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CONDITION ASSESSMENT OF PSC GIRDER BRIDGE NO. 73 OVER VASAI CREEK ON MUMBAI – SURAT SECTION OF

WESTERN RAILWAY 1.0 INTRODUCTION

Bridge No. 73 over Vasai creek on Mumbai-Surat section of Western Railway is one of the important bridge commissioned in 1991. During inspection, some cracks were reported in the PSC girders. As such, CBE/Western Railway vide letter No.W 65/20/80/4 vol.III (W3) dated 25.6.04 ( Annexure-I ) approached RDSO to study the cause of cracks in structure, its durability and to suggest possible repair and rehabilitation strategies for girders of bridge NO 73 Dn line. Accordingly, work was takenup. 2.0 OBJECTIVE Condition assessment of Bridge No. 73 DN by conducting various Non-destructive Tests along with design review and to suggest possible remedial measures. 3.0 DETAILS OF BRIDGE AND PROBLEM The bridge with 1x20 m + 28 x 48.5 m span is located at Km. 43/15 – 45/6 between Bhyandar and Naigaon stations of Western Railway. General view of the bridge is shown in photograph – 1.

Photograph 1 – General view of the bridge

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It is a PSC Box girder bridge constructed in 1991. The track is laid with LWR, 60 Kg rail on PSC sleepers with M+7 sleeper density. There are many fine cracks observed inside the inner faces of the web in most of the box girders. Some fine cracks are also seen on outer face of the girders. 4.0 TECHNIQUE OF INVESTIGATIONS To investigate the cause of cracks, girders were visually inspected and tested with the help of Non Destructive Techniques. Since most of the girders are having problems of cracking, among them span No.1 of 48.5m from Mumbai end, on which, RDSO had conducted field trials during Dec.,2001 and Jan.,2003, has been selected for conducting various Non-destructive tests. Thereafter, design review of end anchorage portion was also done critically. 4.1 VISUAL INSPECTION: During the visual inspection in Jan., 2001, it was observed that nine & five numbers of cracks were present on west and east inner faces respectively of the box girder in the 1st span of 48.5 m from Mumbai end. There are also some cracks on inner side of North diaphragm. The prominent crack of 19.05m length is seen at a height of 1.76 to 1.90 m from the bottom of the west inner face of the box girder. The crack is visible through naked eye from inside the box girder, but not observed on the outer side. Most of the cracks are horizontal and some diagonal cracks passing through the vent holes are also seen in some of the girders at the top corners in both ends of girders. These cracks are seen on the same location on outside of some of the girders. Railway has fixed many glass plates of thickness 1.2 mm by Araldite hardener across the cracks at different locations on 18 th Jan. 2001, to observe the growth of the cracks. During the period of about 3 years, no plate was found loose or broken. It indicates that the cracks are not widening, substantially. However 1.2 mm thickness of glass plate is too thick to break, so it was suggested to provide thinner glass plate for better watch. It is observed, during visual inspection in April 2004 that number of cracks increases to twelve & eight on west and east inner faces respectively of the box girder which includes two new cracks on top corners passing diagonally through vent holes of both the faces of the Naigaon end of the girder. Besides cracks, no other indications of damage, such as spalling, delaminating, scaling, disintegration and rust streaks of concrete are seen inside the girder. However, some hollow sound is observed in some of the girders on tapping the surface of the inside web portion. In span No.10, one small pit has formed in west face of the girder due to falling of concrete cover by tapping, indicating poor quality of concrete. The main crack with glass plate are shown in photograph –2. 4.2 NON DESTRUCTIVE TECHNIQUES: On the basis of visual inspection, following NDT equipments have been used for assessing the condition of the girder:

1. Crack Detection Microscope –for measuring the width of the cracks 2. Acoustic Emission equipments - for analyzing activeness of the cracks 3. Schmidt Rebound Hammer & Windsor Probe- for measuring compressive

strength of the concrete 4. Ultrasonic Pulse Velocity meter- for measuring quality of concrete viz.,

homogeneity, presence of cracks and voids

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5. Profometer- for measuring concrete cover, presence and spacing of

reinforcement bars 6. Resistivity meter & Cannin Corrosion Analyzer - for measuring rate and state of

corrosion.

