FORM-2
THE PATENT ACT,1970
(39 OF 1970)
AND
THE PATENT RULES, 2003
(As Amended)
COMPLETE SPECIFICATION
(See section 10;rule 13)
"PI - GIRDER"
Tata Consulting Engineers Limited, a corporation organized and existing under the laws of India of Unit No. NB 1502
& SB 1501, 15th floor, Empire Tower, Cloud City Campus, Opposite Reliable Tech. Park, Thane-Belapur Road, Airoli,
Navi Mumbai 400708, India
The following specification particularly describes the invention and the manner in which it is to be performed:
2
PI - GIRDER
FIELD OF INVENTION
Embodiments of the present application relates to design of elevated tracks for commuting
5 purposes, more particularly, design of a modified precast prestressed post tensioned concrete
girder of lighter weight that reduces the need for special machinery for erection of large span
during construction procedure.
BACKGROUND OF THE INVENTION
10 Background description includes information that may be useful in understanding the present
invention. It is not an admission that any of the information provided herein is prior art or
relevant to the presently disclosed invention, or that any publication specifically or implicitly
referenced is prior art.
15 In the current scenario, girders are used in the construction of bridges, especially in the
construction of elevated railway tracks such as metro rail transportation. There are primarily
four types of girders, for example, plate girders, I girders, U girders, and box girders. These
girders play a vital role in the construction of metro viaducts. A viaduct is a particular form of
overpass or elevated pass, which includes a sequence of arches, wharfs, piers, or columns that
20 support an extended span of railway track or roadways. In general, a viaduct links two nodes
of almost similar height, which permits direct crossing across an expansive crossroad, water
body, or other obstructions and/ or does not interfere with the traffic running parallel along the
road in the ground. In current practice, U-Girder, I-Girder, plate girders, Box Girder etc., are
used in the construction of such metro viaducts. Furthermore, it is important to note that there
25 is an UP-Line track and a DN-Line track that normally do not cross each other except at
identified locations for functional purposes in the construction of the metro viaducts. The piers
are placed at standard intervals, for example, < 28.0 meters, with usually straight stretches,
namely standard span. There are also cross over locations where tracks cross each other, divert
or the spans become larger (> 28.0 m), namely special span.
30
Here, the U-girder is a standardized design for normal spans corresponding to various span
lengths. However, U-girder has limitations for special spans where corridor widths are varying
due to route alignments and diversions, therefore, width becomes larger and hence poses
3
problem to transport. The box girder due to its heavy weight and size is also not preferred.
Under the circumstances I-girders are preferred, however, the number of I-girders becomes
more and these are prone to toppling unless proper precautions are taken during erection.
Therefore, there is a need for a girder that is customized for special spans, safe, light in weight,
5 easy to transport and erect and be also cheaper in case of straight span of larger length and
aesthetically appealing.
SUMMARY OF THE INVENTION
The following presents a simplified summary of the subject matter to provide a basic
10 understanding of some of the aspects of subject matter embodiments. This summary is not an
extensive overview of the subject matter. It is not intended to identify key/critical elements of
the embodiments or to delineate the scope of the subject matter. Its sole purpose to present
some concepts of the subject matter in a simplified form as a prelude to the more detailed
description that is presented later.
15
The object of the invention is to provide a “Pi Girder” that is installable for normal as well as
special spans. The girder disclosed here is a precast prestressed post tensioned girder and is
erected by full span launching method (FSLM). It is lighter as compared to precast prestressed
box girder and hence can be erected by multiple cranes of lower capacity. Further, in the case
20 of large spans full span launching equipment like launching truss etc., is ruled out as the case
might be for precast prestressed box girder. Hence, erection of the Pi Girder is cheaper.
Furthermore, the loss of prestress is lower compared to box girder making the girder more
efficient. The Pi Girder disclosed here comprises a new and modified geometry of a prestressed
concrete post tensioned girder with better structural efficiency and aesthetics compared to the
25 prior art achieving cost savings, productivity, and enhanced safety. It also perfectly suits to the
beautiful aesthetics of other elements of metro station and standard spans along with
neighbouring urban infrastructures giving an overall “look good” feel.
The present disclosure describes a Pi Girder comprising a solid concrete body with a curved
30 cross section. The curved cross section comprises a wide bottom surface and a relatively wider
upper surface as compared to the bottom surface. The Pi Girder embodies a high base width to
height ratio due to the increase in width at the bottom compared to I-girder, wherein the higher
base width to height ratio reduces over-toppling. The Pi Girder also comprises a partially
4
hollow cavity that is more or less centrally positioned, wherein the partial hollow cavity defines
an elongate opening at the bottom of the girder. The Pi Girder is centrally hollow and is
accessible from the bottom opening throughout the entire span. The central hollow reduces the
weight of the entire span to make it lighter and more economical. The inside of hollow part can
5 be accessed through the bottom opening for inspection and carrying out repairing, if any.
