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Claims  |
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We claim:
1. A box beam for use with bridge structures and the like comprising first
and second, elongate, generally upright side walls; first and second,
elongate, generally horizontal upper and lower chord plates; the walls and
the chord plates being constructed of corrugated plate defined by a
plurality of parallel corrugations extending parallel to a longitudinal
axis of the beam over the longitudinal extent of the walls and the chord
plates; means attached to the side walls for carrying shear stresses
applied to the side walls; and means rigidly connecting respective edge
portions of the walls and of the chord plates to each other so as to form
a rigid, high strength box beam therewith.
2. A box beam according to claim 1 wherein the connecting means comprises a
multiplicity of high strength bolts interconnecting the respective edge
portions.
3. A box beam according to claim 1 wherein the shear stress carrying means
includes shear plates secured to the side walls.
4. A box beam according to claim 3 wherein the shear plates include edge
portions secured to the chord plates.
5. A box beam according to claim 3 wherein the corrugated plates of the
side walls define alternating corrugation peaks and corrugation troughs
arranged side-by-side between lateral edges of the side walls; and
including means for securing each shear plate to at least some of the
corrugation troughs.
6. A box beam according to claim 5 wherein the shear plate is secured to
said some corrugation troughs at a plurality of locations spaced over the
lengths of such corrugation troughs.
7. A box beam according to claim 5 wherein the shear plate comprises a flat
plate.
8. A box beam according to claim 1 including generally vertically oriented
stiffening means attached to the side walls for rigidifying the side walls
in a generally horizontal direction.
9. A box beam according to claim 1 wherein the corrugations have a
corrugation pitch of at least about 16 inches and a corrugation depth of
at least about 5 inches.
10. A box beam according to claim 9 wherein the corrugations of the walls
have a generally trapezoidal cross-section.
11. A box girder according to claim 1 including a bridge deck defined by a
corrugated deck plate having corrugations extending transversely to the
corrugations of the chord plates; and means rigidly attaching the bridge
deck to the upper chord plate.
12. A box beam according to claim 11 wherein the bridge deck is constructed
of checkered metal plate defining a multiplicity of protrusions
substantially evenly arranged over an upwardly facing surface of the deck;
and a layer of concrete poured onto the bridge deck; whereby the
protrusions of the checkered deck plate surface form a mechanical
interlock with the concrete so that the concrete becomes a structurally
integrated, load-bearing part of the box beam.
13. A box beam according to claim 1 wherein at least one of the upright
walls is non-perpendicular with respect to the chord plates.
14. A box beam according to claim 1 wherein the shear stress carrying means
comprises a layer of concrete applied to exterior surfaces of the side
walls.
15. A box beam according to claim 14 wherein the side walls are constructed
of checkered metal plate defining a multiplicity of protrusions
substantially evenly arranged over exterior surfaces of the side walls,
and wherein the concrete layer contacts the protrusions to form a
mechanical interlock between the concrete layer and the sidewalls and to
thereby structurally integrate the former with the latter.
16. A box beam according to claim 14 including a layer of concrete applied
to a downwardly facing side of the lower chord plate; whereby the box beam
has the appearance of a concrete box beam.
17. A box beam according to claim 1 wherein at least the edge of the side
wall proximate the upper chord plate is non-parallel to the side wall
corrugations.
18. A box beam according to claim 17 including a camber trough in the side
wall extending in the direction of the corrugations for generating the
non-parallel side wall edge, the camber trough being positioned proximate
such edge and having a depth in a direction perpendicular to the side wall
which varies over the length of the trough.
19. A box beam according to claim 18 wherein the trough is deepest adjacent
longitudinal ends of the side wall.
20. A box beam according to claim 19 wherein the trough extends from each
end of the side wall towards and terminates in the vicinity of a center of
the side wall.
21. A box beam according to claim 18 including another camber trough in the
side wall extending in the direction of the corrugations and located
proximate a lower side wall edge, the additional trough being arranged so
as to generate a longitudinally concave lower side wall edge.