Photograph 2 – View of the main crack with glass plate

5.0 OBSERVATIONS AND INTERPRETATIONS OF NON DESTRUCTIVE TECHNIQUES 5.1 LENGTH OF CRACKS : Lengths of different cracks have been measured by measuring the co-ordinates of both the ends of the crack tips from the extreme south end of the girder to north end as x-axis and bottom most of the girder to top of the girder as y-axis. Since the cracks are generally horizontal, hence the length is taken as the difference in the values of x-co-ordinates. The measurements have been recorded in Jan.2001 and April 2004. Some more cracks, appeared after Jan.2001 are also recorded during April 2004. The location and length of the cracks are shown in fig.1,1a,1b & 1c and table-1. It is generally observed that the length of the longitudinal cracks is not changing during the period of about three years (Jan.2001 to April 2004). Only crack No.2 and crack No.8 have been joined together and becomes the longest crack of length 34.11 m ( ref. table-1& Fig. 1). However, some diagonal cracks are recently observed, and it needs to further monitor. 5.2 CRACK DETECTION MICROSCOPE: Width of the cracks is measured by this instrument at different locations of all the cracks present inside of the boxgirder. The leastcount of the instrument is 0.02mm. The maximum width of each crack is given table –i. The measured value of maximum width of the crack is 0.40 mm for crack no.-9.

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Table No.- i West face of girder East face of girder North Diaphragm

S.No Crack no Max. width in mm

Crack no. Max. width in mm

Crack no Max. width in mm

1. C-1 0.30 C-1 0.16 C-1 0.30 2. C-2 0.20 C-2 0.06 C-2 0.08 3. C-3 0.30 C-3 0.08 4. C-4 0.08 C-4 0.08 5. C-5 0.20 C-5 0.30 6. C-6 0.08 C-6 0.06 7. C-7 0.10 C-7 0.10 8. C-8 0.10 C-8 0.16 9. C-9 0.40 10. C-10 0.08 11. C-11 0.08 12. C-12 0.24

5.3 ACOUSTIC EMISSION TECHNOLOGY( AET): The activeness of the cracks are observed under the running traffic by using this technology. The test was conducted on three locations on which investigations were conducted during Dec.2001 and Jan.2003. Three more new locations were also selected on new cracks including one diagonal crack C-12 (ref. Fig. 1) in north end of the girder. The brief description of the procedure and instrumentation of AET is given below: . 5.3.1 Principle and procedure : As the train passes over the bridge, the stresses are raised in different members of the bridge and Acoustic Emissions are generated through the weak and the crack portion of the member and received by the precalibrated sensors placed near the weak/cracked portion. The signals from one or more sensors are amplified and produces data for display and interpretation. Following steps are taken for collecting AE data from test locations selected. • Visual inspection of the cracks • Selection of location for placement of sensors • Cleaning of surface by sander and emery paper • Fixing of iron plates by quick fix for placing magnetic holddowns • Grease of good quality for using as couplant • Magnetic hold-downs using for keeping the sensors in position • Calibration of sensors are done by Pencil lead brake technique. • Threshold level is kept 40 dB well above the noise level • Recording of AE data was done for combination of many trains. • Following sets of AE parameters are recorded : i) Amplitude ii) Hits iii) Events iv) Counts v) Energy 5.3.2 Instrumentation: Two AE sensors for each location is used for observing AE parameters in linear locations. The position of sensors with magnetic hold downs for location 1 are shown below in photograph–3. Before placing AE sensors, surface of the location selected are cleaned by sander and emery paper. Four iron plates are

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Photograph 3 – Position of sensors for location 1 fixed by quick fix for placing magnetic hold downs, required to keep sensors in position. Good quality of grease is used as couplant between surface of the location and sensors. The output of the sensors are sent to AE system through 30m long BNC cables. The AE system was kept inside the adjacent box girder. The position of AE sensors are shown in fig. 2 & 3 to 5 for old and new locations respectively. 5.3.3 Collection of AE data : AE test was conducted on six locations of prominent

cracks on west inside face of the box girder of span no.1.

