Note: Descriptions are shown in the official language in which they were submitted.
CA 02316238 2000-06-23
WO 99/34071 PCT/US98/27225
TITLE: STRUCTURAL TIE SHEAR CONNECTOR FOR
CONCRETE AND INSULATION SANDWICH WALLS
BACKGROUND OF THE INVENTION
The present invention relates to the field of precast concrete insulated
sandwich panels. In particular, the invention relates to a connector for
connecting concrete layers in such panels.
The use of precast concrete insulated sandwich panels has increased
with the growing need for energy efficient structures. Today, insulated
sandwich panels are used in the construction of all types of commercial,
industrial, warehouse, correctional, and residential buildings. In service,
the
panels may be constructed to serve as exterior cladding, as bearing or shear
walls, or as roof members. The use of precast concrete panels allows for a
high
level of quality control, economy of scale, and the quick enclosure of a
structure. The sandwich panels can also be fabricated on-site or in high
efficiency manufacturing plants off site.
An insulated sandwich panel is composed of two layers (wythes) of
concrete separated by a high density foam insulation in the center. The
thickness of the concrete layers varies depending upon the structural
2 0 requirements of the building. The most common load requirements include
wind load, roof load, and seismic load. These loads must be collected and then
transferred to the building frame and the building foundation. The two
concrete wythes handle the majority of this work in concert. But, when the
concrete layers are separated by an insulation layer, a structural tie must be
2 5 used to connect the two concrete wythes together across the insulation
layer in
such a manner as to cause the two concrete wythes to function more as a single
composite unit structurally. However, conventional ties allow thermal
bridging, or a loss of heating/cooling energy via the structural tie.
There is an initial bond between the concrete and insulation, but this
30 bond is eventually broken due to handling, temperature differentials and
cycling; or service loads, it is necessary to provide shear connectors to
transfer
~~.~_.a '....,
1
CA 02316238 2000-06-23
WO 99/34071 , , " PCT/US98,/27225
,;. ,:. '..' ... ,.' ,
forces between the wythes due to longitudinal bending of a panel. These
connectors have sufficient strength and stiffness to allow a significant level
of
interaction between the wythes in the resistance of loads. Non-shear
connectors are not designed to transfer longitudinal shear forces between the
wythes and primarily serve as a means to hold the various layers together.
Traditionally, steel inserts or solid concrete penetrations through the
insulating layer have been the primary means of shear connection. These
connectors, however, result in thermal short-circuits across the insulation
layer and decrease the thermal efficiency of the panel. Steel inserts can also
l0 lead to unsightly oxidation or rust on the panel faces.
' In an effort to eliminate the problem of thermal bridging, the use of
fiber reinforced plastic (FRP) materials in the fabrication of wythe
connectors,
such as dowel pin connectors and bent bar connectors, was started. With a
thermal conductivity approximately 1/100 that of stainless steel, FRP material
is seen as an excellent replacement for steel or concrete as wythe connectors.
However, FRP dowel pin connectors are inserted normal to the layers. Thus,
they have glass fibers subjected to bending during loading of the sandwich
panel. The load capacity of the pins is resin-dependent. Many more pins are
typically required to replace a few steel trusses.
2 o EP-A-0 532 140 discloses a connector that includes first and second
spaced parallel prestressed metallic strands 30A and 32A. Furthermore, this
' , reference discloses a web 36A of thermally non-conductive material loosely
wrapped around the first and second strands 30A, 32A. This reference does
not disclose that the first and second strands 30A, 32A are made of a
thermally
2 5 non-conductive material or that the connector is integrally formed as one-
piece. Furthermore, the structure shown in this reference lacks the anchoring
or chairing loop portion discussed below. The anchoring or chairing loop
portion is advantageous in that it allows the form and the concrete itself to
positively locate and hold the connector in place.
AP~~EwD=D SHEET
2
W099/34071 CA o23i623s 2000-06-23 pOT/~598/27225
Therefore, a primary objective of the present invention is the provision
of an improved structural shear tie connector.
A further objective of this invention is the provision of an essentially
thermally non-conductive (non-metallic) shear tie connector having transverse
webs wherein the angled members are in tension under loading conditions.
A further objective of this invention is the provision of a tie connector
that is strong, compact, economical to manufacture, and easy to install.
These and other objectives will become apparent from the drawings, as
well as from the description and claims which follow.
