EVALUATION OF NUMERICAL SYSTEM IN TERMS OF USEFULNESS AT
SITE AND APPLICABILITY OF THE SAME FOR USE BY CENTRALIZED
BRIDGE ORGANIZATION, SUGGESTIONS FOR IMPROVEMENT OF THE
SYSTEM.
A Paper
By
V B Sood, DyCE/B/BL
1. Introduction :
Inspections form the bed rock of any maintenance program based on which the
decisions regarding giving any maintenance inputs and prioritization of maintenance
inputs are taken. The reporting of inspection results is an important part of the
inspection exercise which decides the quality of the inferences drawn on the
inspections and decisions taken thereupon. The bridges are important parts of the
railway system and the inspections are to be done as to ensure proper and timely
maintenance inputs are given to maintain safety of train operations on the bridges at
all times.
In the railway system the results of the inspections done on bridges at the
inspector level and assistant engineer level are entered in the bridge registers which
are sent for scrutiny to the SrDEN/ DyCE/ CE offices and obtaining orders. The
orders given by the scrutinizing officers depend directly on the quality and
methodology of recording the inspection results. Of the two, the quality of recording
depends basically on the aptitude of the inspecting official and his understanding. The
methodology of reporting can be changed/ decided so as to give the best possible
guidance to the scrutinizing officers.
The numerical rating system is an aid in objectively reporting of the results of
the inspections and in giving an idea to the scrutinizing officers as to the type of input
required to be given to the bridge.
2. Numerical Rating System :
The numerical Rating System has been devised to remove some subjectivity
from the reporting of the results of the inspections. For example, the report that a
particular member of steel girder is “corroded” does not convey the full meaning. The
same entry can convey that the member is required to be replaced or strengthened or
may mean that the member is required to be painted and left as it is since the extent of
corrosion is not very much. Some extra clarification such as the reduction in thickness
of the member is required to be given by the inspecting official as to allow the
scrutinizing officer to draw some conclusion. Even then, other data such as the
original thickness of the member, the total corroded area, location of maximum
corrosion etc are required before the decisions can be taken. Reporting all these in
bridge register becomes cumbersome. Instead, if the inspecting official studies all the
aspects at site and gives proper judgement based on all the measurements and data
required and report the action to be taken, the same shall convey a clear and
unambiguous message to the scrutinizing official.
To incorporate the above desirable features into the inspection reporting, the
numerical rating system (NRS) has been devised. The complete bridge is divided into
separate distinct parts – foundation, sub structure, river protection system, bed blocks,
bearings and expansion arrangement, girders/ superstructure and track on bridge. Each
part is inspected and for each part, a number is given by the inspecting official which
denotes the action required to be taken for the defects that exist on the bridge and are
being reported. The numbers denote the various kinds of predefined actions required
to be taken on defects such as immediate rebuilding/repairs, planned repairs, special
repairs, routine repairs or no repairs etc, with lower values denoting severe
deterioration in condition of bridge and more urgent action being required. A part not
existing or not inspected on the bridge are also given CRNs in the system.
These CRNs arranged in a particular order, with a leading digit denoting the
overall unique rating number (URN, which is lowest of all CRNs following other than
zero), is called the overall rating number (ORN). The overall rating number gives the
complete idea of the condition of the parts of the bridge structure and the unique
rating number indicates the most critical action required to be taken in the bridge for
repairs. The Numerical Rating System is covered under para 1103(6) of Indian
Railways Bridge Manual 1998.
3. Advantages of NRS :
a) NRS gives uniformity of reporting the results of inspection and the action
required to be taken is unambiguously conveyed through the same due to the
pre assigned meaning of the various digits in the ORN.
b) The NRS eliminates some subjectivity in reporting the condition of the bridge
and the action to be taken in the defects on the bridge.
c) The NRS pin points the exact part of component requiring attention.
d) The importance of the defect can be easily conveyed through a lower CRN.
e) NRS is very useful for computerization of inspection results and a good
management information system, useful for monitoring bridges requiring
urgent repairs.
f) It is a very simple system to understand and implement and inspection results
of different type of bridges can be easily described by the system.
