Test 39 - Losses of Prestress

Question 1 ప్రశ్న 1

Which statement correctly identifies the principal prestress losses that must be considered under the IS 1343 framework?

A Only creep and shrinkage need be considered B Only friction and anchorage slip need be considered C Creep, shrinkage, relaxation of steel, elastic shortening of concrete, friction and anchorage slip are relevant losses D Prestress is assumed constant after jacking

Question 2 ప్రశ్న 2

Which classification of prestress losses is generally correct?

A Immediate: creep, shrinkage and relaxation; time-dependent: friction and anchorage slip B Immediate: elastic shortening, friction and anchorage slip; time-dependent: creep, shrinkage and relaxation C Immediate: shrinkage only; time-dependent: elastic shortening only D All prestress losses are instantaneous

Question 3 ప్రశ్న 3

Which statement best distinguishes the prestressing force after immediate losses from the final effective prestressing force?

A They are necessarily identical B The final effective force is always greater than the jacking force C The force after immediate losses excludes friction but includes all long-term losses D The force after immediate losses is subsequently reduced by time-dependent losses to obtain the effective prestressing force

Question 4 ప్రశ్న 4

For a concentrically prestressed pre-tensioned member, what simplified expression gives the loss of steel stress due to elastic shortening at transfer?

A Delta fp = m fc, where m = Ep/Ec and fc is the adjacent concrete compressive stress B Delta fp = fc/m C Delta fp = Ep/fc D Delta fp = m/fc

Question 5 ప్రశ్న 5

A pre-tensioned member has Ep = 200000 MPa, Ec = 32000 MPa and concrete compressive stress of 10 MPa at the level of the tendon immediately after transfer. What is the elastic-shortening loss in prestressing steel stress?

A 31.25 MPa B 50.0 MPa C 62.5 MPa D 80.0 MPa

Question 6 ప్రశ్న 6

For post-tensioned tendons that are not stressed simultaneously, which approximate IS 1343 expression may be used for the progressive elastic-shortening loss?

A m fc B 0.5 m fc, using the concrete stress adjacent to the tendons averaged along their length C 2 m fc D fc/(2m)

Question 7 ప్రశ్న 7

For a sequentially post-tensioned member, take Ep/Ec = 6.25 and the relevant average concrete compressive stress adjacent to the tendons as 10 MPa. Using the half-product approximation, what is the elastic-shortening loss?

A 15.63 MPa B 25.00 MPa C 62.50 MPa D 31.25 MPa

Question 8 ప్రశ్న 8

Why is the elastic-shortening treatment of simultaneously stressed post-tensioned tendons different from that of tendons stressed one after another?

A When tendons are stressed simultaneously, there is no progressive loss in earlier tendons caused by later tendons being stressed B Concrete does not shorten in post-tensioning C Simultaneously stressed tendons have zero elastic modulus D Elastic shortening becomes a relaxation loss

Question 9 ప్రశ్న 9

What causes loss of prestress due to anchorage slip or draw-in in a post-tensioned member?

A Increase in concrete compressive strength B Relaxation of steel before jacking C Movement of the tendon or deformation of the anchorage while the tendon is being seated after stressing D Increase in tendon eccentricity under dead load

Question 10 ప్రశ్న 10

A straight post-tensioning tendon 20 m long experiences an anchorage draw-in of 4 mm. If Ep = 200000 MPa and the slip is assumed to produce uniform strain reduction over the full tendon length, what is the loss of steel stress?

A 20 MPa B 40 MPa C 80 MPa D 100 MPa

Question 11 ప్రశ్న 11

For the same anchorage draw-in and the same prestressing-steel modulus, how does the simple anchorage-slip stress loss vary with tendon length?

A It is independent of tendon length B It increases in direct proportion to tendon length C It varies with the square of tendon length D It is greater for a shorter tendon because Delta fp = Ep Delta/L

Question 12 ప్రశ్న 12

Which expression correctly represents frictional reduction of prestressing force along a post-tensioned tendon?

A Px = P0 exp[-(mu alpha + kx)] B Px = P0 exp[+(mu alpha + kx)] C Px = P0(mu alpha + kx) D Px = P0/(mu alpha - kx)

Question 13 ప్రశ్న 13

In the friction-loss expression Px = P0 exp[-(mu alpha + kx)], what do the terms mu alpha and kx primarily represent?

A Elastic shortening and creep respectively B Shrinkage and relaxation respectively C Curvature friction and wobble friction respectively D Anchorage slip and concrete crushing respectively

Question 14 ప్రశ్న 14

A tendon is jacked to 1500 kN from one end. At a section 20 m from the jack, mu = 0.20, cumulative angular change alpha = 0.30 rad and k = 0.0015 per metre. Using Px = P0 exp[-(mu alpha + kx)], what are the tendon force and friction loss approximately?

