A pretensioned beam is to carry a superimposed dead load of 600 plf and live load of 1,200 plf on a 55-ft simple span. A symmetrical I-section with be used. Flange thickness k_{f} = 0.2h and web width b - = 0.4b The member will be prestressed using Grade 270 strands. Time-dependent losses at 20 percent of P, Normal density concrete will be used, with f_{c}' = 5000 psi and -3,000 psi. (a) Using straight strands, find the required concrete dimensions prestress force, and eccentricity. Select an appropriate number and size of tendons, and show by sketch their placement in the section. (b) Revise the design of part (a) using tendons deflected at the third points of the span, with eccentricity reduced in zero at the supports (c) Comment on your results in both cases, ACI stress are to be applied. You may assume that deflections are not critical, and that a tele stress of 12 is permissible at full service load
A pretensioned beam is to carry a superimposed dead load of 600 plf and live load of 1,200 plf on a 55-ft simple span. A symmetrical I-section with be used. Flange thickness k_{f} = 0.2h and web width b - = 0.4b The member will be prestressed using Grade 270 strands. Time-dependent losses at 20 percent of P, Normal density concrete will be used, with f_{c}' = 5000 psi and -3,000 psi. (a) Using straight strands, find the required concrete dimensions prestress force, and eccentricity. Select an appropriate number and size of tendons, and show by sketch their placement in the section. (b) Revise the design of part (a) using tendons deflected at the third points of the span, with eccentricity reduced in zero at the supports (c) Comment on your results in both cases, ACI stress are to be applied. You may assume that deflections are not critical, and that a tele stress of 12 is permissible at full service load
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