Note: Descriptions are shown in the official language in which they were submitted.
2o~s~~s
Title: Composite Concrete-Beam Structure
Backqround to the Invention
It has been appreciated for some time that the load
bearing efficiency of a combination or "composite" concrete
and steel beam can be enhanced by coupling the upper surface
of the steel beam to the lower surface of the concrete through
shear-force transfer devices. Such devices prevent separation
from occurring between the beam and concrete when loads are
applied to the composite structure, and allow the neutral axis
to be displaced downwardly within the concrete to the degree
necessary to ensure that no portion of the concrete is exposed
to tensile stress beyond its tensile limit.
U.S. Patent 3,401,497 to Gregory depicts a beam with an
upper surface that is covered by an array of protuberances
known in the industry as "Nelson Studs". These studs, welded
in arrays of varying density, are used to transfer shear
stress from the lower region of a concrete beam, or slab
portion, to the steel beam lying beneath.
Another form of shear transverse device is depicted in
U.S. patent 2,479,476 to Cueni. In this patent a continuous
upper zig-zag shaped strip is welded intermittently to the
upper surface of a steel beam. While this patent recognizes
that it is customary to provide such shear transverse devices
in the form of spirals or other sinuous shapes, no suggestion
is made as to the possibility of providing a stress transfer
element which is straight and is aligned with the upper surface
of the beam.
CA 02028868 2001-09-14
2
In U. S . patent 3 , 177 , 619 to Benj amin, it is proposed
to form a composite concrete floor slab on a steel beam by
welding corrugated steel sheeting transversely along the side
flanges of the upper surface of the steel beam. Welded on top
of the transversely running corrugated sheeting in this patent
disclosure are a series of reinforcing bars. Also welded to
the upper surface of the corrugated sheet at places overlying
the side flanges of the steel beam are a series of "S"-shaped
connectors which serve as shear transverse devices. The "S"-
shape of these connectors is a variation on the vertical-plate
type of shear transfer device proposed as an alternative to
nelson Studs. Examples of such vertical-plate devices are
shown in Cueni (item 16, 17, 19) and in U.S. patent 3,010,257
to Naillon (item 55). An example of an inclined plate of
similar intended effect is shown in U.S, patent 1,597,298 to
Kahn (item 3).
All of these references rely on discrete, erect
elements, extending upwards from the upper surface of the
steel beam into the body of the overlying concrete in order to
transfer the shear stress within the concrete to the beam.
Figure 4 in Benjamin appears to depict such an arrangement,
but as shown in Figure 5 of the same patent the
longitudinally-oriented reinforcing bars (items 14) are welded
across the tops of the upper peaks of the corrugated sheeting,
outboard from the region above the steel beam. As conceived by
2028868
- 3 -
Benjamin, such reinforcing bars (14) do not participate in the
transfer of shear stress. This is apparent from the fact that
separate "S"-shaped sheet metal strips (16) are proposed to
serve this function.
It has been known to align concrete-imbedded
reinforcing bars in a spaced parallel position above the upper
surface of a supporting steel beam. Two examples of such an
arrangement are shown in U.S. patent 1,688,723 to Lathrop and
in U.S. patent 3,010,257 to Naillon. In both of these
patents, however, no provision is made to transfer shear
stress between the reinforcing bar and the steel beam.
In Lathrop bolts (9) with curved hooks engage the
reinforcing bar (6a) to draw it down towards the upper flange
of the beam (1). By its very nature, such a curved hook, is
incapable of transferring shear stress between the bar (6a) and
the beam (1).
In Naillon, Figure 7 shows a reinforcing rod (43)
mounted on a series of standoff connectors (49) above the
upper surface of a beam 37. In this figure, the beam is
loaded as a cantilever and the reinforcing rod is pretensioned
in order to improve the strength of the beam-rod combination.
This rod serves solely as a tension bearing element and is
incapable of transmitting shear stress from the rod to the
beam. This is apparent from column 8, lines 42-45 of this
patent which states:
CA 02028868 2001-09-14
4
"A plurality of cable connectors 49 is optionally
fixed to the upper flange; these engage the rod 43
with a close sliding fit to prevent lateral movement
between the rod and girder".
