05 Flashcards
(111 cards)
Prestressed Concrete
A type of concrete construction in which the concrete is “prestressed” after it is poured, but before any additional load is placed on it. This results in thinner slabs and beams that have a smaller cross-sectional area than traditional concrete construction.
Deep Foundations
Foundations that penetrate deep into the Earth’s surface. Unlike shallow foundations, deep foundationseither use friction to transfer loads or they bear directly on the bedrock below. Piles and caissons are typicaldeep foundations. Piles are made of steel or timber and are driven into the ground using a pile driver.Caissons are constructed with reinforced concrete and are cast in place.
Purlin
Horizontal structural members that support roof/floor load and transfer them to perpendicular beams; typically shallower than traditional beams.
Dunnage
Nonpermanent structural platform for mechanical equipment used to distribute weight more evenly over an area, typically seen on a roof.
Rooftop Curb
Permanent built-up structure to support roof top units; typically seen on roofs and are flashed and sealed to prevent water intrusion.
Rebar
Reinforcing bar. Provides tensile strength to reinforced concrete. The bar’s number is the diameter of the bar in 1/8s of an inch. For example, a #5 bar is 5/8” inches in diameter.
Spread Footing
A type of shallow foundation where axial loads are distributed in a uniform manner under the footing. Allowable bearing pressure necessary to resist the load determines the size of the footing.
Wall Footing
Continuous strip of concrete below a foundation wall that spreads the load of the building over a larger area. These are used in shallow foundation systems and are among the most common types of footings.
Combined Footing
Foundation system used when columns are located in close proximity to one another or too close to a property line; a footing is poured for all of them together.
Mat Foundations
A continuous foundation system that is used when soils are weak. They cover the entire building footprint to distribute heavy loads, making it a very expensive system.
Pile Foundations
Foundation system that uses piles driven or drilled deep into the earth; typically used when soil is unsuitable for spread footings and the foundation needs to transmit loads through soil to a stronger bearing surface below.
Friction Pile
A type of pile foundation used in softer soil that uses friction to transfer loads across the full height of the pile. The piles do not reach down to harder surfaces below the surface and thus can be driven shallower. Bearing capacity is limited by the weaker of either the pile or soil strength.
Socketed Caissons
Type of foundation system used where deep foundations are required; holes are drilled deep into the earth and into rock or firm strata, and concrete is poured; bearing capacity is dictated by end-bearing and frictional forces.
End-Bearing Piles
Type of foundation system in which a pile reaches down far enough to a strong layer of soil or rock on which the end rests. Loads are thus transferred to the hard soil at this bearing point.
Belled Caisson
Type of foundation system in which holes are drilled into the earth and concrete is poured; for use when deep foundations are required. The ends of these elements are made wider and belled to distribute loads more evenly in the firm strata. This is used in areas where firm soil lies beneath soft or expansive upper soil.
Transfer Beam
A structural beam used to transfer the loads from a column resting on it to its supports. Transfer beams are typically deeper and are used when column grids cannot align between different levels.
Bundled Tube System
A lateral load-resisting system used in high-rise construction. In a bundled tubes system, thinner structural tubes act together to create a more efficient system. Similar to cantilevered tubes, bundled tubes are treated as a rigid connection perpendicular to the ground. The Willis Tower (formerly Sears Tower) in Chicago is an example of a bundled tube.
Cantilevered Tube
A lateral load resisting system used in high-rise construction. Cantilevered tubes place a rigid structural system on the outside of the building and structurally treat it as a fixed connection, perpendicular to the ground. This simplifies the calculations required to size internal members. The John Hancock Center in Chicago, IL is a great example of a cantilevered tube.
Composite Decking
A type of composite construction that combines concrete and steel construction. Composite decking uses a fluted metal deck as the formwork for a concrete floor. This combines the tensile strength of steel with the compressive strength of concrete. Commonly, shear studs are used to connect the composite deck to steel beams below.
Shear Stud
A steel element that is welded to the top of a steel beam and extends into the concrete portion of a composite deck. Shear studs help transfer stresses between the two elements and create a more efficient structural system.
Dr. Fazlur Khan
A pioneer in high-rise design, Dr. Khan was one of the lead structural engineers for Skidmore, Owings & Merrill in the 1960s and 1970s. He is best known his work with tube structural systems for tall buildings. His work on the Willis Tower (formerly Sears Tower) and the John Hancock Center in Chicago exemplify his theories.
Yield Strength of Steel (Fy)
A36 Steel - Fy = 36 ksi;
A992 Steel - Fy = 50 ksi.
Tensile Strength of Steel (Fu)
A36 Steel - Fu = 58 ksi;
A992 Steel - Fu = 65 ksi.
Modulus of Elasticity of Steel (E)
29,000 Kips/Square inch (ksi).
