BHARATHIDASAN ENGINEERING COLLEGE ...library.bec.ac.in/kbc/FAQ BEC/CIVIL/7 SEM/PRESTRESSED...BHARATHIDASAN ENGINEERING COLLEGE DEPARTMENT OF CIVIL ENGINEERING FAQ CE 6702 PRESTRESSED

BHARATHIDASAN ENGINEERING COLLEGE

DEPARTMENT OF CIVIL ENGINEERING

FAQ

CE 6702 PRESTRESSED CONCRETE STRUCTURES

1 Prepared By:Mr.A.Sathiyamoorthy, M.E., AP/Civil

UNIVERSITY QUESTIONS

PART A

UNIT 1: INTRODUCTION – THEORY AND BEHAVIOUR

1. List the loss of prestress. R-13-NOV2016

2. Define axial prestressing. R-13-NOV2016

3. What is the need for the use of high strength concrete and tensile steel in prestressed concrete?

R-13-MAY2017 4. Why high strength steel is essential for prestressed concrete? R-08-MAY&NOV2016

5. List down the factors that influence the deflection of prestressed concrete members.

R-08-MAY&NOV2016

6. What do you understand by unbounded tendon? R-08-MAY&NOV2016

7. List out the advantages of prestressed concrete. R-08 MAY-2015

8. What is concordant prestressing? R-08 MAY-2015

9. What are the classifications of prestressed concrete structures? R-08 MAY-2014

10. Define bonded and non-bonded prestressing concrete. R-08 MAY-2014

11. What is pressure or thrust line? R-08 MAY-2013

12. List out the losses of pretensioned and post tensioned prestress. R-08 MAY-2013

13. What is meant by pretensioned and post tensioned concrete? R-08 MAY-2012

14. Define load balancing concept. R-08 MAY-2012

15. Define pre tensioning and post tensioning. R-08 NOV-2012

16. Define creep strain. R-08 NOV-2012

17. State the advantages of pre stressing concrete. R-08 NOV-2013

18. Name the two materials in prestressing. R-08 NOV-2014

19. Draw the various profiles of the tendons. R-08 NOV-2015

20. Define short term and long term deflection. R-08 NOV-2014

21. Distinguish between concentric and eccentric prestressing. R-08 NOV-2016

22. Explain why steel with a low yield stress is not used in prestressed construction.

UNIT 2: DESIGN FOR FLEXURE AND SHEAR

1. What are the different types of flexural failure modes observed in PSC beams? R-13-NOV2016

2. What is strain compatibility method? R-13-NOV2016

3. How will you classify a structure as Type II or class 2 structure? R-13-MAY2017

4. How to calculate ultimate shear strength of uncracked section in flexure as per IS 1343?

R-13-MAY2017 5. List the types of flexural failure.

