Test 40 - Analysis of Prestressed Concrete Sections

Question 1 ప్రశ్న 1

Which statement correctly describes the usual elastic analysis of an uncracked prestressed-concrete section at transfer or service?

A Only the external-load bending stress is considered and prestress is ignored B Prestress and external loads cannot be superimposed C Direct prestress, eccentric-prestress bending and external-load bending effects are superimposed using the appropriate prestressing force and section properties D The concrete stress is assumed uniform regardless of tendon eccentricity and external moment

Question 2 ప్రశ్న 2

A prestressing force P acts concentrically through the centroid of a concrete section of area A. What concrete stress does this prestress produce before considering external loads?

A Pe/Z only B Uniform compression P/A C Uniform tension P/A D M/Z only

Question 3 ప్రశ్న 3

A rectangular prestressed-concrete member is 300 mm wide and 500 mm deep. A concentric effective prestressing force of 1200 kN acts on the section. What uniform compressive stress is produced?

A 4 MPa B 5 MPa C 6 MPa D 8 MPa

Question 4 ప్రశ్న 4

For a symmetric beam section, take compression as positive. If a prestressing force P acts at eccentricity e below the centroid and Z is the section modulus at both extreme fibres, which pair gives the stresses due to prestress alone?

A Top: P/A - Pe/Z; Bottom: P/A + Pe/Z B Top: P/A + Pe/Z; Bottom: P/A - Pe/Z C Top: Pe/Z only; Bottom: P/A only D Top: P/A + Pe/Z; Bottom: P/A + Pe/Z

Question 5 ప్రశ్న 5

A 300 mm × 600 mm rectangular beam carries an effective prestressing force of 900 kN acting 100 mm below its centroid. Ignoring external loads, what are the top- and bottom-fibre stresses respectively, taking compression as positive?

A 5 MPa and 5 MPa B 10 MPa and 0 MPa C 0 MPa and 10 MPa D 5 MPa tension and 15 MPa compression

Question 6 ప్రశ్న 6

A 300 mm × 600 mm rectangular beam carries an effective prestressing force of 900 kN acting 100 mm below its centroid. A sagging external moment of 90 kN·m acts at the section. Taking compression as positive, what are the resultant top- and bottom-fibre stresses respectively?

A 0 MPa and 10 MPa B 5 MPa compression and 5 MPa compression C 10 MPa compression and 0 MPa D 5 MPa tension and 5 MPa compression

Question 7 ప్రశ్న 7

A 300 mm × 600 mm rectangular beam carries an effective prestressing force P = 900 kN acting 100 mm below the centroid. What are the resultant extreme-fibre stresses when a sagging external moment of 180 kN·m acts at the section, taking compression as positive?

A 0 MPa at top and 10 MPa compression at bottom B 5 MPa compression at both fibres C 10 MPa tension at top and zero at bottom D 10 MPa compression at top and zero stress at bottom

Question 8 ప్రశ్న 8

For the 300 mm × 600 mm beam with effective prestress P = 900 kN located 100 mm below the centroid, what is the maximum sagging external moment that can act before the bottom fibre first reaches zero stress under a specified no-tension condition?

A 180 kN·m B 90 kN·m C 270 kN·m D 360 kN·m

Question 9 ప్రశ్న 9

What is the kern or core of a concrete cross-section in the context of a compressive resultant?

A The region occupied by prestressing steel only B The portion of concrete that is ignored in section-property calculations C The region through which a compressive resultant may act without producing tensile stress anywhere on the section under linear elastic stress distribution D The region in which shear stress is necessarily zero

Question 10 ప్రశ్న 10

What are the kern distances from the centroid for a rectangular section of overall depth 600 mm about its horizontal centroidal axis?

A 50 mm above and below B 100 mm above and below C 150 mm above and below D 300 mm above and below

Question 11 ప్రశ్న 11

A 300 mm × 600 mm rectangular section carries a compressive prestressing force of 900 kN at an eccentricity of 80 mm below the centroid, with no external moment. What are the top- and bottom-fibre stresses respectively?

A 0 MPa and 10 MPa compression B 2 MPa tension and 12 MPa compression C 5 MPa and 5 MPa compression D 1 MPa compression and 9 MPa compression

Question 12 ప్రశ్న 12

A 300 mm × 600 mm rectangular section carries P = 900 kN at an eccentricity of 120 mm below the centroid, with no external moment. What stress state results?

A 1 MPa tension at the top and 11 MPa compression at the bottom B 1 MPa compression at the top and 9 MPa compression at the bottom C 5 MPa compression at both fibres D 11 MPa compression at the top and 1 MPa tension at the bottom

Question 13 ప్రశ్న 13

What is meant by the pressure line or thrust line in the elastic analysis of a prestressed-concrete member?

A The geometric centreline of every prestressing duct regardless of loading B The locus of points of maximum shear stress C The locus of the resultant compressive force in the concrete at successive sections D The line joining only the external load application points

Question 14 ప్రశ్న 14

Take downward tendon eccentricity as positive. A section has effective prestress P = 1000 kN at e = 120 mm below the centroid and a sagging external moment M = 80 kN·m. Using eC = e - M/P, where is the pressure line?