Since a sliding fit is provided, no shear stress can
be transferred. To transfer shear stress the rod would have
to be rigidly attached to each connector. In all events, the
configurations of Naillon does not contemplate the formation
of a composite structure of both concrete and steel.
From the foregoing analysis, it is apparent that the
prior art has contemplated two distinct mechanisms by which
shear stress may be transferred from an overlying body of
concrete to an underlying and supporting beam;
(1) by a series of discrete connectors in the form
of studs or upright plates; and
(2) by a continuous, sinuous or helical shear-
transferring rod or strip.
Neither of these schemes have, however, achieved the
efficiency of the invention herein in transferring shear
stress from concrete to the supporting beam. This is because
no one in the prior art has recognized the advantages of
collecting the shear stress continuously along a shear
collecting rod which is mounted above the supporting beam and
is aligned with the direction of the shear forces within the
concrete.
- 5 -
Summary of the Invention
According to the invention, therefore, a beam for use
in a composite structure comprising concrete overlying said
beam, is provided above the upper surface of such beam with a
continuous shear force-collecting means that is aligned with
the direction of the shear forces that will accumulate in said
concrete once the predetermined design load is applied to the
composite structure, said shear force-collecting means being
further rigidly attached at intervals to the upper surface of
said beam by shear transfer connectors. Customarily the shear
force-collecting means will be a steel reinforcing rod with a
texturized outer surface, and the direction of alignment of
the rod will be parallel to the upper surface of the beam.
It it not necessary for the shear force-collecting
means to be deeply imbedded into the concrete. It is usually
sufficient for it to be positioned above the beam at a
distance which is between an eighth and one-half of the depth
of the supporting beam. Such a positioning will generally
place the neutral axis of the composite concrete beam
structure, when subjected to the predetermined design load
within the concrete and between the beam and the shear force-
collecting means. Preferably the rod will be positioned just
above the upper surface of the beam. The actual preferred
design criteria for the placement of the shear force-
collecting means is to provide that the neutral axis is
~~~8~~8
- 6 -
displaced to such a degree as to ensure that none of the
concrete, under its design load, will be stressed beyond its
tensile limit.
The shear transfer connectors may be any form of
coupling which assures that the shear force-collecting means
is held in a rigid, fixed relationship with the upper surface
of the beam at the points of connection with the beam. This
may be achieved by welding, for example, reinforcing rod to
steel spacing blocks or plates of the requisite height, which
blocks or plates are, in turn, welded to the upper surface of
the supporting beam. Alternately, a flanged beam may be
provided with bolt-holes through the upper flange, and
clamping devices of the type known in the art may fasten the
reinforcing rod to bolts that are seated in and extend
upwardly through the bolt-holes in the beam.
The beam may be of any customary form, but a "C"
cross-section steel beam has been found particularly suited to
this application. Such a beam can be provided with pre-
punched bolt-holes in the upper flange that will allow for on-
site assembly of the beam with the reinforcing bar.
The shear force-collecting means is preferably chosen
from reinforcing bars that have a texturized outer surface.
Such a surface is customarily produced by rolling annular
ridges onto the outer surface of the reinforcing bar, but any
means of effecting a high frictional coupling between the
shear force-collecting means and the concrete may be utilized.
- 228868
A high efficiency coupling between the concrete and the shear
force-collecting means is desirable in order to ensure that a
minimum of creep occurs between the concrete and the bar which
is being grasped therein. Otherwise, the maximum efficiency
of collecting shear stress from within the concrete will be
lost.
While the presence of a continuous shear force-
collecting means within the lower region of the overlying
concrete has the salutary effect of collecting shear stress
in a smooth and regular manner in the region adjacent to the
shear collecting bar itself, not all of the shear forces in
concrete remote from the bar will thereby be collected. To
supplement the transfer of residual shear forces within the
concrete directly above the beam to the beam itself,
traditional upright shear transfer plates may also be
installed across the upper surface of the beam. Conveniently,
these may be combined with, or placed adjacent to, the shear
transfer connectors, relying on the positive attachment of
such connectors to the upper surface of the beam to provide a
secure anchoring of the traditional upright plates to the
beam.
