Bridges (EDocFind - Com)
Bridges (EDocFind - Com)
Bridges (EDocFind - Com)
Arch design evenly distributes stresses Natural concrete made from mud and straw
Low bridge Shallow arch Allows boats and water to pass through
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
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
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
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
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
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!
Bridge Engineering
The first Tacoma Narrows suspension bridge collapsed due to wind-induced vibrations on Nov. 7, 1940. The bridge over engineered it to withstand hurricane winds, but the wind that day was only 40 mph what happened!?