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BACKGROUND OF THE INVENTION
Corrugated plate, in all its forms, is extensively used in a variety of
applications. For example, corrugated plate is widely used for making
corrugated pipe or buildings as is disclosed in U.S. Pat. No. 3,820,295.
Most recently, the use of corrugated plate having trapezoidal corrugations
for the construction of high load bearing structures such as bridges, for
example, has generated great interest. U.S. Pat. No. 4,120,065 discloses
such a bridge construction which extensively employs trapezoidally
corrugated plate as the main structural component of the bridge.
The use of trapezoidal corrugations, particularly for high load
applications, is especially attractive since such corrugations have flat
corrugation peaks and corrugation troughs located at a point furthest
removed from the neutral axis of the corrugation. As is well known, both
the section modulus and the moment of inertia of a given profile increases
rapidly if the amount of material located relatively far from the neutral
axis is increased. The trapezoidal cross section, as contrasted with the
theretofore more common sinusoidally shaped cross sections accomplish this
goal.
In spite of the more efficient use of materials in trapezoidally corrugated
plate there remains a fair amount of material in the normally slanted
corrugation sides (which interconnect the corrugation peaks and troughs)
in relatively close proximity to the neutral axis of the corrugation. This
material, of course, adds little to the section modulus or the moment of
inertia of the corrugation. At least as far as bending stresses are
concerned, a good portion of the material in the corrugation sides is,
therefore, simply deadweight. Such deadweight has heretofore been accepted
as a necessary sacrifice for obtaining the many advantages that can be
derived from a structural use of relatively inexpensive corrugated plate.
SUMMARY OF THE INVENTION
The present invention is specifically directed an improved profile for
corrugated plate, and particularly trapezoidally corrugated plate, so as
to optimize the moment of inertia and the section modulus of a given
profile utilizing a given amount of material, in other words it is
directed to optimizing the strength and rigidity of corrugated plate and
to enable a plate made of a given amount of material to absorb greater
bending moments than was possible with heretofore available corrugated
plate.
Generally speaking, the present invention accomplishes this by giving the
peak and trough portions of the corrugated plate a greater material
thickness than is given to the corrugation sides which interconnect the
peaks and the troughs. As a result, a corrugated plate constructed in
accordance with the present invention and made from a given amount of
material can withstand greater bending moments or, for a given bending
moment, the plate can be constructed of less material. In either case,
expensive raw material, deadweight and, therefore, costs are saved.
The present invention, though generally applicable to corrugated plate, is
particularly advantageous in connection with trapezoidally corrugated
plate. Such plate has longitudinally extending, alternating corrugation
peaks and corrugation troughs which are interconnected by sloping or
slanted corrugation sides. Each of the peaks and the troughs includes a
flat crown section which is parallel to the neutral plane of the plate
(when the plate is otherwise flat). The crown sections have a thickness
which is typically two to three times the thickness of the corrugation
sides. As a result, material savings of between about 15 to 25% are
possible without reducing the strength, i.e. the section modulus or the
moment of inertia of the plate.
Further, the relatively thick crown sections of the peaks and the troughs
can be dimensioned so that curved, longitudinally extending corrugation
segments of the corrugated plate, which form the transition between the
horizontal crown sections and the slanted corrugated sides, are defined by
the relatively thinner material thickness of the sides, thereby greatly
facilitating the ease with which such plate can be corrugated by cold
rolling it from appropriately shaped flat sheet metal stock since much
less metal needs to be worked and deformed. As a result, the corrugating
equipment can be constructed much lighter and consumes significantly less
power, thereby reducing both the initial manufacturing cost for such
equipment and its subsequent operating costs. These costs translate into a
corresponding reduction in the manufacturing cost for the corrugated
sheet. These savings, combined with the material savings due to the more
efficient use of the plate thus significantly reduce the cost of
corrugated plate.