6. Write the design procedure for strain compatibility method. R-08 MAY-2015

7. List the types of shear cracks. R-08 MAY-2015

8. List out the assumptions on the compatibility of strain. R-08 MAY-2014

9. Define shear stress and principal stress. R-08 MAY-2014

10. List the types of shear cracks. R-08 MAY-2013

11. Define cracking load. R-08 MAY-2013

12. What is effective reinforcement ratio? R-08 MAY-2012

13. Draw two layouts of post tensioned beam. R-08 MAY-2012

14. Draw two layouts of pre tensioned beam. R-08 NOV-2012



FAQ



15. What are the ways of improving the shear resistance a prestressed concrete beam?

R-08 NOV-2014

UNIT 3: DEFLECTION AND DESIGN OF ANCHORAGE ZONE

1. Define the term end block. R-13-NOV2016

2. What is meant by bursting force? R-13-NOV2016

3. Why control of deflection is very essential? R-13-MAY2017

4. Mention the functions of end block. R-13-MAY2017

5. Define anchorage. R-08 MAY-2015

6. Sketch the loop reinforcement, hairpin bars in end blocks. R-08 MAY-2015

7. State any two function of end block. R-08 MAY-2014

8. Discuss limiting zone for prestressing force. R-08 MAY-2014

9. State Mohr’s theorems. R-08 MAY-2013

10. Define transmission length. R-08 MAY-2013

11. What is the zone of transmission in end block of prestressed concrete structure? R-08 MAY-2012

12. Enumerate effect of tendon profile on deflection? R-08 NOV-2012

13. Enumerate stress distribution in end block. R-08 NOV-2014

14. Methods to study the stress distribution in end block. R-08 NOV-2013

15. Draw the stress distribution diagram for single anchor plate and double anchor plate in end block.

UNIT 4: COMPOSITE BEAMS AND CONTINUOUS BEAMS

1. How to achieve compositeness between precast and cast in situ part? R-13-NOV2016

2. Distinguish between propped and unpropped construction methods. R-13-NOV2016

3. What are the advantages of composite construction in PSC? R-13-MAY2017

4. What is unpropped construction in composite PSC construction? R-13-MAY2017

5. Define propped construction. R-08-MAY&NOV2016

6. How to achieve compositeness between precast and cast in situ part? R-08-MAY&NOV2016

7. List the advantages of composite prestressed concrete construction. R-08 MAY-2015

8. Define modular ratio. R-08 MAY-2015

9. State the advantages of composite construction. R-08 MAY-2014

10. What is meant by composite construction of prestressed and in situ concrete? R-08 MAY-2014

11. Define the term reduction factor. R-08 MAY-2013

12. Define unpropped construction. R-08 NOV-2014

13. What is meant by shear connectors? R-08 NOV-2013

14. What are the disadvantage of prestressed continuous beams? R-08 NOV-2012

15. What are the various methods of achieving continuity in continuous beam?



FAQ



UNIT 5: MISCELLANEOUS STRUCTURES

1. What is the stress induced in concrete due to circular prestressing? R-13-NOV2016

2. What are the design criteria for prestressed concrete pipes? R-13-NOV2016

3. List the different types of prestressing adopted for the walls of a water tank. R-13-MAY2017

4. Define circular prestressing. R-13-MAY2017

5. Define partial prestressing. R-08-MAY&NOV2016

6. How are the tanks classified based on the joint? R-08-MAY&NOV2016

7. What are the different types of joints used between the walls and floor slab of the prestressed

concrete tank? R-08 MAY-2015

8. Write the merits and demerits of partial prestressing. R-08 MAY-2015

9. Define vertical prestressing. R-08 MAY-2014

10. Principle of circular prestressing. R-08 MAY-2014

11. Write an expression for vertical moment. R-08 MAY-2013

12. Write a short note on tank floor. R-08 MAY-2013

13. Define longitudinal prestressing. R-08 NOV-2012

14. What is the main function of longitudinal prestressing? R-08 NOV-2012

15. What is circumferential prestressing? R-08 NOV-2014

16. Differentiate between prestressed cylindrical and non cylindrical pipes. R-08 NOV-2014

17. State the advantages of partially prestressing. R-08 NOV-2015

18. Define degree of prestressing. R-08 NOV-2015

19. What are needs of prestressing compression member?

20. Sketch the arrangement of tendons and anchorages in circular prestressing of concrete pipes.

PART B

UNIT 1: INTRODUCTION – THEORY AND BEHAVIOUR

1. A rectangular prestressed beam 150mm wide and 300mm deep is used over an effective span of

10m. The cable with zero eccentricity at the supports and linearly varying to 50mm at the centre

carries an effective prestressing force of 500kN. Find the magnitude of the concentrated load

located at the centre of the span for the following conditions at the centre of span section:

A) If the load counteracts the bending effect of the prestressing force(neglecting self weight of

beam) and

B) If the pressure line passes through the upper kern of the section under the action of the

external load, self weight and prestress. 4.11 R-13-NOV2016

2. A prestressed concrete beam, 200mm wide and 300mm deep is used over an effective span of 6m

to support an imposed load of 4kN/m. The density of concrete is 24kN/m3. Find the magnitude of

the eccentric prestressing force located at 100mm from the bottom of the beam which would

nullify the bottom fibre stress due to loading. R-13-NOV2016

3. A concrete beam with a rectangular section 120mm wide and 300mm deep, is stressed by a

straight cable carrying an effective force of 200kN. The span of the beam is 6m. The cable is

straight with a uniform eccentricity of 50mm. If the beam has an uniformly distributed load of

