Fib Various Types of Structures for Namma Metro

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BANGALORE METRO RAIL PROJECT Some Interesting Construction features in Namma Metro Viaducts and Stations. Sudhir Chandra B.S. Director (Project & Planning), BMRCL.

INTRODUCTION The burgeoning growth of population, vehicular traffic and advent of IT and electronic industries in the

last four decades in Bangalore, reminded the need for a Mass Rapid Transit System (MRTS) in Bangalore as far back as in 1983. Several studies were undertaken including a World Bank study in 1988. A Light Rail Transit(LRT) system on Public-Private –Partnership (PPP), based on a feasibility study by IL &FS, after fixing a private partner was also tried; but it failed to takeoff due to a variety of reasons. The success of opening a few sections in Delhi by Delhi Metro Rail Corporation (DMRC) resulted in the award of a contract in 2002 to DMRC to make a DPR for a metro system in Bangalore consisting of two corridors and costing about Rs.5000 crores. DMRC’s report in May 2003 recommended two corridors, one East-West corridor from Byappanahalli to Mysore Road terminal upto Ring Road junction, 18.10 kms long and another North-South corridor from Yeshwantpur to RV Road Terminal 14.90kms long a total length of 33 kms at a completion cost of Rs.4989 crores. GoI approved the project in May 2006 at a completion cost of Rs.6395 crores meeting out the inflation in the intervening period. Equity participation of both governments, GoI and GoK, was equal at 15% each. Total share of GoI was 25% and GoK 30% including subordinate debt and the balance 45% was the senior term debt. Further in 2010, GoI approved extensions of 5.60km on north to Nagasandra and 3.70kms on South to Yelachenahlli on North-South corridor at a completion cost of Rs.1763 crores, making the metro net work Phase-1 in Bangalore, 42.30 kms long, at a completion cost of Rs. 8158 crores. On account of phenomenal increase in prices of cement and steel, building materials -especially sand-and fuel, the estimate was revised and Govt. of India approved the revised cost of Rs.11609 crores on 4th October 2011. (Rs. 1 crore = Rs. 10 millions). The Phase-2 of Bangalore Metro, 72.10 kms in length, consists of 61 stations( 49 elevated and 12 underground) and the cost of the project is INR 264.05 billion( about 5.0 billion USD) It consists of four extensions on the N,S,E & W of N-S and E-W corridors of Phase-1 and two new lines 18.8 kms and 21.2 kms long. Except for a length of 14 kms, rest 58.1 kms is elevated. The Public Investment Board(PIB) has approved the proposal and the Govt.of India sanction is expected shortly. It is planned to be completed in 2019.

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2. Salient features of the Project: Gauge Design speed Commercial speed

: : :

Standard Gauge(1435mm) double line. 80 kmph 34 kmph

Total length of lines

:

    

East-West corridor - 18.10kms North-South corridor - 24.20kms Total - 42.30kms Elevated corridor - 33.50kms Underground corridor - 8.80kms.

Total number of stations

:

  

Centre to centre distance of tracks

:

 

At grade 1 (Byappanahalli) Elevated - 32 Underground -7 (incl. common Majestic interchange station) Elevated 4.20m Underground 15.04m (twin tunnels).

Station platforms: Elevated Underground Sharpest curve (horizontal)

: : :

Side platforms, 4m wide generally. Island platform, 12 to 16m wide. 120m radius in main line in elevated corridor 200m radius in main line in underground corridor 100m radius in depots and yards. 125mm 100mm 1500 m (min) 3.3% (permitted 4%) about 40%  Modern rolling stock with Stainless steel body and air conditioned automatic closing doors.  Motored axles - 67%  Axle load - 15 tonnes  Class of accommodation - One  Capacity of 3 car unit 975 Capacity of 6 car unit 2005.  Size: 20.80 x 2.88 x 3.80m high.

Maximum cant Maximum cant deficiency Vertical curve radius Steepest gradient Percentage of curved track Rolling stock

: : : : : :

Maintenance facilities

:

E-W corridor - Baiyappanahalli depot corridor - Peenya depot

Minimum headway

:

3 mins.

Design Phpdt (peak hour peak direction trips)

:

40,100

Operating hours

:

5.00 hrs to 24.00 hrs

Projected ridership

:

19.7 lakhs by 2021

Financial Internal Rate of Return (FIRR)

:

5.46%

Economic Internal Rate of Return (EIRR)

:

24%

Train operations:

N-S

3 3.

Construction features in brief:

3.1.

