Reg. No.
B.E. B.Tech. DEGREE EXAMINATION, MAY 2017
Seventh Semester
Civil Engineering
01UCE703 PRESTRESSED CONCRETE STRUCTURES
(Regulation 2013)
Duration: Three hours Maximum: 100 Marks
Answer ALL Questions
[IS1343-2012 and IS 3370 (part III and part IV) are permitted]
PART A (10 x 2 20 Marks)
1. What is the basic principle of prestressing?
2. What is Relaxation of steel?
3. What are the types of flexural failure?
4. What is meant by Type 2 structure?
5. What are the factors influencing deflection of prestressed concrete members?
6. What is meant by end zone?
7. What is primary moment?
8. Mention the importance of shrinkage in composite construction.
9. State the critical load conditions for the design of prestressed concrete poles.
10. What is meant by partial prestressing?
Question Paper Code: 31173
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PART B x 16 80 Marks)
11. An unsymmetrical I-section beam is used to support an imposed load of 2 kN/m over a span of 8 m. The sectional details are top flange, 300 mm wide and 60 mm thick; bottom flange 100 mm wide and 60 mm thick; thickness of web 80 mm; overall depth of beam 400 mm. At the centre of span, the effective prestressing force of 100 kN is located at 50 mm from the soffit of beam. Estimate the stresses at the centre of span section of the beam for the following load conditions Prestress self-weight Prestress self-weight live load. Or A prestressed concrete beam 500 x 800 mm size has simply supported span of 10 m. It is stressed with linearly bent tendon with zero eccentricity and an eccentricity of 200 mm below the axis of mid span. The beam carries a point load of 150 kN at centre besides its self weight. Compute the extreme fibre stresses at mid span using the stress concept, strength concept and load balancing concept.
12. A prestressed concrete beam of (span=10 of rectangular cross section, 120 mm wide and 300 mm deep, is axially prestressed by a cable carrying an effective force of 180 N. The beam supports a total udl of 5 kN/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. Or A pretensioned prestressed concrete beam having a rectangular section 150 mm wide and 350 mm deep has an effective cover of 50 mm. If fck 40 N/mm2, fp 1600 N/mm2 and area of prestressing streel Ap 461 mm2, calculate the flexural strength of the section using IS1343 code.
13. The end block of a post tensioned prestressed concrete beam, 300 mm wide and 300 mm deep, is subjected to a concentric anchorage force of 832.8 kN by a Freyssinet anchorage of area 11720 mm2. Design and detail the anchorage reinforcement for the end block. Or The end block of prestressed concrete beam is rectangular section 100 mm wide and 200 mm deep. The prestressing force of 100 kN is transmitted to concrete by a distribution plate 100 mm wide and 50 mm deep concentrically located at the ends. Estimate the position and magnitude of maximum tensile stress and bursting tension on the horizontal section through the centre and edge of anchor plate.
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14. The cross section of a composite beam is of T section having a pretensioned rib, 80 mm wide and 240 mm deep, and an in situ cast slab 350 mm wide and 80 mm thick. The pretensioned beam is reinforced with eight wires of 5 mm dia with an ultimate tensile strength of 1600 N/mm2, located 60 mm from the soffit of the beam. The compressive strength of concrete in the in situ cast and precaste elements is 20 mm and 40 N/mm2 respectively. If adequate reinforcements are provided to prevent shear failure at the interface, estimate the flexural strength of the composite section. Or A continuous prestressed concrete beam ABC (AB BC 10 having a rectangular section with a width of 200 mm and depth of 400 mm is prestressed by a parabolic cable carrying an effective force of 100 kN. The cable is concentric at supports B and C and has an eccentricity of 100 mm towards the soffit of the beam at the centre of span sections. Calculate the secondary and resultant moments developed in the beam due to prestressing at B.
15. Design a non-cylindrical prestressed concrete pipe of 600 mm internal diameter to withstand a working hydrostatic pressure of 1.05 N/mm2 using a 2.5 mm high tensile wire stressed to 1000 N/mm2 at transfer. Permissible maximum and minimum stresses in concrete at transfer and service loads are 14 and 0.7 N/mm2. The loss ratio is 0.8. Calculate the test pressure required to produce a tensile stress of 0.7 N/mm2 in concrete when applied immediately after tensioning and also the winding stress in steel if Es 210 kN/mm2 and Ec 35 kN/mm2. Or
A prestressing cylinder pipe is to be designed using a steel cylinder of 1000 mm internal diameter and thickness 1.6 mm. The circumferntial wire winding consists of a 4 mm high tensile wire, initially tensioned to a stress of 1000 N/mm2.Ultimate tensile strength of wire=1600 N/mm2. Yield stress of a steel cylinder=280 N/mm2. The maximum permissible compressive stress in concrete at transfer is 14 N/mm2 and no tensile stresses are permitted under working pressure of 0.8 N/mm2.Determine the thickness of the concrete lining required, the number of turn of circumferential wire winding and the factor of safety against bursting. Assume modular ratio as 6.
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