1. The permissible stress in prestressing steel should not exceed ___________
a) 80%
b) 60%
c) 50%
d) 70%
Explanation: The maximum tensile stress at initial tensioning time should not exceed 80 percent of ultimate tensile strength of wire and the yield stress for steel and the permissible unit bearing pressure on the concrete should not exceed 0.48Fr (A1/A2)1/2 after accounting for are all the losses due to creep of concrete, elastic shortening, relaxation of steel and seating of anchorages etc.
2. The nominal cover provided for moderate steel is ___________
a) 30
b) 20
c) 40
d) 50
Explanation: The covers may be reduced to 15mm provided that the nominal maximum size of aggregates does not exceed 15mm and the nominal cover provided for moderate steel is 30mm or the size of cable in the case of protected post tensioned members are exposed to an aggressive environment, these cover requirements are increased by 10mm.
3. The nominal cover provided for steel to obtain most effective fire resistance is according to ___________
a) 1992-1-2004
b) 1994-1-2006
c) 1996-1-2005
d) 1998-1-2008
Explanation: According to BSEN (British code): 1993-1-2004, nominal cover is provided for steel to obtain most effective fire resistance and durability and it is ability of the structural member to withstand the effect of fire without reaching any of the limit states
4. The codal provision for reinforcement cover is?
a) IS: 1343-2012
b) IS: 1347-2014
c) IS: 1342-2006
d) IS: 1340-2008
Explanation: Reinforcement cover is provided according to codal provision IS:1343-2012 and it is essential to provide because it leads to corrosion, protecting steel from fire etc, the consequences of providing cover more than requirement leads to increase in width of cracks and weight of the structure.
5. The tendons in the pretensioning system are tensioned between __________
a) Rigid anchorages
b) Hydraulic jacks
c) Concrete beds
d) Variable beams
Explanation: In the prestressing system, the tendons are first tensioned between rigid anchorage blocks cast on the ground or a column or a unit mould type pretensioning bed, prior to the casting of concrete in the moulds
6. When the concrete attains sufficient strength, which elements are released?
a) Jacks
b) Casting bed
c) Tendons
d) Beams
Explanation: High early strength concrete is often used in factory to facilitate early stripping the reuse of moulds and when the concrete attains sufficient strength, the jacking pressure is released and the edge of tendon at its either side is formed to an abutment and its other edge is to be pulled with the application of jack.
7. Which is one of the systems used for pretensioning?
a) Magnel-Balton system
b) Freyssinet system
c) Gifford-Udall system
d) Hoyer’s long line method
Explanation: Hoyer’s long line method is the system used in pretensioning and the other systems like Freyssinet, Gifford-Udall, and Magnel-Balton are post tensioning systems and large numbers of beams are produced in an individual alignment.
8. Hoyer’s system of pre tensioning is generally adopted for ___________
a) Small scale members
b) Large scale members
c) Middle span members
d) End members
Explanation: Hoyer’s system is generally recommended when the production of pretensioned members is required on a large scale is the principle which are used to precast the beams the post tensioning system was considered to pretensioning system when used for large spans, due to this reason the pre tensioning system was replaced by post tensioning system.
9. The transfer of prestress of concrete is achieved by ___________
a) Plates
b) Rings
c) Steel bars
d) Jacks
Explanation: The transfer of prestress to concrete is usually achieved by large hydraulic or screw jacks by which all the wires are simultaneously released after the concrete attains the required compressive strength generally strands of up to 18mm diameter and high tensile wires of up to 7mm diameter anchor themselves satisfactorily with the help of surface bond and the interlocking of the surrounding matrix in the micro indentations on the wires.
10. The bond of prestressing wires in Hoyer’s system can be formed by ___________
a) Helical crimping
b) Tangential crimping
c) Circular crimping
d) Diode crimping
Explanation: Bond of prestressing wires may be considerably improved by forming surface indentations and by helical crimping of wires in Hoyer’s system, strands have considerable better bond characteristics than plain wires of equal cross sectional area supplementary anchoring devices are required when single wires of larger diameter are used in the pretensioned units