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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to the field of prefabricated structural
members and, specifically, to structural slabs which are used as surface
and bridge deckings that are attachable to, and removable from structural
inposts and supports such as steel beams or girders. The methods and
articles of this invention include methods for prefabricating slabs, the
articles themselves containing novel attachment means, and methods for
acquiring a physical coupling of these slabs to supporting beams or
girders.
2. Description of the Background and Relevant Art
It has been common in the road and bridge construction industry to build
roadway surfaces and bridges by use of (concrete) deck slabs that have
been cast in situ and are used to span, and are supported by, other
structural steel or concrete supports girders. Improvement to the above
method has been had by attaching the slabs in a manner by which they
cooperate structurally with the supporting members. This improvement is
termed "composite construction" and has proven to increase the efficiency
and effectiveness of the supporting members. The cast in situ method of
bridge deck construction, with all of its advantages, carries with it some
significant disadvantages. One such disadvantage is that the method
requires a great deal of time in order to build forms, pour and cure the
concrete. Another obvious disadvantage is that field conditions such as
inclement weather, make it difficult to achieve a high degree of quality,
durability and expediency.
Precast concrete slabs have long been viewed as desirable elements to use
in bridge deck construction. Such slabs are generally prefabricated
off-site, under factory controlled conditions, and result in the
production of high quality concrete decks. Since they may be generally
produced well in advance of the use requirement, they may be stock-piled
and prepositioned at the site of construction. During actual
roadway/bridge construction with the precast concrete slabs, traffic time
is interrupted only for a relatively short period while the deck units are
placed into position.
Slab interconnection does not prove as great a problem as connection of the
slab to the underlying structure. Where the slabs or deck portions (if
gratings rather than slabs are used) have had extensions or protrusions
from the margins thereof, connection means are not a problem. As early as
1939, U.S. Pat. No. 2,162,742, was issued to H. Nagin for a flooring
construction. Nagin taught a metal grid structure which was used as deck
surface for a bridge. He showed the use of (elongate) thin metal (strips)
plates to construct a form for a grout receiving region atop an underlying
girder. Although it did not appear to be Nagin's intent to provide a form
for grout which would effect actual connection between the deck sections,
his formation of a grout receiving area presaged the modern use of grout
to provide support and mechanical coupling between deck slabs or gratings
and the supporting structure. Further to Nagin's credit was the use of
metal strips, slotted to fit between grid stringers, to form the sides of
the grout receiving mold. The strips are held by friction and thus are not
rigidly attached (nor attachable), to the grid or deck. Unfortunately,
Nagin went no further with the grout form of his disclosure and it would
appear to have little application to today's precast concrete or composite
slab. Further, the Nagin grouting concept did not entertain use of the
grout as a support for the deck system and a means for securing the deck
slabs to the underlying support structure. Thus, a cost-effective,
structurally sound and versatile method of attaching slabs to supporting
members has been a long-sought goal in the construction industry.
Many methods of attachment have been devised for securing bridge deck
slabs, in particular, to underlying support structures. These methods
range from simply bolting the slabs to the girders to more sophisticated
welded type connectors. King, in U.S. Pat. No. 4,977,636 teaches a bridge
support system in which a cap member is used in combination with a
temporary base support surface to form an enclosed area between a bridge
deck and a support column. The enclosed region inwardly receives
reinforcing rods and is eventually filled with concrete as it is poured
over the deck structure. Thus, the deck structure or slab members are
actually an underlayment and would not themselves serve as a
traffic-contacting road surface. Yet, the King teaching clearly provides a
non-adjustable haunch region that is a corollary of the earlier Nagin art.
In this instance, however, the original deck slabs (underlayment) are
physically coupled to their supporting structure and each other by a
continuous concrete extension of the roadway surface. Significant
disadvantages are realized in the King embodiment in that: firstly, a
special support surface form must be constructed to receive the concrete;
and secondly, some of the support surface must be removed thereafter.
