Masonry Arch Bridges_May_2021.pptx

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1. MASONRY ARCH BRIDGES G S Yadav, PB-2 7420041112 [email protected]

2. Learning Outcomes : Understanding Load Transfer and Failure Mechanism of Arch Bridges Dismantling of Arch bridges Inspection and maintenance of Arch Bridges Assessment of Load carrying Capacity of Arch Bridges Strengthening of Arch Bridges

3. Important References: IRBM UIC Code 778-3R (2011) : Recommendations for Inspections, Assessment and Maintenance of Masonry Arch Bridges UIC Guide to high level assessment of masonry bridges : developed for UIC ( June 2005) by University of Genoa Arch Bridge Code BS 116R ( 2017) : Load Testing of Arch Bridges BS 16(1999) : Report on Preventing Growth of unwanted plants and weeds in buildings and structures BS 6 (1995) : Load test of a MG arch bridge RING1.5: Theory and Modelling Guide RING1.5: User Guide UIC Guide to use of RING2.0 : developed for UIC ( Dec 2005) by University of Sheffield, UK

4. Demography of Arch Bridges on IR

5. Demography of Arch Bridges within the UIC ( Ref UIC 778-3R) About 2,00,000 masonry arch bridges , which is approximately 60% of the total bridge stock In France as much as 77% of Rail bridges are masonry arch bridges In India about 20% of Rail bridges were arch bridges at the time of this survey. This has come down to 15% Majority of masonry arch bridges have short spans – about 60% having spans under 2m, 80% under 5m, and only 8.5% exceed 10 m in span About 85% are single span structures Majority ( about 70%) are between 100 and 150 years old and about 12 % are more than 150 years old

6. Rail Bridge On Kalka Shimla Section

7. Rockville Bridge USA – Longest Railway Arch Bridge 48 spans of 70 feet each – Total length 1160 metres Built in 1902

8. Aqueduct of Segovia – Spain (1st Century AD)

9. Pont Du Gard- France ( 1 st Century AD)

10. Concept first understood by Robert Hooke in 1665 CONCEPT OF AN ARCH

11. ELEMENTS OF AN ARCH BRIDGE

12. ELEMENTS OF AN ARCH BRIDGE

13. Structural Behaviour of Masonry Arch Bridges

14. Flow of forces and load paths The key to understanding arch behaviour is to be able to conceptualise the flow of force ( load paths)

15. Material Properties Masonry : Important aspect of masonry is that it is a composite material made from discrete elements and a softer matrix called mortar The primary objective of mortar is not to bind the units together but to hold them apart, thereby preventing hard contact that would lead to cracking or crushing Masonry is a brittle material with very low tensile strength, but can sustain substantial plastic deformation in compression

16. Fill : Fill contributes to strength of an arch bridge by its ability to distribute the load and resist deformation Water plays an important role in mechanical behaviour of fill. Moist fill is generally stronger than dry fill However, the additional strength is lost on saturation. Saturated fill on rapid loading can lead to high pore water pressure and substantial reduction in strength Fill material should therefore be of freely draining type Material Properties… contd

17. Effect of Fill

18. Destabilising Forces : The live load will spread laterally as it is transmitted downward, the distribution being function of shear capacity and stiffness of backfill The backfill self weight also acts on the loaded side Horizontal active pressure acts on loaded side Stabilising Forces : (iv) Backfill self weight acts on the unloaded side Horizontal passive pressure acts on unloaded side Effect of Fill…. contd

19. Thus the fill generates forces tending to resist the swaying motion of an arch The arch distorts downward under applied load and upwards on the opposite side. Accordingly there will be reduction in soil pressure on the falling side , and an increase on the rising side, however small these movements are. Effect of Fill…. contd

20. Effect Of Construction Details On Arch Behaviour Spandrels : Spandrel walls provide resistance to upward movement The transverse stiffness of arch and stiffness of the spandrel walls combine to create a very stiff load path which reduces the development of passive soil pressures Cracks may develop in the arch at the inner edge of external walls and this may reduce the capacity to transfer load into spandrel walls

21. Effect Of Construction Details On Arch Behaviour… contd Abutments and Piers : As moving load approaches an arch the soil is compressed and horizontal pressure is generated which pushes the nearest abutment away from the fill and shortens the span. The remote abutment will usually move rather less and crown of arch will rise With load near the centre of span , the thrust in the arch is increased and both abutments move back Finally as the load leaves the arch, the increased pressure generated moves the remote abutment away from the fill into the span.

