Structural Engineering CE-407 Lec-04 Structural Engineering Bridges-II ( ACI By Dr. Attaullah Shah Swedish College of Engineering and Technology Wah Cantt.

Elevation and cross section of Bridges

Arch and suspension Bridges

Some important definitions

Bridges

Great Stone Bridge in China History of Bridge Development 100 B.C. Romans 2,104 years ago 700 A.D. Asia 1,304 years ago Clapper Bridge Roman Arch Bridge Tree trunk Stone Arch design evenly distributes stresses Natural concrete made from mud and straw Clapper Bridges employed all over the world, most notably in England. Originally, tree logs used, but they tended to rot. Stones were better, but difficult to maneuver. The Romans developed highways that connected the empire. Bridges helped them do this. Great Stone Bridge in China Low bridge Shallow arch Allows boats and water to pass through

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

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

Basic Concepts Beam - a rigid, usually horizontal, structural element Pier 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

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.

Truss Bridge Typical 40m to 500m 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.

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.

Types of Bridges Forces 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.

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.

Types of Bridges Forces 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.

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.

Types of Bridges Forces 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.

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.

Floating Bridges Retractable! But high maintenance!

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

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

Types of Bridges Arch Truss Cantilever Cable-Stayed Suspension

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

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

Arch Bridges Works by Compression

Arch Bridges Where have you seen these bridges?

Cold Spring Arch Bridge, Santa Barbara, CA

Marsh Rainbow Arch, Riverton, KS

Pont du Gard, Nimes, France

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

Cable-Stayed Bridges Works by Tension AND Compression

Cable-Stayed Bridges Where have you seen these bridges?

Zakim Bridge, Boston, MA

Sunshine Skyway Bridge, Tampa, FL

Sundial Bridge, Redding, CA

Suspension Bridges Similar to Cable-Stayed Different construction method

Suspension Bridges Works by Tension and Compression

Suspension Bridges Where have you seen these bridges?

Golden Gate Bridge, San Francisco, CA

Brooklyn Bridge, Brooklyn, NY

Verrazano-Narrows Bridge, New York, NY

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

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

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

COMPONENTS OF A BRIDGE Deck Girder Abutment Pier

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

Chesapeake Bay Bridge, Virginia GIRDER BRIDGE Typical span length 30 to 650 ft World’s longest: Ponte Costa e Silva, Brazil with a center span of 1000 ft Chesapeake Bay Bridge, Virginia

Firth of Forth Bridge, Scotland TRUSS BRIDGE Typical span length 150 to 1500 ft World’s longest: Pont de Quebec, Canada with a center span of 1800 ft Firth of Forth Bridge, Scotland

RIGID FRAME BRIDGE Girders and piers act together Cross-sections are usually I-shaped or box-shaped. Design calculations for rigid frame bridges are more difficult than those of simple girder bridges.

ARCH BRIDGE Larimer Avenue Bridge, Pittsburgh After girders, arches are the second oldest bridge type. Arches are good choices for crossing valleys and rivers Arches can be one of the more beautiful bridge types. Typical span length 130 ft – 500 ft. World’s longest: New River Gorge Bridge, U.S.A. with a center span of 1700 ft. Larimer Avenue Bridge, Pittsburgh

CABLE STAYED BRIDGE Continuous girder with one or more towers erected above in the middle of the span. From these towers cables stretch down diagonally and support the girder. Typical span length 350 to 1600 ft. World’s largest bridge: Tatara Bridge, Japan center span: 2900 ft. Normandie Bridge

Golden Gate Bridge, California SUSPENSION BRIDGE Continuous girder with one or more towers erected above in the middle of the span. At both ends of the bridge, large anchors or counter weights are placed to hold the ends of the cables. Typical span length 250 to 3000 ft. Golden Gate Bridge, California

Factors Describe a Bridge Four main factors are used in describing a bridge: Span (simple, continuous, cantilever) Material (stone, concrete, metal, etc.) Placement of the travel surface in relation to the structure (deck, through) Form (beam, arch, truss, etc.).

Basic Span Types Simple Span Continuous Span Cantilever Span

LOADS ON BRIDGES Permanent Loads: remain on the bridge for an extended period of time (self weight of the bridge) Transient Loads: loads which are not permanent - gravity loads due to vehicular, railway and pedestrian traffic - lateral loads due to water and wind, ice floes, ship collision, earthquake, etc.

VEHICULAR DESIGN LOADS (HL 93) AASHTO – American Association of State Highway and Transportation Officials This model consists of: Design Truck Design Tandem Design Lane

DESIGN TRUCK 145 kN 35 kN 4.3 to 9.0 m 4.3 m 9.3 N/m DESIGN TRUCK

DESIGN TANDEM 110 kN 9.3 N/m 1.2 m DESIGN TANDEM

DESIGN PRINCIPLES Resistance ≥ effect of the applied loads Strength of the Member ≥ Factor of Safety x Applied Load Allowable Stress Design (ASD): Load and Resistance Factor Design (LRFD): η ∑γiQi ≤ φi Rn Where, Qi = Effect of loads Rn = Nominal resistance γi = Statistically based resistance factor applied to the force effects φi = Statistically based resistance factor applied to the nominal resistance η = Load modification factor

MATERIALS FOR BRIDGES Concrete Steel Wood

CONCRETE BRIDGES Raw materials of concrete: cement, fine aggregate coarse aggregate, water Easily available can be designed to satisfy almost any geometric alignment, straight to curved can be cast-in-place or precast Compressive strength of concrete range from 5000 psi to 8500 psi Reinforced concrete and prestressed concrete

STEEL BRIDGES Minimum construction depth Rapid construction Steel can be formed into any shape or form Predictable life Ease of repair and demolition

WOOD BRIDGES Convenient shipping to the job site Relatively light, lowering transportation and initial construction cost Light, can be handled with smaller construction equipment Approx. 12% of the bridges in US are wood bridges Commonly used for 20-80 ft span

Wood Bridge on Concrete Abutments Three Span Wood Bridge

GIRDER CROSS-SECTIONS COMMONLY USED IN BRIDGES

COLLAPSE OF BRIDGES Poor design Inadequate stability of the foundation Fatigue cracking Wind forces Scour of footing Earthquake

Before Collapse After Collapse

AKASHI KAIKYO BRIDGE, JAPAN Completion Date: 1998 Cost: $4.3 billion Length: 12,828 feet Type: Suspension Materials: Steel Span: 6,527 feet

SUNSHINE SKYWAY BRIDGE, USA Completion Date: 1987 Cost: $244 Million Length: 29,040 feet Type: Cable Stayed Materials: Steel, Concrete Span: 1200 feet

NEW RIVER GORGE BRIDGE, USA Completion Date: 1978 Cost: $37 Million Length: 4,224 feet Type: Arch Materials: Steel Span: 1700 feet