Structure II Exam 3 Concrete Design Design of Reinforced Concrete Structures Reinforced Concrete Design Fundamentals Latest Update 2024-2025 300 Questions and Verified Correct Answers Guaranteed A+ 6000 psi and 4000 psi concrete, which would have a higher E modulus? - CORRECT
ANSWER: 6000 psi
Aggregate for making concrete is intentionally varied in size. Why? - CORRECT
ANSWER: To increase strength and density
Are all primary reinforcing bars required to be continuous over the entire length of the
beam? - CORRECT ANSWER: No, only were required by moment conditions
Based on the same aggregate material which grade would be denser, 3/8" or 3/4" - CORRECT ANSWER: Neither. Density is not significantly affected by size (scale effect)
How does concrete cure (harden)? - CORRECT ANSWER: Concrete curs through the
chemical process of hydration. `
How is concrete workability measured? - CORRECT ANSWER: Slump test using a
slump cone
If a reinforced concrete section was designed to be over reinforced, what would be the
mode of failure? - CORRECT ANSWER: Concrete would fail in compression (sudden
failure)
In a concrete design, what does f'c represent? - CORRECT ANSWER: The ultimate
compressive stress of the concrete?
In a simple span concrete beam, where is the flexural steel placed? - CORRECT
ANSWER: Near the bottom
In a tension controlled beam, what kind of failure can be expected? - CORRECT
ANSWER: Tensile failure of the steel, which is a ductile failure
In analyzing a typical concrete beam, the load carrying capacity of the concrete below
the neutral axis is ignored. Why? - CORRECT ANSWER: Concrete has little if any
ability to resist forces in tension
In determining the nominal strength of concrete fc', for how long is the test cylinder
cured? - CORRECT ANSWER: 28 days
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In the couple method, where is the force C located? - CORRECT ANSWER: The force
C passes through the centroid of the compression forces or the force volume.
In the illustration what is being tested? - CORRECT ANSWER: Tensile strength
In Ultimate Strength Design, is Mc/I equal to the bending stress? - CORRECT
ANSWER: No, it is invalid for stresses beyond elastic limit.
Is it allowed to have a beam with no reinforcing steel? - CORRECT ANSWER: NO
On average what is the tensile strength of concrete as a percentage of its compressive
strength? - CORRECT ANSWER: 10%-20%
What are the main constituent parts of concrete? - CORRECT ANSWER: Aggregate
(sand + rock), cement and water
What does f'c represent in concrete? - CORRECT ANSWER: The cylinder crushing
strength at 28 days
What does the force couple in concrete beam analysis represent? - CORRECT
ANSWER: The internal moment
What factors are considered in a concrete batch design? - CORRECT ANSWER:
Application (pavement, building, water tank, etc), Location (climate), Placement (cast, pumped, vibration), Season (summer or winter)
What factors can be changed in a beam to increase the amount of strain in the tensile
steel, Et without lowering the strength of the beam? - CORRECT ANSWER: Increase
the depth d/increase the width b/increase the concrete strength f'm
What harm can come from over-reinforcing a reinforced concrete beam? - CORRECT
ANSWER: The concrete could fail suddenly before the beam shows signs of failure
What is a deformed reinforcing bar? - CORRECT ANSWER: A bar that has been
formed with ribs to provide better bonding with the concrete
What is a reasonable range for the ratio b/d in concrete beams? - CORRECT
ANSWER: 1/2 to 2/3
What is bleed water? - CORRECT ANSWER: Water that bleeds to the top surface of a concrete slab
What is meant by batching concrete or batch design? - CORRECT ANSWER: Batch
design is the relative proportioning of sand, rock, cement and water
What is measured by a slump test? - CORRECT ANSWER: Workability 2 / 3
What is p (rho) - CORRECT ANSWER: Rho is the ratio of steel to concrete, As/bd
What is the actual weight of normal concrete not counting steel reinforcing, in pounds
per cubic foot? - CORRECT ANSWER: 144 PCF
What is the development (embedment) length of a reinforcing bar? - CORRECT ANSWER: It is the length of embedment in the concrete required to develop the full yield strength of the bar without pulling out of the concrete.
What is the effect of a water reducing agent on concrete workability? - CORRECT ANSWER: A water reducing agent has the effect on workability of adding more water. It increases slump and makes the mix more workable.
What is the effect of raising the water/cement ratio in a concrete batch design? -
CORRECT ANSWER: Higher slump and lower strength
What is the failure mode for an under-reinforced section? - CORRECT ANSWER: The
steel yields before the concrete fails
What is the function of air entrainment? - CORRECT ANSWER: Air entrainment
provides protection against cracking due to freezing temperatures
What is the greatest factor effecting strength of a concrete mix? - CORRECT
ANSWER: Water/cement ratio
What is the meaning of the bar size number e.g. #6 - CORRECT ANSWER: The size is the bar diameter in 1/8th of an inch.
What is the primary purpose of stirrups in a reinforced concrete beam? - CORRECT
ANSWER: They provides shear reinforcement
What is the standard cylinder size used to test for f'c - CORRECT ANSWER: 6"x12" cylinder
What part of the batch design has the greatest effect on the strength of concrete? -
CORRECT ANSWER: The water cement ratio
What value is derived from a concrete cylinder test? - CORRECT ANSWER: f'c
What value is usually used for the density of reinforced concrete members - CORRECT
ANSWER: 150 PCF
What will a higher the value for f'c in concrete produce? - CORRECT ANSWER: A
higher E modulus
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