22. The abutment behaviour will vary with arch shape and relative span. For shallow arch, the forces generated are distributed into the surrounding ground In a semi-circular arch, the thrust at the top of the abutment may be largely vertical and the wall acts as a retaining wall Piers support two adjacent spans, and provide almost no resistance to horizontal movement at the pier head. Thrust flows from span to span Effect Of Construction Details On Arch Behaviour… contd

23. Effect Of Construction Details On Arch Behaviour… contd 3. Backing , haunching, and internal spandrel walls Above construction details may be present in a arch but may not be visible. If present all of them add to load carrying capacity of an arch.

24. Failure Mechanisms

25. Hinge Single span- 4 hinges MODES OF FAILURE OF MASONRY ARCH BRIDGES Line of Thrust

26. 2. Failure due to Sliding

27. 3. Failure due to both hinges and sliding

28. MULTI-SPAN: 7 or 8 HINGES

29. Experimental Investigation of 3 Span Arch

30. Dismantling Of Arch Bridges

31. Bhagalpur accident 3X30 feet arch bridge no. 153 was being dismantled by const. organization Fell in Howrah- Jamalpur Exp. on 02/12/06 36 died, 12 grievous injuries Some portion of other span fell on 30/11/06 before this accident. Attended by open line officers CRS investigated and recommended Plan should be approved as per CS 18 to IRBM CRS sanction should be obtained involving passenger lines Should be taught in IRICEN

32. Fallen arch Train

33. Basic principle to be followed while finalizing dismantling scheme 1. Analyze force diagram at each stage of dismantling 2. At no stage the static equilibrium of forces should be disturbed

34. Dismantling of Single/Multi Span Arch Bridges (CS no 18 to IRBM) (Para 224 added to IRBM detailing procedure for dismantling of single/multi span arch bridges )

35. Dismantling of Arch Bridges.. contd In case of running lines, prior CRS sanction for methodology/safety precautions, drawing etc shall be obtained for dismantling of the arch bridge Arch is a structure, which transmits heavy horizontal thrust to abutments and piers In case of abutments, this load is resisted by heavy section of abutment and soil fill behind it Whenever in multi span arches, if one span is dismantled, large unbalanced horizontal thrust comes on pier and there can be collapse of pier along with other spans

36. Dismantling of Arch Bridges At piers, in case of multi span arches, horizontal thrust due to dead load is balanced. If both spans are loaded, horizontal thrust due to live load also gets balanced, but, in case of only single span being loaded, pier has to bear unbalanced horizontal thrust . Piers are, therefore, designed to take up only unbalanced horizontal thrust which is quite less as compared to total thrust at abutment.

37. Dismantling of Arch Bridges.. contd Three Methods are prescribed in Para 224 of IRBM Dismantling with explosives Dismantling with machinery Part-by-part dismantling

38. (a)Dismantling with explosives Use of explosives to bring down all spans of an arch bridge at one go. Require cordoning off the area likely to be affected by the explosion and long time to remove the debris thereafter. Can only be used if the arch is not near habited area and experts can be engaged to take up such work.

39. (b)Dismantling with machinery Special type of machinery with long jib can be used to dismantle one span of arch in one go. As unbalanced horizontal thrust may cause collapse of all or few other spans of the bridge: whole work should be planned in a single block and all the spans should be dismantled in one block. It must be ensured that work is completed in the block and no portion of the arch is left without dismantling in the block. This procedure will require cordoning off the whole area and engaging suitable machinery .

40. (c)Part-by-part dismantling Dismantling with Explosive or Machinery, though, are safe, may not be possible under many circumstances. In part-by-part dismantling method, dismantling is done in such a systematic manner that at no point, there is excessive unbalanced horizontal thrust on piers.

