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BRIDGE RULES

BRIDGE RULES. PURPOSE. Specifies the rules/loads for Design of superstructure & substructure of Bridges Assessing the strength of existing Bridges

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BRIDGE RULES

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  1. BRIDGE RULES

  2. PURPOSE • Specifies the rules/loads for • Design of superstructure & substructure of Bridges • Assessing the strength of existing Bridges • Any Revision/addition/alteration shall be through correction slip only, no cognizance to be given to any policy directives issued through other means

  3. SCOPE • Loads specified shall be used for • All Railway Bridges • Turn Table girders • Foot Bridges but excluding Road Bridges • Design detailing shall be controlled by appropriate code of practice • Road Bridges shall be as per IRC codes

  4. LOADS • Loads specified in Bridge Rules : • Dead Loads • Live Loads • Dynamic effects • Forces due to curvature/eccentricity of Track • Temperature effect • Friction resistance of expansion bearings

  5. LOADS…. CONT. • Longitudinal Forces • Racking forces • Forces on parapets • Wind pressure effects • Forces & Effects due to earthquake • Erection forces and effects • Derailment loads • PQRS loads

  6. DEAD LOAD • Weight of structure • Permanent Load carried on it • For ballasted deck bridges, 400/300 mm cushion for BG/MG. For checking old bridges 300/250 mm

  7. LIVE LOAD • History • Present Live Loads • For Railway Bridges / Rail-cum-road Bridge • For Foot Bridge / Footpath • Live load distribution

  8. BRIDGE LOADING STANDARDS HISTORY FOR BG

  9. 25 T LOADING Electric Locos Two WAG 9H locos, TE of each 52 T Two 8 axle, twin BO-BO, TE of 84 T each. One in front, one in middle or back Diesel Locos Two 6000 HP locos, TE of 63 T each. Both in front Building/Rebuilding/Strengthening/Rehabilitation of Bridges for all routes except Dedicated Freight Corridor (DFC) feeder routes and DFC loading routes i.e. erstwhile HML routes. Strengthening/Rehabilitation of Bridges on Dedicated Freight Corridor (DFC) feeder routes Superstructure of Bridges being built/rebuilt on Dedicated Freight Corridor (DFC) feeder routes. In case any other loading is proposed specific approval of Railway Board reqd.

  10. DFC LOADING Electric Locos Two pairs of WAG 9 H locos, TE of 52 T each loco. One pair in front, one pair in middle or back Two 1200 HP, 8 axle, twin BO-BO, TE of 84 T each. One in front, one in middle or back Diesel Locos Two 6000 HP locos, TE of 63 T each. Both in front The above standard should be adopted for Bridges on identified routes approved by Railway Board. Building/Rebuilding/Strengthening/Rehabilitation of Bridges on DFC loading routes i.e. erstwhile HML. Besides this, the above standard should be adopted for building/ rebuilding of substructure only on Dedicated Freight Corridor (DFC) feeder routes.

  11. Standard wheel/axle replaced by EUDL • EUDLs applicable to simply supported spans.

  12. EUDL For BM For spans up to 10.00m >> produces BM at center = absolute BM developed by standard load For spans above 10.00m >> produces BM at 1/6 th span = absolute BM developed by standard load at 1/6 th of span For SF Shear force at end of span = Max. SF

  13. EUDL (Span > 10m) Train Loads EUDL (Span up to 10m)

  14. EUDL There are two load configurations for MBG loading, one 22.5 T load and second 25.0 T load. Note that spacing of axles is different Max. BM for spans 12m, 15m, 20m, 30m, 40m and 50 m are caused by 22.5 T configuration No trailing load gets loaded up to 20m span

  15. EUDL CALCULATION EXAMLE FOR 12 m SPAN • The total EUDL for BM as per Bridge rules is 140.4 T • As span is greater than 10m, BM is calculated at L/6 of span, which is 2m in this case. • The total load of 140.4 tonnes is equal to a Uniformly distributed load(w) of 140.4/12 = 11.7 t/m. The Bending Moment at 1/6 of a span equal to L for a uniformly distributed load of ‘w’ t/m is equal to 5wL2 /72. The BM in this case is therefore equal to 117 t-m.  • The configuration of MBG standard loading at which this occurs is ;

