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The Bridge

Why a New Bridge?
Earthquakes and Bridges
East Span Design Basics
Fast FAQs
More on Design
Seismic Safety
Site Challenges
The Bridge and the Environment
Bridging by Numbers
Bridgespeak Glossary


The Language of Engineering and Bridge-Building
Anchor keys Concrete shapes precast into the edges of the Skyway sections and used to aid alignment during the roadway assembly.
Battered Driven at an angle to provide more stability.
Beam A horizontal structure member that supports vertical loads by resisting bending.
Bedrock A solid layer of rock.
Bubble curtain A stream of bubbles, created by pumped air, that encircles piles under water during the work of driving them into the bay mud. The curtain decreases the effects of sound waves on fish.
Cable A large-diameter steel rope made of many smaller steel strands. Suspenders, also called hangers, are attached along its length to support the deck.
Caisson A cylindrical concrete foundation that penetrates through unsuitable soil to rest on good soil or bedrock. Also, a watertight, dry chamber that permits excavation and other work to be performed underwater.
Cantilever A structural member that projects beyond a supporting column or wall and is counterbalanced or supported only at one end, like a shelf bracket or diving board. The old East Span is a cantilever bridge.
Carpenter A worker who builds or repairs wooden structures or their structural parts. On the East Span project, carpenters build frames for concrete work and other structures.
Catenary The curve formed by a cable hanging freely between two supports. The curved cables of a suspension bridge are also called catenaries.
Cellular concrete Concrete containing tiny air pockets. Also known as aerated concrete. Typically a mixture of cement, water and preformed foam. Designs utilizing fly ash, sand and other materials may be included for specific densities and strengths.
Cement mason A worker skilled in the craft of cement work. Includes concrete finishing on highways, sidewalks, curbs and gutters, as well as operating concrete saws and scoring machines.
Civil engineer An engineer who plans, designs and supervises construction of public structures.
Clamshell bucket A large scoop with hinged jaws used to dredge waterways.
Cofferdam A steel or concrete box erected in the water and then pumped dry to provide a work area.
Compressed air chamber The space at the bottom of a caisson into which air is injected to remove water so that excavation or other work can take place.
Compression Stress characterized by pressing together.
Concrete An artificial, stonelike building material made by combining cement with aggregate and water.
Concrete box girder A large, hollow concrete beam with a square or rectangular cross-section.
Contractor A company that contracts to perform work, build structures or provide supplies. A general contractor has responsibility for an entire project. A subcontractor is hired by the contractor to perform a specific portion of a project or supply materials.
Creep Shortening of concrete stressed under heavy loads over time.
Critical-flutter-velocity The wind speed at which a structure's movement by wind generates its own self-feeding movement.
Dead load The weight of a structure itself, independent of loads caused traffic or the environment.
Deck The top, traffic-carrying surface of a bridge.
Deflection The distance a beam bends perpendicularly due to load and span.
Diaphragm In the East Span project, a concrete wall separating chambers beneath the Skyway deck.
Elastomeric Pertaining to any of various polymers having the elastic properties of rubber.
Electrical engineer A specialist in electrical devices and systems, and with the use and nature of electricity.
Engineer Someone who applies a knowledge of math and natural science to practical ends, such as the design, construction and operation of structures.
Expansion joint A meeting between two parts of a structure that is designed to accommodate movement due to heat, moisture and ground motions while protecting the structure from damage.
Falsework A temporary structure used to support construction.
Fill Sand, gravel, rock and other material used to fill an excavated area or to build up an area.
Footing The enlarged lower portion of a substructure or foundation resting directly on the soil, bedrock or piles, usually below grade.
Footing Box A large steel box that houses support piles driven deep into the bay. After the piles are driven, each box is filled with 1,350 cubic yards of concrete. Each of the Skyway's 28 footings has a foundation box.
Foreman A field supervisor in charge of a group of workers.
Gantry crane A large crane that travels on rails.
Geotechnical engineer An expert who evaluates and stabilizes foundations for buildings, roads and other structures. Geotechnical engineering deals with geology, soil and rock mechanics, foundation engineering, ground improvement, land reclamation, deep excavation, underground construction and related work.
Geometry control The task of monitoring and adapting to changes in structural positions and relations caused by shrinkage and expansion.
Girder A horizontal structure member that supports vertical loads. A girder is larger than a beam and can be made of multiple plates of steel or other material.
Hinge beam system A set of steel pipes inset into stainless steel sleeves and set at bridge deck joints to absorb earthquake shock and bridge movement.
Iron worker Someone trained in the erection and fabrication of steel. On the East Span projects, iron workers will be engaged primarily in the erection of the Suspension Section. In the Bay Area, their union is the Iron Workers Union Local 378.
Laborer A worker trained in several areas of construction work, including the handling of hazardous materials . Laborers help build highways, bridges, tunnels, factories, dams, schools, churches and other structures. In the Bay Area, their union is the Northern California District Council of Laborers.