Furthermore, the circular profile of the hollow and smooth curvature of the outer sides
eliminates possibility of stress concentration compared to corners prevalent in the box girder
and I girder making the stress distribution continuous without any abrupt hikes. Aerial work
platform or cherry picker may be used to approach to the bottom opening. The Pi Girder also
10 comprises a predefined orientation of prestressing cables or wires within the concrete cross
section of the girder in such a manner so that entire prestressing is done at a single stage at
ground before erection eliminating later stages of prestressing to be done at a height above
ground level thereby resulting enhanced safety and lesser construction time. Additional cables
as per Code provision can be accommodated to impart higher capacity to take care of
15 degradation of cables/ retrofit in the future. The less depth of the Pi Girder allows lesser lengths
of prestressing cables with anchorages even for large span leading to lesser loss of prestress
compared to box girder making the girder more efficient.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
20 The following drawings are illustrative of particular examples for enabling systems and
methods of the present disclosure, are descriptive of some of the methods and mechanism, and
are not intended to limit the scope of the invention. The drawings are not to scale (unless so
stated) and are intended for use in conjunction with the explanations in the following detailed
description.
25
FIGURE 1 exemplarily illustrates a cross sectional view of the Pi Girder, as an example
embodiment in the present disclosure.
FIGURES 2A-2C exemplarily illustrates different sections across the length of the Pi Girder,
30 which include a mid-section and full view, sectional elevation view, and a plan view
respectively, where FIGURES 2A-1 and 2A-2 exemplarily illustrate different portions of
FIGURE 2A for clarity.
5
FIGURES 3A-3E exemplarily illustrates sectional views across different section lines marked
in FIGURES 2C, wherein the drawings include section B-B in FIGURE 3A, section A-A or
the mid-span in FIGURE 3B, section C-C showing the cable anchorages in FIGURE 3C,
section D-D showing at bearing location in FIGURE 3D, and list of components in FIGURE
5 3E, as example embodiments in the present disclosure.
Persons skilled in the art will appreciate that elements in the figures are illustrated for simplicity
and clarity and may represent both hardware and software components of the system. Further,
the dimensions of some of the elements in the figure may be exaggerated relative to other
10 elements to help to improve understanding of various exemplary embodiments of the present
disclosure. Throughout the drawings, it should be noted that like reference numbers are used
to depict the same or similar elements, features, and structures.
DETAILED DESCRIPTION OF THE INVENTION
15
Exemplary embodiments now will be described. The disclosure may, however, be embodied
in many different forms and should not be construed as limited to the embodiments set forth
herein; rather, these embodiments are provided so that this disclosure will be thorough and
complete, and will fully convey its scope to those skilled in the art. The terminology used in
20 the detailed description of the particular exemplary embodiments illustrated in the
accompanying drawings is not intended to be limiting. In the drawings, like numbers refer to
like elements.
It is to be noted, however, that the reference numerals used herein illustrate only typical
25 embodiments of the present subject matter, and are therefore, not to be considered for limiting
of its scope, for the subject matter may admit to other equally effective embodiments.
The specification may refer to “an”, “one” or “some” embodiment(s) in several locations. This
does not necessarily imply that each such reference is to the same embodiment(s), or that the
30 feature only applies to a single embodiment. Single features of different embodiments may also
be combined to provide other embodiments.
6
As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms
as well, unless expressly stated otherwise. It will be further understood that the terms
“includes”, “comprises”, “including” and/or “comprising” when used in this specification,
specify the presence of stated features, integers, steps, operations, elements, and/or
5 components, but do not preclude the presence or addition of one or more other features,
integers, steps, operations, elements, components, and/or groups thereof. It will be understood
that when an element is referred to as being “connected” or “coupled” to another element, it
can be directly connected or coupled to the other element or intervening elements may be
present. Furthermore, “connected” or “coupled” as used herein may include operatively
10 connected or coupled. As used herein, the term “and/or” includes any and all combinations and
arrangements of one or more of the associated listed items.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have
the same meaning as commonly understood by one of ordinary skill in the art to which this
15 disclosure pertains. It will be further understood that terms, such as those defined in commonly
used dictionaries, should be interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be interpreted in an idealized or overly
formal sense unless expressly so defined herein.