6kN/m. Ec=38kN/mm2. Estimate the deflection at centre of span for the following case:

a) Prestress + self weight of the beam

b) Prestress + self weight of the beam + live load. R-13-NOV2016



FAQ



4. A pretensioned beam 200mmX300mm is prestressed by 10 wires each of 7mm diameter, initially

stressed to 1200 MPa with their centroids located 100mm from the soffit. Estimate the final

percentage loss of stress due to elastic deformation, creep, shrinkage and relaxation. Assume

relaxation of steel stress = 60MPa, Es=210GPa, Ec=36.9GPa, creep coefficient = 1.6 and residual

shrinkage strain = 3x10-4. R-13-NOV2016

5. A PSC beam supports an imposed load of 3kN/mm over a simply supported span of 10m. the

beam has I section with an overall depth of 450mm. the thickness of flange and web are 75mm

and 100mm respectively. The flange width of the beam is 200mm. It is constructed with a

concrete having unit weight of 24kN/m3. The beam is prestressed with an effective prestressing

force of 350kN at a suitable eccentricity such that the resultant stress at the soffit of the beam at

mid span is zero. Find the eccentricity required for the force. Also calculate the stresses at the top

of the section. R-13-MAY2017

6. A PSC beam of 250mm wide and 400mm deep and 12m span is prestressed with 10 wires of

7mm dia located at a constant eccentricity of 75mm and carrying an initial stress of 1200N/mm2.

The modulus of elasticity of steel and concrete are 210kN/mm2 and 38kN/mm2 respectively. The

relaxation of stress in steel is assumed as 6% of initial stress. Take creep coefficient as 1.8 and

slip at anchorage as 1mm. The shrinkage of concrete is 350x10-6 for pretensioning and 160x10-6

for post tensioning. Take the frictional coefficient for wave effect as 0.0012 per m. Calculate the

% of loss of stress if

a) The beam is pretensioned

b) The beam is post tensioned. R-13-MAY2017

7. Explain the systems and methods of prestressing with neat sketches. R-08-MAY&NOV2016

8. A PSC beam of span 8m having a rectangular section of 150mmX300mm. The team is

prestressed by a parabolic cable having an eccentricity of 75mm below the centroidal axis at the

center of the span and an eccentricity of 25mm above the cenroidal axis at the support sections.

The initial force in the cable is 350kN. The beam supports three concentrated loads of loads of

10kN each at intervals of 2m. Ec=38kN/mm2.

a) Neglecting losses of prestress, estimate the short term deflection due to (prestress + self

weight)

b) Allowing for 20% loss in prestress, estimate long term deflection under(prestress + self

weight + live load) assume creep co-efficient as 1.80. R-08-MAY&NOV2016

9. A prestressed concrete beam of section 120 mm wide by 300 mm deep is used over an

effective span of 6 m to support a uniformly distributed load of 4 kN/m, which includes the

self-weight of the beam. The beam is prestressed by a straight cable carrying a force of 180 kN

and located at eccentricity of 50 mm. Determine the location of the thrust line in the beamand

plot its position at quarter and central span section. R-08 MAY-2015

10. A rectangular prestressed beam 150 mm wide and 300 mm deep is used over an effective span of

10 m. The cable with zero eccentricity at the supports and linearly varying to 50 mm at the centre

carries an effective prestressing force of 500 kN. Find the magnitude of the concentrated load

located at the centre of the span for the following conditions at the centre of span section:

a) If the load counteracts the bending effect of the prestressing force (neglecting self-weight

of beam) and

b) If the pressure line passes through the upper kern of the section under the action of the external

load, self-weight and prestress. R-08 MAY-2015

11. A prestressed concrete beam, 200 mm wide and 300 mm deep is used over an effective span of

6 m to support an imposed load of 4 kN/m. the density of concrete is 24 kN/m3. Find the

magnitude of the eccentric prestressing force located at 100 mm from the bottom of the beam

which would nullify the bottom fibre stress due to loading. And also find the magnitude of the



FAQ



concentric prestressing force necessary for zero fibre stress at the soffit when the beam is fully

loaded. R-08 MAY-2014

12. A prestressed concrete beam, 200mmX300mm, is prestressed with wires(area = 320 mm2)

located at a constant eccentricity of 50mm and carrying an initial stress of 1000 N/mm2. The span

of the beam is 10m. Calculate the percentage loss of stress in wires if

(a) the beam is pretensioned, and

(b) the beam is post tensioned, using the data: Es= 210 KN/mm2, Ec= 45 KN/mm2, relaxation of steel

stress o 5% of the initial stress, φ = 1.6, anchorage slip = 1mm, shrinkage of concrete = 300X10-6

for pre & 200X10-6 for post tensioning. & frictional coefficient for wave effect = 0.0015/m. book

