U.S. patent number 3,813,834 [Application Number 05/256,257] was granted by the patent office on 1974-06-04 for joist with nailing strip and positioning members.
This patent grant is currently assigned to Products Engineering, Inc.. Invention is credited to George Bradley Davis, Jr..
United States Patent |
3,813,834 |
Davis, Jr. |
June 4, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
JOIST WITH NAILING STRIP AND POSITIONING MEMBERS
Abstract
A structural element having a fire rating of approximately two
hours when tested with the standard time-temperature curve
established by the American Standards for Testing Materials, said
element including prestressed concrete joists each having a
plate-like body portion and one or more integrally formed
reinforced support ledges wherein each ledge has a nailing strip
integrally molded adjacent the bottom thereof and each nailing
strip including a penetratable area formed internally adjacent
thereof, a plurality of sheets of material disposed adjacent the
ends of said ledges, each sheet of material forming at least one
butt joint with an adjacent sheet wherein said butt joint extends
longitudinally along a portion of one of said ledges, a plurality
of channel-shaped members disposed along each butt joint
intermediate said ledge portion and said sheets and attachment
means for attaching said channel-shaped members to the nailing
strips and, also, for attaching sheets of material to said nailing
strips and channel-shaped members whereby said sheets of material
are secured to the joist while preventing undesirable distortion or
warping thereof during the fire rating tests. This invention also
relates to a pretensioned concrete joist of the T-type comprising a
concrete plate-like body portion, a channel-shaped support ledge, a
nailing strip integrally molded in the bottom of said ledge, said
nailing strip including a channel-shaped member having a
penetratable layer of material disposed therein and a plurality of
positioning members longitudinally spaced along said channel-shaped
member, and pretensioning steel extending longitudinally of said
ledge and disposed in contacting engagement with said positioning
members, said pretensioning steel and said positioning members
cooperating to secure and maintain the nailing strip of the bottom
surface of the ledge prior to and during placement of the concrete
during forming of said joist. This invention also relates to a
novel form member for producing a pretensioned concrete member
having a nailing strip molded therein, and to a novel positioning
member made from a single piece of plastic material.
Inventors: |
Davis, Jr.; George Bradley
(Boulder, CO) |
Assignee: |
Products Engineering, Inc.
(Boulder, CO)
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Family
ID: |
27365896 |
Appl.
No.: |
05/256,257 |
Filed: |
May 24, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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41426 |
May 28, 1970 |
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Current U.S.
Class: |
52/223.8; 52/364;
52/374; 52/699 |
Current CPC
Class: |
E04B
1/4171 (20130101); E04B 9/22 (20130101); B28B
23/024 (20130101); E04C 5/20 (20130101); B28B
23/00 (20130101); E04B 2001/4192 (20130101) |
Current International
Class: |
E04B
9/22 (20060101); E04B 1/41 (20060101); B28B
23/00 (20060101); B28B 23/02 (20060101); E04C
5/20 (20060101); E04b 001/41 (); E04c 003/18 () |
Field of
Search: |
;52/364,368,374,699,223
;249/28,30 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Perham; Alfred C.
Attorney, Agent or Firm: Burton; Duane
Parent Case Text
This is a continuation-in-part application of U.S. Pat. application
Ser. No. 41,426 filed on May 28, 1970 now abandoned.
Claims
I claim:
1. A form member for use with a mold for making a pretensioned
concrete member having a nailing strip molded therein, the mold
having a longitudinally extending, generally channel-shaped portion
in which said form member is adapted to be disposed to form a
nailing strip, said channel-shaped portion of said mold including a
bottom surface and opposed walls, said form member comprising:
a. a longitudinally extending, channel-shaped member having
1. a bottom wall adapted to be disposed in contacting engagement
with the bottom surface of the channel-shaped portion of said
mold,
2. a pair of side walls, each of which has a longitudinally
extending upper edge,
3. a longitudinally extending U-shaped portion formed along the
upper edge of each side wall, the longitudinal axis of each
U-shaped portion lying in a plane disposed generally parallel with
a plane in which is disposed said bottom wall, the bight of said
U-shaped portion extending inwardly of its associated side wall,
and
4. a longitudinally extending attachment-means-penetrating layer of
material disposed within said channel-shaped member, said layer of
material having a lower surface portion disposed adjacent the
bottom wall of said channel-shaped member and upper surface
portions disposed adjacent said U-shaped portions of said
channel-shaped member whereby said U-shaped portions retain said
attachment means-penetrating layer of material within said
channel-shaped member and said layer of material prevents concrete
from entering said channel-shaped member; and
b. a plurality of positioning members longitudinally spaced along
said channel-shaped member and securely disposed within the
U-shaped portions thereof, each positioning member comprising
1. an inverted U-shaped frame member including a bight portion
overlying said upper edges and a pair of leg portions, the outer
surface of said bight portion being generally concave in
configuration and adapted to engage pretensioning steel after the
form member has been positioned within the mold, said frame portion
lying in a plane disposed generally normal to the longitudinal axis
of said channel-shaped member,
2. a pair of legs, each leg having (i) a first part attached to a
corresponding one of the leg portions of said U-shaped frame
member, and (ii) a second part securely disposed within a
corresponding one of the U-shaped portions of said channel-shaped
member, said second parts lying in a plane disposed generaly normal
to the plane in which is disposed said frame member,
3. the outer surfaces of the leg portions of said U-shaped frame
member being spaced such that they are adapted to be received
between the opposed walls of the mold in which same is to be used
whereby said outer surfaces of said leg portions serve as means for
centering and positioning said form member within the
channel-shaped portion of the mold in which same are to be used
upon being dropped therein and are adapted to be disposed adjacent
the inside surfaces of the opposed walls of the mold in which same
are to be used, and
4. said positioning members being constructed for transmitting a
force to said channel-shaped member when positioned within the mold
in which same are to be used and in contacting engagement with the
pretensioning steel to be used within the mold.
2. A form member as described in claim 1 in which the sidewalls of
said channel-shaped member are convergently disposed, taken in a
direction proceeding along said sidewalls toward said bottom wall,
and each of the legs of said positioning members includes an
L-shaped configuration, the first parts of said legs lying in a
plane in which is disposed said U-shaped frame member.
