Jawaharlal Nehru Technological University Hyderabad B.Tech IV PRESTRESSED CONCERETE Previous Question Paper (December - 2019 - R16)

Compare the differentiate between PSC and RCC.

Explain the terms

A pre tensioned concrete beam 200mm wide and 300mm deep and span of 6m is initially prestressed by a force of 400kN applied at a constant eccentricity of 70mm by tendons of cross sectional area 400 mm2. If Es = 2 × 10^5 N/mm2. Ec = 0.333 × 10^5 N/mm2, Creep co efficient in concrete = 2, shrinkage strain in concrete = 0.0002, stress relaxation in steel = 3%. Find the total percentage loss of stress in tendons.

A post tensioned concrete beam of 230 mm wide and 450mm deep spanning over 12m is stressed by successive tensioning and anchoring of three cables 1, 2 and 3 respectively. The cross sectional area of each cable is 200mm2, initial stress in the cable is 1300 N/mm2 and m = 6. The first cable is parabolic with the eccentricity 50mm below centroidal axis at the centre of span and and the 50mm above the centroidal axis at support sections. The second cable is parabolic with zero eccentricity at the support and an eccentricity of 50mm at the centre of span. The third cable is straight with uniform eccentricity of 50mm below centroidal axis. Estimate the percentage loss of stress in each of the cables if they are successively tensioned and anchored.

A post tensioned beam with unbonded tendons is of rectangular section 400mm wide with an effective depth of 800mm. The cross section area of prestressing steel is 2840mm2. The effective prestress in steel after all losses is 900 N/mm2. The effective span of the beam is 16m if the Fck = 40 N/mm2. Estimate the ultimate moment of resistance of the section using IS:1343

An unsymmetrical I section beam is used to support an imposed load 5kN/m over a span of 8m. The sectional details are top flange 450mm wide and 80mm thick. Bottom flange 200mm wide and 80mm thick. Thickness of web is 80mm and overall depth of beam is 600mm. At the quarter of span, effective prestressing force of 100kN is located at 50mm from the soffit of the beam. Estimate the stresses at the quarter of span section of the beam for the following loading conditions.

The end block of a post tensioned beam is 80mm wide and 160mm deep. A pre-stressing wire, 7 mm in diameter, stressed to 1200 N/mm2 has to be anchored against the end block at the centre. The anchorage plate is 50mm by 50mm. The wire bears on the plate through a cone of 20mm diameter. Given the permissible stress in concrete at transfer, fci as 20 N/mm2 and the permissible shear in steel as 94.5 N/mm2, determine the thickness of the anchorage plate.

A PSC beam 300mm wide and 500mm deep has two anchorages of 150mm diameter with the center at 125mm from top and bottom of the beam. The force transmitted by each cable is 800kN. Estimate the maximum tension and bursting tension.

A prestressed concrete beam has a symmetrical I – section with overall depth 320mm. Top and bottom flange width = 160mm. The flange thickness = 70mm. The web is 50mm in thickness and the span = 6m. It is prestressed with 182kN at a constant eccentricity of 105mm. Assume a loss of 15% in prestress. Compute the deflection due to

A rectangular concrete beam of cross section 300mm wide and 600mm deep is simply supported over a span of 8m. it is prestressed by means of symmetric parabolic cable at a distance of 120mm from the bottom fibre at mid span section. Initial prestress in the cable is 350kN. Determine