20 FIGURE 1 exemplarily illustrates a cross sectional view of the Pi Girder (20), as an example
embodiment in the present disclosure. FIGURES 2A, 2A-1, 2A-2, 2B, and 2C exemplarily
illustrate different sections of the Pi Girder (20), which include a mid-section and full view,
sectional elevation view along the length, cable long profile and a plan view, as example
embodiments in the present disclosure. Here, FIGURES 2A-1 and 2A-2 exemplarily illustrate
25 portions of FIGURE 2A for clarity. FIGURES 3A-3E exemplarily illustrates sectional views
across different section lines marked in FIGURE 2C, wherein the drawings include section BB in FIGURE 3A, section A-A or the mid-span in FIGURE 3B, section C-C showing the
cable anchorages in FIGURE 3C, section D-D showing at bearing location in FIGURE 3D,
and list of components in FIGURE 3E, as example embodiments in the present disclosure.
30
As shown in FIGURES 3A-3E, the girder (20), or a Pi Girder (20) disclosed here comprises a
hollow girder with solid concrete body (1) with a curved cross section, a bottom surface (2) of
the solid concrete body (1), an upper surface (5) of the solid concrete body (1), which is
7
relatively wider as compared to the bottom surface (10) or the bottom surface (4) at span. A
hollow cavity (13) is substantially centrally positioned, where the hollow cavity (13) defines
an elongate bottom opening (15) at the bottom of the girder (20). In an embodiment, the girder
(20) comprises a high base width to height ratio due to the increase in width at the bottom
5 surface (10) at span, where the high base width to height ratio reduces over-toppling. The girder
(20) is centrally hollow with the hollow cavity (13) and (6) and is accessible from the bottom
opening throughout the entire span except near the support, where the hollow cavity (13) and
(6) reduces weight of entire span of the girder (20) to make the girder (20) lighter and
economical, and where inner section of the hollow cavity (13) is accessed through the bottom
10 opening for inspection and repair.
As shown in FIGURES 3A and 3B, in an embodiment, the curved cross section defined by the
hollow cavity (13) and smooth curvature of the curved side surface (2) provides smooth
transition across the curved cross section and reduces sharp corners, where the reduction of
15 sharp corners using the smooth curvature of the curved side surface (2) reduces possibility of
stress concentration, making the stress distribution in the girder (20) even without abrupt hikes.
The girder (20) further comprises a predefined orientation of prestressing cables and wires (14
a-d) within a concrete cross section of the girder (20), between the bottom surface (10) and top
surface (5) at bearing support and between the bottom surface (4) and top surface (5) at mid
20 span. Prestressing is done at a single stage at ground before erection of the Pi girder (20), which
eliminates later stages of prestressing to be done at a height above ground level, which provides
safety and reduces construction time. In an embodiment, geometric profile defined by the
reduced height of the Pi girder (20) reduces the length of prestressing cables and wires (14 ad) resulting in reduced loss of prestress due to friction along the length of the girder (20), where
25 the reduced height reduces total loss of prestress. In an embodiment, the solid concrete body
(1) having the curved cross section accommodates additional mass, which increases strength
and is designed for long span as high as 35m that can be launched by cranes by full span
launching method (FSLM).
30 In other words, as shown in FIGURES 3A and 3B, the circular profile due to the hollow cavity
(13) and smooth curvature of the curved side surface (2) provides smooth transition across the
curved cross section and reduces sharp corners. Sharp corners are sources of stress
concentration and reduction of sharp corners reduces possibility of stress concentration
8
compared to corners prevalent in the box girder and I-girder making the stress distribution
smooth without any abrupt hikes. Aerial work platform or cherry picker may be used to
approach to the bottom opening. The Pi Girder (20) also comprises a predefined orientation of
prestressing cables or wires (14 a-d) within the concrete cross section of the Pi-girder (20). The
5 entire prestressing is done at a single stage at ground before erection eliminating later stages of
prestressing to be done at a height above ground level, thereby resulting enhanced safety and
lesser construction time. The geometric profile of the Pi Girder (20), more specifically less
height compared to Box and/ or I girder reduces the length of prestressing cables resulting
reduced loss of prestress due to friction along the length of the girder. In view of this, total loss
10 of prestress is lower compared to box girder making the girder more efficient.
