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Патент USA US3084492

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April 9, 1963
Filed Deo. 18, 1959
2 Sheets-Sheet 1
Wllhelm Johannes Silberkuhl
Uwe Kosîl
April 9, 1963
Filed Dec. 18, 1959
2 Sheets-Sheet 2
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Wilhelm Johannes Silberkuhl
Uwe Kastl
Ernsm` Hoeùssler
Patented Apr. 9, 1953
erally along a fiber subjected to maximum tensile stress
Wilhelm Johannes Silberknhl, Uwe Kastl, and Ernst
Haenssler, all of Brunuenstrasse 29, Essen (Ruhr),
Filed Dec. 1S, 1959, Ser. No. 860,579
Claims priority, application Germany Dec. 19, 1953
4 Claims. (Cl. Sti-129)
Our present invention relates to prestressed elongated
concrete bodies, such as girders or slabs, adapted to be
employed in load-bearing structures (eg. bridges, over
passes, elevated highways and the like).
It is an object of our invention to provide a light-weight,
structurally rigid prestressed concrete body of exceptional
Another object of our invention is to provide a hollow
load-supporting concrete slab adapted to span sizable dis
tances and having a relatively large strength-to-weight
in the unprestressed structure. rIhus, the pitch may be
greatly lengthened in the unsupported intermediate re
gion of the span, where a major part of the moment line
passes underneath the girder axis, so that the prestressing
element extends nearly horizontally and «axially in that
We have found that a concrete girder of annular cross
section, provided in this manner with imbedded sheaves
of oppositely wound, generally helically extending pre
stressing elements (eg. steel wires), is under sufficient
axial and peripheral compression to withstand large and
varying live loads without requiring additional, unpre
stressed reinforcements; this results in a further saving
15 of weight and cost.
The above and other objects, .features and advantages
of the invention will become more readily apparent from
the following description, reference being made to the
accompanying `drawing in which:
FIG. 1 is a side-elevational Iview of a bridge according
A further object of the invention is to provide a con
`to our invention;
FIG. 2 is a fragmentary sectional top view of the struc
crete span adapted to support a large load while obviating
ture of FIG. l, showing the disposition of the reinforcing
the disadvantages of great bulk and high cost encountered
elements therein, taken generally along line Il-II of
in conventional bridge and road construction.
A known type »of prestressed concrete members used 25 FIG. 1;
FIG. 3A is a cross-sectional View taken along line
for single-span or continuous structures are lin the form
of hollow girders of generally rectangular cross-section,
FIG. 3B is a cross-sectional View taken along line
which may be extended sideways at the level of their upper
IlIB-IIIB of FIG. 1; and
flanges to »form a road bed,the lateral webs of these gird
ers being usually of considerable width to accommodate 30 FIG. 3C is a cross-sectional view taken along line
sheaves of prestressing cables or rods extending generally
horizontally therewithin while following a wavy line in
ÁIn the ydrawing we show a continuous, prestressed con
crete bridge comprising a tubular girder 2 supported, via
`the region of maximum tensile stress. Thus, each pre
stressing element rises and falls in a given vertical plane,
anti-friction bea-rings 10, by longitudinally spaced pairs
reaching its zenith a‘bove the supports and its nadir sub 35 of pillars 1, 1’. The girder 2 has its upper wall portion
stantially midway therebetween. Since the wall thickness
integrally extended laterally at -both sides to »form a road
way-supporting slab 3- bounded by curbstones 3". The
of the aforementioned webs greatly exceeds Athat required
inner cavity 7 of the hollow girder structure 2 is of
by static considerations, it is a more particular object of
the instant invention to provide an improved hollow girder
roughly elliptical cross-section (best seen in FIGS. 3A
of this general type in which this Wall thickness, and 40 3C) and extends longitudinally along the bridge axis.
The girder 2 is provided with prestressing rods which are
therefore the overall weight of the structure, is consider
ably reduced for a predetermined load-bearing capacity.
arranged in two sheaves 4a, 4b imbedded in its shell. As
In accordance with the present invention we imbed a
lbest shown in FIG. 2, the sheaves 4a, 4b define fiat sheets
sheaf of prestressing elements in the shell of a hollow
which are helically wound about the girder axis and
concrete girder in such manner that at least the sloping 45 whose major faces are substantially parallel to the wall
portions of these elements, extending between the high
of cavity 7 throughout their length. It will be apparent
and low points thereof, are -relatively staggered in axial
that, as viewed in the direction of the section plane
direction of the girder so as to be substantially equidistant
denoted by line IIIA-IIIA in FIG. 1, shaft 4a is Wound
from the girder axis. These sloping portions, accordingly,
in a clockwise direction about the axis while sheaf 4b is
define a sheet Whose thickness dimension generally coin
cides with that of »the girder webs so that the latter may
be made much narrower than heretofore. Preferably, we
wound in the opposite sense. The rods forming `the
sheaves 4a, 4b are individually anchored under suitable
tension to the concrete at the extremities of the structure,
provide two such sheaves extending around the girder
at the piers (not shown) forming the outermost supports,
axis in opposite directions so as to intersect at their high
in the usual manner.