22. In a long span bridge having a bridge deck, at least one box beam
disposed beneath the deck and forming a structural support therefore, and
means for supporting the box beam at longitudinally spaced apart points,
the improvement to the deck and the box beam comprising in combination: at
least one elongate box beam including substantially parallel, spaced apart
upper and lower chord plates and spaced apart, generally upright sides for
interconnecting the chord plates, the plates and the sides being defined
by a plurality of generally parallel, side-by-side corrugations which
extend over substantially the full length of the box beam; means
positioning respective edge portions of the chord plates and the sides
proximate to each other and rigidly interconnecting such edge portions so
as to render the box beam rigid; shear plate means placed against the
sides and extending over at least a substantial portion thereof; and means
for rigidly securing the shear plate means to the sides at a plurality of
spaced apart points distributed over the lateral and longitudinal extent
of the shear plate means and the sides for enabling the shear plate means
to support generally vertically acting forces while preventing a buckling
of the shear plate means under such forces.
23. A bridge according to claim 22 wherein the deck is at least in part
defined by the upper chord plates.
24. A bridge according to claim 23 wherein the box beam extends in a
longitudinal direction of the bridge.
25. A bridge according to claim 23 wherein the box beam extends
transversely to the length of the bridge.
26. A bridge according to claim 25 including a transversely arranged box
beam at each support joint, and longitudinally extending box beams
disposed intermediate and having ends secured to the transverse box beams.
27. A bridge according to claim 22 wherein the deck is constructed of
corrugated plate, a surface of which is with a multiplicity of protrusions
integrally formed with the plate means and substantially uniformly
distributed thereover, said surface facing upwardly.
28. A bridge according to claim 27 including a layer of structural concrete
poured on top of the bridge deck; whereby the concrete, while plastic,
embeds the protrusions to form a mechanic interlock between the deck and
the concrete layer and to structurally integrate the latter with the
bridge.
29. A bridge according to claim 27 including means for securing the
corrugated deck plate to the upper chord plate.
30. A bridge according to claim 28 wherein at least a portion of the
corrugated deck plate is defined by the upper chord plate.
31. A bridge according to claim 27 wherein the corrugations of the deck are
oriented substantially perpendicularly to the corrugations of the upper
chord plate.
32. A bridge according to claim 22 wherein the shear plate means comprises
relatively thin, flat sheets of metal placed against the box beam sides.
33. A bridge according to claim 32 wherein the sheets extend over the full
width of the box beam sides.
34. A bridge according to claim 33 wherein the sheets extend over
substantially the full length of the box beam sides.
35. A bridge according to claim 22 including a plurality of side-by-side
box beams.
36. A bridge according to claim 34 wherein the box beams are substantially
parallel to the longitudinal extent of the bridge.
37. A bridge according to claim 34 wherein adjoining box beams have a
common box beam side.
38. A bridge according to claim 34 wherein adjoining box beams have
independent, proximate box beam sides.
39. A bridge according to claim 38 wherein the proximate box beam sides of
adjoining box beams are spaced apart, and including means defining a
lateral bracing between the proximate box beam side, the bracing means
being arranged at intermittent points over the length of the proximate box
beam sides.
40. A bridge according to claim 34 wherein sides of the outermost box beams
of the bridge which face away from a center of the bridge which face away
from a center of the bridge have a vertical slope which converges
downwardly towards the center of the bridge.
41. A bridge according to claim 22 wherein at least the box beams are
constructed of a copper bearing, corrosion resisting steel.
42. A bridge according to claim 22 wherein the shear plate means comprises
a layer of concrete applied over and covering the exterior of the side
walls.
43. A bridge according to claim 22 including in the sides of each beam
adjacent the upper edge portion thereof a longitudinally extending camber
trough formed in the sides, having a point of greatest depth adjacent ends
of the beam and a point of least depth adjacent a center of the beam so as
to give the upper edge portion of the side and the upper chord plate
secured thereto a longitudinally convex shape.
44. A bridge according to claim 43 including in the sides of each beam
adjacent the lower edge portions thereof a longitudinally extending lower
camber trough formed in each side, having a point of greatest depth
proximate a center of the beam and points of least depth adjacent ends of
the beam so as to give the lower edge portions of the sides and the lower
chord plate secured thereto a longitudinally concave shape.