13. A prestressed concrete beam of section 150mm wide by 350mm deep is used over an effective

span of 8m to support a uniformly distributed load of 6KN/m, which includes the self weight of

the beam. The beam is prestressed by a straight cable carrying a force of 200KN and located at an

eccentricity of 50mm. Determine the location of thrust-line in the beam and plot its position at

quarter and central span section. R-08 MAY-2013

14. A rectangular concrete beam 100mm wide by 250mm deep spanning over 8m is prestressed by a

straight cable carrying an effective prestressing force of 250kN located at an eccentricity of

40mm. The beam supports a live load of 1.2kN/m.

a) Calculate the resultant stress distribution for the centre-of-span cross-section of the beam

assuming the density of concrete as 24kN/m3. Book R-08 MAY-2013

b) Find the magnitude of the prestressing force with an eccentricity of 40mm which can balance

the stresses due to dead and live loads at the soffit of the centre span section.

15. A rectangular concrete beam of cross section 30cm deep and 20cm wide is prestressed by means

of 15 wires of 5mm diameter located 6.5cm from the bottom of the beam and 3 wires of diameter

of 5mm, 2.5 cm from the top. Assuming the prestress in the steel as 840N/mm2, calculate the

stresses at the extreme fibres of the mid span section when the beam is supporting its own weight

over a span of 6m. If a uniformly distributed live load of 6kN/m is imposed, evaluate the

maximum working stress in concrete. The density of concrete is 24kN/m3. R-08 NOV-2014

16. An unsymmetrical I-section beam is used to support an imposed load of 2kN/m over a span of

8m. The sectional details are top flange, 300mm wide and 60mm thick; bottom flange, 100mm

wide and 60mm thick; thickness of the web=80mm; overall depth of the beam=400mm. At the

centre of the span, the effective prestressing force of 100kN is located at 50mm from the soffit of

the beam. Estimate the stresses at the centre-of-span section of the beam for the following load

condition:

a) Prestress + self-weight

b) Prestress + self-weight + live load. R-08 NOV-2014

17. A psc beam of section 200mm wide by 300mm deep is used over an effective span of 6m to

support an imposed load of 4kN/m. The density of concrete is 24kN/m3. At the centre-of-span

section of the beam, find the magnitude of

a) the concentric prestressing force necessary for zero fibres stress at the soffit when the beam is

fully loaded

b) the eccentricity prestressing force located 100mm from the bottom of the beam which would

nullify the bottom fibres stresses due to loading. R-08 NOV-2015

18. A psc beam with a rectangular section 120mm wide by 300mm deep supports a udl of 4kN/m,

which includes the self-weight of the beam. The effective span of the beam is 6m. The beam is

concentrically prestressed by a cable carrying a force of 180kN. Locate the position of the

pressure line in the beam. R-08 NOV-2015

19. A psc beam of section 120mm wide by 300mm deep is used over an effective span of 6m to

support a udl of 4kN/m, which includes the self-weight of the beam. The beam is prestressed by a



FAQ



straight cable carrying a force of 180kN and located at an eccentricity of 50mm. Determine the

location of the thrust line in the beam and plot its position at quarter and central span section.

20. A rectangular concrete beam 250mm wide by 300mm deep is prestressed by a force of 540kN at

a constant eccentricity of 60mm. The beam supports a concentrated load of 68kN at the centre of

a span of 3m. Determine the location of the pressure line at the centre, quarter span and support

sections of the beam. Neglect the self-weight of the beam. R-08 NOV-2011

21. A rectangular concrete beam 300mm wide and 800mm deep supports two concentrated loads of

20kN each at the third point of a span of 9m.

a) suggest a suitable cable profile. If the eccentricity of the cable profile is 100mm for the middle

third portion of the beam, calculate the prestressing force required to balance the bending effect

of the concentrated loads(neglect the self-weight of the beam).

b) for the same cable profile, find the effective force in the cable if the resultant stress due to sefl-

weight, imposed loads and prestressing force is zero at the bottom fibre of the mid-span section.

Assume Dc=24kN/m3.

