1. The Hoyer’s method of prestressing is done by ___________
a) Pulling out of wires
b) Pushing wires
c) Heating of wires
d) Stressing of wires
Explanation: Hoyer’s system of prestressing involves pulling out of wires between two bulkheads which are separated at large distances in order to produce a larger number of beams in an individual alignment, the concrete is to be poured by providing appropriate shuttering between the beams and then the wires are united after hardening of concrete and cutoff.
2. Hoyer’s system of pretensioning can be done for beams.
a) 1
b) More than 2
c) Less than 2
d) 2
Explanation: United beams more than 2 are hardened in Hoyer’s method of pretensiong in case of large distances between each beam, the most commonly used devices are the Weinberg clip developed in France and the Dorland clip developed in the united states these clips are clamped on to the tensioned wires close on the end diaphragms of the units before concreting operations.
3. The Hoyer’s system of prestressing proves to be economical for __________
a) Pre tensioning system
b) Post tensioning system
c) Beam casting
d) Bed casting
Explanation: The post tensioning system was considered as economical when compared to pre tensioning system, when used for larger spans due to this reason pre tensioning system was replaced by post tensioning system, for mass production of pretensioned elements, the long line process developed by Hoyer is generally used in the factory and in this method the tendons are stretched several hundred meters apart so that a number of similar units may be cast along the same group of tensioned wires.
4. In Hoyer’s system the projection of plugs left in concrete exceeds beyond ___________
a) Middle of member
b) End of member
c) First of member
d) Transfer part of member
Explanation: One of the disadvantages of Hoyer’s system is the projection of plugs which are left in concrete exceeds beyond the end of the member, application of heavy jacks which are uneconomical, projection of plugs which are left in concrete exceeds beyond the ends of the member, additional reinforcement is required to prevent failure of shear.
5. In post tensioning, the concrete units are cast by ___________
a) Ducts
b) Jacks
c) Anchorages
d) Wedges
Explanation: In post tensioning, the concrete units are first cast by incorporating ducts or grooves to house the tendons and when the concrete attains sufficient strength, the high tensile wires are tensioned by means of jack bearing on the end face of the member and anchored by wedges or nuts
6. After the tensioning operation, the space between the tendons and the ducts are ___________
a) Layered
b) Grouted
c) Cemented
d) Drilled
Explanation: The focus are transmitted to the concrete by means of the end anchorages and when the cable is curved through the radial pressure between the cable and the ducts and the space between the tendons and the duct is generally grouted after the tensioning operation.
7. The Freyssinet system of post tensioning anchorages was developed in ___________
a) 1934
b) 1935
c) 1939
d) 1936
Explanation: Freyssinet system of post tensioning anchorages which was developed in 1939, gave impetus to the various new systems devised over the years and at present, according to abeles there are over 64 patent post prominent systems used worldwide.
8. The Freyssinet system of prestressing involves the arrangement of wires of number?
a) 10
b) 14
c) 12
d) 8
Explanation: Freyssinet system of prestressing involves the arrangement of high tensile steel wires of about 12 in number with diameter of 5mm to 8mm forming a group into a cable, cylinder is provided as an anchorage and it has a conical hole at its centre provided with heavy hoop reinforcement these cylinders are is provided as an anchorage and it has a conical hole at its centre provided with heavy hoop reinforcement.
9. In Freyssinet system which element behaves as a guide?
a) Spiral spring
b) Hallow spring
c) Trapezoidal spring
d) Cable spring
Explanation: In Freyssinet system of prestressing spiral spring is provided inside the cable for sufficient clearance between the wires and it even provides a cement grouted channel and the spiral spring behaves as a guide in transferring the reaction to concrete.
10. Which of the following is a disadvantage of Freyssinet system?
a) Stresses in the wires are not similar
b) Rapid attainment of stretching force
c) Safeguarding of wires is economical
d) Projection of plug left in concrete
Explanation: The stresses in the wires are not similar, even though all the wires are been stretched together, Freyssinet system involves the application of heavy jacks which are economical force applied for stretching is about 250kn to 500kn which is maximum and is still inadequate.