BRIDGES by: Tom Wright, P.E. and Jennifer Hall, P.E.

Engineers are problem solvers. → Use available technology to solve → Rely on creativity and academic skills → Use math, science, and computers It is very important to note that even though the tasks are very different, many of the methods used are common to all engineers. Engineers are problem solvers. → Use available technology to solve → Rely on creativity and academic skills → Use math, science, and computers It is very important to note that even though the tasks are very different, many of the methods used are common to all engineers.

THE ENGINEERING PROCESS: IDENTIFY and define a problem IDENTIFY and define a problem SOLVE THE PROBLEM SOLVE THE PROBLEM ANALYZE the problem ANALYZE the problem DESIGN and propose solutions DESIGN and propose solutions REFINE their proposals REFINE their proposals

TYPES OF CIVIL ENGINEERS þ STRUCTURAL þ TRANSPORTATION þ GEOTECHNICAL þ ENVIRONMENTAL þ WATER RESOURCES

STRUCTURAL ENGINEERS Who does this?

TRANSPORTATION ENGINEERS Who does this?

ENVIRONMENTAL ENGINEERS ENVIRONMENTAL ENGINEERS Who does this?

GEOTECHNICAL ENGINEERS GEOTECHNICAL ENGINEERS Who does this?

WATER RESOURCE ENGINEERS Who does this?

BRIDGES!!!! zBridge Material yTimber yConcrete ySteel

EQUILIBRIUM zLOADS zFORCES zMOMENTS zTORSION Summation of Forces Σ F=0 yHorizontal Direction Σ F h =0 yVertical Direction Σ F v =0

LOADS zDead Loads zLive Loads zWind Loads zSnow Loads

FORCESFORCESFORCESFORCES

MOMENTS zSummation of Moments – Σ M=0 zMoment = Force * Distance

TORSION zTorsion is produced when a beam is subjected to loads which cause it to, twist buckle and roll. zDiaphragms are inserted to eliminate torsion.

TORSIONTORSIONTORSIONTORSION

Arch Bridges Bixby Creek Bridge, Monterey, CA zArch bridges are one of the oldest types of bridges zModern arch bridges span between feet zThe structure is completely unstable until the two spans meet in the middle. zHave great natural strength.

Arch Bridges Bixby Creek Bridge, Monterey, CA zHow it works: yInstead of pushing straight down, the weight is carried outward along the curve of the arch to the supports at each end. yThese supports, called abutments, carry the load and keep the ends of the bridge from spreading yWhen supporting its own weight and the weight of crossing traffic, every part of the arch is under compression.

Beam Bridge zLake Ponchartrain Causeway, Louisiana zThe world's longest bridge is a continuous span beam bridge. zAlmost 24 miles long zConsists of two, two-lane sections that run parallel to one another. yThe Southbound Lane, completed in 1956, is made up of 2243 separate spans, yThe Northbound Lane, completed in 1969, is pieced together from 1500 longer spans.

Suspension Bridge zthe cables are made of thousands of individual steel wires bound tightly together. zSteel, which is very strong under tension, is an ideal material for cables; zA single steel wire, only 0.1 inch thick, can support over half a ton without breaking. zBecause suspension bridges are light and flexible, wind is always a serious concern

Cable Stayed Bridge Clark Bridge, Alton, IL zFor medium length spans (those between 500 and 2,800 feet) zRequire less cable zAre quickly built, resulting in a cost-effective bridge and is beautiful. zCable-stayed bridges may look similar to suspensions bridges—both have roadways that hang from cables and both have towers. But the two bridges support the load of the roadway in very different ways. yThe difference lies in how the cables are connected to the towers. yIn suspension bridges, the cables ride freely across the towers, transmitting the load to the anchorages at either end. yIn cable-stayed bridges, the cables are attached to the towers, which alone bear the load. Parallel attachment pattern Radial attachment pattern

zBecause the truss is a hollow skeletal structure, the roadway may pass over or even through the structure allowing for clearance below the bridge often not possible with other bridge types Truss Bridges

zWarren Truss yThe Warren truss pattern features a series of isoceles or equilateral triangles. In contrast to the Pratt and Howe patterns, the diagonals alternate in direction. yWarren trusses are typically used in spans of between feet yThe most common truss. For smaller spans, no vertical members are used lending the structure a simple look. For longer spans vertical members are added providing extra strength Truss Bridges

zPratt Truss yThe Pratt truss design contains a downward pointing V in the center with parallel diagonals on each side. yExcept for those diagonal members near the center, all the diagonal members are subject to tension forces only while the shorter vertical members handle the compressive forces. This allows for thinner diagonal members resulting in a more economic design.

zHowe Truss yThe Howe truss pattern features an upward pointing V formed by the central diagonals with parallel diagonals on either side. Unlike the Pratt pattern the diagonals will be in compression when loaded yIt is the opposite of the Pratt truss. The diagonal members face in the opposite direction and handle compressive forces. This makes it very uneconomic design for steel bridges and is rarely used. Truss Bridges

zWarren Truss zPratt Truss zHowe Truss Build Your Bridge!

Ohio River Bridge Project