This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Transmission by Bond”.
1. In a pretensioned system, when a wire is released from its temporary anchorage the end of the wire swells as a result of:
Explanation: In a pretensioned system, when a wire is released from its temporary anchorage on the prestressing bed, the end of the wire swells as a result of the recovery of the lateral contraction and develops a wedge effect and this is generally referred to as the Hoyer effect and this is to enable the prestressing force to become at the end of the wire.
2. The swelling of the wire produces which action on concrete:
a) Linear pressure
b) Axial pressure
c) Radial pressure
d) Upcoming pressure
Explanation: The swelling of the wire is only a few thousandth of a millimeter, but it nevertheless produces considerable radial pressures on the concrete, giving rise to large frictional forces, the general provisions in the Indian code for the transmission length are expressed in terms of the diameter of the wire, bar or strand, taking into considerations the surface characteristics of the tendons.
3. How many factors are considered while prestressing force in steel is transferred to concrete through bond?
Explanation: The prestressing force in steel is transferred to concrete considering three factors through the bond having adhesion, friction, shearing resistance; the limits were made for wire tendons of 100 to 140 diameter and for 7 wires strands 45 to 90 diameter of tendons.
4. The bond stress in the prestress members is mainly due to:
a) Friction and shrinkage
b) Compression and bondage
c) Tension and torsion
d) Anchorages and tendons
Explanation: The bond stress in the prestress members is mainly due to friction, shearing resistance and for perfect bond; friction is considered generally, the FIP recommendations regarding the anchorage lengths to ensure the transmission of the prestress to the concrete.
5. The bond stress at intermediate points is resisted by:
Explanation: Bond stress at intermediate points is resisted by adhesion and in transfer zone the adhesion is destroyed by invariable slip and sink of tendons into concrete, transversely ribbed steel type of wire has a diameter of 20 to 40 mm2 area of bond length 500mm.
6. Which zone attains maximum bond stress?
a) Transverse tension
b) Transverse anchorage
c) Transverse tendon
d) Transverse compression
Explanation: The zone of transverse compression attains maximum bond stress and when the bond stress becomes zero various changes occur, 2 or 3 strand wire of diameter 2 to 3 has a bond length of 700mm, 7 wire strand of diameter 2 to 4 has a bond length of 1000mm.
7. The steel and concrete reach their maximum values of stress when bond stress is:
Explanation: When the bond stress in zero, the steel and concrete reach their maximum values of stresses with uniform stress distribution in this section, the bond lengths recommended in German specifications are compiled in drawn steel of diameter 3 to 8 and bond length 600mm.
8. The term transmission refers to attainment of uniform:
a) Strain distribution
b) Stress distribution
c) Level distribution
d) Cross section distribution
Explanation: The length needed for achieving uniform stress distribution in a member is termed as transmission length, the transmission length for plain smooth wires is considerably greater than that for deformed bars or strands due to absence of a mechanical interlock.
9. At intermediate points along the length of a beam, the bond stress is resisted by:
Explanation: At intermediate points along the length of a beam, the bond stress is resisted by adhesion, while in the transfer zone the tendons invariably slip and sink into the concrete destroying most of the adhesion.
10. The shearing resistance is also termed as:
Explanation: Shearing resistance is also known as dilatancy, it is considered in case of transmission of prestressing force from steel to concrete through bond, the ACI code recommendations are based on the investigations of Kaar and Hatson it includes the both length required to develop the effective prestress as also the additional length over which the strand must be bonded to the concrete so that the tensile stresses develop in the strand at the limit state of collapse of the member.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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