Note: Descriptions are shown in the official language in which they were submitted.
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TENSION FORCE ADJUSTABLE PRESTRESSED GIRDER
Technical Field
The present invention relates to a girder, and more particularly, to
s a tension force adjustable prestressed girder which can compensate for
sagging or cracks of a girder generated due to a long-term load and is
capable of adjusting a tension force by increasing a load-resisting force of
a bridge or building, if necessary, after the construction thereof.
~o Backg~~round Art
In general, when girders installed on a column of a concrete bridge
become obsolete as time passes or heavy vehicles exceeding the originally
designed weight allowance of a bridge pass over the bridge for a prolonged
period, the beam of the bridge may become damaged and an excessive
~s sagging may occur at the girders. Concurrently, bendingltensile cracks are
generated and, when such damage continues, the bridge may ultimately
collapse. Thus, appropriate repair and reinforcement of the bridge is
required.
Meanwhile, a prestressed concrete (PSC) bridge is repaired and
Zo reinforced by means of an external steel wire reinforcement construction
method. According to the above reinforcement construction method, an
externally installed steel wire is to be fixed appropriately at an end portion
of a girder. However, it is difficult to install a wire fixing apparatus at
the
end portion of a girder and reliability on the load-resisting force of the
wire
is fixing apparatus is not assured. Thus, although other methods have been
suggested and applied, no effective apparatuses have been developed yet.
That is, when cracks and sagging occur in a PCS bridge, it is very difficult
to repair and reinforce the bridge.
Also, as the traffic volume continuously increases and automobile
so manufacturing technologies develop, the weight of a vehicle increases.
With an increase in the weight of a vehicle, the specifications which is a
standard of designing a bridge must be modified. Modifications of the
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specifications necessarily results in an unbalanced load-resisting state,
i.e.,
the load-resisting forces of the existing bridges are not matched. In other
words, in a state in which roads allowing passage of heavy trucks and
roads not allowing passage of heavy trucks exist together, the efficiency of
s transportation network system as a whole is severely lowered. Thus, to
make the unbalanced load-resisting forces of these bridges consistent, an
economical reinforcement method for upgrading the level of the bridge from
2 to 1 must be urgently found.
As the width of a road increases due to an increase in the number
of lanes of a road, the development of a wide span girder for constructing
an elevated road or an overpass crossing a wide road has proceeded.
Although a preflex beam has been developed and used for the above
purposes, conveying the girder is inconvenient due to the length thereof
and because the costs are high.
~s Currently, high strength concrete is used for a girder less than 30 m
long that is nov a wide span girder. However, as a high tension force is
applied to the girder, the amount of creep generated becomes great. As
the creep increases, the girder sags further which directly affects the
longitudinal alignment of the road. When the longitudinal alignment
2o deteriorates, a coefficient of impact by passing vehicles increases. Thus,
in the case of a high strength girder or a wide span girder, when the girder
is used for a long time, an appropriate construction method for
compensating for sagging of the girder is required.
Also, the height of a girder which is long in span is relatively high
Zs such that the girder itself is 2.00 m - 3.00 m high. Such a fact entails an
increase in the height of an upper deck of an overpass so that, to secure
a longitudinal alignment of the overpass matching the designed vehicle
speed, the length of the overpass becomes longer, thus raising the
construction costs. In the case of a bridge crossing a river, to lower the
so height of the girder as low as possible is inevitably needed for improving
the usability and the economic value of the girder.
FIG. 1 shows the structure of a general bridge. As shown in the
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drawing, a plurality of I-type girders 12 are installed on a column 10. An
upper deck slab (not shown) is installed on the girders 12 of the bridge.
FIG. 2 is a sectional view showing a girder in which steel wires are
arranged according to the conventional technology. As shown in the
s drawing, a girder 20 consists of a body portion 22, an upper flange 28, and
a lower flange 24. A plurality of steel wires 26 are built in the body portion
22 in the lengthwise direction. An upper deck of a bridge is installed on the
upper flange 28 and the bottom surface of the lower flange 24 is supported
by the column 10.
After the I-type girder 20 according to the conventional technology
is constructed, when the bridge is damaged, that is, sagging or cracks are
generated due to the increased traffic volume passing over the bridge, or
when the designed passage load must be increased according to the
revision of the specifications, reinforcement of the bridge is required.
~s However, there are no economical and reliable reinforcement methods
applicable therefor.
Disclosure of the Invention
It is an objective of the present invention to provide a prestressed
2o girder of which a tension force can be adjusted by adjusting a tension
force
of a steel wire provided in a body portion or lower flange of the girder to
easily increase a load-resisting force of a bridge or building, when
excessive sagging or cracks are generated in a girder due to long-term use
or when there is a need to increase the load-resisting force of the bridge or
is building without damaging the bridge or building.
