R05420105-PRESTRESSEDCONCRETE
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Code No: R05420105 R05 Set No. 2 IV B.Tech II Semester Examinations,APRIL 2011 PRESTRESSED CONCRETE Civil Engineering Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. A prestressed concrete beam, 200 mm wide and 300 mm deep, is prestressed with wiers (area = 320 mm 2 ) located at a constant eccentricity of 500 mm and carrying an initial stress of 1000 N/mm 2 . The span of the beam is 10 m. Calculate the percentage loss of stress in wires if (a) the beam is pre-tensioned, and (b) the beam is post-tensioned, using the following data: E s = 210kN/mm 2 andE c = 35kN/mm 2 Relaxation of steel stress = 5 percent of initial stress. Slip at anchorage = 1 mm Shrinkage of concrete = 300 ×10 -6 for prestensioning and 200 ×10 -6 for post tensioning. Assume any other missing data. [16] 2. The end block of a prestressed beam, 250 mm wide and 500 mm deep in section, is prestressed by two cables carrying forces of 450 kN each. One of the cables is parabolic, located 125 mm below the centre line at the centre of span (10 m) and anchored at a point 125 mm above the centre line at the ends. The second cable is straight and located 100 mm from the bottom of the beam. The distribution plates for the cables are 100 mm deep and 250 mm wide. Calculate the maximum tensile stress along the axis of the beam using Guyon’s method. Also evaluate the maximum tensile stress on horizontal sections passing through the centre of anchor plates using Rowe’s method. Assume any other missing data. [16] 3. A small precast prestressed concrete beam is to be designed to cover a span of 12 meters and to carry a superimposed load of 15kN/m. The grade of concrete proposed to be used is M45. The permissible stress in compression can be 14N/mm 2 and in tension 1.4N/mm 2 . Force loss in prestressing cables can be assumed to be 15% of the initial force during service load conditions. Design the cross section dimensions; prestressing force and eccentricity. Adopt stress range approach for arriving at the cross sectional dimensions. Assume any other missing data. [16] 4. Explain the effect of tendon profile on deflections of prestressed concrete members of the following cases (a) Parabolic tendons (b) Sloping tendons. [16] 1
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Transcript of R05420105-PRESTRESSEDCONCRETE
Code No: R05420105 R05 Set No. 2
IV B.Tech II Semester Examinations,APRIL 2011PRESTRESSED CONCRETE
Civil EngineeringTime: 3 hours Max Marks: 80
Answer any FIVE QuestionsAll Questions carry equal marks
? ? ? ? ?
1. A prestressed concrete beam, 200 mm wide and 300 mm deep, is prestressed withwiers (area = 320 mm2) located at a constant eccentricity of 500 mm and carryingan initial stress of 1000 N/mm2. The span of the beam is 10 m. Calculate thepercentage loss of stress in wires if
(a) the beam is pre-tensioned, and
(b) the beam is post-tensioned,
using the following data:Es = 210kN/mm2andEc = 35kN/mm2
Relaxation of steel stress = 5 percent of initial stress.Slip at anchorage = 1 mmShrinkage of concrete = 300 ×10−6 for prestensioning and 200 ×10−6 for posttensioning. Assume any other missing data. [16]
2. The end block of a prestressed beam, 250 mm wide and 500 mm deep in section,is prestressed by two cables carrying forces of 450 kN each. One of the cables isparabolic, located 125 mm below the centre line at the centre of span (10 m) andanchored at a point 125 mm above the centre line at the ends. The second cableis straight and located 100 mm from the bottom of the beam. The distributionplates for the cables are 100 mm deep and 250 mm wide. Calculate the maximumtensile stress along the axis of the beam using Guyon’s method. Also evaluate themaximum tensile stress on horizontal sections passing through the centre of anchorplates using Rowe’s method. Assume any other missing data. [16]
