Post-Tension Concrete Test Questions
Fully Solved.
How can we enhance the concrete capacity? - Answer We can apply a pre-compression to
the structure in order to prevent tension stress in concrete
What is the aim of pretension Ing? - Answer To apply a permanent compression to the beam
before putting it into service, in order to provoke compression in all regions where external
forces will provoke tension
What are some advantages? - Answer 1. stiffness in increased because we can consider
uncracked inertia
2. we can support higher bending moments
3. we can reduce the hight of the bridge and the self weight can be reduced
4. they show better behavior under corrosion
5. effective solution is high strength concrete combined with greater amount of tendons
What are some disadvantages? - Answer 1. unit cost of bridge is higher than RC
2. extra initial cost in incurred due to use of prestressing equipment and installation
3. extra labour cost
4. prestressing is uneconomical for short spans and light loads
Methods of prestressing - Answer 1. tension the tendons before casting - anchor the tendons
on abutments and once concrete is cured release the tendons
2. tension the tendons after casting - include ducts in the concrete and after the concrete is
cured introduce tendons and tension them
Post-tensioning types - Answer Internal bonded
Extradosed unbonded
Internal unbonded
External bonded/unbonded
Internal bonded post-tensioning - Answer Structural member is cast leaving the ducts inside
and they are formed by sheet metal tubes. Once concrete is cured and hardened the tendons
are introduced and they are tensioned using jacks. Once desire stretch is reached the end with
the jack is anchored and the ducts are filled with grout
, Internal unbonded post-tensioning - Answer Similar to internal bonded but the ducts are
plastic and the tendons are grouted with grease. This is so the tendons can be replaced in the
future but a main disadvantage is the tendons are not protected as well from corrosion
External post-tensioning - Answer Tendons are not placed inside concrete but outside
between height of beam. Connection between concrete and tendons occur at points called
deviators and the contact between concrete and tendons can be bonded or unbonded
Extradosed post-tensioning - Answer Tendons are placed outside of the height of the beam
and can be below or above the deck.
What kind of responses are reinforced and prestressed concrete? - Answer Reinforced -
passive response
Prestressed - active because it tries to be contrary to what will happen in the future
Can you weld the wires and tendons in post-tensioning? - Answer NO
What is a tendon? - Answer A set of stranded placed inside the same duct
What is relaxation? - Answer The reduction of tension stress with time, of a wire subjected to
constant strain and it provokes a deferred loss of prestressing
Relaxation depends on... - Answer Tensional level
Time
Temperature
What is behavior of steel under high temperature and after cooling? - Answer As
temperature increases young's modulus, yield strength, and ultimate strength decreases. After
cooling the young's modulus stays constant, yield strength and ultimate strength is constant
then at a temperature point the values decrease
What to use for bonded post-tensioning with respect to ducts? - Answer Round/flat steel
ducts
What to use for unbonded post-tensioning with respect to ducts? - Answer Round/flat plastic
ducts but they must be able to maintain its shape during casting
What to use if more duct length is needed? - Answer Use a duct coupler but the main issue is
the connection must be water-tight
Fully Solved.
How can we enhance the concrete capacity? - Answer We can apply a pre-compression to
the structure in order to prevent tension stress in concrete
What is the aim of pretension Ing? - Answer To apply a permanent compression to the beam
before putting it into service, in order to provoke compression in all regions where external
forces will provoke tension
What are some advantages? - Answer 1. stiffness in increased because we can consider
uncracked inertia
2. we can support higher bending moments
3. we can reduce the hight of the bridge and the self weight can be reduced
4. they show better behavior under corrosion
5. effective solution is high strength concrete combined with greater amount of tendons
What are some disadvantages? - Answer 1. unit cost of bridge is higher than RC
2. extra initial cost in incurred due to use of prestressing equipment and installation
3. extra labour cost
4. prestressing is uneconomical for short spans and light loads
Methods of prestressing - Answer 1. tension the tendons before casting - anchor the tendons
on abutments and once concrete is cured release the tendons
2. tension the tendons after casting - include ducts in the concrete and after the concrete is
cured introduce tendons and tension them
Post-tensioning types - Answer Internal bonded
Extradosed unbonded
Internal unbonded
External bonded/unbonded
Internal bonded post-tensioning - Answer Structural member is cast leaving the ducts inside
and they are formed by sheet metal tubes. Once concrete is cured and hardened the tendons
are introduced and they are tensioned using jacks. Once desire stretch is reached the end with
the jack is anchored and the ducts are filled with grout
, Internal unbonded post-tensioning - Answer Similar to internal bonded but the ducts are
plastic and the tendons are grouted with grease. This is so the tendons can be replaced in the
future but a main disadvantage is the tendons are not protected as well from corrosion
External post-tensioning - Answer Tendons are not placed inside concrete but outside
between height of beam. Connection between concrete and tendons occur at points called
deviators and the contact between concrete and tendons can be bonded or unbonded
Extradosed post-tensioning - Answer Tendons are placed outside of the height of the beam
and can be below or above the deck.
What kind of responses are reinforced and prestressed concrete? - Answer Reinforced -
passive response
Prestressed - active because it tries to be contrary to what will happen in the future
Can you weld the wires and tendons in post-tensioning? - Answer NO
What is a tendon? - Answer A set of stranded placed inside the same duct
What is relaxation? - Answer The reduction of tension stress with time, of a wire subjected to
constant strain and it provokes a deferred loss of prestressing
Relaxation depends on... - Answer Tensional level
Time
Temperature
What is behavior of steel under high temperature and after cooling? - Answer As
temperature increases young's modulus, yield strength, and ultimate strength decreases. After
cooling the young's modulus stays constant, yield strength and ultimate strength is constant
then at a temperature point the values decrease
What to use for bonded post-tensioning with respect to ducts? - Answer Round/flat steel
ducts
What to use for unbonded post-tensioning with respect to ducts? - Answer Round/flat plastic
ducts but they must be able to maintain its shape during casting
What to use if more duct length is needed? - Answer Use a duct coupler but the main issue is
the connection must be water-tight
