This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Transverse Tensile Stresses”.
1. The transverse tensile stress in transmission zone is developed due to concentration of ____________
Explanation: Transverse tensile stresses of considerable magnitude develop in the transfer zone due to the concentration of tendons at the ends and these stresses are influenced by jacking and the method of releasing the tendons from the prestressing beds.
2. The transverse tensile stresses are found to be maximum near ____________
a) Centroidal section
b) Mid span section
c) End zone section
d) Shaft cracking
Explanation: The area at or near centroidal sections of the end faces of beams have maximum tensile stress and if the tensile stresses exceed the tensile strength of concrete, horizontal cracking occur, mid span of the section effects the deflection parameters of the structural member.
3. The method of distributing tendons at the ends has a greater influence on ____________
a) Mid zone cracking
b) End zone cracking
c) Equivalent cracking
d) Shaft cracking
Explanation: A number of cases of cracks developed in precast pretensioned members are reported by foundation and it has been found that the method of distributing tendons at the ends have a greater influence on the end zone cracking.
4. The problem of end zone cracking in pretensioned I beams has been experimentally investigated by ____________
a) Warren Hastings
Explanation: The problem of end zone cracking in pretensioned I beams has been experimentally investigated by Marshall, Mattock, Arther and also Ganguli at the centroid of cast in situ slab the compressive force applied is equivalent to direct compressive force acting at composite section together bending moment.
5. The tensile stress is determined by the empirical equation of the type?
a) fv = KM/bwd2
Explanation: The transverse tensile stress is determined by the empirical formula fv = KM/bwd2
fv– Transverse tensile stress at centroid of the end face, M – Resulting bending moment between the prestress force and internal prestress developed in the concrete on the centroidal axis, bw = thickness of web, d = overall depth of beam, K = constant depending upon the slope and distribution of tendons at the ends.
6. The transverse tensile stress distribution in transfer zones can be computed by an expression of the type?
a) 10M/bwhLt (1-x/Lt) e-3.5xLt
b) 10M/bwhLt (1-x/Lt)
Explanation: Investigations by Marshall and Krishna Murthy involving extensive tests on pretensioned I beams indicate that the transverse tensile stress distribution in transfer zone can be computed by an expression of the type: 10M/bwhLt (1-x/Lt) e-3.5xLt
Lt = transmission length, x = distance from end face.
7. The magnitude of maximum tensile stresses found to occur at the centroid of end face when x is zero is ____________
Explanation: The magnitude of the maximum tensile stress which is found to occur at the centroid of each end face when x = 0 is given by:
fv(max) = 10M/bwhLt,
M = moment, Lt = transmission length.
8. The creep coefficient of the concrete varies from ____________
a) 1 to 6
b) 1 to 3
c) 1 to 9
d) 1 to 12
Explanation: The creep coefficient varies from 1 to 3 and it is denoted by ϕ, the composite section carries all the applied loads when the effect of creep is more and on the precast element the cast in situ slab is casted in which the slab has already undergone shrinkage and creep, but creeping starts only after thee in situ slab is casted and is larger due to wet concrete and both precast beams and cast insitu slabs contains differential creep and shrinkage which induced stresses from one element to the another element.
9. The term iw in a section of I beam is termed as ____________
a) Thickness of web
b) Depth of web
c) Self weight of I section
d) Total weight of I section
Explanation: The term iw is thickness of web and this is used in problems of end zone cracking in pretensioned I beams, on applying compressive forces of equal magnitude along the same line the tensile forces can be balanced.
10. A time dependent deformation of concrete is termed as ____________
c) Final stress
Explanation: A time dependant formation of concrete is termed as creep, this deformation is seen due to loadings and applied stress or strain failures and the main effects of creep are it decreases the effects due to shrinkage strain; there is a mutual transfer of loads from beam to the composite section.
Sanfoundry Global Education & Learning Series – Prestressed Concrete Structures.
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