This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “High Tensile Steel”.
1. The ultimate strength of high tensile steel is:
Explanation: High tensile steel are commonly used in prestressed concrete members and ultimate strength of high tensile steel is equal to 2100n/mm2, therefore the losses of prestress due to shrinkage and creep with a stress of 200n/mm2 are restricted.
2. The high tensile steel is obtained by increasing content of:
a) Carbon content in steel
b) Aluminium content in steel
c) Manganese content in steel
d) Sulphur content in steel
Explanation: High tensile steel is required in prestressed concrete member and it is obtained by increasing the carbon content in steel and the percentage of carbon is 0.6-0.85%, 0.7-1% of manganese, 0.05% of sulphur and phosphorus is present in high tensile steel.
3. The properties of cold-drawing through wires can be improved by heating at:
Explanation: As per IS:1785-1983, the nominal size of cold drawn stress are 2.5,3,4,5,7 and 8mm diameter and to improve the properties of wire, they have to be tempered by heating the wires at 150 to 480degrees, which enhances tensile strength.
4. Hard-drawn steel wires used in high tensile steel are considered as:
a) Crimped elements
b) Twisted elements
c) Durable elements
d) Tempered elements
Explanation: As per IS: 6003-1983, the diameter of wires are mostly used in strands of two, three or seven wires and they are considered as indented or crimped pretensioned element, due to their superior bond character and two and three ply strands, 2-3mm diameter wires are used whereas in 7 ply stand a diameter of 2-5mm wires are adopted and the nominal diameter of 7 ply stand varies in between 6.3 to 15.2mm.
5. The atomic hydrogen is liberated as a result of action of:
Explanation: Atomic hydrogen is liberated as a result of the action of acids on high-tensile steel and they penetrate into the steel surface making it brittle and fracture prone on being subjected to tensile stress and even small amounts of hydrogen can cause considerable damage to the tensile strength of high steel wires.
6. The prevention of hydrogen embrittlement can be done by protecting the wires from:
a) Rain water and humidity
b) Reactions and shocks
Explanation: In order to prevent hydrogen embrittlement, it is essential that the steel is properly protected from the action of acids and the wires should be protected from rain water and excessive humidity by storing them in dry conditions.
7. The permissible stress in prestressing steel should not exceed:
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.
8. The nominal cover provided for moderate steel is:
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.
9. The nominal cover provided for steel to obtain most effective fire resistance is according to:
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.
10. 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 structure.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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