced building envelope
damage,
these methods have disadvantages. Specifically, due to cost and complexity,
most
earthquake-resistant wall systems are tailored primarily for new building
construction, not
building retrofits; most earthquake-resistant wall systems axe significantly
more expensive
than conventional wall systems not designed specifically for earthquake
resistance; most
earthquake-resistant wall systems increase glass fallout resistance, but not
all of these
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systems increase the glass cracking resistance; and some earthquake-resistant
wall systems
limit aesthetic choices in the architectural design of a building's exterior.
As a result, there is
an ongoing need to improve both the glass cracking resistance and the glass
fallout resistance
of architectural glass under earthquake loading conditions or conditions that
cause such
damage.
Brief Summarv of the Invention
[12] An advantage of the present invention is that it provides a damage
resistant
architectural glass panel for buildings.
[13] An advantage of the present invention is that it provides a method of
increasing the serviceability (i.e., the glass cracking resistance) of glass
panels used in
various building wall framing systems.
[14J Additional advantages and other features of the invention will be set
forth in
part in the description which follows, and in part will become apparent to
those having
ordinary skill in the art upon examination of the following or may be learned
from the
practice of the invention. The advantages of the invention may be realized and
obtained as
particularly presented in the appended claims.
[15] According to the present invention, the foregoing and other advantages
are
achieved in part by a building comprising at least one rectangular window
frame having an
architectural glass panel with rounded corners and with or without finished
edges properly
glazed therein.
[16] Embodiments of the present invention include architectural glass panels
that
have material removed at panel corners and are fabricated with smooth edge
contours in the
modified-geometry corner regions. Preferred embodiments of the present
invention include
glass panels that have their corners rounded, i.e., formed by curving the area
where at least
two edges or sides of the glass intersect, and/or by finishing their edges.
Buildings that
employ such modified-geometry glass components within a rectangular frame
advantageously resist damage to their glass panels and related damage from
broken and
falling glass fragments caused by seismic motions. The damage resistant
architectural glass
panels of the present invention can be employed with various framing materials
used in wall
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system construction, such as glass, stone, aluminum, steel, additional metals
or alloys,
plastics, rubber, wood, sealants/adhesives and composites of the above.
[17) Another aspect of the present invention is a method of increasing the
serviceability of original glass panels in a building. The method comprises
replacing or
retrofitting the original glass panels in the building with glass panels
having rounded corners.
[18) Additional advantages of the present invention will become readily
apparent
to those having ordinary skill in the art from the following detailed
description, wherein the
embodiments of the invention are described simply by way of illustrating the
best modes
contemplated for carrying out the invention. As will be realized, the
invention is capable of
other and different embodiments, and its several details are capable of
modifications in
various obvious respects, all without departing from the invention.
Accordingly, the
drawings and description are to be regarded as illustrative in nature, and not
as restrictive.
Brief Description of the Drawinss
[19) The various features and advantages of the present invention will become
more apparent and facilitated by reference to the accompanying drawings,
submitted for
purposes of illustration and not to limit the scope of the invention, where
the same numerals
represent like structure and wherein:
[20) Figs. 1(a), 1(b), 1(c), and 1(d) illustrate schematic representations of
the first
three natural in-plane vibration modes of a typical building frame clad with a
conventional
curtain wall system, and their effects on the structural frame and curtain
wall of the building;
[21) Figs. 2(a), 2(b), and 2(c) illustrate schematic representations of
typical in-
plane forces acting on an individual curtain wall element during an
earthquake. Glass
movements and loads are contrasted for a conventional architectural glass
panel with
rectangular corners and a rounded corner architectural glass panel;
[22) FIG. 3 is a front plan view of a rounded corner monolithic glass panel as
fabricated in accordance with an embodiment of the present invention;
[23) FIG. 4 is an isometric view of a rounded corner monolithic glass panel
with
about a three quarter inch (about 19 mm) radius of curvature;
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[24J FIG. S is a graph comparing the dynamic racking performance (tested in
accordance with AAMA 501.6) of monolithic rounded corner glass panels to the
performance of identically constructed glass panels with rectangular corners;
[25] FIG. 6 is an isometric view of a rounded corner monolithic glass panel
with
about a three quarter inch (about 19 mm) radius of curvature and including
beveled and
polished edges;
[26J FIG. 7(a) is a cross-sectional side view of the edges of a rounded corner
glass
panel fabricated in accordance with an embodiment of the present invention,
including a
ground or polished edge; and Fig. 7(b) shows a rounded corner glass panel
fabricated in
accordance with the invention, that includes a shaped edge (e.g., a pencil
edge);
[27] FIG. 8(a) is an elevation view of one corner of a monolithic glass panel
constructed with asymmetrically rounded corners; and FIG. 8(b) is an elevation
view of one
corner of a monolithic glass panel constructed in accordance with the
invention by removing
material and smoothing the edge surfaces from the corners of the panel.