A patent issued to Slaw, Sr., U.S. Pat. No. 4,972,537, disclosed, in late
1990, a composite prefabricated deck panel and a method of construction
therefor. Slaw, Sr. discloses the use of metal connecting rods to secure
prefabricated deck panels to an underlying support structure. Haunch type
enclosed areas are formed between the underside of the panels and the top
of each of several girder support members. Located within each enclosed
area is a plurality of metal connectors. Once the panels are properly
positioned, grout is pumped into the enclosed areas to permanently secure
the panels to the support members. According to the Slaw, Sr. teaching,
the sides are preformed in the deck sections and rest atop a girder with a
flexible seal therebetween. Nonadjustable, preformed concrete shoulders
serve as the sides of a haunch mold and depend from the deck panels
proper. As in the case of King, Slaw, Sr. does not provide, in the
prefabricated panels, a means for acquiring an adjustable haunch mold.
Instead, the aforesaid concrete shoulders rest ontop the supporting girder
or beam and require a seal therebetween in order to ensure containment of
the grout that is to be pumped into the haunch region.
Final to this discussion of relevant art is the patent issued to Eskew et
al. in mid 1991, U.S. Pat. No. 5,025,522. Essentially, these patentees
teach a bridge deck panel support system and method for supporting precast
bridge deck panels on a bridge girder. The deck panels are initially
supported through a grout layer that is located between the bottom of the
panel and the top of the structural support member. An elongate anchor
plate atop, and partially girdling, the beam top surface bears an
ascending flange, termed "a plate", by Eskew et al., and which, on each
side thereof, anchors a grade bar. A continuous seal between the grade bar
completes, with a grout filler (placed between the bar and beam), an
enclosure or haunch region that is to be filled with concrete. An
alternate embodiment eliminates the grade bar and uses the ascending plate
or flange member only. Once the panel members have been properly
positioned, they rest on a seal means placed between (preferably) the
grade bar and the undersurface of the panels. Concrete from an overlay
then fills the enclosed (haunch) area between the adjacent plate members
and their support. As with the preceding art, a most notable disadvantage
of the Eskew et al. teaching is the lack of an easily made mold or form
that may be used to create a haunch region that is defined by the top
surface of the support member (girder), adjustable form sides and the
overlaying and haunch filling with concrete.
Some of the aforesaid attachment methods have been successful from an
attachment standpoint, but most, if not all, methods have failed to
provide a method of attachment which allows the top or the bottom of the
panel to be attached to match a predetermined grade or elevation. To
compensate for this deficiency, a concrete topping is generally poured
over the slab to provide a uniform surface which meets predetermined grade
and elevation requirements. This cast in situ topping requires a
significant amount of cure time before the structure may be used.
Additional to the aforementioned grading problem, most of the previous
attachment methods have also failed to allow the slab and structural
support member to act cooperatively as a composite structure. Some methods
do achieve partial composite action, as may be seen in the discussion of
relevant art; but, they fail to adequately convince bridge construction
engineers that full composite action is developed. In compensation for
this deficiency, larger structural support members are currently being
used. Still, a further disadvantage of presently used support systems is
recognized in relation to the structural supporting members themselves.
These members deflect significantly when loads are placed upon them and
their final geometry is not realized until all of the precast slabs are
situated in final position. Thus, the top surface of the structural
supporting members, and therefore the surface of the tops of all of the
slabs, is not defined until all of the slabs have been placed on the
structural members. I am unaware of any modern and reliable system that
offers postplacement adjustment of the tops of the slabs (roadway surface)
to the proper elevation.
SUMMARY OF THE INVENTION
I have overcome the aforementioned disadvantages by providing an improved
method for attaching precast slabs to supporting structural members, a
system which is cost effective and easy to use. The slab subsystem is
precast, easily attached and provides positive composite action in
conjunction with the support subsystem. Discrete precast slabs are easily
adjustable to the correct (desired) elevation before it is finally
fastened in place by a coupling to a support member and/or an adjacent
slab; and, when the time comes to replace the slabs, or a discrete slab,
my system allows for easy slab removal from the supporting structural
member(s).
Slabs are individually precast, away from the assembly site, preferably in
a rectangular or square shape and upside-down relative to the finished
orientation in a bridge or roadway structure. Various reinforcement bars
and brackets may be used so as to effect the placement of at least one
adjusting screw in each corner of the generally rectangular shaped slab.
