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    Sample Prestress

    Uploaded by

    Hilton D. Calawen
    This document contains the solutions to two problems related to the design of prestressed concrete beams. Problem 1 involves calculating the maximum live load capacity of a given prestressed concrete beam. Problem 2 involves designing a post-tensioned T-section beam to carry a specified service load over a 12m span, calculating the required section properties, prestressing, and verifying stresses satisfy limits. Short answers are also provided for questions about prestressing transfer length, options to satisfy stress limits at beam ends, and actions required if tension limits are exceeded.

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    © All Rights Reserved
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    Sample Prestress

    Uploaded by

    Hilton D. Calawen
    149 views4 pages
    This document contains the solutions to two problems related to the design of prestressed concrete beams. Problem 1 involves calculating the maximum live load capacity of a given prestressed concrete beam. Problem 2 involves designing a post-tensioned T-section beam to carry a specified service load over a 12m span, calculating the required section properties, prestressing, and verifying stresses satisfy limits. Short answers are also provided for questions about prestressing transfer length, options to satisfy stress limits at beam ends, and actions required if tension limits are exceeded.

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    SAMPLE PRESTRESS

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    This document contains the solutions to two problems related to the design of prestressed concrete beams. Problem 1 involves calculating the maximum live load capacity of a given prestressed concrete beam. Problem 2 involves designing a post-tensioned T-section beam to carry a specified service load over a 12m span, calculating the required section properties, prestressing, and verifying stresses satisfy limits. Short answers are also provided for questions about prestressing transfer length, options to satisfy stress limits at beam ends, and actions required if tension limits are exceeded.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    149 views4 pages

    Sample Prestress

    Uploaded by

    Hilton D. Calawen
    This document contains the solutions to two problems related to the design of prestressed concrete beams. Problem 1 involves calculating the maximum live load capacity of a given prestressed concrete beam. Problem 2 involves designing a post-tensioned T-section beam to carry a specified service load over a 12m span, calculating the required section properties, prestressing, and verifying stresses satisfy limits. Short answers are also provided for questions about prestressing transfer length, options to satisfy stress limits at beam ends, and actions required if tension limits are exceeded.

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    You are on page 1of 4

    Prestressed Concrete 50 minutes

    Second Exam Solution


    Name:………………………….. ID.:………………..
    (7 points)
    Problem 1: Consider the prestressed concrete beam shown below, which is to be used in an industrial
    building construction. The beam is only reinforced with prestressing steel and no mild reinforcement
    is used. What is the maximum live load that this beam can carry (in addition to the self weight)
    considering only the allowable section stresses at Midspan?
    The material properties and prestressing are as follow:
    WLL

    300mm

    600mm

    15 m

    f’c = 40MPa f’ci = 35MPa 70mm 300mm


    fpu = 1860 MPa fpi = 1120MPa
    ΔfpT = 140MPa (total losses) Aps = 8φs13 = 8 x 99mm2/strand

    SOLUTION:
    At service limit state
    0.3 0.6 25 4.5 /
    8 99 1120 140 /1000 776.16
    300 70 230 ; 300 600 180,000 ; 300 600 /12 5.4 10
    5.4 10 /180,000 30,000
    5.4 10 /300 18 10

    1
    776,160 230 300
    0.45 40 1
    180,000 30,000 18 10

    424.9 . 4.5 15 /8
    10.61 /

    1
    776,160 230 300
    0.5√40 1
    180,000 30,000 18 10

    313.1 . 4.5 15 /8
    6.631 /

    . /

    Page 1 of 4
    Prestressed Concrete
    Second Exam Solution

    (6 points)

    Problem 2: Answer the following three questions with short and precise answers:

    (a) What do you understand from the term “prestressing transfer length”

    The distance over which the strand should be bonded to the concrete to
    develop the effective prestress after losses

    (b) If allowable stress limits are not satisfied at the end of a beam with straight strands, write down at
    least two options that can be used to satisfy these limits.

    1. Use Raised-up tendons near the ends


    2. Use Debonding some tendons near the ends
    3. Use Supplementary nonprestressed steel

    (c) In case the tension limit is exceeded, which of the following is true:

    1. Extra tension force resulting from extra tension stressed should be carried by mild steel

    2. Concrete cover should be increased by 30%

    3. All tension force resulting from the entire tension stresses should be carried by mild steel

    4. This case is not allowed to occur in the design by standard codes.

    Page 2 of 4
    Prestressed Concrete
    Second Exam Solution
    (12 points)
    Problem 2: Design, for service load condition, a post-tensioned T-section to carry a total service load
    of 15 kN/m (not including self weight) on a 12m simply supported span. Design the section for zero-
    tension, for fci = 12.5MPa and fc = 11.0MPa at transfer and service conditions, respectively. Assume
    that the sectional properties are bf = 0.5h, hf = 0.2h, and bw = 0.25h and use multiples of 50mm for h.
    Assume the self weight of the beam is 6.0 kN/m and the following prestressing data:
    f’c = 35MPa f’ci = 30MPa bf
    fpu = 1860 MPa fpi = 1300MPa
    ΔfpT = 250MPa Aps = 1φs13 = 99 mm2/strand
    hf
    Ct=0.43h

    SOLUTION: bw
    1 250/1300 0.192 h
    6 12 /8 108kN. m
    e Cb=0.57h
    15 12 /8 270kN. m

    0.192 108 270


    10 26.431 10
    0 11

    1 0.192 108 270


    10 28.786 10
    0 0.808 12.5

    0.5 0.2 0.25 0.8


    0.5 0.2 0.33 0.25 0.8 0.17 0.02767
    12 12

    0.02767
    26.431 10 743.3 ;
    0.43

    0.02767
    28.786 10 840 ;
    0.57

    Î Use h = 850mm; A=216,750mm2 I=1.444 x 1010mm4 ; St=39.20 x 106 mm3


    Sb = 30.00 x 106 mm3 ; r2 = 66,621 mm2 ; MD = 97.54 kN.m

    Analysis at Initial Stage:

    .
    0.43 850 5.375
    5.375 216,750/1000 1,165
    1,165 10 /1300 896.2 Î USE 9φs13= 891mm2
    891 1300/1000 1,158.3
    . .
    0 5.375 266.00
    , , , ,

    Î Use 9φs13= 891mm2 ; Pi = 1,158.3 kN ; ec = 265 mm ; Pe = 935.91 kN

    Page 3 of 4
    Prestressed Concrete
    Second Exam Solution
    Check Stresses:

    1. At initial stage:

    1
    1,158,300 265 365.5 97.54 10
    1
    216,750 66,621 39.2 10
    2.425 2.488 0.063 0.0 !

    1
    1,158,300 265 484.5 97.54 10
    1
    216,750 66,621 30.0 10
    15.643 3.251 12.392 12.5 !

    2. At final stage:

    1
    935,910 265 365.5 367.54 10
    1
    216,750 66,621 39.2 10
    1.960 9.376 7.416 11 !

    1
    935,910 265 484.5 367.54 10
    1
    216,750 66,621 30.0 10
    12.639 12.251 0.388 0.0 !

    450

    170

    212.5
    850
    265

    9φs13

    Page 4 of 4

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