UNIT 2: DESIGN FOR FLEXURE AND SHEAR

1. A pretension T-section has a flange 1200mm wide and 150mm thick. The width and depth of rib

are 300mm and 1500mm respectively. The high tensile steel has an area 4700mm2 and is located

at an effective depth of 1600mm. If the characteristic cube strength of the concrete and the tensile

strength of steel are 40N/mm2 and 1600N/mm2 respectively, calculate the flexural strength of the

T- section. Ex 7.5 R-13-NOV2016

2. Explain the various methods of flexural failure encountered in prestressed concrete member.

R-13-NOV2016

3. Design a simply supported type I prestressed beam with MT=435kNm (including an estimated

MSW=55kNm). The height of the beam is restricted to 920mm. The prestress at transfer fpo=

1035N/mm2 at transfer and 11.0 N/mm2 at service. The properties of the prestressing strands are

given below:

a) Type of prestressing tendon 7 wire strand

b) Nominal diameter = 12.8mm

c) Nominal area = 99.3 mm2. R-13-NOV2016

4. A post tensioned prestressed beam of rectangular section 300mm wide is to be designed for an

imposed load of 14kN/m over a span of 10m. The stress in concrete must not exceed 17N/mm2 in

compression and 1.4N/mm2 in tension at any time. The loss of prestress may be assumed as 18%.

Calculate

a) The minimum possible depth of the beam

b) The minimum prestressing force required for the given section

c) The minimum eccentricity for the above prestressing force. R-13-MAY2017

5. Design a post tensioned girder for a span of 22m to support a live load of 6kN/m. The M50 grade

mix is used for construction with a permissible compressive stress of 35N/mm2, and a tensile

stress of 1.7N/mm2. The permissible stress in concrete shall not exceed 17.5N/mm2 and

16.5N/mm2 in compression and 1.15N/mm2 and zero in tension for both transfer and working

loads respectively. Take the modulus of elasticity of concrete as 38kN/mm2. The loss of prestress

at transfer is15%. High tensile strength wires of 8mm dia and having a characteristic tensile

strength of 1600N/mm2 should be used for prestressing the member. The modulus of elasticity of

wires is 210kN/mm2. Design the beam as a class 1 structure and carryout the flexural and shear

check alone. R-13-MAY2017



FAQ



6. A post-tensioned bridge girder with unbonded tendons is of box section of overall dimensions

1200mm wide by 1800mm deep, with wall thickness of 150mm. The high-tensile steel has an

area of 4000mm2 and is located at an effective depth of 1600mm. The effective prestress in steel

after all losses is 1000N/mm2 and the effective span of the girder is 24m. If fck=40N/mm2 and

fp=1600N/mm2, estimate the ultimate flexural strength of the section. R-08 MAY-2015

7. A pretensioned, T-section has a flange 1200mm wide and 150mm thick. The width and depth of

the rib are 300mm and 1500mm respectively. The high tensile steel has an area of 4700mm2 and

is located at an effective depth of 1600mm. If the characteristics cube strength of the concrete and

the tensile strength of steel are 40 N/mm2 and 1600N/mm2, respectively, calculate the flexural

strength of the T-section. R-08 MAY-2015

8. A pre tensioned concrete beam (span=10m) of rectangular section, 120mm wide and 300mm

deep, is axially prestressed by a cable carrying an effective force of 180kN. The beam supports a

total udl of 5kN/m which includes the self-weight of the member. Compare the magnitude of the

principal tension developed in the beam with and without the axial prestress. R-08 MAY-2014

9. A rectangular concrete beam of c/s 150mmX300mm is ss over a span of 8m and is prestressed by

means of a symmetric parabolic cable, at a distance of 75mm from the bottom of the beam at

amid span and 125mm from the top of the beam at support sections. If the force in the cable is

350kN and Ec=38kN/mm2, calculate a) the deflection at mid span when the beam is supporting its

own weight, b) the concentrated load which must be applied at mid span to restore it to the level

of supports. R-08 MAY-2014

10. A pretensioned, T-section has a flange which is 300mm wide and 200mm thick. The rib is

150mm wide by 350mm deep. The effective depth of the c/s is 500mm. Given Ap=200mm2,

fck=50N/mm2 and fp=1600N/mm2, estimate the ultimate moment capacity of the T-section using

the IS codes. R-08 MAY-2013

11. A pretensioned psc beam having a rectangular section, 150mm wide and 350mm deep, has an

effective cover of 50mm. If fck=40N/mm2, fp=1600N/mm2, and the area of prestressing steel

Ap=461mm2, calculate the ultimate flexural strength of the section using IS:1343 code provisions.