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5.3.4 Description of prominent cracks and AE test of the girder: Crack No.9- It is 19.21m long horizontal crack, existing 1.76m to 1.90m away from the bottom of the girder. AE tests were carried out at three locations ( both ends and in the middle ) on this crack during Dec.2001 and Jan.2003 also. For the present AE test, the details of the position of the sensors are shown in fig.2. AE parameters of above three locations are recorded at the time of passing of 55 trains which includes Mail, Express and Local trains on route. Crack No.12-It is a new crack noticed during April 2004. It is 0.56m long existing diagonally in the Virar side top corner of the west side of the girder. It passes through the vent hole and one of its end reaches up the joint of top floor and other end reaches upto the diaphragm. On the same location, the crack is also visible from out side of the girder also. The sensors are kept along the length of the crack at 320mm distance. The details of the location is shown in fig.3. AE parameters for this location recorded on 60 trains consisting Mail, Express and Local trains on route. Crack No.11-It is a new crack noticed during April 2004. It is 2.19m long horizontal crack existing between 1.37m to 1.39m away from the bottom of the girder. The two sensors are kept at 380mm across Bhyandar side of the crack end. The details of the location is shown in fig.4. AE parameters for this location recorded on 60 trains consisting Mail, Express and Local trains on route Crack No .8- This crack was noticed during Jan.2001. In April 2004, this crack in joined with crack No.2 and its total length becomes 34.11m. The two sensors are kept at 300mm across Virar side of the crack end. The details of the location is shown in fig.5. AE parameters for this location recorded on 60 trains consisting Mail, Express and Local trains on route 5.3.5 Analysis of AE data : Data recorded of all the trains are linked together and taken as the original data in separate file. Analysis of AE data was conducted by rejecting AE signals of counts less than 25 have been rejected, as it is assumed that these low counts may not emanates from the cracks. Following correlation graphs are taken out from original data and data after analysis. 1. Amplitude vs x-axis 2. Counts vs x-axis The original and data after analysis are given in fig.6 to 8 for three locations of crack no. 9 and fig. 9 to11 for crack no.12,11 and 8 respectively. The values of AE parameters viz., total Hits, Events, Counts and Energy are shown below each graph. For comparison of results, AE parameters viz., Events* and Counts** have been considered. The following observations are made by the analysis of AE data. 5,3.5.1 Crack no.9: AE tests have been conducted on this crack at three locations during dec.2001 and Jan. 2003 also. The values of total Events & Counts per train during the three tests are shown in Table No.- ii. * Event is an unique AE signals obtained during the passage of traffic and received by the sensors which subsequently plotted on the location graph. ** Counts are the number of peaks having magnitude more than 40 dB, due to AE signals obtained during passage of traffic which subsequently plotted on the location graph.

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Table No.- ii Values of AE parameters for

test %age variation

S.N. Parameters

Location 1st test

Dec.01 2nd Test Jan-03

3rd test July -04

2nd with 1st test

3rd with 1st test

1 Total Events 1 14 30 02 +114 -086 2 02 06 04 +200 +100 3 28 49 85 +075 +204 2 Total Counts 1 7178 7914 8276 +103 +153 2 0400 2908 5048 +627 +1162 3 26731 38565 75877 +44 +184

It is observed that total Events are increasing during each test for location 3 only and total counts are increasing in all the three locations. The percentage variation in counts is much more for location 2 than other locations with respect to tests conducted earlier . Observations of the AE analysis for the current test are as follows: i) Location 1- Concentration of AE data is not seen in the original as well as in the data after analysis in the location graph, hence there is no possibility of activeness of the crack (ref. Fig.6). The total events and counts for 55 trains after analysis are 121 & 455160 respectively. ii) Location 2- Concentration of AE data is not seen in the original as well as in the data after analysis in the location graph, hence there is no possibility of activeness of crack (ref. Fig. 7) . The total events and counts for 55 trains after analysis are 224 & 277653 respectively. The percentage variation in total counts are much more in the 2 nd & 3rd test as compared to 1st test. iii) Location 3- Concentration of AE data is not seen in the original as well as in the data after analysis in the location graph, hence there is no possibility of activeness of crack (ref. Fig. 8). However, the AE signals emitted from this location are more as compared to location 1&2. The total events and counts for 55 trains after analysis are 4656 & 4173277 respectively. 5.3.5.2 Crack no.12: Concentration of AE data is not seen in the original as well as in the data after analysis in the location graph, hence there is no possibility of activeness of the crack (ref. Fig.9). The total event and counts after analysis are 43 & 29233 respectively. 5.3.5.3 Crack no.11: Concentration of AE data is not seen in the original as well as in the data after analysis in the location graph, hence there is no possibility of activeness of the crack (ref. Fig.10). The total event and counts after analysis are 79 & 34966 respectively. 5.3.5.4 Crack no.8: Concentration of AE data is not seen in the original as well as in the data after analysis in the location graph, hence there is no possibility of activeness of the crack (ref. Fig.11). The total event and counts after analysis are 1735 & 790622 respectively.

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5.4 STRENGTH MEASURING NDT EQUIPMENTS AND THEIR OBSERVATIONS: 5.4.1 Schmidt Rebound Hammer: Compressive Strength of the concrete was checked by using schmidt rebound hammer at different grids on 11 locations on both the web of the box girder. Testing locations are shown in Fig.12a to12d. The corrected Rebound Number is obtained by discarding the values which are deviating by more than +5 units and less than –5 units from the average value of observed Rebound Number for calculating the average value of corrected Rebound Number. The age factor of the concrete is taken as 0.7. Out of 257 observations on 11 locations the max., min., mean, standard deviation, coefficient of variation and 95% confidence limit of the compressive strength of the concrete for different locations are shown in Table No -iii.