2A
~~~N~~~ s~~~~
CA 02316238 2000-06-23
WO 99/34071 PCT/US98I27225
SU1~IMARY OF THE INVENTION
The present invention relates to concrete and insulation sandwich wall
panels having first and second layers or wythes and an insulation layer
interposed therebetween. Disclosed herein is a structural shear tie connector,
which includes first and second spaced horizontal strands of thermally non-
conductive material. The first and second strands are adapted to be encased
respectively by the first and second concrete wythes. A web of thermally non-
conductive material interconnects the first and second strands through the
insulation layer and forms at least one loop. At least one of the strands of
the
loop extends at an angle with respect to one of the first and second strands
such that the angled strand is in tension when a load is applied to the
sandwich wall panel.
Preferably the strands are formed of fiberglass reinforced plastic and
are formed as a continuous unwelded structure. The first and second strands
of the connector are preferably substantially parallel to each other so that
the
strands and the intersection of the web thereto are wholly disposed in the
respective concrete layer.
The web has a anchoring loop portion which extends outwardly beyond
one of the first or second horizontal strands. Concrete is allowed to fill the
loop
2 0 portion in the concrete layer, thus anchoring the connector. This loop
also
positively locates, gauges, "chairs" or spaces the tie with respect to the
bottom
face of the form and consequently to the bottom surface of one of the concrete
layers.
A method of forming sandwich wall panels with such tie connectors is
2 5 also disclosed.
3
CA 02316238 2000-06-23
WO 99/34071 PCT/US98I27225
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a concrete and insulation sandwich
wall panel having the tie connectors of the present invention.
5. Figure 2 is a partial sectional view showing the bow tie connector of the
present invention.
Figure 3 is a front elevation view of the bow tie connector of this
invention.
Figure 4 is a side elevation view of the bow tie connector of Figure 3.
Figure 5 is a perspective view illustrating the formation of a concrete
and insulation sandwich panel utilizing the bow tie connector of this
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
In the drawings and the description which follows, like features are
denoted with like reference numerals.
A concrete and insulation sandwich (wall) panel appears in Figure 1. As
best seen in Figures 2 and 3, the panel 10 includes first and second concrete
wythes (layers) 12, 14 and an insulation layer 16 interposed therebetween.
The insulation layer 16 includes a high density polystyrene foam insulation or
2 0 similar material having high thermal resistance. The panel 10 is
preferably
precast and is frequently used to provide an insulated outer shell to
buildings.
However, the panel can also be formed on the site where the building is being
erected.
Figure 2 illustrates the preferred embodiment of the present invention,
2 5 wherein a tie shear connector in the form of a compact double looped "bow
tie"
shear connector is provided. The term bow tie is used because this
configuration resembles the similarly named clothing accessory. The bow tie
connector 20 extends thmugh the insulation layer 16. The bow tie design is
more compact than conventional truss style designs.
4
CA 02316238 2000-06-23
WO 99/34071 PCT/US98/27225
The bow tie 20 includes a first horizontal strand 22 spaced apart from a
second horizontal strand 24. Preferably the horizontal strands 22, 24 are
parallel and near the top and bottom of the shear tie connector, respectively.
The strand 22 or 24 need not be a single straight member. A gap can exist
between left and right portions 22A, 22B, 24A, 24B of the respective strands
22, 24. In fact, such a gap is useful in accommodating other reinforcing
structures in the concrete layers, such as rebar or prestressed strands. Thus,
the gap can even be used to position the bow tie 20.
The horizontal strands 22, 24 should reside in the concrete layers 12, 14
respectively. When installed in the panel 10, the first strand 22 remains
above
the insulation layer I6 and the second strand 24 remains below the insulation
layer 16. When the concrete is poured to form the panel 10, the first strand
22
is encased by the first concrete wythe 12 and the second strand 24 is encased
by the second concrete wythe 14. The first and second strands 22, 24 will also
be referred to herein as the top and bottom strands or cords respectively.
However, the bow tie shear connector can be rotated or inverted if the
expected
load or placement conditions dictate.
A web 26 is continuously formed with the strands 22, 24 in the concrete
layers 12, 14. The web 26 includes substantially vertical legs 28 which extend
2 0 inwardly from the strands 22, 24 toward the insulation layer 16 (see Fig.
2).
The web 26 includes the legs 28 and angled members 30 which extend at an
angle a with respect to the first and second horizontal strands 22, 24.
