PRESTRESSED SCAFFOLDING SYSTEM
FIELD OF THE INVENTION
The present invention relates to a scaffolding system that is temporarily placed
underground for preventing the collapse of excavated earth while an underground
structure is built and, more particularly, to a prestressed scaffolding system using
tendons with vertical piles (e.g., H-beams) and horizontal piles (e.g., wales), whereby
the number of struts supporting the vertical piles is considerably reduced.
BACKGROUND OF THE INVENTION
It is well known that excavation work for constructing a subway or a basement
of a building is started by excavating holes into the ground surface to a designed depth
on the basis of technical drawings, and then vertical piles are installed in the excavated
holes. After the installation of the vertical piles, excavation is partially carried out,
and then main girders and cover plates are placed. After the placement of the cover
plates, additional works are repeatedly performed by alternately excavating and
placing the struts.
Accordingly, in order to design a scaffolding system, the earth pressure on
each excavation level and load applied onto the struts are repeatedly calculated,
thereby enabling to design struts that can withstand the maximum load applied to the
beams. As a result, a large number of struts are required. In most cases, the struts
are closely arranged, e.g., within intervals of approximately 2-3 m, for primarily
obstructing the delivery of construction materials in a working area, the transportation
of heavy equipments, and performance of the construction works. The struts also
give rise to a severe impediment to a molding or steel work when the main structure is
built. For example, a plurality of holes is unavoidably formed in the main structure,
such that the finished underground structure is subject to penetration of water.
In the conventional scaffolding system, steel H-piles are used as the vertical
piles, while concrete piles for filling concrete into the excavated holes may be used as
the vertical piles instead of using steel H-piles. Additionally, the steel piles and the
concrete piles may be simultaneously used, or sheet piles may be used. However, the
basic principle of supporting the load of excavated earth by making holes in the ground
and then forming a wall by piles is almost identical to that of the aforementioned
works. Preflexed beams may also be used as the vertical piles, and the H-piles may
be attached to the sheet piles to strengthen the sheet piles.
The earth anchor system is used for supporting steel piles in the scaffolding
system for constructing underground structures in place of systems using the aforesaid
struts. According to this system, inclined holes are drilled into the ground behind the
piles, tendons or high strength steel bars are inserted into the drilled holes, ends of the
inserted bars are anchored by a mechanical method or a chemical method such as
epoxy or cement grouting, and then the bars are tensioned and fixed to the steel piles.
This system has an advantage in that the inner space of the scaffolding system is very
spacious, allowing the earth works and the support works to be easily performed. On
the other hand, there is a disadvantage in the system in that the works have to be
placed in the vicinity of private properties when this system is applied in a crowded
city, thus causing a lot of civil appeals from the neighbors. The high cost of the
construction is another disadvantage.
Korean Utility Model Registration No. 258949 discloses a method using truss
for removing struts, which pass across the excavated space of the scaffolding system.
This method is expected to be applied to a case where the depth of the excavated
ground is relatively shallow. H-beams are doubly placed in a grid-type near the earth
surface. The H-beams are reinforced with vertical beams and inclined beams so that
the earth pressure is supported by two floor trusses placed at the upper portion of the
scaffolding system. This method has been proposed to overcome difficulties in
excavating and constructing the structure, which occur due to the many struts of the
scaffolding system for supporting the ground. Consequently, this method is useful for
a construction to contain a wide structure at the bottom and a narrow structure at the
top of the excavated ground.
Korean Patent No. 188465, Korean Utility Model Registration No. 247053,
and Japanese Patent 837994 disclose a method for reinforcing a wale using
prestressing. In this method, an additional wale is placed on top of the existing wale
for tensioning the tendon and expanding the distance between the struts. This method
may be performed by using an additional wale or by reinforcing the flange of existing
H-beams. These two methods are expected to be effective in increasing the distance
between the struts. However, since the tendon is linearly disposed, a constant support
bending moment occurs, which is different from the parabola-shaped moment
distribution generated on the wale by the earth pressure. Different moments and the
distribution thereof in relation to the load restrict the length of the reinforced wale.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide a safe and effective method of
greatly reducing or removing the number of struts, which interfere in structure work
and cause an increase in construction costs, thereby obtaining an underground
construction space and minimizing construction costs.