Table No- iii

Compressive strength (N/mm2) 95% Confidence Limit

Loca- tion

No of readings Max. Min. Mean (m) SD(σ) m+2σ m-2σ

Coefficient of variation (σ /m) * 100

1 16 37.00 26.90 31.63 3.23 38.09 25.17 10.21 2 16 38.70 30.10 35.30 2.84 40.98 29.62 8.05 3 81 42.40 31.80 37.74 2.84 43.42 32.06 7.53 4 28 38.70 30.10 33.80 2.93 39.66 27.94 8.67 5 16 42.40 30.10 34.96 3.91 42.78 27.14 11.18 6 20 37.00 26.90 32.06 3.08 38.22 25.90 9.61 7 16 42.40 30.10 35.73 4.50 44.73 26.73 12.59 8 16 42.40 31.80 37.56 3.45 44.46 30.66 9.19 9 16 38.70 30.10 34.32 2.91 40.14 28.50 8.48

10 16 38.70 31.80 35.79 2.87 41.53 30.05 8.02 11 16 42.40 30.10 36.09 3.69 43.47 28.71 10.22

The maximum and minimum values of the compressive strength as measured by Rebound Hammer are 42.40 & 26.90 N/mm2 respectively as average value more than 30N/ mm2 for all the 11 locations tested. The statistical analysis viz., mean, standard deviation, 95% confidence limit and coefficient of variation shows the consistency in the recorded values of compressive strength. The low values of standard deviation shows that the strength of concrete is almost same in the tested locations. 5.4.2 Windsor Probe: The strength of the concrete was also checked by Windsor probe system This system tests concrete strength by driving a steel probe into the surface of concrete with a precisely governed explosive charge. The shallower the depth of probe penetration, the stronger the concrete. The observations of the Windsor probe at location 6 & 7 (ref. Fig.12b & 12c ), on three grids are shown in Table No. iv.

Table No.-iv

Location No. Test No. Grid No.

No. of read- ings

Strength of Concrete (MPa)

Strength of Concrete X Age factor (0.7) (MPa)

Average Value of Strength of Concrete (MPa)

1 6 1 79.19 55.4 2 7 1 84.32 59.0 6 3 12 1 85.61 59.9

58.1

1 9 1 77.26 54.1 2 10 1 68.92 48.2 7 3 14 1 68.92 48.2

50.2

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It is observed that the average value of concrete strength as measured by Windsor Probe lies between 50.2 to 58.1 MPa. 5.4.3 Ultrasonic Pulse Velocity (UPV) meter: The quality of concrete in terms of density , uniformity, homogeneity , etc. can be obtained by using this instrument. This is based on the principle that the velocity of an Ultrasonic Pulse through any material depends upon the density, modulus of elasticity and poison’s ratio. Comparatively higher velocity is obtained when concrete quality is good. Ultrasonic Pulse is produced by a transducer held in contact with one surface of concrete member under test. After traversing a known path length, vibration pulse is picked up by another transducer held in contact with other surface at the predetermined place. The time of travel of pulse is noted and UPV calculated. Velocity criteria for concrete quality grading according to IS 13311 (Part I) 1992 is given below:

SN Pulse velocity by cross probing (km/sec) Concrete quality grading 1 Above 4.5 Excellent 2 3.5 to 4.5 Good 3 3.0 to 3.5 Medium 4 Below 3.0 Doubtful

The instrument is used for observing UPV at four locations at different grids and the statistical analysis of the data is shown in Table No-v

Table No.-v

Ultrasonic Pulse Velocity in m/sec.

95% confidence limit

Coefficient of variation

Loca- tion

No of read -ings Min Max Mean

(m)

SD (σ)

m+2σ m-2σ (σ/m)*100

1 & 2 8 3800 4150 4001.25 126.86 4255.01 3747.49 3.17 5 & 6 8 3990 4390 4190.00 176.72 4543.44 3836.56 4.22 7 & 8 8 3940 4240 4107.50 94.98 4297.46 3917.54 2.31

10 & 11 16 3580 4150 3941.25 160.12 4261.49 3621.01 4.06 The total of 40 observations on different locations, it shows that the average velocity of ultrasonic pulses lies between 3941.25 to 4190 m/sec. As per the classification table, the quality of the concrete is good. The statistical analysis viz., mean , standard deviation, 95% confidence limit and coefficient of variation shows that the quality of concrete is homogeneous in the tested locations. 5.5 PROFOMETER : The concrete cover and scanning of rebars are observed by using this instrument. The instrument is based upon measurement of the change of an electromagnetic field caused by the steel embedded in the concrete. Diameter and spacing of rebars can also be observed by this instrument. The summarized values of the cover are given in Table No.-vi. Out of 92 observations on 11 locations, the highest and lowest values of concrete cover is 74mm at location 4 (ref. Fig. 12a) and 43mm at location 9 (ref. Fig. 12d) respectively against the design value of concrete cover as 50 mm. A sample sheet of scanning of rebars are shown in Fig-13. Five horizontal and seven vertical rebars and their spacing are shown in the figure.

