Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITE FLOOR SYSTEM
FIELD OF THE INVENTION
The present invention relates generally to composite steel and concrete floor
systems of the type including reinforced concrete slabs supported by secondary
framing members such as steel joists, which in turn are spanned across primary
framing members, such as hot rolled steel, beams, girders, or trusses. More
particularly, it concerns a composite concrete floor system comprising
secondary framing members provided with shear shoes at their ends. These
shear shoes are adapted to provide to the whole system an increased
1 o resistance to horizontal shear forces.
BACKGROUND OF THE INVENTION
In composite floor structures, it is known to couple the concrete and steel
components to provide composite action, thereby reducing the amount of
material in the floor system for a given required strength. By using the
concrete
slab as the top chord of a composite beam, a significant reduction in the
amount
of steel in the floor system is achieved. Such floor systems are known in the
art.
One well known system of secondary members is sold as the HambroTM
structural system. This system is disclosed in US patent no. 5,544,464.
In residential buildings, it is common to arrange the structure to span open
web
joists between load bearing walls, and no primary framing members are required
to support the joists. In larger structures, the joists are generally
supported by
primary framing members in the form of steel beams or trusses. This is
particularly the case for steel framed buildings which are erected as steel
columns connected by and supporting primary steel framing members.
Secondary steel framing members, for example in the form of open web steel
joists, are spanned across the primary members, and loads are transferred by
the primary members to the columns, and to the foundations of the building.
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These structures must resist to many forces, both horizontal and vertical and,
as
such, their design is complex and require the application of much scientific
skill
and knowledge. One of the forces encountered in these structures is known as
horizontal shear. This is a horizontal force which occurs along the
longitudinal
top of primary and secondary frame members. The HambroTM joist described in
US 5,544,464 is provided with a unique S-shaped top chord which, when
embedded in the concrete slab, forms a shear connector to prevent slippage
from occurring between the concrete slab and the joist, due to horizontal
shear
along the joist.
1 o Various forms of shear connectors have been developed for the primary
steel
framing members, the most common being the headed shear stud, or NelsonTM
stud, an elongated vertical device, which has an enlarged head, much like an
oversized nail. This stud is welded to the steel beam after the beam has been
connected to the structure during erection. This stud provides the necessary
shear capacity between the embedded stud and the concrete slab, thereby
providing a composite steel beam or girder. The stud is intended to be
imbedded
in the concrete, thereby transferring horizontal shear forces from the slab to
the
beam.
The most cost effective way to provide shear studs is to install them in the
shop.
2 o However, one drawback with such shear connector is that these studs
constitute
a tripping hazard for steel workers who have to walk on these beams during
erection of the frame. The seriousness of the problem is highlighted by the
fact
that for more than 25 years, the lnternational Ironworker Agreement has
rejected
the use of such studs on steel beams. These rules were adopted by safety
committees as they were formed in Canada and the USA, such as OSHA. In
order to overcome that problem, the studs are generally welded to the primary
steel members on the site of construction. In such a case, the secondary
framing members (also referred to as steel joists) are first installed on the
primary steel member, then the steel deck is installed, and then the studs are
welded through the metal decking on the steel top chord. The installation of
the
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shear studs on the site of construction creates quality problems due to the
very
nature of the welding process. Also, since the installation of these studs is
weather dependant, another drawback encountered with such "on site"
installation comes from the fact that it is often very difficult to schedule
the
skilled labour required and to manage such schedule so as to follow the fast
pace of structural steel erection program.
Other examples of concrete floor systems are given in US 4,729,201;
US 6,061,992; US 2003/0024205; US 200310084629; US 4,454,695;
US 4,700,519 and US 4,592,184.
1 o Thus there is a need for a new form of shear connector for the primary
framing
members which leaves the top flange essentially flat for walking purposes, and
avoids the installation and scheduling problems.