45. A long span bridge comprising in combination: a plurality of
side-by-side, generally parallel box beams, the box beams having
transverse dimensions at least one of which does not substantially exceed
about 8 feet and being further defined by generally upright, spaced apart
box beam sides and generally parallel, upper and lower chord plates,
proximate edge portions of the sides and the chord plates being rigidly
secured to each other, the sides and the chord plates being constructed of
relatively thin walled corrugated plate made of a corrosion resisting
material, corrugations of the plate having a generally trapezoidal
cross-section and being arranged parallel to a longitudinal axis of the
beams, the corrugations further having a pitch of at least about 16 inches
and a depth of at least about 5 inches; means for rigidly securing the box
beams to each other; a relatively thin shear plate attached to each box
beam side, the shear plates being substantially flat and placed against
the corresponding box beam sides so as to contact corrugation troughs of
the side protruding towards the shear plate; means for rigidly securing
the shear plates to at least some of the corrugation troughs over
substantially the full height of the box beam sides to rigidify the shear
plates and to prevent their buckling when subjected to vertically acting
shear loads; a bridge deck constructed of corrugated plate carried by the
box beams, the corrugations of the deck being oriented transversely to the
corrugations of the chord plates; and a road bed placed on top of and
carried by the bridge deck.
46. A bridge according to claim 45 wherein the road bed is constructed of a
structurally sound material, and including means for mechanically locking
said material to the deck to thereby structurally integrate the material
with a remainder of the bridge.
47. A bridge according to claim 46 wherein the material comprises concrete,
and wherein the means for mechanically locking is defined by the bridge
deck constructed of standard checkered plate having integrally formed
protrusions which are disposed on an upwardly facing surface of such
plate.
48. A bridge according to claim 45 wherein the means for rigidly securing
the chord plates to the sides comprises spaced apart bolt means
distributed over the length of the box beam.
49. A bridge according to claim 48 wherein the chord plates and the sides
of each box beam define at least four longitudinally extending flanges
formed to be substantially parallel to and to snugly engage corresponding,
longitudinally extending sections of the corrugations of the next
adjoining box beam chord plate or side, and wherein the bolt means extends
through such section and the corresponding flange.
50. A bridge according to claim 49 wherein the flanges are arranged
substantially perpendicular to a remainder of the box beam chord plate or
side from which they protrude.
51. A bridge according to claim 50 including bolt means for bolting
together at spaced apart intervals the bridge deck and the upper box beam
chord plate.
52. A bridge according to claim 51 including a tie bar means disposed on an
underside of the lower chord plate, having a sufficient length to
interconnect the plurality of box beams, and bolt means for rigidly
securing the tie bar means to the lower chord plate.
53. A bridge according to claim 52 wherein the tie bar means has a width in
a direction parallel to the box beams which is substantially less than its
length, and including a plurality of spaced apart, generally parallel tie
bar means secured to the underside of the lower chord plates. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
At the present, there are in the U.S. alone upwards of 105,000 inadequate
bridges. A majority of them are functionally obsolete while a lesser
number of them are structurally deficient. The latter are defined as
bridges which had to be restricted to light vehicles only or closed, while
the former are identified as bridges which can no longer safely service
the system of which they are an integral part. The replacement cost for
these bridges is in the tens of billions of dollars. A majority of these
bridges are relatively short span bridges, say bridges having a length of
30 to about 100 feet. Applicants have recently invented a bridge system
ideally suited for building such bridges with relatively low production
and erection costs. Although this system is expected to greatly facilitate
the replacement of these shorter bridges, it is relatively less well
suited for incorporation in long span bridges, say bridges which have a
clear span of 100 feet or more up to several hundred feet. Generally, such
bridges are constructed as continuous, cantilivered, suspension, or arch
bridges.
Whatever the particular construction of the bridge, the load or traffic
carrying surface is intermittently supported over its length, either by
piers or with suspension cables. The bridge deck and more specifically the
support structure for the deck must have sufficient strength and rigidity
to carry the load between the support points.
