Chapter 11, Problem 11.1QPP

8. A prestressed concrete beam is subjected to the following stress distributions: Pi is the initial prestressing force, Pe is the effective prestressing force, M, is the bending moment due to self- weight, Ma and M, are the dead load and live load bending moment, respectively. The concrete has the following properties: fr = 6000 psi and fri = 4200 psi +250 -85 -2500 +550 Pe+ Mo+Ma+Mi P alone P₁+ Mo -2450 -3500 Stress at midspan +210 +250 P, alone Pe alone -2500 -3500 Stress at ends Using Table 22.1, evaluate whether the stresses at the center of the span and the end of the span comply with the permissible stress limits. The beam is classified as U-class. Provide justifications for each condition listed in the table. Note: Calculated stresses are to be taken from the above diagram, and permissible stresses are to be calculated using Table 22.1. Compressive stresses immediately after transfer Tensile stresses immediately after transfer Compressive stresses under sustained and total…

10. A short column is subjected to an eccentric loading. The axial load P = 1000 kips and the eccentricity e = 12 in. The material strengths are fy = 60 ksi and f = 6000 psi. The Young's modulus of steel is 29000 ksi. (a) Fill in the blanks in the interaction diagram shown below. (2pts each, 10pt total) Po Pn (1) failure range H 3" 30" Ast 6 No. 10 bars = P 22" I e H 3" (4) e = e small Load path for given e Radial lines show constant (2) eb (3) e large failure range Mn (5) e= Mo (b) Compute the balanced failure point, i.e., P and Mb.

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