Viaducts

Metro corridors are passing through one of the densest areas in Bangalore City. The roads are narrow; at times it is hardly 14m wide. Immediately, alongside the road are the utilities (water supply pipelines, sewers, communication cables, electric cables, etc) buried hardly 600mm below the ground. There is storm water drain thereafter with a foot-path on top of it. Hugging on to the footpath are the shops or residences with or without setbacks and compound walls. When the viaduct pier is located in the centre of the road, the road which is already narrow becomes narrower still to the extent of the foot print of the pier. Hence in narrow roads, the lateral dimension of the pier had to be kept to the minimum to affect the road width least. So design of pier had to be suited accordingly. Similarly, the superstructure girders were designed to suit the segmental construction with launching girders (overhead and under slung) single cell, box shaped, deck type to support both tracks (Up and Down). I –girders were used as an exception. Typical viaduct structure

3.2

Elevated Stations:

Design of elevated stations had to be done depending on the local conditions, road widths, foot path widths available, etc. Broadly Station structures designed in Bangalore Metro Project can be classified into two categories: (i)

Cantilever structure - Tracks, platforms & concourses are on single central pier.

Staircases/Escalators from concourse to platform have been housed in off road structure. Station entry is also in off road structure. Off road structures provided are connected through linking bridges to the station structure.

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(ii)

Portal structure- It houses entire station including staircases & escalators from

concourse to platform. Only station entry staircases/escalators are on footpath or off road.

4.

Viaducts Construction details:

4.1

Nature of foundation –Open individual footing,Strip footing,Raft,Pile

Open /Raft foundations are seldon used as the availability of rock at shallow depths is rare. This is also limited to availability of hard strata at depths less than 4 to 5 meters. Beyond this depth, pile foundations are adopted. The substrata consist of silty sand, sandy silt, disintegrated rock and hard rock (230 to 300 mpa). For Viaduct, pile foundations, circular piles of 1200mm dia have been used. The bearing piles capacity is taken as 500t and friction piles capacity as 300t to 400t the lateral load capacity is taken as 20 to 28t depending on strata & site constraints and conditions.

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OPEN FOUNDATION :

6

RAFT FOUNDATION :

7

STRIP FOOTING :

PILE FOUNDATION :

8

PILES CASTED :

4.2

Sub structure Pier and Pier cap for Viaduct:

The pier width of 1.6m is chosen normal to traffic direction to minimize occupation of the road foot print and least reduction in the carriageway. 4.2.1

Elliptical Piers:

Circular pier is the best shape for a pier- most efficient cross section. But since Bangalore metro goes in narrow roads, the lateral dimension of pier should be reduced to have more carriageway width. So, in the first reach ‘elliptical pier’ was designed with the minor axis kept square to the road and major axis parallel to the road. Since the pier is elliptical in shape, the shuttering for pier becomes cumbersome, costly and time taking. So in other reaches, it was changed to Double-‘D’ shape, shutters for which is comparatively easier to make; Pier cap shuttering is also not complicated. In the case of elliptical piers the pier cap shuttering is also very complicated. All piers are having flutes’ (serrations) with horizontal bands in between. This helps in easy tearing of bills pasted on piers by miscreants.

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Elliptical Piers

10

11 Double ‘D’ Pier:

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4.2.2

Eccentric/ Inverted L-shaped Piers:

At certain locations, where the piers cannot be placed in the road lanes, as it becomes an obstruction, the piers are placed in the road median and eccentric piers are constructed, ie, the box girder centre is eccentric wrt the centre of the pier. However, the maximum eccentricity is limited to 1900mm.

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4.2.3

Portal Piers:

Where eccentricity goes beyond 1.80m, eccentric piers are not preferred. But a Portal is constructed with two legs and a beam on top to span the legs, which will support the Box girder. In such a case, the rail level goes up compared to standard piers/eccentric piers. 4.2.4. Shuttering used for piers in both the above cases(4.2.2 and 4.2.3) are not interchangeable with the standard circular piers shuttering, whereas the Double D pier shuttering are interchangeable. Hence, the non-circular pier scores over circular pier in this respect.

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4.3

Superstructure for Viaduct

Single cell, box type, segmental girder has been mostly used on viaducts. They are post tensioned. Blisters are left in 2nd and 3rd segments for future pristressing, if required.

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4.3.1

The standard viaduct span is 28m. Each segment is 3m long except the pier segments (first and last which are 1.95m long). The 3m modules when taken out / added in from the standard span make the spans 25m, 22m and 31m. On sharp curves (120m radius) shorter spans of 22m are used as otherwise there is uplift of bearings in larger spans.