3. A form member as described in claim 1 in which the second parts
of the legs of said positioning members cooperate with the U-shaped
portions of said channel-shaped member to secure the frame member
of said positioning members in a plane disposed normal to the
longitudinal axis of said channel-shaped member.
4. A form member for use with a mold for making a pretensioned
concrete member having a nailing strip molded therein, the mold
having a longitudinally extending, generaly channel-shaped portion
in which said form member is adapted to be disposed to form a
nailing strip, said channel-shaped portion of said mold including a
bottom surface and opposed walls, said form member comprising:
a. a longitudinally extending, channel-shaped member having
1. a bottom wall adapted to be disposed in contacting engagement
with the bottom surface of the channel-shaped portion of said
mold,
2. a pair of side walls, each of which has a longitudinally
extending upper edge,
3. a longitudinally extending U-shaped portion formed along the
upper edge of each side wall, the longitudinal axis of each
U-shaped portion lying in a plane disposed generally parallel with
a plane in which is disposed said bottom wall, the bight of said
U-shaped portion extending inwardly of its associated side wall,
and
4. a longitudinally extending attachment-means-penetrating layer of
material disposed within said channel-shaped member, said layer of
material having a lower surface portion disposed adjacent the
bottom wall of said channel-shaped member and upper surface
portions disposed adjacent said U-shaped portions of said
channel-shaped member whereby said U-shaped portions retain said
attachment-means-penetrating layer of material within said
channel-shaped member and said layer of material prevents concrete
from entering said channel-shaped member; and
b. a plurality of positioning members longitudinally spaced along
said channel-shaped member and disposed within the U-shaped
portions thereof, each positioning member being formed from a
single piece of plastic material and comprising:
1. an elongate support portion, and
2. a pair of L-shaped portions (i) each L-shaped portion including
a pair of arms, (ii) each L-shaped portion depending from a
corresponding one of the ends of said support portions and having
one of said arms disposed generally parallel with said support
portion, (iii) each L-shaped portion being constructed for limited
pivotal movement relative to said support portion, (iv) the free
end of each arm that is disposed generally parallel with said
support portion being disposed within a corresponding one of the
U-shaped portions of said channel-shaped member, and (v) said
positioning member being constructed for transmitting a force to
said channel-shaped member when positioned within the mold in which
same are to be used and in contacting engagement with the
pretensioning steel to be used within the mold.
5. A form member as described in claim 4 in which said support
portion has an upper surface concave in configuration, each of the
arms of said L-shaped portions of said positioning members that are
integrally attached to said support portion are convergently
disposed one to the other in a direction proceeding from said
support portion toward the arms disposed generally parallel with
said support portion, and each free end of the arms that are
disposed generally parallel with said support portion includes a
portion disposed generally normal to the longitudinal axis of its
corresponding arm, said normally disposed portion being positioned
within a corresponding one of said longitudinally extending
U-shaped portions of said channel-shaped member.
6. A pretensioned concrete joist of the T-type comprising:
a. a concrete plate-like body portion;
b. a channel-shaped concrete support ledge disposed normal to said
body portion along the length thereof, said ledge having a bottom
surface and opposed side walls;
c. a nailing strip integrally molded in the bottom of said ledge,
said strip comprising
1. a channel-shaped member having (i) a bottom wall disposed along
the bottom surface of said ledge, (ii) a pair of side walls each of
which has a longitudinally extending upper edge, (iii) a
longitudinally extending U-shaped portion formed along the upper
edge of each side wall, the longitudinal axis of each U-shaped
portion lying in a plane disposed generally parallel with a plane
in which is disposed said bottom wall, the bight of each U-shaped
portion extending inwardly of its associated side wall, and (iv) a
longitudinally extending, attachment-means-penetrating layer of
material disposed within said channel shaped member, said layer of
material having a lower surface portion disposed in contact with
the bottom wall of said channel-shaped member and upper surface
portions disposed in abutting contact with said U-shaped portions
of said channel-shaped member, said attachment-means-penetrating
layer of material preventing concrete from entering into said
channel-shaped member, and
2. a plurality of positioning members longitudinally spaced along
said channel-shaped member and disposed within the U-shaped
portions thereof, each positioning member comprising (i) an
inverted U-shaped frame member including a bight portion and a pair
of leg portions, the outer surface of said bight portion being
generally concave in configuration, said frame portion lying in a
plane disposed generally normal to the longitudinal axis of said
channel-shaped member, (ii) a pair of legs, each leg having a first
part attached to the corresponding one of the leg portions of said
U-shaped frame member and a second part securely disposed within
one of the U-shaped portions of said channel-shaped member, said
second parts lying in a plane disposed generally normal to the
plane in which is disposed said frame member, and (iii) the
distance separating the outer surfaces of said U-shaped frame
member being less than the distance separating the opposed walls of
said ledge whereby said outer surfaces are disposed adjacent the
inside surfaces of the opposed side walls of said ledge; and
d. pretensioning steel extending longitudinally of said ledge and
disposed in contacting engagement with the concave surface of the
frame members of said positioning members, said pretensioning steel
and said positioning members cooperating to secure and maintain the
nailing strip on the bottom surface of the ledge prior to and
during placing of the concrete during forming of said joist.
7. A pretensioned concrete joist as described in Claim 6 in which
the side walls of said channel-shaped member are convergently
disposed, taken in a direction proceeding along said side walls
toward said bottom wall, and each of the legs of said positioning
members includes an L-shaped configuration the first parts of said
legs lying in a plane in which is disposed said U-shaped frame
member.
