Glorious 150 years of Indian Railways’ service to the nation

Since the inaugural run of the first train on the Indian sub-continent on 16th April 1853 from Bombay to Thane, Railways in Greater India has completed glorious 167 years of service.

• Indian Railways: With Rail network of 64,000 route Kms has a total of 1,27,768 bridges, out of which:
  

  - approx 640 are Important bridges,

  - approx. 10,500 major bridges, and rest minor bridges.

• Most of these bridges are steel plate girder, triangulated truss, and arch type bridges built primarily to earlier Bridge Design Standards of 1903, or later from 1926 year.
  

  - Design vertical axle and longitudinal loads have gone up successively in 1926, 1933, 1975, 1987.

  - In the last 35-50 years or so, RCC and PSC type span bridges were built to later Bridge Loading Standards of RBG (1975) and MBG (1987) specifying higher axle loads.

• On Indian Railways, age-wise profile of the in-service bridges reflect 44% bridges are over 100 years old, whereas 62% are over 80 years, and 75% are over 60% old.
• Concurrently, in the last 20 years or so, quite a few steel bridges have been strengthened and rehabilitated/girders replaced in recent years, on conditionbasis, or being of early steel metallurgy, and traffic intensity loads requirements.
  All the early steel bridges, pre 1905 period had been undertaken for replacement under Special Safety Funds. Still, majority of the steel bridges in service conform to earlier BGML loading standards continue, with some attempts of strengthening in recent years.
  Most of these bridges, though built to design standards of earlier years (1903, 1926) have withstood the test of time, and with minimum inputs been able to carry heavier axle loads as per present demand of freight traffic.

BRIDGE CHALLENGES ON IR: increased requirements of Rail Traffic, higher Axle loads

• Maintain the Bridges for increased loading: Vertical and longitudinal loads have gone up successively since 1926, 1933 to 1975 (RBG), and 1987 (MBG) standards. RCC and PSC type span bridges have also been added to inventory in the last 25-30 years, built to MBG standards with 25 tonnes maximum load.
• Carry increased axle loads on existing/ old Bridges: Since 2007-08, freight train axle loads have gone up to 22.32t ( CC+8+2) Loading, now on all major routes, & 25t axle loads on certain specified Feeder routes. Railway engineers met the challenge of moving increased axle loads on the existing network and bridges by systematic assessment, inspection and making the bridges fit by rehabilitation/ strengthening/ rebuilding.
• Additional GMT on the existing Rail network: Besides the increase in axle loads in the last two decades, freight loading has registered an annual incremental increase of about 60 to 80 Million Tonnes. Now, 1000- 1100 Million Tonnes freight loading per annum is the norm on IR.
• Plan, design and construct new Bridges to higher Loading Standards: Approach is also to design the new bridges for 32.5t axle loads on Dedicated Freight Corridor Routes. The challenge is to design, innovate, revisit constructability issues at site, and adopt fast-paced construction methods.
• Related issues: Innovative design and construction strategies for Road over and under Bridges (ROB and RUBs): For increased throughput of Rail Traffic, and to enhance Safety at Rail/ road conflict points viz. level crossings, large number of ROBs/RUBs shall have to be constructed to replace the existing busy level crossings (based on criteria of more than 1 lakh TVU). Cost effective and fast-track construction methods are being adopted. Practically, all Unmanned Level Crossings have been eliminated on major routes of IR.

STRATEGIES FOR INCREASED LOADING on Indian Railways

• Background: Increase in Design Loads Standards for Rail bridges:
  

  S.No.	Loading standard	TLD (t/m)	Max Tractive effort for two locos (t)
  (a)	BGML- 1926	7.67	47.6
  (b)	RBG - 1975	7.67	75.0
  (c)	MBG - 1987	8.25	100
  (d)	25t loading – 2008	9.33	126
  (e)	DFC loading -2008	12.8	126

• Introduction of Dedicated Freight Corridors (DFC): To meet the growing needs of traffic, it has decided to construct the following Dedicated Freight Corridors for the exclusive use of freight traffic:

  (i) Western DFC- Dadri to Jawahar Lal Nehru Port Trust (JNPT) (1483km)

  (ii) Eastern DFC - Son Nagar to Dhandarikalan (1190km)

Feasibility studies are also in progress for the following proposed Dedicated Freight Corridors:

(a) East-West corridor - Kolkata – Nagpur- Mumbai

(b) East Coast corridor - Kharagpur – Vijayawada (1097km)

(c) Southern corridor - Chennai- Goa (902km)

(d) North-South corridor – Delhi–Chennai (2190km)

• Maintenance strategies: For bridges subjected to heavier axle loads, apart from the Annual inspection, Brief Review inspection at closer interval has been adopted, to closely monitor critical portions namely: Masonry pier/Abutments, Bearings, and bearing pad area, and critically stressed member(s). Distressed bridges are to be inspected at 6 months interval regularly.
  For enhancing the life and serviceability condition, strategy involves:

  - Early repair and rehabilitation to masonry cracks, mortar leaching, etc. by way of local repairs, jacketing, etc.

