Prestressed Concrete Quiz
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What is the primary purpose of applying pre-stressing forces in concrete?

  • To increase the tensile strength of the concrete.
  • To counteract bending from structural loads. (correct)
  • To reduce the overall weight of the concrete structure.
  • To enhance the thermal resistance of concrete.

    • Which material is particularly emphasized for use in prestressed concrete due to its high tensile strength?

  • Portland Slag Cement
  • High Strength Ordinary Portland Cement
  • Ordinary Portland Cement
  • High Tensile Steel (correct)

    • What is the minimum grade of concrete recommended for use in prestressed concrete?

  • M20 (correct)
  • M25
  • M15
  • M30

    • How does pre-stressing affect the tensile stress within a concrete section?

    <p>It balances the tensile stress to prevent it from exceeding the cracking stress.</p> Signup and view all the answers

    What type of cement is commonly used in prestressed concrete due to its rapid setting properties?

    <p>Rapid Hardening Portland Cement</p> Signup and view all the answers

    What are pre-stressing tendons primarily made of in prestressed concrete?

    <p>High tensile steel cables or rods</p> Signup and view all the answers

    What two types of forces can be visualized in a prestressed concrete member?

    <p>Internal pre-stressing force and external force</p> Signup and view all the answers

    What key property of concrete allows it to be treated as an elastic material in prestressed concrete structures?

    <p>Reduction of tensile stress below the cracking stress</p> Signup and view all the answers

    What is the length of the Runyang Bridge?

    <p>1,490 meters</p> Signup and view all the answers

    Which bridge opened in 2016?

    <p>Osman Gazi Bridge</p> Signup and view all the answers

    Which of the following bridges crosses the Gwangyang Bay?

    <p>Yi Sun-sin Bridge</p> Signup and view all the answers

    What is the name of the bridge that has the longest span length of 2,023 meters?

    <p>1915 Çanakkale Bridge</p> Signup and view all the answers

    What is the classification of the cable structure used in bridges such as the Osman Gazi Bridge?

    <p>Cable-stayed Type Structures</p> Signup and view all the answers

    Which water body does the Great Belt Bridge cross?

    <p>Great Belt</p> Signup and view all the answers

    How tall are the towers of the 1915 Çanakkale Bridge?

    <p>318 meters</p> Signup and view all the answers

    What year did the Akashi Kaikyō Bridge open?

    <p>1998</p> Signup and view all the answers

    What is the primary benefit of using composite columns in construction?

    <p>They combine the beneficial properties of steel and concrete.</p> Signup and view all the answers

    Which characteristic differentiates deep decking from shallow decking in composite slabs?

    <p>The depth exceeding 200 mm.</p> Signup and view all the answers

    What is an example of a composite structure used in civil engineering?

    <p>Steel-concrete composite beams.</p> Signup and view all the answers

    What is the function of profiled steel decking in composite slabs?

    <p>To act as formwork during construction and as reinforcement.</p> Signup and view all the answers

    What improves the strength and strain capacity of concrete in circular concrete-filled tubes (CFTs)?

    <p>The triaxial compression created by the steel confinement.</p> Signup and view all the answers

    What is a key characteristic of composite beams in construction?

    <p>They are designed to act as a unit despite being made of different materials.</p> Signup and view all the answers

    Why are composite columns considered structurally efficient?

    <p>Their interactive behavior enhances structural performance.</p> Signup and view all the answers

    Which type of composite beam involves a combination of wood and concrete?

    <p>Wood-concrete composite beam.</p> Signup and view all the answers

    What is the primary difference between pre-tensioning and post-tensioning methods of prestressed concrete?

    <p>Pre-tensioning involves tensioning before concrete hardens, while post-tensioning occurs after.</p> Signup and view all the answers

    In the post-tensioning process, what role do ducts play?

    <p>They act as chambers for the tendons to be placed during casting.</p> Signup and view all the answers

    During pre-tensioning, what occurs after the concrete has cured?

    <p>The stressing force is released and the tendons anchor.</p> Signup and view all the answers

    In the post-tensioning method, what percentage of the tendons' ultimate strength are they typically tensioned to?

    <p>70%</p> Signup and view all the answers

    What happens to the tendons after they are tensioned in the post-tensioning process?

    <p>They are cut away and tensioning force is released.</p> Signup and view all the answers

    What is the first step in the post-tensioning process of prestressed concrete?

    <p>Steel cables are positioned within the ducts.</p> Signup and view all the answers

    How does the bond between tendons and concrete affect the prestressing process during pre-tensioning?

    <p>It enables the concrete to induce a compressive force.</p> Signup and view all the answers

    What is a characteristic of post-tensioning compared to pre-tensioning regarding its location?