8. A pretensioned concrete joist of the T-type comprising:
a. a concrete plate-like body portion;
b. a channel-shaped concrete support ledge disposed normal to said
body portion along the length thereof, said ledge having a bottom
surface and opposed side walls;
c. a nailing strip integrally molded in the bottom of said ledge,
said strip comprising
1. a channel-shaped member having (i) a bottom wall disposed along
the bottom surface of said ledge, (ii) a pair of side walls each of
which has a longitudinally extending upper edge, (iii) a
longitudinally extending U-shaped portion formed along the upper
edge of each side wall, the longitudinal axis of each U-shaped
portion lying in a plane disposed generally parallel with a plane
in which is disposed said bottom wall, the bight of each U-shaped
portion extending inwardly of its associated side wall, and (iv) a
longitudinally extending, attachment-means penetrating layer of
material disposed within said channel shaped member, said layer of
material having a lower surface portion disposed in contact with
the bottom wall of said channel-shaped member and upper surface
portions disposed in abutting contact with said U-shaped portions
of said channel-shaped member, said attachment-means-penetrating
layer of material preventing concrete from entering into said
channel-shaped member, and
2. a plurality of positioning members longitudinally spaced along
said channel-shaped member and disposed within the U-shaped portion
thereof, each positioning member comprising (i) an elongate support
portion, and (ii) a pair of L-shaped portions, each L-shaped
portion including a pair of arms, each L-shaped portion depending
from a corresponding one of the ends of said support portions and
having one of said arms disposed parallel with said support
portion, each L-shaped portion being constructed for limited
pivotal movement relative to said support portion, each free end of
the arms that are disposed generally parallel with said support
portion being positioned within a corresponding one of the
longitudinally extending U-shaped portions formed along the upper
edge of each side wall of said channel-shaped member; and
d. pretensioning steel extending longitudinally of said ledge and
disposed in contacting engagement with the upper surface of said
positioning members, said pretensioning steel and said positioning
members cooperating to secure and maintain the nailing strip on the
bottom surface of said ledge prior to and during placing of the
concrete during forming of said joist.
9. A pretensioned concrete joist as described in claim 8 in which
said elongate support portion has an upper surface concave in
configuration, each of the arms of said L-shaped portions of said
positioning members that are integrally attached to said support
portion are convergently disposed one to the other in a direction
proceeding from said support portion twoard the arms that are
disposed generally parallel with said support portion, and each
free end of the arms of said L-shaped portion that are disposed
generally parallel with said support portion includes a portion
disposed generally normal to the longitudinal axis of its
corresponding arm, said normally disposed portion being positioned
within a corresponding one of said longitudinally extending
U-shaped portions formed along the upper edge of each side wall of
said channel-shaped member.
Description
BACKGROUND OF THE INVENTION
Joists or structural beams of the T-type (as used herein the term
T-type shall also include twin T and quad T-types) are well known
in the art. The ledge or ledges of this type of joists contain the
main reinforcing of the structural member and act as the supporting
member from which the ceiling is suspended. In the past, various
expedients have been used to attach the wall or ceiling board to
the ends of the ledges of the joists. The most common expedient is
the use of the so-called "nailing strips" incorporated into the
ends of the ledges. The nailing strips are ordinarily mechanically
attached to the outside of a ledge as exemplified by the structure
shown in U.S. Pat. No. 2,123,923. They are adapted to reeive bolts,
screws, nails and the like to secure the wall board or other
structural element to the ledges. The nails or screws are driven or
screwed into a wooden beam, disposed behind the plate, after
passing through the nailing plate itself.
Various means have been used to affix the nailing plate to the end
of the ledges as shown in the above-referenced patent and in U.S.
Pat. No. 1,466,264, for example. Anchors for supporting structural
elements on the end of the ledges have been incorporated into the
ends of the ledges by various means as illustrated by U.S. Pat.
Nos. 1,251,150 and 1,953,138. Other patents relating generally to
the field of the invention are U.S. Pat. No. 1,470,727 and British
Pat. No. 838,452.
The known expedients for attaching nailing plates to the ends of
the ledges of T-type joists are subject to various disadvantages.
Wooden nailing plates are subject to shrinkage, rotting,
destruction by termites and the like so that they are not generally
satisfactory for permanent installations. The metal anchors, hooks
and the like are subject to the disadvantage, along with the wooden
nailing plates, that their installation is difficult and
time-consuming and, consequently, expensive.
Heretofore, various structural elements have been proposed which
have a fire rating of approximately two hours when tested with the
standard time-temperature curve established by the American
Standards for Testing Materials. However, any such structural
element incorporating therein a T-type joist and which has
successfully met this requirement involves the use of a T-type
joist requiring approximately twice as much concrete to form as
required in the structural element of this invention. More concrete
was required to form the prior art type of joist since either
thicker plate-like body portions and/or more massive ledges were
required in order to withstand the temperatures involved.
Accordingly, it is a principal object of this invention to provide
a novel structural element having a fire rating of approximately
two hours when tested with the standard time-temperature curve
established by the American Standards for Testing Materials,
particularly when tested under the unrestrained assembly
classification.
Another object of this invention is to provide a structural element
as aforeaid comprising one or more prestressed concrete joists,
each joist having a plate-like body portion forming at least a part
of a first side of said element, one or more integrally formed,
reinforced support ledges disposed normal to the plate-like body
portion, and a nailing strip integrally molded in the bottom of
each ledge, each nailing strip including a penetratable area formed
internally adjacent thereof, a plurality of sheets of material
disposed adjacent the ends of said ledges, each sheet being formed
from a material from the class consisting of gypsum or a mineral
fiber mixture, said sheets forming the second side of said element
and having a thickness equalling one-half inch or more, each sheet
of material forming at least one butt joint with an adjacent sheet
wherein said butt joint extends longitudinally along a portion of
one of said ledges, a plurality of channel-shaped members disposed
along each butt joint and intermediate said ledge portion and said
sheets, attachment means for attaching said channel-shaped member
to the nailing strips of said ledge portions, and additional
attachment means for attaching said sheets of material to said
nailing strips and said channel-shaped members, said additional
attachment means, channel-shaped members and nailing strips
cooperating to secure the sheets to said joist while preventing
undesirable distortion or warping thereof during the fire rating
test.
Another object of this invention is to provide a structural element
as aforesaid in which each of the additional attachment means used
to attach the sheets of material to the channel-shaped members
disposed along said butt joints is positioned a minimum ditance of
approximately one and one-fourth inches from the adjacent edge of
each sheet.
Another object of this invention is to provide a structural element
as aforedescribed in which each ledge of each joist has a
plate-like body portion associated therewith, each ledge being
disposed generally centrally of said associated therewith, each
ledge being disposed generally centrally of said associated part,
each associated part extending laterally of both sides of its
associated ledge, taken along a line disposed normal to the
longitudinal axis of its associated ledge to a point midway between
said associated ledge and an adjacent ledge or the end of said
plate-like body portion, whichever is the closer, the ratio of the
cross-sectional area of the part of said plate-like body portion
taken along a line disposed normal to the longitudinal axis of said
ledge, to the width of its associated ledge, said width of said
ledge being measureed along a line normal to the longitudinal axis
of said associated ledge at the line of intersection of said ledge
with said part, varying between approximately 7.5 to 10 inches, and
the ratio of the cross-sectional area of its associated part, taken
along a line disposed normal to the longitudinal axis of said
ledge, being equal to approximately 2 or less.