12. A pretensioned, T-section has a flange which is 300mm wide 200mm thick. The rib is 150mm

wide by 350mm deep. The effective depth of the cross section is 500mm. Given Ap=200mm2,

fck=50N/mm2 and fp=1600N/mm2, estimate the ultimate moment capacity of the T-section using

the IS codes. R-08 MAY-2013

13. A post tensioned prestressed concrete Tee beam having a flange width of 1200mm and flange

thickness of 200mm, thickness of web being 300mm is prestressed by 2000mm2 of high-tensile

steel located at an effective depth of 1600mm. If fck=40N/mm2 and fp=1600N/mm2, estimate the

ultimate flexural strength of the unbonded tee section, assuming span/depth ratio as 20 and

fpe=1000N/mm2. R-08 NOV-2015

14. A psc beam (span=10m) of rectangular section, 120mm wide and 300mm deep, is axially

prestressed by a cable carrying an effective force of 180kN. The beam supports a total udl of

5kN/m which includes the self weight of the member. Compare the magnitude of the principal

tension developed in the beam with and without the axial prestress. R-08 NOV-2016



FAQ



UNIT 3: DEFLECTION AND DESIGN OF ANCHORAGE ZONE

1. The end block of a post tensioned PSC beam 300mm wide and 300mm deep is subjected to a

concentric anchorage force of 800kN by a Freyssinet anchorage system of area 11000mm2.

Design and detail the anchorage reinforcement for the end block. R-13-NOV2016

2. The end block of a prestressed concrete beam, rectangular in shape, 100mm wide and 200mm

deep. The prestressing force of 100kN is transmitted to concrete through distribution plate,

100mm wide and 50mm deep, concentrically located at ends. Using, Guyon’s method, compute

the position and magnitude of maximum tensile stress and bursting tension for the end block with

concentric anchor force of 100kN. R-13-NOV2016

3. Estimate the transmission length at the end of a pretensioned beam prestressed by 7mm diameter

wires. Assume the cube strength of concrete at transfer as 42N/mm2. R-13-NOV2016

4. A ssb is having dimensions 200mmX450mm is post tensioned with two cables of each having

area of 150mm2. The first cable is parabolic with an eccentricity of 70mm at mid span and zero at

support whereas the second cable is having straight profile with uniform eccentricity of 70mm

throughout. The initial prestress applied to each cable is 1100mm2. The modulus of elasticity of

concrete is 40kN/mm2. The length of beam is 7.5m carry two point loads of 25kN at 1/3rd of span.

Determine

a) The instantaneous deflection at the centre of span

b) The deflection at the centre of span after two years, assuming 18% loss in prestress and

effective modulus of elasticity to be 3/4th of the short term modulus of elasticity.

R-13-MAY2017 5. Briefly explain about the stress distribution in anchorage zone of a post tensioned prestressed

member. R-13-MAY2017

6. Write short note on: Magnel’s method, Guyon’s method; IS code Provisions. R-13-MAY2017

7. The end block of a post tensioned bridge girder is 500mm wide by 1000mm deep. Two cables,

each comprising 90 high tensile wires of 7mm dia. Are anchored using square anchor plates of

side length 400mm with their centres located at 500mm from the top and bottom of the edges of

the beam. The jacking force in each cable is 4000kN. Design a suitable anchorage zone

reinforcement using Fe415 grade HYSD bars conforming to IS:1343 provision.

R-08-MAY&NOV2016

8. A psc beam of ⌷ section 120mmX300mm, spans over 6m. The beam is prestressed by a straight

cable carrying an effective force of 200kN at an eccentricity of 50mm. E = 38 KN/mm2.

Compute (a) deflection under (prestress + self weight) & (b) find magnitude of udl which will

nullify the deflection due to prestress and self weight. 6.2 R-08 MAY-2015

9. A post tensioned roof girder spanning over 30m has an unsymmetrical I section with a second

moment of area of section of 72490 X 106 mm4 and overall depth of 1300mm. The eccentricity of

the group of parabolic cables at the centre of span is 580mm towards the soffit and 170mm

towards the top of beam at supports. The cables carry an initial prestressing force of 3200kN. The

self weight of the girder is 10.8kN/m and the l.l. on the girder is 9kN/m. E = 38 KN/mm2. φ =

1.6, the total loss of prestress is 15%. Estimate (a) deflection (prestress + self weight) and (b)

resultant maximum long term deflection allowing for loss of prestress & creep of concrete. 6.4

10. A rectangular concrete beam of cross section 150mm wide and 300mm deep is simply supported

over a span of 8m and is prestressed by means of a symmetric parabolic cable, at a distance of

75mm from the bottom of the beam at mid span and 125mm from the top of the beam at support

sections. If the force in the cable is 350kN and the modulus of elasticity of concrete is 38kN/mm2,

calculate 6.3 R-08 MAY-2014

a) The deflection at mid-span when the beam is supporting its own weight



FAQ



b) The concentrated load which must be applied at mid span to restore it to the level of supports.