[28] FIG. 9 is an isometric view of one corner of an insulating glass unit
comprised
of glass panes with rounded corners;
[29] FIG. 10 is an isometric view of one corner of a laminated glass unit
comprised
of glass plies with rounded corners;
[30J FIG. 11 is an isometric view of one corner of a filmed glass panel
employing
rounded corners;
[31] FIG. 12 is an elevation view and corresponding cross sectional view of
the
glazing details for an anchored film glass installation in-a dry-glazed,
curtain wall frame used
in mid-rise building construction.
Description of the Invention
[32) Laboratory investigations performed by the inventors have revealed that
modifying the corner geometry of rectangular glass panels, for example, by
rounding the
corners of a glass panel and, optionally, by finishing the glass panel edges,
economically
increases the glass cracking resistance and, to a lesser degree, the glass
fallout resistance of
virtually any glass component within conventional wall systems. The addition
of modified-
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geometry, or rounded corner glass components within a wall system provides
damage
resistance in a variety of glass types (e.g., monolithic glass plates,
laminated glass units, or
insulating glass units) and in a variety of wall system types including
curtain walls and
storefronts. Research performed by the inventors has also indicated that glass
damage under
dynamic racking conditions is initiated at the corners of rectangular glass
panels. Glass
panels having modified corner geometries (e.g., rounded corners) experience
reduced contact
friction between the glass corners and the glazing pocket, and have slightly
reduced glass
plate diagonal lengths, which allows them to rotate and translate more freely
within the
curtain wall frame when the frame is subj ected to dynamic, horizontal racking
movements as
would be expected during an earthquake. The increased mobility of the modified-
geometry
glass panel within its glazing pocket allows the glass panel to adjust more
readily to
increased frame deformation and can increase both the serviceability (glass
cracking) and
ultimate (glass fallout) drift limits of architectural glass panels. [The term
"drift limit" is
used herein to mean the amount of horizontal racking displacement or drift,
that can be
tolerated by a given element or component without reaching a defined limit
state, such as
glass cracking (a serviceability limit state) or glass fallout (an ultimate
limit state).] These
improvements in glass performance can be attained more economically with
modified
geometry (e.g., rounded) corner glass panels than with other seismic
mitigation methods.
The seismic resistance benefit of glass components fabricated with modified
corner
geometries, with or without finished edges, is provided at only modest cost
increments
relative to conventional glass components.
[33] The architectural glass panels, made according to the present-invention
and
used in commercial and residential building wall systems, advantageously have
an increased
ability to accommodate, without glass damage, earthquake-induced building
motions as
compared to conventional architectural glass panels with rectangular corners.
[34] Glass panels of the present invention can be used as components in simple
structural walls or more elaborate wall systems that are designed to provide
seismic
resistance. Some seismic isolation designs achieve isolation through a special
connection of
the wall system frame to the building structural frame. It is believed seismic
isolated walls
would benefit by using glass panels of the present invention. The glass panels
of the present
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invention may also be used with wide mullions (vertical member in various wall
framing
systems) with large glass-to-frame clearances (i.e., deep glazing pockets),
and to improve
incrementally the seismic resistance of architectural glass components
installed in a variety
of specially constructed wall framing systems designed to accommodate in-plane
racking
displacements (Zarghamee 1996 and Ting 2001).
[35) Glass panels of the present invention can be used advantageously in both
new
building construction and building retrofit situations, and within various
framing types
including, but not limited to, curtain wall and storefront framing with or
without seismic
isolation connections, and window framing used as infill in exterior building
envelope wall
systems. When properly fabricated and glazed, glass panels of the present
invention can
achieve seismic resistance at a lower cost and with less construction
complexity than existing
seismic isolation methods.