SUMMARY OF THE INVENTION
In accordance with the present invention, that object is achieved with a
framing
system for a composite concrete floor of the type comprising horizontally
extending primary framing members supporting secondary framing members
spanning across the primary framing members, the primary and secondary
framing members being made of a metallic structural material. Each of the
secondary members has two opposite ends provided with a shear shoe that is
fixed to the primary members by means of a structural joint sufficient to
provide
a shear connection between the concrete floor and the primary framing
members.
The metallic structural material is preferably steel or any other metallic
structural
material known in the art. The present invention. is thus not limited to steel
framing members. Therefore, whenever reference is made throughout the
present description to steel beams, steel joists, one should understand beams,
joists or framing members made of a metallic structural material.
The shear shoes of the secondary members preferably consist of an iron angle
having one horizontally extending face fixed by means of the structural joint
to a
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horizontal face of a respective one of the primary framing members, and one
vertically extending face fixed to said secondary framing member.
Also preferably, the structural joint is selected from the group consisting of
a
weld joint and a bolt joint.
As can be appreciated, the present invention forms a mechanical shear
connection for primary framing members which does not create a tripping
hazard during erection and prior to the composite stage, when the concrete
floor
slab has been formed and is cured, which shear connection effectively
transfers
horizontal shear forces to the primary frame members.
1 o Thus, the present invention provides, among other things, all the
advantages of
composite steel/concrete floor slab construction, with the added advantage of
an
efficient horizontal shear connection to primary steel floor members, allowing
a
continuous poured slab for an entire floor of a building to be formed with no
tripping hazards for iron workers, due to shear connectors. Such a structure
is
ls also designed by structural engineers to meet all other loads encountered
in
usual building construction.
In a further aspect, the present invention provides a method of assembling the
framing members to concrete. The method comprises the steps of :
- providing primary and secondary framing members made of a metallic
20 structural material, each of the secondary framing members having two
opposite ends provided with a shoe;
- placing the primary framing members in parallel relation;
- placing the secondary framing members across the primary members
with the shoes bearing on the primary framing members; and
25 -fixing the shoes to the primary framing members with a structural joint
sufficient to provide a shear connection for said primary members.
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Preferably, the step of fixing consists of welding the shoes to the primary
framing members. Also preferably, the secondary framing members have a
continuous shear connector.
More preferably, the shear connector is a continuous top chord adapted to be
5 embedded in the concrete floor.
The present invention further provides a new end shoe concept or a novel end
shoe for connecting the joist to the beam. The invention also provides a novel
joist with an end shoe which serves as the shear connector for the beam to
which it is attached.
1 o BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of the invention will become apparent
upon reading the detailed description and upon referring to the drawings in
which:
Figure 1 is an overhead perspective view of a composite floor in accordance
with the present invention, with the concrete slab partially removed to show
the
steel frame members;
Figure 2 is a cross-sectional view through a floor system in accordance with a
first preferred embodiment of the invention, the cross-sectional view being
perpendicular to a primary framing member;
Figure 3 is a cross-sectional view at right angle to the section of Figure 2
along
line 3-3 and showing the shear force applied on a shear shoe;
Figure 4 is a cross-sectional view of the mounting of secondary frame members
in the form of open web steel joists on a primary steel beam member of the
floor
system of Figure 2;
Figure 5 is a cross-sectional view of a primary frame truss supporting open
web
steel joists;
Figure 6 is an enlarged perspective view of the frame members of Figure 5;
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Figure 7 is an end elevation view of a frame truss or joist girder for use in
the
floor system of the invention;
Figure 8 is an end elevation view of the joist truss supporting two joists of
the
present invention;
Figure 9 is a plan view of the joist truss supporting a plurality of open web
joists
of the invention;
Figures 10 and 11 are side elevation views of joist truss girders before and
after
the concrete has been poured;
Figure 12 is a plan view of a primary framing member supporting staggered
1 o secondary framing members, with end shoes welded to the primary framing
member;
Figure 13 is a cross-sectional view through a floor system in accordance with
a
second preferred embodiment of the invention, the cross section being
perpendicular to a primary framing member;
Figure 14 is a cross-sectional view at right angle to the section of Figure 13
along line 14-14, and showing the shear force applied on a shear shoe; and
Figure 15 is a cross-sectional view of the mounting of secondary framing
members in the form of open web steel joists on a primary steel beam member
of the floor system shown in Figure 13.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE
INVENTION
In the following description, similar features in the drawings have been given
similar reference numerals and in order to lighten the figures, some elements
are not referred to in some figures if they were already identified in a
precedent
figure.