The ancillary use of discrete shear transfer devices
in combination with the continuous shear transfer effect
achieved by the invention will reduce the demands being placed
on the interface between the concrete and the continuous shear
force-collecting means. At the same time, the presence of the
~~~ss~s
_8_
continuous system will reduce the need for a high density of
discrete shear transfer devices that might otherwise be
required to transfer a specific load.
A further advantage of the invention arises from the
avoidance of the necessity to use a high density array of
discrete shear transfer devices. It is preferable that such
devices be in the form of bolts that pass through holes in the
upper flange of the beam. However, a high density array of
bolt-holes will weaken a beam, leaving fabricators with the
less desireable option of welding shear transfer devices to
the beam. By reason of the lower density of shear tranfer
connectors that is made possible by the use of a continuous
shear force-collecting system, the option of utilizing bolt-
holes is made available in cases where such option could not
otherwise be chosen.
In the foregoing description, the shear collecting
means has been described as being continuous. It is
sufficient for such means to be continuous only between the
shear transfer points established by the shear transfer
connectors. While it is highly convenient to run a single
piece of reinforcing bar along the length of a beam in order
to provide a continuous shear collecting means, the invention
would still be present where the bar is interrupted and
supported in segments down a portion of the length of the
beam.
_ g _
The beam referred to in the above
description has customarily been described as
being made of steel. The beam may also be made of
aluminum or other equivalent material of
sufficient strength and rigidity to carry the
weight of the concrete and absorb the shear
stress.
Summary of the Figures
In drawings which illustrate embodiments
of the invention:
Figure 1 is a cross section normal to the
span of the cold formed elements;
Figure 2 is an enlarged cross section of
an arrangement at a cold formed section;
Figure 3 is an elevation view of a cold
formed section with attached bond bar;
Figure 4 is a large scale elevation view
of the welded shear transfer device;
Figure 5 is an elevational view of a
bolted shear transfer device using a spring clip;
Figure 6 is a cross section view of a
bolted shear transfer device using steel castings:
~~2~~~~
- 10 -
Figure 10 is a shear force transfer device to be used
at the end extremity of the bond bar;
Figure 11 is an elevational view of the end bearing
arrangement of the cold formed section;
Figure 12 is a cross section view of the same;
Figure 13 is a small scale plan view of the forming
system;
Figure 14 is a large scale cross section showing
detail for the support of the soffit form;
Figure 15 is a cross section view showing the support
of the forming at the edge of a floor area;
Figure 16 is a cross view of a floor in which the
concrete slab has an increased thickness in the proximity of
the cold formed section:
Figure 17 is a cross section view of the soffit form
used in the thickened slab arrangement;
Figure 18 is a cross section view of the soffit form
support system;
Figure 19 is a section view showing the end of the
cold formed section embedded in a cast in place concrete
beam; and
Figure 20 is a large scale cross section showing the
end bearing reinforcement of the cold formed section.
~Q2~t~~~8
- 11 -
Description of Embodiments
Figure 1 illustrates the overall arrangement of a
typical cross section. In this 1 is the concrete slab, and 2
is the wire mesh which functions as the transverse reinforcing
and as longitudinal shrinkage reinforcing. The cold formed
section 3 functions as the tension flange in conjunction with
the compression flange comprised by the concrete slab 1. The
necessary shear flow is gathered by the bond bar 4 and
transferred intermittently to the top flange of the cold formed
section 3. The soffit form 5 is a standard width waferboard
or plywood sheet. This soffit form supports the freshly
poured concrete by bearing upon the soffit form support pieces
6. These soffit support pieces consist in inverted top hat
cold formed sections. The wire mesh 2 is draped over the
bond bar 4 and then allowed to sag to the bottom part of the
slab 1 mid span. In the cross section of Figure 2 the
arrangement for the support of the soffit form is shown. The
soffit form support piece 6 bearings upon the cold formed
saddle 7 which is placed loose on top of the cold formed beam
section. In this view, holes 8 in the top flange permit
bolting of the necessary shear transfer device (not shown).