4.3.2

At road junctions or while crossing rail tracks,etc non-standard spans, cast-in-situ, post tensioned girders are used viz 41m,50m,66m on Bangalore Metro project. The 66m span only one of its kind is on a 136m radius sharp curve crossing electrified railway tracks, a single cell box girder, post-tensioned. To prevent uplift of the bearings, vertical prestressing with 96 strands, 7 ply is being done for both the piers. A dummy hole has also been left in each pier, for future use, if need be.

4.3.3

The viaduct spans are designed as simply supported spans except for those at track cross over and turnout locations where the slabs are designed as continuously supported over girders.

4.3.4. Elastomeric bearings have been used for spans upto 31m and POT and PTFE bearings for longer spans as well as spans carrying track cross-overs and turnouts.

16 ELASTOMETRIC ( UPTO 31M SPANS GENERALLY ) :

17 POT-PTFE ( FOR SPANS ABOVE 31 M , SHARP CURVES – 120M RADIUS ,CROSSOVERS AND TURNOUT SPANS)

5.

Elevated stations Construction details:

18 There are two types of elevated stations in Bangalore Metro Rail. 5.1

Cantilever stations:

There is a central pier carrying the tracks; the concourse and the platforms cantilever out from this pier. They are spaced 15 to 20m apart. It has limitations in that the cantilever length is limited as otherwise there will be excessive deflections. Also resonance is to be specially checked up. But it gives a very sleek and pleasant look. The diversion of utilities is minimized in this configuration of stations. The concourse girders are I type (precast, pretensioned/post tensioned) or Pi type (precast RCC). There are pier arms at concourse and platform levels to support I type or Pi type girders. Platform girders are I type (precast, pretensioned/ post tensioned, steel) or Pi type (precast RCC). Track girders are I type posttensioned girders (4 nos) or U type pretensioned girders (3 nos). U type girders are not suitable in the spans where the d.c. electric traction cables have to be brought from the track level to the Traction substation in the station building at concourse level as there is no space between the girders to puncture hole/slit through the deck slab. Hence, in such spans, I-girders have been used as there is enough space available between the top flanges of the adjacent girders for hole/slit to be made through the deck slab. They rest on elastomeric bearings. Roofing is supported on steel trusses. Galvalume sheeting of different colors with polycarbonate sheets interspersed for adequate lighting is used. Sides of the platform to the extent possible are kept open for good ventilation. Station entry to concourse is provided in off road structures.

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REACH - 2 (ALL SIX STATIONS): CANTILEVER STATION (EXAMPLE – MAGADI ROAD).

SUPER STRUCTURE FOR TRACK SUPPORT : I – GIRDER (POST-TENSIONED)

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PLATFORM LEVEL AND CONCOURSE LEVEL PIER ARM DETAIL :

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SUPERSTRUCTURE CONCOURSE SUPPORT : Pi - GIRDER (PRE-CAST RCC)

(SUPERSTRUCTURE PLATFORM SUPPORT : Pi – GIRDER (PRE-CAST RCC)

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23 PLATFORM SUPPORT – TT-GIRDERS PIER ARMS WITH LBEAMS SUPPORT THE CONCOURSE GIRDERS AND PLATFORM GIRDERS

CONCOURSE SUPPORT – TT-GIRDERS

DOUBLE DCOLUMNS

ROOF STRUCTURE – STEEL FRAME WITH GALVALUME SHEETING.

24 5.2 Portal structure stations:

Station structure consists of portals, generally three-legged, to span the road widths. The other members and components remain more or less the same. Such structures have been adopted in reaches R-1, 3b and 4a. The merit of this structure is that it is more stable and the internal stair cases & escalators are within the main structure. With such a configuration, the land acquisition is minimum at the sides.

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SUPER STRUCTURE FOR TRACK SUPPORT: I – GIRDER (POST-TENSIONED)

SUPERSTRUCTURE PLATFORM SUPPORT: I– GIRDER (PRE-TENSIONED)

SUPERSTRUCTURE CONCOURSE SUPPORT : I - GIRDER (PRE-TENSIONED)

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CONCOURSE SUPPORT I6. Some unique design of Viaduct and Stations. 6.1

Special Curved span 66m flyover over Electrified Railway tracks (Cast-in-situ):

The Northern line of Bangalore Metro from Peenya to Sampige Road station flies over the SWR Tumkur electrified main lines at Malleshwaram (Kuvempu Road). It is a skew crossing with curvature of 136 mtrs radius. The span across the railway land is 66mtrs. It consists of a single cell box girder, post tensioned. Due to the sharp curvature and long span, the outer bearings are subject to ‘uplift’; replacement of bearings often over running tracks will be difficult. To prevent uplift of the bearings, ‘vertical prestressing’ was thought of in the beginning, but was given up considering the durability, the need to have spare arrangements for prestressing during service, if the need arises, as very limited periods will be available for repairs, retrofitting, etc once the commercial operations are commenced.