Referring to Figure 1, there is shown, in perspective, an overhead view of a
composite floor system of the invention. A primary framing member 11, which is
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shown here as a steel-truss or-girder, supportsa pluFality of secondary
framing
members 12 formed as open web steel joists which span perpendicularly
between adjacent primary framing members (not shown). Each joist 12 is
provided with an end shoe 13 on each end of the joist for attachment to the
primary framing member 11. Figure 6 shows this in greater detail, as explained
below. Preferably, the secondary framing member 12 used is a HambroTM joist
provided with an S-shaped top chord which forms a shear connector between
the primary framing member 11 and the concrete slab 14. A concrete slab 14
with reinforcing mesh 9 is poured onto form-work (not shown for simplicity)
and
embeds the top chord 16 of the joists 12 and the top chord 17 of the primary
framing members 11. The end shoes 13 of the joists 12 are fixed to the primary
framing member 11 by means of a structural joint 15 sufficient to provide a
shear
connection between the concrete floor 14 and the primary framing members 11.
The shear shoe thus acts as a shear connector able to transfer the horizontal
loading from the slab to the primary framing member 11 by the end shoe
structurally fixed to the primary framing member 11. The structural joint 15
is
preferably a weld joint between the shear shoe 13 and the primary framing
member 11, the weld having a length sufficiently long so as to provide such
structural joint. Although not simple, the determination of shear capacity
between two components is of common knowledge for a person in the art.
Hence, such person, having knowledge of the forces applied on the floor, the
length and height of the primary and secondary framing members used for the
floor system, knows how to calculate the shear necessary to develop the
composite action between secondary and primary framing members and the
right spacing between the connectors. As for example, in one preferred
embodiment, an end shoe Hambro D500TM with a concrete slab of 2 3/4 inches
reinforced by a wire mesh 6 x 6 6/6 fixed to the primary framing members by a
weld of at least 2 inches provided on each side of the shoe can provide a
capacity of 30.2 Kips per shoe. The total capacity provided will be the number
of
shoes installed on the primary framing member by 30.2 Kips per shoe.
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Figure 2 shows a primary framing member in the form of a steel beam 11'
supporting a joist 12 fitted with an end shoe 13 welded to the beam 11'. This
weld is shown in greater detail in Figure 6 below. The end shoe 13 is also
referred to hereinafter as a "shear shoe".
In Figure 3, the same beam 11' as shown in Figure 2 is shown in elevation,
with
the arrow 20 indicating the direction of the horizontal shear force. The
combination of the joist 12, the end shoe 13 and the welding of the end shoe
12
to the primary member 11 creates a shear connector to resist the horizontal
shear forces between the slab 14 and the primary framing member 11 or 11'.
1 o The advantages of this new shear connector are many. First, there is the
utilization of the joist end shoe 13 designed and analyzed to provide a bond
included in each secondary framing member 11. The shear shoe 13 performs a
double function of supporting the gravity load on the joist and also provides
a
mechanical shear connector able to transfer the bond between the slab 14 and
the primary framing member 11. This type of shear connection also avoids the
tripping hazard on the site, according to labour union rules, and increases
erection speed of the steel building frame.
The present invention features the use of special ends or shear shoes 13 which
act as shear connectors to the flange of a steel beam or the top chord of a
truss.