3. A small precast prestressed concrete beam is to be designed to cover a span of12 meters and to carry a superimposed load of 15kN/m. The grade of concreteproposed to be used is M45. The permissible stress in compression can be 14N/mm2
and in tension 1.4N/mm2. Force loss in prestressing cables can be assumed to be15% of the initial force during service load conditions. Design the cross sectiondimensions; prestressing force and eccentricity. Adopt stress range approach forarriving at the cross sectional dimensions. Assume any other missing data. [16]
4. Explain the effect of tendon profile on deflections of prestressed concrete membersof the following cases
(a) Parabolic tendons
(b) Sloping tendons. [16]
1
Code No: R05420105 R05 Set No. 2
5. A rectangular pre-tensioned concrete beam has a breadth of 100 mm and depthof 230 mm, and the prestress after all losses have occurred is 12 N/ mm2at thesoffit and zero at the top. The beam is incorporated in a composite T-beam bycasting a top flange of breadth 300 mm and depth 50 mm. Calculate the maximumuniformly distributed live load that can be supported on a simply supported spanof 4.5 m, without any tensile stresses occurring, if the slab is externally supportedwhile casting. [16]
6. A simply supported prestressed concrete beam spanning over 10 m is of rectangularsection 500 mm wide by 750 mm deep. The beam is prestressed by a paraboliccable having an eccentricity of 200 mm at the centre of the span and zero at theend supports. The effective force in the cable is 1600 kN. If the beam supports atotal uniformly distributed load, of 40 kN/m, which includes the selfweight,
(a) Evaluate the extreme fibre stresses at the mid-span section using the internalresisting couple method, and
(b) Calculate the force required in the cable having the same eccentricity to bal-ance a total load of 50 kN/m on the beam. (Assume any other missing data)
[16]
7. Explain the following prestressing methods along with neat sketches
(a) Magnel system
(b) Freyssit system [16]
8. (a) Why did the early attempts in presstressing failed using ordinary mild steel.
(b) What are the advantages of presstressed concrete? [8+8]
? ? ? ? ?
2
Code No: R05420105 R05 Set No. 4
IV B.Tech II Semester Examinations,APRIL 2011PRESTRESSED CONCRETE
Civil EngineeringTime: 3 hours Max Marks: 80
Answer any FIVE QuestionsAll Questions carry equal marks
? ? ? ? ?
1. A simply supported prestressed concrete beam spanning over 10 m is of rectangularsection 500 mm wide by 750 mm deep. The beam is prestressed by a paraboliccable having an eccentricity of 200 mm at the centre of the span and zero at theend supports. The effective force in the cable is 1600 kN. If the beam supports atotal uniformly distributed load, of 40 kN/m, which includes the selfweight,
(a) Evaluate the extreme fibre stresses at the mid-span section using the internalresisting couple method, and
(b) Calculate the force required in the cable having the same eccentricity to bal-ance a total load of 50 kN/m on the beam. (Assume any other missing data)
[16]
2. The end block of a prestressed beam, 250 mm wide and 500 mm deep in section,is prestressed by two cables carrying forces of 450 kN each. One of the cables isparabolic, located 125 mm below the centre line at the centre of span (10 m) andanchored at a point 125 mm above the centre line at the ends. The second cableis straight and located 100 mm from the bottom of the beam. The distributionplates for the cables are 100 mm deep and 250 mm wide. Calculate the maximumtensile stress along the axis of the beam using Guyon’s method. Also evaluate themaximum tensile stress on horizontal sections passing through the centre of anchorplates using Rowe’s method. Assume any other missing data. [16]
3. (a) Why did the early attempts in presstressing failed using ordinary mild steel.