In one preferred embodiment of the present invention, a prestressed
scaffolding system for supporting the excavated earth retaining wall by forming a
polygonal closed section comprises a prestressed wale comprising a plurality of
triangular tendon supports in the middle portion, a tendon-anchoring unit at both ends
of the wale, and a connecting brace for connecting the supports and the tendon-
anchoring unit. A strut is constituted by a truss or a plurality of H-beams or an H-
beam having a large cross section and strengthened for supporting the tendon-
The triangular tendon support is constituted by .a vertical member and an
inclined member, or only by vertical members, or only by inclined members for
forming a triangle and supporting the wale. The triangular tendon support is
supported and connected by an intermediate pile and a support beam for the tendon
The tendon-anchoring unit fastens a tendon and couples with the wale for
applying the compression force and also couples with the inclined or vertical member
for supporting the generated force.
BRD2F DESCRIPTION OF THE DRAWINGS
For a better understanding of the nature and objects of the present invention,
reference should be made to the following detailed description with the accompanying
drawings, in which:
FIG. 1 is a plan view of a scaffolding system applied to a closed section
according to an embodiment of the present invention; •
FIG. 2 is a plan view of a scaffolding system applied to another closed section
according to an embodiment of the present invention;
FIG. 3 is a cross-sectional view illustrating a scaffolding system applied to a
closed section according to an embodiment of the present invention;
FIG. 4 is a cross-sectional view of a scaffolding system applied to one
direction of a cross-section according to an embodiment of the present invention;
FIG. 5 is a cross-sectional view illustrating a scaffolding system applied to one
direction of a cross-section according to an embodiment of the present invention;
FIGS. 6a to 6d are detailed views of a tendon support used in the scaffolding
system according to an embodiment of the present invention;
FIGS. 7a and 7b are detailed views of a corner tendon-anchoring unit used in
the scaffolding system according to an embodiment of the present invention;
FIGS. 8a to 8d are detailed views of a horizontal tendon-anchoring unit used
in the scaffolding system according to an embodiment of the present invention; and
FIG. 9 is a detailed view of a vertical tendon- anchoring unit used in the
scaffolding system according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the present invention will now be described in
detail with reference to the attached drawings.
FIG. 1 is a plan view of the present invention applied to a closed section of an
architecture site. According to an exemplary embodiment of the present invention, a
prestressed wale 1 is disposed at four lateral sides of the closed section. A strut 3
made by a truss is placed at four corners and supports the wale. A conventional
corner support beam 5 is situated behind the strut. The prestressed wale 1 of each
lateral side includes three triangular tendon supports 12, a triangular anchoring unit 13,
and a connecting brace 10 for connecting the triangular tendon supports 12 and the
triangular anchoring unit 13. An intermediate pile 23 is equipped to support the
triangular tendon supports 12, and a support beam for the tendon support 16 is fixed at
the intermediate pile 23 by, for example, a bolt or welding. The support beam for the
tendon support 16 supports the triangular tendon supports 12 during the installation of
the scaffolding system. The triangular tendon supports 12 and the support beam for
the tendon support 16 are connected via a U-bolt in order to prevent a vertical buckling
which may occur in the event of prestressing, carried out after the assembly work of
the scaffolding system.
The truss strut 3 of each corner is positioned between two triangular anchoring
units 13 to transmit the compression force of the anchoring units. The truss structure
of the embodiment of the present invention may be substituted by, for example, an H-
shaped steel having a large cross section, a plurality of H-shaped steels, or the like, as
long as the structure can withstand high compression force. The constructional
method of the corner support beam 5 behind the truss strut 3 is identical to that of the
conventional system and illustrated in the drawing for explaining the present invention.
The element numeral 60 is a tendon.
The configuration of FIG. 2 may be used when the excavating plane is small.
A corner anchoring unit 14 substitutes the conventional corner support beam 5 and
truss strut 3 of FIG. 1. A T-shaped connecting brace 11 is used where the interval
between the prestressed wale 1 and the corner anchoring unit is narrow. The rest of
the figures and methods for carrying out the construction work are identical to that of
FIG. 3 is a cross-sectional view of FIGS. 1 and 2 and illustrates a horizontal
prestressed scaffolding system 2 and main structure 7 according to an embodiment of
the present invention. Unlike the conventional method, no equipment interferes the
middle portion of the system, and a wale 25 is arranged on four stages along the depth
of the excavated underground. A soldier pile 22 is located at a distal external wall in
a conventional way, and the wale 25 is mounted to support the soldier pile 22. The
support beam for the tendon support 16 and intermediate pile 23 are also illustrated in
FIG. 4, a cross-sectional view of a scaffolding system for a subway, includes a
main structure 8, vertical prestressed scaffolding system 6, and horizontal prestressed
scaffolding system 2. The horizontal prestressed scaffolding system 2 illustrated at
an upper portion of the drawing is identical in its figure and construction method to
that of the embodiment of FIG. 2, and thus, explanation of this system will be omitted.