Holes 9 in the web permit the passage of electric wiring and
domestic water piping. The theoretical composite action of
the concrete slab in compression and the cold formed steel
channel section acting in tension is achieved by the transfer of
the horizontal shear flow between the concrete slab 1 and the
CA 02028868 2001-09-14
12
cold formed section 3. This transfer starts with the transfer
of incremental compression force from the slab 1 to the bond
bar 4 throughout its length and its transfer at intermittent
points from the bond bar to the cold formed section. Figure
3 is an elevation view of a cold formed section 3 with bond
bar 4 and intermediate shear transfer device 10 and end shear
transfer device 11. The cold formed channel is supported by
end reactions 12. The bond bar 4 consists in a suitable size
ordinary deformed reinforcing bar. The number if interior
shear transfer devices 10 is dependent upon the total shear
flow to be transferred, which is in turn dependent on the load
and span.
Typical interior shear transfer devices 10 may take
a variety of forms. Figure 4 illustrates solid steel block in
which the bond bar 4 is fastened by weld 11 to the shear/block
10 and this in turn is fastened by weld 12 to the top flange
of the cold formed channel 3. In this arrangement the bond
bar 4 accumulates incremental compression on the side towards
the center of the span and incremental tension on the side
away from the center of the span. The total accumulated force
from the length tributary to each transfer device is then
transferred to the cold formed channel 3. In addition the
shear transfer device 10 acts directly as a stress compression
block to transfer compressive force from the concrete to the
cold formed channel 3. Figure 5 illustrates an alternate
shear transfer device consisting in a spring steel clip 13
2~2$$~$
- 13 -
equal in width to the cold formed channel flange
width. Said steel clip has eccentric holes 14
through which the bond bar 4 passes. The steel
clip also has a vertical eccentric hole through
its high central point through which the bolt 15
is passed. Tightening of this bolt deforms the
spring. steel clip 14 so that it bears at
numerous points on the bond bar 4 to effectively
anchor it.
Another alternate shear transfer device
is illustrated in Figure 6 which consists in a
lower cast steel piece 16 and an upper cast
steel piece 17. The bond bar 4 is gripped by
the serrated surfaces of the semi-circular
grooves 18, when the bolt is tightened. Said
clamp action is enhanced by the prying action
resulting from the eccentric location of the
bolt 15. The faces of the upper and lower pieces
16 and 17 and the bolt head provide a direct
compression block for the concrete to the cold
formed section.
CA 02028868 2001-09-14
14
Figure 7 illustrates an end shear transfer device to
be located at the end of the bond bar. This end shear
transfer device, 11 in Figure 3, consists in a steel casting
29 with closed end hole 30 to receive the bond bar 4. The
weld 31 affixes the device to the cold formed section 3.
Alternate arrangements using bolts, comparable to the various
forms of bolt affixed intermediate shear transfer devices,
could also be used for end shear transfer devices.
Figure 8 is an elevation view of the open side of a
cold formed section at its end bearing. In the case
illustrated the end bearing support consists in a steel beam
32. The end stiffener 33 is welded into the web space, this
end stiffener 33 is of rectangular shape with corners cut off
and is seen in elevation in Figure 9. This end stiffener
transfers the shear reaction of the C section to the bottom
flange bearing. It also serves as a bulkhead in cases where
the ends of the beam are embedded in concrete. Also in Figure
11 are the end clips 34 and 35. These are bolted to the end
stiffener 33 with the bolt 36. In the case illustrated clips
34 are needed to stabilize the beam 32. In the case of the
floor system being continuous at both sides of the beam 32
clips 35 only would be required.
Figure 10 is a plan view to a small scale
illustrating the arrangement of the form system prior to the
placing of concrete. In Figure 10 the cold formed sections 3
are supported on a poured concrete or concrete block wall 37
CA 02028868 2001-09-14
and a steel beam 32 for example. The cold formed section 3
are spaced apart to have a clear inside dimension slightly
greater than the width of a standard waferboard or plywood
sheet 5. Said plywood sheet 5 serves as the soffit form for
5 the concrete slab. Spaces less than the standard board size
are made up from cut sheets 39. The soffit form is in turn
supported by the soffit support pieces 6. In the case of a
space 38 between cold formed sections being less than the
standard sheet width the soffit form support pieces are
10 echeloned to suit.
