Maintenance of Bridge Bearing

 This Blog covers the requirements for inspection and maintenance of Pot bearings during service period(as per IRC code)

Inspection Frequency :The bearings are required to be inspected at an interval of one year for the first five years and at an interval of two years thereafter. However the bearings shall also be examined carefully after unusual occurrences like heavy traffic, earthquakes, cyclones and battering from debris in high floods.

Elements of inspection:

1) Measurement of movement :During inspection at site, measurements are required to be taken and documented to compute its movement and rotation values. To ascertain maximum movement, measurement should be taken once during peak winter (early morning) and once during peak summer (afternoon) and corresponding atmospheric temperature should be recorded. The recorded value of movement shall be compared with the design values.

2)Measurement of dimensions : Overall dimensions of the bearings are required to be measured and compared with the actual dimensions to ascertain any excessive stress or strain on the bearing.

3)Evidence of locked in condition: If any movable or rotating part of a bearing is found to be in locked-in / jammed condition, necessary rectification measures shall be taken immediately.

4) Evidence of corrosion:  If corrosion of any part of exterior exposed steel surface of the bearing is detected the following measures may be taken.

- Detect affected part - Wire brush the affected portion to clean of its rust. - Apply protective coating as per manufacturer’s specifications.

In addition, the root cause of defect should be searched and proper actions should be taken to avoid recurrence of the problem. 

5)Condition of the adjacent bridge structure: The adjacent structure of the bearings are also required to be inspected for any damage and necessary actions to repair the same, should be taken immediately.

Results and Actions:

The results of every inspection has to be recorded in the inspection report and shall be classified in each case into the following types of action:

A)No action.

B)Further measurements / long-term monitoring or design analysis needed (e.g. considering extreme temperatures / exposures, variation of loads etc.). Actions to be outlined in a report.

C)Minor repair works e.g. cleaning, repainting etc.

D)Repair or replacement of entire bearings or parts of the bearings. Actions to be outlined in a report.

Note :In case of defects where the cause of necessary actions cannot be determined by the inspecting person or the responsible bridge engineer, the bearing manufacturer shall be consulted.

The inspection shall be preceded by careful cleaning of the bearings as well as its surrounding space e.g. deposit of salt, debris, dust or other foreign material. The surrounding area of the bearings shall always be kept clean and dry to avoid damage to the bearings.

Suitable easy access to the bearing shall be provided for inspection and maintenance. It is advisable to provide adequate maneuvering space all around the bearing. Provision shall be made for jacking up the superstructure so as to allow repair/ replacement of the bearings.

Inspection & Acceptance criteria for Bridge Bearings

Inspection and tests may be classified into the following categories: 

a) Raw materials inspection. 

b)Inspection and testing of finished bearings.

 Inspection of  Finished Bearing (as per IRC 83-2018):

Routine test, which includes inspection and testing (S No 1,2,& 3 below) shall be carried out by the manufacturer for all the bearings of each lot under acceptance.

Type test, which includes inspection and testing (S No 2,& 3 below)shall be carried out by detailed  GREF officer on at least one bearings of each type and load capacity selected at random.The  detailed GREF officer may also carry out random tests on Sno 1.

1)All bearings of the lot shall be visually inspected for absence of any defects in surface finish, shape or any other discernible superficial defects.

2)All bearings shall be checked for overall dimensions as per manufacturing tolerances.

3)At least one or a pair of bearings (depending on the requirement) of each type and different vertical load capacity selected at random shall be load tested as described below:

3a)Proof Load test: Bearings shall be load tested for a test load equal to 1.5 times the specified design vertical load in SLS condition. Load shall be applied gradually and the test load shall be held for 30 minutes. The load shall then be removed and the bearing shall be dismantled and visually examined both during and after the test. Any resultant visual defects such as physical destruction, cold flow of sliding material with reduction of projected height beyond 0.5 mm, damage of internal seal and/or extrusion of the confined elastomeric pressure pad for Pot bearing, defects / cracks at metal-to-metal contact surfaces etc. shall cause rejection.

3b)Friction test: For bearings with sliding component, friction test shall be performed to determine static coefficient of friction of properly lubricated sliding interface at constant vertical load equal to the design vertical load in SLS condition. Test assembly may comprise of a pair of bearing or a bearing and dummy sliding interface made of similar material. The horizontal load shall be applied till sliding occurs. Coefficient of friction (μ) shall be determined as the ratio of Horizontal Load at which sliding occurs divided by 2 times the applied Vertical Load (two times the vertical load in denominator represents two sliding interface due to use of a pair of bearing or a bearing with dummy sliding interface).The value of coefficient of friction shall not exceed the value specified (i.e. 0.08).

