Form Active structure systems STRUCTURES REPORT DEEKSHA MALHOTRA PRATYUSH GUPTA SHUBHANGI PAHUJA SWARNIM JAIN
Form active structures are those structures in which load is taken by the form or the shape of the structure. They are non-rigid, flexible matter shaped in a certain way and secured at the ends, can support itself and span space. Only tensile and compressive stresses persists. These are mainly categorized into 4 types:# Cable Structure # Arch Structure # Tents Structures # Pneumatic Structures
Cable structure, Form of long-span structure that is subject to tension and uses suspension cables for support. Highly efficient, cable
structures include the suspension bridge, the cable-stayed roof, and the bicycle-wheel roof. A tensile structure is a construction of elements carrying only tension and no compression or bending. The term tensile should not be confused with tensegrity, which is a structural form with both tension and compression elements. Tensile structures are the most common type of thin-shell structures. Most tensile structures are supported by some form of compression or bending elements, such as masts (as in The O2, formerly theMillennium Dome), compression rings or beams. Membrane materials[edit] Common materials for doubly curved fabric structures are PTFEcoated fiberglass and PVC-coated polyester. These are woven materials with different strengths in different directions. The warp fibers (those fibers which are originally straight—equivalent to the starting fibers on a loom) can carry greater load than the weft or fill fibers, which are woven between the warp fibers. Other structures make use of ETFE film, either as single layer or in cushion form (which can be inflated, to provide good insulation properties or for aesthetic effect—as on the Allianz Arena in Munich). ETFE cushions can also be etched with patterns in order to let different levels of light through when inflated to different levels. They are most often supported by a structural frame as they cannot derive their strength from double curvature. Cables[edit] Cables can be of mild steel, high strength steel (drawn carbon steel), stainless steel, polyester or aramid fibres. Structural cables are made of a series of small strands twisted or bound together to form a much larger cable. Steel cables are either spiral strand, where circular rods are twisted together and "glued" using a polymer, or locked coil strand, where individual interlocking steel strands form the cable (often with a spiral strand core).
Spiral strand is slightly weaker than locked coil strand. Steel spiral strand cables have a Young's modulus, E of 150±10 kN/mm² (or 150±10 GPa) and come in sizes from 3 to 90 mm diameter.[citation needed] Spiral strand suffers from construction stretch, where the strands compact when the cable is loaded. This is normally removed by pre-stretching the cable and cycling the load up and down to 45% of the ultimate tensile load. Locked coil strand typically has a Young's Modulus of 160±10 kN/mm² and comes in sizes from 20 mm to 160 mm diameter. The properties of the individuals strands of different materials are shown in the table below, where UTS is ultimate tensile strength, or the breaking load.
Arch structures An arch is a curved structure that spans a space and may or may not support weight above it.[1] Arch may be synonymous with vault, but a vault may be distinguished as a continuous arch[2] forming a roof. Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture,[3] and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures. The most common true arch configurations are the fixed arch, the twohinged arch, and the three-hinged arch.[8] The fixed arch is most often used in reinforced concrete bridge and tunnel construction, where the spans are short. Because it is subject to additional internal stress caused by thermal expansion and contraction, this type of arch is considered to be statically indeterminate.[7] The two-hinged arch is most often used to bridge long spans.[7] This type of arch has pinned connections at the base. Unlike the fixed arch, the pinned base is able to rotate,[9] allowing the structure to move freely and compensate for the thermal expansion and contraction caused by changes in outdoor temperature. However, this can result in additional stresses, so the
two-hinged arch is also statically indeterminate, although not to the degree of the fixed arch.[7] The three-hinged arch is not only hinged at its base, like the two-hinged arch, but at the mid-span as well. The additional connection at the mid-span allows the three-hinged arch to move in two opposite directions and compensate for any expansion and contraction. This type of arch is thus not subject to additional stress caused by thermal change. The three-hinged arch is therefore said to be statically determinate.[8] It is most often used for medium-span structures, such as large building roofs.
Segmental arch Round arch or Semi-circular arch
Segmental arch or arch that is less than a semicircle
Pneumatic structure, Membrane structure that is stabilized by the pressure of compressed air. Air-supported structures are supported by internal air pressure. A network of cables stiffens the fabric, and the assembly is supported by a rigid ring at the edge. The air pressure within this bubble is increased slightly above normal atmospheric pressure and maintained by compressors or fans. Air locks are required at entrances to prevent loss of internal air pressure. Air-supported membranes were first devised by Walter Bird in the late 1940s and were soon put to use as covers for swimming pools, temporary warehouses, and exhibition buildings. Air-inflated structures are supported by pressurized air within inflated building elements that are shaped to carry loads in a traditional manner. Pneumatic structures are perhaps the most cost-effective type of building for very long spans.