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Table No.-vi

Cover in (mm) Location No. of readings Maximum Minimum Average

1 9 71 52 64 2 8 70 60 68 3 12 62 42 54 4 8 81 56 74 5 9 70 64 68 6 7 74 58 67 7 8 72 66 68 8 8 70 53 61 9 8 46 38 43

10 7 62 45 57 11 8 70 45 63

5.6 CORROSION MEASURING NDT EQUIPMENTS AND THEIR OBSERVATIONS: 5.6.1 Resistivity meter: The corrosion of steel in concrete is an electro-chemical process which generates a flow of current and can dissolve metals. The lower the electrical resistance, the more readily the corrosion current flows through the concrete and the greater is the probability of corrosion. The metal loss as a function of time i.e., the rate of corrosion increases with time. By knowing the resistivity of the path between steel bars and concrete surface, the rate of corrosion can be obtained. It can be measured with the instrument known as Resistivity meter. The resistance of concrete may differ very greatly depending on the local conditions and the environmental influences. An extensive investigation with the Resistivity meter and the graphical display of the measured values permits the determination of spots where corrosion may occur. The combination of resistance and potential measurement further more improves the information about the corrosion condition of the rebars. The relationship between Resistivity and rate of corrosion is given below:

Resistivity ( kΩcm ) Corrosion Rate ≥12 Corrosion is improbable 8 to 12 Corrosion is possible ≤ 8 Corrosion is fairly certain

Out of 82 observations on 11 locations, the minimum, maximum and average values of resistivity is given in Table No-vii

Table No-vii Resistivity in kΩcm Location No. of

readings Minimum Maximum Average 1 8 42 67 54 2 8 40 80 60 3 8 99 99 99 4 8 93 99 98 5 8 51 99 76 6 6 27 82 50 7 8 20 53 36 8 8 38 68 50 9 4 41 68 54

10 8 44 84 68 11 8 38 74 55

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The average value of resistivity of the concrete lies between 36 to 99 kΩcm and as per the classification table the corrosion is improbable. 5.6.2 Corrosion Analyzer: Status of the corrosion can be observed by this instrument. It measures the potential of an electric field on the surface of the concrete with an electrode known as a half-cell. The corresponding status of corrosion is known by this potential difference. By making measurements over the whole surface, a distinction can be made between corroding and non-corroding locations. As per ASTM – C 876 –80 , Co-relation of potential values for corrosion activity of embedded steel in concrete are given below:

Corrosion Potential (mili Volt) Corrosion Status 0 to -100 No corrosion -100 to -200 Very low corrosion -200 to -300 Corrosion -300 to -400 High corrosion -400 to -450 Very high corrosion

The observations of Corrosion Analyzer are given in Fig. -14. Total 10 reading are taken on location – 3 . The readings were varying between –62 to –185. The minium observed value of corrosion potential is –185 mV on grid no. 47 and as per table above, the observed value corresponds to very low corrosion. This also satisfy the observations of resistivity meter. 6.0 DESIGN REVIEW Considering the above problem, design review of the above bridge, has been done on the basis of the design documents and drawings. Checking has been done for bending stresses, ultimate moment of resistance, shear and principal stresses. In proof checking it has been found that the design is safe for ultimate moment of resistance, bending stresses, shear and principal stresses taking into account initial pre-stressing force of 75% of UTS and Live Load for RBG loading. The cable profile near the support for cable no. 1,2 & 3 have sharp change in angle i.e. 21o, 19 o & 17 o at the end. The vertical component of pre-stressing force for these cables at support, in upper part of girder is comparatively on higher side, which creates complex imbalance with downward and horizontal pre-stressing forces. The cracks near the support may be due this reason. The stresses developed in shear stirrups provided near the support ( approx. @ 200 mm av. 18 mm Ф ) due to unbalanced vertical force of inclined pre-stressing cable, combined with shear force near the support, is close to the ultimate tensile stress of reinforcement. While designing the PSC Box girder, consultant might have ignored the aspect of checking of localized stresses resulting from inclination of pre-stressed cables. The crack pattern near support ( i.e. inclined cracks moving from end-diaphragm to top slab, in side walls of box ) indicates the same cause for failure. The self-weight of box above crack, along with SDL is only resistive force against vertical component of pre-stressing force. As the top slab is provided with bottom reinforcement with approx. 250 mm thickness, it is still able to resist the B.M. caused due to unbalance vertical load due to vertical component of pre-stressing cables.

