Inspection and Maintenance of Steel Girders-11

8/12/2019 Inspection and Maintenance of Steel Girders-11

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FIRSTFLANGE

PLATE

SECOND

FLANGE

PLATE

TH

IRD

FLANGE

PLATE

SPLICE

PLATE

Fig

.3.6

DETAILS

OF

TOPF

LANGE

PLATE

OF

RIVET

TED

PLATE

GIRDER

18.3

M

SPAN

(B.G.)

CL


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flange plate provide 175x230mm sleeper with requiredsteel packing to ensure that all sleepers top in one level

on entire span.

Accordingly the different thickness of packing plates anddifferent size of sleepers are to be worked out on onespan and same will be fabricated.

Note: Welded plate girder top flange plate is in one levelhence the packing plate and size of sleeper can be

worked out without layout.

3.7.1 Fixing steel channel sleeper on plate girder(rivetted span)

a) Cleaning of top flange plate with wire brush and applyof one coat of cover paint on entire top flange plate.

b) Mark the sleeper position on the top flange plate ofentire span/bridge.

c) Place 150x230mm size sleeper with rubber pad andsteel packing on splice plate and ensure all sleeperon in one level.

d) Place the 150x230mm size sleeper with rubber andsteel packing on 3rd flange plate ensure level of allsleepers (including over splice plate) in one level.

e) Place the 175 x 230mm size sleeper with rubberpacking and steel packing on 2ndand 1stflange plateand ensure all sleeper on entire span in one level.

f) Sleeper center shall concide with the center line ofgirder to ensure alignment of rail gauge face.

g) After ensuring all sleepers are in one level andcocentric to the span, sleepers to be anchored with


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3.7.3 Fixing of steel channel sleeper on open web steelgirder (through type BG)

As per steel bridge code all open web steel girder spansare to be fabricated with camber and prestreessed.Therefore same thickness of steel packing plate toaccommodate rivet heads are required on entire spanand use of 150x230x2440mm size channel sleepers arerequired. The rail profile will be similar to camber profileof span to ensure rail in level under passage of train.

Note: So far RDSO Lucknow has not issued anydrawing for steel channel sleeper for 30.5m under slung(deck) open web steel girder.

3.7.3.1 After cleaning with wire brush, provide one cover coatpaint on top flange plate of stringer (rail bearer). Markthe location of channel sleeper with prescribed spacing

on entire span/bridge.

3.7.3.2 Place the steel packing plate on marked position toaccommodate the rivet heads. Place the rubber pad onthe steel packing.

3.7.3.3 Steel channel sleeper of size 150 x 230 x 2440mm areplaced on packing plate ensuring that center of sleeperand center of stringer concides to ensure alignment ofrail gauge face.

3.7.3.4 Provide hook bolts on either side to anchor sleeper toflange plate of stringer and tighten the nut.

3.7.3.5 Place the rubber pad on bearing plate and fix the railwith the help of T bolt and clips on either side andtighten the nuts ensuring alignment and gauge.

3.7.3.6 Rail level on each span will coincide to camber profile ofspan.


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CHAPTER - 4

INSPECTION OF STEEL GIRDER

4.0 Bridge steel superstructure are expensive assets andinvolve heavy investment. Hence they must be managedwell to give maximum service. Bridges should live theirfull designed life with minimum maintenance cost. Toensure this, a good bridge management system isessential to watch the bridge structure periodically duringservice. Inspection is a vital link in the chain of bettermanagement.

4.1 OBJECTIVES OF INSPECTION

The bridge inspection is done to ensure safety andserviceability. The purposes of inspection of a bridge canbe identified as follows:

(a) to ensure that the bridge is structurally sound andsafe and fit for its designed use. This relates tothe gradual deterioration of the bridge with time or toan accidental occurrence such as impact oroverloading.

(b) to identify actual and potential sources of trouble atthe earliest possible stage.

(c) to record systematically and periodically the conditionof the structure. This enables the management toidentify any significant structural changes anddefects.

(d) to provide necessary information, on which decisioncan be taken for carrying out maintenance repairs,strengthening or replacement of the structure.

4.2 TYPES OF INSPECTION OF STEEL GIRDERS

(a) Routine or general inspection

This consists of broad general visual inspection by Asst.


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Engineer once a year after monsoon.

(b) Detailed Technical lnspection

During this inspection thorough examination of each andevery component of the superstructure is carried out withthe help of equipment covering all points of a preparedcheck-list (Inspection Proforma). This inspection is doneby the Section Engineer Bridges once in 5 years.Inspection Proforma is placed at annexure 4.1.

4.3 INSPECTION OF STEEL GIRDER-RIVETTEDCONSTRUCTION

The following aspects should be noted while inspectingrivetted construction.

4.3.1 Loss of Camber

All standard plate girders are of less than 35 metre

span, hence camber is not provided. All open webgirders of railway track bridges are pre-stressed. Deadload camber recorded after assembly and erectionshould be retained during the service life of girder if thereis no distress. Therefore, during technical inspection,first, camber is checked at every panel point of bottomchords of both truss with the help of dumpy level orprecision level, which will facilitate the inspection officials

to understand the structural condition. As far as possiblecamber observations are required to be taken at theambient temperature mentioned in the stress sheet.