On the underside of each slab (upper surface during the molding or casting
procedure), there is disposed a strip-like region running transverse the
slab from one margin to the opposite margin. This region is demarcated by
either two rows of bolt holes or a set of slotted voids running parallel
to each other between the aforesaid margins. Two elongate, right-angled,
"L" shaped plates are bolt-mounted in the parallel slots or bolt holes so
that the shorter (if any) leg of the plates are mounted flush to the
underside surface of the slab and oriented outwardly of the demarcated
region. Further, these surface-mounted legs are transversely slotted so
that the plates may be adjusted inwardly and outwardly of the same region.
The longer legs of the plates depend perpendicularly downward of the slab
underside and are parallel to each other, forming with the surface of the
slab a three sided form or containment geometry. Final to the slab
definition, there are encasted also a plurality of protruding mechanisms
that depend downwardly of the slab (in proper, operational orientation)
and that are exposed within the aforementioned region, which I define as a
haunch (which is the shoulder portion of an arch or cap located
principally between the apex and the inpost regions).
The support beams or principal supporting structure which is used with my
improved slab geometry is conventional and otherwise unremarkable. Mostly
of the I-beam type, there is the requirement that such support surfaces
have protruding (vertically) upward, from the top contact surface, a
plurality of studs. These studs are conventional and are generally
installed in the field. Irrespective of the situs of installation, their
placement must be such as to not interfere with the encasted protrusions
from the slab at the haunch area, when the slab is superposed over the
support structure top, which is encircled by the haunch plates. Once this
posture is effected, the haunch becomes totally and peripherally enclosed
and the only ingress thereto/from is through a series of orifices in the
slab which pass from the slab top surface through to the underside, and
into the haunch region. It is through these orifices that grout, under
considerable pressure, is forced into the haunches so that, upon
solidification of the grout, a rigid and permanent mechanical coupling is
effected between the slab and the support structure via the encasted slab
protrusions and the projecting support surface studs. The grout filled
haunch also provides a firmament between one or more slabs and the support
structure to effect the aforesaid positive composite action of the total
system.
Before the grout is actually inserted to complete the finished system,
individual slabs may be adjusted by turning the adjusting screws so as to
obtain a uniform deck or roadway surface. Adjusting bolts or screws are
not new to this construction industry; however, to my knowledge they have
not been used before in the combination that I employ in my slab
subsystem. These bolts/screws allow all of the dead load of the slabs to
be placed on the girders before final adjustment for grade. This means the
surface and orientation of the slab attained at adjustment time will be
the same surface existing in the final product. After the grout has fully
cured throughout the system, the leveling screws/bolts may be removed and
the remaining holes filled with fresh grout. Thereafter, if desired, an
overlayment of another surface such as asphalt, concrete or other
composition may be made.
As the reader may now deduce, my method for connecting precast slabs to a
support structure is a considerable improvement over current techniques.
It comprises the steps of preparing a slab by precasting it, generally
topside-down so that the denser aggregates will accumulate over the
operational topside region of the slab, encasting, by the slab pouring,
the aforementioned projections and the haunch-forming adjustable plate
adjusting and capturing mechanisms, positioning the slab relative to a
girder, so that the slab haunch region superposes and partially encircles
the girder top surface, leveling the slab as desired by use of the
included adjusting screws and finally filling the haunch region with a
grout by passing the grout through several orifices in the slab which
communicate with the haunch region. Closure of haunch ends is done by
conventional form-making.
Having presented this general overview of the bridge deck replacement
system, the reader is referred to the following description of drawings
and system details for further instruction in my invention.
