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

Calculate and sketch the resultant stress distribution at the central (mid-span) cross-section (and end section) of a simply supported prestressed rectangular concrete beam under prestress plus dead and live loads.

Calculate loss of prestress due to elastic deformation in a post-tensioned beam with multiple cables of given profiles.

Write short notes on flexural failures, Hoye's system of prestressing, pre-tensioned vs post-tensioned differences, and why mild steel cannot be used in prestressing.

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

Write down the merits and demerits of pre-stressed concrete.

OR

What are the basic assumptions of pre-stressed concrete theory?

Design a post-tensioned girder, which is spaced $2.40\, \text{m}$ c/c and has an effective span of $9.0\, \text{m}$. The dead load over beam is $3.0\, \text{kN/m}^2$ excluding self weight. The beam is subjected to a live load $15\, \text{kN/m}^2$ over whole span. The permissible compressive stress at transfer stage and at working stage is $14\, \text{N/mm}^2$ and $12\, \text{N/mm}^2$ respectively. The permissible tensile stress at all stages of loading is $1.0\, \text{N/mm}^2$. Consider loss ratio of $0.80$. Determine number of $7.0\, \text{mm}$ wires required if permissible tensile stress in wire is $1000\, \text{N/mm}^2$. Assume cover equal to $100\, \text{mm}$.

OR

Design a pre-stressed concrete I-beam to carry load of $12\, \text{kN/m}$ over simply supported span of $25.0\, \text{m}$. The permissible stress in concrete at transfer stage and at working stage is $14\, \text{N/mm}^2$ and $12\, \text{N/mm}^2$ respectively. Initial stress in cable is $1000\, \text{N/mm}^2$. Loss of pre-stress is $20.0\%$. Adopt Freyssinet cable 12 numbers and $5.0\, \text{mm}$ diameter.

Calculate the ultimate flexural strength / moment capacity of a post-tensioned unbounded prestressed concrete section (rectangular or T-section) using IS:1343 provisions.

In the pre-stressed beam shown below, pre-stressing is done by a parabolic cable carrying an effective pre-stress of $200\, \text{kN}$. The beam supports a uniformly distributed load of $15\, \text{kN/m}$ including self weight over whole span. Use $f_{ck} = 40\, \text{N/mm}^2$. Find the shear resistance of un-cracked section at the support.

OR

Explain the concordant cable and concept of linear transformation in pre-stressed concrete beam.

Short note on anchorage zone / end block stress distribution and end zone reinforcement

The end block of post tensioned beam of $500\, \text{mm} \times 1000\, \text{mm}$ is pre-stressed by 2 cables each comprising of 5 wires of $7\, \text{mm}$ diameter. The cable is anchored by square anchor plate of $400\, \text{mm} \times 400\, \text{mm}$ with their center located at $250\, \text{mm}$ from the top and bottom edge of beam. The jacking force in the cable is $3000\, \text{kN}$. Design a suitable anchorage zone reinforcement as per the provisions of IS 1343.

OR

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.

Explain the methods of achieving continuity in continuous prestressed concrete beams/members

Determine shrinkage stresses in composite precast prestressed beam with cast in-situ slab OR explain methods of achieving partial prestressing.

Explain composite construction in prestressed concrete members OR describe merits and demerits of partial prestressing.