(b) What are the advantages of presstressed concrete? [8+8]
4. A rectangular pre-tensioned concrete beam has a breadth of 100 mm and depthof 230 mm, and the prestress after all losses have occurred is 12 N/ mm2at thesoffit and zero at the top. The beam is incorporated in a composite T-beam bycasting a top flange of breadth 300 mm and depth 50 mm. Calculate the maximumuniformly distributed live load that can be supported on a simply supported spanof 4.5 m, without any tensile stresses occurring, if the slab is externally supportedwhile casting. [16]
5. Explain the following prestressing methods along with neat sketches
(a) Magnel system
(b) Freyssit system [16]
3
Code No: R05420105 R05 Set No. 4
6. A prestressed concrete beam, 200 mm wide and 300 mm deep, is prestressed withwiers (area = 320 mm2) located at a constant eccentricity of 500 mm and carryingan initial stress of 1000 N/mm2. The span of the beam is 10 m. Calculate thepercentage loss of stress in wires if
(a) the beam is pre-tensioned, and
(b) the beam is post-tensioned,
using the following data:Es = 210kN/mm2andEc = 35kN/mm2
Relaxation of steel stress = 5 percent of initial stress.Slip at anchorage = 1 mmShrinkage of concrete = 300 ×10−6 for prestensioning and 200 ×10−6 for posttensioning. Assume any other missing data. [16]
7. Explain the effect of tendon profile on deflections of prestressed concrete membersof the following cases
(a) Parabolic tendons
(b) Sloping tendons. [16]
8. A small precast prestressed concrete beam is to be designed to cover a span of12 meters and to carry a superimposed load of 15kN/m. The grade of concreteproposed to be used is M45. The permissible stress in compression can be 14N/mm2
and in tension 1.4N/mm2. Force loss in prestressing cables can be assumed to be15% of the initial force during service load conditions. Design the cross sectiondimensions; prestressing force and eccentricity. Adopt stress range approach forarriving at the cross sectional dimensions. Assume any other missing data. [16]
? ? ? ? ?
4
Code No: R05420105 R05 Set No. 1
IV B.Tech II Semester Examinations,APRIL 2011PRESTRESSED CONCRETE
Civil EngineeringTime: 3 hours Max Marks: 80
Answer any FIVE QuestionsAll Questions carry equal marks
? ? ? ? ?
1. The end block of a prestressed beam, 250 mm wide and 500 mm deep in section,is prestressed by two cables carrying forces of 450 kN each. One of the cables isparabolic, located 125 mm below the centre line at the centre of span (10 m) andanchored at a point 125 mm above the centre line at the ends. The second cableis straight and located 100 mm from the bottom of the beam. The distributionplates for the cables are 100 mm deep and 250 mm wide. Calculate the maximumtensile stress along the axis of the beam using Guyon’s method. Also evaluate themaximum tensile stress on horizontal sections passing through the centre of anchorplates using Rowe’s method. Assume any other missing data. [16]
2. A small precast prestressed concrete beam is to be designed to cover a span of12 meters and to carry a superimposed load of 15kN/m. The grade of concreteproposed to be used is M45. The permissible stress in compression can be 14N/mm2
and in tension 1.4N/mm2. Force loss in prestressing cables can be assumed to be15% of the initial force during service load conditions. Design the cross sectiondimensions; prestressing force and eccentricity. Adopt stress range approach forarriving at the cross sectional dimensions. Assume any other missing data. [16]
3. Explain the effect of tendon profile on deflections of prestressed concrete membersof the following cases
(a) Parabolic tendons
(b) Sloping tendons. [16]
4. A prestressed concrete beam, 200 mm wide and 300 mm deep, is prestressed withwiers (area = 320 mm2) located at a constant eccentricity of 500 mm and carryingan initial stress of 1000 N/mm2. The span of the beam is 10 m. Calculate thepercentage loss of stress in wires if
(a) the beam is pre-tensioned, and
(b) the beam is post-tensioned,
using the following data:Es = 210kN/mm2andEc = 35kN/mm2
Relaxation of steel stress = 5 percent of initial stress.Slip at anchorage = 1 mmShrinkage of concrete = 300 ×10−6 for prestensioning and 200 ×10−6 for posttensioning. Assume any other missing data. [16]
5
Code No: R05420105 R05 Set No. 1
5. Explain the following prestressing methods along with neat sketches
(a) Magnel system
(b) Freyssit system [16]
6. A rectangular pre-tensioned concrete beam has a breadth of 100 mm and depthof 230 mm, and the prestress after all losses have occurred is 12 N/ mm2at thesoffit and zero at the top. The beam is incorporated in a composite T-beam bycasting a top flange of breadth 300 mm and depth 50 mm. Calculate the maximumuniformly distributed live load that can be supported on a simply supported spanof 4.5 m, without any tensile stresses occurring, if the slab is externally supportedwhile casting. [16]
7. (a) Why did the early attempts in presstressing failed using ordinary mild steel.
