Important RGPV Question

CE-702 (A) Prestressed Concrete Structures

VII Sem, CE

Unit I Introduction – Theory and Behaviour

Q.1 Classify the Pre-stressed concrete.  (RGPV Nov 2022)

Q.2   Explain Freyssinet’s system of pre-stressing.  (RGPV Nov 2022)

Q.3 A simply supported pre-stressed concrete beam of rectangular cross section 400mm * 600 mm is loaded with a total uniformly distributed load of 256 kN over a span of 6.0 m. Sketch the distribution of stress at mid span and at end section, if the pre-stressing force is 1920.0 KN and the tendon is concentric with beam section.  (RGPV Nov 2022)

Q.4 Explain in detail the load balancing concept of pre-stressed structures with suitable sketches.  (RGPV Nov 2022)

Q.5 Write down the merits and demerits of pre-stressed concrete.  (RGPV Nov 2022)

Q.6 What are the basic assumptions of pre-stressed concrete theory? (RGPV Nov 2022)

Q.7A rectangular concrete beam, 100 mm wide by 250 mm deep, spanning over 8 m is prestressed by a straight cable carrying an effective prestressing force of 250 kN located at an eccentricity of 40 mm. The beam supports a live load of 1.2 kN/m. (RGPV Dec 2020)

a) Calculate the resultant stress distribution for the central cross section of the beam. The density of concrete is 24 kN/m3.

b) Find the magnitude of the prestressing force with an eccentricity of 40 mm which can balance the stresses due to dead and live loads at the bottom fibre of the central section of the beam. 

Q.8 Explain Load Balancing Concept with suitable examples. (RGPV Dec 2020)

Q.9 What are the advantages and disadvantages of prestressed concrete member over RCC member? (RGPV Jun 2020) 

Unit II Design for Flexure and Shear

Q.1 A post tensioned unbounded beam section 120mm * 300mm is pre-stressed by 7 wires of 5 mm diameter with an effective cover of 50 mm and effective stress of 1200N / m * m ^ 2 The beam is of 7.50 m span. If M40 concrete is used and f_{\mathfrak{p}} = 1600N / m * m ^ 2 Find the ultimate flexural strength of the section. (RGPV Nov 2022)

Q.2 A post tensioned unbounded T-section has a flange width of 800mm * 250 mm. The size of web of beam is 200 mm x 1000 mm. The area of high tensile wire is 4000m * m ^ 2 located at 1200 mm from top of flange. The characteristics strength of steel and concrete are 1500N / m * m ^ 2 and 40N / m * m ^ 2 respectively. Calculate the ultimate moment capacity of section using IS 1343 recommendations. (RGPV Nov 2022)

Q.3 A post tensioned concrete beam 100mm * 300mm of 10 m span is pre-stressed successively tensioned and anchored by 3 cables each having cross sectional area 200m * m ^ 2 Initial pre-stress is 1200N / m * m ^ 2 First cable is parabolic with e=50 mm at mid span and 50 mm above neutral axis at support. Second cable is also parabolic with c = 50 mm at mid span and zero eccentricity at support. Third cable is straight with 50 mm eccentricity. Calculate the loss of pre-stress due to elastic deformation. Take m I = 6 (RGPV Nov 2022)

Q.4 Define loss of pre-stress. Explain different losses of pre-stress in pre-tensioned and post-tensioned concrete. (RGPV Nov 2022)

 Q.5 Design a post-tensioned girder, which is spaced 2.40 m c/c and has an effective span of 9.0 m. The dead load over beam is 3kN / (m ^ 2) excluding self weight. The beam is subjected to a 15kN / (m ^ 2) over whole span. The permissible compressive stress at transfer stage and at working stage is 14N / m * m ^ 2 and 12N / m * m ^ 2 * 1 respectively. The permissible tensile stress at all stages of loading is 1N / m * m ^ 2 Consider loss ratio of 0.80. Determine number of 7.0 mm wires required if permissible tensile stress in wire is 1000N / m * m ^ 2 Assume cover equal to 100 mm.  (RGPV Nov 2022)

Q.6 Design a pre-stressed concrete I-beam to carry load of 12 kN/m over simply supported span of 25.0 m. The permissible stress in concrete at transfer stage and at working stage is 14N / m * m ^ 2 and 12N / m * m ^ 2 respectively. Initial stress in cable is 1000N / m * m ^ 2 Loss of pre-stress is 20.0%. Adopt Freyssinet cable 12 numbers and 5.0 mm diameter. (RGPV Nov 2022)

Q.7 A pre-tensioned prestressed concrete beam having a rectangular section, 300 mm wide and 500mm deep has an effective cover of 40 mm. If fck = 40 N/mm2, fp =1600 N/mm2 and the area of prestressing steel AP = 461 mm2. Calculate the ultimate flexural strength of the section using IS:1343 code provisions. (RGPV Dec 2020)

Q.8 Classify various method of post tensioning system based on wedge action. Describe any one method of post tensioning in details with sketches. (RGPV Jun 2020)

Q.9 A post tensioned prestressed beam of rectangular section 250mm wide is to be designed for an imposed load of 12 kN/m, over 12m span. The stress in the concrete must not exceed 17 N/mm2 in compression and 1.4 N/mm2 in tension at any time and the loss of prestress may be assumed to be 15%. Calculate the minimum possible depth of beam. Also calculate minimum prestressing force and eccentricity for provided depth. (RGPV Jun 2020)

Unit III Deflection and Design of Anchorage Zone

Q.1 Write a short note on Anchorage zone stress.  (RGPV Nov 2022)

Q.2 Explain end zone reinforcement.  (RGPV Nov 2022)