UNIT 4: COMPOSITE BEAMS AND CONTINUOUS BEAMS

1. A precast pretensioned beam of rectangular section has a breadth of 100mm and a depth of

200mm. The beam with an effective span of 5m is prestressed by tendons with their centroids

coinciding with the bottom kern. The initial force in the tendons is 150kN. The loss of prestress

may be assumed to be 15 percent. The beam is incorporated in a composite T-beam by casting a

top flange of breadth 400 mm and thickness 40 mm. If the composite beam supports a live load of

8 KN/m2.calculate the resultant stresses developed in the precast and insitu concrete assuming the

pretensioned beam beam as:

a) Unpropped,

b) Propped during the casting of the slab.

Assume the same modulus of elasticity for concrete in precast beam and insitu cast slab. 14.1

R-13-NOV2016 2. Explain the advantages of using precast prestressed elements along with in-situ concrete.

R-13-NOV2016 3. Write step by step design procedure for composite construction. R-13-NOV2016

4. A precast pretensioned beam of 150mm wide and 300mm deep is prestressed with tendons with

their centroids coinciding with the bottom kern. The length of beam is 9m and prestressing force

applied to the tendons is 400kN with a loss of prestress of 15%. A cast in situ slab of size

500mmX50mm is constructed over the pretensioned beam to form the composite construction. If

the composite beam supports a live load of 3kN/m2, calculate the resultant stresses developed in

the precast and in situ cast concrete by assuming the pretensioned beam as:

a) Unpropped

b) Propped during the construction.

The modulus of elasticity of concrete is 38kN/mm2 for both precast and a cast-in-situ

elements. The unit weight of concrete is 24kN/m3. R-13-MAY2017

5. A continuous PSC beam ABC(AB=BC=8m) has a uniform rectangular section of width 100mm

and depth 250mm. The cable carrying an effective prestressing force of 300kN is parallel to the

axis of the beam and located at 75mm from the soffit. Take density of concrete as 24kN/m3.

a) Determine the secondary and resultant moment at central support B

b) If the beam supports an imposed load of 1.2kN/m, calculate the resultant stresses at top and

bottom of the beam at B

c) Locate the resultant line of thrust through beam AB. R-13-MAY2017

6. A precast pretensioned beam of rectangular section has a breadth of 100mm and a depth of

200mm. The beam with an effective span of 5m is prestressed by tendons with their centroids

coinciding with the bottom kern. The initial force in the tendons is 150kN. The loss of prestress

may be assumed to be 15 percent. The beam is incorporated in a composite T-beam by casting a

top flange of breadth 400 mm and thickness 40 mm. If the composite beam supports a live load of

8 KN/m2.calculate the resultant stresses developed in the precast and insitu concrete assuming the

pretensioned beam beam as:

a) Unpropped,

b) Propped during the casting of the slab.

Assume the modulus of elasticity for concrete in precast beam and insitu cast slab are different.

Assume Ec=35kN/mm2. R-08 MAY-2015

7. A composite T-beam is made up of a prestensioned rib 100mm wide and 200mm deep, and a cast

in situ slab 400mm wide and 40mm thick having a modulus of elasticity of 28kN/mm2. If the



FAQ



differential shrinkage is 100X10-6 units, determine the shrinkage stresses developed in the precast

and cast in situ units. 14.3 R-08 MAY-2015

8. A composite beam of rectangular section is made up of a pretensioned in inverted T-beam having

a slab thickness and width of 150mm and 1000mm, respectively. The rib size is 150mm by

850mm. The cast in situ concrete has a thickness and width of 1000mm with a modulus of

elasticity of 30kN/mm2. If the differential shrinkage is 100x10-6 units, estimate the shrinkage

stresses developed in the precast and cast in situ units. 14.4 R-08 MAY-2014

9. Design a continuous prestressed beam of two spans(AB=BC=12m)to support a uniformly

distributed live load of 10kN/m. Tensile stresses are not permitted in concrete and the

compressive stress in concrete is not to exceed 13N/mm2. Sketch the details of the cable profile

and check for stresses developed at the support and span sections.

