Note: Descriptions are shown in the official language in which they were submitted.
BRIDGE STRUCTURE WJf'I'H CU~TCRETE
DECK HAV'~1G PRECAST S1~AR
Field of the I»,vention
[0001] This invention relates to a bridge superstructure, and more
particularly relates to the
construction of a concrete deck made of precast concrete slabs and which rest
on a series of
precast concrete beams or steel girders
_Back~roumd of the Invention
[0002] Typically, the construction of bridges is a time consuming task where
precast concrete
support beams or steel girders are erected on location and customized form
work is created
between the beams in order to support concrete to be poured onto the form
work. To sorx~e
extent, the form work which is made from Wood beams and plywood may be pre-
fabricated
but all the components must be trimmed to their final dimensions and assembled
on
location. After the poured concrete deck has set, the fon~n work is removed.
In order to
minimize the danger of ixaaterials falling from scaffolding onto an underlying
roadvs~ay and
to minimize disruptions to traffic flow, such form work is typically erected
and dis~nnantled
at night When the roadway is less busy and the roadway may be closed to
general
circulation.
[0003] A system for building a concrete deck with precast concrete slabs is
described in US Patent
Number 4,604,841. The slabs are reinforced with prestressed reinforcement rods
which
must extend throughout the width of the deck across support beams and through
adjacent
slabs_ Because the precast slabs and prestressed rod system is unwieldy, the
inv~ntioz~
described in US Patent Number 4,604,841 proposes a precast slab having a width
which
corresponds to the width of the bridge and which has prestressed reinforcement
rods
extending throughout the width of the precast slab. The sheer size of such a
slab is in itself
a deterrent to its use since it is very heavy and difficult to manipulate.
[0004] Another problem which is encountered with decks constructed with
precast slabs occurs at
the joint between slabs placed end to end along the length of the bridge.
Because of
imperkections inherent in pouring concrete, and the likelihood of slabs
becoming dazziaged
during transportation, particularly at the bottom edges of slabs having large
dizzxensiotls, the
forward and trailing edges often do not mate. As a result, some form of
sealant must be
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applied to the joints between slabs before pouring a concrete topping to build
the deck to
the reduired thickness.
(0005] An object o~this invention is to sizxiplify the construction of a
bridge superstructure in order
to minimize the time required for creatazlg a concrete deck and to minimize
the safety
hazards to both the patrons using the roadway and the personnel who erect such
structures,
usually at night, when visibility is poor.
Summary of the Invention
[0006] In accordance with this invention, there is provided a precast concrete
slab which is
dimerisioned to locate between beams and which is reinforced with steel rods
at
predetermined spaced locations, a selected number of said reinforcement bars
extending
upwardly above the surface of the precast concrete slab to define anchors for
securing a
concrete topping to be poured onto the precast concrete slab.
[0007] The reinforcement bars comprising said anchors are preferably bezxt
ir<to a castellated shape
o~ which invented U-shaped portions extend above the sur~aee of the precast
coz~erete slab.
[0008] Preferably, the slabs are shaped to abut on each other end tv end and
have chamfered
bottom edges to ensure mating ofthe upper edges on slabs disposed adjacent tv
one another.
[0009] In accordance with another aspect of the invention, a bridge is
constructed by first erecting
support beams at predetermined spaced locations and by placing screed
adjusters comprising
high density expanded polystyrene foam strips along opposed lateral edges of
the support
beams, locating precast slabs made according to the invention oz~ said screed
adjusters to
bridge the spaces defined between the beams and form a deck, and pouring a
fresh concrete
toppizxg over said deck to build the deck to a final pre-determined
thickz~.ess in accordance
with prevailing design considerations. Preferably, the precast slabs are
coupled to anchors
in the support beams with deck rexziforcement bars and ties securing the deck
reinforcement
bars to the beam anchors and to the slab reinforcement bars.
Brief Description of Dra~cvinQs
[0010] In order that the invention be more clearly understood, a preferred
embodiment thereof is
described below with reference to the accompanying drawings, in which:
Fig. 1 is a schematic side elevation view of a prior art bridge construction
including Iuznber
framework;
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Fig. 2 is a schematic side elevation view of a bridge construction made using
a precast
concrete slab in accordance with the invention;
Fig. 3 is a perspective view of a precast concrete slab in accordance with the
invention
spanning a pair of beams to form a deck;
Fig. 4 is a plan view of the precast concrete slab of Fig. 3;
Fig. 5 is a cross-sectional view on line 5-5 of the slab of Fig. 3;
Fig. 6 is a side elevation view of a pair of precast concrete slabs disposed
end to end;
Fig. 7 is a detailed view of circled area 7 of Fig. 6 with a concrete topping,
waterproof
sheeting and asphalt applied to th,e surface of the concrete slabs;.
