Note: Descriptions are shown in the official language in which they were submitted.
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BRIDGE DECK SYSTEM
Field of the ~nvention
This invention relates to a concrete and steel deck system used for bridge
super-structures supported by beams. More specifically, this invention relates to a
bridge deck system which utilizes the concept of post-tensioning in combination with
a unique deck section design to achieve a significant weight reduction in the bridge
deck and which provides adequate load carrying capacity.
Back~round of the Invention
The concrete slab reinforced by steel bars has been the most commonly used
type of bridge deck construction for highways. However, many of these highway
bridge decks have failed, because of the corrosion of the steel bars and the
int~ogration of the concrete. Concrete decks are susceptible to transverse cracking
and del~min~tion.
Concrete and steel structural combination bridge decks have been used for
many years in an attempt to overcome the disadvantage of the low tensile strength of
concrete and improve performance. Many of these concrete-steel composite bridge
decks include a steel grid which is filled and/or covered with concrete. Typically,
these decks use a large quantity of concrete which increases the m~t~ri~l cost and
weight of the deck. In addition, many of these bridge decks require reinforcing bars
or expanded metal to strengthen the concrete. While these reinforcing members may
help strengthen the concrete, they are also susceptible to corrosion which contributes
to structural failures.
It would be desirable to have a reduced-weight bridge deck which would have
excellent strength characteristics, a reduced tendency for cracking, and which would
be inexpensive to manufacture and assemble. In addition, it would be desirable to
have a bridge deck which does not require reinforcing bars. Further, it would beadvantageous if the bridge deck design was adaptable so that it could either be cast-in-
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place or made of precast panels.
Summarv of the Invention
It is an object of this invention to provide a concrete-steel deck system which
includes a number of adjacent sections or panels post-tensioned together to provide
a reduced-weight bridge deck of adequate strength.
It is another object of this invention to provide a concrete-steel deck system
which includes panels or sections having spaced parallel structural steel bars which
are longitudinal to the panels or sections and does not require a grid with structural
steel bars extending in both the transverse and longitudinal directions.
It is yet another object of this invention to provide a concrete-steel deck
system which does not require reinforcing bars or expanded metal to strengthen the
concrete.
Further, it is an object of this invention to provide a bridge deck inclu-ling aconcrete component having downwardly projecting protrusions. Structural ~uppoll
bars extending only longitudinally to bridge deck sections are partially embedded in
the concrete component. Post-tensioning ducts are oriented perpendicular to the
structural support bars, i.e., lateral to the bridge deck sections, and extend through
the concrete component. The post-tensioning ducts extend parallel to the downwardly
projecting protrusions. Post-tensioning tendons are located in the post-tensioning
ducts.
It is another object of this invention to provide a method of manl-f~l tllring abridge deck to be supported on beams. The method of manufacturing in~ lu(1es
prec~ting or casting-in-place deck panels or sections. The method includes
depositing concrete around structural support bars and post-tensioning ducts such that
the structural support bars and the post-tensioning ducts are embedded in the concrete
and that a lower portion of the deck panel or section includes downwardly e~ct~onlling
concrete formations and void sections free of concrete located between the
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formations. The post-tensioning ducts of adjacent deck panels are aligned and
structurally coupled to form continuous coaxial ducts. Tendon members are
positioned within the aligned ducts. The deck is post-tensioned after the concrete is
iUed to substantially cure.
These and other objects and features of the invention will be a~palent upon
consideration of the following detailed description of preferred embo-limrnt~ thereof,
presented in connection with the following drawings in which like reference numerals
identify like elements throughout.
Brief Des~ lion of the Drawin~s
Figure 1 is a general plan view of the post-tensioned structural support-
concrete bridge deck system of the present invention;
Figure 2 is a detailed plan view of the post-tensioned structural support-
concrete bridge deck system of Figure l;
Figure 3 is a vertical section taken through A-A of Figure 2;
Figure 4 is a vertical section taken through B-B of Figure 2;
Figure SA is a vertical section of a post-tensioning duct and structural
supporting bar connection; and
Figure 5B is a vertical section of an alternate embodiment of a post-tensioning
duct and structural supporting bar connection.
D~.;~ lion of the Preferred Embodiment
The deck of the present invention is depicted in Figure 1 and is generally
represented by reference numeral 10. The primary application of deck 10 is for, but
not restricted to, bridge super-structures including beams of structural steel, concrete
or wood.
Bridge deck 10 includes a plurality of longitudinally spaced panels or sections
12 which rest upon and transfer forces to structural beams 14. In the ~L~;f~l.ed
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embodiment, structural beams 14 extend parallel to the roadway. However, it is
possible to utilize the deck of the present invention with structural beams that extend
perpendicular to the roadway.
