1. The linear prestressing is mostly applicable for ___________
a) Bent members
b) Straight members
c) Cracked members
d) Overloaded members
Explanation: Linear prestressing is mostly applicable for straight members such as slabs, beams etc and the members are prestressed in a linear manner, tendons are spliced in case of continuous prestressed concrete members to gain continuity and the various types of splices used as tendons are screw connector, torpedo splices, clamp splice and wrapped splice.
2. In pre-tensioning system, after curing and hardening of concrete the reinforcement is set ___________
a) Free
b) Fixed
c) Locked
d) Jacked
Explanation: In pre-tensioning system, the tendons are tensioned first and then the casting of concrete is carried out and the edge of the tendon at its either side is fixed to an abutment and its other edge is pulled with the application of jack and then the reinforcements are set free after curing and hardening.
3. The method of prestressing the concrete after it attains its strength is known as ___________
a) Pre tensioning
b) Post tensioning
c) Chemical prestressing
d) Axial prestressing
Explanation: The method of prestressing the concrete after it attains its strength is known as post tensioning and ducts are made in the member at the time of placing the concrete, the suitability of post tensioning is good for medium to long span-insitu work, where the cost of tensioning is very less.
4. In which method the prestress is developed due to the bond between the concrete and steel?
a) Pre tensioning
b) Post tensioning
c) Thermo electric prestressing
d) Prefix beam prestressing
Explanation: The prestress developed in pre tensioning is due to the bond between concrete and steel tendons, a method of prestressing concrete in which the tendons are tensioned before the concrete is placed at the work site.
5. The developments in the field of concrete mix design gave compressive strength ranging between ___________
a) 30-70
b) 70-100
c) 35-45
d) 30-80
Explanation: Recent developments in the field of concrete mix design have indicated that it is now possible to produce even ultra high strength concrete, of any desired 28 day cube compressive strength ranging from 70-100n/mm2 without taking resource to unusual materials.
6. High strength concrete resists ___________
a) Levelling
b) Bursting
c) Tangent moments
d) Trapezoidal moments
Explanation: The concrete in a prestressed concrete member is subjected to high bearing stresses due to anchoring at its ends and hence, high strength concrete is required to safely resist the bursting stresses at the end of the beam.
7. In high strength concrete, high modulus of elasticity in the beam is due to ___________
a) Elastic and creep strains
b) Principle tensile stresses
c) Reinforced beams
d) Vibration
Explanation: Low shrinkage, minimum creep characteristics and a high value of young’s modulus are generally deemed necessary for concrete used for prestressed members and the loss of prestress in steel reinforcement is minimum because the elastic and creep strain are very small due to high modulus of elasticity.
8. Which of the following is one of the standard codes used for designing high strength concrete mixes
a) BS 8110-1985
b) BS 883-1974
c) BS 8113-1986
d) BS 886-1976
Explanation: The various methods adopted for designing high strength concrete mixes are Erntroy and Shack lock’s empirical method, American concrete institute method, British DOE method, Indian standard code and British code BS 8110-1985 stipulates that not more than 5 percent of the test results should fall below 28 days characteristic strength.
9. Which of the following is the Indian code used for high strength concrete mixes?
a) IS 1343-1980
b) IS 10263-1982
c) IS 384-1980
d) IS 457-1979
Explanation: Indian standard code IS 1343-1980 and IS 456-1978 stipulates that only controlled concrete should be used for prestressed concrete construction and the exact specifications with regard to the acceptance criteria for concrete generally vary from one code to another.
10. The cube strength of concrete required for both pre tensioning and post tensioning according to Indian standard codes are ___________
a) 30 and 20
b) 15 and 25
c) 40 and 30
d) 45 and 35
Explanation: The minimum 28 day cube compressive strength prescribed in the Indian standard code IS 1343-1980 is 45n/mm2 for pretensioned members and 35n/mm2 for post tensioned members with the development of vibration techniques in 1930, it became possible to produce without much difficult, high strength concrete having 28 day compression strength in the range of 30-70n/mm2.