[36J In practicing certain embodiments of the present invention, previously
rectangular or other angular (e.g., obtuse or acute angle) glass corners are
curved and
optionally finished during the fabrication of the glass. It has been
discovered that modifying
the geometry (e.g., rounding) the corners of a conventional glass panel
provides the glass
panel with the freedom to reposition itself within the glazing pocket of the
conventional wall
system frame during earthquake-induced wall frame racking deformations,
thereby
increasing the in-plane lateral displacement capacity of the wall system as
compared to
conventional rectangular glass panels with rectangular or otherwise angular
corners. As a
result, glass panels of the present invention are able to sustain additional
inter-story drift
before any sign of glass cracking. The term "rounded corner" as used herein
includes corners
formed by removing glass from the conventional rectangular or angular corner
of a glass
panel, such as by curving the rectangular or angular corner using a single
radius, double or
asymmetric radii, or multiple radii. Additionally, the term includes any flat
or curved
segment formed by the removal of glass from the rectangular or angular corner
portion of the
conventional glass panel and smoothing the resulting edge surface profile.
[37] It is believed that the mechanics of how this invention improves the
performance of architectural glass panels during an earthquake relates to the
removal of
glass-to-frame contact stress concentration points at the angular corners,
which typically
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occur in conventional, rectangular-cornered glass panels undergoing dynamic
racking
displacements within a wall system frame.
[38] For example, as depicted schematically in Figs. 1(a) to 1(d), under in-
plane
lateral displacements of buildings during earthquakes, the main structural
frame 1 of the
building will distort 3. The schematic depictions of the first three natural
vibration modes of
a typical building frame clad with a conventional curtain wall system 2 shown
in FIG. 1 have
been limited to in-plane lateral interstory drifts because these are, in
general, the most
damaging movements to building wall systems. These interstory movements in the
building's main structural frame, as shown in Figs. 1 (b), 1 (c), and 1 (d),
typically distort the
structural frame 3, causing the normally rectangular curtain wall frame to
distort into
parallelograms 4, which can Lead to subsequent wall system panel (e.g.,
architectural glass
panels, stone and concrete panels, etc.) damage.
[39] Most earthquake-induced damage to architectural glass stems from the
distortion of the glazing frame that holds the glass component as depicted in
FIG. 1 and
isolated to an individual frame 11 and glass panel 12 element in the schematic
depiction of
FIG. 2. As noted by Bouwkamp 1960 and Sucuoglu and Vallabhan 1997, in-plane
deformation of the frame 11 in FIG. 2a holding the architectural glass panel
under horizontal
racking motion (shear force shown) 13 causes the glass panel to translate and
rotate within
the glazing frame. As shown in FIG. 2b, when the corners of one diagonal of
the glass plate
14 and 15 make contact with the corners corresponding to the shorter diagonal
of the
distorted curtain wall frame 16 (in the shape of a parallelogram having inter-
story drift 17),
additional inter-story drift causes glass to crush and fracture under the in-
plane compressive
contact forces generated between the glass corners and the corners of the wall
system frame.
For design purposes, it is preferred that the interaction of brittle glass
plates and glazing
frame pockets during inter-story drift be accommodated by accepted, verified,
seismic design
features. The glass panels of the present invention are now one such verified
seismic design
feature. As shown in Figure 2c, the modified geometry (e.g., rounded corners)
shorten the
diagonal length of the glass panel 20 and increase the ability of the glass
panel of the present
invention to accommodate a larger interstory drift 21 of the distorted curtain
wall frame 24
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before damage due to diagonal compressive forces as compared with the
interstory drift 17 of
a conventional rectangular-cornered glass panel 12.
[40] In an embodiment of the present invention, rounded-corner glass panels
are
installed in lieu of rectangular-cornered glass panels in dry-glazed wall
system glazing
applications employing monolithic, insulating, conventionally laminated,
specially laminated
(e.g., with advanced interlayers and/or various alternate material layers
including polymeric
materials such as polycarbonate) or applied film architectural glass panels.
It is believed that
glass panels of the present invention will find wide application in dry-glazed
curtain wall and
storefront wall systems. However, a wide variety of wall framing systems may
be
constructed with glass panels of the present invention to impart increased
seismic resistance
to the architectural glass panels. Such wall systems use various methods of
forming the
weather seal (e.g., rubber gaskets, structural sealants or a combination
thereof) along the
glazed panel perimeter, and in some configurations include provisions for
anchoring the glass
panel to the framing system. Regardless of the framing system or weather seal
materials
used, it is preferred that neither the framing nor the weather seal completely
impede relative
movement of a glass panel of the present invention with respect to its frame.
