# Questions & Answers of Prestressed Concrete

## Weightage of Prestressed Concrete

Total 13 Questions have been asked from Prestressed Concrete topic of Concrete Structures subject in previous GATE papers. Average marks 1.77.

A 6 m long simply-supported beam is prestressed as shown in the figure.

The beam carries a uniformly distributed load of 6 kN/m over its entire span. If the effective flexural rigidity $EI=2\times10^4$ kNm2 and the effective prestressing force is 200 kN, the net increase in length of the prestressing cable (in mm, up to two decimal places) is ______

A pre-tensioned rectangular concrete beam 150 mm wide and 300 mm depth is prestressed with three straight tendons, each having a cross-sectional area of 50 mm2, to an inital stress of 1200 N/mm2. The tendons are located at 100 mm from the soffit of the beam. If the modular ratio is 6, the loss of prestressing force (in kN, up to one decimal place) due to the elastic deformation of concrete only is _________

A simply supported rectangular concrete beam of span 8 m has to be prestressed with a force of 1600 kN. The tendon is of parabolic profile having zero eccentricity at the supports. The beam has to carry an external uniformly distributed load of intensity 30 kN/m. Neglecting the self-weight of the beam, the maximum dip (in meters, up to two decimal places) of the tendon at the mid-span to balance the external load should be _________________

In a pre-stressed concrete beam section shown in the figure, the net loss is 10% and the final pre-stressing force applied at X is 750 kN. The initial fiber stresses (in N/mm2) at the top and bottom of the beam were:

The creep strains are

A rectangular concrete beam 250 mm wide and 600 mm deep is pre-stressed by means of 16 high tensile wires, each of 7 mm diameter, located at 200 mm from the bottom face of the beam at a given section. If the effective pre-stress in the wires is 700 MPa, what is the maximum sagging bending moment (in kNm) (correct to 1-decimal place) due to live load that this section of the beam can withstand without causing tensile stress at the bottom face of the beam ? Neglect the effect of dead load of beam. ________________

Which one of the following is categorised as a long-term loss of prestress in a prestressed concrete member?

A concrete beam prestressed with a parabolic tendon is shown in the sketch. The eccentricity of the tendon is measured from the centroid of the cross-section. The applied prestressing force at service is 1620 kN. The uniformly distributed load of 45 kN/m includes the self-weight.

The stress (in N/mm2) in the bottom fibre at mid-span is

As per India standard code of practice for prestressed concrete (IS:1343-1980) the minimum grades of concrete to be used for post-tensioned and pre-tensioned structural elements are respectively

A rectangular concrete beam of width 120 mm and depth 200 mm is prestressed by pretensioning to a force of 150 kN at an eccentricity of 20 mm. The cross sectional area of the prestressing steel is 187.5 mm2. Take modulus of elasticity of steel and concrete as 2.1×105 MPa and 3.0×104 MPa respectively. The percentage loss of stress in the prestressing steel due to elastic deformation of concrete is

A pre-tensioned concrete member of section 200mm × 250mm contains tendons of area 500 mm2 at the centre of gravity of the section. The prestress in tendons is 1000N/mm2. Assuming modular ratio as 10, the stress (N/mm2) in concrete is