Case Studies Airport Terminal Building, Dulles International Airport. Architects :Eero Saarinen Location: Chantilly, Virginia, United States
Architect: Eero Saarinen References: Eero Saarinen, Antonio Roman Project Year: 1962
Located 26 miles west of the central business district of Washington D.C. in Chantilly, Virginia, the Washington Dulles International Airport is named after John Foster Dulles, who was Secretary of State under President Eisenhower. It occupies 11,830 acres of land right on the border of Fairfax County and Loudoun County. Ranked the fifth largest hub for United Airlines, the Dulles Airport is one of the nation's busiest airports as it handles over 23 million passengers a day, flying to more than 125 destinations. Structural and Architectural Aspects The spacious terminal building of Washington DC's international airport is structurally exciting both outside and in. A huge concrete sheet is slung between two asymmetric rows of concrete hooks, creating an inviting and dynamic curve as you approach. Invisibly within the concrete, it is steel suspension-bridge cables between the hooks that support the weight of the concrete roof, which Saarinen described as 'like a huge, continuous hammock suspended between concrete trees.' The simplicity of the design allowed for elegant expansion of the building in the 1990s, by adding more concrete trees at each end of the row and suspending further hammocks between them.
The outward slope of the concrete hooks counterbalances the tension in the cables supporting the roof sheet; Saarinen, in his own words, 'exaggerated and dramatized' the slope to create the building's 'dynamic and soaring
The design of the roof, with concrete panels supported by catenary cables, stands out as an important technical feature of the building and allows for an uninterrupted interior space to streamline the flow of passengers from the unloading area up to the mobile lounges and onto the plane. The Heavy concrete support towers lean outwards against the tension of the cables to provide stability, their geometric configuration maximises their overturning moment,
The design of the roof, with concrete panels supported by catenary cables, stands out as an important technical feature of the building and allows for an uninterrupted interior space to streamline the flow of passengers from the unloading area up to the mobile lounges and onto the plane. The Heavy concrete support towers lean outwards against the tension of the cables to provide stability, their geometric configuration maximises their overturning moment,
Madison Square Architects Garden, New York :Charles Luckman Location: New York, United States,
Madison Square Garden, often abbreviated as MSG, known colloquially simply as The Garden or The World's Most Project Year: Famous Arena, has been the name of four 1968 arenas in New York City, United States. It is also the name of the entity which owns the arena and several of the professional Type : Theater sports franchises which play there. There have been four incarnations of the arena. The first two were located at the Northeast corner of Madison Square (Madison Ave. & 26th St.) from which the arena derived its name. Subsequently a new 17,000-seat Garden (opened December 15, 1925) was built at 50th Street and 8th Avenue, and the current Garden (opened February 14, 1968) is at 7th Avenue between 31st and 33rd Streets, situated on top of Pennsylvania Station.
Structural and Architectural Aspects
Madison Square Garden's, in New York City, roof structure uses a network of cables arranged in a bike wheel formation. The structure was completed in 1968. It has 48 radial cables spreading a diameter of 404ft. The outer ring is made of steel blocks in compression for the cables to attach to. The center ring is a steel cable ring which is under tension once the cables pull on it due to the load above. Madison Square Garden is one of the very few examples in which the cables were not pretensioned before installation. To keep the cables in tension the roof has heavy concrete blocks as roof panels and weights hanging from the cables.
Total weight of the 48 zinc-coated steel cables in the roof system is 163 tons. Each cable is 1¾ in diameter, the largest ever used in any roof structure, and composed of 271 steel wires: the rated ultimate strength of 822 tons sets a
new record for a building of this type. Two sockets hold each cable in place, those for the inner tension ring each weighing 659 lb. This column-free area – almost 3 acres – is believed to be the only one of its size in the world with two steel framed storeys above the cables
Marquette Plaza, Minneapolis Architects :Gunnar Birkerts Location: United States Project Year: 1973 Designed by Gunnar Birkerts, it was home to the Federal Reserve Bank of Minneapolis from 1973 to 1997 (hence, many people refer to it as "the old Federal Reserve building"). Designed much like a suspension bridge, most of the original floors are supported by two sets of catenary cables. Underground chambers were used for vault space, and an external elevator shaft was attached on the east face of the building to connect a ground-floor lobby with the rest of the building. There was originally a gap between the lobby and the rest of the above ground structure to emphasize the construction method.