41. Divide the depth of soil into two part i.e. Part ‘A’ from top of soil to the depth up to the level of Crown of arch. Part ‘B’ is from Crown level to the top of Abutment / Pier. As shown in Fig. 1(a). Divide the width of Bridge into equal parts each about 50cm wide for the length of each span as shown in Fig. 1(b). ( Fig 1(b) shows bridge divided into seven parts, it will be more for wider bridges). No. of division should be odd number. (c)Part-by-part dismantling….

42. (c)Part-by-part dismantling

43. iii). Engage four parties to remove soil. First party will start removing soil from the Section ‘A1’ . It means start removing soil in the section- 1 from top level and depth upto the level of crown of arch i.e. Part ‘A’ as shown in the sketch. Second party will simultaneously remove the soil from Section– 2 , Part ‘A’ i.e A2 . It means soil from top level to the depth up to the crown. Third and four parties shall work in section A3 & A4. iv). After completing A1, A2, A3 & A4, follow the sequence Section – A5, A6, A7, A8, and then A9, A10, A11 & A12 and then A13 & A14. After this exercise Section A is cleared. This procedure ensures that there are no unbalanced lateral forces. (c)Part-by-part dismantling….

44. (c)Part-by-part dismantling…. v). Similarly follow the same sequence for removing soil of Section – B. vi). Provide thick nylon netting supported on piers so as to arrest any falling debris as shown in fig 1(c ) vii). Now each of four parties should break spandrel wall S1, S2, S3 & S4 simultaneously under block, as some debris can fall on track. viii). After breaking spandrel wall, arch barrel of section 1, 2, 3 & 4 shall be broken under block protection by each of four parties. In next block, section 5, 6, 7 & 8 shall be broken and so on.

45. ix). At the end, last middle section 13 and 14 will remain (since arch has been divided into odd nos of parts), which should be dismantled by pulling it down with the help of ropes or some long jib machinery. While dismantling last section, no person should be on top of arch. x). Afterwards piers can be dismantled in systematic manner from top to bottom In case of 3 span arch, no. of parties required shall be 6. For larger nos of spans, no. of parties required shall increase @2 per span. (c)Part-by-part dismantling….

46. In case of 3 span arch, no. of parties required shall be 6. For larger nos of spans, no. of parties required shall increase @2 per span. (c)Part-by-part dismantling….

47. Inspections & Maintenance of Masonry Bridges

48. Objectives of Bridge Inspection Safety Economy (to extend service life) Identify problems as early as possible Feedback for technological development Inputs for repairs /strengthening/rebuilding etc.

49. Common Defects In Masonry Weathering of Masonry Units - Results in loss of strength of masonry units Loss of mortar ( weathering/leaching) Results in loss of mortar strength Cracks in masonry Results in loss of structural integrity Problems associated with bed blocks Cracks Shaken bed block Loose/ sheared holding down bolts 55

50. Weathering: Damage to masonry due to long term exposure to adverse environmental conditions. This is indicated by layers of material spalling off Remedial Measures: Weathered material should be removed, surface exposed and thoroughly cleaned. If weathering is not deep , plastering with CM will suffice. In case damage is more than 5cm deep in Brick Masonry and 7-10cmdeep in stone masonry, replacement of masonry units should be done

51. Weathering of Masonry Units 57

52. Weathering of Masonry Units 58

53. Leaching/loss of Mortar : mortar deteriorate with time due to action of rain and running water and lose its binding power gradually If on raking out such joints the material comes out easily and is powdery, it is sure indication of loss of strength If tapping of such masonry gives hollow sound, it indicates leaching out from deep inside the structure

54. Loss of Mortar 60

55. Leaching of mortar through Joints 61

56. Loss of Mortar: Effects Individuals blocks can get loose and fall off Process of loosening of blocks accelerates after the first block is loosened. The effective area of transfer of load will reduce May lead to failure due to overloading of balance area Exposes more area for weathering and chemical action thus accelerating the process of damage 62

57. Loss of Mortar: Remedy For surface leaching, joins should be thoroughly cleaned and pointing done with CM In case of deep leaching grouting with lime/cement mortar should be done Jacketing to shield the masonry from further erosion/ degradation if the damage is too much 63

58. Cracks in Masonry: Identification Separation of masonry along joints or through blocks Parameters Location Length Width Rate of increase Behaviour under traffic Orientation 64

