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Arch Bridge Code (1941, Revised 1962) - Design, Analysis, and Strengthening Guidelines

This code provides guidelines for the design, analysis, and strengthening of arch bridges constructed using brick, stone masonry, or plain concrete. It includes information on design loads, shape of arch ring, analysis of stresses, certification of existing bridges, load tests, and abutment design.

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Arch Bridge Code (1941, Revised 1962) - Design, Analysis, and Strengthening Guidelines

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  1. ARCH BRIDGE CODEAdopted – 1941Revised – 1962Correcredupto –CS 8

  2. Components of Arch

  3. SCOPE • Applied to arch bridges constructed of • Brick woks • Stone masonry • Plain concrete • Bridges excluded from scope of this code • open spandrel • reinforced concrete arch bridge

  4. Design Loads • Dead Load • Includes arch ring & permanent load on it • Neglect horizontal component of earth pressure • Live Load • Live load & Impact as per Bridge rule • Neglect horizontal loads due to TE & BF • Temperature stresses • Neglected where rise span ratio < 1/3

  5. Design Loads ..contd • Rib shortening stress • Due to thrust be accounted for • Shrinkage stresses • neglected • Precaution be taken in plain concrete – concreting be done in strips. For span > 6 mt. light reinforcement (min 0.16% of area of concrete) be provided.

  6. SHAPE OF ARCH RING • Rise should be large • To reduce horizontal load • Normally not less than 1/3rd of span • In any case not less than 1/5 th of span • Spans upto12 m • Simple segments or semi circular curve be used

  7. Span exceeding 12 m • Match axis as near to equilibrium polygon for D.L. + 50% EUDL covering entire span • Thickness of rib • Fixed as per condition of stresses, economy & appearance in mind • Vary gradually • Generally constant section for span < 12m

  8. ANALYSIS OF STRESSES IN ARCH RING • Condition of Load line • For span < 12 m • For constant thickness Sufficient toconsider LL at end 5/8 of span For variable thickness Three critical sections Sec Moment Max. + Max. - Crown Middle 1/4th of whole span End 3/8(both end) Quarter point End 3/8 span End 5/8 span (adjacent end) (opposite end) Spring point End 5/8 End 3/8 span (opposite end) (adjacent end)

  9. ANALYSIS CONT. • Span > 12 m • No. of sections throughout the arch depending on span • The line of pressure under the condition of loading shall everywhere lie • within middle half of the arch ring if determined by elastic theory • within the middle third if graphical or other approximate methods are adopted • Method of Analysis • Preferably by elastic method of analysis • Purely analytical • combination of analytical & graphical method which is simplest in practice

  10. Certification of Existing Arch Bridges • Except for GC - based on physical condition • Heavier loading density/axle loads shall not be permitted on distress bridge • unless rehabilitated • At discretion C.E. if found safe after conducting load test on representative span • For GC - certificate of all bridges whether sound or distress be based on load test of representative type of bridge provided • condition of masonry & its behavior under load test is satisfactory • Type of foundation / founding soil is suitable.

  11. LOAD TEST • Shall be conducted on bridges having ORN 1 and 2 after complete pressure grouting of the masonry • The criteria for arriving safe load shall be • under the proposed load crown deflection & spread do not exceed • 0.75 mm and 0.4 mm respectively for spans upto 1 m • 0.75+(L-1)/3.5X(1.25 – 0.75)mm and 0.4 mm for spans > 1m and < 4.5m

  12. LOAD TEST • 1.25 mm and 0.4 mm for spans 4.5 m and upto 15 m. • No residual deflection or spread after release of load • No crack appearing on the intrados of bridge • Above criteria applicable to segmental and non segmental arches of span upto 15 m provided span/rise ratio lies between 2 & 5.

  13. STRENGTHENING OF WEAK/DISTRESSED EXISTING ARCHES • Preferably by jacketting at the intrados if • reduction in the water way is permissible • new arch ring be designed • to take full load -if existing arch has transverse crack(s) • composite action - where existing cracks are longitudinal or there is no sign of distress. • The space between new/ existing arch ring be grouted under pressure to ensure effective bond

  14. STRENGTHENING ..contd • In case of strengthening over extrados new arch ring be designed to take full load • In case of cracked masonry, pressure grouting be done before additional material is provided

  15. Effective Length • Full length between skew back to skew back • Between points obtained by producing the inside vertical face of skew back in case spandrel is filled with masonry or concrete and has proper bonding with arch ring

