Find the require concrete dimension prestressed force – Civil Engineering

A pretentioned beam is to carry a superimposed dead load of 600 plf and service live load of 1,200 plf on a 55ft simple span. A symmetrical I-beam with b = 0.5h will be used. Flange thickness hf= 0.2h and web width bw=0.4. The member will be prestress using graded 270 strand. Time dependant losses are estimate at 20% of Pi. Normal density concrete will be used with f’c = 5000 psi and f’ci = 3000psi. Question

a) Using straight strands, find the require concrete dimension, prestressed force , and eccentricity. select an appropriate number and size of tendons, and show by a sketch their placement in the section.

B) revised the design of part (A) using tendon deflected at the third point of span, with eccentricity reduce to zero at the support.

C) comment on your results. in both cases, ACI stress limit are to be apply, you may assume that deflection are not critical, and that a tensile stress of 12*f’c^0.5 is permissible at full service loads.