3c)Rotation test: Rotation test shall be performed on Pot bearing with properly lubricated elastomeric pressure pad under a constant vertical load equal to design load in SLS condition and for rotation value of 0.02 radian or design rotation, whichever is higher. Rotation may be applied using tapered plate having slope of test rotation value.

Proof Load test, Friction Test and Rotation Test are normally not applicable for Pin and Metallic Guide Bearings.These Test are for PTFE-POT bearing(used mostly in BRO)

Tests on raw materials :

A) Mill Test Certificates (MTC) or material test report carried out by manufacturer shall at least include the materials and control parameters described in Annexure G (IRC:83 part 3).

B) Major metallic components as specified in Annexure G (IRC:83 part 3), shall be ultrasonically tested for soundness as per Level: 3 of IS: 9565 prior to use in bearings.

C) All structural welds shall be visually checked for weld size and location as per drawing as well as controlled as per the following tests: 1)Visual test (all structural welds), 2)Liquid penetration test as per IS: 822 (all structural welds) & 3) All full penetration butt welds shall be controlled through ultrasonic testing as per IS 4260 / AWS D1.5 / ASME Section VIII.

Result :

If the raw material testing result of any material is unsatisfactory, the component(s) involving that material shall be rejected for the entire lot.

If a finished bearing fails in load test the complete bearing shall be rejected and all the bearings of that type and load capacity shall be load tested before acceptance. 

All the test reports duly certified by the certified inspector shall be furnished by the manufacturer at the time of despatch of the bearing.

Certification and marking on Bearing should be done as follows:

All bearings shall have suitable index markings made of indelible ink or flexible paint, which if practicable shall be visible after installation, identifying the following information:

  Name of manufacturer  Month and year of manufacture  Bearing designation  Type of bearing  Load and movement capacity  Centreline markings to facilitate installation  Direction of major and minor movement, if any  Pre-set, if any

Preparation of Hydraulic Data (As per TI -03)

 AIM : To decide final Bridge location & Bridge scheme.

Principle Factor in finalising Bridge scheme:

    i) Total cost of Bridge & its approaches

    ii)Upto 60m :  bridge location governed by alignment of approaches

        60m to 300m : bridge location governed by  both alignment of approaches & bridge site.

        above 300m : bridge location governed by Bridge site primarily.

General points to remember while selecting bridge site 

i) on stable & well defined banks

ii) right angle to direction of flow.

iii)across narrowest width of river.

iv)15m straight stretch on both side of bridge approach.

Preparation of Hydraulic report (Check List )

      a) Statement of Case

     b) Recommendation of OC , CDR , CE & ADGBR (E/NW)

     c) TBOO ( Comparative study of alternatives sites , Finding, opinion & Recommendation of Board.

Comparative study of alternatives sites includes Rough cost Assessment of all proposed sites (based on last estimate/ per meter cost) , Merits & demerits.

d) Appendix I of TI 3:Data for alternative bridge sites ( for all proposed Bridge sites)

e) Appendix II of TI 3 :Hydraulic data of selected bridge site ): only for finally selected bridge.

f)Appendix III of TI 3 : SSI :Sub surface investigation data (  required if applicable ).

g) Appendix IV of TI 3 :calculation of Design Discharge , Scour depth (silt factor) & Depth of foundation 

h) Standard Authentication Sheet & additional information sheet (site investigation & hydraulic data)

j) Sketches & Plans:

    i)Toposheet marked with alternative sites

    ii)Images clicked with camera .

    iii) google map/ google earth images with latitude & longitude

    iii)Index map / Site Plan of Area near Bridge site (1:50000) showing proposed location, alternative  bridge sites, existing road and bridge & physical features (town etc))

    iv) Contour plan of stream with contour interval usually 2m (100m and 300m upstream & downstream of proposed site for catchment area upto 3 sq km &  3 to 15 sq km respectively)

    v) (a)cross section of river at proposed bridge site & existing bridge site (horizontal : 1:1000, vertical :1 :100)

         (b)Additional cross section of stream : one upstream , one downstream ( for smaller stream )

:two upstream & two downstream (for large rivers)

            cross section : including bed level, HFL, OWL, LWL

    vi)Longitudinal Section of stream (bed levels, HFL,OWL,LWL)

    vii) Longitudinal section of road (upto distance 300m or more): showing ground level & proposed approach road level

    viii) Alignment Plan of existing &Proposed approaches to bridge sites.

Note :

-Select atleast 2/3  Proposal of bridges

-Mark TBM on ground

RBAT : 

- will prepare draft bridge scheme ( covering bridge site, type of superstructure with span arrangement, location & type of sub structure  &deck level.

-will also indicate number of boreholes & extent of exploration.