This set of Prestressed Concrete Structures Multiple Choice Questions & Answers (MCQs) focuses on “Analysis by Zielinski and Rowe”.
1. The Zielinski and Rowe conducted experiments on concrete prismatic specimens using the technique?
a) Surface stress
b) Surface strain
c) Surface tension
d) Surface edge
Explanation: Experimental investigation on concrete prismatic specimen was conducted by Zielinski and Rowe using the technique of surface strain measurements, if groups of anchorages are encountered the end block is divided into a series of symmetrically loaded prisms and each prism is analyzed for bursting tensile forces using the recommended Indian code provision expressions.
2. The parameters considered for concrete prisms are:
c) Cross sectional area
d) End block
Explanation: The concrete prisms act as end blocks and the investigations were carried out on parameters like cable duct or hole, the ratio of loaded to cross sectional area, the cracking, type of anchorages and ultimate loads.
3. The distribution of transverse stress and ultimate load of the end block is not effected by:
a) Anchorage material
b) Curing concrete
c) Tendons applied
d) Jacking provided
Explanation: The studies revealed that the distribution of transverse stress and ultimate load of the end block is not affected by: the anchorage being either embedded or external, the material of the anchorage, the method of anchoring the wires.
4. The Zielinski and Rowe developed empirical relations for computation of:
a) Maximum transverse tensile stress
b) Minimum transverse tensile stress
Explanation: Zienlinski and Rowe developed empirical relations to compute the maximum transverse tensile stress and the bursting tension and when an end block is subjected to a concentrated load at the end face and at equal distances to 0.5ẙ the distribution of transverse stress is found to be maximum.
5. The equation for maximum tensile stress, fmax is given as:
Explanation: The maximum tensile stress, fvmax = fc(0.98-0.825(ypo/yo) which is valid for ypo/yo = 0.3 to 0.7 bursting tension, Fbst = pk(0.48-0.4(ypo/yo), (ypo/yo) = ratio of sides of loaded area to bearing area of the prism, fv = transverse tensile stress, fc = average compressive stress in the prism, pk = applied compressive force on the end block.
6. The creating bursting tension is given by:
Explanation: When allowance is provided for tension taken by concrete, the creating bursting tension is given by Fbst, corred = Fbst(3-(fv/fv,max)2), ft = permissible tensile strength of concrete.
To resist bursting tension, the reinforcement should be arranged between 0.2y0 and 2y0 providing the maximum intensity of stress.
7. Estimate the position and magnitude of the maximum transverse tensile stress and bursting tension for the end block with a concentric anchor force of 100kn using Rowe’s method?
Explanation: pk = 100kn, 2ypo = 50mm, 2ypo = 100mm, ypo/yo =0.5, fc = (100×103/100×100) = 10n/mm2, fv(max) = fc(0.98-0.825(ypo/y0)) = 10(0.98-0.825(0.5)) = 5.68n/mm2.
8. The end block and a prestressed beam, 200mm wide and 300mm deep, has two Freyssinet anchorages (100mm diameter) with their centre at 75mm from the top and bottom of the beam. The force transmitted by each anchorage being 200kn, estimate the maximum tensile and bursting tension?
Explanation: Anchorage diameter = 100mm, equivalent side of square 2ypo = (π/4×1002) = 89mm, side of the surrounding prism 2yo = 150mm, ypo /yo = 0.593, average compressive stress fc = (200×103/150×150) = 8.9n/mm2, Tensile stress fv(max) = 8.9(0.98-0.825(0.593)) = 4.45n/mm2, Transverse tension Fbst = 200×103(0.48-0.4(0.593)) = 50000n = 50kn.
9. In case of large bridge girders with massive end block, for computation of bursting tension end block is divided into:
Explanation: In the case of large bridge girders with massive end block supporting multiple anchorages, the end block is divided into a series of symmetrically loaded prisms for the computation of the bursting tension.
10. The design strength assumed to act to sustain bursting tension is:
Explanation: The reinforcement is designed to sustain this bursting tension and it is assumed to act at its design strength of 0.87fy and the stress however is limited to value corresponding to a strain of 0.1% when the concrete cover is less than 50mm.
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