Fig. 8 is a front elevation view of the deck of Fig. 3 with a concrete
topping, waterproof
sheeting and asphalt applied to the surface of the concrete slabs;
Fig. 9 is a top plan view of a single span foz a bridge superstructure showing
a precast slab
layout;
Fig_ 10 is a top plan view of a deck slab of Fig. 9 and drawn to a larger
scale;
Fig. 11 is a top plan view of a deck slab of Fig. 9 and drawn to a larger
scale;
Fig. I2 is a top plan view of a deck slab of Fig. 9 and dzawn to a larger
scale;
Fig. 13 is an end elevation view of a bridge superstructure showing a
sidewalk;
Fig. 14 is an isometric view showing the shape of a precast concrete slab in
accordance with
the invention;
Fig. 15 is a front side view of the slab of Fig. 14;
Fig. 16 is a top plan view of the slab of Fig. I4; and
Fig. 17 is a right side elevation view of the slab of Fig. 14.
Descri tion of Preferred )Cxiabodime t wrath Reference to D win
[0011] A typical bridge construction made in accordance with the prior art is
illustrated in Fig. 1
in which the bridge superstructure is generally indicated by reference numeral
20. The
bridge superstructuze 20 comprises a series of support beams 22 which, in this
case, are
made of precast concrete and which generally have an r-shaped cross-section
defining a
wide support base 24 and a wide deck platform 26. The support beams 22 are
reinforced
with reinforcement bars 28 disposed at spaced intervals along the length of
the beams 22
and bent into an inverted U-shape witlu a loop 30 extendiung above the surface
of the deck
platform 26 and defining a beam anck~or.
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[0012] Typically form work 32 made in accordance with the prior art spans the
separation between
the beams 22 and is constructed from lumber in order to provide a platform
onto which
concrete is poured to form a deck 34. 7"he fi>nn work 32 comprises 2x12
doubled bearers
36 supported at each end by steel hangers 38 spaced at approximately three
foot intervals
on support beams 22. 1'he 2x 1'? bearers 36 in turn support a plurality of 4x4
beams 40 lying
transversely to the 2x12 bearers 36 and spaced a maximum of 400 millimetres
apart. The
form work 32 is completed by a plywood sheet 42, 17 millimetres in thickness.
[0013] All of this form work 32 is trimmed and assembled on location. Once the
concrete to form
the deck 34 has been poured onto the form work 36 and over the beams 22, and
it has set,
the form work 32 is removed. The deck is normally completed by laying
waterproof
sheeting over the concrete, znd asphalt (not shown).
[0014] In accordance with the invention, the form work 32 is replaced by a
precast concrete slab
generally indicated by numeral 44 in Fig. 2 of the accompanying drawings.
Other features
of the resulting bridge superstructure 46 which are similar to the prior art
bridge
superstructure 20 of Fig. 1 ~~re identified by like numerals.
(0015] A detailed drawing of the precast slab 44 is shown in Fig. 3 and
essentially comprises a
rectangular slab which typically will have a length of about 3 metres and a
width of 2050
millimetres with a thickness of 90 millimetres. As will be seen more clearly
in Figs 14 to
17 the top face 48 of the slab is orthogonal to its sides whereas the bottom
face 4R is
somewhat recessed to define a 20 millimetre chamfer 50 (shown in more detail
in Fig. 7 on
forward and trailing edges fi>r the slab). A plurality of slab reinforcement
bars 52, 53 extend
throughout the width and length respectively of the slab 44 in a grid pattern
shown in ghost
outline in Fig. 4 of the accompanying drawings. T'he reinforcement bars 52
which extend
across the width of the slab 44 have extremities which protrude laterally from
both sides of
the slab over the deck platform 26 o:f the associated support beams 22. Since
the slab
reinforcement bars 52 are not pre-stressed, they nmy be trimmed and cut, as
necessary, for
the slabs 44 to follow the contour of an underlying roadway (see Fig. 9).
[0016] A number of the slab reinforcement bars ~2 extend upwardly above the
top face 48 of the
precast concrete slab 44 to define slab anchors 54 for securing a concrete
topping 55 (Fig.
8) to be poured onto the precast concrete slabs 44 and form the deck 34. The
reinforcement
bars 52 comprising the slab anchors 54 are preferably bent into a castellated
shape of which
inverted U-shaped portions extend above the top face 48 of the precast
concrete slab 44, as
_; _.
will be seen in Figs. 4 to 6, where 'the ghost outline shows portions of the
slab reinforcement
bars 52 which are imbedded i~t~ the precast slab and the solid lines show slab
reinforcement
bars which are exposed until the concrete topping 55 is poured.
j0017] The precast concrete slabs 44 are placed end to end adjacent one
another to extend along the
length of the bridge as shown in Figs. 6 and 9. 'Where the forward and
trailing ends of
adjacent slabs 44 meet, the upper edges mate as shown in Fig. 7 and operate to
provide a
flush surface upon which concrete may be poured without having to use sealants
57 or fillers
between. adj acent slabs other than in exceptional circumstances in selected
locations. When
viewed from the bottom, the ehaxn~ers 50 of abutting adjacent slabs 44 give
the deck 34 a
grooved appearance and architectural appeal.