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The horizontal cracks observed at mid depth of box walls cannot be examined in design, as design is safe in bending, shear & principal stresses. There are no localized forces. These cracks may be due to construction joints. 7.0 CONCLUSIONS

Based on tests conducted on the girder of span 1, the conclusions drawn are as follows:

7.1 The cracks observed are very fine and mostly dormant in nature. 7.2 Some recent cracks observed near the end also not showing any activeness by AE analysis, but this might be due to the reason that AE analysis detects activeness under loading and these cracks might be due to the under lying pre-stressing forces. 7.3 Latest observation of AE parameters on the crack monitored by AET earlier, showing increase in emissions, but no concentration of AE data at crack tips suggests that the crack is not very active but it can’t be treated as dormant too. 7.4 The compressive strength of the concrete is consistent and good. 7.5 The quality of concrete is homogeneous and good. 7.6 The concrete cover is adequate. 7.7 The probability of corrosion in rebars is very less. 7.8 The horizontal cracks are not looking unsafe, but the emergence of diagonal cracks at the ends need to be kept under watch. These cracks might have been occurred due to sharp curvature provided in the pre-stressing tendons compounded with the presence of vent holes in the vicinity, so they appears to be structural cracks. Similar girders were also provided at Thane creek bridge, but without vent holes near end anchorage zone, are not showing any cracks. This further supports our logic.

Cracking in pre-stressed concrete is an indication of serious problem. The

significance of cracks depends upon structure type, crack origin and increase in length and width with time. Generally, most of the cracks observed, are horizontal and are at different levels along the length of the girder walls, but the diagonal cracks appears in the top corners of the box girder is a cause of concern. Although the cracks monitored are not active under present loading as shown by AE testing. But appearance of some new hair cracks and extensions in the crack length as measured in few cracks is cause of concern. Other cracks may also become active after the passage of time. Though the rebound hammer readings were found consistent and good, but some hollow sound is experienced on tapping the surface of the concrete in other spans, which indicates poor quality of the concrete. 8.0 RECOMMENDATIONS 8.1 All the existing cracks and exposed surfaces of all the box girders shall be given

suitable surface treatment to prevent any possible corrosion through cracks and further deterioration of concrete.

8.2 Diagonal cracks near the end of the box girders need to be kept under constant watch, with proper fixing of tale tales

8.3 The condition of the bridge shall be monitored by special inspections at frequent intervals and appearance of new cracks or activity of the cracks treated earlier should be noted.

8.4 Vent holes near the vicinity of Pre-stressed Tendons or end anchorage zone should not be provided in future constructions.

--------------

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Table - 1

Details of cracks

Location Crack

No. Measurement during Jan 2001 Measurement during April 2004

Initial coordinate

Final coordinate

Crack Length

Initial coordinate Final coordinate

Crack Length

X1 Y1 X2 Y2 In Mts X1 Y1 X2 Y2 In Mts Inside West

Face 1 1.35 2.53 1.90 2.75 0.55 1.35 2.53 1.90 2.75 0.55

2 2.05 2.29 19.04 1.93 16.99 2.05 2.29 36.16 2.40 34.11 3 0.94 1.22 5.31 1.17 4.37 0.94 1.22 5.31 1.17 4.37 4 4.82 1.66 5.30 1.65 0.48 4.82 1.66 5.30 1.65 0.48 5 6.43 1.63 22.66 2.16 16.23 6.43 1.63 22.66 2.16 16.23 6 18.05 1.40 31.70 1.18 13.65 18.05 1.40 31.70 1.18 13.65 7 18.76 0.88 22.60 1.07 3.84 18.76 0.88 22.60 1.07 3.84 8 25.94 2.32 30.44 2.30 4.50 2.05 2.29 36.16 2.40 34.11 9 25.91 1.90 45.12 1.76 19.21 25.91 1.90 45.12 1.76 19.21 10 - - - - - 38.43 1.45 40.61 1.37 2.18 11 - - - - - 41.35 1.37 43.54 1.39 2.19 12 - - - - - 45.60 2.91 46.16 2.58 0.56

Inside East Face

1 4.19 2.25 11.40 2.19 7.21 4.19 2.25 11.40 2.19 7.21

2 19.40 2.00 22.90 2.04 3.50 19.40 2.00 22.90 2.04 3.50 3 17.80 0.92 28.20 0.85 10.40 17.80 0.92 28.20 0.55 10.40 4 27.14 1.51 33.83 1.19 6.69 27.14 1.51 33.83 1.19 6.69 5 28.36 2.16 39.30 1.73 10.94 28.36 2.16 39.30 1.73 10.94 6 - - - - - 31.52 2.30 35.20 2.24 3.68 7 - - - - - 40.31 1.43 45.71 1.30 5.40 8 - - - - - 45.80 3.00 46.00 3.20 0.20

Inside North Diaphragm

1 0.53 2.45 1.18 2.00 0.65 0.53 2.45 1.18 2.00 0.65

2 0.64 1.82 0.81 1.76 0.17 0.64 1.82 0.81 1.76 0.17

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Fig –1

Location of cracks Box Girder-1 ( Inner face east side )

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

Length in mts.

