Distressed bridges and schedule of inspection by official

Distressed bridges and schedule of inspection by official.

Definition of distressed bridge:- A distressed bridge is one which shows some physical deterioration of its physical condition, indicating the need for rehabilitation through special repairs strengthening or rebuilding (including replacement of griders).

Classification of distressed bridges

Category - i: Those requiring rehabilitation to be done immediately, say within a year’s time. Category-ii: those requiring to be kept under observation and to be taken up for rehabilitation on a programme basis. Signs of distress for Group I bridges:

Short Note On Distressed bridges

Distressed Bridge:- A distress bridge is one which show any physical sign of deterioration of its physical condition, indicating the needs for rehabilitation through special repairs, strengthening or rebuilding (including replacement of girders) 

1. The DEN/Sr. DEN, while including a bridge in the distressed bridge list should also indicate the priority classification depending on nature and severity of distress as detailed below:- 

Short Note On Schedule of Inspection of Bridges

 Schedule of inspection of bridges

The schedule of inspection for various officials is prescribed in Indian Railways Bridge Manual (IRBM). As per this, all the bridges are to be inspected by PWIs/ IOWs once a year before monsoon and by AENs once a year after monsoon, and important bridges by DENs once a year.

Short Note on Numerical rating system (NRS)

Numerical rating system (NRS)

a) The “Numerical Rating System” for bridge inspection assigns a “Unique Rating Number” (URN) to represent the physical condition of a bridge. Lower the URN more serious is the deteriorated condition of a bridge. The system thus helps in identifying progressive deterioration in the condition of a bridge. URN can be stored in a computer for quick retrieval and fixing priorities for repairs or rehabilitation. 

b) The URN of a bridge is arrived at based on the condition of components and a “condition rating number” (CRN) assigned to each of them. The various components of a bridge in sequence, are : i. Foundations and flooring, if any, ii. Masonry / concrete in substructure, iii. Training and protective works, if any, iv. Bed blocks, v. Bearings and expansion arrangements, vi. Superstructure – Girders / Arch / Pipe / Slab etc. vii. Track structure.

Short Note on Inspection of Fob and Other Steel Structures

 INSPECTION OF FOB AND OTHER STEEL STRUCTURES 

Every structure on the section/sub division shall be inspected in details by the section engineer (works) and Assistant Engineer.

Short Note on Types of Bearings in Bridge

Types of bearings in bridge

1. Shoe-plates: Shoe plates are attached to the underside girder and these rest directly on masonry. This is an unsatisfactory arrangement, as due to figh action between masonry &steel, expansion is resisted and heavy longitudinal and forces are imparted to the masonry, these type of bearings are gradually being replaced by centralized bearings.

Short Note on Causes of Rehabilitation of Bridges

Causes of rehabilitation of bridges 

i. Causes of Rehabilitation A bridge may require rehabilitation on account of the various reasons some of the reasons may be as under:

(i) Physical distress 

(ii) Vulnerability on hydrological consideration 

(iii) Use of obsolete/non standard materials such as 

a. Early steel girders 

b. Laterite stones 

c. Cast iron screw piles 

d. Corrugated steel pipes

e. Earthen ware pipes In case, due to introduction of new rolling stock, existing bridge is not safe, both its strengthening is to be done and, if not possible, rebuilding is to be done. 

Short Note On Controlled Concretes

Controlled Concretes :- 

These mixes the performance of the concrete is specified by the designer but the mix proportions are determined by the producer of concrete, except that the minimum cement content can be laid down. This is most rational approach to the selection of mix proportions with specific materials in mind possessing more or less unique characteristics. The approach results in the production of concrete with the appropriate properties most economically. However, the designed mix does not serve as a guide since this does not guarantee the correct mix proportions for the prescribed performance.