An unsymmetrical I section prestressed concrete beam of top flange (350 X 40 mm) in size,...

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Civil Engineering

An unsymmetrical I section prestressed concrete beam of topflange (350 X 40 mm) in size, bottom flange of (200 X 40 mm), 30mmthickness of web and overall depth of 400 mm is prestressed with 19numbers straight steel wires of 7 mm diameter located at a distanceof 15 mm from the bottom of the soffit and 9 numbers of straightsteel wires of 6 mm diameter located at a distance of 15 mm fromthe top of the beam. The wires were initially tensioned on theprestressing bed with an initial prestress of 1.2 GPa. The lengthof the beam is 10 m. Calculate the total percentage loss of stressin the wires at top and bottom. Assume the beam is post tensionedbeam and all the wires stressed simultaneously by using thefollowing data: [9] Relaxation of steel stress= 4.5% of initialstress -6 Shrinkage strain in concrete for post tensioning = 200 x10 Creep Coefficient ɸ=1.6 Friction coefficient for waveeffect=0.0015 per metre Slip at anchorage= 1.5 mm Modulus ofelasticity for steel = 210 GPa Modulus of elasticity for concrete=35 GPa

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