In the question that follow, the loss of prestress is calculated for a 60 ft long AASHTO Type III beam, Fig. below The beam has a cross-sectional area of 560 in.², a moment of inertia of 125,390 in., a weight of 583 plf, and a surface volume-to-surface ratio of 4.09. Section properties can be found in Appendix C.2. One beam is pretensioned with 16½ in. diameter strands which are deflected to an eccentricity of 13 in. at midspan. A second beam is post-tensioned with two 8-strand tendons placed in a parabolic drape creating an eccentricity of 13 in. at midspan, shown in the figure below. For this, and the question that follow, the specified transfer strength of the concrete is f, of 3500 psi and the 28-day strength is 6000 psi. The beams are cured in a relative humidity of 35%. A ½ in. strand has an area of 0.153 in. a tensile strength of 270 ksi, and a modulus of elasticity of Ep=28,500 ksi. The post-tensioned beam uses a corrugated steel duct with a wobble friction of 0.0001 and a curvature friction of 0.20. Answer today
Q- In the question that follow, the loss of prestress is calculated for a 60 ft long AASHTO Type III beam, Fig. below The beam has a cross-sectional area of 560 in.², a moment of inertia of 125,390 in., a weight of 583 plf, and a surface volume-to-surface ratio of 4.09. Section properties can be found in Appendix C.2. One beam is pretensioned with 16½ in. diameter strands which are deflected to an eccentricity of 13 in. at midspan. A second beam is post-tensioned with two 8-strand tendons placed in a parabolic drape creating an eccentricity of 13 in. at midspan, shown in the figure below. For this, and the question that follow, the specified transfer strength of the concrete is f, of 3500 psi and the 28-day strength is 6000 psi. The beams are cured in a relative humidity of 35%. A ½ in. strand has an area of 0.153 in. a tensile strength of 270 ksi, and a modulus of elasticity of Ep=28,500 ksi. The post-tensioned beam uses a corrugated steel duct with a wobble friction of 0.0001 and a curvature friction of 0.20.
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