Another object of this invention is to provide a structural element
as aforesaid in which the ratio of the cross-sectional area of the
part of the plate-like body portion to the width of its associated
ledge varies between approximately 8 to 9 inches and the ratio of
the cross-sectional area of each ledge to each cross-sectional area
of its associated part is equal to approximately one or less.
Another object of this invention is to provide a pretensioned
concrete joist of T-type comprising a concrete plate-like body
portion, a channel-shaped concrete support ledge disposed normal to
said body portion along the length thereof, a nailing strip
integrally molded in the bottom of said ledge, said nailing strip
comprising a channel-shaped member, a longitudinally extending
U-shaped portion formed along the upper edge of each side wall of
each channel-shaped member with the longitudinal axis of each
U-shaped portion lying in a plane in which is disposed generally
parallel with the plane in which is disposed the bottom wall of
said channel-shaped member and the bight of each U-shaped portion
extending inwardly of its associated side wall, and a
longitudinally extending penetratable layer of material disposed
within said channel-shaped member and upper surface portions of
said channel-shaped member and having portions thereof disposed
within the U-shaped portions extending longitudinally along the
upper edge of each side wall of said channel-shaped member, and
pretensioning steel extending longitudinally of said ledge and
disposed in contacting engagement with the upper surface of said
positioning members, said pretensioning steel and said positioning
members cooperating to secure and maintain the nailing strip on the
bottom surface of the ledge prior to and during placing of the
concrete during forming of the joist.
Another object of this invention is to provide a pretensioned
concrete joist as aforedescribed in which each of said positioning
members comprises an elongate support portion, and a pair of
L-shaped portions each L-shaped portion including a pair of arms,
each L-shaped portion depending from a corresponding one of the
arms of said support portions and having one of said arms disposed
parallel with said support portion, each L-shaped portion being
contructed for limited pivotal movement relative to said support
portion, each free end of the arms that are disposed generally
parallel with said support portion being positioned within a
corresponding one of the longitudinally extending U-shaped portions
formed along the upper edge of each side wall of said
channel-shaped member
Another object of this invention is to provide a form member for
use with a mold for making a pretensioned concrete member having a
nailing strip molded therein, said form member comprising a
longitudinally extending, channel-shaped member for disposition in
the bottom of said mold member and a plurality of positioning
members longitudinally spaced along said channel-shaped member and
secured thereto.
Another object of this invention is to provide a novel positioning
member for positioning an object in a hollow member such as a mold
member, said positioning member being formed from a single piece of
plastic material and comprising an elongate support portion the
upper surface of which is concave in configuration, and a pair of
L-shaped portions, each L-shaped portion including a pair of arms,
each L-shaped portion depending from a corresponding one of the
ends of said support portions and having one of said arms disposed
parallel with said support portion, each L-shaped portion being
constructed for limited pivotal movement relative to said support
portion, and the free ends of said arms that are disposed generally
parallel with said support portion, lying generally in a common
plane and spaced apart one from the other, said free ends being
constructed for engaging a portion of the object.
Another object of this invention is to provide a novel positioning
member as aforesaid in which each of the arms of said L-shaped
portions that are integrally attached to said support portion are
convergently disposed one to the other in a direction proceeding
from said support portion toward the arms disposed generally
parallel with said support portion.
Another object of this invention is to provide a novel positioning
member as aforedescribed in which the angle of convergence of the
arms that are integrally attached to said support portion equals at
least approximately 4.degree. or more, and preferably approximately
6.degree..
Another object of this invention is to provide a novel positioning
member as aforedescribed in which the upper surface of said support
portion is concave in configuration.
Another object of this invention is to provide a novel positioning
member as aforedescribed including means interconnecting a portion
adjacent the free end of each arm disposed generally parallel with
said support portion thereby preventing undesirable entanglement of
one plastic member with another when packed "loosely" in a
contaier.
Another object of this invention is to provide a novel positioning
member including tab means extending longitudinally outwardly of
the opposite ends of said support portion and longitudinally
outwardly of the pair of arms disposed generally parallel with said
support portion.
Another object of this invention is to provide a novel positioning
member as aforedescribed in which each free end of each arm lying
genernally in a common plane includes a portion disposed generally
normal to the longitudinal axis of its corresponding arm and
likewise is disposed within said common plane.
Another object of this invention is to provide a novel positioning
member as aforedescribed in which each L-shaped portion includes
stiffening means for controlling the overall stiffness thereof
wherein said stiffening means preferably includes a diagonally
disposed member interconnecting the arms of each L-shaped
portion.
Another object of this invention is to provide a novel positioning
member as aforedescribed in which the outer ends of said support
portion and said L-shaped portions are connected by a pair of
convergently disposed lines proceeding along said lines in a
direction from each outer end of said support portion to the
corresponding outer end of said L-shaped portion.