Q.3 The end block of post tensioned beam of 500mm * 1000 mm is pre-stressed by 2 cables each comprising of 5 wires of 7 mm diameter. The cable is anchored by square anchor plate of 400mm * 400 mm with their center located at 250 mm from the top and bottom edge of beam. The jacking force in the cable is 3000 kN. Design a suitable anchorage zone reinforcement as per the provisions of IS 1343. (RGPV Nov 2022)

Q.4 Explain the important factors influencing the deflection in a pre-stressed concrete beam and also describe differences between short term deflection and long term deflection. (RGPV Nov 2022)

Q.5 In the pre-stressed beam shown below, pre-stressing is done by a parabolic cable carrying an effective pre-stress of 200 kN. The beam supports a uniformly distributed load of 15 kN/m including self weight over whole span. Use fcx40 N/mm². Find the shear resistance of un-cracked section at the support.  (RGPV Nov 2022)

Q.6 A rectangular beam 250 × 500 mm in section is simply supported over a span of 10m. It is prestressed with a parabolic cable which has a maximum eccentricity of 200 mm at midspan and 40 mm at support sections. Effective prestressing force is 1450 kN. Concrete grade is M40. Determine the deflection due to prestress and self-weight. (RGPV Dec 2020)

Q.7 What is the anchorage zone? (RGPV Dec 2020)

Q.8 What is relaxation of stress in steel? How do you account for it in prestressed members? Explain the provisions made in IS: 1343 for relaxation loss. (RGPV Dec 2020)

Q.9 A prestressed concrete beam 400 mm × 400 mm, is prestressedby 10 wires, each of 8 mm diameter. The wires are initially stressed to 1200 N/mm2 with their centroids located 60 mm from the soffit. Calculate the final percentage loss of stress due to elastic deformation, creep, shrinkage and relaxation using the following data: ES =210 kN/mm2 and Ec=32 kN/mm2, Creep coefficient =1.6, Residual shear strain = 3 × 10–4 Relaxation of steel stress = 90N/mm2. (RGPV Dec 2020)

Q.10 Briefly outline the magnet’s method of computing the horizontal and transverse stress in end blocks subjected to concentrated force from anchorage. (RGPV Jun 2020)

Q.11 Define the following: (RGPV Jun 2020)

i) Tendon

ii) Pretensioning

iii) Post tensioning

iv) Load balancing

Q.12 Explain the analysis of anchorage zone stresses in post tensioned members. How is the bursting tensile force calculated? (RGPV Jun 2020)

Unit IV Composite and Continuous Beams and Slabs

Q.1 Explain the methods of achieving continuity in continuous pre-stressed beam.  (RGPV Nov 2022)

Q.2 Explain composite construction in Pre-stressed concrete members.  (RGPV Nov 2022)

Q.3 A composite T-beam is made up of pre-tensioned web 100 mm wide and 200 mm deep with a cast in situ slab of 400 mm wide and 40 mm thick, having a modulus of elasticity 28 kN/m². If the differential shrinkage is 100×106 units, determined shrinkage stress developed in the precast and cast in situ units. (RGPV Nov 2022)

Q.4 Explain the various methods of achieving continuity of PSC members. (RGPV Dec 2020)

Q.5 A continuous PSC beam PQR (PQ = QR = 10 m) has a uniform rectangular section with a width of 100 mm and depth of 300 mm. The cable carrying an effective prestressing force of 360 kN is parallel to the axis of the beam and located at 300 mm from the soffit. Determine the secondary and resultant moment at the central support. If the beam supports an imposed load if 1.5 kN/m, calculate the resultant stresses at top and bottom of the beam at B. (RGPV Dec 2020)

Q.6 How will you improve shear resistance of a P.S.C. beam? (RGPV Jun 2020)

Q.7 Sketch the layout of tendons of a PSC continuous beam: (RGPV Jun 2020)

i) Straight

ii) Curved in elevation

Unit V Miscellaneous Structures

Q.1 Describe the merits and demerits of partial pre-stressing.  (RGPV Nov 2022)

Q.2 What are the methods of achieving partial pre-stressing? Explain in details. (RGPV Nov 2022)

Q.3  Explain the objectives and methods of partial prestressing. (RGPV Dec 2020)

Extra Questions

Q.1 What is meant by primary moments, secondary moments and resultant moments in pre-stressed concrete? (RGPV Nov 2022)

Q.2 Explain the concordant cable and concept of linear transformation in pre-stressed concrete beam. (RGPV Nov 2022)

Q.3 Write short notes on any two: (RGPV Nov 2022)

i) Stress concept in pre-stress

ii) Tendon and tendon profile

iii) Guyon’s method

iv) Concept of stress distribution in end block

Q.4 Write short note on any two: (RGPV Nov 2022)

i) Types of flexural failures in concrete

ii) Hoye’s system of pre-stressing with neat sketch

iii) Differences between pre-tensioned and post-tensioned

iv) Why mild steel cannot be used in pre-stressing.

Q.5 Why is the high strength of concrete and high grade of steel required for prestressed concrete? Explain in detail. (RGPV Dec 2020)

Q.6 Explain the following: (RGPV Dec 2020)

i) Difference between pre-tensioned and post-tensioned members.

ii) Advantages of composite construction.

iii) Explain any two methods of prestressing systems.

iv) Factors influencing deflections of PSC members

Q.7 Write a short note on need of high strength concrete and steel. (RGPV Jun 2020)

Q.8 Write short notes on any two of the following: (RGPV Jun 2020)

a) Principles of prestressing

b) End zone reinforcement

c) Design of continuous beams

d) Design of purlin

e) Design of railway sleepers

— Best of Luck for Exam —