For example,
structural sealants are sufficiently flexible to allow movement of the glass
panel, but hard
glazing components (e.g., dried putty) designed to fix glass within a wall
system frame
would restrict movement, and wall systems using such glazing components would
not fully
benefit from glass panels of the present invention. Another feature of the
various wall
systems employing glass panels of the present invention is that they may
employ various
methods of attachment of the exterior wall system frame to the underlying main
building
frame.
[41] Modified-geometry (e.g., rounded) corners may be added to annealed, heat-
strengthened, fully tempered or chemically strengthened architectural glass
vision or spandrel
panels with no change in their method of fabrication, except that the addition
of the modified
geometry (e.g., rounded) corners should be made at the appropriate stage in
their fabrication
(e.g., before placement in the heat treatment furnace for heat-strengthened
and fully tempered
panels, and before the ion-exchange process for chemically strengthened glass
panels). The
addition of modified geometry (e.g., rounded) corners does not affect the use
of solar
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coatings, thermal coatings, architectural coatings, etc. on glass panels.
Glass panels
fabricated in accordance with the present invention may be employed as
monolithic
architectural glass panels or may be used to produce value-added glazing
components such as
insulating glass units, conventional and specialty laminated glass units
including glass-plastic
laminates (laminates with multiple layers of glass and/or plastic, and all-
plastic laminates),
glass-clad-polycarbonate units, and filmed glass units.
[42] Embodiments of the present invention include modified-geometry (e.g.,
rounded) corner glass panels of any feasible dimension comprising annealed
monolithic
glass, heat-strengthened monolithic glass, fully tempered monolithic glass,
chemically
strengthened monolithic glass, etc. Such glass panels may comprise of any
number and
combination of the above types of glass individually or as glass units, such
as insulating glass
units, laminated glass units, or as glass composites including, glass-clad-
polycarbonate, or
glass-plastic laminated panes, and of any feasible dimension and with any
appropriate
polymeric interlayers/layers and spacer and fill gas.
[43] The various features and advantages of the present invention will become
more apparent and facilitated by the following drawings. In one embodiment,
rounded
corner monolithic glass panels are used to replace square or rectangular-
cornered monolithic
glass panels. FIG. 3 is an elevation view of a monolithic glass panel 31
having four rounded
corners 32, each of which has a radius of about 3/4 in. (about I9 mm). The
scaled dimensions
of the panel of this embodiment are about 6 ft (about I .82 m) high by about 5
ft (about I.52
m) wide, but the panel as drawn is not intended to limit the use of this
invention to a
particular glass panel aspect ratio or to particular panel dimensions or to a
particular panel
corner radius, or to a particular panel corner geometry.
[44] An isometric enlarged view of one corner section of the monolithic
rounded
corner glass panel in accordance with another embodiment of the present
invention is
depicted in FIG. 4. In this embodiment, the panel has a thickness of about %4
in. (6 mm).
The panel thickness of this embodiment is not meant to restxict monolithic
rounded corner
glass panels to a particular thickness. However, such panels are typically of
thickness
normally used in architectural applications (e.g., as specified in ASTM
C1036). The glass
panel is drawn with a cut edge 41 as is typically employed for annealed glass
panels. In
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general, modified geometry (e.g., rounded) glass corners may be used in
conjunction with the
standard edge finish applied to panels of a given glass type (e.g., cut or
scored edges in
annealed glass; belt seamed edges fox heat-strengthened and fully tempered
glass; etc.).
However, in a preferred embodiment of the invention, refined edge finishes may
be used as
subsequently described. The glass panel corner 42 in FIG 4 is also drawn with
a corner
radius of about'/4 in. (about 19 mm), which is not meant to limit application
to this embodied
corner radius. Corner radii within the preferred range of about '/Z in. (about
13mm) to about
2 in. (about 51 mm) provide glass cracking resistance, and, for most radii,
glass fallout
resistance superior to that of a comparable rectangular-cornered glass panel.