The present invention, therefore, not only relates to the above-described
improved and more efficient profile of corrugated plate but further to a
method of corrugating such plate. This aspect of the present invention
generally contemplates to provide as a raw material substantially flat
sheet which, however, has alternating, longitudinally extending, side by
side relatively thin and relatively thick sections. These sections of the
sheet are then corrugated so that the thick sections define the crown
sections of the corrugation peaks and troughs of the corrugated plate
while the thin sections define the corrugation sides which interconnect
the peaks and the troughs. The corrugation step includes the step of
forming a longitudinally extending curved segment in the relatively thin
sections of the corrugated plate which interconnect edge portions of the
crown sections with adjoining corrugation sides. By placing the curved
segments in the thin sections of the plate, the above-discussed advantages
of having to cold form relatively thin material (as contrasted with the
thickness of the crown sections) are attained. The flat sheet may have the
alternating relatively thin and relatively thick sections uniformly formed
as by hot rolling steel plate to the desired profile. Alternatively, the
relatively thick plate sections can be formed by initially providing a
thin sheet which has a uniform thickness and by folding over through an
arc of substantially 180.degree. relatively narrow portions of the sheet
so that two or more sheet material layers define the above-discussed
relatively thick sheet sections. The material layers can be welded
together to rigidify them. The sheet is then corrugated in the
above-described manner.
Another aspect of the invention contemplates to additionally strengthen the
corrugation peaks and troughs at certain points over their length, e.g. at
the longitudinal center region of the corrugated plate to enhance its
bending strength and rigidity.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the profile of a corrugated plate constructed in accordance
with the present invention;
FIGS. 2-5 show the profile of corrugated plates constructed in accordance
with alternative embodiments of the present invention;
FIGS. 6-8 show the cross section of flat plate from which the corrugated
plate of the present invention can be formed; and
FIGS. 9 and 10 illustrate the present invention as it relates to variations
in the thickness of the corrugation peaks and troughs over their
longitudinal extent.
FIG. 11 schematically illustrates the manner in which the corrugated plate
profile shown in FIG. 1 can be cold rolled in accordance with the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring first to FIG. 1, a corrugated plate 2 constructed in accordance
with the present invention generally comprises longitudinally extending,
parallel, side by side corrugations 4 which have a generally trapezoidal
cross section. The corrugations are defined by alternating, longitudinally
extending and parallel corrugation peaks 6 and corrugation troughs 8 each
of which has an elongated, essentially flat and relatively narrow crown
section 10 of a thickness "T" which extends over the length of the
respective peak or trough. Angularly inclined or slanted corrugation sides
14 have a thickness "t" and each of them interconnects a corrugation peak
with an adjacent corrugation trough. A curved corrugation segment 14
extends over the length of the corrugations and forms the connection
between lateral edges 16 of the crown sections and the corrugation sides.
As is apparent from FIG. 1 "T" is larger than "t", in other words, the
corrugation sides are relatively thin while the crown sections of the
corrugation peaks and troughs are relatively thick. Although the benefits
of the present invention are attained irrespective of the ratio between
"T" and "t", it is preferred that the ratio is at least 2:1 and preferably
3:1 or more. The exact dimension and resulting ratio between "T" and "t"
depends on the overall size of the corrugations, the type and magnitude of
loads to which the corrugated plate 2 is subjected and the need to give
the corrugation sides a sufficient thickness to prevent the sides from
buckling under the loads imposed on the plate.
In a particularly advantageous embodiment of the corrugated plate 2 for
high load applications in which the corrugated plate has a corrugation
pitch "P" of about 28 inches and a corrugation depth "D" of about 12
inches, the thickness "T" of the corrugation sides 12 is about 0.25 inches
while the thickness "T" of the crown sections is about 0.75 inches. Such a
corrugated plate has a cross sectional area (per corrugation pitch) of
19.01 sq. in., a weight of about 64.6 lbs. per linear foot, moment of
inertia of 530.5 in.sup.4 and a section modulus of 83.2 in..sup.3.
In contrast thereto, a corrugated plate constructed in accordance with
prior art, i.e. one which has a constant material thickness, a like pitch
"P" and corrugation depth "D", requires a material thickness of 0.515 in.