59. Cracks in Masonry: Critical ? Cracks at 90 to the stress direction Cracks at critical locations such as keystone of arch, heavy wear location, etc Cracks near concentrated loads Cracks which are increasing Cracks which ‘breath’ under traffic 65

60. Cracks: Tell Tales Paper or glass strip pasted across a crack Good quality, non flexible epoxy shall be used for pasting Flexible epoxy allows the crack to ‘breath’ without the tell tale breaking Glass shall be thin ~ 0.5 mm, so that it breaks easily Plastic strips are also available but cannot be used as these are flexible 66

61. Cracks: Tell Tales 67

62. Inadequate/abnormal clearance between ballast wall and end girder leaning, bulging of abutments Abnormal level difference Tilting of pier Unequal settlement Sinking of foundation Cracks Uneven settlement Excessive longitudinal forces Weathering Piers/ Abutments: what to see ? 68

63. Measurement of Tilt in Substructure Due to front batter in masonry , it is difficult to measure tilt. Drive rows of tie bars horizontally at the top and another row at bottom Plumb line is dropped from edge of top tie bar and mark is made on corresponding bottom tie bar. Observations are taken from time to time and new markings are compared with previous ones to assess any tendency of tilting. Alternately, record of clear span would also indicate indication of tilting. 69

64. 70

65. Cracks in Substructure: Reasons Horizontal Excessive longitudinal force Settlement of supports Vertical Differential settlement Over loading on one track with common support for multiple tracks Poor bond between masonry blocks Random Vegetation Chemical disintegration Vibrations Heavy overstress 71

66. Cracks in Pier

67. Transverse Cracks on Piers 73

68. Crack Due To Settlement/Differential Settlement 74

69. Structural Crack 75

70. Differential Settlement of Structure: Reasons Due to poor soil condition Especially in shallow foundations Structures supported on two different types of soils Structures supported on different types of foundations Excessive load in lateral direction Earthquake 76

71. UNEVEN SETTLEMENT OF FOUNDATION 77

72. Cracks in Masonry Piers. 78

73. 79

74. Kink formation of dn track Condition of DN Track 80

75. 81

76. Photo Just prior to collapse of wall on 11.04 2008 82

77. Insp & Maintenance of Arch Bridges 83

78. Insp & Maintenance of Arch Bridges Defects in arch barrel : Extension of vertical cracks from substructure to arch barrel. These cracks appear as longitudinal cracks in arch barrel. Cause – differential settlement of foundation Transverse or diagonal cracks in arch barrel( intrados). These are of serious nature and indicate tensile stresses at intrados. Generally noticed in the vicinity of crown at initial stage. Indicate serious weakness in arch requiring strengthening on priority. Weathering of masonry , Crushing of masonry, leaching of mortar from joints, loosening of masonry units.

79. Extension of vertical crack from Substructure

80. 86 Transverse Crack seen at Intrados

81. Loosening of stones/leaching of mortar 87

82. Defects Associated With Spandrel wall Defect Causes Remedial Measures 1) Longitudinal Crack in the barrel along the inner face of spandrel wall which do not widen with time Large difference in stiffness between deep spandrel wall and barrel Excessive back pressure on spandrel due to inadequate drainage Cement /lime grouting and pointing and monitoring Improving drainage of fill by cleaning weep holes/providing new weep holes and providing granular fill

83. Para 5.3.2.2 ( UIC 778-3R) – use of Lime mortar Repairs, whether in reconstruction, pointing, or for surface repairs, should use lime based mortars Lime mortar with properties similar to original construction allows the masonry to breathe and for water to pass through it rather than the masonry Portland cement based mortars should not be used unless the structure was originally constructed with this material as further damage can be caused. Creep is normal in masonry and adding a harder material such as Portland cement mortar can produce severe stress concentration, which can lead to spalling of adjacent stone or brick near the surface. It is best to think of the mortar as a cushion between hard materials rather than as an adhesive. Portland cement mortars prevent the passage of water , and cause water to pass through the masonry thus causing permanent damage. 89

84. Defects Associated With Spandrel wall.. contd Defect Causes Remedial Measures 2) Longitudinal Crack in the barrel along the inner face of spandrel wall which widen with time Excessive back pressure on spandrel due to inadequate drainage Excessive surcharge Improving drainage of fill by cleaning weep holes/providing new weep holes and providing granular fill Reducing overburden Cement / lime grouting and monitoring

