By Dr. Attaullah Shah Swedish College of Engineering and Technology Wah Cantt.

2. ByDr. Attaullah ShahSwedish College of Engineering and Technology Wah Cantt. CE-407 Lec-03 Structural Engineering Bridges

3. Bridges

4. Roman Arch Bridge History of Bridge Development 100 B.C. Romans 2,104 years ago 700 A.D. Asia 1,304 years ago Clapper Bridge • Tree trunk • Stone • Arch design evenly distributes stresses • Natural concrete made from mud and straw Great Stone Bridge in China • Low bridge • Shallow arch • Allows boats and water to pass through

5. History of Bridge Development 1900 1920 Truss Bridges • Mechanics of Design • Wood 2000 Suspension Bridges • Use of steel in suspending cables • Prestressed Concrete • Steel

6. Tension Compression Basic Concepts Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon. Force - Compression – Tension - Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?

7. Beam Pier Basic Concepts Beam - a rigid, usually horizontal, structural element Pier - a vertical supporting structure, such as a pillar Cantilever - a projecting structure supported only at one end, like a shelf bracket or a diving board Load - weight on a structure

8. Types of Bridges • Basic Types: • Truss Bridge • Beam Bridge • Arch Bridge • Suspension Bridge • Floating Bridge Floating Truss Beam Arch Suspension The type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle.

9. Truss Bridge All beams in a truss bridge are straight. Trusses are comprised of many small beams that together can support a large amount of weight and span great distances.

10. Types of Bridges Beam Bridge Consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.

11. Types of Bridges Beam Bridge Forces When something pushes down on the beam, the beam bends. Its top edge is pushed together, and its bottom edge is pulled apart.

12. Types of Bridges Arch Bridges The arch has great natural strength. Thousands of years ago, Romans built arches out of stone. Today, most arch bridges are made of steel or concrete, and they can span up to 800 feet.

13. Types of Bridges Arch Bridges Forces The arch is squeezed together, and this squeezing force is carried outward along the curve to the supports at each end. The supports, called abutments, push back on the arch and prevent the ends of the arch from spreading apart.

14. Types of Bridges Suspension Bridges This kind of bridges can span 2,000 to 7,000 feet -- way farther than any other type of bridge! Most suspension bridges have a truss system beneath the roadway to resist bending and twisting.

15. Types of Bridges Suspension Bridges Forces In all suspension bridges, the roadway hangs from massive steel cables, which are draped over two towers and secured into solid concrete blocks, called anchorages, on both ends of the bridge. The cars push down on the roadway, but because the roadway is suspended, the cables transfer the load into compression in the two towers. The two towers support most of the bridge's weight.

16. Types of Bridges Floating Bridge • Pontoon bridges are supported by floating pontoons with sufficient buoyancy to support the bridge and dynamic loads. • While pontoon bridges are usually temporary structures, some are used for long periods of time. • Permanent floating bridges are useful for traversing features lacking strong bedrock for traditional piers. • Such bridges can require a section that is elevated, or can be raised or removed, to allow ships to pass.

17. Floating Bridges Retractable! But high maintenance!

18. Bridge Engineering • How do the following affect your structure? • Ground below bridge • Loads • Materials • Shapes

19. Some Uses of Bridges • Walkways • Highways/Roads • Railways • Pipelines • Connecting lands • Crossing rivers and canyons

20. Types of Bridges • Arch • Truss • Cantilever • Cable-Stayed • Suspension

27. What makes a bridge stay up? • Forces • Compression – a pushing or squeezing force • Tension – a pulling or stretching force

28. Arch Bridges • Keystone – the wedge-shaped stone of an arch that locks its parts together • Abutments – the structures that support the ends of the bridge

29. Arch Bridges • Works by Compression

30. Arch Bridges • Where have you seen these bridges?

31. Cold Spring Arch Bridge, Santa Barbara, CA

32. Marsh Rainbow Arch, Riverton, KS

33. Pont du Gard, Nimes, France

34. Cable-Stayed Bridges • Piers – the vertical supporting structures • Cables – thick steel ropes from which the decking is suspended • Decking – the supported roadway on a bridge

35. Cable-Stayed Bridges • Works by Tension AND Compression

36. Cable-Stayed Bridges • Where have you seen these bridges?

37. Zakim Bridge, Boston, MA

38. Sunshine Skyway Bridge, Tampa, FL

39. Sundial Bridge, Redding, CA

40. Suspension Bridges • Similar to Cable-Stayed • Different construction method

41. Suspension Bridges • Works by Tension and Compression

42. Suspension Bridges • Where have you seen these bridges?

43. Golden Gate Bridge, San Francisco, CA

44. Brooklyn Bridge, Brooklyn, NY

45. Verrazano-Narrows Bridge, New York, NY

46. Other Types Truss Southern Pacific Railroad Bridge, Tempe, AZ Cantilever Firth of Forth-Forth Rail Bridge, Edinburgh, Scotland

47. FUNCTION OF A BRIDGE Bosporus Straits Bridge at Istanbul, Turkey – To connect two communities which are separated by streams, valley, railroads, etc. • Replaces a slow ferry • boat trip • Connects two continent • Built in 1973 • Total length is 5000 ft

48. COMPONENTS OF A BRIDGE • Deck or Slab: supported roadway on abridge • Beam or Girder: A rigid, usually horizontal, • structural element • Abutment: The outermost end supports on a • bridge, which carry the load from • the deck • Pier: A vertical supporting structure, such as a • pillar • Foundation

49. Deck Girder Abutment Pier COMPONENTS OF A BRIDGE

50. TYPES OF BRIDGES • Beam or Girder Bridge • Truss Bridge • Rigid Frame Bridge • Arch Bridge • Cable Stayed Bridge • Suspension Bridge