(b) What are the advantages of presstressed concrete? [8+8]
8. A simply supported prestressed concrete beam spanning over 10 m is of rectangularsection 500 mm wide by 750 mm deep. The beam is prestressed by a paraboliccable having an eccentricity of 200 mm at the centre of the span and zero at theend supports. The effective force in the cable is 1600 kN. If the beam supports atotal uniformly distributed load, of 40 kN/m, which includes the selfweight,
(a) Evaluate the extreme fibre stresses at the mid-span section using the internalresisting couple method, and
(b) Calculate the force required in the cable having the same eccentricity to bal-ance a total load of 50 kN/m on the beam. (Assume any other missing data)
[16]
? ? ? ? ?
6
Code No: R05420105 R05 Set No. 3
IV B.Tech II Semester Examinations,APRIL 2011PRESTRESSED CONCRETE
Civil EngineeringTime: 3 hours Max Marks: 80
Answer any FIVE QuestionsAll Questions carry equal marks
? ? ? ? ?
1. A small precast prestressed concrete beam is to be designed to cover a span of12 meters and to carry a superimposed load of 15kN/m. The grade of concreteproposed to be used is M45. The permissible stress in compression can be 14N/mm2
and in tension 1.4N/mm2. Force loss in prestressing cables can be assumed to be15% of the initial force during service load conditions. Design the cross sectiondimensions; prestressing force and eccentricity. Adopt stress range approach forarriving at the cross sectional dimensions. Assume any other missing data. [16]
2. A rectangular pre-tensioned concrete beam has a breadth of 100 mm and depthof 230 mm, and the prestress after all losses have occurred is 12 N/ mm2at thesoffit and zero at the top. The beam is incorporated in a composite T-beam bycasting a top flange of breadth 300 mm and depth 50 mm. Calculate the maximumuniformly distributed live load that can be supported on a simply supported spanof 4.5 m, without any tensile stresses occurring, if the slab is externally supportedwhile casting. [16]
3. A simply supported prestressed concrete beam spanning over 10 m is of rectangularsection 500 mm wide by 750 mm deep. The beam is prestressed by a paraboliccable having an eccentricity of 200 mm at the centre of the span and zero at theend supports. The effective force in the cable is 1600 kN. If the beam supports atotal uniformly distributed load, of 40 kN/m, which includes the selfweight,
(a) Evaluate the extreme fibre stresses at the mid-span section using the internalresisting couple method, and
(b) Calculate the force required in the cable having the same eccentricity to bal-ance a total load of 50 kN/m on the beam. (Assume any other missing data)
[16]
4. Explain the effect of tendon profile on deflections of prestressed concrete membersof the following cases
(a) Parabolic tendons
(b) Sloping tendons. [16]
5. A prestressed concrete beam, 200 mm wide and 300 mm deep, is prestressed withwiers (area = 320 mm2) located at a constant eccentricity of 500 mm and carryingan initial stress of 1000 N/mm2. The span of the beam is 10 m. Calculate thepercentage loss of stress in wires if
7
Code No: R05420105 R05 Set No. 3
(a) the beam is pre-tensioned, and
(b) the beam is post-tensioned,
using the following data:Es = 210kN/mm2andEc = 35kN/mm2
Relaxation of steel stress = 5 percent of initial stress.Slip at anchorage = 1 mmShrinkage of concrete = 300 ×10−6 for prestensioning and 200 ×10−6 for posttensioning. Assume any other missing data. [16]
6. (a) Why did the early attempts in presstressing failed using ordinary mild steel.
(b) What are the advantages of presstressed concrete? [8+8]
7. The end block of a prestressed beam, 250 mm wide and 500 mm deep in section,is prestressed by two cables carrying forces of 450 kN each. One of the cables isparabolic, located 125 mm below the centre line at the centre of span (10 m) andanchored at a point 125 mm above the centre line at the ends. The second cableis straight and located 100 mm from the bottom of the beam. The distributionplates for the cables are 100 mm deep and 250 mm wide. Calculate the maximumtensile stress along the axis of the beam using Guyon’s method. Also evaluate themaximum tensile stress on horizontal sections passing through the centre of anchorplates using Rowe’s method. Assume any other missing data. [16]
8. Explain the following prestressing methods along with neat sketches
(a) Magnel system
(b) Freyssit system [16]
? ? ? ? ?
8