85. Defects Associated With Spandrel wall… contd Defect Cause(s) Remedial Measure 3) Sliding of spandrel wall over arch barrel ; bulging or tilting of spandrel wall Excessive back pressure on spandrel due to inadequate drainage Excessive surcharge Spandrel wall not monolithic with arch Improving drainage of fill by cleaning weep holes/providing new weep holes and providing granular fill Reducing overburden Tying the spandrel wall with tie bars or rails Cement /lime grouting and monitoring

86. Crack at arch & spandrel wall junction noticed since year 2000 during annual inspection of AEN BS 16 can be referred for method for vegetation control

87. Leaning of Parapet/Spandrel :Cross level measured on track and found LH side low

88. BRIDGE NO 129

89. VIEW ALONG THE TRACK BRIDGE NO-129

90. Defects Associated With Spandrel wall… contd Defect Cause(s) Remedial Measure 4) Cracks on the face of the bridge at the junction of spandrel and arch ring Rib shortening Distortion of arch ring Excessive back pressure Improving drainage of fill by cleaning weep holes/providing new weep holes and providing granular fill Cement / lime grouting and monitoring iii)Strengthening of arch

91. Defects Associated With Spandrel wall… contd Defect Cause(s) Remedial Measure 5) Cracks in spandrel wall above pier Sinking of pier Remedial measures for arresting sinking of foundation and grouting cracks there after

92. General Guidelines for Maintenance of Arch Bridges Rail Joints on arch should be eliminated. In multiple span arch bridges , these should be located over the haunches Ensure clean ballast cushion by periodic screening of ballast For arch bridges on curve it should be ensured that track is centrally located While carrying out repair works for arches , the filling should not be disturbed as far as possible, as the compacted fill increases load carrying capacity

93. 102

94. Crack Repairs In Masonry/concrete Cement Pressure Grouting : is used when Cracks are dormant Cracks are active but cause of cracking has been determined and remedial action has been taken When masonry is hollow When deep leached mortar joints are present

95. Cement Grouting Grouting Pressure 2 to 4 kg/cm2….. pressure may be kept low for severely damaged masonry. W/c ratio 0.4 to 0.5 Admixture to impart non-shrinkable properties and to improve flowability of grout may be added with approval of Divisional Engineer

96. Procedure of Cement Grouting Holes are drilled in structure along cracks and in and around hollow spots Spacing of holes 500 to 750 mm covering adequately the area proposed to be grouted. Holes spacing can be altered as per site condition GI pipes ( 12mm to 20 mm dia x 200 mm long) with one end threaded are fixed in the holes with rich cement mortar All the cracks are cut open to a V groove and cleaned All the cracks and annular space around GI pipes are sealed with rich cement mortar

97. Procedure of Cement Grouting All grout holes should be sluiced with water using same equipment a day before grouting so as to saturate masonry All holes are first plugged with wooden plugs The bottom most plug 1 and two adjacent plugs 2 and 9 are removed and water injected in the hole 1 under pressure. When the clear water comes out of holes 2 & 9 , the injection of water is stopped and holes 1 & 9 are plugged The procedure is repeated with holes 2,3 & 8 etc till all holes are covered.

98. Procedure of Cement Grouting On the day of grouting all plugs are removed to drain out water and re-plugged before commencing grouting. The same sequence as above is followed for grouting also . After grouting curing is done for 14 days and tell tales are provided. Only such quantities of grout that can be used within 15 minutes of mixing should be prepared

99. Epoxy Grouting As compared to CG , EG is quick setting Low shrinkage High strength Low viscosity enables it to penetrate fine cracks Good resistance to chemicals Much more Expensive, should be used only it is techno economically justified

100. Epoxy Grouting Composition of EG : Consists of epoxy resin and a hardener which react chemically when mixed By suitably proportioning of the mix of resin, hardener and thinner ( if necessary) , the viscosity of the mix can be varied to suit all type of conditions Grouting of wide cracks requires large quantity of grout material, in such cases suitable fillers e.g. dry silicon flour etc can be added based on manufacturers recommendation

