An AASHTO Type II bridge girder (see Appendix A, Table A11) isused for a 50 foot span. The beam is prestressed using strandedcables that apply a compressive force Pi = 432 kips at the time oftransfer. After all the time-dependent losses have occurred, aneffective prestress of Pe = 367 kips is obtained. The steelconsists of 29 3/8 in. wires. Degree 70 and the centroid has aconstant eccentricity of 12.5 in. (a) Since the beam sags upwardimmediately after the transfer of the prestressing force to thebeam, what stresses are produced in the concrete in the center ofthe span for that load state? (b) What stresses are produced in theunloaded member (prestress plus self-weight only) after all majorlosses have occurred? (c) What stresses occur after application ofthe full service load (sum of superimposed live and dead loads) of1630 kips/ft? (d) What is the factor of safety against cracking(defined with respect to increasing superimposed loads), themodulus of rupture being 0.53 kips/in2? (e) If the strength of theconcrete is fc' = 5 kips/in2 and the steel has a stress-straincurve as shown in Fig. 2.4, what is the total loadthat will cause the member to fail? (Use approximate ACI equationfor steel stresses and apply strength reduction factor to nominalmember strength.)
An Aashto Type Ii Bridge Girder See Appendix A Table A11 Is Used For A 50 Foot Span The Beam Is Prestressed Using St 1 (243.18 KiB) Viewed 33 times
An Aashto Type Ii Bridge Girder See Appendix A Table A11 Is Used For A 50 Foot Span The Beam Is Prestressed Using St 2 (122.32 KiB) Viewed 33 times
Esfuerzo, en kilolibras/pulg. 300 280 260 240 220 200 180 160 140 120 100 80 60 40 20 T fpy Torón de Torón de grado 270 grado 250 Spy fpy Alambre de 0.192 pulg. de diámetro Varilla de acero aleado, grado 160 -ĺpy Varilla de acero aleado, grado 145 Extensión de 1% Extensión de 0.7% 2000 1800 1600 1400 1200 1000 800 600 400 200 0 1 1 1 0 5 10 15 20 25 30 35 40 45 50 55 60 65 Deformación X 10³ Esfuerzo, N/mm² para los alambres Ep 29,000 kilolibras/pulg² para los torones Ep 27,000 kilolibras/pulg para las varillas Ep 27,000 kilolibras/pulg² Figura 2.4 Curvas de esfuerzo-deformación típicas para aceros de presfuerzo.
TABLA A.11 Propiedades de Sección de las Trabes de Puente AASHTO Wo 7.2 pulg.2 Lb/pie Ac h Tipo pulg. pulg.² pulg." I II III IV V VI 28 36 45 54 63 72 276 369 560 789 1013 1085 21 22,750 50.979 C1 C₂ pulg. pulg. 15.41 12.59 82 20.17 15.83 138 125,390 24.73 20.27 224 260,741 29.27 24.73 330 521,180 31.04 31.96 514 733,320 35.62 36.38 676 288 384 583 822 1055 1130
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