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A pretensioned prestressed concrete beam of rectangular section is required to support a design ultimate moment of 100knm. Design the section if fck is 50n/mm2 and fp 1600n/mm2, xu/d is 0.5?

A pretensioned prestressed concrete beam of rectangular section is required to support a design ultimate moment of 100knm. Design the section if fck is 50n/mm2 and fp 1600n/mm2, xu/d is 0.5? Correct Answer 300

Mu = 0.36fckbxu(d-0.42xu) = 0.14fckbd2, b = 0.5d, d3 = (mu/0.14fck0.5) = (100×106/0.15x50x0.5), d = 300mm, b = 150mm, xu = (0.5×300) = 150mm for (xu/d) = 0.5, fpu = 0.87fp, Ap = (mu/0.87fp(d-0.42xu)) = (100×1006/0.87×1600(300-0.42×150)) = 300mm2, adopt a section 150mm wide by 350mm deep with 300mm2 of high tensile steel located at an effective depth of 300mm.

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