UNIT 5: MISCELLANEOUS STRUCTURES

1. A non-cylinder PSC pipe of internal diameter 1000mm and thickness of cone shell 75mm in

required to convey water at a working pressure of 1.5 N/mm2. The length of each pipe is 6m. The

loss ratio is 0.8

a) Design the circumferential wire winding using 5mm dia wires stretched 1000/mm2

b) Design the longitudinal prestressing using 7mm dia wires tensioned to 1000/mm2. The max

permissible tensile stress under the critical transient loading not greater than 0.8 where

fci=40N/mm2. 16.3 R-13-NOV2016

2. A PSC circular cylindrical tank is required to store 24500 million litres of water. The permissible

compressive stress in concrete at transfer should not exceed 13 N/mm2 & min compressive stress

under working pressure should not be less than 1N/mm2. The loss ratio is 0.75. HYSD wires of

7mm dia with an initial stress of 1000N/mm2 are available for winding round the tank. Freyssinet

cables of 12 wires of 8mm dia which are stressed to 1200N/mm2 are available for vertical

prestressing. The cube strength of concrete is 40N/mm2. Design the tank walls. 16.7

R-13-NOV2016 3. Define the partial prestressing. Explain the merits and demerits of partial prestressing.

R-13-MAY2017 4. Briefly explain the various steps involved in designing of a prestressed concrete circular pipes.

R-13-MAY2017 5. Design a free edge water tank with base hinged of diameter of 36m to store water to a depth of

6m. The permissible compressive stress in concrete at transfer is 15N/mm2 and minimum

compressive stress under working pressure is 1.2N/mm2. The loss of prestress in 12%. For

circumferential winding use 6mm dia wires with an initial prestress of 1200N/mm2. The 8mm dia

Freyessinet cables with initial prestress of 1500N/mm2 are available for vertical prestressing. M45

grade concrete is used for the construction. R-13-MAY2017

6. Design a cylindrical prestressed concrete water tank to suit the following data:

Capacity of tank=3.5x106 liters. Ratio of diameter to height=4. Maximum compressive stress in

concrete at transfer not to exceed 14N/mm2. The prestress is to be provided by circumferential

winding of 5mm dia wires and by vertical cables of 12 wires of 7mm dia. The stress in wires at

transfer 1000N/mm2. Loss ratio=0.75. Design the walls of the tank and details of circumferential

wire winding and vertical cables for the following joint condition at the base: Sliding

base(Assume coefficient of friction as 0.5) R-08-MAY&NOV2016



FAQ



7. A prestressed concrete pipe of 1.2m diameter, having a core thickness of 75mm is required to

withstand a service pressure intensity of 1.2N/mm2. Estimate the pitch of 5mm diameter high

tensile wire winding if the initial stress is limited to 1000N/mm2. Permissible stresses in concrete

being 12.0N/mm2 in compression and zero in tension. The loss ratio is 0.8 if the direct tensile

strength of concrete is 2.5N/mm2, estimate load factor against cracking. R-08-MAY&NOV2016

8. A psc cylinder pipe is to be designed using a steel cylinder of 1200mm internal diameter and

thickness 1.5mm. The service internal hydrostatic pressure in the pipe is 0.8N/mm2. 4mm

diameter high tensile wires initially tensioned to a stress of 1kN/mm2 are available for

circumferential winding. The yield stress of mild steel cylinder is 280N/mm2. The maximum

permissible compressive stress in concrete at transfer is 14N/mm2 and no tensile stress is

permitted under service load conditions. Determine the thickness of the concrete lining and the

number of turns circumferential wire winding and the factor of safety against bursting. Assume

modular ratio as 6 and loss ratio as 0.8 and fpu=1600N/mm2.16.4 R-08 NOV-2015

9. A cylindrical prestressed concrete water tank of internal diameter 30m is required to store water

over a depth of 7.5m The permissible compressive stress in concrete at transfer is 13N/mm2 and

the minimum compressive stress under working pressure is 1N/mm2. The loss ratio is 0.75. Wires

of 5mm diameter with an initial stress of 1000N/mm2 are available for circumferential winding

and Freyssinet cables made up of 12 wires of 8mm diameter stressed to 1200N/mm2 are to be

used for vertical prestressing. Design the tank walls assuming the base as fixed. The cube strength

of concrete is 40N/mm2.16.5 R-08 MAY-2016

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