CIVE 421 Test your Knowledge - Chapter
4
What are the assumptions used in the analysis of reinforced concrete beams in
bending? - CORRECT ANSWER-Bernoulli's theory of plane sections before bending
remain plane after bending. Thus strains are proportional to the distance from the
neutral axis.; Steel and concrete are perfectly bonded. Thus, the stress in steel is
equal to the stress in neighboring concrete that has the same distance from N.A.;
Limit state or failure is defined by concrete crushing at a compressive strain of
0.003.; Concrete flexural tensile strength or modulus of rupture f_r = 0.; Compression
stress distribution in the concrete compression zone is according to Whitney's
rectangular compression block.
What is the stress beyond which concrete ceases to be elastic? - CORRECT
ANSWER-f'c/3 (See chapter 2)
What is the stress beyond which steel ceases to be elastic? - CORRECT
ANSWER-f'y (see chapter 2)
How is slow or gradual failure achieved in reinforced concrete beams? - CORRECT
ANSWER-By making sure that steel yields prior to concrete crushing. With steel
yielding, failure is gradual, large deformation become visible and failure is
accompanied by absorption of large amount of energy. Thereby, lives can be saved
and we can take remedial actions.
What phase of behavior of concrete beams is closest to service conditions? -
CORRECT ANSWER-Phase 2 - so concrete is cracked under service condition.
However, accurately, it is between phase 2 and phase 3 as concrete is not elastic.
List the four phases of behavior of reinforced concrete beams and the theme for
each phase. - CORRECT ANSWER-Phase 1 - Elastic Uncracked. Phase 2 - Elastic
Cracked. Phase 3 - Inelastic and Cracked. Phase 4 - Limit State or Failure.
4
What are the assumptions used in the analysis of reinforced concrete beams in
bending? - CORRECT ANSWER-Bernoulli's theory of plane sections before bending
remain plane after bending. Thus strains are proportional to the distance from the
neutral axis.; Steel and concrete are perfectly bonded. Thus, the stress in steel is
equal to the stress in neighboring concrete that has the same distance from N.A.;
Limit state or failure is defined by concrete crushing at a compressive strain of
0.003.; Concrete flexural tensile strength or modulus of rupture f_r = 0.; Compression
stress distribution in the concrete compression zone is according to Whitney's
rectangular compression block.
What is the stress beyond which concrete ceases to be elastic? - CORRECT
ANSWER-f'c/3 (See chapter 2)
What is the stress beyond which steel ceases to be elastic? - CORRECT
ANSWER-f'y (see chapter 2)
How is slow or gradual failure achieved in reinforced concrete beams? - CORRECT
ANSWER-By making sure that steel yields prior to concrete crushing. With steel
yielding, failure is gradual, large deformation become visible and failure is
accompanied by absorption of large amount of energy. Thereby, lives can be saved
and we can take remedial actions.
What phase of behavior of concrete beams is closest to service conditions? -
CORRECT ANSWER-Phase 2 - so concrete is cracked under service condition.
However, accurately, it is between phase 2 and phase 3 as concrete is not elastic.
List the four phases of behavior of reinforced concrete beams and the theme for
each phase. - CORRECT ANSWER-Phase 1 - Elastic Uncracked. Phase 2 - Elastic
Cracked. Phase 3 - Inelastic and Cracked. Phase 4 - Limit State or Failure.