SUMMARY OF THE INVENTION
A structural element having a fire rating of approximately two
hours when tested with the standard time-temperature curve
established by the American Standards for Testing Materials, said
element having first and second sides, said second side, during the
fire rating test of said element being exposed to flames, said
element comprising one or more prestressed concrete joists wherein
each joist has a plate-like body portion forming at least a part of
the first side of said element and one or more integrally formed,
reinforced support ledges disposed normal to the plate-like body
portion, each ledge having a nailing strip integrally molded at the
bottom thereof, each nailing strip including a penetratable area
formed internally adjacent thereof, a plurality of sheets of
material disposed adjacent the ends of said ledges, said sheets
being formed from a material selected from the class consisting of
gypsum or a mineral fiber mixture, said sheets forming the second
side of said element and having the thickness of said material
equaling one-half inch or more, each sheet forming at least one
butt joint with an adjacent sheet, said butt joint extending
longitudinally along a portion of one of said ledges, a plurality
of channel-shaped members, each channel-shaped member being
disposed along each butt joint and intermediate said ledge portions
and said sheets, and attachment means for attaching said channel
shaped members to the nailing strips of said ledge means and, also,
for attaching said sheets of material to said nailing strips and
said channel-shaped members, said attachement means, channel-shaped
members and nailing strips cooperating to secure the sheets to said
joist while preventing undesirable distortion or warping thereof
during the fire rating test. The channel-shaped members prevent the
edge of the sheet adjacent said butt joint from pulling away from
the adjacent sheet as a result of the stresses to which same is
subjected during the fire rating test. The pretensioned concrete
joist of the T-type includes a nailing strip integrally molded in
the bottom of said ledge, said nailing strip comprising a
channel-shaped member having longitudinally extending U-shaped
portions formed along the upper edge of each side wall of each
channel-shaped member, the longitudinal axis of each U-shaped
portion lying in a plane disposed generally parallel with a plane
in which is disposed a bottom wall of said channel-shaped member,
the bight of each U-shaped portion extending inwardly of its
associated side wall, and a longitudinally extending attachment
means-penetrating layer of material disposed within said
channel-shaped member, said layer of material having a lower
surface portion disposed in contact with the botton wall of said
channel-shaped member and upper surface portions disposed in
abutting contact with said U-shaped portions of said channel-shaped
member, said attachment-means-penetrating layer of material
preventing concrete from entering into said channel-shaped member,
and a plurality of positioning members longitudinally spaced along
said channel-shaped member and having portions thereof disposed
within the U-shaped portion thereof, and pretensioning steel
extending longitudinally of said ledge and disposed in contacting
engagement with the concave surface of the frame members of said
positioning members, said pretensioning steel and said positioning
members cooperating to secure and maintain the nailing strip on the
bottom surface of the ledge prior to and during placing of the
concrete during forming of said joist. The nailing strip includes a
channel-shaped member as aforedescribed and the plurality of
positioning members as aforedescribed.
One preferred embodiment of a novel positioning member is formed
from a single piece of plastic material and comprises an elongate
support portion and a pair of L-shaped portions, each L-shaped
portion including a pair of arms, each L-shaped portion depending
from a corresponding one of the ends of said support portion and
having one of said arms disposed generally parallel with said
support portion, each L-shaped portion being contructed for limited
pivotal movement relative to said support portion, and the free
ends of said arms, that are disposed generally parallel with said
support portion, lying generally in a common plane and spaced apart
one from the other, said free ends being constructed for engaging a
portion of the channel-shaped member with which same is to be
used.
Another embodiment of a positioning member useful in the form,
joist and structural element of this invention is a member
comprising an inverted U-shaped frame member including a bight
portion overlying the upper edges of the channel-shaped member of
the nailing strip and a pair of leg portions, the outer surface of
said bight portion being generally concave in configuration and
adapted to engage a pretensioning steel after the form member has
been positioned within the mold, said frame portion lying in a
plane disposed generally normal to the longitudinal axis of said
channel-shaped member, a pair of legs, each leg having a first part
attached to a corresponding one of the leg portions of the U-shaped
frame member and a second part securely disposed within a
corresponding one of the U-shaped portions of said channel-shaped
member of said nailing strip, said second parts lying in a plane
disposed generally normal to the plane in which is disposed said
frame member, the outer surfaces of said U-shaped frame member
being spaced such that they are adapted to be received between the
opposed walls of the mold in which same is to be used whereby said
outer surfaces of said leg portions serve as means for centering
and positioning said form member within the channel-shaped portion
of the mold in which same are to be used upon being dropped therein
and are adapted to be disposed adjacent the inside surfaces of the
opposed walls of the mold within which same are to be used.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the
accompanying drawings in which:
FIG. 1 is an end view of a T-type joist;
FIG. 2 is a partial cross section of the mold form in which a
T-type joist is molded;
FIG. 3 is a partial cross section of the end of one of the legs of
the mold of FIG. 2 showing the nailing strip and positioning member
supported in the leg section of the mold;
FIG. 4 is a view taken on lines 4--4 of FIG. 3;
FIG. 5 is a cross-sectional view of a portion of a structural
element constructed in accordance with the subject invention;
FIG. 6 is an elevational view of another embodiment of a structural
element constructed in accordance with the subject invention, said
element incorporating therein F-type joists;
FIG. 7 is a partial view showing the reflected ceiling plan of a
structural element constructed in accordance with this
invention;
FIG. 8 is a cross-sectional view of a portion of the structural
element illustrated in FIG. 7 and showing a butt joint;
FIG. 9 is a perspective view of a preferred embodiment of a
positioning member constructed in accordance with this
invention:
FIG. 10 is a front elevational view of the positioning member shown
in FIG. 9; and
FIG. 11 is a cross-sectional view taken on line 11-11 of FIG.
10.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown a structural element
constructed in accordance with the subject invention, said element
including an assembly of typical T-type joists 10 usually
constructed of prestressed reinforced concrete. Each joist
comprises a relatively thin concrete plate-like body portion 12
having integrally molded support ledges or ribs 14 that contain the
main reinforcing steel and the nailing strip or plate which
supports a sheet of material 16 forming the ceiling or wall board.
The sheet of material 16 is schematically shown attached to the
ends of the ledges 14. The two joists 10 are connected by a joint
17 filled with grout. The structural element also includes means
(not shown in FIG. 1) for satisfactorily attaching the sheet of
material 16 to the ends of the ledge 14.
Referring to FIG. 2, a mold form 18 is shown in which a typical
T-type joist shown in FIG. 1 is molded. The form 18 is comprised of
a body section 20 in which the plate-like body portion of the joist
is molded, and integral leg sections 22 in which the integral
ledges or ribs 14 are molded. The form 18 is conventionally
supported by means of gussets 24 and braces 26 suitably positioned
to support the mold 18 when concrete is poured into it. The
structure for supporting the mold forms no part of this
invention.