  16. RB= 22.5(2+3.65+5.3+8.3+9.95+11.6)/12 = 76.5t RA= 6*22.5-76.5 = 58.5t BM at Section X = 58.5*2 = 117tm

  17. LOCATIONS FOR MAX. EUDL FOR BM • Span span/6 Wheel at span/6 • 12m 2 m Second Loco(First Bogie) Third wheel • 15m 2.5m Second Loco(First Bogie) Third wheel • 20m 3.33 m Second Loco(First Bogie) second wheel • 25m 4.167 m Second Loco(First Bogie) second wheel • 30m 5 m Second Loco(First Bogie) second wheel • 40m 6.67 m Second Loco(First Bogie) First wheel • 50 m 8.33 m First Loco(Second Bogie) Third wheel

  18. EUDL For spans up to 10m, EUDL for BM gives same result as actual calculation For spans > 10m to 75 m, EUDL for BM gives 2 to 8.67 % higher result as compared to actual calculation Max. difference of 8.67 % is for 23m span For spans > 75m, EUDL for BM gives same result as actual calculation

  19. EUDL As per C.S. 37 For new bridges>> Use EUDL or actual analysis For existing bridges >> Use EUDL, in case found inadequate- use exact calculations A locomotive with axle loads heavier than standard loading or trailing load higher than specified >>> load may be considered to fall in corresponding standard loading if EUDL is less than or equal to standard loading EUDL

  20. Foot Bridges and Foot Path • For Foot bridge/Footpath on rail bridge (for design of foot path portion) • 4.8 kPa (490 Kg/sqm) of Footpath area • Foot path on Rail cum Road or Road Bridge • 4.07 kPa (415 Kg/sqm) or 4.8 kPa (490 Kg/sqm) where crowd loading is expected

  21. Foot Bridge & Foot Path Cont. • Loads on Footpath for designing main girder for • Road or Rail bridge as per effective span < 7.5 m 4.07 kPa (415 Kg/sqm) > 7.5 m < 30 m 4.07 kPa (415 Kg/sqm) – 2.89 kPa (295 Kg/sqm) • 30 m as per formula • For Rail cum road Bridge - 1.91 kPa (195 Kg/sqm)

  22. Foot Bridge & Foot Path Cont. • Loads on Kerbs • 600 mm wide or more • Live Load + horizontal load of 7.35 kN/m • Less than 600 mm wide • No live load only Horizontal load of 7.35 kN/m • These loads need not be taken for design of main structure

  23. LIVE LOAD DISTRIBUTION

  24. CLAUSE 2.3.4.2 • Distribution through sleepers & ballast • distribution area of live load on top of ballast Type IType II ( under each rail seat ) BG 2745 mm x 254 mm 760 mm x 330 mm MG 1830 mm x 203 mm 610 mm x 270 mm • Further dispersal through fill / ballast at a slope half horizontal to one vertical. • All deck slabs to be designed for both type of sleepers

  25. Clause 2.3.4.2… Cont. • Distribution through R.C. Slab in right angle to slab • For simply supported, fixed and continuous span • 1/4 span on each side of loaded area • For cantilever slabs • 1/4 of loaded length on each side of loaded area. • Distribution through steel troughing or beam spanning transversely • As per appendix H of Steel Bridge Code

  26. DYNAMIC EFFECT • Accounted for by a static load equivalent to CDA multiply by LL. • For Railway Bridges (Steel) • CDA for BG /MG Single Track (speed 160/100) CDA = 0.15 + 8 / (6+L), Max. Value-1.0 where L is i) Loaded length giving maximum stress ii) 1.5* Spacing of cross girder ( For Stingers) iii) 2.5* Spacing of cross girder (For Cross girder)

  27. DYNAMIC EFFECT CONT. • For Multiple Track further multiply by • Main girders (outer) / Cross girders - 0.72 • Main girders (Intermediate) - 0.6 • Fish plated Track on steel troughing / steel sleeper • CDA = 7.32 / (B + 5.49) For BG • CDA = 5.49 / (B + 4.27) For MG where B is spacing between main girder • CDA for narrow gauge (762mm or 610mm) • CDA = 91.5 / (91.5 + L)

  28. DYNAMIC EFFECT CONT. • CDA for Foot Bridge • No allowance • CDA for combined Rail - Road Bridge • As per Rail Bridge • Turn table girders • Designed for CDA of 10% of LL • Additional allowance of 100% in all on an axle which is placed at one end of turn table.

