Prestressed Concrete Structures (CE-702 (A)) - Important Questions

Classify prestressed concrete and explain Freyssinet's system of prestressing.

A simply supported prestressed concrete beam of rectangular cross-section 400 mm x 600 mm over a span of 6.0 m is loaded with a total uniformly distributed load of 256 kN and prestressed by a straight tendon with effective force 1200 kN at eccentricity 100 mm at mid-span. Calculate and sketch the resultant stress distribution at the central mid-span cross-section and end section under prestress plus dead and live loads.

Write down the merits and demerits of prestressed concrete. OR What are the basic assumptions of prestressed concrete theory?

A post-tensioned unbounded beam section 120 mm x 300 mm is prestressed by 7 wires of 5 mm diameter with an effective cover of 50 mm and effective stress of 1200 N/mm2. Calculate the ultimate flexural strength / moment capacity of the section using IS:1343 provisions.

A post-tensioned concrete beam 100 mm x 300 mm of 10 m span is successively tensioned and anchored by 3 cables each having cross-sectional area 200 mm2 with initial stress 1200 N/mm2. The cables are parabolic with zero eccentricity at supports and 50 mm at centre. Calculate loss of prestress due to elastic deformation.

In the prestressed beam prestressing is done by a parabolic cable carrying an effective prestress of 200 kN. The beam supports a uniformly distributed load of 15 kN/m including self-weight. Calculate the resultant extreme fibre stresses at mid-span and support sections and check the section for serviceability.

Write a short note on anchorage zone / end block stress distribution and end zone reinforcement.

The end block of a post-tensioned beam of 500 mm x 1000 mm is prestressed by 2 cables each comprising 5 wires of 7 mm diameter. The cable is anchored by square anchor plate of 400 mm x 400 mm with duct diameter 100 mm. Determine the bursting tensile force and design the anchorage zone reinforcement as per IS:1343.

Explain the methods of achieving continuity in continuous prestressed concrete beams/members. What is meant by primary moments, secondary moments and resultant moments?

A composite T-beam is made up of pre-tensioned web 100 mm wide and 200 mm deep with a cast in-situ slab 400 mm wide and 40 mm thick having modulus of elasticity 28 kN/mm2. Determine shrinkage stresses in the composite section and stresses due to composite action.

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 3.0 kN/m2 excluding self-weight and live load is 5.0 kN/m2. Design the Type-II section, determine the prestressing force and eccentricity, and check for strength limit based on IS:1343.

Explain design for shear based on IS:1343 Code. A post-tensioned beam 300 mm x 600 mm with effective prestress 800 kN with inclined parabolic cable is subjected to ultimate shear force 150 kN. Calculate the ultimate shear resistance of the section with and without shear reinforcement.

Write short notes on any two: (i) flexural failures in prestressed concrete (ii) Hoye's system of prestressing (iii) pre-tensioned vs post-tensioned differences and why mild steel cannot be used in prestressing.

Explain determination of anchorage zone stresses in post-tensioned beams by Magnel's method, Guyon's method and IS:1343 code with design of anchorage zone reinforcement.