The probably most common manner of supporting the bridge deck between the
above discussed support points is by providing suitable beams or girders
which carry the deck. For relatively short spans (between support points)
extruded steel profiles may suffice. For longer spans, however, it is
necessary to fabricate structures to achieve the necessary strength and
rigidity without requiring excessive amounts of materials. Here, one of
the most common forms of construction is to provide a supporting steel
framework, usually made up of plate, angle, channel, etc. which are welded
or riveted together. For relatively long spans and/or for heavy loads an
efficient support structure are so-called box beams which have a
relatively high strength to weight ratio.
Conventional box beams are made of flat plates that are typically welded to
each other. Inspite of their advantages over prior art forms of long span,
high strength and rigidly fabricated support beams, they remain relatively
heavy. Flat plate in many instances is an inefficient geometric
configuration for carrying a variety of loads, particularly shear and
bending loads. The latter and in particular, the shear stresses that must
be carried by the box beam, which typically is several feet in height, may
result in a buckling of the vertical beam wall unless it is supported at
intermediate points over its height. According to the prior art, this is
accomplished by securing, typically welding stiffeners which have
substantial depths (perpendicular to the flat sheets of which the box
beams are constructed) such as angle irons, channels and the like to
either the inside, the outside, or both of the walls. Since at least the
upper chord plate of the box beam is subjected to significant compression
forces, which may again cause the buckling of the plate, it too must be
stiffened in a manner analogous to that of the side walls of the beam.
The stiffening members attached to the flat walls of prior art box beams
are normally welded thereto, frequently over their entire length to avoid
the formation of pockets which may collect moisture and which may result
in an accelerated corrosion of the underlying metal. The great deal of
welding that is required is not only time consuming and, therefore,
expensive, it normally results in locked in stresses or outright damage to
the base metal adjacent the welds. Further, stresses due to strinkage when
the weld metal cools may lead to hairline cracks which may not form until
some time after the beam has been assembled and installed. Needless to
say, such cracks are difficult and, therefore, expensive to detect and,
more seriously, if they go undetected they pose a serious danger to life
and property. At the very least, once detected they may require expensive
corrective work in the field.
U.S. Pat. No. 3,181,187 is illustrative of a bridge construction which
employs longitudinally extending box beams for supporting the bridge deck
and road surface.
SUMMARY OF THE INVENTION
The present invention is particularly adapted for long span bridges.
Generally speaking, it provides a box beam support for the bridge deck
which normally is disposed longitudinal, i.e. parallel to the road bed and
the length of the bridge. For certain applications, notably suspension
bridges, the box beams may also extend perpendicular to the road bed. In
the latter case, the length of a box beam coincides rougly with the width
of the bridge.
The box beam itself is constructed of relatively thin walled corrugated
plate in which the corrugations run parallel to the length of the beam.
Preferably, the corrugations have a trapezoidal cross-section and a pitch
and a depth of at least about 16 inches and 5 inches, respectively. In
this manner, the corrugated sheets can be constructed from standard flat
sheet stock, such as 48 or 52 inch wide stock, and can be provided with at
least two full corrugations. These corrugations have the further advantage
that they enable the fabrication of the plate from flat sheet stock which
may have a yield stress of up to 50,000 psi or more without overstressing
the material while it is being corrugated in conventional corrugating
equipment.
Furthermore, the corrugated sections are preferably constructed of copper
bearing steel, such as is marketed under the trade designation COR-TEN by
the U.S. Steel Corportion of Pittsburgh, Pa. Briefly, upon exposure to the
atmosphere, these materials' surface oxidize and form a self-protective
coating, assuring that even prolonged exposure to the atmosphere does not
adversely affect the structural integrity of the underlying metal.
Accordingly, by constructing the box beam components of such corrosion
resistant materials, thinner cross-section materials can be employed
which, in turn, are more readily worked and enable one, for example, to
construct the box beam members from flat sheet metal stock of a thickness
of as little as 3/16 to 1/4 inch since the heretofore necessary "safety
thickness" to protect against undetected corrosion can be greatly reduced
or eliminated. The thinner cross-section, however, allows one to form
relatively inexpensive metal such as flat sheet metal stock, into more
intricate, stronger shapes, such as corrugated plate at relatively low
cost. Equally important, by constructing the box beam in the above
discussed manner and of such corrosion resisting material, the need for
the initial application of a protective coating and for subsequent
maintenance are eliminated, thus enhancing the economies provided by the
present invention.
