Government of India Ministry of Railways

REPORT REGARDING COLLAPSE OF FOOT PATH SLAB OF ROAD OVER

BRIDGE (SHASTRI BRIDGE) IN JABALPUR DIVISION OF WEST

CENTRAL RAILWAY

REPORT NO. BS – 59

NOVEMBER - 2003

RESEARCH DESIGNS & STANDARDS ORGANISATION LUCKNOW –226011

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INDEX

SN Description Page No. 1 Title 1 of 06 2 Reference 1 of 06 3 Objective 1 of 06 4 Details of the bridge 1 of 06 5 Inspection 2 of 06 6 Visual Inspection 3 of 06 7 NDT Testing 4 of 06 8 Findings 5 of 06 9 Recommendation 06 of 06 10 Acknowledgement 06 of 06 11 Annexure I 01-12

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1. TITLE REPORT REGARDING COLLAPSE OF FOOT PATH SLAB OF ROAD OVER BRIDGE (SHASTRI BRIDGE) IN JABALPUR DIVISION OF WEST CENTRAL RAILWAY

2. REFERENCE Railway Board’s letter No. EDCE/B&S/Misc/2003 dated

8.10.2003 3. OBJECTIVE To inspect the bridge so as to find out the causes of failure

as well as to recommend the future precautionary measures.

4. DETAILS OF THE BRIDGE Br. No. : 987/3 “Shastri Bridge” Year of Construction : 1964 Location : 987/8 RP (987/11-12 TP) – about 3 Km from

Jabalpur Railway station towards Itarsi. Section : ET – JBP Block station : MML – JBP AEN’s section : AEN (HQ) JBP Span : 2 spans of 11.85 m each Skew : 1106’50” Superstructure :23.0 cm (9”) thick deck slab supported on 7 mild

steel built up girders in each span at 2.175 m centre to centre under carriage way and 2 ISMB 600 under footpath slab.

Road Width : 12.78 m Footpath Width : 2.75 m on either side of the bridge totaling to 5.5m

(i) ROB at Km 987/11-12 had been constructed in Year 1964 for Jabalpur Municipal Corporation & named as Shastri Bridge.

(ii) Substructure of the ROB consists of stone masonry pier and

abutments with isolated RCC bed blocks. Superstructure consists of 230 mm (9”) thick RCC Deck slab on steel girder support for carriageway.

(iii) Footpath structure is simply supported slab supported on steel T

section on railing side and on RCC parapet continuously supported on composite girder on carriage wayside.

(iv) The grade of concrete as per structural drawing is equivalent to

M15 which has been found safe in design by W.C.Railway.

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5. INSPECTION

The bridge was inspected by Sh. S.C.Gupta Director B&S Testing & Sh. A.k.Chakraborty, SRE/B&S from RDSO, and CE, CBE, ADEN(HQ) , ABEN/JHS, SSE ,P.Way, SE/Br. Jabalpur of West Central Railway . The following observations were recorded.

5.1 Visual Inspection -

I. Thickness of footpath deck slab is 125mm (5”) with 12.0 mm (1/2”) cover at bottom. The slab is provided with 12mm dia m bars @ 11.4 cm (41/2”) c/c as main reinforcement i.e. parallel to track and normal to carriage way, 10 mm dia m bars @ 200 mm (8”) c/c as distribution reinforcement. Spacing of bars in damaged structure has been found as per drawing.

II. Diameter of main bars has reduced up to 3mm at many places. Cross section of rusted reinforcement has become elliptical. Bars have become totally brittle and they can be broken simply by reverse bending of two to three cycles only.

III. Depth of concrete from top up to main bars has been measured from 8 cm to 10 cm as against design depth of 10.16 cm.

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IV. Incrustation of silt/dust have been seen in thickness of 2 to 5 cm

showing poor quality control during construction as shown below.

V. Bridge Deck near Railing has been used as urinating place by public at large since commissioning of bridge. Urine nuisance has been found maximum at four comers of the bridge. Photograph of one of the corners situated directly above bearing of foot path girder and near damaged portion of slab is given below:

VI. Four regular urinals have been found located on top landing of stairs, without any proper drainage arrangement. However urine discharge from these urinals is not affecting footpath or deck slab of bridge but affecting the abutment.

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VII. On footpath chequered tiles have been provided over 8 cm layer of

cement mortar on the original slab surface about 6 months back by denting top surface of footpath slab as shown below.

VIII. This certainly has resulted in increase of over burden over the slab

apart from making it more prone for penetration of urine in slab by making to the surface of concrete more porous.