Referring to FIGS. 3 and 4, there is shown an assembly of nailing
strip and positioning member positioned inside the leg of the mold
prior to pouring concrete for molding a typical T-type joist and
molding a nailing strip in the support ledge thereof. The nailing
strip 28, suitably made of sheet metal, such as a 25 ga. hot dipped
galvanized sheet metal, extends the entire length of the leg 22 of
the mold. The nailing stip 28 is of channel-shaped construction, as
shown, with its base 30 resting on the inside or bottom surface of
the end of leg 22 and its open channel section facing upwardly. The
legs 22 are convergently formed, proceeding in a direction along
said legs toward the base 30, and this feature enhances the
securement of said nailing strip within the concrete after it has
set up. It includes sides 32 integrally connected to the base 30
and terminating at their upper ends in U-shaped sections 34 for a
purpose to be described later. The longitudinal axis of each of the
U-shaped sections 34 lie in a plane disposed generally parallel
with a plane in which is disposed the base or bottom wall 30. The
bight of each said U-shaped portion extends inwardly of its
associated side wall. The interior 36 of the channel-shaped nailing
strip 28, which is enclosed by the base 30 and the sides 32,
comprises a penetrable area into which nails, screw and the like
used to attach the sheet of material 16 to the base 30, penetrate.
In order to prevent the space 36 from filling with concrete when
the joist is molded, it is filled with a blocking material, such as
expanded polystyrene, which is preferably secured to said nailing
strip with contact cement. This prevents concrete from entering the
interior of the channel-shaped nailing strip and still provides a
penetrable area into which screws, nails and the like may penetrate
when a wall or ceiling board is attached to the base 30 of the
nailing strip.
In order to center properly the nailing strip 28 in the leg 22,
longitudinally spaced centering and hold down frames 38 are
attached to the nailing strip 30 and inserted in the end of the leg
22 with it. The positioning frames 38 are suitably constructed from
an elongated piece of material, such as metal wire, plastic and the
like, and comprise a rectangular frame member having sides 40
joined at the top by U-shaped bridge member 42 and comprising a
pair of legs having end members. Each leg has a first part 44
attached to a corresponding one of the sides 40 and extending
inwardly in the same plane as the bridge member 42. Each leg also
has a second part 46 extending perpendicular to the plane of the
frame 38 and disposed or seated in one of the U-shaped sections 34
of the nailing plate 28. This construction maintains the U-shaped
bridge member 42, the sides 40 and the end the first parts 44 of
said legs in a vertical plane, as viewed in FIGS. 3 and 4, and
precludes the necessity of forming notches or openings within the
sides 32 and eliminates the time and labor required for precise
positioning of said second parts 46 within any such openings. The
positioning and supporting frames 38 are so dimensioned that their
sides are disposed adjacent the inside surfaces of the sides of the
leg 22 to center the nailing plate 28. The bottom of the trough of
the U-shaped bridge member 42 is the point at which the
pretensioned reinforcing steel 15 exerts a downward force on the
positioning frame 38 which in turn exerts a downward and inward
locking force on the U-shaped channel 28. It has been found that
the application of a downwardly directed force by the steel 15
against members 42 causes the sides 40 to bow outwardly thereby
increasing the securement of the frames 38 within the U-shaped
sections 34.
The molding of a prestressed reinforced joist of the T-type in
accordance with the invention is performed as follows. The mold is
cleaned and conventional release agents are applied to the interior
thereof. The assembly of nailing strip 28 and its assembled
centering and hold down frames 38, with the channel-shaped nailing
strip 28 being filled with expanded polystyrene or suitable
material, is positioned in the end of leg 22 of the mold form 18.
Continuous reinforcing steel 15 is then positioned in the trough of
the bridge section 42 of the support frames 38 disposed in the
legs. The reinforcing steel 15 is then put under tension, thus
making it rigid and causing it to exert a downward force on the
frames 38. The mold form 18 is then filled with concrete which is
allowed to set properly. After the concrete is properly set, the
finished joist is removed from the mold. The ledges 14 of the joist
will have the nailing strip 28 integrally molded in the ends or
along the bottoms thereof, as well as the support frames 38 and the
reinforcing steel 15.
FIG. 5 shows a support ledge of the T-type joist of the invention
in which a ceiling or wall board element 50 is shown attached by
screws 52 to the base 30 of nailing plate 28 with the screws
penetrating into the penetrable area 36 and the penetrable material
therein.
In FIG. 6 is shown another, although generally less commonly used,
embodiment of a structural element constructed in accordance with
the subject invention. The structural element 54 comprises one or
more prestressed, concrete, F-type joists 56, one or more sheets of
material 58, and attachement means (not shown) for attaching the
sheet of material to the joist 56. Each joist 56 includes a
plate-like body portion 60 and one or more integrally formed,
reinforced support ledges 62 disposed normal to the plate-like body
portion 60. Each ledge 62 of the element 54 has a nailing strip
(not shown) integrally molded in the end thereof. Each ledge 62 of
the element 54 has a part of said plate-like body 60 associated
therewith, the length of each part being indicated generally by the
arrow 64, it being noted that each ledge 62 is disposed generally
centrally of its associated part, taken along a line disposed
normal to the longitudinal axis of said ledge. The rato of the
cross-sectional area of the part of said plate-like body portion,
taken along a line disposed normal to the longitudinal axis of said
ledge, to the width of its associated ledge, said width of said
ledge being measured along the line of intersection of the sides of
said ledge with the lower surface of the plate-like body portion,
varies between approximately 7.5 to 10 inches. Although a transfer
or preferably an arcuate surface may interconnect the ledges to the
body portion, the width of the ledge referred to herein is limited
to the distance between an extension of the sides of the ledge as
aforesaid. The ratio of the cross-sectional area of each ledge to
the cross-sectional area of its associated part, taken along a line
disposed normal to the longitudinal axis of said ledge, is equal to
approximately two or less, and preferably to approximately one or
less. The sheet of material 58 disposed adjacent the ends of the
ledges 62 is formed from a material selected from the class
consisting of gypsum or mineral-fiber mixture, said mixture being
non-combustible. The thickness of the material used to form the
sheet 58 equals approximately one-half inch or more and preferably
five-eigths inch or more where gypsum material is involved. It will
be understood that the flames are exposed to the sheet of material
58 during the fire rating test.
