Strongback attachment system for concrete panel tilt-up construction

A fastener system for temporarily securing a reinforcing beam or the like to a poured concrete structural member includes an anchor to be set in poured concrete with an exposed handle portion free of said concrete, and a shaft with a slotted end for receiving the handle portion. A spring loaded pin in the slot retains the handle portion in interlocking engagement with the shaft. An opposite end of the shaft secures a strongback beam to the concrete structure.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention pertains generally to the field of poured or cast 
concrete construction and in particular pertains to devices used to attach 
so called strongback beams to horizontally cast panels prior to reinforce 
and preserve the panel against fracture or damage during tilt-up. 
State of the Prior Art 
A widely practiced technique for quickly erecting concrete structures 
involves the use of a previously finished floor of the building as the 
curing surface upon which new slabs or panels, to be used as wall 
components, are formed. The floor is covered with paper or other sheet 
material treated with a release agent which prevents adhesion of freshly 
poured concrete to either the sheet covering or the underlying floor. A 
suitable frame is assembled on the covered floor to define the margins or 
edges of the slab to be formed. Fresh concrete is then poured into the 
form to cast the wall panel. 
In typical construction, the floor used as the casting surface is quickly 
filled with new wall panels which must be erected in order to make space 
for the casting of more wall sections. The need to clear the working area 
precludes allowing the wall sections to cure the time necessary to achieve 
maximum strength. Consequently the wall sections must be tilted up into 
final erect position in a relatively fragile condition which necessitates 
that these panels be handled with considerable care and, in particular, 
that they not be subject to shock or excessive bending under their own 
weight as they are tilted from a horizontal to a vertical position. 
It is common practice in the industry to attach temporary reinforcements, 
known as "strongbacks", by which additional rigidity is provided during 
panel tilt up. At present, commonly used strongbacks involve heavy lumber 
or steel beams which are attached to the wall section by cumbersome 
hardware which requires time consuming installation. Because of the 
complexity of this operation, strongback installation must be planned and 
completed well in advance of the hoisting of the wall sections to their 
installed position, to avoid costly delays and disruptions in the 
construction schedule. 
For this reason, improvement is needed in strongback attachment devices and 
systems, to allow quick, easy and dependable attachment and detachment of 
strongback reinforcements in order to speed up the hoisting and 
installation of tilt-up precast concrete panels and similar construction 
techniques. 
SUMMARY OF THE INVENTION 
In response to the aforementioned needs, the present invention provides a 
simple, reliable and easy-to-use attachment system for temporarily 
securing a reinforcing beam, strongback or the like to a precast 
structural member, particularly in tilt-up concrete panel construction. 
The fastener system of this invention includes two main components which 
cooperate to facilitate quick and simple attachment and removal of 
strongback reinforcements to concrete tilt-up panels, so that the 
strongback installation can be carried out immediately prior to hoisting 
of the panel without significant delay or interference with the hoisting 
operation. The two components are an anchor insert which is set into the 
concrete panel, and a threaded shaft one end of which engages the insert. 
The anchor insert is made, for example, of heavy gauge steel wire, which is 
partially embedded in the concrete panel, leaving a portion of the insert 
accessible within a cavity defined in the panel by means of a disposable 
plastic void, which keeps the fluid concrete from fully encasing the 
insert. 
The threaded shaft is machined at one end to make a fastener head adapted 
to releasably engage the exposed portion of the embedded insert. The free 
end of the threaded shaft can be attached to a strongback beam by means of 
nuts or equivalent hardware. A strongback beam can be attached to a panel 
by means of two or more such shafts anchored to the panel along the length 
of the beam, and more than one strongback may be used for a single panel. 
The fastener head on the threaded shaft may be a press-in type fastener 
which interlocks with and engages the exposed portion of the anchor 
insert. The press-in fastener includes a diametric slot in the shaft end 
dimensioned to receive the exposed portion of the anchored insert, a pair 
of hook elements adjacent to the slot and oriented to engage the anchor 
insert by a twist of the shaft about its long axis, and a spring loaded 
pin which retains the anchor insert in engagement with the hook elements 
to avoid premature disengagement of the shaft from the anchor insert. The 
retaining pin is movable within an axial bore in the shaft and is biased 
by a spring captive within the bore. The hook elements may be machined 
integrally with the shaft by defining arcuate lateral slots communicating 
with diagonally opposite ends of the diametric slot. 