Evidence of this
is found in FIG 5, which is a presentation of the drift limit states observed
for various
monolithic glass panels dry-glazed with rubber gaskets, rubber side spacers
and rubber
setting blocks in a conventional extruded aluminum curtain wall frame and
tested in
accordance with the AAMA 501.6 recommended dynamic test method for determining
the
seismic drift causing glass fallout from a wall system. Thus, the choice of
corner radii for
monolithic glass panels of any glass type is based primarily on the
requirement that no
modifications to the glazing components for a particular wall system be
required. For
example monolithic glass panels with corners rounded within the range of radii
from about'/z
in. (about l3mm) to about 2 in. (about 51 mm) may be used with conventional
framing
systems.
[45] In the case of the framing system used for the concept verification tests
whose
results are presented in FIG. 5, based on the test results for corner radii
of'/a in. (13 .mm) and
1 in. (25 mm) shown in FIG. 5, it is concluded that a corner radius of about
3/4 in. (about 19
mm) is preferred, because it would provide the highest glass cracking and
glass fallout
resistance, while still maintaining. the weather seal (i.e., air and moisture
cannot pass
through) in the corner regions of the glazed frame if the glass panel were
shied entirely to
one side or the other of the glazing frame. FIG. 5 also shows the comparative
test results of
annealed and fully tempered monolithic glass panels glazed in a conventional
curtain wall
frame with about a %z in. (13 mm) and about a 3/16 in. (5 mm) nominal glass-to-
frame
clearances.
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[46] . Standard or conventional cutting tolerances for fabricating the
modified
geometry (e.g., rounded) corners may be used. However, as indicated by the
test results
presented in FIG 5, results are enhanced by improving the quality of the edge
finish. During
the tests underlying the data presented in FIG. 5, it was observed that glass
panels fabricated
with protrusions along the rounded corners did not perform as well under
dynamic racking
motions as similarly fabricated rounded corners with no protrusions. AAMA
501.6 testing
on glass panels manufactured with visible protrusions and other edge defects
(such as chips
and spells) along their perimeter edges have also been observed to exhibit
lower drift limits
than counterparts with no visible edge defects. Hence, in a preferred
embodiment of the
invention, it is preferred that the edges of rounded corner glass panels have
smooth surfaces
to avoid the possible detrimental effects of edge surface defects.
[47] FIG. 6 illustrates another embodiment of a rounded corned glass panel.
This
figure shows an isometric view of one corner section of a '/4 in. (6 mm) thick
monolithic
rounded corner glass panel with a 3/4 in. (19 mm) corner radius 63. This
embodiment is an
example of a rounded corner glass panel having a ground or polished edge 61.
As previously
noted, these thickness and corner radii dimensions are not meant to limit the
construction of a
beveled and polished rounded corner glass panel to these dimensions. FIG 7a
shows a cross
sectional view of a portion of an edge of a rounded corner glass panel 70
having a ground or
polished edge 71-72. Grinding and polishing operations may be achieved by
conventional
additional fabricating steps as known to those skilled in the art of glass
fabrication. The
additional steps of grinding and polishing the edges of modified geometry
(e.g., rounded)
corner glass panels may be practiced on practically any panel constructed of
any glass type,
and, in addition to corner rounding, represents another embodiment of the
invention whose
improved level of glass edge surface refinement provides a more consistent (if
not higher)
level of seismic resistance to a given glass panel. Fig. 7(b) shows a rounded
corner glass
panel 73 fabricated in accordance with the invention, that includes a shaped
edge 74 (e.g., a
pencil edge), which rnay be ground or polished.
[48] Another embodiment of the present invention applicable to architectural
glass
panel of any glass type is depicted in FIG 8(a). In this schematic elevation
view of one
corner of a monolithic rounded corner glass panel, asymmetric rounding has
been employed
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to provide one radius 81 along the vertical rounded corner edge 82 and another
radius 83
along the horizontal rounded corner edge 84. Asymmetric rounding can be used
to provide
additional drift capacity of a rounded corner glass panel used in framing
systems with small
glass-to-frame clearances.
[49] Another embodiment of a damage resistant glass panel of the present
invention, which is illustrated by the exemplary glass panel 85 shown in Fig.