Structurally, a bridge constructed in accordance with the present invention
comprises a bridge deck and at least one and normally a plurality of
side-by-side box beams. Each beam has first and second, elongate,
generally upright walls joined by, e.g. bolted to upper and lower box beam
chord plates. The walls and the chord plates are constructed of the above
discussed corrugated plate and the corrugations are arranged so that they
run parallel to the length of the beam.
Attached to the side walls are shear plates. The shear plates are flat,
generally rectangular and relatively thin plates which carry the shear
(vertical) load to which the beam is subjected and thus relieve the
corrugated side walls of the beam of such loads. To prevent the buckling
of the thin shear plate under the normally substantial shear loads it is
secured, e.g. bolted to at least some and preferably to all corrugation
troughs of the box beam side walls which protrude towards the shear plate.
The bolt locations are longitudinally equally distributed over the common
length of the shear plate and the side wall. Thus, the connections between
the two are substantially evenly distributed over the area of the shear
plate, that is over its lateral and longitudinal extent. The shear plate
is continuous, extends over substantially the full length of the side
wall, and can be applied to the exterior or the interior thereof. In the
former case, the shear plates can be employed to achieve desired aesthetic
effects and, for example, to give the box beam the appearance of a
conventional box beam constructed of flat plate.
In a preferred embodiment, the lateral edge portions of the shear plate are
bent 90.degree. to define flanges which are secured to lateral sides of
the chord plates. To adequately rigidify the box beam and the overall
bridge against horizontally acting (wind) forces vertically oriented
stiffeners are intermittently secured to the side walls, preferably their
inside. The stiffeners may be single corrugation profiles or channels
which are preferably bolted the side wall with high strength, corrosion
resistant bolts.
As a result of this construction, no or very few welds are required for
assemblying the box beam of the present invention. This saves significant
labor and, therefore, cost. More importantly, the vertical and horizontal
box beam members are all constructed of relatively lightweight corrugated
plate, yet they are extremely rigid longitudinally to absorb the large
bending moments encountered by bridges while the simple, relatively
inexpensive shear plates bolted to the box beam side walls not only take
the shear loads but also enable one to achieve desired architectural
effects.
Further, a bridge constructed in accordance with the present invention is
provided with a bridge deck. For some applications, the upper chord plates
of the box beams may be employed to simultaneously define at least a
portion of the deck. Normally, however, the deck is constructed separately
of the chord plates and is also corrugated with its corrugations running
transversely, e.g. perpendicular to the corrugations of the box beam
members. The bridge deck is corrugated from what is customarily referred
to as "checkered plate" which may have any desired pattern, such as a
diamond pattern and which is defined by intermittent protrusions on one
side of the plate which can extend up to about 1/8 inch above the
remainder of the plate. Such plate is in wide use as flooring and the
like. By constructing the deck of such corrugated plate a subsequently
poured structural layer becomes mechanically locked to the deck. This, in
turn, structurally integrates the concrete with the deck and, by
correspondingly securing the deck to the box beams renders the overall
bridge a unitary structure in which all components perform a structural
function rather than constituting deadweight as was so often the case in
the past.
Also disclosed are a variety of different embodiments all of which employ
the above-discussed main features of the present invention to a greater or
lesser extent. For example, in a presently preferred embodiment, the box
beams are unitary, that is each box beam has two side walls and the
associated horizontal chord plates. Furthermore, the box beams are
constructed so that they can be prefabricated at a plant and then
transported to the erection site. Accordingly, these beams preferably have
at least one transverse dimension, e.g. a width which does not exceed
acceptable rail and/or highway width limits, preferably which does not
exceed about 8 feet.
In an alternative embodiment, the box beams may be directly joined so that
each pair of adjoining beams has a common vertical beam wall. Moreover,
for aesthetic or other reasons, the outermost side walls of the box beams,
or the side walls of a single box beam, may be tapered upwardly and
outwardly so as to create special architectural effects or, particularly,
for single beam constructions, so as to increase the usable deck width.
In a further embodiment of the invention a layer of concrete is applied to
the exterior of the corrugated side walls and/or the underside of the
lower chord plate. When applied to the side walls the concrete layer
functions as the shear plate. In addition, the concrete layer gives the
box beam the appearance of a concrete structure which may sometimes be
desirable for architectural reasons. Further, the concrete layer
constitutes a highly efficient corrosion protection for the metal of the
underlying box beam.
