***DESIGN OF PRESTRESSED CONCRETE PROBLEM***

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***DESIGN OF PRESTRESSED CONCRETE PROBLEM***

Design Of Prestressed Concrete Problem 1 (338.39 KiB) Viewed 44 times

Design Of Prestressed Concrete Problem 2 (27.7 KiB) Viewed 44 times

. A simply supported precast pre-tensioned normal weight concrete beam with symmetrical I section supports the uniform distributed loads listed below in addition to self-weight. Typical cross section properties and available dimensions are given in the Figure below (where cı = yt and c2 = y). The following information is also given: Geometry: Span = 70 ft; (eo) mp = yo – 4 in.; • Loads: Superimposed dead load = 300lbf/ft; Live load = 600 lbf/ft (You may ignore the sustained load condition) • Steel: fpu = 270 ksi; fpe = 155 ksi; Area of one strand = 0.153 in?; n=0.8, Grade 270 stress-relieved bonded strands • Concrete: fo = 5000 psi; fái = 4000 psi • Allowable stresses: āti = -3fci; õci 0.6fci; āts = -7.57 f. (Class U member per ACI 318); Öcs = 0.6$. 12 L1, 12 r2 0.160 m2 0.146 0.123 Table A.8 Section Properties of Symmetrical l-and Box Beams bb hn А. lo C C2 0.1 0.1 0.280bh 0.0449bh3 0.500 h 0.500 h 0.1 0.2 0.460 0.0671 0.500 0.500 0.1 0.3 0.640 0.0785 0.500 0.500 0.2 0.1 0.360 0.0492 0.500 0.500 0.2 0.2 0.520 0.0689 0.500 0.500 0.2 0.3 0.680 0.0791 0.500 0.500 0.3 0.1 0.440 0.0535 0.500 0.500 0.3 0.2 0.580 0.0707 0.500 0.500 0.3 0.3 0.720 0.0796 0.500 0.500 0.4 0.1 0.520 0.0577 0.500 0.500 0.4 0.2 0.640 0.0725 0.500 0.500 0.4 0.3 0.760 0.0801 0.500 0.500 0.137 0.132 0.117 . 0.121 0.122 0.111 0.111 0.113 0.105 Figure 1: Beam section and cross sectional properties in Problem 1
(a) Select the cross sectional dimensions that lead to the least weight beam which satisfies the allowable stresses listed above. (20 points)
(b) Use the inequalities to sketch the feasibility domain and determine the corresponding values of Fpi and e, at midspan. (20 points) (c) Select the number and size of strands required. (5 points) (d) Use the strain-compatibility method to determine the nominal moment capacity of the beam at mid- span. Please, use the stress-strain relationship based on the Menegotto and Pinto model shown in Table 2.13 in your textbook. (15 points) (e) Determine the value of the strength reduction factor for flexure • per ACI 318. (10 points)