8(b), is obtained
by fabricating the glass panel by removing material from the corners of the
panel and
providing a smooth contour along the edges of its corners 86-87. Glass panels
fabricated in
this manner may have corners with a modified geometry that deviates from the
well formed
standard and asymmetric radii previously discussed, yet still provide superior
glass cracking
and glass fallout resistance to comparable rectangular cornered glass panels
during
earthquake racking motions. Moreover, these panels can be used in lieu of the
rounded
corner glass panels formed with standard and asymmetric radii in the glass
unit constructions
set forth in the embodiments below.
[50] FIG. 9 depicts another embodiment of the present invention, wherein an
isometric view of one corner of an insulating glass unit (IGU) is shown. The
IGU is
constructed with two rounded-corner radius 91 monolithic glass panes 93 and
95. The panes
in this embodiment are nominally'/4 in. (6 mm) thick and each pane corner has
a nominally
3/4 in. (19 mm) rounded-corner radius 91. A perimeter spacer 94 separates the
two panes of
glass. This spacer in this embodiment is about'/Z in. (13 mm) thick and the
interior may be
filled with air or an inert gas (e.g., argon) and the exterior may be sealed
with a perimeter
structural sealant 92 IGUs constructed with any number and combination of
monolithic,
laminated or filmed glass panes can be formed from modified-geometry (e.g.,
rounded)
corner glass panes with the same dimensions or with any other dimensions
suitable for
constructing IGUs. Some considerations in the fabrication of insulating glass
units
constructed with modified-geometry (e.g., rounded) corner glass panes include
glass pane
alignment (minimal in-plane alignment offset of one pane with respect to the
other), spacer
design and the specific corner geometry and edge surface conditions of the
individual panes.
IGUs constructed with aligned glass panes offer maximum in-plane racking
resistance. A
variety of spacer technologies are available for IGUs, all of which may be
used in IGUs
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16
constructed with modified-geometry (e.g., rounded) glass corners, but could
require some
adjustment to accommodate the IGU corner geometry selected for a particular
application.
For most currently used IGU spacer systems, about a %i in. (13 mm) corner
radius on the
glass panes may be employed without requiring the use of anything but a
conventional IGU
spacer. Generally, details regarding corner geometry and glass edge surface
finishes
specified above for monolithic glass panels are applicable to the individual
glass panes used
in a given IGU construction. Moreover, glass beveling and polishing
operations, and
asymmetric rounding are also applicable to the individual panes of IGUs of the
present
invention.
[S1] FIG. 10 is yet another embodiment of the present invention illustrating
the
invention. Therein, a laminated glass unit is illustrated by an isometric view
of one corner of
a fabricated and glazed laminated glass unit. The laminated glass unit is
constructed with
two, 3116 in. (5 mm) thick, 3/4 in. (19 mm) rounded-corner radius 104
monolithic glass panes
101 and 103 adhered to each other with a polymeric interlayer 102 having a
thickness of
about 0.060 in. (1.52 mm). The present invention contemplates the use of a
variety of
laminated glass units. These laminated glass,unit5 may be constructed with any
number or
combination of monolithic glass (of any glass type) and/or polymeric layers
(e.g., plastic
panes) and can be formed from glass panels of any type and dimensions with
modified
geometry (e.g., rounded) comers. As with insulating glass units, alignment of
glass plies is a
consideration in the manufacture of laminated glass units employing the
present invention.
Selection of an appropriate corner geometry can be made in the same manner as
that
described for monolithic glass panels. Although polyvinyl butyral (PVB) is
typically used as
the interlayer material to bond glass plies in conventional two glass ply
laminated glass unit
construction, other interlayer/layer materials may also be used in laminated
glass units
constructed with modified-geometry (e.g., rounded) corner glass panels with no
modifications required in their fabrication. It is preferred that the
polymeric
interlayer(s)/layer(s) materials) be trimmed to the profile of the glass at
the modified-
geometry corner regions. Such laminated panels would include specialty
laminated panels
comprised of a glass ply and single or multiple polymeric layers adhered to
the glass and/or
each other for the purposes of imparting impact and abrasion resistance to the
panel, among
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I7
other desirable performance attributes. Generally, details regarding corner
geometry
modifications and glass edge surface finishes specified above for monolithic
glass panels are
applicable to the individual glass plies in a given laminated glass unit
configuration.
Moreover, glass beveling and polishing operations and asymmetric rounding are
also
applicable to the individual plies of laminated glass units of the present
invention.
