The section of a prestressed box girder is shown. Unit weight of concrete is 20 kN/m3. The total prestressing force is 3400 kN. Assume that there is a loss of prestress of 15% at service loads. Simple span L = 20 m. a.What is the stress at the bottom fibers due to prestress in MPa? b.What is the stress at the top fibers due to prestress in MPa? c.What is the stress at the top fibers at midspan due to combined beam weight and prestressing force, in MPa? d.What additional uniform service load over the entire span will cause zero stress at the bottom fibers at midspan, in kN/m.
The section of a prestressed box girder is shown. Unit weight of concrete is 20 kN/m3. The total prestressing force is 3400 kN. Assume that there is a loss of prestress of 15% at service loads. Simple span L = 20 m. a.What is the stress at the bottom fibers due to prestress in MPa? b.What is the stress at the top fibers due to prestress in MPa? c.What is the stress at the top fibers at midspan due to combined beam weight and prestressing force, in MPa? d.What additional uniform service load over the entire span will cause zero stress at the bottom fibers at midspan, in kN/m.
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
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The section of a prestressed box girder is shown. Unit weight of concrete is 20 kN/m3. The total prestressing force is 3400 kN. Assume that there is a loss of prestress of 15% at service loads. Simple span L = 20 m.
a.What is the stress at the bottom fibers due to prestress in MPa?
b.What is the stress at the top fibers due to prestress in MPa?
c.What is the stress at the top fibers at midspan due to combined beam weight and prestressing force, in MPa?
d.What additional uniform service load over the entire span will cause zero stress at the bottom fibers at midspan, in kN/m.
Transcribed Image Text:O
900 mm
N.A.
A = 350,000 mm2
Ik = 15,000 x 106 mm4
O O O
O
O
280 mm
600 mm
90 mm
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