The soffit support pieces 6 are supported at their
ends as shown in Figure 11. Cold formed steel top hat section
7 rests loose on the channel 3. The soffit form 5 is carried
by soffit support piece 6 which consists in an inverted top
15 hat section. The dimensions of the hanger piece 7 are such
that the concrete extends slightly below the top of the cold
formed section 3. To strip the soffit forms the support
pieces 6 are knocked out from the saddle 7 and this permits
the removal of the soffit from 5. The support of the freshly
poured concrete at an edge parallel to the cold formed section
3 is achieved by a modified saddle 40, C.F. Figure 12. On its
inner edge it carries a typical support piece. Its outer edge
is bent to support lumber form pieces 41 to serve as the
bottom and side forms for the edge of the slab.
The alternate arrangement for the whole of the floor
system is depicted in Figure 13. This features a slab 1 that
CA 02028868 2001-09-14
16
is of increased depth 42 adjacent to and above the cold formed
section 3. This increased the shear capacity of the slab in
its transverse action thereby increasing the distributed load
strength. It also greatly increases the flexural strength of
the composite section in longitudinal action, thus permitting
the use of longer spans. Also illustrated in Figure 13 is a
continuous chair 43 which is used to retain the wire mesh in
its desired location. The wire mesh passes above and is tied
to the bond bar 4 and then is supported and tied down to the
chair 43 which is in turn tied to the soffit form. The curved
soffit of Figure 13 is formed by the use of waferboard panels
as illustrated in Figure 14. In this arrangement the
waferboard or plywood sheet 44 is arched into the desired
shape by the cold formed steel tie 45. The plywood is
retained at its edges by end pieces 46. A continuous center
block 47 is used to stabilize the arched soffit form under
during construction loads.
The support of the curved soffit form is illustrated
in Figure 15. The cold formed saddle 48 rests loosely on the
channel section 3. The lower ends of the saddle are bent into
180 degrees reversal to receive the form support anchors 49
and 50. These support anchors are fabricated with an end
fillet to permit their removal by hammering. The support
piece 49 is used on the web side of the channel 3 and the
support of the curved soffit 44 and tie 45 is illustrated.
Soffit form support piece 50 is for use on the open side of
CA 02028868 2001-09-14
17
the channel 3 and at one end it has a stabilizing pin 51
welded to it. Upon the concrete achieving its required
strength, the form support pieces 49 and 59 are removed by
hammering and the soffit forms 44 removed.
During pouring and curing of the concrete slab 1 the
cold formed channels 3 are supported on temporary shoring at
their mid-span point. This permits the floor to be built
without other shoring and also reduces the dead load
deflection prior to composite action being achieved.
In an alternate arrangement to which all of the
foregoing is applicable, the cold formed section 3 may be
replaced by a cold formed ZEE section.
In another alternate arrangement two parallel but
spaced bond bars may be used.
In a further alternate arrangement, the described
flooring system may be used in a concrete frame building in
which the major beams and girders are either precast or cast
in place. Such an arrangement is shown in Figure 16. The
cold formed channels 3 would have their ends 52 set into the
side forms (not shown) of the beam 53. The cold formed
channels 3 would have an internal stiffener 54 which would
also serve as a bulkhead to contain the freshly poured
concrete. A splice bar 55 would lap with the bond bars 4 to
provide negative moment capacity over the beam 53. In this
arrangement the concrete slab 1 would be monolithic with the
concrete of the beam 53.
CA 02028868 2001-09-14
18
Figure 17 illustrates an arrangement in which the
combination end stiffener and bulkhead 54 is installed in the
end of the cold formed channel 3. The bond bar 4 and end
shear transfer piece 11 are also shown. The cold formed
section 56 is shaped to be tightly internally fitting to the
cold formed channel 3. An extension of its web is bent to
serve as the combination stiffener bulkhead 54. The cold
formed section piece 56 is inserted in the cold formed channel
3 so that the open side of the piece 56 is adjacent of the web
side of the cold formed channel 3.
In an alternate arrangement in a concrete building
the cold form channels may be placed on the top surface of a
precast beam and the upper part of said beam may be poured in
situ to embed the ends of the cold formed channels, and to be
monolithic with the floor slab.