Hei

ght i

n m

ts.

C1 C2 C3 C4 C5 C6 C7 C8

BYR VR

Location of cracks Box Girder-1 ( Inner face west side )

0

0.5

1

1.5

2

2.5

3

3.5

Length in mts. H

eigh

t in

mts

.

C1 C2 & C8 C3 C4C5 C6 C7 C9C10 C11 C12

BYR VR

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DIAGONAL CRACK LOCATION NO. C-1 IN SIDE THE WEST WEB OF THE BOX GIRDER

253027

50

3300

350

1900

1500

300

675

155 O

350

1150

1700

C-1

100400

375

300

12375

CHURCH GATE END

300

Fig. 1a

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DIAGONAL CRACK LOCATION NO. C-12

IN SIDE THE WEST WEB OF THE BOX GIRDER

3300

350

2910

300

575

155 O

350

C-12

1570

1000

375

300

12375

VIRAR END

12101770

2580

300

400 100

Fig. 1b

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DIAGONAL CRACK LOCATION NO. C-8

IN SIDE THE EAST WEB OF THE BOX GIRDER

3300

350

3 200

300

575

155 O

350

C-8

100400

1320

1100

375

300

12375

VIRAR END

13701570

300

3000

Fig. 1c

- 18 -

Old crack location of BR. No. 73 DN

Position of sensors at 3 locations for crack No. 9

Fig – 2

New crack location of BR. No. 73 DN

Position of sensors for crack No. 12

(Diagonal crack in top of the north side of inner west face of the box girder 1)

Fig – 3

- 19 -

New crack location of BR. No. 73 DN

Position of sensors for crack No. 11

Fig – 4

Position of sensors for crack No. 8

Fig – 5

- 20 -

Analysis of crack No. 9 – location – 1

Fig – 6

- 21 -

Analysis of crack No. - 9 location – 2

Fig – 7

- 22 -

Analysis of crack No. - 9 location – 3

Fig – 8

- 23 -

Analysis of crack No. – 12

Fig – 9

- 24 -

Analysis of crack No. – 11

Fig – 10

- 25 -

Analysis of crack No. – 8

Fig – 11

- 26 -

345234

Locations of different NDT

Inside face of west web All dimensions are in mm Fig – 12a

Location 5

Location 4

Location 3

Location 2

North End South End

970

762

21860

882

41620

1340

3820

700

48500

3300

- 27 -

345234

Locations of different NDT

Outside face of west web All dimensions are in mm Fig – 12b

Location 1

Location 6

North End South End

636

800

730

990

48500

3300

- 28 -

Locations of different NDT

Outside face of east web All dimensions are in mm Fig – 12c

990

766

962

565

South End North End

Location 7 Location 11

48500

3300

- 29 -

345234 345234

Locations of different NDT

Location 8

Location 9

Location 10

North End South End

775

970

22200

1400

45415

Inside face of east web All dimensions are in mm Fig – 12d

725

48500

3300

- 1 -

POSITION OF REBARS AT LOCATION – 3 Spacing of horizontal rebars – 220 mm Spacing of vertical rebars ( from left to right ) between

1st and 2nd – 140 mm 2nd and 3rd – 180 mm 3rd and 4th – 140 mm 4th and 5th – 140 mm 5th and 6th – 160 mm 6th and 7th – 180 mm

Fig – 13

#200026d2647 mm / 39 mm

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

- 2 -

Fig. –14

Observations of Corrosion Analyzer (CANIN)

Location No.

Readings taken in Grid No.

Potential difference (mV)

20 -60 21 -75 22 × 23 × 24 × 47 -185 48 -165 49 -135 50 -120

3

51 -130

C A N I N Object X-Grid Y-Grid Min Max Dim. Dim. [mm] [mm] [mV] [mV] [ x ] [ y ] 13 150 150 -100 -450 5 3

m 0.00 0.15 0.30 0.45 0.60 0.00 -60 -75 x x x 0.15 -185 -165 -135 -120 -130

C A N I N Object 13

87.5s 62.5s 25.0s 0.0s 0.0s 0.0s 0.0s 0.0s 0.0s (%)

28.6r 42.9r 28.6r 0.0r 0.0r 0.0r 0.0r 0.0r 0.0r (%)