  16. ABUTMENT FOR ARCH BRIDGES • Thickness at the skew backs: • To be designed to resist shearing stresses of horizontal thrust from arch ring by combined friction ( Coefficient of friction= 0.7) and shearing strength of the joint (1/40 of crushing strength). • Forces acting on Abutment • Reaction from arch • Pressure of earth at back • Weight of abutment & overlying fill • Water pressure & buoyancy if depth of water exceed 6 m • Impact may be neglected in calculating thrust of arch ring

  17. ABUTMENT FOR ARCH BRIDGES …contd • Total thrust on abutment assumed to be distributed over whole length of abutment or the length bound by lines drawn at a slope of ½ H : 1V for bottom edge of sleepers to the section under investigation; whichever is less • Active E/P at back of abutment (which adds to its stability) shall not be taken more than the pressure of a fluid weighing 240 kg/m3. Assumed to act over a ht. from bed level to springing level only. • Surcharge due to fill is considered but not Live load.

  18. ABUTMENT …CONT. • Condition of stability • Line of pressure shall lie in middle half • Stresses shall not exceed the working stresses as per clause 12 • Should be checked for • DL + L.L On 5/8 span adjacent to the abutment • D.L+ LL On other 5/8 span • D.L + LL On entire span In all these conditions the line of pressure shall lie within middle half of every section of abutment.

  19. ABUTMENT …CONT. • Foundation • No risk of unequal settlement • permissible pressure as per clause 13 • Line of pressure within middle 1/3rd of f/n. Effort be made to keep as near possible as to center. • Minimum depth of foundation 1.25 m

  20. PIERS OF ARCH BRIDGES • Thickness at top • to accommodate both skew backs • to resist stresses under most unfavorable conditions • Forces acting on the pier • Reaction from adjacent arches • Weight of pier and overlying fill. • Water pressure & buoyancy as for abutment • Impact & distribution of loads as for abutment.

  21. PIERS CONT. • Condition of stability • Line of pressure shall lie in middle half at every section. • Stresses shall not exceed the working stresses as per clause 12 • Should be checked for • one of the adjacent span carries live load - max stress in masonry • both adjacent span carries live load -max. intensity of F/N pressure • Foundation for Piers • As for abutments

  22. ECONOMY IN DESIGN OF BRIDGES • Proportion of dimensions for max. economy • To avoid lateral tension in arch ring or excessive loads on the ends of barrel the ht. of parapet wall above crown > 1000 mm when depth of fill is considerable.

  23. WORKING STRESSES • Masonry arches • where actual compression test are made • compressive stress in masonry shall not exceed 1/8 of crushing strength • Tensile & shear stresses 1/40 of crushing strength • In absence of test • Brick work in Lime mortar crushing strength 4.3 N/mm 2 • Brick work in cement mortar 6.9 N/mm 2 • Plain concrete arches • as per concrete bridge code

  24. FOUNDATION PRESSURE • As per experience on test conducted • Depth of foundation not less than 1.25 m unless resting on rock • permissible bearing pressure can be increased by 17647 N/m2 for each additional m of depth beyond 1.25 m

  25. SEISMIC EFFECT • No masonry & Plain cement concrete arches in zone V • No masonry & Plain cement concrete arches in zone IV of span exceeding 6 m and in zone III of span exceeding 10 m.

  26. SKEW ARCHES • Courses are every where of right angles to the lines of thrust • WEEP HOLES • Through abutments, wing or return walls & parapets as necessary & adequate arrangement be made to lead water to the weep holes.

  27. FILLING OVER ARCHES • Depth of fill not less than 1 m between under side of sleeper to crown • By porous material such as brick bats or ballast for 300mm over extrados of arch from crown • Earth filling should be done in layers, each being consolidated by ramming & by sprinkling with water • Black cotton soil shall not be used. • In existing arches, filling should be disturbed as little as possible. Over the time the filling relieves the arching of a considerable portion of super imposed loads.

  28. STRIKING OF CENTRES AND APPLICATION OF LOAD • Striking of centers • should not be struck before one week after completion of arch. • Application of Load • After completion of any portion of the masonry of an arch bridge, the following minimum periods of time should be allowed before applying specified load Description 50% of 75% of Full Design loadDesign loadDesign load Ordinary cement 7 days 14 days 28 days mortar & concrete Rapid- Hardening 5 days 10 days 28 days. Cement mortar & concrete • Load includes impact allowance. The above period should be increased if temp < 160C.

  29. Thank You

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