The plurality of panels or sections 12 includes an end panel or section 12e at
one end, at least one intermediate panel or section 12i, and an end panel or section
12e at the other end. As discussed in detail hereinafter, panels or sections 12 in~ de
provisions so that bridge deck 10 may be post-tensioned by post-tensioning devices
in the direction of arrows 15 to provide additional strength to deck 10.
As will be evident from the description hereinafter, the post-tensioning of deck10 yields many benefits. One such benefit is the ability to reduce the amount ofconcrete used in deck 10, since areas 17 on the lower portion of deck 10 are notfilled with concrete. The invention allows deck 10 to maintain adequate strengthwhile reducing material costs and weight. This necessarily reduces the dead loadforces transferred to structural beams 14.
As best depicted in Figures 2-4, each panel or section 12 includes a concrete
component 18 and a skeletal frame. Skeletal frame includes a plurality of spacedsteel structural support bars 16, schematically shown in Figure 2 by their center lines,
oriented substantially perpendicular to structural beams 14 and post-tensioning ducts
20 which extend through and are oriented perpendicular to structural support bars 16.
To form skeletal frame, structural support bars 16 include holes 22 therein
permitting the insertion of post-tensioning ducts 20 perpendicular thereto. Post-
tensioning ducts 20 may be made of plastic or metal and are attached to structural
support bars 16 by a suitable method. For example, if ducts 20 are metal, they may
be welded to structural support bars 16, as shown in Figure SA. Another suitablemethod for attaching ducts 20 to bars 16 is to configure holes 22 to be web slotted
and crimped, as shown in Figure SB, so that a mechanical fit is achieved when duct
20 is inserted therein. These attachment methods are merely illustrative and those
skilled in the art will recognize other methods and devices for ~tt~c~hing ducts 20 to
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structural support bars 16.
Post-tensioning ducts 20 of adjacent sections 12 are coupled together to form
continuous coaxial ducts which extend between both end sections 12e. Ducts 20 are
coupled by a suitable coupling device, schematically indicated in Figure 3 by
reference numeral 24. Coupling device 24 can take the form of duct tape and/or apipe section which has an interior diameter slightly larger than the exterior diameter
of ducts 20. Howeverj other appropriate methods or devices
could also be used. It is preferable that any coupling device 24 create a waterproof
seal which prevents water or concrete from entering the interior of duct 20.
Concrete component 18 is shaped in a manner which results in deck 10 having
a ~ignific~nt weight reduction over other bridge decks. Instead of a continuous thick
or high profile slab, concrete component 18 includes a smaller profile or thickn~
26 throughout a significant portion of the deck 10 and inclu(les h~llnch~-s or
downwardly depending protrusions 28 in other areas of deck 10. The elimin~tion of
concrete in the areas 17 between downwardly extending protrusions 28 amounts to
a significant weight reduction and a significant reduction of dead load forces. For
example, many existing bridge decks weigh up to, or in excess of, 100-pounds persquare foot while bridge deck 10 of the present invention weighs appro~imately 56-
pounds per square foot.
To support concrete component 18 during the manufacturing process,
structural support bars 16 include an intermediate section 30 having outwardly
ext.onding lips 32. Lips 32 provide a supporting surface for pans 34 which are
inserted between adjacent structural support bars 16 for providing a lower supporting
surface for concrete component 18 until it cures. While, pans 34 are shaped to form
the lower contour of concrete component 18, including downwardly depending
protrusions 28, one in the art would recognize that other supporting elemP~nt~ and
techniques could be used to support concrete component 18 until it cures.
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--6--
Structural support bar 16 also includes a lower horizontal section 36 and an
upper section 38. Upper section 38 extends laterally outward from intermt~Ai~ttosection 30 and includes lower horizontal surfaces 40. When concrete component 18is poured, concrete extends under lower horizontal surfaces 40, and upon curing,forms a mechanical lock to prevent vertical separation between concrete component
18 and structural support bar 16.
To post-tension deck 10, tendons 42 which may be high strength steel wires,
strands, rods, or other highly stressable elements, are positioned within post-
tensioning ducts 20. Tendons 42 are tightened, as described hereinafter, so that an
already hardened concrete component 18 is pre-compressed. The ends of tendons 42are anchored to post-tensioning anchorage elements 44. During the post-tensioning,
deck 10 also shortens with respect to structural beams 14 because of the stressing of
tendons 42. The post-tensioning prevents transverse, i.e., transverse to beams 14,
cracking of concrete component 18. The post-tensioning also elimin~tes the neces~ity
for shear connectors between bars 16 and concrete component 18.
