Numerical Rating System of Railway Bridges

The number of bridges on the railways being very large, it is difficult to have an overall picture of the condition of the bridges. The numerical rating system is essentially a method that gives by means of a single code, a quick appreciation of the physical condition of the bridge. The system provides a means of recording progressive deterioration and provides a way of assessing the relative importance of factors that should be taken into account to establish priorities for undertaking repairs/rehabilitation. The main emphasis has been to ensure that the proposed system involves minimum additional work and yet gives the desired information for managerial decisions. In addition, the system being numeric based is adaptable to computerization with all the relevant advantages following it.

Condition Rating Number(CRN)

A condition rating number is recorded for each of the bridge components i.e. foundation and flooring, sub-structure, training and protection works, bed blocks and expansion arrangements, superstructure, and track structure. The CRNs have numerical values from 0 to 6. The values of CRN and a brief description of the corresponding conditions are given in the table below.

CRN	Description
1	A condition which warrants rebuilding/rehabilitation immediately.
2	A condition which requires rebuilding/rehabilitation on a programmed basis.
3	A condition which requires major/special repairs.
4	A condition which requires routine maintenance.
5	Sound condition
6	Not applicable
0	Not inspected

The condition rating attempts only to rate the physical condition of the bridge component. It cannot be used to derive the capacity to carry the load.

Overall Rating Number (ORN)

In addition to CRN or different bridge components, an overall rating number for the bridge as a whole is also proposed, which in general, will be the lowest number except 0, given to the bridge components. The physical condition of a minor bridge is to be represented by only one digit ORN to indicate the overall condition of the bridge

Unique Rating Number (URN)

The physical condition of each major bridge is to be represented by a unique Rating Number (URN) consisting of eight digits, in which the first digit represents the ORN and each of the subsequent digits represents the CRN of the different bridge components in the following sequence:

1. Foundation and flooring
2. Masonry/concrete in the substructure
3. Training and protective works
4. Bed Block
5. Bearing and expansion arrangements
6. Superstructure- girder/arch/pipe/slab etc.
7. Track structure

From the URN it will be possible to easily judge the condition of the extent of distress (if any) in the bridge components and identify the attention required.

CRN of a bridge component shall be the lowest rating number applicable to the worst element of that component. For example, if a bridge has 5 piers and 2 abutments which, on a physical condition basis, would require a rating of 5,4,3,2,5,5,4, then the CRN to be recorded for the substructure component shall be the minimum of the above i.e. 2.

If in any bridge, one or more components (say, training and protection works) do not exist, the CRN for this component will be 6.

For example, URN 20362544 indicates the following:

Digit	Value	Indication
1	2	The whole bridge or one or more of its (ORN) components required rebuilding/rehabilitation on programmed basis.
2	0	Foundation and flooring were not inspected.
3	3	Substructure requires major/special repairs.
4	6	Not applicable i.e. the bridge does not have any training or protection works.
5	2	Bed blocks are cracked and shaking
6	5	Bearings and expansion arrangements are in sound condition.
7	4	Superstructure requires routine maintenance.
8	4	The track requires routine maintenance.

The physical condition of a road overbridge is to be represented similar to a rail bridge.

During the annual bridge inspection, the condition of different components of the bridge should be recorded by the AEN in the Bridge Inspection on Register, as hitherto being done. He should record the overall condition of the bridge given CRN in red ink in the existing registers.