  - Metallizing of the flooring system in case of steel structures – cross girder and Stringer.

  - Attention to corroded and minor cracked steel members on early priority.

  - inspection and close attention to the upkeep of the existing bearings in service – e.g: oil bath of rocker & roller, regular greasing of plate bearings, etc.

  - Repair /strengthening wherever required.

• Reliability and Instrumentation Methods for assessing condition:
• Efforts undertaken to assess the load-carrying capacity and determine the Residual life of the bridge to ensure reliability of the bridges to carry heavy axle loads, following approach and methods have been considered on Indian Railways, apart from the visual examination based Annual Inspections.
  • Vibration signature analysis for overall bridge superstructure.
  • NDT methods for joints (both welded and rivetted), critically loaded steel members.
  • Bridge Condition Monitoring (BCM) of few bridges on heavy axle routes by way of:
  • Numerical Model & Analysis of the bridge super-structure.
  • Instrumentation of the Bridge: Adopt a live-load monitoring system and take quarterly readings to measure long term effects.
  • Sensors include: Electrical foil strain gauges, vibrating wire strain gauges (VWSG), tilt sensors, piezo- accelerometers.
  • Measure and monitor inputs from sensors using data-loggers and determine the highly stressed members.
  • Residual life assessment and degradation prediction

    Based on the stress data acquired using sensors, on quarterly basis, together with S-N curves and lab tests on steel test specimen from the girders, the Residual life of steel bridges considering the past, present and the future traffic projection can be determined and has been assessed for a few bridges on IR. This has helped assess the load carrying capacity and also ensure reliability of existing bridges.

• Instrumentation: To Introduce (CC+8+2) axle loading: Sample representative bridges (about 80 nos.) were selected on 14 Zonal Railways for instrumentation covering various types of bridge loadings (such as BGML, RBG, MBG), span types (such as through, semi through, under slung, plate girder, arch, PSC etc.), bearings, materials, and different age groups for monitoring the effects of increased higher axle and longitudinal loads on the bridge components i.e., foundations, piers and abutments, bearings and super structure. The study planned was carried over 3 years.
  
  Interim results of instrumentation obtained so far indicated, stresses in the members are by and large within permissible limits. More inference, when additional results are available. In any case, balance fatigue life is likely to get reduced. Certain (steel) Bridges would be required to be kept under observation more closely.
• Strengthening, Rebuilding & Replacement Strategies: Existing and old bridges on condition basis only are identified for repairs, rebuilding or replacement. Concurrently over the years, quite a few steel bridges have been strengthened, rebuilt and replaced. Early steel bridges, pre - 1905 period, have been practically replaced under Special Safety Fund. With Annual inspection, close monitoring, and Bridge Condition Monitoring & Assessment for increased axle loads, the bridges are likely to serve the purpose without major rebuilding or replacement.

REVISION OF CODES OF PRACTICE FOR BRIDGES

• IRS codes are under review and updation to keep pace with new technology. IRS Concrete Bridge Code, which was earlier based on working stress concepts, has been recently revised based on Limit State Design concepts.
• 4.1.1 A Bridge Technology Development Group (BTDG), with eminent Engineers and Consultants, has been constituted by Ministry of Railways. Provisions of IRS Concrete Bridge Code are under finalization. While revising the provisions, due consideration is being taken about provisions in International Codes such as BS codes, UIC codes, EURO codes, with their applicability in Indian scenario.
• 4.1.2 Related to the issue of revision in codes, Railway Board had recently constituted Various Sub- Groups at Railway Board Level, and at RDSO level with view to have Recommendations on Specific Topics.
• 4.1.3 Based on the discussions in the meeting of Elite Specialist Group, RDSO examined comparison of various provisions in IRS concrete bridge code & steel bridge code w.r.t. IS codes & BS codes. Railways Board has nominated a committee of six senior officers for revision of IRS Concrete Bridge Code and IRS Steel Bridge Code.