Deck 10 is also mechanically connected to structural beams 14 to transfer
shear forces thereto. Connectors 46 are affixed to beams 14 and vertical slots or
holes 48 in concrete component 18 should accommodate connectors 46. During a
secondary operation, after deck 10 has been post-tensioned, holes 48 are filled by
concrete to provide a mechanical lock between beam 14 and concrete component 18,via connectors 46. The type, number, and placement of connectors 46 can vary
according to the size of bridge deck 10, spacing and m~tPn~l of beams 14, and
numerous other factors. If desired, seals 50 may be placed between beam 14 and
concrete component 18 to prevent the egress of concrete during this secondary
operation.
To maximize the performance of deck 10, the prestressing force should be
evenly distributed as much as possible along the width of the deck. This requires an
end-zone area 52 of solid concrete with applop~iate length and reinforcement. Deck
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10 is most economical when the number of end zone areas 52 is kept to two. For
multi-span structures, this results in a preference for continuous struetures and
ninterrupted decks.
Deck 10 has the capability of being assembled with precast panels 12 or
manufactured with sections 12 cast-in-place. If it is desired to manufacture deck 10
from precast panels, two end panels 12e and the required number of interme~ t~
panels 12i are typically formed off-site. Panels 12 are formed by first assembling
a skeletal unit. Structural support bars 16 are cut to a length preferably equal to the
width of the bridge. Bars 16 are bored or stamped creating holes 22 to receive the
post-tensioning ducts 20 and are bent to accommodate the vertical ~ nm-ont of the
deek, if necessary. Ducts 20 cut into lengths equal to the width of panel 12 are then
mechanically attached to structural support bars 16 in a manner previously clesçrihe~i
The duct-structural support bar connection should be reasonably rigid to hold until the
concrete is poured and subsequently cures. Once the concrete has cured, the
conneetion has no further structural purpose. Pans 34 are positioned on lips 32 of
bars 16 and concrete is poured thereon.
Precast panels 12 are then transported to the site and are arranged on
structural beams 14 with ducts 20 of adjacent panels in horizontal ~lignment and with
shear connectors 46 and vertical holes 48 in vertical alignment. Ducts 20 are then
coupled. Post-tensioning tendons 42 are inserted through the continuous ducts 20.
Concrete or grout is poured in a keyway, not shown, located between ~ ent panels12 and is permitted to substantially cure. Upon substantial curing of the concrete,
tendons 42 are tightened and anchored to end panels 12e via post-tensioning
anchorage elements 44. Then holes 48 are filled with concrete or grout.
If it is desired to form bridge deck 10 using panels with a east-in-plaee
eonstruetion, a number of skeletal units are formed off-site, as described above. If
the length of structural support bars 16 either exceeds 6Q.0-feet or is eurtailed by
transportation regulations, field splicing of the bars should be considered. The duet-
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structural support bar connection should be reasonably rigid and should hold during
transportation and construction, however, as previously described, once the concrete
has cured, the connection has no further structural purpose. The çstim~t~d weight of
a 60.0-feet x 8.5-feet steel skeletal unit is 3,400-pounds, thus easily transportable by
trucks.
The skeletal units are positioned on the beams with the help of inorganic
shims, then the duct-ends are coupled by either duct-taping or other ap~ropliatemethod. Pans 34 are placed on lips 32 to support concrete to be poured and to form
downwardly projecting protrusions 28. Next the concrete is poured and vertical edges
of concrete component 18 are formed at the sides, in end-zone areas 52, and overbeams 14.
The concrete strength should preferably be at least 4,500-pounds per square
inch at 28 days, although the hard-pack overlay is known to produce easily 6,000-
pounds per square inch in three days. The concrete should preferably be wet-cured
for 72-hours and protected by plastic cover for another 120 hours to reduce
$hr-nk~ge During the curing period the post-tensioning tendons 42 can be pulled in
and ~r~aled for stressing. During and because of the post-tensioning, the deck
shortens and moves with respect to the beams. If time permits the tendons may berestressed to reduce effective shrinkage and creep.
The top edges of the beams are sealed by seals 50, as shown in Figure 4.
Prior to pouring the secondary concrete, the vertical edges of the primary concrete
at holes 48 should be preferably smeared with a sand-cement slurry of al,pr~ iate
mix. The secondary concrete should be cured in a manner similar to the primary
concrete. Grinding of the concrete surface in the vicinity of the interface between the
primary and secondary concretes may be required
Due to strength of deck 10 achieved by post-tensioning, concrete col"ponent
18 does not require reinforcing bars. Specifically, concrete component 18 is void of
reinforcing bars above a horizontal plane defined by the top surfaces 54 of structural
-
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support bars 16, which is where many existing decks position reinforcing bars.
While particular embodiments of the invention have been shown and
described, it is recognized that various modifications thereof will occur to those
skilled in the art. Therefore, the scope of the herein-described invention shall be
limited solely by the claims appended hereto.