BRIEF DESCRIPTION OF THE DRAWINGS
Of the Drawings:
FIG. 1 is an isometric illustration of the basic components of the bridge
deck replacement system;
FIG. 2 is a cross section of the detailed area encircled in FIG. 1;
FIG. 3 is a cross sectional illustration of adjustable screw supports
located at the end of a slab;
FIG. 4 is a slab joint detail illustration;
FIG. 5 is a cross sectional illustration of depicting the haunch and
adjusting screws;
FIG. 6 is a cross sectional illustration of the basic invention-slab,
joined to girder by use of slab protrusion and anchor studs in the haunch
grout;
FIG. 7 is an elevational cross-section of the FIG. 6 embodiment;
FIG. 8 is a cross-sectional illustration of yet another slab-encasted
protrusion and the completed haunch area;
FIG. 9 is a elevational cross-section of the FIG. 8 embodiment;
FIG. 10 is a cross-sectional illustration of the FIG. 8 embodiment, absent
heads on the slab protrusions to facilitate easy removal of the slab; and
FIG. 11 is an elevational cross-section of the FIG. 10 embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring particularly to FIG. 1, several salient elements of the invention
10 are depicted in isometric illustration. Most prominently featured are
the girders 12, representative of an underlying supporting structure,
slabs 14 and grouted haunches 16 disposed between the slabs 14 and the top
surfaces of the girders 12. Ascending vertically from the girder top
surface of the furthermost structural member is a series of short
projections, termed bolts 18. Descending from the underside of the slabs
14 are many of (prospective) grout-engaging devices 24, herein a slab
encased reinforcing bar which protrudes from the underside of the slab as
a hook or U-shaped device. Greater detail 20 of the aforesaid devices is
depicted in FIG. 2. Of FIG. 2: it is representative of the detail 20 in
FIG. 1 and depicts in cross-section, the slab 14, the hook or U-shaped
protrusion 24, the grout haunch 16, as it encases the hook 24, and the
girder's 12 ascending projections/bolts 18. As mentioned earlier, I prefer
to cast concrete slabs, or any compositional slab, in the upside-down or
topside-down mold orientation because the denser aggregate tends to
accumulate in the region that will later serve as the upper or
traffic-contacting surface of the slab. Although an overlayment such as
asphalt is oftentimes desired, my invention deals conceptually with the
use of the finished slab 14 as the exposed, traffic-contacting surface.
Such a usage certainly facilitates discrete removal of slabs for bridge
deck or roadway repair.
Details not discernable in the preceding drawings are now depicted in FIG.
3 et. seg. More particularly, at FIG. 3, there is depicted two abutting
slab margins or ends equipped with adjustable screw support mechanisms
26/28. Mounting brackets 26 are deeply embedded in the slab 14 and the
adjuster screws or bolts 28 are located at the extreme projecting end of
the brackets 26. As may be seen in this illustration, the slab weight, on
a support, is borne by the screws 28. The use of such adjusting screws is
known in the industry, however, and the most salient factors seen in FIG.
3 comprise the elements 26,29,30,32, which create or establish the mold in
which the invention's haunch 16 will be formed. As mentioned in the
preceding Summary, the haunch is a grout casting which serves to join the
slabs to the support structure by acting as a physical coupling mechanism
between the two subsystems (deck slabs and supporting structure). It is
this coupling that effects the desired composite action of which I spoke
earlier in this disclosure. Thus, in FIG. 3, slab-peculiar elements are
detailed: parallel slots or anchor holes 30 are formed in the underside of
the slab into which will be fitted a plurality of bolts 32. The bolts have
the function of fixedly securing haunch mold sides, i.e., angle irons 29
which run parallel and (in this instance) flush with the edges of slabs
14, along the entire margins thereof. These right-angled or L-shaped
plates are termed throughout by the latter designation and form the sides
of the mold which is used to create a haunch region S. The bottom portion
of the form, which like the relevant art discussed in an earlier section
of this disclosure, is the actual supporting structure 12 and will not be
removed. It may be seen clearly how the slab haunch region S is superposed
over the girder 12 top surface. The sides of the haunch mold 29 comprise
the downwardly depending plates which are adjusted to snugly abut the
girder 12 by moving them inwardly of the haunch region S along transverse
slots 29' while passing under the bolt 32 heads. The reader should note
here that many disadvantages of the earlier discussed relevant art are
overcome by the instant invention, notably in that I have eliminated the
permanent, nonadjustable haunch mold elements and, since the plates 29
have no other function after the haunch is filled with grout and cured,
there is no actual physical contact between the slab 14 and the
underlaying support structure 12. Clearly, the slab 14 will remain coupled
to the support structure 12 by the fact that brackets 26 will cooperate,
through the grouted haunch 16 in unison with support 12 bolts 18, to
acquire the requisite (true) composite action. As detailed earlier, the
adjusting screws 28 may be removed, after the grout has cured, and holes
formed thereby may be refilled with similar non-shrink grout such as
CHRYSTEX (.TM.).