[0018] The construction of a bridge superstructure 46 is schematically shown
in Fig- 8 and
comprises erection of the support beams 22 at predetermined spaced locations
and placing
screed adjusters 56 comprising high density expanded polystyrene foam strips
along
opposed edges of the suppozt beam deck platform 26. The polystyrene foam
bedding
material is typically 50 millimetres wide and will have a height of 40
millimetres to 125
millimetres to suit the screed elevations. The precast concrete slab 44 is
lowered by crane
over the support beams 22 so as to rest on the screed adjusters 56.
Conveniently, the slabs
44 may be transported to a bridge site by hooking into the slab anchors 54.
Once the precast
concrete slabs 44 are installed, which can b~ done very quickly and with a
miniamum of
preparation, wet concrete may be poured to form a concrete topping 55. It will
be
appreciated that the slab anchors 54 serve to mechanically lock the freshly
poured concrete
of the concrete topping 55 to the precast concrete slabs 44.
[0019] The concrete topping 55 extends to a greater depth over the support
beams 22 where it is
locked by the laterally extending slab reinforcement bars 52 and by the beam
anchors ox
loops 30. Deck reinforcement bars (not shown) are placed over the precast
slabs 44 before
pouring the concrete topping 55 and will be supported by a number of base
structures
commonly called a chair and which are placed on the precast slabs 44. Special
deck
reinforcement bars 58 are used to couple the precast conczete slabs 44 to the
beam anchors
30 and comprise leztgths of rod haviung ends which extend horizontally on
opposite sides of
a support beam 22 over the associated precast slabs 44 and a central poztion
which reaches
the deck platform 26 of the associated support beam 22. Such deck
reinforcement bars 58
are placed to cross the laterally extending slab reinforcement bans 52 and
beam anchors 30.
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Ties (not shown) are provided to secure the deck reinforcement bars 58 to the
beam anchors
30 and slab reinforcement bars 52. In this way, the invention vbvnates the
need for
prestressing the reiz~forcement provided in the pzecast slabs.
[0020] The slab layout for a typical bridge span is shown in Fig. 9 where the
support beams 22 are
shown in chain dotted lines and compzise eight in number and spanning a pair
of oppositely
disposed abutmeztts 60 extending across the widih of the bridge. It will be
understood that
a bridge may cozzaprise a single span as illustrated or a number of spans
disposed end to end
and supported on a corresponding number of piers in the associated bridge
substzucture.
Typically, a single span, as illustrated, is sufficiently Iong to bridge two
lanes of highway
traffic ruru~ing transversely below the bridge.
[002I] The precast slabs 44 are shown in solid lines disposed end to end with
forward and trailing
edges abutting one another along the length of the associated support beams
22. The deck
slabs 44 identified by the numeral 2 have rectangular upper and lower faces,
as shown in
Fig. 10 and occupy most of the area of the span. Custom formed deck slabs 44
identified
by the numerals 1 and 3 and shown in Fxgs. 11, and 12 are disposed at the ends
of the span
and have respective forward and trailing edges which are not orthogonal to
their lateral
edges. This layout would be typical in bridges where the abutments GO are not
orthogonal
to the support beams 22 as a result of changes in the terrain or topography in
the area whew
ye bridge is being erected. The deck slabs ide~atified by numerals 1 and 3
could also be cut
to the required shape on location, the reinfozcement bars not being
prestressed.
[0022] The deck 34 is completed by laying waterproof sheeting 61. over the
concrete topping 55,
and asphalt 63 (Figs- 7 and 8).
[0023] It will be appreciated that the concrete topping 55 formed on the~outer
support beams 22a,
22b is roughened as shown in Fig. 13 on a top surface thereof prior to a
second cvnerete
pour for forming a sidewalk 62, as is comnnonly dvz~e. The outer edges of the
sidewalk 62
support an upwardly extending barriez wall 64 or railings for protecting
motorists and
pedestrians from falling off the budge.
[0024] Those skilled in the art will appreciate that several variaxions may be
made to the invention
and that the rights associated with the invention are not limited by the
details of the
preceding description but are defined by the appended claims. In particular,
dimensions
which aze provided are typical and it will clearly be understood that these
may vary, as
required, to suit the applicatioxx and accozding to materials available.
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