As will be apparent from the preceding discussion, the present invention
provides a box beam structure particularly adapted for supporting bridge
decks over relatively long spans which result in significant material and
labor savings due to the structurally highly efficient profile given to
each member of the beam and the simple manufacturing and assembly of the
beam components. Moreover, by employing the above discussed corrosion
resistant materials, the heretofore common protective coatings and concern
with an undue loss of structural metal to corrosion are substantially
eliminated, thus making it possible to employ the structurally
advantageous design, particularly the large pitch and depth corrugations
for the box beam members while reducing manufacturing and maintenance
costs. Still further, in view of the substantial reduction in the overall
weight of the box beam, the erection of the bridge is correspondingly
simplified, leading to further cost savings. The overall savings provided
by the present invention should greatly facilitate the task of
replenishing the above-discussed huge bridge deficit with which we are
presently confronted.
Lastly, the present invention provides means for incorporating in the box
beam a longitudinal camber of at least the upper chord plate and,
therewith the bridge deck carried thereon. The camber is formed by rolling
into the corrugated side walls of the box beam adjacent the upper,
longitudinal edge of the side wall a trough which is deepest adjacent the
ends of the side wall and which becomes successively shallower towards the
center of the side wall until the trough disappears at the center. In this
manner, the uppermost edge of the side wall is drawn downwardly from the
center of the side wall towards the ends to give it a convex shape. Both
the upper chord plate and the bridge deck carried thereon are given a
correspondingly convex shape.
Although, for the proper use of the bridge it is not necessary, for
aesthetic reasons it might be desirable to include a corresponding camber
in the lower longitudinal edge of the side walls and the lower chord
plate. This is done in the same manner by reversing the depth of the
trough so that it is deepest at the center of the box beam and disappears
at the ends thereof. The lower side wall edge and chord plate are thus
given a concave shape.
It should be noted that the camber is incorporated in the box beam of the
present invention without requiring a corresponding curvature of the
longitudinally extending corrugations. The corrugations remain straight;
only the longitudinal edges of the corrugated side walls are convexly and
concavely cambered. The corrugated side walls can, therefore, be
corrugated on standard equipment. Accordingly, except for the relatively
minor cost of rolling the camber troughs into the side walls, the
provision of a camber does not add to the overall cost of the bridge.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic, side elevational view, with parts broken away,
illustrating a bridge constructed in accordance with the present invention
with the lefthand and the righthand portions of the figure showing
different embodiments;
FIG. 2 is an enlarged, elevational view of the bridge shown in the lefthand
side of FIG. 1 and is taken on line 2--2 of FIG. 1;
FIG. 3 is a fragmentary, enlarged detail of the construction of the bridge
deck and is taken on line 3--3 of FIG. 2;
FIG. 4 is an elevational view, in section, similar to FIG. 2 but shows
another embodiment of the invention;
FIG. 5 is a fragmentary, elevational view, in section, similar to FIG. 2
but shows yet another embodiment of the invention;
FIG. 6 is a fragmentary, elevational view, in section, and illustrates
another embodiment of the invention in which a layer of concrete
constitutes a shear plate;
FIg. 7 is a schematic side elevational view of a box beam such as is shown
in FIGS. 2, 4 and 5, and illustrates the manner in which a longitudinal
camber can be incorporated in such a beam in accordance with the present
invention;
FIG. 8 is a fragmentary front elevational view illustrating the formation
of the camber producing trough of the present invention and is taken on
line 8--8 of FIG. 7; and
FIG. 9 is a fragmentary, front elevational view, in section, similar to
FIG. 8 and is taken on line 9--9 of FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to the lefthand half of FIG. 1, a continuous bridge 2
generally comprises piers 6 sunk into the ground 8, which intermittently
support a main, longitudinally extending bridge truss 12. A road bed 14 is
carried by the truss. Conventional guard rails 18 form lateral barriers
for the roadway.