FIGS. 4 and 5 are joint detail 31 and elevational cross-sections,
respectively, of earlier discussed features. FIG. 4 depicts a typical
joint detail showing two non-contacting abutting slabs 14 being joined. A
backer rod 37 is installed at the base of the joint, generally by
contracting personnel in the field. Most of the joint is filled with a
non-shrink grout such as the previously mentioned CHRYSTEX (.TM.). This is
depicted as element 34 in the drawing. Generally, a void is left in the
top one inch of the joint 34, which is then filled with an elastomeric
concrete such as POLYCRETE II (.TM.). FIG. 5 shows the FIG. 4 detail 31 in
cross-section as well as the typical grout hole 22 and other previously
mentioned elements. Hereinafter, grout holes 22 will be omitted from the
elevational cross-sections in order to provide better clarity of
illustration.
One of the most important facets of my invention is the selection of
grout-engaging devices which are anchored to or encased within the slab
14. It is these devices 24 that allow me to acquire much of the
versatility that I have sought by this invention. Turning particularly to
FIG. 6, one such grout engaging means is realized in the reinforcing bar
25 which protrudes from beneath the slab as a D ring or U-shaped
projection 24. It may be seen how the grout haunch 16 securely captures
the slab 14 to the girder 12 bolts 18 while isolating the slab and girder
12 (proper), from each other. As mentioned earlier, the adjustable mold
side plates 29 do not enter into the shear equation since their purpose is
strictly formational of the haunch mold and any frictional effect they
exhibit on either the lateral portion of the girder 12 (upper portion) or
the haunch 16 is minuscule. All other elements of the FIG. 6
representation have been previously noted in this disclosure with the
exception of longitudinal reinforcement bars 23, an option. FIG. 7, the
elevational cross-section relating to FIG. 6, depicts the relationship, as
did FIG. 6, between the reinforcing bar 25 protrusions 24 and the girder
bolts 18.
Similar to the FIG. 6 embodiment, I have used the FIG. 8 alternative
embodiment with a great deal of success. In this article, the slab encases
a protruding stud 40 shear connector 38 which joins a pair of stud shafts
39, from which the protruding studs 40 depend the subsurface of the slab.
The reader should note that the protruding stud devices 40 have heads
similar to the ascending girder studs 18. These stud heads serve the same
function as did the D ring or U projection 24 in the FIG. 6 embodiment.
All other features of the slab and support structure subsystems that are
depicted in FIG. 8 have been previously discussed. I have chosen to
highlight the haunch plate slots 29' in a somewhat exaggerated detail in
order to reinforce my teaching on this particular member. As with the
earlier elevational cross sections, FIG. 9 depicts the salient elements of
the preceding FIG. 8. Final to my disclosure and perhaps one of the most
useful features herein is the alternate slab stud embodiment 40'. The
elements of FIG. 10 and 11 are practically identical to those depicted in
FIGS. 8 and 9, respectively. However, in FIG. 10, I have depicted the
alternate embodiment wherein headless studs 40' are employed. This has no
affect on the structural shear equation (function) of the embodiment as it
appears in the field. Additional to the headless morphology, a bond
breaker, well known in the industry, is applied to the length of the
protruding (headless) portions 40' of the shear studs 39 before the haunch
grout is pumped into the haunch area 16 (S). Thus, at a time for changeout
of the slab, this device allows an ease of removal that makes it highly
facilitative in temporary or detour bridges.
In my disclosure of just the preferred embodiments of my invention, I have
put forth that which has, in my experience, proved of significant value.
Practice with the invention will lead to alternate embodiments and perhaps
more useful improvements in this art. Such endeavor is commended to those
who might practice it consistent with the hereinafter appended claims.
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