This results in a cross sectional area, per corrugation pitch, of 23.07
in..sup.2 and gives the plate a comparable moment of inertia of 522
in..sup.4 and section modulus of 83.4 in..sup.3. However, such a prior art
plate, which exhibits roughly the same strength as the above-discussed
plate constructed in accordance with the present invention, has a weight
of 78.4 lbs. per linear foot. In other words, the prior art corrugated
plate requires roughly 21.5% more material than the plate of the present
invention.
Comparable material savings are attained with differently dimensioned
corrugated plate constructed in accordance with the present invention. For
example, the corrugated plate may have a corrugation pitch "P" of 16
inches and a corrugation depth "D" of 6 inches. By giving sides 12 a
thickness "t" of 0.0747 inch and the crown sections 10 a thickness "T" of
0.2242 inch, the weight saving is about 16 to 17% compared to a prior art
corrugated plate since the latter must have a constant material thickness
of 0.15 inch to provide a comparable moment of inertia and section
modulus.
Referring now to FIGS. 1, 6 and 11, the corrugated plate 2 illustrated in
FIG. 1 is constructed from a flat sheet 18 which has the desired length
and a width sufficient to form the required number of corrugations. The
sheet defines alternating, side by side, longitudinally extending
relatively thin sheet sections 20 which have a thickness "t" equal to the
desired thickness for the corrugation sides 12 and relatively thick sheet
sections 22 which have a thickness "T" equal to the desired thickness of
crown sections 10. The width of the thin and thick sheet sections is
chosen so that when the flat sheet is corrugated into the corrugated plate
2 the thin sections define the corrugation sides 12 and the curved
corrugation segments 14 while the relatively thick sheet sections 22
define the crown sections 10 of the corrugated plate.
Preferably, the actual corrugating of the flat sheet 18 is performed in
corrugating equipment such as is illustrated, for example in U.S. Pat.
Nos. 726,691; 3,750,439; or 3,940,965. Briefly, a flat sheet is corrugated
by passing the sheet through successive, power driven roller pairs which
have a periphery that is shaped to incrementally deform the sheet from its
flat configuration into the ultimate corrugated shape. FIG. 11 illustrates
portions of a cooperating pair of such rollers 24, 26 which have
peripheries 28, 30, respectively, shaped to conform to the profile of
corrugated plate 32. It will be appreciated that it is normally desirable
or necessary to provide a series of such roller pairs in which the flat
plate 18 is deformed in multiple steps until it reaches the ultimate
profile shown in FIG. 11. It should be noted, however, that as the flat
plate is deformed, the relatively thick sheet sections 22 remain flat and
require no deformation. The actual material deformation takes place in the
curved corrugation segments 14 provided the relatively thin sheet sections
20 have a sufficient width so that they extend from the lateral edge 16 of
a corrugation peak to the lateral edge 16 of the proximate corrugation
trough. For this purpose, the peripheries 28, 30 of the rollers 24, 26
include, in cross section, a curved surface 32 which has a radius of
curvature "R" which is the same as the radius of curvature "R" for the
inside radius of the curved corrugated segments 14.
Thus, the present invention requires the deformation of the relatively thin
material of the corrugation sides only. This significantly reduces the
power consumption for corrugating the plate and makes possible a lighter
construction of the corrugating equipment as compared to corrugating
equipment that would be necessary for prior art (constant material
thickness) corrugations having a strength and rigidity comparable to that
of the corrugated plate of the present invention.
From the preceding it is apparent that the present invention lowers
material consumption and the deadweight of the corrugated plate as well as
the manufacturing costs. Thus, the initial cost of the corrugated plate is
less. In addition, where the corrugated plate of the present invention is
used in vehicles or vessels the continued use of the corrugated plate is
substantially less costly than the use of comparable prior art corrugated
plate since less dead weight needs to be moved, thereby reducing fuel
and/or other operating costs.
Referring momentarily to FIGS. 1 and 7, in an alternative embodiment, the
corrugated plate 2 may be constructed of a flat sheet 34 which is again
defined by relatively narrow, side by side, relatively thin sections 36
and relatively thick sections 38 having the above-discussed thicknesses
"t" and "T", respectively, and which extend over the full length of the
plate. However, instead of alternatingly extending the additional material
thickness of the relatively thick sections of the plate in opposite
directions (as is shown in FIG. 6) the sheet 34 shown in FIG. 7 is
symmetric so that the additional thickness of the relatively thick
sections 38 projects equally to both sides of the sheet. Upon corrugation
crown sections 40 are formed as is illustrated in the righthand portion of
FIG. 1 in dotted lines.