LATEST BRIDGE TECHNOLOGIES: Adoption therof-

• Latest Bridge Technologies
  • Latest State of Art has been adopted in design & construction of Railway Bridges such as use of submerged arc Welding in fabrication of steel bridge girders, use of large span PSC girders, NDT testing etc.
  • A number of research projects are in progress in association with IITs and other leading institutes.
  • We actively associate with all National and International forums on bridges to continuously upgrade ourselves.
  • A Railway Bridge chair was established at IIT, Roorkee in 1999. The main objective of the chair is to promote research & development in the area of bridge engineering. An important activity related to chair is dissemination of advance knowledge & technology transfer.
  • Cable-stayed Road over bridges have been constructed at Bangalore and Patna, to introduce new technology.
  • Extra- dosed ( main span of 92m) PSC Metro bridge at Pragati Maidan for Delhi metro Lines permitted over Trunk Route lines of NR for South bound Shatabdi/ Rajdhani route.
  • Large Span Steel Arch Bridge across Chenab River
  • Welded Rail cum Road Bridge Box truss Bogibeel Bridge across Brahmaputra River
• Inspection and maintenance of Railway Bridges by Mobile Bridge Inspection Units (MBIU) -

  Integrated Railway Modernisation Plan (2005-2010) issued by Ministry of Railways in Nov 2004 provides for Inspection and maintenance of Railway Bridges by Mobile Bridge Inspection Units (16 Nos) at a cost of Rs 90 Cr. two nos. Mobile Bridge Inspection Units (MBIU) were sanctioned in RSP 1998-99 and have since been procured and commissioning is in final stage at RCF, Kapurthala.

• Pilot Projects: A number of Pilot Projects have been undertaken on Indian Railways with reputed specialized agencies from abroad. Engineers and supervisors from Railways have been trained in latest bridge technologies:-
  • Determination of unknown bridge foundations and integrity assessment of foundations and condition assessment of brick masonry structures by NDT methods by M/S OLSON, USA.
  • Acoustic Emission Testing by M/S TISEC, Canada and M/S Dunegan Engineering Company, USA.
  • Fatigue testing and remaining life analysis of steel bridges by M/S Sharma & Associates, Chicago, USA.
  • Strain gauging instrumentation and load rating of bridges by M/S Bridge Diagnostics, USA.
  • Under Water bridge inspection by M/S L&T RAMBOLL, Denmark.
  • -destructive testing of Railway Bridges by M/S RAMBOLL, Denmark.
• Arch bridges: Masonry arch bridges form an integral part of the Indian Railways infrastructure. They are the oldest structure type in the railway bridge population with 19,500 Nos. bridges in service. In order that the railways accommodate increased axle loads, train speeds and a greater volume of freight traffic, it is necessary to assess the load carrying capacity of existing masonry arch bridges. Assessment of existing masonry arch bridges is due to inability to assess material strength, and much of the structure is hidden from view. Following major technical inputs have been given.
• Association with UIC group on arch bridges

  (a) UIC has taken up a comprehensive project on ‘Improving Assessment, Optimization of Maintenance & Development of data base for Masonry Arch Bridges in 2002/03. Keeping in view large number of Masonry Arch Bridges on Indian Railways, IR joined this project in 2004. The principle objective of this UIC project on masonry arch bridges is to collect and develop tools that help optimizing the life-cycle management of masonry arch bridges, help reducing the maintenance costs and promote an effective exchange of good practices among various world railways.

  (b) 14 Railways such as SNCF, DB etc. have taken part in this group with association of 10 expert institutions.

• Benefits to Indian Railways – The project has given better understanding of behavior of Arch bridges, how to inspect and assess load carrying capacity of such bridges and what methods of repairs can be adopted economically. It has given exposure to modern methods available for the above purpose in World Railway Systems including Ring 1.5, Ring 2.0 etc. Knowledge gained through the project has been used to train engineers and supervisors.
  
  (ii) Earlier IR also used Syntex technology on trial basis for rehabilitation and strengthening of arch bridges.

BRIDGE CONSTRUCTION AND THE WAY AHEAD

• Indian Railways are going ahead with the development of bridge Infrastructure in a big way in all parts of the country, esp. at USBRL Project ( J&K), and North Eastern States (NF Railways), and the DFCCIL Corridors. This is in process and would require:
  • The Indian Bridge Industry to develop expertise in design, construction and maintenance of large span bridges with the assistance of International and Local Consultants and Construction Companies to arrive at optimum solutions.
  • Acquire construction & Launching capability for special tbridges structures for specific applications, such as large span continuous steel bridges by end cantilever launching method.
  • Construction industry to give attention to Quality of Construction, evolve QA/QC procedure and practices.
  • Adopt modern Bridge Condition Monitoring approach and gain experience in quick assessment of Load Carrying Capacity and Residual Life Analysis of a bridge.
  • Adopt New Technology in the area of - Special Structural Steel for superstructure, Welding Technology, high strength concrete, applications to check corrosion in adverse conditions, and Special Bearings types.
  • Improved construction methods to achieve Fast-paced construction.
  • Risk Analysis approach for important bridge project. & Preventive Maintenance strategies pre-empting serious failure conditions.

‘I hope and wish Indian Bridge Industry would adapt to meet the challenges in the years to come and live up to increased expectations of Public and users’ – words by S. K Vij, Member Engineering, Railway Board at Indian Institution of Bridge Engineers- National Seminar on ‘Advances and Future Trends In Design and Construction Of Bridges’, 11 – 13 JULY 2008