A 120 mm below the centroid B 40 mm below the centroid C 40 mm above the centroid D 200 mm below the centroid

Question 15 ప్రశ్న 15

Under the usual elastic force-concept idealization with the prestressing force P treated as constant, a tendon lies at eccentricity e below the centroid. What happens to the pressure line when a sagging external moment satisfies M = Pe?

A It moves to an infinite eccentricity B It must coincide with the tendon C It moves to the lower kern point D It passes through the centroid, producing only the uniform direct-compression component P/A in the ideal elastic stress representation

Question 16 ప్రశ్న 16

Under a specified no-tension elastic analysis, what does it imply if the pressure line lies outside the kern of the concrete section?

A At least one extreme fibre develops tensile stress under the corresponding linear stress distribution B The entire section must be in uniform compression C The tendon force is necessarily zero D The external bending moment must also be zero

Question 17 ప్రశ్న 17

For a symmetric section with a tendon located below the centroid, compression taken as positive and a positive sagging external moment M, which pair correctly gives the combined extreme-fibre stresses?

A Top = P/A + Pe/Z - M/Z; Bottom = P/A - Pe/Z + M/Z B Top = P/A + Pe/Z + M/Z; Bottom = P/A + Pe/Z + M/Z C Top = P/A - Pe/Z + M/Z; Bottom = P/A + Pe/Z - M/Z D Top = Pe/Z + M/Z; Bottom = Pe/Z - M/Z

Question 18 ప్రశ్న 18

Which statement correctly distinguishes section analysis at transfer from section analysis under service loading?

A The same prestressing force and the same loads must always be used at both stages B Transfer analysis uses the prestress existing at transfer and the loads acting at that stage, whereas service analysis uses effective prestress after relevant losses together with the applicable service loads C Prestress is ignored at transfer but included at service D External bending moment is never considered at service

Question 19 ప్రశ్న 19

Under the usual small-slope load-balancing idealization, a simply supported beam has a parabolic tendon with zero eccentricity at the supports, midspan eccentricity e below the centroid and approximately constant horizontal prestressing-force component P. What uniform equivalent upward load represents the tendon curvature?

A Pe/L B 4Pe/L^2 C Pe/L^2 D 8Pe/L^2

Question 20 ప్రశ్న 20

Under the usual small-slope load-balancing idealization, a simply supported prestressed beam has span L = 12 m, effective horizontal prestressing-force component P = 1200 kN and a parabolic tendon having zero eccentricity at the supports and 150 mm eccentricity below the centroid at midspan. What is the equivalent uniform upward load?

A 10 kN/m B 5 kN/m C 15 kN/m D 20 kN/m

Question 21 ప్రశ్న 21

Under the usual small-slope load-balancing idealization, a simply supported beam of span 10 m is to balance a uniform downward load of 12 kN/m using an effective horizontal prestressing-force component of 1500 kN and a parabolic tendon with zero eccentricity at the supports. What midspan eccentricity is required?

A 50 mm B 75 mm C 100 mm D 150 mm

Question 22 ప్రశ్న 22

A parabolic tendon produces an equivalent upward load of 10 kN/m on a simply supported beam, while the specified downward load being considered is also 10 kN/m. Under the ideal load-balancing assumptions and ignoring other loads, which statement is correct?

A The prestressing force itself becomes zero B The transverse-load bending effect is balanced, but the direct compressive effect of prestress remains C The beam has zero stress everywhere D The tendon ceases to require anchorage

Question 23 ప్రశ్న 23

Why is a parabolic tendon profile particularly suitable for balancing an approximately uniform gravity load on a simply supported beam under the usual small-slope load-balancing idealization?

A A parabolic profile makes the prestressing force increase linearly from zero to infinity B It eliminates all prestress losses C It produces only a concentrated upward force at midspan D With an approximately constant horizontal prestressing-force component, its constant curvature parameter produces an approximately uniform equivalent upward load

Question 24 ప్రశ్న 24

Which statement about a no-tension service condition in prestressed concrete is correct?

A It is a possible design requirement for an applicable service condition, but it should not be assumed that every prestressed member under every code classification must have zero concrete tension B All prestressed concrete must remain completely free of tensile stress under every conceivable load combination C A no-tension condition means the prestressing tendon carries no tension D No-tension analysis makes kern and pressure-line concepts irrelevant

Question 25 ప్రశ్న 25

A 400 mm × 800 mm rectangular section carries an effective prestressing force of 1600 kN acting 120 mm below the centroid and a sagging external moment of 256 kN·m. Taking compression as positive, what are the resultant top- and bottom-fibre stresses respectively?

A 5 MPa and 5 MPa B 3.5 MPa and 6.5 MPa C 6.5 MPa compression and 3.5 MPa compression D 10.5 MPa compression and 0.5 MPa tension

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