    <p>Post-tensioning is typically performed on-site at the project location.</p> Signup and view all the answers

    What common practice in construction has influenced the design of membrane structures?

    <p>Tent making</p> Signup and view all the answers

    Which technology has become predominant in the engineering design of membrane structures?

    <p>Computer software</p> Signup and view all the answers

    What defines the construction and fabrication industry related to membrane structures?

    <p>It has undergone significant development.</p> Signup and view all the answers

    What is a key feature of the materials used in membrane structures?

    <p>They are designed for specific purposes.</p> Signup and view all the answers

    What historical context influenced the use of fabric in architecture?

    <p>Nomadic tribes utilizing fabric for shelter.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of contemporary membrane structures?

    <p>Low cost materials</p> Signup and view all the answers

    How have design skills for membrane structures evolved over time?

    <p>They have been refined through challenging work experiences.</p> Signup and view all the answers

    What is a significant characteristic of the surface of membrane structures?

    <p>It is held under a continuously applied prestress force.</p> Signup and view all the answers

    What is the main span length of the Russky Bridge?

    <p>1104 m</p> Signup and view all the answers

    Which characteristic distinguishes cable-stayed structures from suspension-type structures?

    <p>A cable-stayed structure has lower deflection.</p> Signup and view all the answers

    What type of cable construction should be used when the radius of curvature is not a major requirement?

    <p>Strand</p> Signup and view all the answers

    What is the total length of the Russky Bridge?

    <p>3100 m</p> Signup and view all the answers

    Which statement is true regarding suspension-type cable structures?

    <p>They are limited to two towers.</p> Signup and view all the answers

    The Russky Bridge crosses which body of water?

    <p>Eastern Bosphorus strait</p> Signup and view all the answers

    What does a rope consist of in the context of cable materials?

    <p>A plurality of strands</p> Signup and view all the answers

    How does the construction time of cable-stayed structures compare to suspension-type structures?

    <p>It is shorter for cable-stayed structures.</p> Signup and view all the answers

    Study Notes

    Construction Systems

    • Alternative building construction systems are covered in this presentation.

    Prestressed Concrete

    • Definition (1): Prestress is a method of applying pre-compression to control stresses resulting from external loads below the neutral axis. This method aims to exceed the permissible limits of plain concrete, overcoming its weakness in tension.
    • Definition (2): Prestressed concrete builds in compressive stresses during construction to counter the tensile stresses during use. A combination of steel and concrete leverages the strength of each material.
    • Definition (3): Applying forces to bend and compress a concrete element to counteract bending from structural load. The force involves tensioning the steel component (high tensile strands, wires, or bars).
    • Principles: Pre-stressing uses tendons (high tensile steel cable or rods) to provide clamping load and compressive stress, balancing the tensile stress caused by bending loads. This reduces tensile stress to below the cracking stress, preventing cracks. Concrete can then be treated as an elastic material. Concrete has two compressive forces: internal pre-stressing force and external force.
    • Materials:
      • Cement: Ordinary Portland cement, Portland slag cement, rapid hardening Portland cement, and high-strength ordinary Portland cement.
      • Concrete: High-strength concrete with high compressive and comparatively high tensile strength than ordinary concrete. Composed of gravel, crushed stones, sand, and cement. Minimum grade of M20 is used.
      • Steel: High tensile steel, tendons and strands. Tensile strength of around 2000MPa is required, adhering to IS: 1343-1980 prestressed concrete design.
    • Forms of Pre-stressing Steel: Includes wire, strands (two, three or seven wires wound together), tendons (group of strands or wires wound together), and bars (single steel bar, larger than a wire).
    • Pre-stressing Methods: Mechanical, hydraulic, electrical, and chemical devices are used.
    • Mechanical Devices: Weights (with or without lever transmission), geared transmission, pulley blocks, screw jacks, and wire-winding machines. Employed for mass-produced components.
    • Hydraulic Devices: Simplest means of producing large prestressing force, used extensively as tensioning devices.
    • Electrical Devices: Involves electrically heating wires before placement. Often referred to as thermo-prestressing.
    • Chemical Devices: Use expanding cements, controlling the degree of expansion by varying curing conditions.
    • Pre-tensioning: Tendons are tensioned before concrete placement; concrete is introduced by bond between steel and concrete.
    • Post-tensioning: Tendons are tensioned against hardened concrete; a duct is positioned in the concrete structure.