The strands 22, 24 and the web 26, including the angled members 30
and legs 28 are preferably formed of a thermally non-conductive material, such
2 5 as fiberglass reinforced vinyl-ester (FRP). The material is non-metallic
in
order to have the desired thermal properties. The strands of the web 26 are
preferably continuously formed so that no welding is required and no thermal
bridge is provided between the concrete layers 12, 14.
The strands 22, 24, 28, 30 and 32 are continuous and are integrally
3 0 formed by a conventional winding process. The strands of fiberglass are
5
WO 99/34071 CA o23i623s 2000-06-23 pOT/US98,/272,25
wound around a mancliel and impregnated with ester resins to form a
continuous roving. The web 26 can be formed of a left-angled loop and a right-
angled loop which are then glued together with resin, but preferably the loops
are wound together on the same mandrel.
Referring to Figure 3, the angle a is preferably approximately 30°
to
60°, more preferably 50°. The strands 22, 24 and the transverse
web 26 lie in
a common plane. Chairing loop portions 32 extend below the second horizontal
strand 24. Non-chairing loops could also be formed so as to extend above the
first horizontal strand 22. Interstitial spaces 34 are formed between the
strands 22, 24, 28, 30 and 32.
The chairing loop portions 32 can occur at almost any frequency, as
desired. One purpose of the chairing loop portions 32 is to allow a concrete
bar
to be formed between the loop portion 32 and the horizontal strand 22 or 24.
This provides additional strength and rigidity to the sandwich panel 10 and
helps anchor the tie connector 20 in place.
The bow tie shear connector 20 is relatively small sturdy, and compact.
A plurality of bow tie connectors 20 can be placed in the sandwich panel 10 to
meet the load requirements. Referring to Figure 4, the thickness or effective
diameter of the strands 22, 24, 28, 30, 32 is preferably approximately 3/16"
2 0 (.5 cm). However, the required thickness or cross sectional area can be
calculated based upon the load conditions which are expected to be
encountered. Thus, the invention is not restricted to strands of this
thickness.
In this embodiment, the bow tie connector 20 is approximately 7~/2" (19 cm)
long and 51/" (13 cm) high. However, other dimensional combinations are
2 5 possible due to the flexibility of this invention.
Advantageously, the angled members 30 of the bow tie connector 20
resolve the bending stresses into linear stresses having vertical and
horizontal
components. The angled members 30 are in tension when a load is applied to
the sandwich wall panel 10. The bow tie is functionally complete when it
3 0 forms two crossing main loops. One main loop includes two angled members
6
~t~lihEvCt? ~~ _~-,
CA 02316238 2000-06-23
WO 99/34071 PCT/US98/27225
30 extending to the right from bottom to top and interconnected by horizontal
strands 22, 24. The other main loop includes two angled members 30
extending to the left from bottom to top and interconnected by horizontal
strands 22, 24. However, additional loops, strands, and angled members 30
can be added as desired.
The angled members 30 resolve the bending stresses placed on the wall
panel 10 into linear stresses which are transferable between the wythes 12, 14
so as to form a fully composite panel. Since the strands have negligible
thermal conductivity and are non-metallic, no thermal bridging occurs
between the wythes 12, 14. Oxidation or rust will not occur on the faces of
the
panel 10. The tie connector of this invention resolves the loads into a
horizontal component and a vertical component. For the purposes of this
discussion, the vertical component is normal (90°) to the plane of the
wythes
12, 14. The horizontal component is parallel to the plane of the wythes 12,
14.
For the wall panel 10 to resist wind, roof, and seismic loads, the horizontal
component is the larger component by a great magnitude. The angled web
members 30 of the tie connector handle this high load component in tension,
which takes full advantage of the tensile strength of the glass fibers.
The tie connector transfers loads without depending upon the resin
2 0 matrix between the glass fibers. The resin matrix is merely a facilitating
medium to position the glass while the insulated precast panel is being
manufactured. The fiberglass has a coefficient of thermal expansion nearly
the same as concrete. This is extremely important in that thermal stresses
between two incompatible mediums would and could exceed the mechanical
2 5 load stress limits. Furthermore, the thermal conductivity of glass is very
close
to zero.