2 o The shoe 13 is also a gravity shoe for the secondary steel framing member
12
and shear connector tested and designed according to the capacity required for
the composite trusses. The welding between the top chord of the truss or beam
forming the primary framing member 11 and the shoe 13 is designed according
to the capacity required. The open web joist of the secondary framing members
12 can be used in a deck-slab system such as Hambro MD2000TM system or
with a removable plywood system such as Hambro D500T""
Depending on the loading and span of the primary framing member 11, single
shoe connectors 13 can be used, or groups of connectors. The total capacity in
bond will be the total capacity of all shoe connectors and other connectors.
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Figure 4 illustrates a pair of open web joist secondary members 12, which may
be aligned or staggered, mounted on a primary framing member 11. Each joist
12 is provided with a dual purpose shear shoe 13 which is welded to the joist
12
in manufacture, and delivered to the job-site, ready for installation. Each
shoe 13
is then welded or bolted to the top flange of the regular beam primary framing
member 11. Similarly, Figure 5 illustrates a pair of joists 12 with shear
shoes 13
mounted on a primary truss framing member 11. As before the shoes are
welded to the top flanges of the truss 11. In both of these cases, horizontal
shear between the primary framing member and the slab is transferred from the
slab to the primary framing member by the shear shoes 13.
Figure 6 is a perspective view from above of the connection of the secondary
open web joists 12 and the primary truss framing member 11. Welds 15 are
provided on both sides of shear shoes 13 to fix the shoes 13 to the top
flanges
of the truss 11.
Figure 7 is a vertical section of a primary steel truss framing member 11
consisting of a bottom chord formed of angles 30 welded back-to-back between
web members 31 which in turn are welded to a gusset plate 32 which in turn is
welded to a back-to-back top chord angle 33. The vertical legs of the angles
33
are slotted at intervals, the slots being staggered, and rod segments 34 are
welded to the vertical legs of the angles 33.
This novel truss construction provides a strong, light primary framing member
with maximum openings in the web through which building services such as
heating, plumbing, electricity, and communication services can be located.
Figure 8 shows the connection of primary and secondary framing members
using the truss of Figure 7, integrating the whole frame structure to resist
horizontal shear forces, and support the gravity load of the floor system.
Figure 9 is a plan view of a portion of a floor frame system 10 including a
primary truss 11, and secondary joists 12 with end shoes 13, in which the
joists
are aligned rather than staggered.
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Figures 10 and 11 show alternate truss configurations depending on building
requirements, Figure 10 being the standard configuration and Figure 11 being a
configuration for maximum size openings in the truss for accommodating large
ducts.
5 Figure 12 is a plan view of a primary steel beam framing member 11
supporting
staggered secondary open web joist members 12 with shear shoes 13 welded to
the member 11. Such staggering of the secondary members is required when
shear connectors are required at intervals less than the normal joist spacing.
Referring to Figure 13, a concrete floor system according to a second
preferred
10 embodiment of the invention is illustrated. As for the first preferred
embodiment
shown in Figure 2, the floor system comprises a primary framing member in the
form of a steel beam 11' supporting a joist 12 fitted with an end shoe 13
welded
to the beam 11', the whole structure supporting a concrete floor 14. The
difference between the first preferred embodiment shown in Figures 2 to 12 and
the second embodiment resides mainly in the fact that, in the first
embodiment,
the shear shoes 13 are embedded in the concrete, whereas the shear shoes 13
in the second embodiment are not, the concrete being poured on top of the
secondary framing members 12.
In Figure 14, the same beam as shown in Figure 13 is shown in elevation, with
the arrow 20 indicating the direction of the horizontal shear force. The
combination of the primary framing member 12, the end shoe 13 and the
welding 15 of the end shoe 13 to the primary framing member 11 creates a
shear connector to resist the horizontal shear forces between the slab 14 and
the primary framing member 11 or 11'.
Although preferred embodiments of the present invention have been described
in detail herein and illustrated in the accompanying drawings, it is to be
understood that the invention is not limited to these precise embodiments and
that various changes and modifications may be effected therein without
departing from the scope or spirit of the present invention.
