Reinforced Concrete I - Chapter 1
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Reinforced Concrete I - Chapter 1

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Questions and Answers

What characteristic of concrete is specifically enhanced by the addition of steel reinforcement?

  • Tensile strength (correct)
  • Durability
  • Workability
  • Compressive strength

    • Which individual is credited with obtaining the patent for Portland cement?

  • William E. Ward
  • Joseph Lambot
  • Francois Le Brun
  • Joseph Aspdin (correct)

    • What was the primary use of the early versions of Portland cement?

  • Stuccos (correct)
  • Structural beams
  • Reinforced concrete slabs
  • Concrete houses

    • Which year saw the first reinforced concrete construction in the United States?

    <p>1875</p> Signup and view all the answers

    Which of the following historical figures is associated with constructing a concrete boat?

    <p>Joseph Lambot</p> Signup and view all the answers

    What issue did François Coignet highlight regarding concrete mixes?

    <p>Too much water reduces strength</p> Signup and view all the answers

    What were iron wire mesh constructions primarily used for according to Joseph Monier's patents?

    <p>Water basins and tubs</p> Signup and view all the answers

    What was a significant contribution of François Coignet to reinforced concrete?

    <p>Written documentation of construction methods</p> Signup and view all the answers

    What is a characteristic of Type II Portland Cement?

    <p>It has a lower heat of hydration than Type I.</p> Signup and view all the answers

    Which admixture is specifically used to slow down the setting process of concrete?

    <p>Retarding admixture</p> Signup and view all the answers

    What benefit does an air-entraining admixture provide to concrete?

    <p>Increases resistance to freezing and thawing.</p> Signup and view all the answers

    Which type of Portland Cement is best suited for very large concrete structures due to its low heat generation?

    <p>Type IV</p> Signup and view all the answers

    What is the primary purpose of using superplasticizers in concrete mixes?

    <p>To improve workability while reducing water content.</p> Signup and view all the answers

    Which type of cement is known for its high early strength gain?

    <p>Type III</p> Signup and view all the answers

    What issue can arise from the variability in concrete properties?

    <p>Reduced compressive strength.</p> Signup and view all the answers

    What aspect does not contribute to the cost of shoring in concrete construction?

    <p>Infrequency of concrete mixing.</p> Signup and view all the answers

    What is the typical range of compressive strength for most concretes used?

    <p>21MPa to 50MPa</p> Signup and view all the answers

    What is considered high-strength concrete?

    <p>Concrete with a compressive strength exceeding 70MPa</p> Signup and view all the answers

    Which of the following factors does NOT influence the modulus of elasticity of concrete?

    <p>Ambient temperature during mixing</p> Signup and view all the answers

    What is the primary testing method for determining the compressive strength of concrete?

    <p>Compression test on 150 mm cylinders aged for 28 days</p> Signup and view all the answers

    What is the trend observed between the strength of 150mm by 300mm cylinders and 150mm cubes?

    <p>Cylinders have roughly 80% of the strength values of cubes</p> Signup and view all the answers

    Which term is used for concretes with strengths exceeding 140MPa?

    <p>Super-high-strength concretes</p> Signup and view all the answers

    When measuring the modulus of elasticity, what does the 'initial modulus' represent?

    <p>The slope of the stress-strain diagram at the curve's origin</p> Signup and view all the answers

    Which of the following is a characteristic of high-performance concretes?

    <p>Low permeability and increased durability</p> Signup and view all the answers

    Which steel grade corresponds to a yield strength of 520MPa?

    <p>Grade 75</p> Signup and view all the answers

    What is the primary concern when reinforced concrete is exposed to corrosive environments?

    <p>Reduced bonding between steel and concrete</p> Signup and view all the answers

    What role does the modulus of elasticity play in the compatibility of concrete and steel?

    <p>It ensures consistent thermal expansion and contraction.</p> Signup and view all the answers

    What type of loads are characterized as consistent in magnitude and fixed in position?

    <p>Dead loads</p> Signup and view all the answers

    Which bar size does NOT exist in SI units according to the provided data?

    <p>28 mm</p> Signup and view all the answers

    What is a consequence of reinforcement corrosion in concrete structures?

    <p>Formation of more space-occupying oxides</p> Signup and view all the answers

    Which of the following notations corresponds to 3500 psi concrete strength?

    <p>24 MPa</p> Signup and view all the answers

    In reinforced concrete, what is a major benefit of using steel with a high modulus of elasticity?

    <p>It ensures uniform expansion under temperature changes.</p> Signup and view all the answers

    What is the primary purpose of load factors in structural design?