However, the vertical prestressed scaffolding system 6 illustrated at a lower portion of
the drawing is supported at one side by a floor slab 9 of the main structure after the
slab is hardened. The other side of the system 6 is supported by a conventional
typical strut 26.
The vertical prestressed scaffolding system is useful when the main structure
is long such as a subway. In the vertical prestressed scaffolding system, a vertical H-
beam 19 is inserted from behind the pre-installed wale 25, and a short support 18 is
attached to the opposite side of the wale 25 for supporting the tension of the tendon 60.
The tendon is placed at both ends of the H-beam 19 and is fixed to a separate tendon-
anchoring unit 20, which is pre-coupled with the vertical H-beam. Thus, the
anchoring unit of the lower end of the vertical prestressed scaffolding system is
configured to be supported by the hardened concrete slab 9 of the main structure, while
the anchoring unit of the upper end is supported by the typical strut 26. The element
numeral 24 is an earth retaining plate.
FIG. 5 is a plan view of FIG. 4 and is used when the excavating plane is long,
e.g., a subway or a channel construction. The prestressed wale 1 is arranged along
both lateral sides, and the truss strut 3 is located at each place where the tendon of the
prestressed wale is fixed. The configuration of the prestressed wale is identical to the
wale of the closed-section of FIG. 1, and thus, further explanation will be omitted.
The enlarged portion of the drawing illustrates the relative location of H-beam
19 in relation to the soldier piles 22, in which the H-beam 19 for the vertical
prestressed scaffolding system described in FIG. 4 is installed between the existing
soldier piles 22. In the vertical prestressed scaffolding system, the earth retaining
plate 24 should be mounted at a flange behind the existing vertical pile to thereby
allow the installation of the H-beam of the vertical prestressed scaffolding system.
Provided that the vertical pile is a sheet pile 21 in place of the soldier pile 22, the
vertical H-beam 19 is inserted into an empty space between the sheet pile 21 and the
FIGS. 6a to 6d illustrate various shapes and sizes of the triangular tendon
support utilized in the embodiments of the prestressed scaffolding system of the
present invention. The triangular tendon support is provided with a vertical member
32 and an inclined member 33 and is configured to reduce the number of support
points 31 being in contact with the tendon. The triangular tendon support is also
configured to support a wale 30 having a long length. When the compression force is
applied on the support point 31 making contact with the tendon, the force functions to
support the long wale 30 via the vertical member 32 and inclined member 33.
In FIG. 6a, two inclined members are welded or connected by a bolt (not
shown) to thereby form an isosceles triangle and support the wale 30 having a short
length. FIG. 6b is a second embodiment of the present invention and illustrates a pair
of inclined members 33 connected to each other at a 45 degree angle extended laterally
from the vertical member 32. The inclined and vertical members are all connected to
the wale 30 by, for example, a bolt or welding. According to a third embodiment in
relation to the case that the length of the wale 30 is long, two pairs of inclined
members 33 of FIG. 6c are connected to both lateral sides of the vertical member 32,
respectively. A plurality of vertical members and inclined members are used in FIG.
6d for supporting the long wale 30. The structure of the triangular tendon support is
not limited to the embodiments of the present invention, and thus, may be configured
to form a triangle and support the wale by using the vertical member and inclined
member, or only by vertical members, or only by inclined members.
FIGS. 7a and 7b are detailed views of the corner anchoring unit 14 of FIG. 2
that are designed to connect a wale 35 of the corner via reinforcing members 36 to
thereby secure the tendon 60. That is, when the tendon 60, which is used for
constructing the prestressed scaffolding system, passes through the reinforcing
member 36 of the anchoring unit, the tendon is tensioned by a hydraulic jack 70. The
tensioned tendon is then fixed by an anchoring unit 71, which anchors the tendon.
The force pulled via the tendon transmits the compression force to an adjacent wale
(not shown) via a length adjusting unit 72, e.g., a precedent load jack or a screw jack.
As another embodiment of the present invention, the configuration of FIG. 7b is
adapted to anchor the tendon only by a reinforcing member 38 without a gusset plate.
The figures of the above embodiments may be varied in the scope of the basic concept
and function of the present invention. The reference numeral 39 refers to an inlet of
the anchoring unit.
FIGS. 8a to 8d illustrate various anchoring units of the horizontal prestressed
wale. FIG. 8a illustrates a small anchoring unit used when a small amount of tension
is applied thereto. The tendon 60 supporting a wale 41 is supported by an inclined
brace 43 or a vertical brace 44. The anchoring unit is formed with holes, thereby the
inclined brace 43 or vertical brace 44 may be inserted into the anchoring unit through
the holes as illustrated in the drawing, or may protrude out (not shown). The inlet 39
of the anchoring unit may preferably be formed in a curved shape in consideration of
the flexibility of the tendon. The tendon is fixed via the tendon-anchoring unit 73 at
an opposite side of the inlet 39. Further, the length adjusting unit 72 (e.g., precedent
load jack or screw jack) is equipped to add the compression force to the corner support
beam 5 after the tendon is tensioned.