As shown in FIGURES 3B and 3C, the central hollow (6 and 13) section with the elongate
bottom opening (15) in the Pi Girder (20) provides access and allows workers to inspect from
the elongate opening (15) at the bottom, which eliminates requirement of minimum headroom,
15 if required which is not possible in case of box girder as the bottom is closed. A hollow cavity
(13) encircled by curved surface (3) provides working space for workers during maintenance.
Since hollow cavity (13) provides working space and is accessible from bottom opening (15),
minimum headroom as per standards as provided inside the box making the height of the box
girder larger is not necessary for Pi girder (20) resulting reduced depth of the Pi girder (20)
20 compared to Box girder. The Pi Girder (20) has greater mass compared to I girder and thereby
higher moment of Inertia and strength resulting lesser depth compared to I girder. The Pi Girder
(20) having a lesser depth as compared to box girder/ I girder and lesser number as compared
to I girder, consumes lesser quantities of concrete, reinforcement, prestressing cables and
associated auxiliaries like bearings, bearing pads, seismic arrestors, cross diaphragms when
25 calculated in totality for an overall span. This makes Pi Girder (20) cost economic. A hollow
cavity (6) is also positioned beyond the bearing support as shown in FIGURE. 3C, which
shows the inner surface of an embodiment of the hollow cavity (13). The vertical side surface
(7) on extreme sides of the Pi Girder (20) allows a thickness from the top surface (5) to form
the hollow cavity (6) beyond bearing support location towards end and hollow cavity (13) at
30 other locations all along the span and is the minimum from design requirement to reduce overall
depth.
9
As shown in FIGURES 3A, the Pi girder (20) is supported on bearings (11), where the bearings
(11) are placed on the vertical piers (columns) constructed at intervals along the route to
transmit the load to the foundations. The bearing (11) is an interface element in between the Pi
girder (20) and the pier. The bearings (11) are fixed at the top of the pier and the Pi girder (20)
5 rests on the bearing. Thus, bearing (11) transmits the vertical load from the Pi girder (20) and
allows horizontal movements of the Pi girder (20) as per technical requirement. As shown in
FIGURE 3C, the Pi girder (20) comprises an anchorage block (12), where Pi girders (20) are
made of prestressed concrete and the prestressed concrete is made by applying tension
externally to the cables (14a-d). The anchorage blocks (12) are fixtures that help to retain the
10 externally applied tension to the cables (14a-d). FIGURE. 3B shows rod embedment (8),
which are steel rods that are placed in position at specified intervals along the length of the Pi
girder (20) and embedded in the concrete during casting. The rails are placed on concrete pads
at certain intervals. These pads are cast at site encompassing the rod embedment (8) after
erection of the Pi girder (20). The rod embedment (8) connects the concrete pad with the Pi
15 girder (20) firmly in position. The plate embedment (9) as shown in FIG. 3B, which include
steel plates that are placed in position at specified intervals along the length of the Pi girder
(20) and embedded in the concrete during casting. Railings on either side of the Pi girder (20)
are fixed subsequently on the plate embedment (9).
20 The Pi Girder (20) is precast prestressed post tensioned girder and is erected by full span
launching method (FSLM). In Pi Girder (20), prestressing is done in single stage in the casting
yard eliminating prestressing activity after erection at site. This makes construction easier,
quicker and enhances safety as no on-site activity for prestressing at a height above ground is
required. The Pi Girder (20) is lighter as compared to precast prestressed box girder and hence
25 can be erected by multiple cranes of lower capacity. Further, in case of large spans, full span
launching equipment like a launching truss is not necessary for the Pi Girder (20) but the same
may be necessary for precast prestressed box girder due to heavy weight. Hence, erection of Pi
Girder (20) is cheaper.
30 Precast prestressed I-girder shall be more (almost double) in numbers compared to Pi Girder
(20) for same span inviting higher cost. In special spans like rail crossing and diversions,
viaduct becomes wider and savings in cost and time is more pronounced for Pi Girder (20) as
the number of girders becomes half compared to I-girder. The curved flaring from bottom to
10
the top of the Pi Girder (20) allows to accommodate more mass compared to I girder/U girder
resulting more strength and hence can be designed for long span as high as 35m that can be
launched by cranes by full span launching (FSLM) method. Prestressed box girder becomes
heavier for large span resulting in costlier erection equipment. Cost economy of Pi Girder (20)
5 in respect of production and erection by crane for large span shall enable the stakeholders to
go for larger span which in turn reduces number of piers and foundations saving the cost and
time of a project.
