Structures What things do I need to find out in order to predict if what I design will stand up to the use I intend to put it through?

Structures Key Terms: Force: A push or pull exerted by one object on another. Compression: The effect of a force which tends to shorten an object in the direction of the force.

Structures Key Terms: Compression cont.: A compressive force compresses or shortens the object it is acting on.

Structures Key Terms: Compression cont.: The stand is in compression

Structures Key Terms: Tension: A situation, in which force is applied to an object that stretches, expands or lengthens the object.

Structures Key Terms: Tension cont.: A tensile force expands or lengthens the object it is acting on.

Structures Key Terms: Tension cont.: The rope is in tension.

Structures Key Terms: Deflection: A measure of deformation of a structure due to applied loads. Stress: All objects can be deformed with the application of an external force. The external force is called stress.

Structures Key Terms: Strain: It is the degree of deformation. The elongation of a material under stress divided by the material’s length prior to stress.

Structures Key Terms: Equilibrium: A state of balance due to the equal action of opposing forces in a structure. Friction: A force that opposes the motion or intended motion of a body in contact with another body.

Newton’s 1 st Law of Motion Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

Newton’s 1 st Law of Motion

Newton’s 2 nd Law of Motion Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

Newton’s 2 nd Law of Motion

Newton’s 3 rd Law of Motion For every action there is an equal and opposite reaction.

Newton’s 3 rd Law of Motion

Bridges There are basically 4 different types of bridges: Arch Bridge Suspension Bridge Beam/Truss Bridge Cable-stayed Bridge

Bridge Types: Arch Bridge Arch bridges are not stable during construction until the two sides meet. Therefore, scaffolding, or "centering,” must be assembled below, or cables must be anchored to hold it up. The latter allows the traffic below to continue until the bridge is complete.

Bridge Types: Arch Bridge

Bridge Types: Suspension Bridge Suspension Bridges use steel cables to support weight. Steel wire is very strong and can support large tensile forces. A single 0.1” thick wire can support more than half a ton without breaking!

Bridge Types: Suspension Bridge

Bridge Types: Beam/Truss Bridge Beam Bridges consist of a horizontal beam supported at each end by piers. The weight of the bridge and traffic on it pushes straight down on the piers, so the beam itself must be strong. Beam bridges are categorized by the design, location and composition of the trusses used.

Bridge Types: Beam/Truss Bridge These are a few common types (notice the location of the roadway colored gray in each):

Bridge Types: Beam/Truss Bridge Pratt or Through Truss Howe Kingpost Truss

Bridge Types: Beam/Truss Bridge Warren Truss Deck Truss

Bridge Types: Beam/Truss Bridge

Bridge Types: Cable-Stayed Bridge Cable-stayed bridges differ from suspensions bridges in the way that the cables are connected to the towers. In cable-stayed bridges, the cables are attached to the towers, which bear the load alone.

Bridge Types: Cable-Stayed Bridge The cables of a suspension bridges ride freely across the towers, transmitting the load to the anchorages at either end. Cable-stayed bridges are distinguished by the number of spans, number of towers, girder type, number of cables and the arrangement of their cables.

Bridge Types: Cable-Stayed Bridge Typical towers include:

Bridge Types: Cable-Stayed Bridge Typical cable arrangements include: Mono Fan

Bridge Types: Cable-Stayed Bridge

Bridges: An engineer would choose the correct bridge based on how far it must span from one support to the next. Each bridge deals differently with tension and compression. If part of the bridge cannot stand the compression it will buckle. If part of the bridge cannot stand the tension it will snap.

Bridges: Engineers consider shapes under heavy loads when building large structures. Triangles are the only shapes that cannot be deformed without changing the length of one of its sides Arches are strong because the force resulting from a heavy load placed at the top spreads down the sides to the foundation.

Bridges Key Terms: Abutment: Is a part of a structure that bears the weight of an arch, it supports the end of a bridge or anchors the cables of a suspension bridge.

Bridge Key Terms: Abutment Cont.:

Bridges Key Terms: Key Stone: The central wedge-shaped stone of an arch that locks its parts together.

Bridges Key Term: Buckling: Failure caused by bending, giving way, or crumpling due to excessive force.