axis, its pitch corresponding to the spacing of adjacent
span supports. The girder proñle is, for this purpose,
preferably rounded into broadly elliptical shape, with the
major axis of the ellipse or ovoid extending horizontally,
a relatively long lay so as to extend substantially hori
zontally and more nearly parallel to the axis of the
so that each prestressing element describes an elliptically
gered relationship, as `shown at 5 and `6. As best illus
and low points in the upper and ythe lower Wall portion 55
The two sheaves. are crossed within the lower girder
of the girder, respectively.
wall at a single intermediate location ‘8 and within the
Advantageously, each sheaf of prestressing elements
upper wall portion, above the pillars 1 and 1', at 9. In
deñnes a sheet wrapped with a long lay about the girder
their lower reaches the sheaves 4a, 4b are wound with
girder 2. Between the crossings 8 and 9, the prestressing
elements of sheaves slope up and down in axially stag
deformed helicoidal line. The pitch of this deformed
trated in FIGS. 3A-3C, the wall of girder 2 is thickened
helicoidal line may be varied throughout the length of 65 somewhat in the region above the pillars 1, 1’ to absorb
the girder so ythat the prestressing element follows more
the added compressive forces there. Since at all loca
or less closely the curvature of a line whose vertical po
tions each of the sheaves 4a, 4b defines a curved sheet
sition in the structure is in accordance with the magni
hugging the cavity 7, the entire girder shell may be of a
tude of the moments along the girder, and which there
70 minimum thickness while manifesting full load-bearing
fore may be referred to as a moment line and the av
er-age direction of all of these elements extends gen
strength. The curved configuration of the girder, whose
cross-sectional outline rises arcuately upwardly from the
magnitude of the bending moments along the length of
said fgirder.
median zone 8 (FIG. 3A) along an approximately el
liptical are at least in the middle region between sup
ports 1 and 1', is maintained over the major part of
the length `of the girder between these supports, as will
be apparent «from FIGS. 3A and 3B, and in particular
will -be seen to exist beyond the points of intersection
2. A structure according to claim 1 wherein said lower
wall portion has a cross-section whose outline substan
>tially extends along an arc of an ellipse with horizontal
major axis at least in the region of said intermediate lo
3. A structure according to claim 1 wherein said ele
of the prestressing elements 4a, 4b with the plane of
FIG. 2 which approximately corresponds to the horizon
tal mid-plane of the girder; it will be noted that these
points vof intersection lie closer to the piers 1, 1’ than
to the intervening midpoint 8.
In the erection of the structure, the rods 4a, 4b may
be post-tensioned in the usual manner against the hard
ened concrete after having `been imbedded therein with
ments are wound with relatively short pitch in the upper
part of said girder and with relatively long pitch in the
lower part thereof, thereby traversing the horizontal mid
plane of said girder at points closer to said supports than
to the mid-point therebetween.
4. A structure according to claim 1 wherein said girder
is provided with roadway-supporting lateral extensions in
tegral and level with said upper flange, said girder being
suitable bond-breaking means known per se, such as
sheathing or asphalting.
Although the invention has been specifically described
of lgreater lateral -wallthickness above said supports than
at said intermediate location, said girder extending be
with reference to a bridge structure, it will be readily
apparent that many modifications and variations may be
made without departing from the spirit and scope of our
_yond said supports, said prestressing elements continuing
substantially helicoidally beyond said supports after in
Vtersecting in said spaced locations.
invention except as further limited by the appended claims.
We claim:
1. A load-bearing structure comprising at least two hori
References Cited in the tile of this patent
zontally spaced-apart supports, a tubular concrete girder
with an upper wall portion forming a roadway~support-
ing slab, said girder resting substantially horizontally on
said Isupports and being provided with a lower wall por~
tion of reduced wall thickness whose outer surface rises
Ligonnet _____________ __ Aug. 17I 1926
Schorer _______________ __ Dec. 1, 1942
Billner ________________ __ Ian. 7, 1947
arcuately upwardly from a median zone at least over
the major part of »its length between said supports, said
girder having lan interior surface generally paralleling said
outer surface over said major part of the length of said'
girder, and two sheaves of elongated prestressing ele
-ments extending under tension along lgenerally helicoidal
,lines of opposite pitch within the rgîrder wall, said sheaves
intersecting at two spaced locations in said upper wall
portion above said supports, respectively, and at a single
intermediate location in said lower wall portion substan
tially midway between said supports, said sheaves de
scending from said two spaced locations to said inter
mediate location substantially along a line whose ver
tical position in the structure is in accordance with the
Luten ________________ __ May 6, 1913
Great Britain ______________ __
Germany _________________ __
Great Britain ______________ __
Belgium __________________ __
Engineering News-Record, June 10, 1948 (pages 80,
Engineering News-Record, September 1, 1949 (pages
Civil Engineering, January 1953 (pages 42, 43). .
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