101. Epoxy Grouting Specification of EG : Considering the width, depth and extent of cracks and other relevant details, the viscosity of resin hardener mix, their proportions, pot life, application procedure etc. Should be chosen in consultation with the manufacturer The shear strength on a specimen of MS plates should not be less than 100 kg/cm2 Epoxy mortar should not be susceptible to fire and explosion during injection and must be stable under varying climatic conditions

102. Procedure for Epoxy grouting The area to be grouted should be dry and free from oil, grease , dust and all loose materials All cracks should be cut open to a V groove about 10mm deep. Loose material should be removed by compressed air and groove fully sealed using epoxy modified mortar at least one day in advance Holes of 7-10 mm dia are drilled along the cracks and copper or aluminium or polyethylene pipe pieces of 6-9 mm dia fixed as grout nipples Epoxy is injected from the bottom most pipe, keeping all other pipes, except the adjacent ones , blocked by wooden plugs. Injection is done at pressure of 3.5 to 7 kg per sq. Cm

103. Procedure for Epoxy grouting As soon as epoxy comes out from adjacent open pipes, they are plugged and the pressure increased to the desired level and maintained for 2 to 3 minutes The injection nozzle is then withdrawn and the hole sealed with epoxy mortar This procedure is repeated for other pipes also Due to restricted pot life , it is advisable to mix only small quantities of epoxy at a time. Low viscosity resins should be adopted for thin cracks A record of materials consumed should be maintained

104. Precautions While Handling Epoxy Resin s Manufacture’s detailed instructions should be followed for safe handling and processing Direct skin contact should be avoided The gun syringe should be washed with acetone immediately after use

105. Thanks… .

106. Strength Assessment of Arch Bridges

107. Strength of an Arch Bridge is made up of two important factors : Strength of arch ring which may be calculated based on the elastic theory Contribution of cushion(fill), spandrel walls, track and haunch filling

108. Strength of arch ring depends upon : Thickness of arch ring Effective width Shape of arch Span to rise ratio Ratio of quarter point rise to mid point rise Angle of skew Type of masonry material

109. Effective Width : Ref. Survey & Tabulation method For single bridge – half the barrel length, or length of the sleeper, whichever is less + twice the ring thickness + 2/3 rd of cushion ( including ballast), subject to a maximum of actual barrel length For double line bridge – barrel length/4 or length of sleeper, whichever is less + twice the ring thickness + 2/3 rd of cushion ( including ballast), subject to a maximum of half of the barrel length Note : Effective width may be restricted by presence of longitudinal cracks in the barrel and proximity of adjacent tracks

110. RING 2.0

111. RING user guide does not specify what shall be the effective width. We can use guidelines in UIC 778-3R As per UIC 778-3R

112. Contribution of cushion(fill), spandrel walls, track and haunch filling

113. Strength Contribution due to Cushion(fill) Cushion contributes to strength in following four ways : Reduces the dynamic augment Distributes the load in lateral direction over effective width Distributes the load in longitudinal direction. For an arch a single axle or pair or axles produce the worst loading condition. Cushion helps to distribute this load in longitudinal direction. Cushion ( fill) resists the swaying motion of arch when load enters or leaves the arch.

114. Strength contribution due to Spandrel Walls and Parapets Condition Additional strength as percentage of arch ring strength Barrel length 6.1 m or less 20% Barrel length 6.1 m to 9.15 m 15% Barrel length more than 9.15 m 10% Strength contribution due to spandrel walls and parapets should be ignored in the following circumstances : Where there are longitudinal cracks in arch ring adjacent to inner face of spandrel walls, (2) Where spandrel walls and parapets are bulging due to excessive thrust, (3) Where there are vertical cracks in spandrel walls and parapets

115. Strength Contribution due to Track In railway bridges, track helps to distribute load over a number of sleepers in longitudinal direction

116. Strength contribution due to haunch fill Nature of haunch fill Additional strength as percentage of arch ring strength Concreting increasing the thickness at springing level by 50% 25% Concreting level upto crown 50% Sand, gravel or boulder grouted with cement slurry 10% Sand, gravel, boulder Nil

117. Methods of Strength Assessment

118. UIC 778-3R suggests three levels of strength assessment : Level 1 assessment : simplest level which uses conservative assumptions ( MEXE method as per UIC 778-3R , Survey & Tabulation method suggested by RDSO is similar to MEXE method) Level 2 assessment : when bridge is found to have insufficient capacity in Level 1 assessment, Level 2 assessment should be carried out. RING software ( limit analysis in 2D – version 3.0 is currently available ) can be used for this purpose. Level 3 assessment : may become necessary if structure is found to have insufficient load capacity using level 2 assessment. 2D or 3D FEM analysis, and load testing comes in this category.