    <p>To increase the estimated loads applied to structures</p> Signup and view all the answers

    Which organization is responsible for revising the ACI Code?

    <p>American Concrete Institute</p> Signup and view all the answers

    In structural design, which type of load is more likely to have a higher load factor?

    <p>Seismic load</p> Signup and view all the answers

    What does section 5.3 of the ACI Code address?

    <p>Reinforced concrete member design strength</p> Signup and view all the answers

    Which of the following is NOT one of the primary loads described in the ACI equations?

    <p>Temperature load</p> Signup and view all the answers

    How do load factors reflect on the potential consequences of failure?

    <p>They remain constant regardless of the structure type</p> Signup and view all the answers

    What influence does ACI Code 318 have beyond the United States?

    <p>It serves as a global influence on concrete codes</p> Signup and view all the answers

    Which of the following is a source of reinforced concrete specifications?

    <p>American Railway Engineering Association</p> Signup and view all the answers

    What does the secant modulus represent on the stress-strain curve?

    <p>The slope from the origin to a point between 25% and 50% of the ultimate compressive strength</p> Signup and view all the answers

    How is the modulus of elasticity of concrete calculated according to the ACI Code?

    <p>$E_c = w^{1.5}(0.043) ext{ } ext{ } ext{sqrt}(f_c)$</p> Signup and view all the answers

    What is Poisson's ratio in concrete?

    <p>The ratio of the lateral expansion to longitudinal shortening</p> Signup and view all the answers

    What factor greatly influences the rate of shrinkage in concrete?

    <p>The surface area of the member relative to its volume</p> Signup and view all the answers

    Approximately what percentage of concrete shrinkage occurs within the first year?

    <p>90%</p> Signup and view all the answers

    Which method can help minimize shrinkage in concrete?

    <p>Minimize the amount of mixing water</p> Signup and view all the answers

    Which of the following correctly indicates the range of Poisson's ratio for concrete?

    <p>0.11 to 0.21</p> Signup and view all the answers

    What is the simplified formula for calculating the modulus of elasticity of normal-weight concrete?

    <p>$E_c = 4700 ext{ } ext{sqrt}(f_c)$</p> Signup and view all the answers

    Study Notes

    Reinforced Concrete I - Chapter 1

    • Introduction and Overview: Concrete is a mixture of sand, gravel, crushed rock, or aggregates held together with cement and water. Sometimes admixtures are added to adjust its properties.
    • High compressive strength: Concrete has high compressive strength but low tensile strength.
    • Reinforced Concrete: Reinforced concrete combines concrete with steel reinforcement to provide the tensile strength lacking in plain concrete. Steel resists compression forces, too.
    • Historical Background: Joseph Aspdin created Portland cement in 1824, a cement similar to Portland stone. Early work on concrete structures was done by the Frenchmen Francois Le Brun, Joseph Lambot, and Joseph Monier.
    • Early Reinforced Concrete: Monier is credited with inventing reinforced concrete. He patented reinforced concrete basin and tub construction, as well as reinforced railroad ties.
    • Advantages: Reinforced concrete has high compressive strength and great fire and water resistance. It's a versatile material, easily shaped into various forms. It also uses readily available local materials.
    • Disadvantages: Concrete has low tensile strength, requiring reinforcing. Formwork for concrete projects can be expensive. Concrete placement, proportioning, and curing aren't always controlled. Concrete also shrinks and creeps. These factors need to be considered for good design.

    Reinforced Concrete I - Chapter 1

    • Types of Portland Cement: Normal Portland Cement (NPC) is the common, all-purpose cement. Type II cement has a lower heat of hydration and resists sulfate attack. Type III cement has high early strength, useful for precast members and repairs. Type IV cement produces concrete with slow heat generation, suitable for large structures. Type V cement resists sulfate attack.
    • Admixtures: Materials added to concrete to improve performance include air-entraining admixtures (to increase frost resistance), accelerating admixtures (to hasten early strength development), and retarding admixtures (to slow setting).
    • Water-Cement Ratio: The amount of water used relative to cement is critical and impacts the strength of the concrete. Less water results in stronger concrete.
    • Superplasticizers: Admixtures that reduce the water content in concrete without compromising its workability. These admixtures allow for increased strength along with less cement use.

