Presentation on theme: "Bridge Engineering: Lessons from Rome to Tacoma Clear Lake MS Engineering 03-27-2006."— Presentation transcript:
Bridge Engineering: Lessons from Rome to Tacoma Clear Lake MS Engineering
700 A.D. Asia 1,304 years ago 100 B.C. Romans 2,104 years ago Clapper Bridge Tree trunk Stone Arch design evenly distributes stresses Natural concrete made from mud and straw Roman Arch Bridge History of Bridge Development Great Stone Bridge in China Low bridge Shallow arch Allows boats and water to pass through
History of Bridge Development Truss Bridges Mechanics of Design Wood Suspension Bridges Use of steel in suspending cables Prestressed Concrete Steel 2000
Compression Tension Basic Concepts Span - the distance between two bridge supports, whether they are columns, towers or the wall of a canyon. Compression – Tension - Force - Concrete has good compressive strength, but extremely weak tensile strength. What about steel cables?
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 Beam Pier Load - weight on a structure
The type of bridge used depends on the obstacle. The main feature that controls the bridge type is the size of the obstacle. Types of Bridges Basic Types: Truss Bridge Beam Bridge Arch Bridge Suspension Bridge Floating Bridge TrussBeamArch Suspension Floating
Truss Bridge Typical Span Lengths 40m - 500m World's Longest Pont de Quebec Total Length863m Center Span549m A Matsuo Example 2 nd Mameyaki 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.
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.
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 Beam Bridge
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 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 Arch 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 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 Suspension Bridges
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. Types of Bridges Floating Bridge
Floating Bridges Retractable! But high maintenance!
How do the following affect your structure? Ground below bridge Loads Materials Shapes Bridge Engineering
To design a bridge like you need to take into account all the forces acting on it: The friction of the earth on every part The strength of the ground pushing up the supports The resistance of the ground to the pull of the cables The dead weight and all vehicle loads Then there is the drag and lift produced by wind and water The turbulence as fluids pass the towers Summary Bridge Engineering Need to use appropriate materials and structural shapes in the cheapest way, yet maintaining a certain degree of safety. To account for natural disasters, engineers design bridges with a factor of safety: usually around 3 or 4.
Case Study: Tacoma Narrows Failure The first Tacoma Narrows suspension bridge collapsed due to wind-induced vibrations on Nov. 7, The bridge over engineered it to withstand hurricane winds, but the wind that day was only 40 mph… what happened!?