119. MEXE Method Simple empirical procedure Method uses critical dimensions and observations of condition of arch to determine the load capacity of the arch There is no requirement to determine parameters of the material of construction

120. MEXE Method.. contd MEXE method is approximate and should be used when following conditions are met : Clear spa less than 20 m Span/rise ratio does not exceed 8 Angle of skew does not exceed 35 degrees Arch barrel is not visibly deformed Should be used with caution when clear span is less than 5 m, and depth from top of rail to arch extrados at the crown is less than 1 m as there is some evidence that method can overestimate the load capacity

121. MEXE Method… contd The assessed capacity is dependent upon several factors : Arch ring thickness Arch shape, span and rise Depth of fill Material of construction Condition of arch masonry including joints

122. MEXE Method… contd For an assessment of a brick arch with MEXE, one less ring should be assumed when : There is evidence of significant ring separation A large number of bricks are missing ( over 10% of arch surface) The joints are only partly filled with mortar, or the jointing material is in very poor and deteriorated condition The method should not be used if significant diagonal cracks in the arch are present, as these may be an indicator of differential settlement of the abutments.

123. MEXE Method… contd Determination of Provisional Axle capacity Qp : MEXE method requires 5 dimensions as input Ring depth d (2) Fill depth ( below sleeper) h (3) Arch span S ( measured between the faces of abutments or piers at springing level) (4) Arch rise Rc measured from the line of the span measurement to the arch intrados (5) Arch quarter point rise Rq measured from the line of the span measurement to the arch intrados Provisional axle capacity Qp can be obtained from the graphs ( in Para B.1.2 of UIC 778-3 ( page 98 to 105) Note : method is sensitive to the ratio Rq / Rc , so accurate measurement of these values must be obtained.

124. Determination of Permissible axle capacity : Permissible axle capacity = Qp * Kp * Ks* Km* Kv * Kc Where Kp is profile factor Ks is shape factor Km is material factor Kv is Condition factor Kc is Crack factor MEXE method… contd

125. Demo of RING 1.5

126. IR Practice for certification of Existing Arch Bridges for Higher Loads Para 5.3.1 of ABC : Except in GC, the certification is done on the basis of physical condition Arch Bridges should be kept under observation when new type of locomotive and rolling stock is permitted. Bridges with ORN 1&2 : Higher axle load not permitted unless they are rehabilitated . However, on discretion of CE, heavier loads may be permitted on these bridges on the basis of load test on representative span as per criteria in para 5.3.3

127. Span Criteria Deflection at crown ( mm ) Spread (mm ) upto 1 m 0.75 0.4 1 m < span < 4.5 m 0.75 + (L -1)(1.75-.75)/3.5 0.4 4.5 m  span  15 m 1.25 0.4 Criteria for safe load : Para 5.3.3 of ABC (2) There is no residual deflection or spread after release of load (3) There is no crack appearing on intrados of bridge (1) Note : Above criteria is applicable for arches of span from 4.5 m to 15 m provided the span to rise ratio is between 2 and 5

128. Certification of Arch bridges in GC : certification shall be done on the basis of load test on representative bridges as per criteria in para 5.3.3 and subject to fulfilment of following: The condition of masonry and its behaviour under test load are satisfactory. Type of foundation and nature of soil on which it is founded are suitable Special cases may be dealt with on individual basis in consultation with RDSO Detailed procedure of load testing is given in BS 116R ( June 2017)

129. Strengthening of Weak Arch Bridges

130. Aim of strengthening is to either restore the load capacity of the bridge, when the existing bridge capacity determined by assessment is below the required capacity, or to permit increased traffic loads and speeds Empirical assessment methods such as MEXE or Survey &Tabulation should not be used as the basis for strengthening

131. Strengthening of Arch Bridges Following methods may be adopted, depending upon suitability and feasibility Transverse tie bars in Arch Barrel Internal Spandrel walls Over ringing Near Surface Reinforcement Under arching

132. Transverse Tie Bars in Arch Barrel This method originates from the reinforced concrete concept that transverse reinforcement increases the compressive strength and its inelastic strain capacity Since arch barrels are mainly compressed, they are assumed to be similar to reinforced concrete pillars, and therefore, transvers R/F may have beneficial effects.