    Reinforced Concrete I - Chapter 1 - Properties of Concrete

    • Compressive Strength (fc): Measured by testing 28-day-old cylinders. Standard test specimens are cubes (150mm side) or cylinders (150mm diameter by 300mm). Testing provides relatively accurate compressive strength.
    • Stress-Strain Curves: Graphs of stress versus strain provide critical insights into concrete behavior. The curves are roughly linear for a portion of the load but become non-linear as the load increases to nearly the ultimate strength of the concrete.
    • High-Strength Concretes: Concretes with compressive strengths exceeding 70MPa. These high-performance concretes possess high strength and low permeability aiding in durability.
    • Modulus of Elasticity (Ec): Measures the stiffness of a material. A few ways to quantify concrete modulus of elasticity are initial modulus, tangent modulus, and secant modulus.
    • Poisson's Ratio: Measures how much a material expands laterally when compressed.
    • Shrinkage: Concrete shrinks as water evaporates from it. Curing and using appropriate aggregates can help mitigate shrinkage.

    Reinforced Concrete I - Chapter 1 - Shrinkage

    • Mechanism of Shrinkage: As concrete dries, the water evaporates, causing the concrete to shrink. Initial shrinkage occurs quickly but more slowly as drying progresses (about 90% of contraction occurring within the first year).
    • Effect of Shrinkage: Shrinkage induces cracks which can reduce the shear strength/bond between steel and the concrete, hindering the structural performance and appearance.
    • Minimizing Shrinkage: Strategies for reducing shrinkage include minimizing the amount of mixing water, curing the concrete properly, controlling placement sections at construction joints, using shrinkage reinforcement and specifying appropriate aggregates.

    Reinforced Concrete I - Chapter 1 - Fatigue

    • Fatigue Failures: For structures under repeated loading cycles, fatigue effects are relevant. Failure can result from a large number of loading cycles at a low stress.
    • Factors Influencing Fatigue: The fatigue strength of concrete is approximately 50 – 70% of its static strength, and is relatively unaffected by temperature and moisture.

    Reinforced Concrete I - Chapter 1 - Creep

    • Creep: Creep is the time-dependent deformation of concrete under sustained load. A prolonged period of sustained stress will continue to cause material deformation.
    • Relationship to other Factors: Creep is dependent on factors such as concrete strength and temperature.

    Reinforced Concrete I - Chapter 1 - Tensile Strength

    • Low Tensile Strength: Concrete's tensile strength is typically lower than its compressive strength, which is why reinforcing steel is utilized in reinforced concrete.
    • Testing Methods: Two methods to measure tensile strength of concrete indirectly, including modulus of rupture tests and split-cylinder tests, are used in construction. The modulus of rupture is the flexural tensile strength value for rectangular beams while the split-cylinder tensile strength is measured by loading a cylinder on its side inside a machine resulting in a tensile crack.

    Reinforced Concrete I - Chapter 1 - Reinforcing Steel

    • Reinforcing Steel Types: Reinforcing is often in the form of bars (plain or deformed), wires, or strands. Deformed reinforcing is more suitable in most applications as it increases the bond adhesion between concrete and steel.
    • Grades of Reinforcing Steel: Typical reinforcing steel grades are 280, 350 420, 520 and 690MPa. Other important quantities to be considered include tensile strength, yield strength, and bar sizes.
    • Yield Strength (fy): Indicates the stress at which the steel begins to deform plastically. Important to be considered when using reinforced concrete structures and construction.
    • Modulus of Elasticity (Es): A measure of the steel's stiffness. A typical value is 200GPa.

    Reinforced Concrete I - Chapter 1 - Corrosive Environments

    • Corrosion of Reinforcing Steel: Concrete exposed to deicing salts, seawater, or similar corrosive environments can cause reinforcement corrosion reducing the service life of the structure.
    • Consequences of Corrosion: Corrosion products increase the volume of materials, causing concrete cracking and spalling, and reducing the bond adhesion between the steel and concrete.
    • Compatibility of Concrete and Steel: Concrete and steel work well together with similar thermal expansion coefficients.

    Reinforced Concrete I - Chapter 1 - Introduction to Loads

    • Loads: Understanding the loads acting on a structure is crucial for proper design.
    • Dead Loads: Permanently attached components like walls, floors, and ceilings.
    • Live Loads: Occupancy loads, equipment, materials, and other transient loads.
    • Environmental Loads: Caused by the surrounding environment such as wind, rain, snow, and earthquakes.
    • Load Combinations: Analyzing the most likely combinations of loads is necessary during structural design, and should account for any potential load cases.

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    Description

    This quiz covers the introduction and overview of reinforced concrete, discussing its composition, strength properties, and historical development. Key figures in the advancement of concrete technology, such as Joseph Aspdin and Joseph Monier, are highlighted. Learn about the advantages and applications of reinforced concrete.

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