Foot overbridge truss type girders are fabricated ascambered girder (unprestressed). Camber recorded atcentre of span during inspection should be comparedwith the initial dead load camber as recorded in theCamber Register and camber recorded during the last

inspection to detect any loss of dead load camber insteel truss or sagging of plate girder. Details of deadload camber is given in Table 2.3 for open web throughstandard track bridge girders for guidance.


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In plate girders, levels have to be recorded on top flangeplate to ascertain that there is no sagging of girder when

recorded levels are compared with last inspectionrecorded levels. In foot over bridge truss type girder,camber is to be recorded at midpoint of truss andcompared with dead load camber in register as well ascamber recorded during last inspection to ascertain anyloss of camber. In open web through span girders,camber is to be recorded at every panel point of bottomchords of both trusses of span and compared with dead

load camber in register as well as camber recordedduring last inspection to ascertain any loss of camber. Inopen web deck type (underslung) girder camber is to berecorded at every panel point of top chords of bothtrusses of span and compared with dead load camber inregister as well as camber recorded during lastinspection to ascertain any loss of camber. Goodpractice is to draw dead load camber, last inspection

camber readings and present recorded readings of eachpanel points on graph paper with different colour for eachgirder of bridge to ascertain any loss of camber whichwill be a permanent record.

If there is no loss of camber when compared to deadload, camber recorded in bridge register or the lastinspection report, it will assure inspecting official that nointernal structural change is taking place and structure is

not distressed.

Loss of camber in a girder can be due to :

i) Heavy overstressing of girder or component due toloss of cross section on account of corrosion orincreased load than the designed load or due tofatigue of the structure.

ii) Overstressing of joint rivets i.e. in open web girder atany panel point.


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iii) Play between holes and rivet shank on account ofelongation of holes or crushing of rivet shanks.

If any loss of camber is noticed during inspection, as afirst step, 30 kmph speed restriction is to be imposedand following investigation is to be carried out:

1. Girder should be thoroughly inspected to establishthe cause by critically checking for loose rivets atpanel joints or at splices. Also all members should

be thoroughly inspected for distortion or deformation.

2. Stress reading of critical members under maximumload should also be taken either by Faraday PalmerStress Recorder or strain gauge methods to check ifany member is over-stressed. Check whetherbearings are frozen.

After investigation, speed restriction should be relaxedwith the approval of Chief Bridge Engineer. Loss ofcamber and other details of investigation report should berecorded in bridge register for future guidance.

Based on the investigation, proposal should be made toreplace all the loose rivets of panel joints, with oversizerivets or for strengthening of members with the approvalof Chief Bridge Engineer as a special work.

4.3.2 Distortion

In plate girders following members are likely to showdistortion:

i) Top flange plate being a member carryingcompressive stresses.

ii) Web plate near the bearings due to heavyconcentration of stress.


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iii) Cross frame angles and top lateral bracing anglesdue to excessive lateral vibration

In open web girders the following members are likely toshow distortion.

i) Top chord members carrying compressive stresses ifnot sufficiently restrained.

ii) Diagonal web members particularly if they are madeup of flats and most likely at mid-span due to stress

reversal and vibration during passage of train.iii) Bottom chord members which carry tension and

longitudinal forces if not properly braced. The mostlikely location is near the bearings in case of frozenbearings.

iv) Top lateral and portal bracings are likely to distortdue to excessive lateral forces.

Distortion is also possible when longitudinal rnovement ofgirders due to temperature variation is arrested onaccount of frozen bearings.

Distortion can be checked visually as well as by a pianowire stretched between panel points over the members orby special distance gauges.

Sometimes web member i.e. diagonal, vertical and endrakers in through girder bridges are hit by moving loadsdue to shifting of load in wagons, particularlyoverdimensioned consignment (ODC). Hence, thesemembers should be checked at 1.2 meters above raillevel for any damage.

If distortion is noticed, cause of distortion is to beascertained. First, if it is due to frozen bearing, corrective

measure should be taken immediately to restore themobility of bearings. Further, strengthening the membersas well as providing lateral restraint by providingadditional lacings, battens and diaphragms should be


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contemplated. If lateral bracings and cross frame of plategirders are showing signs of distortion, they should be

replaced by higher section angles.

4.3.3 Loose Rivets

It is experienced in the past that no loose rivets arenoticed in steel girders of foot over-bridges and road overbridges. Rivets may get loose only when girders haveoutlived their design life or overstressed. Rivets of steelgirder of track bridges tend to become loose after 40 to

50 years of service life. Earlier to this, only if rivets werenot driven properly during fabrication and erection, thesehave to be replaced.

The rivets in steel girders of track bridges fall in thefollowing 3 groups:

a) First group called as stitch rivets are driven to form a

member. These rivets are driven in workshop andmostly do not become loose in service life of girderupto 80 to 100 years. 75% of total rivets in steelgirders fall in this category. (Diameter of rivets is20mm and hole diameter is 21.5mm).

b) Second group are rivets at joints connectingmembers. [These are also called as field rivets]These rivets transfer the load from member to joint.

They are driven at site with hand-driven pneumatichammer and hence tend to become loose after 40 to50 years. (Diameter of rivets is 22mm and hole is23.5mm). All joints are provided with 10% extra rivetsin design stage. The rivets which transfer load fromcomponent to component are very important forchecking.

c) Third group rivets connecting top and bottom lateralbracings including sway and portal bracings tend tobecome loose on account of vibrations. If found loosethey should be replaced.

Inspection and Maintenance of Steel Girders-11

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