Prestressed Concrete Structures Multiple Choice Questions on “Ultimate Load Analysis”.
1. The reduction in the magnitude of prestressing force occurs due to __________
a) Re block
b) Restraint
c) Relock
d) Re tension
Answer: b
Clarification: According to Bennet the main effects due to axial deformation and tertiary moments are: Reduction in the magnitude of prestressing force in a particular member due to the restraint of the adjacent members, the development of tertiary moments due to bending deformation of the indeterminate structure due to axial contraction under the action of the prestressing force.
2. The ultimate load carrying capacity is controlled by __________
a) Tensile strength
b) Compressive strength
c) Flexural strength
d) Axial strength
Answer: c
Clarification: The ultimate load carrying capacity of a statically determinate prestressed concrete structure is mainly controlled by the flexural strength of a critical section in the member and in contrast to this, the ultimate load carrying capacity of an indeterminate prestressed concrete structure depends upon the flexural strength of several critical sections and their rotation capacity.
3. A conservative estimate of the ultimate resistance is obtained by assuming __________
a) Extra reinforcement
b) Tensile reinforcement
c) Factor of safety
d) Collapse
Answer: d
Clarification: However a highly conservative estimate of the ultimate resistance of the structure is obtained by assuming the collapse to occur when the moment, calculated by the linear elastic theory first reaches a value equal to the flexural strength at any section.
4. Due to large deformations at the critical sections which concentration develops?
a) Equilibrium
b) Curvature
c) Resultant
d) Loads
Answer: b
Clarification: Due to large deformations at the critical sections in a statically indeterminate structure a concentration of curvature builds up over a few clearly defined short length of the member, such as the interior supports and midspan points of a continuous beam and these plastic zones are idealized as hinges at which a rotation is considered to take place.
5. If the partial redistribution takes place by the limited hinge rotations, the ultimate strength of the structure lies between __________
a) Upper limit
b) Lower limit
c) Upper limit above and lower limit
d) Zero
Answer: c
Clarification: If the partial redistribution takes place due to the constraints imposed by limited hinge rotations, the ultimate strength of the structure lies in between the upper limit above and the lower limit corresponding to the computations based on the linear elastic theory.
6. The equilibrium between the internal forces and the external loads is maintained for __________
a) Stress combinations
b) Load combinations
c) Deformation combinations
d) Elastic combinations
Answer: b
Clarification: The redistribution of moments is permitted under the following conditions: equilibrium between the internal forces and the external loads is maintained for approximate load combinations, at sections where the moment capacity after redistribution is less than that from the elastic maximum moment diagram the following relationship should be satisfied ((xu/d) + δm/100)) < 0.8, xu = depth of neutral axis, d = effective depth, δm = percentage reduction in moment.
7. The ultimate moment of resistance provided at any section of a member is not less than?
a) 80%
b) 40%
c) 25%
d) 95%