Liquefaction The state of being liquefied. Commonly refers to the destabilization of ground from earthquake shaking.
Live load The dynamic weight, such as traffic, carried by a structure.
Long-line casting A method of match casting in which several concrete components are precast at once in succession.
Match-cast Cast in matching sets. For example, the roadway sections for the Skyway will be precast in Stockton in matching sets to assure smooth joints.
Maximum credible earthquake The biggest earthquake likely to occur in a particular area over a particular period of time.
Midden A trash heap created by prolonged human occupation. The Yerba Buena Island construction site contains a Native American midden that has been excavated to protect any artifacts.
Operating engineer A worker trained in the operation of heavy equipment, such as bulldozers, graders and cranes. Operating engineers also perform equipment repair and maintenance, surveying, soil testing, inspecting and dredging.
Pier A vertical bridge support.
Pier table A section of road deck cast in place on a pier.
Pile A long column driven deep into the earth as part of a foundation or substructure.
Pile cap The top portion of the pile assembly where it connects to the pier.
Piledriver A worker trained to drive piles that support bridge foundations. A piledriver is also called a pilebutt.
Pile driving template A large steel structure similar to an oil rig used to guide the pile driving for the new East Span.
Post-tensioning A type of prestressing in which reinforcing tendons are fed through tubes that are covered by the concrete poured into a form. Once the concrete cures and the forms are removed, the tendon is clamped on one end and jacked tighter on the other until the required tension is achieved. This produces a reinforced concrete beam with a positive camber that is able to withstand greater loads without bending.
Precast concrete Concrete cast and cured offsite rather than in its final position on a structure.
Prestressing Methods of increasing the load-bearing capacity of concrete by applying increased tension on steel tendons or bars within a beam.
Reinforced concrete Concrete that has been reinforced with embedded steel rods or mesh.
Reinforcing steel Lengths of solid steel bar placed within concrete for support. Also called rebar. One variety is coated with epoxy to protect the bar from salty water and air.
Resident engineer A project's supervising engineer, usually working for a project owner, such as Caltrans.
Roller screed A rolling guide that ensures the even application and level finish of concrete.
Shear Stress placed transversely on a member in opposite directions.
Shear keys Concrete shapes precast in the Skyway roadway sections to aid in separation during the precasting process.
Short-line casting A method of match-casting in which one or two concrete components are precast at a time.
Shrinkage The shortening of concrete due to water loss.
Sled In the East Span project, a giant moveable structure anchored atop a pier and used to winch deck sections into place.
Soffit The underside of a structural component, such as a beam, arch, staircase or cornice.
Soffit form On the East Span job, a giant form for casting the bottom of the roadway sections.
Span The horizontal space between two supports of a structure. Also refers to the structure itself.
Spreader beam A large load-bearing pipe or beam that spreads the lifting cables of a crane or hoist, allowing a wider connection to the object being lifted.
Straddle carrier crane A giant, wheeled crane capable of lifting precast roadway sections weighing nearly 800 tons.
Strain The deformation of an object caused by a force acting upon it. Compressive strain is the shortening of an object in compression. Tensile strain is the elongation of an object in tension. Shearing strain is a lateral deformation caused by a force that moves part of an object more than another.
Stress The resistance of an object to external force. Compressive, tensile and shearing stress develop as an object resists being compressed, stretched or twisted.
Structural engineer An expert in the behavior and design of structures. Structural engineering concerns itself with structural analysis and design of concrete and steel structures, structural dynamics and mechanics, concrete technology, computational mechanics, structural safety and other related work.
Structural steel Steel members, such as beams, girders and plates, used in the construction of a structure.
Substructure The portion of a bridge structure including abutments and piers that support the substructure.
Superstructure The portion of a bridge that carries the traffic load and passes that load onto the substructure.
Surcharge A temporary layer of fill placed on a job site to help compact soil.
Suspenders Cables of a suspension bridge that hang from the main cable to support the deck. Also called hangers.
Tension Stress characterized by pulling apart.
Tension rods Steel cables imbedded in East Span road sections for strength.
Thrust A force caused by one part of a structure pushing outward against another.
Torsion An action that twists a material.
Transportation engineering The discipline that concerns itself with traffic engineering, transportation system planning, highway materials and pavement design, construction and maintenance.
Trestle A horizontal beam or bar held up by two pair of divergent legs and used as a support.
Trestle pier A loading dock extending over water and supported by trestles.
Viaduct An elevated roadway. More precisely, a series of spans or arches used to carry a road or railroad over terrain or other roadways.
Vibratory hammer An electric, cable-operated machine that uses a vibrating motion rather a striking motion to drive piles.
Wings In the East Span project, the diagonal concrete panels between the overhanging road deck and the box core of the roadway section
Wire rope A rope made of steel strands. The breaking strength of wire ropes seldom exceeds 90 percent of the aggregate strength of all the wires.

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