IX. No works has ever been done on this Bridge for assessing extent of

corrosion in exposed reinforcement bars of this Bridge, by Jabalpur Division.

5.2 NDT Testing –

The results of NDT Testing are discussed below :-

5.2.1 Footpath slab:- The average compressive strength obtained is 17.7N/mm2 at test location no. 2 and 22.1N/mm2 at test location no.4 (reference sketch no.1 Annexure 1) and the electrical potential recorded are between –55mV and –220mV. The observe data indicates satisfactory concrete strength some probability of reinforcement corrosion. The variation in recorded and visual observation are due to the dryness of concrete and electrical discontinuity of reinforcement bars. The higher compressive strength recorded may be due to the carbonation of the top surface, which was quite visible so the results of these equipments are to be ignored here.

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5.2.2. Parapet beam:- The observed concrete strength at test location no. 1 & 3 (Reference Sketch No.1) is 19.1N/mm2 and 31.8N/mm2 respectively and measured electrical potential values at test location no.1 varies between –195mV and -310mV whereas at test location no.3 potation values varies between –60mV and –210mV. These results shows high probability of corrosion. 5.2.3 Deck Slab:- The observed compressive strength values measured at test location 5,6, and 7 are 40.5N/mm2, 42.4N/mm2 and 40.5N/mm2 respectively. The electrical potential recorded at loc ation No.5 are between the range of –325mV to –385mV. This indicates that concrete of deck slab is having sufficient compressive strength but probability of corrosion are very high and needs immediate attention. The details of all these readings are enclosed in Annexure-I page 7 to 18.

6. FINDINGS The cause of the mishap is heavy corrosion of reinforcing bars due to:-

i) Non provision of sufficient cover to reinforcement which affected the durability of the concrete.

ii) Continuous negligence by the inspecting authorities as the corrosion have been prevailing since many years.

iii) Increase of Dead Load over the foot path slab due to provision of chequered tiles, which has not been incorporated in the original design.

iv) Prolong and continuous ingress of highly corrosive urine discharge on foot path slabs.

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7. RECOMMENDATIONS The footpath slabs on both side shall be replaced with RCC slab of minimum M-30 grade concrete with covers as per the latest codal guidelines. The urinals at the four corners of the bridge shall be abolished and not to be allowed in future. The inspection schedule shall be strictly adhered to by inspecting authorities. Inspecting authorities shall not only strictly follow the inspection schedule but shall also take effective remedial measures as prescribed in the Indian Railway Bridge manual instead of going for simply plastering of the exposed reinforcement which may not give fruitful results. The deck slab of the bridge is also showing high probability of corrosion. Therefore, immediate remedial measures are required. 8. ACKNOWLEDGEMENT The field test were conducted by RDSO team comprises of – 1. Shri S.C. Gupta (Director/B&S/testing) 2. Shri A.K. Chakraborty (JRE-I/B&S Testing) It is acknowledged that support and assistance has been provided by following officers of W.C.Rly. 1. shri V.B. Tiwary (Dy. CE Br. WCR) 2. shri R.N. Shankar (Sr. DEN (Co) Jabalpur) 3. shri Alok Mittal (ADEN – Jabalpur) 4. shri Mr. Saxena (PWI)

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Table No. 1

Road over bridge no. 987/3. Jabalpur division. W.C.Railways. Existing concrete beam 450 mm thickness Madan Mohan Lal ( MML) end,

Jabalpur facing. Rebound nos. taking horizontal position, at test location No. 1.

S.

No. Observed Rebound

nos.

Mean value of Rebound

nos.

Corrected Rebound

nos.

Mean value of

corrected Rebound

nos.

Compressive strength of concrete

N/mm2

1 30 30 2 (38) - 3 30 30 4 (36) - 5 27 27 6 26 26 7 26 26 8 26 26 9 26 26 10 (38)

30

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27

19.1

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Table No. 2

Road over bridge no. 987/3. Jabal pur division. W.C.Railways.

Release concrete slab thickness 125 mm on without railway track span

At Jabalpur facing. Rebound nos. taking vertical downwards 900, At test location No. 2.

S.

No. Observe

d Rebound nos.

Corrected of Rebound

nos. for non-

horizontal impact

(downwards)

+ 3.4

Mean value of correcte

d Rebound nos.

Corrected

Rebound nos.

Mean value of

corrected Rebound

nos.