>-100 >-150 >-200 >-250 >-300 >-350 >-400 >-450 <=-450 (mV)

m 0.00 0.15 0.30 0.45 0.60

0.00 x x x 0.15

- 3 -

ANNEXURE - I WESTERN RAILWAY

Swami Nandan Singh Chief Bridge Engineer Churchgate Mumbai – 400020 Phone: 22015154(DOT) 22101 (Rly)

E-Mail: cbe@wr.railnet.gov.in Already faxed on 25.06.04 No. W65/20/80/4 Vol. III (W3) Dated: 25.06.04 Shri R. K. Gupta ED (B&S) RDSO Lucknow

Sub: Condition of PSC box girders of bridge No. 73 & 75 in CCG-VR section of Mumbai division on Western Railway.

Ref: Dy.CE/B/BL’s report vide No. W/BR/-BL/284/1 dated 14.06.04. Bridges No. 73 (28 x 48.5 + 1 x 20 m) and 75 (11 x 48.5 m) are PSC box type

girders located over Bassein creek between BYR and NIG stations in CCG-VR section of Western Railway. The girders were constructed in 1993. Cracks were appeared in almost all the PSC box girders of bridges, which require detailed investigations at your end. There are horizontal cracks in web of PSC box type girders which are growing in nos. and length and appear to be increasing in width. The cracks in span 1 Dn and 10 Dn were studied by RDSO in 2001 and 2002 for which no report was submitted . The tell tales fixed at the time on bridge do not show any movement in cracks. In view of above , you are requested to:

a) arrange to study the cause of cracks. b) arrange for study of cracks on structure and its durability. c) suggest possible repair and rehabilitation strategies for girders.

Sd/- (Krishan Chand Sainsi) Chief Bridge Engineer

- 4 -

PREFACE

Prestressed concrete bridges are now being widely adopted on Indian Railways. Functional life of such bridges is observed to be getting adversely effected due to factors such as aggressive environment, atmospheric pollution, quality of materials, workmanship etc. In recent years, the deterioration and cracking of concrete structures has been posing significant problems for engineers in the maintenance and their upkeep. Non Destructive Testing (NDT) methods are useful for estimating compressive strength, establishing the uniformity and homogeneity of concrete, detection of crack, voids and other imperfections, position and size of reinforcement and corrosion activity or its likelihood. Acoustic Emission technology can be used to study the presence and activeness of the cracks in the structures. CBE, Western Railway asked RDSO, to study the cause of cracks and suggestions for repair and rehabilitation strategies for the girders of long span prestressed concrete bridge No. 73 in Mumbai Division. A test team of the following staff under the guidance of Shri S.C. Gupta, Director/ B&S / Testing has takenup the study and this report has been prepared. S/Shri Ramji Lal, SRE, A.K. Chakraborty, Samir Paul, S.K. Awasthi, B. Kumar, R.R. Sinha, J.E.-1. All the necessary help/assistance provided by the officers and staff of Western Railway in conducting different tests is highly acknowledged. Contribution of all the team members is highly appreciated. Guidance provided by Shri S.C.Gupta, to the team members is sincerely acknowledged. The report is submitted herewith for further necessary action to W. Rly.

( R.K. Gupta ) Executive Director/ B&S

- 5 -

Index S.No Contents Pa

ge No.

1. Introduction 1 2. Objective 1 3. Details of bridge 1 4. Techniques of investigations 2 5. Observations and interpretations of Non destructive Techniques 3 6. Design review 11 7. Conclusions 12 8. Recommendations 12 Table 1. Details of cracks 13 Figures & Annexure.

1 to 1c Location of cracks 14 2. Position of sensors for crack no. 9 18 3. Position of sensors for crack no. 12 18 4. Position of sensors for crack no.11 19 5. Position of sensors for crack no. 8 19 6. AE data for location 1 of crack no. 9 20 7. AE data for location 2 of crack no. 9 21 8. AE data for location 3 of crack no. 9 22 9. AE data for crack no.12 23 10. AE data for crack no. 11 24 11. AE data for crack no. 8 25 12a to 12d Locations of different NDT testing 26 13 A sample sheet of scanning of Rebars by Profometer 30 14 Observations by Corrosion Analyzer 31 Annexure.-I CBE’s letter no. W65/20/80/4 Vol.III(w3) 32

- 6 -

Government of India Ministry of Railways

CONDITION ASSESSMENT OF

PSC GIRDER BRIDGE NO. 73 OVER VASAI CREEK ON MUMBAI- SURAT SECTION OF

WESTERN RAILWAY

REPORT NO. BS – 71

MARCH-2005

RESEARCH DESIGNS & STANDARDS ORGANISATION LUCKNOW –226011