A 1500 kN and 0 kN B 1371 kN and 129 kN C 1250 kN and 250 kN D 1096 kN and 404 kN

Question 15 ప్రశ్న 15

What is an important structural effect of stressing a long post-tensioning tendon from both ends rather than from only one end?

A It eliminates creep of concrete B It eliminates shrinkage of concrete C It makes the prestressing steel incapable of relaxation D It reduces the maximum distance over which friction accumulates from a live end and can improve the tendon-force distribution

Question 16 ప్రశ్న 16

Which statement correctly describes loss of prestress due to creep of concrete under IS 1343?

A Creep loss is calculated only from transient live-load stress B Creep loss is associated with sustained concrete stresses from permanently applied loads including prestress, while short-duration stresses may be ignored C Creep is an immediate anchorage phenomenon D Creep increases the prestressing-steel stress with time

Question 17 ప్రశ్న 17

For a simplified bonded member with constant sustained concrete stress fc at tendon level, creep coefficient phi and modular ratio m = Ep/Ec, which expression gives the corresponding prestressing-steel stress loss?

A Delta fp = fc/(m phi) B Delta fp = m fc/phi C Delta fp = m phi fc D Delta fp = Ep/(phi fc)

Question 18 ప్రశ్న 18

For a bonded prestressed member, Ep = 200000 MPa, Ec = 32000 MPa, creep coefficient phi = 1.6 and sustained concrete compressive stress at tendon level fc = 10 MPa. Using Delta fp = (Ep/Ec)phi fc, what is the creep loss?

A 100 MPa B 62.5 MPa C 80 MPa D 160 MPa

Question 19 ప్రశ్న 19

Which statement correctly represents the IS 1343 treatment of prestress loss due to shrinkage of concrete?

A Shrinkage loss is always exactly 30 MPa for every member B Shrinkage loss is treated as an anchorage-slip loss C Shrinkage has no effect on bonded prestressing steel D The steel stress loss is obtained from Ep times the applicable concrete shrinkage strain calculated using the current shrinkage provisions

Question 20 ప్రశ్న 20

The residual shrinkage strain applicable to a prestressed member has been calculated as 250 microstrain. If Ep = 200000 MPa, what loss of prestressing-steel stress results?

A 25 MPa B 50 MPa C 75 MPa D 100 MPa

Question 21 ప్రశ్న 21

Which statement most accurately describes relaxation loss in prestressing steel?

A It is a gradual reduction of steel stress with time under sustained strain and depends on steel type, initial stress level, age and temperature B It is the instantaneous crushing of concrete beneath an anchorage C It is caused only by duct curvature D It occurs only when concrete is completely unrestrained

Question 22 ప్రశ్న 22

For a low-relaxation prestressing steel stressed initially at 0.7fp, take the IS 1343 1000-hour relaxation value as 2.5 percent and use the code provision that the tabulated value may be multiplied by 3 for long-term relaxation. If the initial steel stress is 1200 MPa, what long-term relaxation loss is obtained?

A 30 MPa B 60 MPa C 90 MPa D 120 MPa

Question 23 ప్రశ్న 23

A tendon has area Ap = 1500 mm^2 and experiences a prestressing-steel stress loss of 50 MPa from one specified loss mechanism. What is the corresponding loss of prestressing force?

A 25 kN B 50 kN C 60 kN D 75 kN

Question 24 ప్రశ్న 24

A calculation states that the tendon force P0 is already the force after friction, anchorage slip and elastic-shortening losses. What is the correct procedure when subsequently calculating the final effective prestress?

A Subtract friction, anchorage slip and elastic shortening a second time B Apply only the additional distinct time-dependent losses, with any required interaction treated consistently C Restore the immediate losses before calculating creep D Ignore creep, shrinkage and relaxation

Question 25 ప్రశ్న 25

For an objective calculation, an initial prestressing-steel stress is 1400 MPa. Distinct immediate losses are 100 MPa from friction, 30 MPa from anchorage slip and 50 MPa from elastic shortening; subsequent distinct losses are 80 MPa from creep, 40 MPa from shrinkage and 60 MPa from relaxation. Neglect interaction among the stated losses. What are the final effective steel stress and total percentage loss?

A 1040 MPa and approximately 25.7 percent B 1220 MPa and approximately 12.9 percent C 860 MPa and approximately 38.6 percent D 1180 MPa and approximately 15.7 percent

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