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Salient Features:

OVERALL SPAN (C/C OF EXP JT)

:

66M

RADIUS AT CENTRELINE OF ALIGNMENT

:

136M

DEPTH OF THE BOX GIRDER

:

4.0 M

WIDTH OF THE BOX GIRDER AT TOP

:

8.8 M

WIDTH OF THE BOX GIRDER AT BOTTOM

:

3.6 M

TYPE OF BEARING PROPOSED

:POT-CUM-PTFE

MAX. NO OF AXLES ON THE SPANS

:

13 AXLES / TRACK (OF 15 TONS)

TOTAL NO OF PRESTRESSING CABLES (LONG.)

:

24 NOS OF 19 T 15

TOTAL NO OF VERTICAL PRESTRESS STRANDS

:

95 NOS OF 15 DIA

HEIGHT FROM RAIL LEVEL TO PILE CAP TOP

:13.7M (MAX)

OVERALL HEIGHT OF PIER

:

PIER SIZE

:

PIER CAP SIZE AT TOP

:

4.9M X 4.5M

THICKNESS OF PIER CAP

:

0.6 M ST + 0.9M VARYING

NO. OF PILES

:

8 & 9NOS RESPECTIVELY.

8.82M (MAX) 4M X 2.5 M

28 6.2

Deepanjalinagar Station:

Deepanjalinagar station is the penultimate station on the Magadi Road-Mysore Road stretch of E-W Corridor. The station is sandwiched between the ROB across the Mysore Bangalore SWR lines and the National Highway to Mysore. The topography on either side of the station is undulating and the formation is in deep cutting. It is also surrounded by three built up areas and an important temple just at the edge of the station which have to be saved and these constraints make entire station (three legged portal structure) an ‘indeterminate structure’ with unequal spans. The portals have also unequal legs.

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6.3 Some special features at stations: 6.3.1

Foundations: Mono Piles:

At times the extreme rows of columns go very near to the property line making construction of multipiles and pile cap construction impossible. Mono piles of higher diameter 1600mm have been used (normal piles are 1200mm diameter)

MONOPILES (1600MM

6.3.2

Floating columns:

Due to space constraints and shifting of utilities (sewer lines especially) not becoming feasible, ‘floating column concept’ has also been adopted.

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FLOATING COLUMN 6.3.3

Replacement of girders/bearings during maintenance:

Generally elastomeric bearings are provided for all standard spans and at stations. POT and PTFE bearings are provided for special spans greater than 31m and cross over spans. The bearings have life of 20-25 years. Bearings have to be replaced in viaduct by lifting girders by taking temporary block for train movement. In case of station, replacement of bearings will be required only on the track girder where trains are moving. This can be replaced by opening the rail fastening system and connection to the bearings and refitted after replacement of the bearings. Other bearings of the stations at concourse are not subjected to heavy load thus unlikely to be replaced. 6.3.4 Transition spans: In the station lengths the track supporting structure is either I-girders or U-girders whereas the viaduct in the approaches of the station consists of segmental box girders. Hence the first pier, just after the station ends, is a ‘transition pier’ on which from one side I or U girders of station rest and on the other side the segmental box girder rests. As the depths of girders vary, the bearings are at different levels and the pier cap has to be meticulously designed to take care of the extra moments due to the ‘couple action’. These transition spans are kept normally not more than 20m in length.

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Electrostatic insulating membrane:

As the mode of traction is 750 v dc, to prevent electrocution of passengers while alighting or boarding the train (one hand being held against the coach and the foot being on the platform) special electrostatic membranes are placed below the floor finish for a width of about 4 meters, which acts as an insulating medium. 7

Stray current protection:

A special feature of this metro is that since 750V dc third rail system is used, there is the problem of ‘stray current corrosion’ which doesn’t arise in other metro systems where AC traction is used. We have to guard against it. Special measures have been adopted to minimize the corrosion of neighboring utilities, of steel members, rebar of metro structures which will otherwise weaken the structure and reduce its life. This has been done by inter connecting rebar’s from the track level to the foundation bottom level of piers, columns, etc so that they get earthed. MAHATMA GANDHI ROAD STATION:

32 SWAMI VIVEKANAND ROAD STATION:

BYAPPANAHALLI STATION:

33 YESHWANTHPUR STATION:

VIJAYANAGAR STATION:

34 NATIONAL COLLEGE STATION

Conclusions:

Stations have been designed passenger -friendly, persons with disabilities- friendly (lifts and tactile provision), etc. Bangaloreans, being especially aesthetic loving and connoisseurs, the stations have been architecturally designed to give a pleasing look in the Bangalore sky line.

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