4. Shortcomings of NRS:
a) The NRS has been designed for general inspection of the bridges by AEN
open line and does not fully meet the objectives of specialized agency such as
centralized bridge organization’s reporting of conditions of inspection results.
b) The NRS does not fully serve the purpose where some component such as
river protection system or the steel girders are very elaborate and having many
important sub parts.
c) The format of NRS is rigid and the same cannot be easily altered for catering
to the special conditions in bridges such as describing the bridges having early
steel bridges or CI screw piles foundations.
d) The NRS is not completely free from subjectivity in allotting the CRNs.
e) The gravity of the action taken is conveyed by ORN, however the action
required to be taken is still to be referred from the detailed description of the
defects. The NRS does not eliminate the need for the describing the defects in
detail.
f) The NRS masks the importance of the description of defects/ condition of the
structure. A tool that is meant for easy identification of the problems and
action taken may sometimes lead to gloss over the actual defects.
g) There is no differentiation in the URN given by inspectors/ officers and by
centralized bridge organization or open line etc.
h) Erroneous CRNs may lead to wrong URN and the same may lead to errors in
planning and prioritizing the repair works.
i) In certain circumstances, the whole may be more than the parts i.e. the
description of the defects warrant special repairs in several parts of a bridge or
girder whereas considering the condition/ defects as a whole, the bridge might
require urgent/ planned repairs.
j) All recommendations after the inspections are to be reviewed during the
scrutiny. The NRS does not have any provision for the URN/CRN to be
changed at stages subsequent to inspection.
5. Adopting NRS to Centralized Bridge Organization:
The NRS has been adopted to the requirements of centralized bridge
organization with some modifications based on local instructions as follows :
a) The ORN has eight digits and five of the digits are always zero since the same
are not inspected by officials of centralized bridge organization. Only the
digits pertaining to girders and bearings change as per inspection results by
centralized bridge organization. The same URN has been adopted in the
absence of any other recommendation in bridge manual.
b) The inspecting officials i.e. BRIs give CRNs for all components of the girders
i.e. main girders, bracing, splices, bearings, painting etc are given separate
CRNs as described in NRS by the BRIs.
c) The Assistant Engineer (Bridges) who test check the inspections done by the
BRIs give the URNs for all bridges as described in NRS.
d) The scrutinizing officers i.e. XEN/Bridges and DyCE/Bridges confirm/ revise
the ORNs based on their assessment of the condition of defects.
e) The NRS has been considered effective only if the same is considered in
conjunction with the accurate and technical description of the defects existing
on the bridge. The NRS has been implemented by centralized bridge
organization along with extra emphasis on complete description of type of
girders, type of defects, previous defects and history of the bridge. A concept
of bridge history file has been evolved. The bridge history file gives detailed
description of the defects on the bridge along with backup data such as
sketches, photographs of bridge or defects, history of events such as SSP,
painting, greasing, repairs carried out, notes taken during inspections etc. the
bridge history file creates a chronological, continuous and detailed record of
the condition of bridge at various points of time and monitors minor defects
not worth mentioning in bridge registers also. There is no limitation of the
space availability of recording the condition of the structure as in case of the
bridge registers and there is no loss of continuity as in case of opening of new
bridge registers. The bridge registers record the summary of record of the
condition of the bridge recorded in the history file.
f) The early steel girders have been planned for replacement by the railway on a
planned basis and the URN is 2 for all such bridges. However, if all the steel
work is described as 2 for being early steel, the actual maintenance inputs such
as painting, repairs to gussets etc required to maintain safety on such girders
can get masked. The URN for such girders is kept as 2 however, the CRNs for
various components of the girders and to the superstructure/girder as a whole
are given as for normal girders.
6. Suggestions for improving NRS :
a) A few more digits may be added to the URN to describe the type of structure
and the inspecting official to make the URN more comprehensive.
b) During scrutiny, the ORNs shall be confirmed/ revised by the inspecting
officials to establish a positive confirmation of the gravity of the condition of
the bridge.
c) All bridges having condition of “Planned repair” or severe( CRN 2 or 1) shall
be inspected by an official one rank higher i.e. SrDEN in open line and
XEN/Br in bridge organization and the bridges in the CRN of 2 or 1 in three
successive inspections (years) shall be inspected at two levels higher than the
inspecting officials i.e. THOD in open line and DyCE/Bridges in bridge
organization.
d) Bridge history shall be separately maintained for major/important bridges by
PWIs for the bridges to assist decision making in respect of bridges. The
history of minor bridges can be kept in the section register and separate reports
as at present.
7. Conclusion:
The NRS, and the CRNs, are a handy management tool for planning and
prioritizing the bridge repair and rehabilitation works and are very well suited for
computers based monitoring also. However, the NRS is not an end in itself and is not
a substitute for technical and exhaustive description of the condition of the defects in
the bridges. Only the CRNs given after applying proper engineering judgement to the
condition of bridge can serve the intended purpose.
8. Bibliography:
a) Indian Railways Bridge Manual 1998.
b) “Handbook on bridge maintenance” published by CAMTECH Gwalior, ….
c) A Book on “Indian Railway Track” by M M Agarwal.