133. Holes with 30-40 mm dia are drilled through the barrel transversely to the direction of span at a spacing of 80-150 cm around the ring, usually midway between extrados and intrados , and tie bars inserted. Tie bars can be moderately pre-stressed to induce friction across the crack

134. Shortcomings of Transverse Tie Bars in Arch Barrel Damage induced in the barrel during the drilling may be grater than the beneficial effects As the collapse mechanisms of masonry arch bridges never induce lateral expansion of the barrel, the effect of transverse tie bars may not be significant. This is demonstrated through experimental tests also This technique may however be suitable when there is longitudinal cracking of the barrel in the vicinity of external spandrel walls or at the centre of arch

135. Internal Spandrel Walls This technique is effective but not possible to implement in running traffic. However, this method can be used easily in GC projects.

136. Concrete Saddle This method also not possible to execute in running traffic condition The fill is completely substituted by a block of concrete, normally un-reinforced, with an horizontal extrados of the concrete saddle; concrete is connected to the arch extrados by means of a rough surface only or also by means of mechanical connectors. This technique is usually applied to very shallow arches (rise-to-span ratio ≤ 0.2) in order to limit the thickness of the concrete block .

137. Over Ringing Over-ringing by a new reinforced arch on the extrados of the original masonry arch . The new arch ring should be designed to take the entire load ( para 5.3.5.2 of ABC) This method can easily be adopted in GC projects.

138. NEAR SURFACE REINFORCEMENT The collapse mechanism of an arch assumes, four hinges to be needed for a single span arch to collapse, opening alternatively at the extrados and at the intrados The main idea is that providing tensile reinforcement (either in the form of CFRP trips or SS bars) to the arch, either at the extrados or at the intrados, locks the activation of such a mechanism. Few firms like “ Helifix ” are doing this type of work.

139. NEAR SURFACE REINFORCEMENT.. contd

140. NEAR SURFACE REINFORCEMENT Brickwork grouting: Grout (if needed) and do re-pointing Transverse reinforcement: Transversal reinforcement is placed on the arch before longitudinal reinforcement. Careful attention in filling the rebates, looking at the best possible connection between reinforcing bars and arch. Longitudinal reinforcement : Longitudinal bars are placed on the arch intrados and the rebates are all filled with mortar or epoxy resins.

141. UNDER ARCHING Under arching may be in three forms all of which require that secondary arch is fixed to the original abutment skewbacks of the arch (1) Sprayed concrete with R/F flexed to intrados of original arch (2) a second brick or stone ring constructed under the original intrados (3) steel arches under the arch barrel connected to the original abutment skewbacks of the arch , and the space between the steel arch and the arch barrel grouted with expansive mortars or separated by steel wedges

142. UNDER ARCHING.. contd Surface R/F of steel mesh is fixed to arch intrados and abutments, and concrete upto 100 mm thick is sprayed onto the masonry to provide a RCC protective skin Concrete helps in preventing detachment of masonry from intrados Prior to any concrete is sprayed onto the intrados of an arch, the condition of the waterproofing and the drainage system should be confirmed as adequate. Improved drainage must be ensured before taking up this method as poor damage will exacerbate the damage

143. UNDER-ARCHING STEEL CONCRETE

144. Interning and Jacketing This method is commonly adopted on IR. ABC specifically recommends this method.

145. For strengthening of Piers and Abutments , the composite action is always considered

146. Thank You G S Yadav, PB-2 7420041112 [email protected]

147. Strengthening of Abutment/Piers

148. Strengthening By Jacketing

149. Preparatory works before Jacketing Before jacketing is done, cracks should be thoroughly grouted Resulting reduction in waterway due to jacketing should be within permissible limits ( as per Substructure and Foundation Code) Face of existing masonry or concrete should be thoroughly cleaned