[52J Monolithic glass panels having a polymeric film thereon can also be used
in
accordance with the present invention. An embodiment of which is shown in FIG
1 l, which
shows an isometric view of one corner of a fabricated 1/4 in. (6 mm) thick,
'/4 in. (19 mm)
rounded corner radius 113 monolithic glass panel 112 with a 0.007 in. (0.178
mm) applied
polymeric film 111. Any glass type with dimensions and modified geomeixy
(e.g., rounded)
corners and glass panel edges fabricated as described previously, or
architectural applied film
type, may be used without modification, although it is preferred that the
polymeric film be
trimmed to the profile of the glass at the modified-geometry corner regions.
Selection of an
appropriate corner geometry may be made in the same manner as that described
for
monolithic glass panels. Generally, details regarding corner geometry
modifications and
glass edge surface finishes specified above for monolithic, IGU and laminated
glass panels
also are applicable for the glass panels used in a given applied film glass
unit construction.
Glass beveling and polishing, and asymmetric rounding are also applicable to
the individual
panels used in an applied film glass unit of the present invention.
[53] Additional glass fallout resistance can be imparted to applied film glass
installations with modified-geometry (e.g., rounded) glass corners, as
described previously,
by anchorage of the film perimeter to the frame. One such embodiment of an
anchored film
rounded glass corner unit is shown in the elevation view and corresponding
sectional view in
FIG. 12. With reference to FIG. 12, the glass panel 121 with glass boundary
2I6 within the
dry-glazed curtain wall frame section shown and bounded by extruded aluminum
vertical
mullions 123 and horizontal mullions 122, which are connected with shear
blocks 126, rests
upon rubber setting blocks 125 and maintains its side spacing 213 within the
frame glazing
pocket 2I5 with side blocks I24. The panel is secured within the frame with
extruded
aluminum pressure plates 128 and rubber gaskets 210 and 211. Additional glass
panel
attachment to the frame is provided by the structural silicone anchor bead 127
adhered to the
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film 212, which is applied to the glass panel and to the vertical and
horizontal framing
members along the entire glass panel perimeter. In framing those portions of a
wall system
that do not have glass panels on both sides of a given glazing pocket, an
extruded aluminum
perimeter filler is used 129. The use of anchored applied film is applicable
to any of the
aforementioned applied film glass panels of the present invention within a
wide variety of
wall framing systems.
[54] For existing building wall systems constructed with glass panels
containing
annealed monolithic glass, it would be possible to retrofit those panels with
modified-
geometry (e.g., rounded) glass comers on site using commercially available,
portable, glass
cutting, sanding and grinding/polishing equipment. Alternatively, the original
glass panels
can be replaced with glass panels fabricated with modified-geometry (e.g.,
rounded) corners
off site.
[55] Glass panels of the present invention offer an economical seismic damage
mitigation approach for architectural glass in both new buildings and existing
buildings in
earthquake-prone regions and elsewhere.
[56] In accordance with the invention, the present invention is applicable to
any
window system, including, but not limited to curtain wall systems, storefront
wall systems,
punched opening window systems, ribbon window systems, and strip window
systems.
[57] Conventional framing for glass units has substantially rectangular or
angular
corner glazing pockets fox receiving the rectangular or angular corners of
conventional
rectangular or angular glass panels. In accordance with our invention, a glass
panels of the
invention is mounted in conventional framing, which results in reducing the
contact friction
between the glass corners and the glazing pocket. The glass panels of the
invention have a
slightly reduced glass plate diagonal length, which allows them to rotate and
translate more
freely within the frame when the frame is subjected to dynamic, horizontal
racking
movements as would be expected during an earthquake. The increased mobility of
the glass
panel within its glazing pocket allows the glass panel to adjust more readily
to increased
frame deformation and can increase both the serviceability (glass cracking)
and ultimate
(glass fallout) drift limits of architectural glass panels.
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[58J In the preceding detailed descriptions, the present invention is
described with
reference to specific exemplary embodiments thereof. It will, however, be
evident that
various modifications and changes may be made thereto without departing from
the broader
spirit and scope of the present invention, as set forth in the claims. The
specifications and
drawings are, accordingly, to be regarded as illustrative and not restrictive.
It is understood
that the present invention is capable of using various other combinations and
environments
and is capable of changes or modifications within the scope of the inventive
concept as
expressed herein.
