1. In which place thermo electric pre stressing found to be more economical?
a) Canada
b) USSR
c) France
d) Switzerland
Explanation: In the erstwhile USSR, the Thermo electric pre stressing method has been widely used since 1958 for pre tensioning bar reinforcements of pre cast units and this method has been found to be more economical than conventional mechanical devices.
2. The thermo electric pre stressing is also used in ___________
a) Pre-block units
b) Pre-cast units
c) Pre-beam units
d) Pre-anchorage units
Explanation: Thermo electric pre stressing is adopted in many foreign countries as it is most economical when compared to the other conventional mechanical devices; it is also used in precast units, precast are only used within ranges of exterior and interior walls compressed in concrete and stone, creating a solid but maneuverable wall or face, precast concrete production performed on ground level, which helps with safety throughout a project.
3. The tensioning of oval section ribbed wires with an ultimate tensile strength was adopted in ___________
a) Germany
b) France
c) Switzerland
d) Britain
Explanation: Thermo electric pre stressing has also been adopted in Germany for the tensioning of oval section ribbed wires with an ultimate tensile strength of 1600n/mm2, the wrapping wire of 1mm diameter is generally used for splicing wires up to 6mm diameter and the length of splice may vary from 20-30cm and the splice formed in this manner has a strength almost equal to that of the normal wire and this type of splice is generally used for the wires of circular concrete tanks and anchorage loops.
4. The estimation of the current, voltage and power requirements of the transformer are for ___________
a) Theoretical equations
b) Empirical relations
c) Global relations
d) Quadratic equations
Explanation: A temperature of about 4600c was necessary to induce an initial stress of 55 percent of the ultimate tensile strength the heating time being 40-90s at 30v and 300-1100 A and Empirical relations for the estimation of the current, voltage and power requirements of the transformer are reported by Graduck.
5. In thermo electric pre stressing, the elongation is observed in case of ___________
a) Bar after cooling
b) Bar after heating
c) Bar after anchoring
d) Simple bar
Explanation: In case of heating the bar gets elongated and shortens after heating and after anchorages are applied on both sides which stretch the bar, clamp splices are equipped with bolts and nuts since there will be a considerable reduction in the tensile strength of up to 50 percent, these type of splice can be used only in locations where the prestressing force can be sufficiently reduced by the curvature of tendon due to friction.
6. How many wedges are considered in the case of torpedo splices?
a) 3
b) 4
c) 5
d) 2
Explanation: Tendons are spliced in case of continuous pre stressed concrete members to gain continuity and the various types of splices used as tendons are screw connector, torpedo splices, clamp splice and wrapped splice and torpedo splices consists of triple wedges for securing the wires and the entire unit is covered and protected by a sleeve and this type of splice is largely used for splicing cold drawn wires.
7. The chemical pre stressing is also called as ___________
a) Self stressing
b) Whole stressing
c) Half stressing
d) Model stressing
Explanation: Self stressing or chemical pre stressing of concrete was made possible by the development of expanding cements by Lossier of France in 1944 and generally expanding cement consist of 75% Portland cement, 15% alumina cement and 10 % gypsum which result in formation of calcium Sulpho aluminate.
8. The linear expansion of the cement in chemical pre stressing is about ___________
a) 5-10%
b) 2-3%
c) 3-4%
d) 6-7%
Explanation: The linear expansion of the cement in chemical prestressing is about 3 to 4% Mikhailov has reported that expansive cements have been used for pre stressing purposes in erstwhile in USSR since 1949 and splices are adopted for circular prestressing of tanks and the advantage is that there is no reduction in the strength of wire.
9. The degree of expansion can be controlled by varying the conditions of __________
a) Bending
b) Bonding
c) Heating
d) Curing
Explanation: The degree of expansion can be controlled by varying the curing conditions in expanding cements and when the concrete is subjected to compression the amount and rate of expansion is controlled by controlling the curing conditions of the member.
10. The expansion of the concrete is restrained by ___________
a) High-tensile steel
b) High-strength concrete
c) Precast members
d) Concrete members
Explanation: concrete is composite material consisting of an aggregate and a binder phase and the binder phase is hardened cement and the expansion of concrete is restrained by high tensile steel wires, the compressive stresses that develop in concrete and steel wires are subjected to tensile stresses.