In FIG. 7 is shown a partial view of a structural element 68
constructed in accordance with this invention and having a fire
rating of approximately two hours when tested with the standard
time-temperature curve established by the American Standards for
Testing Materials where said element has an unrestrained
classification. More specifically, the structural element 68
comprises a pair of longitudinally extending prestressed concrete
joists 70 and 72. One of the joists 70 has four longitudinally
extending support ledges 74 while the other joist 72 has three
longitudinally extending support ledges 76. A grout joint (not
shown) similar to grout joint 17 shown in FIG. 1 interconnects the
adjacent sides of said joist 70 and 72. Each joist includes a
plate-like body portion forming at least a part of the first side
of said element 68. Each support ledge of each joist is integrally
formed with the plate-like body portion of each joist disposed
generally normal to said plate-like body portion. Each ledge is
suitably reinforced with pretensioned steel 78, see FIG. 8, and has
a nailing strip 80 integrally molded at the end or along the bottom
surface of each ledge. A layer of penetrable material 82 is
disposed within the channel-shaped member from which the nailing
strip 80 is constructed.
The element 68 includes a plurality of sheets of material 84, 86,
88, 90, 92, 94 and 96 attached to the ends or the bottom surfaces
of said ledges 72 and 74. Said sheets are formed from a material
selected from the class consisting of gypsum or a mineral fiber
mixture. The sheets of material form the second side of said
structural element 68 and the thickness of the material from which
said sheets are made equals one-half inch or more and preferably
five-eighths inches or more. Each sheet of material forms at least
one butt joint 98 with an adjacent sheet of material. The butt
joints 98 extend longitudinally along a portion of a corresponding
one of said ledges.
The structural element 68 also includes a plurality of
channel-shaped members 100, shown only in FIG. 8. The
channel-shaped members 100 are disposed along each butt joint 98
and intermediate said ledge portion and said sheets of material.
The channel-shaped member 100 is securely attached to the nailing
strip 80 of its associated ledge through the use of attachment
means 102 which extend through the bottom wall of the
channel-shaped member forming the nailing strip 80 and into the
penetrable layer of material 82. The bottom wall of the
channel-shaped member 100 extends laterally of the opposite sides
of the ledge by a sufficient amount to permit ready attachment of
the sheets of material to said channel-shaped member by attachment
means 104. For example, where the width of the bottom surface of
the ledge, as shown in FIG. 8, is approximately 3 to 3 1/4 inches,
the width of the bottom wall of the channel-shaped member 100 is
approximately 6 inches. The use of a 1 and 1/4 inches by 6 inches,
20 gauge hot dipped galvanized metal 54 inches in length to form
the channel-shaped member 100 has been found to be adequate. In
this connection, it must be realized that channel-shaped member 100
must be sufficiently rigid to prevent undesirable distortion of the
sheets of material attached thereto during the fire rating test
and, at the same time, to provide a minimum distance of
approximately 1 and 1/4 inches between the edges of the sheets of
material forming the butt joint 98 and the attachment means 104.
This insures that the edges of the sheets of material will not pull
away from the butt joint 98 during the fire rating test.
As shown in FIG. 8, a positioning member 108 formed from a single
piece of plastic material and also shown in greater detail in FIGS.
9-11, may be used in lieu of the positioning members or frames 38
as shown in FIGS. 2-5. The positioning member 108 is made from a
suitable plastic material such as polyethylene. The members are
spaced longitudinally along the channel-shaped member used to form
the nailing strip 80 by any suitable spacing such as approximately
4 feet apart. The member 108 comprises an elongate support portion
110 having an upper surface formed to position therein the
pretensioning steel 78. An upper surface concave in configuration
has been found to be a prefered configuration. The member 108 also
includes a pair of L-shaped portions 112. Each L-shaped portion 112
includes a pair of arms 114 and 116 with arm 114 being integrally
attached adjacent one end of the support portion 110 and generally
depending therefrom while the other arm 116 is disposed generally
parallel with the support portion 110. Each L-shaped portion 112 is
constructed for limited pivotal movement, approximately 3.degree.
to 8.degree., relative to said support portion, said pivotal
movement occuring in a plane in which is disposed said support
portion and said L-shaped portions. Each of the arms 114 of said
L-shaped portion that are integrally attached to said support
portion are convergently disposed one to the other, taken in a
direction proceeding away from said support portion 110 toward the
arms 116 that are disposed generally parallel with said support
portion. The angle of convergence of said arms 114 equals at least
approximately 4.degree. or more and preferably approximately
6.degree.. With the arms 114 being convergently formed as aforesaid
and the L-shaped portions being mounted for limited pivotal
movement relative to said support portion, it has been found that
upon application of a force downwardly against the upper surface of
the support portion 110 (such as occurs from contacting engagement
of the pretensioning steel 78 upon the support portion 110), the
L-shaped portions 112 will pivot a limited amount, depending in
part upon the amount of the applied force and the resistance
encountered by the channel-shaped member used to form the nailing
strip 80, when the member 108 is mounted upon the nailing strip 80.
A positioning member 108 constructed in this manner has been found
to be quite advantageous since the pretensioning steel 78, see FIG.
8, when positioned upon the upper surface of the support portion
110 provides a downwardly directed force thereagainst.
The free ends 118 of the arms 116 are constructed for engaging the
nailing strip 80 in a manner to secure the member 108 to said
nailing strip 80 as shown in FIG. 8. More specifically, as shown in
FIG. 8, the channel-shaped member used to form the nailing strip 80
includes a pair of side walls each of which has a longitudinally
extending U-shaped portion formed adjacent the upper edge thereof.
The longitudinal axis of each U-shaped portion lies in a plane
disposed generally parallel with a plane in which is disposed the
bottom wall of said channel-shaped member and the bight of said
U-shaped portion extends inwardly of its associated side wall.
Each L-shaped portion 112 includes stiffening means for controlling
the overall stiffness thereof. The stiffening means includes a
diagonally disposed member 120 having one end thereof integrally
attached to each of the arms 114 (below the pivot point) and 116.
The stiffening means may also include a rib 122 extending
longitudinally along the inner surface of each of the arms 114 from
the attachment of the member 120 to arm 114 down to the
intersection of arm 114 with arm 116 where same flares out by a
sufficient amount to provide increased rigidity of the intersection
itself.
The member 108 also includes means 124 interconnecting a portion
adjacent the free ends of each arm 116. The means 124 preferably
comprises a thin strip of plastic constructed as shown. The strip
of plastic is generally rectangular in cross-section and has its
largest dimension, when viewed in cross-section, disposed in a
plane disposed normal to the plane in which lies the support
portion 110 and the L-shaped portions 112. The means 124 prevents
undesirable entanglement of one plastic member with another when a
plurality of plastic members 108 are loosely packed in a container.
