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    2012 Exam

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    Jagannathan
    1. A testing system was used to determine friction loss coefficients for tendons in straight and curved concrete elements. The loads measured at load cells were 95.7% and 89.9% of jacking loads, respectively. The values of friction coefficient μ and its rate of change k need to be determined. 2. A 3m prestressed concrete member subjected to axial tension is given. The new length needs to be evaluated assuming negligible crack width and given material properties and stresses. 3. Stresses in a pretensioned box girder carrying steam pipes need to be estimated at midspan on a cold winter day, given temperatures, material properties, geometry, and self-weight.

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    2012 Exam

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    Jagannathan
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    1. A testing system was used to determine friction loss coefficients for tendons in straight and curved concrete elements. The loads measured at load cells were 95.7% and 89.9% of jacking loads, respectively. The values of friction coefficient μ and its rate of change k need to be determined. 2. A 3m prestressed concrete member subjected to axial tension is given. The new length needs to be evaluated assuming negligible crack width and given material properties and stresses. 3. Stresses in a pretensioned box girder carrying steam pipes need to be estimated at midspan on a cold winter day, given temperatures, material properties, geometry, and self-weight.

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    1. A testing system was used to determine friction loss coefficients for tendons in straight and curved concrete elements. The loads measured at load cells were 95.7% and 89.9% of jacking loads, respectively. The values of friction coefficient μ and its rate of change k need to be determined. 2. A 3m prestressed concrete member subjected to axial tension is given. The new length needs to be evaluated assuming negligible crack width and given material properties and stresses. 3. Stresses in a pretensioned box girder carrying steam pipes need to be estimated at midspan on a cold winter day, given temperatures, material properties, geometry, and self-weight.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    27 views3 pages

    2012 Exam

    Uploaded by

    Jagannathan
    1. A testing system was used to determine friction loss coefficients for tendons in straight and curved concrete elements. The loads measured at load cells were 95.7% and 89.9% of jacking loads, respectively. The values of friction coefficient μ and its rate of change k need to be determined. 2. A 3m prestressed concrete member subjected to axial tension is given. The new length needs to be evaluated assuming negligible crack width and given material properties and stresses. 3. Stresses in a pretensioned box girder carrying steam pipes need to be estimated at midspan on a cold winter day, given temperatures, material properties, geometry, and self-weight.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    of 3

    The University of Western Ontario - Faculty of Engineering

    Department of Civil and Environmental Engineering

    Final Examination - April 2012

    CEE 9628b – Prestressed Concrete Dr. M.A. Youssef, P.Eng. Page 1/3

    Problem 1: (9 marks – 15 minutes)


    Load
    A post-tensioning supplier has developed a Jack
    Cell
    testing system to determine experimentally the
    friction loss coefficients (μ and k) for different 9m
    tendon systems. Two concrete elements have

    R 23 m
    been cast, one being straight and the other
    being a circular arc with radius of 23 m, Fig. 1.
    The loads measured at the shown load cells
    Load
    were 95.7% and 89.9% of the jacking loads for Jack
    Cell
    the straight and circular tendon shapes,
    respectively. Determine the values of μ and k. 9m

    Fig. 1 Determination of Friction Coefficients

    Problem 2: (18 marks – 30 minutes)

    A three meter long prestressed concrete member (original length, i.e. when εc=0), Fig. 2, is subjected to
    an axial tensile force N. If the stress in the deformed reinforcing bars is equal to 300 MPa at a crack
    location, evaluate the new length of the member assuming that width of cracks is almost zero. Given:
    * Δεp = 0.006, fc’ = 30 MPa, fcr = 2 MPa, fsy = 400 MPa, fspy = 1600 MPa, Es = Ep = 200,000 MPa
    * For concrete in tension, you have to consider tension stiffening.
    * For steel bars and prestressing strands, assume a bilinear stress-strain relationship (f = fy for ε ≥ εy).
    .

    50 mm (typ.)

    2 No. 15M bars


    300 mm

    2-15 mm seven wire


    150 mm

    strands

    2 No. 15M bars

    100 100
    300 mm

    Figure 2 Prestress Concrete Member


    The University of Western Ontario - Faculty of Engineering
    Department of Civil and Environmental Engineering

    Final Examination - April 2012

    CEE 9628b – Prestressed Concrete Dr. M.A. Youssef, P.Eng. Page 2/3

    50 mm
    150 mm
    Problem 3: (30 marks – 50 minutes)

    The pretensioned box girder, Fig. 3, is simply 2-13 mm Seven Wire


    supported with a span of 20 m. It is used to carry the Strands
    steam pipes shown. Assuming uncracked elastic
    response, estimate the concrete stresses at midspan on

    900 mm
    a cold winter day. Steam
    Pipes

    150 mm

    50 mm
    Given:
    * Δεp = 0.0065, w = 10 kN/m,
    * Temperature at casting = 20 oC, 6-13 mm Seven Wire
    Strands
    * Ec eff =10,000 MPa, Ep eff = 194000 MPa
    * εsh = -0.4×10-3, αc=αp= 10×10-6 / oC 150 mm 150 mm
    * Temperature of shaded area = +30 oC 600 mm
    * Temperature of remaining areas = -20 oC
    Figure 3 Pretensioned Box Girder

    Problem 4: (27 marks – 45 minutes) P


    Horizontally e
    A prestressed concrete column, Figure 4, contains four size 15 seven wire Restrained

    strands that were pretensioned to 1350 MPa. After the column was loaded with
    an axial compression P at end eccentricities e, the concrete strains were
    measured at points A and B and found equal to -3.16×10-3 and +0.5×10-3,
    respectively. Given that fc’=65 MPa, εo=-0.002 and fpy=0.85fpu, estimate the axial
    load P and the end eccentricity e.
    Stress

    B A
    4m

    fpu
    f 40 mm (typ.)
    py
    2m
    240 mm

    Ep
    Strain
    Horizontally
    0.05 Restrained
    e
    240 mm P

    Figure 4 Eccentrically Loaded Column


    The University of Western Ontario - Faculty of Engineering
    Department of Civil and Environmental Engineering

    Final Examination - April 2012

    CEE 9628b – Prestressed Concrete Dr. M.A. Youssef, P.Eng. Page 3/3

    Problem 5: (24 marks – 40 minutes)

    The prestressed concrete beam, shown in Fig. 5, is fixed at the left end and roller-supported at the right.
    It is post-tensioned with a single tendon with a parabolic profile.
    (1) Calculate the primary, secondary, and total moments due to prestressing.
    (2) What minor adjustment could be made in the tendon profile to produce a concordant tendon?
    250 mm

    600 mm
    300 mm
    150 mm

    6000 mm 6000 mm

    Fig. 5 Prestressed Concrete Beam

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