Questions and Answers
Which material is the most fire resistant? (Select all that apply)
What are brittle materials?
A brittle material is one having hardness and rigidity but little tensile strength that breaks when subjected to tensile stress and without significant plastic deformation.
What are ductile materials?
A ductile material is one having the ability to elastically and then plastically deform under tensile stress.
Which material has the most modulus of elasticity, E?
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The thermal expansion coefficient of steel is relatively equal to the thermal expansion coefficient of concrete.
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What is the most common quality control test on hardened concrete?
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Which choice is important in the selection of nominal maximum aggregate size of concrete material in a reinforced concrete structure?
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What is the required air content for a concrete element with nominal maximum aggregate size of 2 in located in exposure class F3?
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Which type of cement is used for high early strength concrete?
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Type V cement is used for making high __________ resistant concrete.
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Higher water content in concrete leads to lower strength.
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Workable concrete with low water to cement ratio can be achieved by using __________.
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By using Type F fly ash in concrete, long-term strength will __________ and permeability __________.
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Air entrainment of concrete is not desired in any condition.
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How are expansion/contraction joints in concrete pavement created?
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What equation determines the modulus of elasticity for normal-weight concrete (in psi units), according to ACI 318?
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What equation represents the tensile strength of concrete (in psi units) with respect to compressive strength, according to ACI 318?
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What is the variable f'c represent in reinforced concrete design?
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What does f'ci represent in prestressed concrete design?
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What is the resistance factor ϕ for tension-controlled prestressed concrete sections in bridge structures, according to AASHTO?
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What is the resistance factor ϕ for tension-controlled reinforced concrete sections, according to ACI 318 and AASHTO?
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What is the approximate range of rupture for steel?
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Compressive strength of concrete is specified based only on structural strength requirements.
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The modulus of elasticity of normal weight concrete can be estimated using the specified compressive strength.
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The durability of concrete is influenced by its resistance to fluid penetration.
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The addition of which material can reduce the permeability of concrete and thus improve its durability?
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What should be the maximum W/C ratio of a concrete element exposed to freezing-and-thawing cycles and frequent exposure to water?
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For a concrete element in an environment with SO42- = 15,000 ppm, the use of type V cement suffices to mitigate the sulfate attack.
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For a reinforced concrete structure in exposure class C2, the minimum f'c should be __________.
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What is the most common technique used to improve the durability of concrete exposed to a freezing-and-thawing condition?
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A limit on which of the following is a grout durability requirement for bonded tendons according to ACI 318-14?
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What two methods are used to determine the yield strength of non-prestressed bars and wires?
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What is the permitted modulus of elasticity of non-prestressed bars and wires according to ACI 318-14?
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According to ACI 318-14, the modulus of elasticity of prestressed reinforcement is permitted to be 29,000 ksi.
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__________ should be accounted for in the calculation of the effective tensile stress in prestressed bars.
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Concrete floor finishes are permitted as part of the required cover for non-structural purposes.
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Ducts for grouted tendons should be maintained free of __________.
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The reference design modulus of elasticity of a timber member at 70°F should be __________ 90°F.
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The modulus of elasticity of steel will __________ at elevated temperatures.
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Suitable solvent should be used to remove the light oil coatings before welding in an HSS member.
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An HSS steel member partially filled with concrete should be sealed.
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In the design of clay masonry, the modulus of elasticity should be __________.
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The coefficient of thermal expansion for clay masonry is lower than that of concrete masonry.
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Fired clay masonry expands upon contact with water, but it returns to its original shape upon drying.
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Concrete masonry shrinks due to __________ and __________.
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Creep in concrete and clay masonry is caused by which of the following?
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Generally, class C fly ash is used to make high strength concrete.
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What specified concrete cover is required for a cast-in-place non-prestressed concrete member that is cast against and permanently in contact with the ground?
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What is the minimum concrete compressive strength for concrete used to construct special moment frames and special structural walls?
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What is the value of β1 for equivalent rectangular concrete stress distribution when concrete compressive strength is 5,000 psi?