Accordingly, to achieve the above objective, there is provided a
tension force adjustable prestressed girder for adjusting a load-resisting
force which consists of an upper flange supporting an upper deck of a
bridge installed thereon, a body portion, and a lower flange, which includes
so tension steel wires provided in a lengthwise direction of the girder and
tensioned to compensate for the load-resisting force, and at least one or
more non-tension steel wires provided in the lengthwise direction of the
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girder, so that the load-resisting force of the bridge can be increased by
tensioning the non-tension steel wires.
It is preferred in the present invention that the tension force
adjustable prestressed girder further comprises a cut-open portion at a
s predetermined portion in the lengthwise direction of the girder and a
coupling member installed at the cut-open portion for fixing one ends of the
steel wires of which the other ends are fixed at an end portion of the girder.
According to another preferred embodiment of the present invention,
there is provided a tension force adjustable prestressed girder for adjusting
,o a load-resisting force which consists of an upper flange supporting an
upper deck of a bridge installed thereon, a body portion, and a lower
flange, which includes tension steel wires provided in a lengthwise direction
of the girder and tensioned to compensate for the load-resisting force, and
one or more non-tension steel wires provided in the lengthwise direction of
~s the girder, so that the load-resisting force of the bridge can be increased
by tensioning the non-tension steel wires during construction of the girder
andlor after the construction thereof.
Although the present invention can be applied to any type of girder
regardless of the shape of the section of the girder such as an I-type girder
or a bulb T-type girder, the t-type girder is described in the below preferred
embodiment.
Brief Description of the Drawinas
FIG. 1 is a perspective view showing the structure of a general
is bridge;
FIG. 2 is a sectional view showing the arrangement of steel wires in
the girder according to conventional technology;
FIG. 3A is a sectional view showing the arrangement of steel wires
in the middle portion of a girder according to the present invention;
so FIG. 3B is a sectional view showing the steel wires according to
another preferred embodiment of the present invention;
FIG. 4A is a sectional view showing the arrangement of steel wires
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at the end portion of the girder of FIG. 3A;
FIG. 4B is a sectional view showing the arrangement of steel wires
at the end portion of the girder of FIG. 3B;
FIG. 5 is a view showing a cut-open portion located at the middle
s portion of the girder and the arrangement of the steel wires in the girder;
FIG. 6 is a side view showing an example of a steel wire fixed at the
end portion of the girder; and
FIG. 7 is a perspective view showing an example of the steel wires
in the cut-open portion.
Best mode for carrying out the Invention
In FIG. 3A , a girder 40 includes an upper flange 28, a lower flange
24, and a body portion 22. One or more tension steel wires 26 and non-
tension steel wires 27 are built in and across the lower portion of the body
~s portion 22 and the lower flange 24 of the girder 40 in the lengthwise
direction of the girder 40.
Preferably, the non-tension steel wires 27 are built in the lower
flange 28 horizontally parallel to each other, as shown in FIG. 3A. The
upper flange 28 is provided above the body portion 22 in the latitudinal
Zo direction in the section of the girder 40 and an upper deck of a bridge is
installed on the upper flange 28. The lower flange 24 is provided below the
body portion 22 in the latitudinal direction in the section of the girder 40
and
the bottom surface thereof is supported by a column (not shown).
FIG. 3B shows a steel wire according to another preferred
is embodiment of the present invention. As shown in the drawing, a plurality
of non-tension steel wires 27a are provided in the lengthwise direction of
the girder 40 outside the lower portion of the body portion 22. The non-
tension steel wires 27a have the same function as that of the non-tension
steel wire 27 provided in the lower flange 24, as shown in FIG. 3A. That is,
so after a bridge is constructed, sagging of the girder 40 is compensated for
by tensioning the non-tension steel wires 27a. Also, the non-tension steel
wires 27a can be more easily installed compared to a case of being
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installed inside the lower flange 24.
FIG. 4A shows the arrangement of the steel wires built in the girder
of FIG. 3A. As shown in the drawing, the tension steel wires 26 and the
non-tension steel wires 27 concentrated at the lower portion of the girder
s 40 are distributed throughout the entire sectional portion of the girder 40.
That is, the steel wires are evenly distributed symmetrically in upldown and
left/right sides of the girder 40 so that the tension force by the tension
steel
wires 26 and the non-tension steel wires 27 can be evenly distributed
throughout the entire portion of the girder40.
FIG. 4B shows the arrangement of the steel wires at the end portion
of the girder shown in FIG. 3B. As shown in the drawing, the tension steel
wires 26 or the non-tension steel wires 27 and 27a concentrated at the
lower portion of the girder as shown in FIG. 3B are evenly distributed
symmetrically in the up/down and leftlright sides so that the tension force
~s by the tension or non-tension steel wires 26, 27 or 27a are evenly
distributed throughout the entire portion of the girder 40.
