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Concrete and steel bridges
This document discusses different types of bridges, focusing on steel and concrete bridges. It describes the main advantages and disadvantages of steel and concrete as materials for bridge construction. It then outlines different structural types of steel bridges like beam/girder, truss, plate girder, box girder, and cable-stayed bridges. For concrete bridges, it discusses slab, beam, box girder, and continuous girder bridges.
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Introduction to bridges, focusing on materials utilized: concrete and steel.
Highlights steel advantages such as strength and versatility, and disadvantages including corrosion and high maintenance.
Identification of various steel bridge types: beam, girder, truss, arch and movable designs.
Explores truss bridges, efficiency, span capabilities up to 200m, and types like Warren and Pratt.
Discusses plate girder bridges and box girder bridges emphasizing torsional rigidity and span capabilities.
Details on cantilever bridge design, utilizing arms for long clear spans, supporting navigation.
Explains arch bridges and their structural properties with reduced bending moments compared to standard bridges.
Describes cable stayed bridges,span capabilities ranging from 200-500m, structure relies on cables and pylons.
Focus on suspension bridges with spans over 600m, known for being lightweight yet expensive.
Introduces movable bridges that allow navigation by swinging, with designs facilitating vertical clearance.
Examines temporary bridges for urgent scenarios, erected quickly without permanent structures, often post-disaster.
Overview of concrete bridges, outlining their advantages like durability and low maintenance, and drawbacks.
Describes reinforced concrete (RC) bridges including slab, beam, and box girder types for various spans.
Detailed discussion on bridge design requirements, loads influenced by codes and specific design stresses. Utilization of finite element analysis to evaluate structural integrity and performance of bridge designs.
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Concrete and steel bridges
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- 3. 3 Advantages of Steel •High tensile and compressive strength • High strength to weight ratio – low self weight & less loading on substructure • Uniformity • High quality material • Speed of construction • Versatility of construction • Elasticity – follows Hooke’s Law very accurately • Ductility – can withstand high deformations before failure ➔ gives a warning before failure • Modifications can be made easily – strengthening of beams
- 4. 4 4 Design Stress StrainCurve for Concrete – BS8110
- 5. 55 Design Stress StrainCurve for Reinforcement – BS8110
- 6. 6 Disadvantages of Steel •Maintenance cost is high – corrodes when exposed to air, water and humidity • Fire proofing cost – strength reduces at high temperatures • Susceptible to buckling – slender structures • Fatigue – strength reduces due to cyclic loading
- 7. 7 Types of SteelBridges • Beam / Girder • Truss • Plate girder • Box girder • Cantilever • Arch • Cable stayed • Suspension • Movable • Temporary / emergency
- 8. 8 Beam / GirderBridges
- 9. 9 Beam / GirderBridges (Contd.) • Rolled I sections are used as the main support system • Other members – cross girders, stringers, deck, bracings • Two beam/girder system or multiple beam/girder system with cross beams (cross girders)
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- 13. 13 Truss Bridges (Contd.) •Spans up to 200m possible • Structurally efficient • Reduced self weight • Several types of truss arrangements possible – Warren, Modified Warren, Pratt, Fink, Howe etc.
- 14. 14 Truss Bridges (Contd.) Componentsof a truss bridge
- 15. Warren Truss PrattTruss Equal length members Easy fabrication economy Longer members in tension Slender diagonals are possible Efficient structure Truss Bridges (Contd.)
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- 18. 18 Box Girder Bridges(Contd.) • Very high torsional rigidity • Effective use of construction materials • Longer spans possible • Complex execution
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- 20. 20 Cantilever Bridges (Contd.) •Permits a long clear span for navigation • Main structural elements are anchor arm, cantilever arm and suspended span
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- 23. 23 Arch Bridges (Contd.) •Structural action similar to old masonry arches – bending moments much lower than in typical bridges • Deck support – Hangers or struts
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- 25. 25 Cable Stayed Bridges •Spans : 200 – 500m • Main structural elements – Cables, towers (pylons) and deck
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- 27. 27 Suspension Bridges (Contd.) •Spans exceeding 600m • Main structural elements – Flexible cables, towers (pylons), anchorages, hangers, deck • Light and strong • Very expensive
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- 30. 30 Movable Bridges (Contd.) •Permits passage for navigation by moving / swinging the bridge deck • When it is either impractical or too expensive to provide a bridge with sufficient vertical clearance • Moving action – Lift/sink or swing
- 31. 31 Temporary / EmergencyBridges
- 32. 32 Temporary / EmergencyBridges (Contd.)
- 33. 33 Temporary / EmergencyBridges (Contd.) • Erected within a very short period (1 day) • No permanent abutments / piers • Specially provided during wars and after natural disasters
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- 35. 35 Advantages of Concrete •Ingredients of concrete are easily available. • Unlike natural stones Concrete is free from defects and flaws (faults, joints, stratifications etc.). • Concrete can be manufactured to desired strength with economy. • The durability of concrete is very high. • It can be cast to any desired shape. • Casting of concrete can be done at work site which makes it economical. • Maintenance cost of concrete is almost negligible.
- 36. 36 Disadvantages of Concrete •Compared to other binding materials, the tensile strength of concreter is relatively low. • Concrete is less ductile. • The weight is high compared to its strength.
- 37. 37 RC Bridges • Suitablefor small and medium spans • Special requirements – restriction on provision of formwork, construction period • Most of highway bridges are RC • Several types available • Slab • Beam • Box girder • Continuous girder • Balanced cantilever • Arch
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- 39. 39 Slab Bridges RC Slabserves as the main superstructure member, requiring no other beams or girders to carry the loads. Not suitable for larger spans since the slab becomes thicker increasing the dead weight. • Economical • Simple design • Solid / hollow slabs
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- 41. 41 Beam Bridge RC beamsserve as the main superstructure member. Widely used due to simplicity, economy, wide availability of the standard sections, and speed of erection. Precast beams are placed on the supporting piers or abutments, usually on rubber bearings which are maintenance free. • I beams are used • A deck is constructed on top of beams spanning between the beams
- 42. 42 Box Girder Bridges Forspans greater than around 45 metres, pre- stressed concrete box girders are the most common method of concrete bridge construction. The main spans are hollow and the shape of the 'box' will vary from bridge to bridge and along the span, being deeper in cross-section at the abutments and piers and shallower at mid span. • Incrementally launched • Span by span • Balanced cantilever
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- 45. 45 Loads on Bridges(BS Code)
- 46. 46 Loads on Bridges(Eurocode)
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- 52. 52 Stresses in aPlate Girder
- 53. 53 Stresses in aBox Girder
- 54. 54 Bending of BoxGirders
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