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What must the net tensile strain of reinforcement steel within a reinforced concrete member be in order to be considered tension-controlled in flexure?
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What is the strength reduction factor (Φ) when the net tensile strain of Grade 60 deformed reinforcement within a reinforced concrete member, with transverse reinforcement other than spiral, is less than the strain at yield point?
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What is the governing limit state when determining the nominal flexural strength for a compact square HSS member?
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What value should the effective slenderness ratio not exceed for members designed based on compression?
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What is the minimum reinforcement ratio for continuous longitudinal reinforcing (ρsr) within an encased composite member?
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Study Notes
Fire Resistance of Materials
- Concrete is the most fire-resistant material compared to steel and wood.
- Steel requires protection in fire conditions, wood is less effective in fire safety than concrete.
Material Properties
- Brittle materials, like concrete, exhibit hardness and rigidity but lack tensile strength, leading to sudden failure under tensile stress.
- Ductile materials, such as steel, can deform plastically under tensile stress and have a capacity to stretch, indicating a higher toughness.
Modulus of Elasticity
- Steel has the highest modulus of elasticity (29,000 ksi), whereas light weight structural concrete (2,100 ksi) and wood (Douglas fir at 1,500 ksi) have lower values.
- The modulus of elasticity for normal-weight concrete is given by the formula E = 57,000f'c.
Thermal Expansion and Strength Tests
- The thermal expansion coefficients of steel and concrete are similar, impacting their performance in construction.
- Compression tests are the most common quality control test for hardened concrete, typically using cylinder samples.
Concrete Mixtures and Air Content
- The selection of nominal maximum aggregate size in reinforced concrete is influenced by factors such as slab thickness, spacing of rebars, and cover between rebar and forms.
- Required air content for concrete with a maximum aggregate size of 2 inches in exposure class F3 is 5%.
Cement Types and Water-Cement Ratio
- Type III cement is used for high early strength concrete, while Type V cement is essential for sulfate-resistant applications.
- Increasing water content in concrete reduces strength; a lower water-to-cement ratio leads to higher strength.
Admixtures and Durability
- Water-reducing admixtures or superplasticizers improve concrete workability while maintaining a low water-to-cement ratio.
- Type F fly ash increases long-term strength and decreases permeability, enhancing durability.
Freeze-Thaw Resistance
- Air entrainment protects concrete against freeze-thaw cycles, vital in cold climates.
- The maximum water-cement ratio for a concrete element exposed to such conditions is 0.45.
Special Design Considerations
- High sulfate environments require Type V cement combined with a pozzolan or slag cement for effective mitigation.
- Minimum compressive strength for concrete in special moment frames and structural walls is set at 3,000 psi.
Stress and Strength Relationships
- The tensile strength equation for concrete based on compressive strength is fct = 7.5f'c.
- The effective tensile stress calculation in prestressed bars should account for prestressing losses.
Reinforcement and Modulus
- The permitted modulus of elasticity for non-prestressed bars is 29,000 ksi, but this must be specifically tested for prestressed reinforcement.
- Creep in concrete is caused by sustained load and impacts long-term structural behavior.
Durability and Deformation
- Concrete durability is linked to low permeability, which inhibits fluid penetration and enhances longevity.
- Proper detailing, such as using ducts free of water, prevents corrosion in structures with grouted tendons.
Masonry and Thermal Properties
- Clay masonry has a lower coefficient of thermal expansion compared to concrete masonry.
- Fired clay masonry will not revert to its original size upon drying after water exposure.
Construction and Engineering Standards
- Codes from ACI 318-14 and other standards govern minimum reinforcement ratios, slenderness ratios, and strength reduction factors in concrete design.
- Effective slenderness ratio for compression members must not exceed 200, ensuring stability and durability in structural applications.
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Description
Test your knowledge on materials and their properties with this quiz on structural depth. Questions will cover fire resistance and characteristics of brittle materials, helping you understand essential material properties. Challenge yourself and see how much you really know!