    Reinforced Concrete

    • Overview: Concrete is strong in compression but weak in tension. Steel is strong in tension. Reinforced concrete uses concrete to resist compression and steel to resist tension. Tensile strength of concrete is neglected. Reinforced concrete beams allow cracking under service load. In ordinary reinforced concrete, the beam supports a load by developing compressive stresses at the top, but since the concrete cannot resist tension at the bottom, it cracks. Reinforcing steel bars are placed within this tension zone to resist tension and control cracking.

    Composite Construction

    • Definition (1): Two or more different materials bonded securely to act as one structural unit. This interaction is known as composite action.
    • Benefits: Speed of construction, performance, value.
    • Materials: Reinforced concrete, masonry, composite wood (plywood, laminated veneer lumber, LVL, Parallel strand lumber (PSL), laminated strand lumber (LSL), oriented strand board (OSB), particleboard, and fiberboard), reinforced plastics (FRP/fiber-reinforced polymer), ceramic matrix composites, metal matrix composites, hybrid composites.
    • Composite Beams: Combination of concrete and steel, similar to a T-beam. Shear connectors transfer forces between the materials.
    • Composite Columns: Combination of structural steel and concrete.
    • Composite Slabs: Reinforced concrete cast on top of profiled steel decking, which serves as formwork during construction and external reinforcement once complete.
    • Composite Connections: Includes shear connectors (essential for composite construction) to provide longitudinal shear resistance. Examples include shear studs, shear bolt/pin, oscillating perfobond strip, continuous perfobond strip, welded T-section/T-rib connectors, and waveform strips.

    Cable Structure

    • Definition (1): A flexible structural component offering zero resistance to shear and bending, subjected to tensile forces.
    • Structural Cables: Used in engineering structures as support and to transmit load between points, forming the main load-carrying element.
    • Loading Mechanism: High tensile strength of steel combined with the efficiency of simple tension makes steel cable ideal for spanning large distances.
    • Cable Sag: The triangular shape of a cable under load is characterized by sag (vertical distance between supports and lowest point). Without sag, horizontal forces cannot balance vertical load. Sagging cable's pull on supports is divided into a downward force equal to half the load and a horizontal inward pull/thrust. Cable deformation under load takes the funicular shape.
    • Geometric Funicular Forms: As loads increase, funicular polygon approaches a geometrical curve—the parabola. Evenly distributed loads create a catenary shape.
    • Classification of Cable Structures: Suspension, cable-stayed, radial, harp, fan, star-shaped, and classification by pylon shape (A, H, Y).
    • Suspension-type Cable: Composed of stiffening girders/trusses, main suspension cables, main towers, and anchorages. The main load-carrying member is the main cable made of high-strength steel. It can only carry straight bridges across a water body, such as the Akashi Kaikyō Bridge. The longest suspension bridge is the 1915 Çanakkale Bridge which is 2023 meters in length.
    • Cable-stayed Type: Supported by inclined stayed-cables from towers. It has fewer components than suspension bridges and can handle curved bridges.
    • Cable Materials: Constructed from structural ropes, strands (assemblies of wires around a central wire in layered forms), or parallel wire strands.
    • Types of Cable Materials: Parallel bars, Parallel wires, Parallel strands, Helical/Locked coil strands, Ropes, Standards, Strand Compacted, and Swage Compacted.
    • Cable Construction (Cable-stayed type) stages: Erection of piers and support spans, central tower erection, temporary stay cable installation, extension of central span and temporary cable removal, and completion of central span and removal of temporary cables.

    Membrane Structure

    • Definition (1): A flexible surface (skin, fabric) that transmits only tensile stress, relying on double curvature for stability under load.
    • History: Developed from tent-making craftsmanship, using modern materials and techniques. Pioneered by Fred Severud, Frei Otto, and Walter Bird.
    • Design: Employing computers for design and fabrication, employing skilled and experienced fabrication teams.
    • Structural Materials: Coated or woven synthetic fabrics, such as PTFE fiberglass, ETFE film, PVC, and ePTFE.
    • Properties of Membrane Materials: High inherent strength, resistance to environmental pollution, service life, fire safety, thermal properties, acoustics, lighting, color fastness, and special shading materials.
    • Styles and Shapes: Conical, hypar (anticlastic), parallel arch (barrel vault), cable net structures. Examples: White Rhino II, National Aquatics Center of China, Shanghai Expo axis, Tokyo Dome, Millennium Dome.
    • Design Considerations: Shape determination, structural analysis, cutting patterns, and cost considerations.
    • Environmental Issues: Low environmental footprint, PVC is intrinsically recyclable, energy-efficient, and low consumer of non-renewable resources.
    • Special Construction Features: How membranes can span large distances, keep tension maintained, how roofs are designed to resist wind loads, avoid flat planar surfaces, and use pre-tensioned cables.

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