Referring now to FIGS. 2 and 3, the advantages of the present invention can
be attained even in those instances in which flat plate having alternating
relatively thin and relatively thick, longitudinally extending sections,
(as shown in FIGS. 6 and 7) is not readily available. In such instances,
the corrugated plate 42 can be conventionally corrugated from flat plate
having a uniform thickness which equals the desired thickness of
corrugation sides 44. Flat steel bars or strips 46 having a length equal
to the length of the corrugated plate and a width equal to the width of
crown sections 48 (as above defined) of the corrugation peaks 50 and
trough 52 are then secured with spot welds, fillet welds or the like to
the inside of the corrugations (FIG. 2) or the outside of the corrugations
(FIG. 3). In this manner, both the weight savings and the increase in the
strength and rigidity of the corrugated plate is attained without
requiring flat plate into which the varying material thicknesses have been
rolled during the manufacture of the plate.
Referring now to FIG. 4 in an alternative embodiment of the invention
similar to the one illustrated in FIG. 1, but exhibiting greater strength,
a corrugated plate 54 again has alternating corrugation troughs of a
material thickness "T" interconnected by corrugation sides 60 of a
thickness "t". The difference between corrugated plate 54 and corrugated
plate illustrated in FIG. 1 lies in the fact that the relatively thicker
material extends past the corrugation peaks and troughs over all or at
least a portion of the curved corrugation segments 62 which interconnect
lateral edges of the peaks and troughs with the adjoining corrugation
sides. This profile can yield slightly greater material savings than the
earlier discussed profiles of the present invention. However, it also
increases the strength requirements for the corrugating equipment and its
power consumption.
Referring now to FIGS. 5 and 8, in yet another embodiment of the present
invention, a corrugated plate 64 again has alternating corrugation peaks
and troughs 66, 68 interconnected by slanted corrugation sides 70. The
corrugated plate is constructed from a flat sheet 72 having a uniform
thickness throughout by folding or doubling over through an arc of
180.degree. spaced apart strips 74 of the sheet so as to define parallel,
longitudinally extending relatively thick sheet sections 76 which have a
width about equal to the desired width of the corrugation peaks and
troughs 66, 68 and which are interconnected by longitudinally extending
bands 78 of the sheet which have a sufficient width so that the bands,
upon corrugation of the sheet, define the slanted corrugation sides 70.
The doubled over sheet strips 74 are rigidly secured to each other, as
with spot welds 69 or fasteners 71 (such as bolts or rivets) located at
intermittent points distributed over their lengths and the sheet is
corrugated as above described and essentially as is shown in FIG. 9. It
should be noted that the doubling over of the sheet strips 74 can be
performed independently or as part of the corrugation process. Further, it
should be noted that in the embodiment of the invention shown in FIG. 5
the thickness "T" of the corrugation peaks and troughs 66, 68 will always
be a multiple of the material thickness "t" of the corrugation sides 70
and normally it will be an odd multiple so that the corrugation sides
slope from the lateral edges of the peaks and troughs.
Referring now to FIGS. 9 and 10 in instances in which the corrugations are
subjected to bending movements, as when a corrugated plate 80 forms a
bridge or bridge deck and is suspended between abutments (not shown) the
section modulus and the movement of inertia of the bridge at its center
region 82 can be increased over those of its end sections 84 as follows. A
flat steel bar 86 may be secured to the corrugation peaks and troughs 88,
90 in the same manner as is shown in FIGS. 2 and 3 and as described above.
Additional flat steel bars 92, 94 are placed on top of bar 86, centered
relative to the corrugated plate (see FIG. 9) and secured to the bar 86
with welds, bolts rivets or the like. In this manner the material
thickness of the corrugation peaks and troughs can be arranged to vary
over the length of the corrugations so as to correspond to the stresses to
which the plate is subjected. As a result significant material savings can
be attained.
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