It will be noted that without the use of the means 124, each of the
free ends of the L-shaped portions 112 would function in the manner
of a hook thereby becoming intermixed with other members 108 which
would require some time on the part of the user to separate one
member 108 from another such member.
As shown in FIGS. 9-11, the member 108 may also include tab means
126 and 128 extending longitudinally outwardly of the opposite ends
of the support portion 110 and longitudinally outwardly of the pair
of arms 116. It will be understood that the member 108 may be
formed either with or without these tab means 126 and 128. The
purpose of the tab means is to permit the use of one size of member
108 within leg sections 22 having different widths without the
necessity of having separate molds for each member 108. The
formation of member 108 either with or without such tab means, as
aforesaid, is accomplished by means well known in the art of
forming plastic items.
When tab means 126 and 128 are formed on the member 108, said tab
means are preferably L-shaped, in plan form, as shown in FIG. 11.
The purpose for using this configuration is to provide increased
flexibility thereof adjacent the outer ends of the tab means
thereby minimizing the effects of tolerance differences in the
width of the leg sections 22 of various mold members 18.
The free end 118 of each of the arms 116 preferably includes a
portion or portions 130 disposed generally normal to the
longitudinal axis of the arm 116. The portions 130 are disposed
within the same plane within which lies the free ends 118 of the
arms 116. It will be understood that the portions 130 provide an
additional bearing area for the member 108 when the free ends 118
and the portions 130 are disposed within the bight of the U-shaped
portion formed along the upper edges of the side walls of the
channel-shaped member used to form the nailing strip 80.
The outer ends of the support portion 110 and the L-shaped portions
are preferably formed such that said outer ends are connected or
circumscribed by a pair of convergently disposed lines, taken in a
direction proceeding along said lines from said outer end of each
support portion to the corresponding outer end of each L-shaped
portion, such that the outer ends of said member 108 will be
readily accomodated by the convergently formed sides of the leg
sections 22 of the mold 18.
Although each of the positioning members described herein are
suitable for the intended purpose, it has been found that the
positioning member 108 formed from a plastic material is
advantageous under many applications since the surface portions
thereof are never coated with rust. Additionally, it has also been
found that the positioning member 108 is more readily attached to
the nailing trip than is the positioning member 38. Thus, at the
present time, the prefered embodiment for a positioning member is
considered to be that shown in FIGS. 9-11.
In order for a structural element constructed in accordance with
the subject invention to be used in certain applications, it must
have a fire rating classification of approximately two hours when
tested with the standard time-temperature curve established by the
American Standards for Testing Materials. Two tests made on a
structural element similar to that shown in FIGS. 1 and 7 (frame 38
having been used rather than member 108), one structural element
measuring approximately 9 feet long by 8 feet wide, the other
element measuring approximately 17 feet long by 14 feet wide, each
element containing one grout joint to connect two individual T-type
joists together, and the sheet of material 16 being formed from a
gypsum material having a thickness of approximately five-eights of
an inch, showed that such structural elements had a fire rating
classification of 2 hours, the first element above described
lasting 2 hours and 8 minutes before reaching a specified end point
in the test and the second above described element lasting two
hours and eleven minutes before reaching a specified end point in
the test. Based upon the known fact that each additional one-eighth
inch of gypsum material used is considered to extend by
approximately eight minutes the time that a structural element can
withstand the fire rating test as aforespecified and since the
above-referenced test exceeded the 2-hour period by 8 minutes, it
is concluded that a structural element constructed in accordance
with the subject invention and using a sheet of material formed
from gypsum in which the thickness of the gypsum is approximately
one-half inch or more would meet the fire rating test
requirement.
In view of the foregoing, it will be readily appreciated that a
novel structural element, concrete prestressed joists of either the
T-type or F-type (the terms F-type and T-type being generally used
interchangeably herein), form members for use with a mold for
making such joists, and positioning members have been described. It
is an advantage of the subject invention that the metal nailing
strip is securely embedded in the center of the end of the ledge
and flush with the surface of the concrete ledge, and that same
will not swell, rot, warp or the like. A nailing strip can be
readily incorporated into the ledges of the joist during molding
simply by dropping the assembly of nailing strip and supporting
frames in the ends of the mold sections in which the ledges are
molded. The use of the positioning member 38 or 108 insures that
the nailing strip is centrally positioned and is held down in
contact with the form surface. Through the use of suitabe
attachment means, the sheet of material will be securely anchored
to the ledges of the joist either directly or indirectly in the
case of attachment adjacent the butt joints. The number of parts
necessary to attach elements to the ledges of the joist is reduced
to a minimum. Precise position of the attachment means
longitudinally along the ledges is not a requirement since
attachment of the sheet of material to the nailing strip may be
effected anywhere therealong. A suitable leeway laterally of the
ledges is also permitted due to the width of the nailing strips.
The use of the nailing strip of this invention insures the
formation and retention of a penetrable area inside same into which
attachment means for structural elements can readily penetrate. The
filling material, which prevents concrete from entering the
interior of the nailing strip, serves the function of providing a
medium into which the attachment means for the element secured to
the nailing strip can penetrate. The cost of manufacturing a joist
in accordance with the subject invention has been substantiall
reduced since the amount of concrete required is approximately
one-half of that of prior art joists. For example, a joist
constructed in accordance with the subject invention from 150
pounds per cubic feet concrete and having the following dimensions
will weigh only approximately 35 pounds per square foot:
Thickness of the plate-like body portion 1 1/2" Width of joist 8'
Height of ledge 8 1/2" No. of ledges 4 Width of ledge measured at
intersection of an extension of the sides thereof with the bottom
ssurface of the plate- like body portion 4" Width at bottom of
ledge 3.25" Cross-sectional area of ledge 30.8 in..sup.2 Nailing
strip (includes 1/8" diameter U-shaped portion formed along upper
edge of side walls) 11/16" .times. 1 3/8", 25 ga. hot dipped galva-
nized metal Layer of penetrable material (expanded polyethylene)
1/2" .times. 1 3/8"
* * * * *