EN10138 - Geometry and Materials Properties Assignment

Assignment Task

Question

1. Consider the post-tensioned beam of a residential building in Sydney shown in the figure below with an initial load applied to the structure on each side of 75 kN. It can be further assumed that after the structure is fully operational and over the years, the load will gradually increase to 120 kN on each side and no other loads are applied (including self-weight).

a) Determine the prestressing force and cable profile to completely balance the external load represented in the structure.

b) Define the minimum width of the cross-section to accommodate the anchorage plate.

c) For the tendon profile and prestress determined previously, calculate the immediate and time-dependent losses, and jacking force.

d) Calculate if the beam is fully or partially prestressed and argue on the advantages/drawbacks of the designed solution.

Note: Please state all assumptions needed to solve the problem. For example, you may need to define a concrete grade, as well as the concrete cover and work out an available eccentricity.

2. Consider the figure below. There are 3N18 at the top, 4N18 at the bottom, and a bonded tendon made by 12 units of 12.7mm strands. The prestressing force is 1,200 kN immediately before the transfer. The Young’s modulus of concrete is 32 GPa, whereas for steel reinforcements a value of 200 GPa can be taken for both prestressed and non-prestressed steel. The external moment is 600 kNm.

Calculate the diagram of stresses assuming:

a) Uncracked cross-section.

b) Cracked cross-section.

3. Calculate the immediate and long-term deflections for the example presented in tutorial. You may assume that the cross-section remains uncracked and that there are no other applied loads.

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