  29. DYNAMIC EFFECT CONT. • CDA on pipe culvert, Arch Bridge, Concrete slab / conc. girder (span < 25m) • At zero fill -- Same as steel girder • At fill < 900mm -- Gradually reduced to 1/2 • At fill > 900mm -- reduced to zero in next 3m. • Applicable to multiple tracks also- except Arch Bridge span > 15m, where CDA reduce to 2/3rd

  30. FORCES DUE TO CURVETURE AND ECCENTRICITY OF TRACK • On ballasted deck, even on straight line • Designed for 100mm eccentricity • On a curved Bridge • Designed for centrifugal action of moving load taking all tracks occupied • Horizontal load due to centrifugal force is C = WV2 / 12.95R kN/m run Where W= Equivalent distributed live load in kN/m V= Maximum speed in Kmph R= Radius of curve in m • It assumed to act at 1830/1450mm for BG/MG above rail level

  31. TEMPRATURE EFFECT • Applicable for • Portion of Bridge not free to expand / contract • Temperature limits be specified by Engineer. • Coefficient of expansion • For steel & RCC -- 11.7*10-6per degree C • For plain concrete -- 10.8*10-6per degree C

  32. FRICTIONAL RESTISTANCE OF EXPANSION BEARING • Coefficient of frictional resistance of expansion bearings are • Roller bearing 0.03 • Sliding bearings of steel on • Cast Iron or Steel 0.25 • Ferrobestas 0.20 • Hard copper alloy 0.15 • Sliding bearing of PTFE / Elastomeric 0.10 • Conc. Over conc. with bitumen layer 0.50 • Conc. Over conc. Not intentionally roughened 0.60

  33. LONGITUDINAL FORCES • One or more of following be considered • Tractive Efforts • Braking Force • Resistance to movement of bearing due to change of temperature and deformation of girder • should not be more than the limiting resistance at the bearing. • Forces due to continuation of LWR/CWR on Bridges

  34. Long. Forces Cont • Loaded Length for simple supported span • One span for • Girders • stability of abutments • stability of pier carrying one fixed/ one free bearing • One span / two span • Stability of pier carrying fixed / sliding or elastomeric bearings • Longitudinal force shall be divided proportional to their length for two span loading condition. • Loaded Length for continuous span • Appropriate loaded length giving worst effect

  35. Long. Forces …Cont • No increase for dynamic effects • Transferred horizontally through • Knuckle pin for bearing having rocking arrangements. • Girder seats for sliding, elastomeric or PTFE bearings

  36. Long. Forces Cont. • Continuation Of LWR/CWR

  37. Long. Forces ..Cont • Distribution of Longitudinal Forces • Substructure with sliding / elastomeric bearings • Abutment 50% • Pier 40% • Multi-span Bridge • Also check for 20% net longitudinal force from adjoining span with directly supported span as unloaded. • Spans with roller / PTFE bearings at one end • 100% at fixed end

  38. Long. Forces.. Cont. • Dispersion of longitudinal forces • 25% of longitudinal force subject to minimum of • 16t for BG, • 12t for MMG or MGML and • 10t for MGBL • This applies to • open deck bridges having through welded rails, rail-free fastening and adequate anchorage of welded rails on approaches(minimum 30 m). • open deck having jointed track with rail free fastening or ballasted deck, however without any SEJ or mittred joints in either case. • Can increased to 35% in case suitably designed elastomeric bearings provided

  39. Long. Forces Cont. • Dispersion shall not exceed the capacity of track for dispersing the longitudinal force nor shall exceed the capacity of anchored length of track on approaches to resist dispersed longitudinal force. • In case multi-span bridges having continuous spans, or flexible supports, or flexible bearings on all supports, or any other special features which are likely to affect distribution/dispersion of longitudinal forces significantly, the dispersion/distribution of longitudinal forces shall be determined by suitable analysis. • For design of new bridges or rebuilding of existing bridges, dispersion of longitudinal forces shall not be allowed (CS no 36)

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