Beam bridge Truss bridge Arch bridge Suspension bridge Bridge Design Beam bridge Truss bridge Arch bridge Suspension bridge Mr. Klokman Computer / Technology King Philip Middle School

Beam bridge beam supported at each end by piers. This is why beam bridges rarely span more than 250 feet. Pros: Easy to build; inexpensive relative to other bridge types; used widely in urban and rural settings Cons: Limited span; does not allow large ships or heavy boat traffic to pass underneath; design generally not considered very interesting or eye-catching

Beam bridge Live Load Compression: the tendency to push or squash a material Dead Load Tension: the tendency for a material to be pulled apart 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. BRIDGE BRAG It’s the loooooooonnnnnnngest bridge in the world, and it’s a beam bridge! The Lake Pontchartrain Causeway in Louisiana is approximately 24 miles long, and its twin spans are supported by over 9,000 pilings.

Truss bridge The truss bridge... consists of an assembly of triangles. Truss bridges are commonly made from a series of straight, steel bars. Rigid arms extend from both sides of two piers. Diagonal steel tubes, projecting from the top and bottom of each pier, hold the arms in place. The arms that project toward the middle are only supported on one side, like really strong diving boards. These "diving boards," called cantilever arms, support a third, central span.

Truss Bridge Tension: the tendency for a material to be pulled apart Compression: the tendency to push or squash a material Truss Bridge: Forces Every bar in this cantilever bridge experiences either a pushing or pulling force. The bars rarely bend. This is why cantilever bridges can span farther than beam bridges. Pros: Very strong; frequently used as a draw bridge Cons: Difficult to construct; high maintenance; difficult to widen if necessary; generally not considered attractive Wooden truss bridges were used as early as the 1700s, but the first metal one was completed in 1841. They are very strong and have been used for railroad bridges mainly because of the heavy loads they can support. A truss, a rigid support structure that is made up of interlocking triangles, holds up the roadbed and is set between two piers. The triangle is used because it is the only shape that is inherently rigid.

Arch bridge Live Load: would be the water Dead Load: would be the stone The arch bridge... 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.

Arch bridge Arch Bridge: 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. Pros: Wide range of materials can be used; considered attractive; very strong Cons: Relatively expensive; typically designs are limited to certain sites (for example, where the ground can support the large forces at the base of the arch; where the span-to-depth ratio of the arch is proportional; or where an arch is visually appropriate)

How are arch bridges built How are arch bridges built? Building an arch bridge isn't easy, since the structure is completely unstable until the two spans meet in the middle. For years, engineers used a technique called centering, in which a wooden form supported both spans until they locked together at the top. A newer method supports the spans using cables anchored to the ground on either side of the bridge. This is how the New River Gorge Bridge in West Virginia was built.

Suspension bridge The suspension bridge... 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.

Suspension Bridge Torsion: twisting material Tension: the tendency for a material to be pulled apart Suspension Bridge: 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 transferthe load into compression in the two towers. The two towers support most of the bridge's weight.

Beam bridge Truss bridge 250 feet Longest Single Span: 350 feet (center span) Arch Bridge Suspension Bridge 800 feet 2,000 to 7,000 feet

Structures Girders Braces Columns Beams