FIG. 5 shows the arrangement of the steel wires in the lengthwise
direction in the girder of FIG. 3A and a cut-open portion located in the
middle of the girder. The tension steel wires 26 and the non-tension steel
2o wires 27 provided inside the girder 40 are concentrated in the lower
portion
at the middle portion of the girder 40 and evenly distributed throughout the
entire sectional portion of the girder 40 at both end portions of the girder
40. The tension and non-tension steel wires 26 and 27 are fixed at both
ends of the girder 40 by a fixing means 32 which is an anchoring device.
2s The fixing member 32 is covered with concrete (not shown) after the girder
40 is constructed.
Here, when the girders are installed having intervals therebetween,
or when a portion of the end of the girder is cut away, as shown in the
drawing, a space is formed between the adjacent girders. Thus, a
3o tensioning work can be performed in the space when the tension and non-
tension steel wires 26 and 27 are to be re-tensioned later. However, in this
case, the end portion of the girder 40 must not be covered with concrete.
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Here, one end of the non-tension steel wires 26 and 27 is
exposed at either end portions of the girder 40 to apply a
tension force.
Also, in a preferred embodiment, the girder is provided
with a cut-open portion 36 for adjusting the tension force of
the non-tension steel wires 27 at the middle portion of the
girder or at another appropriated position. The cut-open
portion 36 is used as a space for accommodating a coupling
member of the non-tension steel wires 27. That is, the cut-open
portion 36 is used as a working space for adjusting the tension
force of the non-tension steel wires 27 later.
When cracks 34 or excessive sagging 35 indicated by a
dotted line is generated to the girder 40 according to the
present invention, as shown in FIG. 5, one or more non-tension
steel wires 27 and 27a installed inside or outside the girder 40
are additionally tensioned for reinforcement. Here, the
additional tensioning work for the non-tension steel wires 27
and 27a is performed using a hydraulic jack. Also, the tension
forces of the non-tension steel wires 27 and 27a are adjusted
during or after slab casting and after construction, the tension
force is adjusted while the bridge is in use. That is, in the
case of a continuous bridge, re-tensioning can be performed
before slab casting. However, in the present invention, the re-
tensioning is performed shortly after the slab casting before
slab concrete is hardened to prevent application of a tension
force on the slab.
FIG. 6 shows a preferred embodiment of fixing each steel
wire at the end portion of the girder. The steel wire 26 is
anchored using a support member 50 as an anchoring device. For
example, the steel wire 26 is inserted into a hole formed at the
center of the support member 50 at one end of the girder 40. A
plurality of wedges 52 are inserted between the steel wire 26
and the support member 50. Here, the steel wire 26 is tensioned
by a hydraulic jack and the tensioned steel wire 26 is fixed by
the wedges 52.
FIG. 7 shows that the non-tension steel wires are coupled
by the coupling member as a preferred embodiment of a steel wire
connection in the cut-open portion. As shown in the drawing,
the cut-open portion 36 is formed in the middle of the bottom
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surface of the girder 40 in the lengthwise direction. The non-
tension steel wires 27 fixed at both ends of the girder 40 are
connected to a coupling member 62 such that forces of different
directions are applied. Here, the non-tension steel wires 27 to
be connected at the coupling member 62 are connected using the
support member 50 and the wedges 52.
Thus, the non-tension steel wires 27 connected to each
other by the coupling member 62 are tensioned and fixed by using
the wedges 52 so that the tension force by the non-tension steel
wire 27 can be maintained. Also, by applying a tension force to
the non-tension steel wires 27 provided at left and right sides
of the girder 40, bending of the girder 40 to the left or right
can be compensated for.
According to the arrangement of steel wires and the
coupling apparatus of the present invention, when a bridge is
constructed or at an initial stage of construction, the non-
tension steel wires 27 are connected to the coupling member 62
to be capable of moving to a degree, and are not tensioned at
all or tensioned by a small tension force so as to increase the
tension forces of the steel wire later.
Although a bridge is described as an example in the above
preferred embodiment, the tension force adjustable prestressed
according to the present invention can be applied to other
concrete structure such as a building as another preferred
embodiment.
It is noted that the present invention is not limited to
the preferred embodiment described above, and it is apparent
that variations and modifications by those skilled in the art
can be effected within the spirit and scope of the present
invention defined in the appended claims.
Industrial Applicability
As described above, according to the present invention, cracks
and sagging of a bridge generated due to long-term
deterioration, creep or overload can be corrected by
additionally tensioning steel wires installed internally or
externally at a girder of the bridge. Thus, repair and
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reinforcement of the bridge is easy so that the load-resisting force of the
bridge can be easily increased. Also, by adjusting the tension force step
by step, the girder can be economically manufactured or the height of the
girder can be decreased.