Compressi-ve

strength of

concrete N/mm2

1 20 23 23 2 20 23 23 3 29 32 32 4 30 (33) - 5 30 (33) - 6 24 27 27 7 26 29 29 8 27 30 30 9 19 22 22 10 20 23

27

23

26

17.7

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Table No. 3

Road over bridge no. 987/3. Jabal pur division. W.C.Railways.

Existing concrete beam 450 mm thickness Madan Mohan Lal ( MML) end,

At the test location center of the two span , Jabalpur facing. Rebound nos. taking horizontal position, Test location No. 3.

S.

No. Observed Rebound

nos.

Mean value of Rebound

nos.

Corrected Rebound

nos.

Mean value of

corrected Rebound

nos.

Compressive strength of concrete

N/mm2

1 50 - 2 43 - 3 34 34 4 30 30 5 40 40 6 40 40 7 40 40 8 33 33 9 28 - 10 31 31 11 34 34 12 36 36 13 38 38 14 36 36 15 34

36

34

35

31.8

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Table No. 4

Road over bridge no. 987/3. Jabal pur division. W.C.Railways.

Release concrete slab thickness 125 mm, at the location center of the two

span at Jabalpur facing. Rebound nos. taking vertical downwards 900, At test location No. 4.

S.

No. Observe

d Rebound nos.

Corrected of Rebound

nos. for non-

horizontal impact

(downwards)

+ 3.4

Mean value of correcte

d Rebound nos.

Corrected

Rebound nos.

Mean value of

corrected Rebound

nos.

Compressi-ve

strength of

concrete N/mm2

1 20 23 23 2 16 (19) - 3 30 33 33 4 14 (17) - 5 15 (18) - 6 30 33 33 7 34 (37) - 8 22 25 25 9 36 (39) - 10 16 (19) - 11 29 32 32 12 36 (39) - 13 25 28 28 14 24 27 27 15 36 (39)

28

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28.7 say 29

22.1

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Table No. 5

Road over bridge no. 987/3. Jabalpur division. W.C.Railways.

Existing concrete slab 225 mm thickness on without railway track span at

Madan Mohan Lal ( MML) end, at the test location bottom of the slab , Rebound nos. taking vertical upward position 900 , Test location No. 5.

S.

No. Observe

d Rebound nos.

Corrected of Rebound

nos. for non-

horizontal impact

(upwards 900) - 3.9 say 4.0

Mean value of correcte

d Rebound nos.

Corrected

Rebound nos.

Mean value of

corrected Rebound

nos.

Compressi-ve

strength of

concrete N/mm2

1 40 36 36 2 49 45 45 3 54 51 - 4 42 38 38 5 40 36 36 6 46 42 42 7 48 44 44 8 43 39

41

39

40

40.5

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Table No. 6

Road over bridge no. 987/3. Jabalpur division. W.C.Railways. Existing concrete slab 225 mm thickness on without railway track span at

Madan Mohan Lal ( MML) end, at the test location bottom of the slab , Rebound nos. taking vertical upward position 900 , Test location No.6.

S.

No. Observe

d Rebound nos.

Corrected of Rebound

nos. for non-

horizontal impact

(upwards -900) - 3.9 say 4.0 -4.7

say 5.0

Mean value of correcte

d Rebound nos.

Corrected

Rebound nos.

Mean value of

corrected Rebound

nos.

Compressi-ve

strength of

concrete N/mm2

1 42 38 38 2 38 33 - 3 46 42 42 4 42 38 38 5 46 42 42 6 48 44 44 7 42 38 38 8 38 33 - 9 48 44 44 10 48 44

40

44

41

42.4

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Table No. 7

Road over bridge no. 987/3. Jabalpur division. W.C.Railways.

Existing concrete slab 225 mm thickness on without railway track span at

Madan Mohan Lal ( MML) end, at the test location bottom of the slab , Rebound nos. taking vertical upward position 900 , Test location No. 7.

S.

No. Observe

d Rebound nos.

Corrected of Rebound

nos. for non-

horizontal impact

(upwards 900) - 3.9 say 4.0 -4.7

say 5.0

Mean value of correcte

d Rebound nos.

Corrected

Rebound nos.

Mean value of

corrected Rebound

nos.

Compressi-ve

strength of

concrete N/mm2

1 44 40 40 2 46 42 42 3 46 42 42 4 49 45 45 5 44 40 40 6 42 38 38 7 40 36 36 8 40 36 36 9 42 38 38 10 40 36 36 11 45 41 41 12 52 49 - 13 42 38 38 14 48 44 44 15 50 47

40.8 say 41.0

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39.6 say 40.0

40.5

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