In a presently preferred form of the invention, the anchor insert is a 
frame assembled of welded metal rod, preferably made of three welded 
elements: a central U-shaped section and a spacer segment attached to each 
end of the central section for supporting the central U-shaped section in 
inverted upright position on the concrete pouring form or surface. A void 
element is used to cover the inverted U portion during pouring and setting 
of the concrete. Once the concrete is hardened, the void element is 
removed and discarded to expose the upper portion of the inverted U 
section of the anchor insert protruding in a cavity defined in the 
hardened concrete. This exposed portion of the insert presents a closed 
half loop of heavy wire or steel rod which can be engaged by the fastener 
head on the threaded shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
With reference to the attached drawings, FIG. 1 shows a concrete slab S 
with a plane top surface T. The slab S is in a horizontal position and is 
to be hoisted or tilted-up to a vertical installed position. In order to 
reinforce slab S during the hoisting operation a strongback B, which is an 
I-beam of aluminum or other suitable material, is secured against the 
surface T of the slab S to provide additional rigidity to the slab while 
it is tilted from a horizontal to a vertical condition. The strongback B 
is secured to slab S by means of fasteners each of which is generally 
designated by the numeral 10. Two fasteners 10 are shown spaced along the 
length of the beam B, although a greater number may be used for a 
particular beam, as may be needed. 
Each fastener 10 consists of three separate elements which together 
cooperate to secure the strongback B to the slab S. The three elements 
comprising the fastener assembly 10 are a threaded shaft 12 which is 
engaged at its lower end to an anchor insert 14 partially embedded in the 
slab S, and a nut 16 threaded onto the shaft 12 to hold the strongback B 
against slab surface T. The threaded shaft 12 passes through a hole in the 
strongback beam B so that a free end of the shaft 12 extends above the 
beam, and the nut 16 is threaded onto the free end and tightened against 
the beam to hold the latter against the slab S. 
Turning now to FIG. 2, the concrete slab S is shown in vertical section 
between its top surface T and a bottom surface F, and an anchor insert 14 
is set in the concrete mass of the slab. The anchor insert 14 is a frame 
assembled from heavy gauge steel wire or rod stock, and as better seen in 
FIGS. 3 and 4, includes a center section 16 bent into a U-shape, the ends 
of which are welded to two standoffs 18 such that the U-shaped portion is 
supported in a vertical plane transverse to the standoffs with the closed 
end of the U oriented upwardly. Each standoff 18 is a rod segment provided 
with plastic feet 20 at both ends, bent to a shallow, obtuse angle at its 
center, and welded to the center section 16 at the apex of its angle. The 
two standoffs thus provide four legs which support the inverted U-shaped 
center, and which anchor the exposed portion of the insert to the cast 
concrete slab. 
An insert 14 is placed on the bottom of the slab form at each location 
where a fastener 10 is to be attached to a strongback reinforcement B. A 
void form of suitable shape and configuration (not shown) is fitted over 
the handle shaped center section 16 so as to cover about the upper half of 
the inverted U portion, leaving exposed the remainder of the insert 14. 
Fluid concrete is then poured into the slab form to the desired thickness 
and allowed to harden. The void form is then pulled off the center section 
16, leaving a cavity or recess V in the top surface T of the slab S, as 
seen FIG. 2. The top of the U section 16 of the insert 14 is a rod section 
16a generally parallel to the slab casting surface and is exposed and 
accessible within the cavity V below the top surface T of the slab S, 
forming a half loop which is closed by the concrete bottom surface of the 
cavity V. 
The anchor insert 14 makes contact with the underlying casting surface, 
i.e. the floor which serves as the bottom of the concrete form, only at 
four points i.e. the four plastic feet 20. When embedded in concrete, the 
exposed metal surfaces of the standoffs 18 are encased by the concrete and 
only small portions of the plastic feet 20 appear at the slab surface F, 
as seen in FIG. 2. These small areas of exposed plastic are easily painted 
over and do not detract from the appearance or structural integrity of the 
slab of the surface F. Also, the plastic is inert and will not deteriorate 
significantly by exposure to the elements. The metal standoffs 18 are 
embedded deeper in the concrete and are consequently protected against 
corrosion, etc.. The cavity V is eventually filled, after installation of 
the panel S, with a suitable inert filler to likewise prevent 
deterioration of the portion of the insert 14 exposed in the cavity V. 
Turning now to FIGS. 5 and 6, the shaft 12 has a male thread 22 which 
terminates at an upper end 24 of the shaft. The lower end of the shaft has 
a cylindrical fastener head 26 which is machined integrally with the 
threaded portion of the shaft 12. A diametric slot 28 is cut into the 
lower end 30 and terminates in an end wall 32. The slot 28 divides the 
cylindrical head 26 into two prongs 34 with beveled end surfaces 36 which 
spread outwardly from the slot 28 in a V configuration for guiding the 
slot 28 into engagement with the center section 16 of the anchor insert 
14, as illustrated in FIG. 3. 
