Prestressed Concrete Structures Multiple Choice Questions on “Stress Distribution in End Block”.
1. During stress distribution in end blocks the prestressing force is applied as ______________
a) Concentrated force
b) Deviated force
c) Tension force
d) Torsion force
Answer: a
Clarification: The prestressing force is applied as a concentrated force in a tendon along the anchorages during stress distribution in end blocks, the compressive stresses of concrete ahead of the anchorage devices, location and magnitude of the bursting force and the edge tension forces can be estimated with approximate method of design of end blocks when the accurate analysis are not available.
2. The stress distribution in concrete member which is away from the anchorage and in the region of the anchorage will be ____________
a) Non uniform
b) Zero
c) Constant
d) Uniform
Answer: d
Clarification: The stress distribution in concrete member which is away from the anchorage and in the region of the anchorage will be uniform reasonably and complex respectively this is stated by st.venant’s principle, a product of the correction factor in each direction is used if a group of anchorage are closely spaced in two directions in case of computation of compressive stresses.
3. The tensile stresses which tend to split the concrete are placed in the transverse direction to the ____________
a) Edge of member
b) Span of member
c) Axis of member
d) End of member
Answer: c
Clarification: The tensile stresses which tend to split the concrete are placed in the transverse direction to the axis of the member which is the more important effect for the design, the spalling and longitudinal edge tension forces are induced when the location of centroid of all the tendons is considered to be outside the keen of the section.
4. The bursting tensile forces in end bocks with proportion Pi is given as ____________
a) Fbst = Pi(0.32-0.3(ypo/yo))
b) Fbst = fi(0.32-0.3(ypo/yo))
c) Fbst = Ti(0.32-0.3(ypo/yo))
d) Fbst = πi(0.32-0.3(ypo/yo))
Answer: a
Clarification: The bursting tensile force in end blocks with proportion pi is given as:
Fbst = Pi(0.32-0.3(ypo/yo)), ypo/yo < or equal 0.3, Fbsr/Pi = 0.23,
ypo/yo > or equal 0.3, Fbst/Pi = 0.11.
5. The longitudinal extent of the concrete member which is rectangular in cross section is ____________
a) Zero
b) Equal
c) Constant
d) Unity
Answer: b
Clarification: The longitudinal extent of the concrete member which is rectangular in cross section is at least equal to the largest transverse dimension of the cross section; the axial flexural beam analysis at one half the depth of section away from the loaded area enables to determine the longitudinal edge tension force.
6. The member within or ahead of the anchorage zone will not have any ____________
a) Strain
b) Stress
c) Discontinous
d) Torsion
Answer: c
Clarification: The member within or ahead of the anchorage zone will not have any discontinuities but they are subjected to stress during prestressing, the more detailed analysis is required such as strut-and-ties models or another analytical procedures to find out the spalling forces for larger spacing.
7. The main plate of the member in the anchorage zone has minimum edge distance of at least ____________
a) 2.0
b) 1.5
c) 1.8
d) 3.0
Answer: b
Clarification: The main plate of the member in the anchorage zone has minimum edge of at least 1.5 times the corresponding lateral dimension compressive stresses of the anchorage devices, the basic anchorage devices which satisfies below condition will have no additional check of compressive stresses of concrete fb< 0.7ϕf”ci(A/Ag).
8. The anchorage zone consists of how many devices?
a) 5
b) 3
c) 2
d) 1
Answer: d
Clarification: The anchorage zone consists of only one anchorage device or group of anchorages devices which are closely spaced, at the interface between the local zone and the general zone of the special anchorage devices ahead, the concrete compressive stresses.
9. If the centre to centre spacing of the anchorage devices will not exceed 1.5 times width then they are considered as ____________
a) Closely spaced
b) Gapely spaced
c) Farley spaced
d) Rectangular spaced
Answer: a
Clarification: If the center spacing of the anchorage devices will not exceed 1.5 times the width of these devices in the direction in which it is considered is treated as closely spaced devices and if the centre to centre spacing for multiple anchorages is less than 0.4 times the depth of section, the spalling forces will not be less than 2% of the total factored tendon force in any case.
10. If the anchor force points are towards the centroid, the center line of the member will not be greater than ____________
a) 15o
b) 10o
c) 20o
d) 25o
Answer: b
Clarification: If the anchorage force points are towards and away from the centroid of the section, the center line of the sectional member will not be greater than 20o and 5o respectively will be the angle of inclination of a tendon.