Q Bank for Civil Engineer LDCE Exam - Write short Notes on (5)

Q.No.4. Write short Notes on. 

1. Track tolerances. 

2. Define super elevation,  cabtt   deficiency, cant excess & equilibrium cant.  

3. Distressed bridge. 

4. Inspection schedule of bridges of SSE/W, ADEN in field. 

5. Numerical rating of bridges after inspection. 

1. TRACK MAINTENANCE TOLERANCES (EXTRACT OF PARA 607(2) OF IRPWM) 

Track  Tolerances  for  standard  of  maintenance  of  track  for  sanctioned  speed  

above 100 KMPH and upto 140 KMPH. 

• Few Isolated Location – Not Exceeding 10 Per KM 

These  Tolerances  are  For  Good  Riding  Comfort  &  Not  Safety  Tolerances  (Para  607(3) of IRPWM).   

2.Transitions, safe speed and super elevation on curves  

1) Cant or super elevation is the amount by which one rail is raised above the other  rail. It is positive when the outer rail on a curved track is raised above inner rail  and is negative when the inner rail on a curved track is raised above the outer rail. 

2) Equilibrium speed is the speed at which the centrifugal force developed during the  movement of the vehicle on a curved track is exactly balanced by the cant  provided. 

3) Cant deficiency- cant deficiency occurs when a train travels around a curve at a  speed higher than the equilibrium speed. It is the difference between the actual  cant and the theoretical cant required for such a lower speed. 

4) Cant excess – cant excess occurs when a train travels around a curve at a speed  lower than the equilibrium speed. It is the difference between the actual cant and  the theoretical cant required for such a lower speed.    

3.Distressed bridges 

As per the standards  laid down,a distressed bridge is one which shows any physical sign of deterioration of its physical condition, indicating the need for rehabilitation through special repairs, strengthening or rebuilding including replacement of girders. This definitation does not include those bridges which are considered vulnerable due to hydrological factors.  The distressed bridges have been classified in 2 categories as under:- 

Category I : The requiring rehabilitation to be done immediately say within a year’s time.  

Category II : Those required to be kept under observation and to be taken up for rehabilitation on a programmed basis.  There are a large number of distressed bridges on Indian Railways and as these are safety  hazards, their repairs and rehabilitation including rebuilding has to be done on high priority. To  keep watch on the rehabilitation of the bridges. It has been decided by Railway Board that the  railway should maintain diagram of distressed bridges similar to track diagram.  

4.Schedule of inspection of bridges. 

5.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.        

c)  The CRN is allotted to each of the above components based on their condition at the time of inspection, using the following scale: 

d) when any component in a bridge is more than one in number CRN is assigned to each of them  and the lowest value used. For example, if a bridge has five piers and two abutments, and these  are given the CRN of 5,4,3,2,5,5,4 then the CRN for the substructure component of the bridge  would be minimum of the above i,e. 2. 

e) If in any bridge one or more components do not exist, the CRN for such components shall be  shown as 6 

f) From the CRNs for different components of a bridge, an overall Rating Number (ORN) for the  bridge as a whole is then given. The ORN is th lowest of the seven CRNs of a bridge, except 0. 

g) For a major bridge, the URN would comprise of eight digits, the first digit indication the ORN  and the following seven digits the CRNs of each of its above seven components in sequence.  

h) URN of minor bridge shall be represented by its ORN only, i,e. by a single digit to indicate its  overall condition.

j) The physical condition of a road over bridge is to be represented as for rail bridge. 

k) The CRN of different components of a bridge as evaluated above shall be entered in the  “Box” to be provided in the register at appropriate places.