A cylindrical pin 40 is reciprocable within an axial blind bore 38 which 
opens in the end wall 32 of the diametric slot 28. The pin 40 has neck 42 
of reduced diameter and an end cap 44 which is of diameter equal to the 
pin 40. A set screw 46 is threaded into a radial bore 48. The set screw 46 
is advanced into the axial bore 28 short of contact with the neck 42, but 
into axial interference with both the end cap 44 and pin 40. The inner end 
of the set screw 46 thus acts to stop the pin 40 at an extended position, 
shown in FIGS. 5 and 6, where the end cap 44 is stopped against the set 
screw 46 and prevents the pin from leaving the bore 28. A coil spring 50 
is in compression between the blind end of the axial bore 38 and the end 
cap 44, urging the pin 40 into the diametric slot 28, to its extended 
position as shown in FIG. 6. 
The fastener head 26 also includes a pair of integral hook elements 52 
which are arranged on opposite sides of the diametric slot 28 and at 
opposite ends of the slot 28, in diagonally opposed relationship. Each 
hook 52 is defined by an arcuate lateral slot 54 which extends from the 
slot 28, first transversely to the shaft axis and then turns at a right 
angle to an axial direction towards the lower end 30 of the fastener head 
26. Each slot 54 defines a curved hook 52 which terminates in a point 56, 
which points along the axis of the shaft 12 towards its upper end 24, as 
shown in FIGS. 5, 6 and 7. The two lateral slots 54 together define a 
keyway which extends diametrically through the fastener head 26, at 
approximately 45 degrees to the diametric slot 28 in a plane transverse to 
the shaft axis, as best seen in FIG. 7. The widths of slot 28 and keyway 
52 are such as to closely receive the thickness of the rod or wire of the 
center section 16 of the insert anchor 14. 
Engagement of the fastener head 26 to the anchor insert 14 is shown in the 
sequence of FIGS. 3 and 4. The fastener head 26 is lowered into the cavity 
V in the slab S with the diametric slot 28 in alignment with the exposed 
horizontal portion 16a of the insert 14 which lies transverse to the shaft 
axis. The fastener head is pushed against the insert portion 16a until the 
pin 40 is driven back into the axial bore 38 against the urging of spring 
50, and the portion 16a makes contact with the end wall 32 of the slot 28. 
The shaft 12 is then turned clockwise about its axis, as indicated by the 
arrow in FIG. 4, to move the section 16a into longitudinal alignment with 
the keyway 54. At this point, the portion 16a is still in contact with the 
end wall 32 and overlyies in spaced relationship the keyway surface 
indicated by the numerals 54 in FIGS. 5 thru 7. Axial force is now 
withdrawn from the shaft 12, allowing the spring 50, acting through pin 
40, to move the insert section 16a into the bottom of the keyway 54. In 
actuality, the insert does not move, since it is set in the concrete slab; 
rather, the shaft 12 reacts to the bias of spring 50 and moves axially 
upwardly to bring the keyway surface against the insert section 16a. In an 
engaged condition of the shaft 12 with anchor insert 14 shown in FIGS. 1, 
2 and 4, the insert section 16a is retained captive within the keyway 54 
against accidental withdrawal therefrom by cooperation of the two hook 
elements 52 and retaining pin 40 under bias of spring 50. 
Engagement of the shaft 12 with the anchor insert 14 is therefore simple, 
rapid and secure. Many shafts 12 can be quickly attached to a concrete 
slab provided with a sufficient number of embedded anchor inserts 14, and 
the strongback beams then fastened by means of nuts 16 threaded onto the 
free ends of the shafts 12, as shown in FIG. 1. A number of strongback 
beams B can be quickly and reliably fastened to a concrete slab S just 
prior to tilting of the slab to its installed position, and once 
installed, the strongback B can be just as rapidly and easily detached by 
removing the nuts 16, and separating the strongback beams B from the slab 
S. Each shaft 12 is then pushed against the anchor insert 14 to depress 
the retaining pin 14 into the bore 38 and to lift the insert section 16a 
out of the keyway 54 and up against the end wall 32. The shaft 12 is then 
turned about its axis in a direction opposite to that indicated by the 
arrow in FIG. 4 to bring anchor section 16a alignment with the diametric 
slot 28. The shaft 12 can then be pulled up and away from the insert 14. 
The shaft 12 and nut 16 are recovered after such use. The anchor insert 14 
remains embedded in the concrete slab S. Each void or cavity V in the slab 
is then filled with a suitable filler material to create a smooth slab 
surface T and to prevent corrosion or deterioration of the metallic insert 
14, which could lead to discoloration and other damage of the concrete 
material. 
While a presently preferred embodiment of the invention has been described 
and illustrated for purposes of clarity and example, it must be understood 
that many changes, substitutions and modifications to the described 
embodiment will become apparent to those possessesed of ordinary skill in 
the art without departing from the scope and spirit of the present 
invention, which is defined by the following claims.