In order to make a sandwich wall panel 10 using the bow tie connector
of the present invention, a form 50 is utilized. See Fig. 5. Preferably one of
the concrete wythes 12 or 14, here the bottom wythe 14, is poured in the form
50. Next, strips of insulation material 16A, 16B, 16C, etc. are laid on top of
7
CA 02316238 2000-06-23
WO 99/34071 PC'T/US98/27225
the bottom concrete layer 14. Then the shear connectors 20 are placed or
"plunged" into the still plastic concrete layer 14 through the gaps 52 between
the insulation strips 16A, 16B, 16C, etc. Care should be taken to make sure
that the bottom horizontal strand 24 of the tie connector 20 and the
connections of the web 26 thereto are wholly disposed in the bottom concrete
layer 14. The "self chairing" feature of the bow tie facilitates this
placement
requirement by gauging the depth of strand 24 when the chairing loop or chair
leg 32 is in contact with the form 50. The chairing loop 32 rests on the form
50
to positively locate the connector 20. The top concrete layer 12 is then
poured
on top of the insulation layer 16. Care must again be taken to make sure that
the top horizontal strand of the web 26 thereto is wholly disposed in the top
concrete layer 12.
Other methods of manufacturing the sandwich wall panel can be used
with acceptable results, For example, the tie connectors 20 can be chaired
(vertically) and tied (horizontally) in the desired positions by primary and
secondary reinforcing strands or other preexisting structures extending across
the lower portion of the form 50. Then the concrete for the bottom wythe 14 is
poured into the form 50. The insulation strips 16A, 16B, 16C, etc. and the top
layer 12 of concrete are then added. Alternately, the connectors 20 can be
tied,
2 0 affixed, or otherwise attached to the side edges of the insulation strips.
While multiple, spaced apart, crossing double loop connectors have been
shown in the preferred embodiment, it will understood that single loop
configuration will also since and one large connector may be substituted for
many smaller connectors in the gaps) between insulation strips.
2 5 From the foregoing it can be seen that the present invention is easily
incorporated into the manufacture of the sandwich panel 10. The size, shape
and number of tie connectors 20 used can be varied to meet the particular load
conditions to be encountered. The invention facilitates mass production of
sandwich wall panels, which has not heretofore been achieved.
CA 02316238 2000-06-23
WO 99/34071 PCT/US98/27225
Some of the other advantageous features of the bow tie connector are
discussed below.
1. The two loops composing the bow tie connector are manufactured in a
continuous winding process, thus eliminating structurally dependent
intersections between the angled web and the horizontal chords at the top and
bottom. The intersections of the left-angled web main loop and the right-
angled web main loop is not a structural intersection in that each loop is
designed for tension only and, under load conditions only the left or right
loop
in transferring tension stresses.
2. The "notched" zones between the left and right main loops of the bow tie
connector eliminate conflicts with transverse reinforcing members such as
rebar and prestressed strands. Other "truss" type ties have continuous top
and bottom horizontal chord elements which interfere with reinforcements pre-
placed and post-placed in the concrete wythes during the manufacturing of the
sandwiched insulated panels. This conflict often precludes the use of mass
production processes for forming the panels.
The notched feature of the bow tie connector allows this shear tie to be
placed into the still plastic concrete without "pre-tying" the insert to the
reinforcement of the rigid insulation. This facilitates the use of mass
2 0 production processes for forming the panels.
3. The continuous loop design of the bow tie connector fully imbeds into
the concrete wythes and with mild consolidation of the concrete, the full
capacity of the insert is fully developed. This concrete-to-insert
developments
allows the concrete itself to act as the tension/compression chords associated
2 5 with full truss designs. The compactness of the bow tie connector design
allows the concrete to span from one development loop to the other without the
need of secondary or primary reinforcements.
4. The load development capacity of the bow tie connector is higher than
typical full truss inserts due to the elimination of structural intersections
of
30 the web and chords (continuous loop design). The main loops are designed
for
9
WO 99/34071 ca o23i6,23s 2000-06-23 p~T/US98,/272,25
full tension only. The FRP insert is not matrix dependent, thus the full
tension capacity of glass fibers is utilized. The compact design utilizes the
compression strength of the concrete as part of the total design.
5. The bow tie connector is self chairing. The chairing loop below the
lower horizontal chord serves to gauge the depth to which the bow tie
connector is imbedded into the concrete wythes. The proper gauging of the
depth is critical to the design of the sandwiched insulated panel. This chair
gauging is critical to facilitating mass production processes for forming the
panels. The chair is dimensioned to allow the bow tie connector to be plunged
1 o into the plastic concrete until the lower tip of the chairing loop is in
contact
with the bottom of the concrete form surface. The FRP material will not cause
rusting on the surface of the panel.
Therefore, it can be seen that the present invention at least achieves its
stated objectives.
~.:;,_. _
~%:1;4,''''r':.