The Pi Girder (20) has wider base and lesser height compared to I girder which enables higher
10 restoring moment and lesser overturning moment yielding more stability. As such, Pi Girder
(20) is much more stable and safer during erection and eliminates possibility of tilting and
toppling as has been experienced in the case of I-girders and is aesthetically superior to I- girder
and box-girder, thereby showcasing better appearance which is important for infrastructure at
an urban landscape. A bigger space is required at casting yard for prestressed box-girder which
15 increases rent cost of the casting yard. Box Girders are designed considering both up and down
rail tracks (4 rails) on single Box Girder and therefore the entire width of Box Girder happens
to be so wide that lifting and erection pose challenges to the running traffic, whereas single Pi
Girder (20) consists of one rail track (2 rails) and acquires lesser road space and can easily be
erected during daytime running traffic.
20
Although the invention has been described with reference to specific embodiments, this
description is not meant to be construed in a limiting sense. Various modifications of the
disclosed embodiments, as well as alternate embodiments of the invention, will become
apparent to persons skilled in the art upon reference to the description of the invention. It is
25 therefore, contemplated that such modifications can be made without departing from the scope
of the present invention as defined.
11
We claim:
5 1. A girder (20) comprising:
a solid concrete body (1) with a curved cross section;
a bottom surface (2) of the solid concrete body (1);
an upper surface (5) of the solid concrete body (1), which is relatively wider as
compared to the bottom surface (2); and
10 a hollow cavity (13) that is substantially centrally positioned, wherein the hollow cavity
(13) defines an elongate opening (15) at the bottom of the girder (20).
2. The girder (20) as claimed in claim 1 comprises a high base width to height ratio due
to the increase in width at the bottom surface (2), wherein the high base width to height ratio
15 reduces over-toppling.
3. The girder (20) as claimed in claim 1 is centrally hollow with the hollow cavity (13)
and is accessible from the bottom opening throughout the entire span, wherein the hollow
cavity (13) reduces weight of entire span of the girder (20) to make the girder (20) lighter and
20 economical, and wherein inner section of the hollow cavity (13) is accessed through the bottom
opening for inspection and repair.
4. The girder (20) as claimed in claim 1, wherein the curved cross section defined by the
hollow cavity (13) and smooth curvature of the curved side surface (2) allows smooth transition
25 across the curved cross section and reduces sharp corners, wherein the reduction of sharp
corners using the smooth curvature of the curved side surface (2) reduces possibility of stress
concentration, making the stress distribution in the girder (20) even without abrupt hikes.
5. The girder (20) as claimed in claim 1, further comprises a predefined orientation of
30 prestressing cables and wires (14 a-d) within a concrete cross section of the girder (20) in a
manner in which the prestressing is done at a single stage at ground before erection, which
eliminates later stages of prestressing to be done at a height above ground level, which provides
safety and reduces construction time.
12
6. The girder (20) as claimed in claim 1, wherein geometric profile defined by the reduced
height of the girder (20) reduces the length of prestressing cables and wires (14 a-d) resulting
in reduced loss of prestress due to friction along the length of the girder (20), and wherein the
5 reduced height reduces total loss of prestress.
7. The girder (20) as claimed in claim 1, wherein the solid concrete body (1) comprising
the curved cross section accommodates additional mass, which increases strength and is
designed for long span as high as 35 meters(m) that can be launched by cranes by full span
10 launching method (FSLM).
8. The girder (20) as claimed in claim 1, wherein central hollow (6 and 13) section with
the elongate bottom opening (15) in the girder (20) provides access and allows workers to
inspect from the elongate opening (15) at the bottom, which eliminates requirement of
15 minimum headroom and carry out work inside the girder (20).
9. The girder (20) as claimed in claim 1, further comprises a hollow surface (3) that is
encircled by the hollow cavity (13), which provides working space for workers during
maintenance.
20
10. The girder (20) as claimed in claim 1, further comprises a rod embedment (8), which
are steel rods that are placed in position at specified intervals along length of the Pi girder (20)
and embedded in the concrete during casting, wherein rails are placed on concrete pads at
certain intervals and the pads are cast at site encompassing the rod embedment (8) after erection
25 of the Pi girder (20).
11. The girder (20) as claimed in claim 1, further comprises a plate embedment (9) that
comprises steel plates that are placed at specified intervals along the length of the Pi girder (20)
and embedded in the concrete during casting, wherein railings on either side of the Pi girder
30 (20) are fixed subsequently on the plate embedment (9).
13
12. The girder (20) as claimed in claim 1, further comprises a plurality of anchorage blocks
(12), which are fixtures to retain externally applied tension to the cables (14 a-d) that are used
to prepare prestressed concrete for the Pi girders (20).