Referring now to FIGS. 1-3, in one embodiment of the invention, truss 12 is
defined by a plurality, e.g. three spaced apart, longitudinally (in the
direction of the bridge length) running box beams 20 each of which is
defined by a pair of generally upright box beam side walls 22 and spaced
apart upper and lower box beam chord plates 24, 26, respectively, which
are secured to the side walls in the manner further described below.
As earlier discussed, each of the side walls and the chord plates is
constructed of corrugated plate which has corrugations 28 of a generally
trapezoidal cross-section and the relatively large corrugation pitch "P"
and corrugation depth "D". The corrugations run parallel to the
longitudinal axes of the box beams. Further, the box beam may have a
generally square cross-section or its height "H" or width "W" may be
relatively larger or shorter to give the box beam a rectangular
cross-section. For purposes of this application, however, the term "square
cross-section" relative to the box beam includes such rectangular
cross-sections. In any event, it is preferred that the cross-section of
the beam is chosen so that at least one of its height or width does not
exceed 8 feet to enable its fabrication at a plant and subsequent shipment
to the erection site via conventional transportion means such as railroad
cars or trucks.
As is well-known, under normal loading the box beam side walls are stressed
by bending moments to which truss 12 as a whole and the box beams 20
individually are subjected and by vertically acting shear forces. Thus,
the shear forces act perpendicular to corrugations 28. Since corrugated
plate as such cannot be subjected to significant forces which act
transversely to the corrugations a shear plate 30 is placed against each
box beam side wall. The shear plate is relatively thin, say in the order
of between about 1/8 to 5/16 inch, and its ends are preferably bent
90.degree. to define flanges 34 which are dimensioned so that they fit
between lateral edge portions 32 of the upper and lower chord plates 24,
26. The flanges are secured to the chord plate edge portions with bolts 36
or the like.
Intermediate sections of the shear plate are intermittently secured to
corrugation troughs 38 of side walls 22 with a plurality of bolts 40 which
are evenly distributed over the width and length of the shear plate.
The multiple connections between the shear plate and the corrugation
troughs rigidify the former and prevent its buckling under the shear
forces so as to effectively rigidify the side wall in a vertical
direction, that is in the direction perpendicular to corrugations 28. The
shear plate 30 extends over substantially the full length of the
corresponding box beam so that the box beam, from the exterior, appears as
if it were constructed from flat plate as was conventional in the past.
The box beam is further stiffened or rigidified against laterally acting
forces such as wind forces by affixing to the inside of the corrugated box
beam side walls intermittently placed, vertically oriented stiffening
members 44 which are bolted to corrugation peaks 42 contacted by them. In
a typical embodiment of the invention the stiffening members may comprise
slightly more than one-half corrugation, so as to define a channel and
they are attached to the box beam side walls at about 20 foot intervals.
The actual assembly of a box beam 20 constructed in accordance with the
present invention is very simple. Initially flat plate stock is
corrugated. To the extent that the plate stock is of an insufficient width
to corrugate the full beam side wall 22 or chord plates 24, 26 from a
single plate, two or more plates may be independently corrugated and then
longitudinally welded together with high speed, conventional automatic
welding equipment (not separately shown) so as to obtain the desired
corrugated plate width. Alternatively, the plates may be bolted, riveted,
etc. together. One of the side walls and the chord plates, say the side
walls (as shown in FIG. 2) are formed so that they have an outermost
flange 46 which is perpendicular to the plane of the side wall. The
flanges 46 are spaced so that they fit flush against adjacent corrugation
troughs 38 of the upper and lower chord plates 24, 26. Bolts rigidly
interconnect the side wall flanges 46 with the chord plates as is
illustrated in FIG. 2 to form a unitary, high strength but lightweight box
beam 20. Next, the shear plates 30 and the stiffening channels 44 are
bolted to the side walls in the earlier described manner to complete the
beam and ready it for shipment to the erection site. The box beam must, of
course, be constructed of much shorter sections (usually having a length
of no more than between about 40 to 80 feet in length) than its overall
length. At the erection site, the beams are hoisted into position and
assembled end to end by overlapping end portions of the side walls and the
chord plates and bolting them together.
To effect the proper nesting of the overlapping corrugations, it is
normally necessary to take into consideration the material thickness of
the corrugated plate. In accordance with o | | |
