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OHE-Mast

By on June 13, 2013

Mast is erected on the foundation to hold the entire static and dynamic load of the OHE.

Mast are designed to suit different application and standardized accordingly. There are three major applications namely: Independent Structures, Portal and Two/Three Track Cantilever Structures.

 Independent Structures

When structures hold OHE of one line including two/three cantilever assembly of the same elementary section. These structures are classified as RSJ (Rolled Steel Joists) and BFB (Broad Flange Beam).

  • RSJ Mast: It is an I or H cross-section beam. The horizontal and vertical elements are called flanges and web respectively. Beam theory shows that I shaped section is very efficient for carrying both bending and shear loads in the plane of the web. Size used is 203x152mm. The mast is further classified into A, B, C, E &H depending upon drilling hole for supporting different type of OHE equipment.
  • BFB Mast: The Horizontal and vertical dimensions are same in this design of mast. Sizes vary from 152x152mm to 400x400mm depending upon the load which the mast is required to carry. These masts are good for resisting bending moment but weak in arresting twisting moment. These masts are further classified into three category depending upon the drilling holes for mounting. Weight of 152x152mm size mast is 30.4kg./meter
  • Fabricated Mast (K-series): These masts are fabricated by channels and flats welded in K design. The dimensions across the track is fixed as 300mm and varied along the track as K100 (23.12Kg/m) , K125 (29.56Kg/m) K150 (37.25Kg/m) K175 (42.65Kg/m) K200 (48.64Kg/m), K225 (56.10Kg/m) K250 (65.11Kg/m) where the suffix indicates the dimension and weight in Kg/meter. K100 is used for mounting auxiliary transformer and K125 de-standardized.  Due to higher width they are unsuitable where minimum track center of 4.72 is available.

Independent structures having mechanical independence makes the best OHE design.

Portal Structures
  • Portal structures are used to accommodate OHE of many lines (2 to 8 tracks) where it is not possible to erect independent mast due to restriction of track center.
  • There are three types of portal namely N, O and R type.
    • Clear span (distance between inner face) in N type- 10-20M (4 tracks), O type – 20-30M (upto 6 tracks), R type – 30-40M (upto 8 tracks). Portal of maximum     M has recently been designed.
    • Cantilever for the extreme tracks is provided on the uprights
    • Cantilever on the middle tracks is provided on the drop arm suspended from the boom.
    • Drop Arm
      • Drop arms are classified  as A (single cantilever on either or both side), B ( multiple cantilever on  side) C (multiple cantilever on both side)
      • Drop arms are fabricated from angles and are rod laced.
Two/three track Cantilever Structure (TTC)

This is an alternative where it is not possible to manage with mast as well as portal is difficult to erect or uneconomical.

This is generally used at turnouts and crossover, platform to provide adequate implantation (4.5m – distance between track center and inner face of mast). This can support OHE upto a distance of 10.5m from the upright. TTC is not used for supporting OHE of two main lines

TTC consists of Mast 12.21 m long 225x300mm Boom 5.0 long or 8.0m long Tie Road 20mm dia – 2 nos Drop arms : D type

 Selection of Mast

General guidelines for use of different design of mast is as follows:

  • Normal location and OHE on tangent Track :            BFB Mast
  • Normal Location on curves:                                            RSJ Mast
  • Structures with multiple OHE with anchorage:        K150, 175
  • Turn-out location with higher torsion stress:           K200, 250
Implantation

This is the most important dimension measuring the horizontal distance of the inner face of the mast from the track center.

As per schedule of dimensions ( popularly called SOD in Railways) prescribed, there should not be any permanent structure at distance less then 2.16m from the track center. In view of this, implantation in initial stages of electrification was fixed at 2.36m and permitted upto 2.21 with some conditions.

With the introduction of 8 wheel BOX wagon, incidence of door opening during run and hitting the OHE were reported and thus minimum implantation increased to 2.5m.

With the introduction of mechanized ballast cleaning machine, and OHE foundation interfering with the showels, it was again revised to 2.8m. See Latest SOD 

 

 

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There Are 29 Comments

  1. GOPAL PRASAD GAUR says:

    The mast grouting in foundation is 1.35 meters from the top of the foundation. The top of the foundation is kept 0.50 meters below the top of the rail. The measurement of rail=17.2cm, rubber pad =0.06cm, sleeper =21.0cm, normal ballast cushion =35.0cm in all the rail top is 73.80cm above ground. step distnce is taken 50cm than the top of the foundation above ground level is 23.80cm projected. but if the foundation isfully embeded in soil of ground a super block of 23.8cm is to be casted .

    • Rahul says:

      If cess level is less than 50 cm then we gives ED and adjust the embeded length 1.35 m. It is not necessary to make foundation, taking step distance 50 cm ,it changes as per site condition, if there is less cess level . Standard step distance is 48 cm and it can taken 50 to 40 cm also.

  2. prem says:

    What is the length of upright of R type special portal in OHE

  3. A.N.Moraskar says:

    What should be the minimum distance of any part of ROB or any structures from OHE horizontally and vertically?

  4. Ashish Garg says:

    How to calculate reverse deflection of a mast?

  5. randhir says:

    very useful

  6. ravikant rakhans says:

    verygood knoweledge about the mast erection.

  7. Sumit says:

    I am ohe engineer . Here the company is taking minimum implantation is 2.90 . Will u tell me minimum implantation of ohe as per latest sod

  8. Parshant soniya says:

    What is the full form of SPS

  9. Ankur saini says:

    What’s the full form of SPS in ohe erection.

  10. Bhupesh kumar says:

    What is the minimum implementation of DA

  11. UMESH says:

    0lease tel me the implatation of

    TTC. BFB R , O, &N type portels

  12. K. R. Panakala says:

    The information is a ready reckoner.

  13. Jplahre says:

    N type portal exact weight in tons??

  14. P.c.mahto says:

    Mast reaction fundetion

  15. shaik. subhani says:

    Good evening sir, minimum implantation of mast changed from 2.5m to 2.8m for tangenet track —- can you share the letter please sir.

  16. Lalan Tiwary Ex SrDEETRd SE5 says:

    Very good Matters

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