FIG. 8b illustrates an anchoring unit having an additional wale 42 for
strengthening the wale in a case where the wale 41 gets lengthened and the
compression force applied on the wale greatly increases thereby. FIG. 8b is identical
to FIG. 8a in that the curve-shaped inlet 39 is formed where the tendon 60 supporting
the wale 42 is inserted into the anchoring unit, and the tendon-anchoring unit 73 is
placed oppositely from the inlet 39. The difference from FIG. 8a is that the inclined
brace 43 for supporting the anchoring unit is doubly placed to withstand the increased
compression force and earth pressure. In addition, when the compression force is
applied on the double wale, the force may differently be applied on each wale, and thus
the compression force between the two wales is intended to be equally adjusted by
using the screw jack 72 of the high load.
FIG. 8c illustrates the triangular anchoring unit 13 of FIG. 1 configured to
secure the tendon 60, which supports the wale 41, via the tendon-anchoring unit 73.
FIG. 8c is also configured to transmit the load to the truss strut 3 supporting the
triangular anchoring unit 13. In the triangular anchoring unit, an inclined member 47
of H-shaped steel is disposed to form an isosceles triangle to withstand the load
applied on the unit. An apex at which these members contact each other is enhanced
by an appropriate gusset plate 46. A screw jack 74 is equipped to adjust the
compression force of the double wale, and the precedent load jack 72 is equipped to
add the compression force to the corner support beam 5. The screw jack 74 is further
connected with the truss strut, which supports the entire anchoring unit. A hydraulic
jack 75 is provided to add a great amount of compression force between the anchoring
unit and the truss strut. That is, after the tendon is tensioned via the hydraulic jack 70,
the hydraulic jack 75 applies a compression force to the truss strut 3.
FIG 8d shows an anchoring unit used for the scaffolding system illustrated in
FIG. 4. The tendon 60 for supporting the wale 41 is tensioned via the hydraulic jack
70 and then secured by the tendon-anchoring unit 73. The tendon is designed to pass
through the inclined member 47 at its inlet portion. The truss strut 3 may be
connected with the anchoring unit by the screw jack 74 and hydraulic jack 75, or may
directly be connected without the aid of these members. The proper gusset plate 46 is
mounted for withstanding high compression force between a vertical member and a
horizontal member 48, which connects both sides of the anchoring unit. Since the
member receives only the prestressing force and the compression force is small, a
single wale is illustrated in the drawing. However, a double wale may preferably be
used depending on the case.
FIG. 9 is a detailed view of the anchoring unit 20 for the vertical prestressed
scaffolding system 6 illustrated in FIG. 4. Similar to the embodiment of FIG. 4, the
slab of the existing structure and intermediate strut are used as supports, and an H-
beam is inserted from behind the built wale. A short support is attached to the front
of the wale and the tendon fixed to the anchoring unit of both ends of the H-beam is
supported by the tendon support. This method is for a vertical prestressed scaffolding
system, which supports a channel-type excavating surface. In particular, the screw
jack or precedent load jack 72, connected with the horizontal strut 26, is coupled with
the anchoring unit 20 If the anchoring unit 20 is placed at a lower end of the
scaffolding system, the anchoring unit 20 can directly contact the existing slab (not
shown) instead of the strut 26 The vertical H-beam is coupled to the anchoring unit
by being inserted into a vertical hole 50 This contact or coupling part may be firmly
connected by, for example, welding or a bolt, preferably by a bolt for facilitating the
disassembly of the members Once the tendon 60 for supporting the vertical H-beam
is inserted into the anchoring unit, the tendon is fixed by the tendon-anchoring unit 73
at an opposite side of the anchoring unit Accordingly, this anchoring unit is used in
the vertical prestressed scaffolding system, wherein the wale or the vertical beam is
As apparent from the foregoing, there is an advantage in the prestressed
scaffolding system of the present invention in that vertical piles or horizontal beams
are prestressed by using a plurality of supports, anchoring units, and tendons The
number of struts and intermediate piles, which caused serious obstacles in carrying out
conventional constructional works, is considerably reduced
There is another advantage in that the excavation and scaffolding system
together with the construction cost are remarkably improved
Also, the formation of holes in the structure, which is inevitable in the
conventional scaffolding system, is effectively eliminated, thus facilitating the steel
reinforcing works and molding works, reducing the construction period and greatly
improving the water-tightness and durability of the finished structure.