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    CE 76B - Midterm-Module 2.3b

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    Kristelle
    Dams are structures built across waterways to raise the water level for purposes like irrigation, power generation, navigation, and flood control. There are several types of dams including gravity dams, embankment dams, arch dams, and buttress dams. Gravity dams resist water pressure through their massive weight alone. Analyzing dams involves determining forces like water weight and uplift, calculating moments that cause sliding and overturning, and ensuring safety factors are above 1. Foundation pressure beneath dams is also analyzed to prevent tensile stresses in the soil.

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    CE 76B - Midterm-Module 2.3b

    Uploaded by

    Kristelle
    20 views7 pages
    Dams are structures built across waterways to raise the water level for purposes like irrigation, power generation, navigation, and flood control. There are several types of dams including gravity dams, embankment dams, arch dams, and buttress dams. Gravity dams resist water pressure through their massive weight alone. Analyzing dams involves determining forces like water weight and uplift, calculating moments that cause sliding and overturning, and ensuring safety factors are above 1. Foundation pressure beneath dams is also analyzed to prevent tensile stresses in the soil.

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    CE 76B -Midterm-Module 2.3b

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    Dams are structures built across waterways to raise the water level for purposes like irrigation, power generation, navigation, and flood control. There are several types of dams including gravity dams, embankment dams, arch dams, and buttress dams. Gravity dams resist water pressure through their massive weight alone. Analyzing dams involves determining forces like water weight and uplift, calculating moments that cause sliding and overturning, and ensuring safety factors are above 1. Foundation pressure beneath dams is also analyzed to prevent tensile stresses in the soil.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    20 views7 pages

    CE 76B - Midterm-Module 2.3b

    Uploaded by

    Kristelle
    Dams are structures built across waterways to raise the water level for purposes like irrigation, power generation, navigation, and flood control. There are several types of dams including gravity dams, embankment dams, arch dams, and buttress dams. Gravity dams resist water pressure through their massive weight alone. Analyzing dams involves determining forces like water weight and uplift, calculating moments that cause sliding and overturning, and ensuring safety factors are above 1. Foundation pressure beneath dams is also analyzed to prevent tensile stresses in the soil.

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    © All Rights Reserved
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    ISABELA STATE UNIVERSITY: ILAGAN CITY CAMPUS

    CE 76B: COURSE CORRELATION II


    (GEOTECHNICAL ENGINEERING, FLUIDS AND MECHANICS AND STRUCTURAL ENGINEERING)

    Module 2.3b
    Chapter 3: Total Hydrostatic Force on Surfaces: DAMS

    DAMS

    Dams are structures whose purpose is to raise the water level on the upstream side of river, stream, or
    other waterway. The rising water will cause hydrostatic force which will tend the dam to slide
    horizontally and overturn about its downstream edge or toe. The raised water level on the upstream
    edge or heel will also cause the water to seep under the dam. The pressure due to this seepage is
    commonly called hydrostatic uplift and will reduce the stability of the dam against sliding and against
    overturning.

    PURPOSE OF DAM
    Dams are built for th following purposes
    1. Irrigation and drinking water
    2. Power Supply (Hydroelectic)
    3. Navigation
    4. Flood Control
    5. Multi Purposes

    Figure 2.3.1b Section of a dam used for hydroelectric

    TYPESOF DAMS
    1. Gravity Dams – use only the force of gravity to resist water pressure that is, they hold back the
    water by the sheer force of their weight pushing downward. To do this, gravity dam must

    Prepared By: Engr. Chezanie Miya S. Asuncion


    1st Semester, S.Y. 2021-2022
    ISABELA STATE UNIVERSITY: ILAGAN CITY CAMPUS
    CE 76B: COURSE CORRELATION II
    (GEOTECHNICAL ENGINEERING, FLUIDS AND MECHANICS AND STRUCTURAL ENGINEERING)

    consist of a mass so heavy that the water in a reservoir cannot push the dam downstream to trip it
    over.

    2. Embankment Dam is a gravity dam formed out of loose rock, earth or a combination of these
    materials. The upstream and downstream slopes of embankment dams are flatter than those of
    concrete gravity dams.

    Prepared By: Engr. Chezanie Miya S. Asuncion


    1st Semester, S.Y. 2021-2022
    ISABELA STATE UNIVERSITY: ILAGAN CITY CAMPUS
    CE 76B: COURSE CORRELATION II
    (GEOTECHNICAL ENGINEERING, FLUIDS AND MECHANICS AND STRUCTURAL ENGINEERING)

    3. Arch Dams are concrete masonry structures that curve upstream into reservoir, stretching from
    one wall of a river canyon to the other.

    4. Buttress Dam consist of a wall, or face, supported by several buttresses on the downstream
    side. The vast majority of buttress dams are made of concrete that is reinforced with steel.

    GRAVITY DAM ANALYSIS

    The weight of gravity dam will cause a moment opposite to the overturning moment and the friction on
    the base will prevent the dam from sliding. The dam may also be prevented from sliding by keying its

    Prepared By: Engr. Chezanie Miya S. Asuncion


    1st Semester, S.Y. 2021-2022
    ISABELA STATE UNIVERSITY: ILAGAN CITY CAMPUS
    CE 76B: COURSE CORRELATION II
    (GEOTECHNICAL ENGINEERING, FLUIDS AND MECHANICS AND STRUCTURAL ENGINEERING)

    base into the bedrock.

    Figure 2.3.2b Typical section on gravity dam showing the possible forces acting

    STEPS OF SOLUTION

    Step 1
    Consider 1 unit length (1 m length) of dam perpendicular to the cross section.

    Step 2
    Determine all the forces acting:
    1. Vertical forces
     WW = Weight of dam
    W1=γ1V 1; W2=γ2V 2; W3=γ3V 3;
     FV/ W4 = Weight of water in the upstream side (if any)
    W4=γ4V 4
     Weight or permanent structures on the dam
     U = Hydrostatic uplift

    Prepared By: Engr. Chezanie Miya S. Asuncion


    1st Semester, S.Y. 2021-2022
    ISABELA STATE UNIVERSITY: ILAGAN CITY CAMPUS
    CE 76B: COURSE CORRELATION II
    (GEOTECHNICAL ENGINEERING, FLUIDS AND MECHANICS AND STRUCTURAL ENGINEERING)

    U1=γV U1 ; U2=γV U2

    2. Horizontal forces
     FH = Horizontal component of total hydrostatic force
    FH=γhA
     Wind pressure, wave action, floating bodies, earthquake load, etc.

    Step 3
    Solve for the reaction
    1. Horizontal component of the reaction
    Rx=ΣFHRx=ΣFH
    2. Vertical component of the reaction
    Ry=ΣFVRy=ΣFV

    Step 4
    Moment about the toe
    1. Righting moment, RM(Rotation towards the upstream side)
    RM = Sum of all rotation towards the upstream side
    2. Overturning moment, OM(rotation towards the downstream sides
    OM = Sum of all rotation towards the downstream side

    Step 5
    Location of Ry as measured from the toe
    x¯=( RM − OM)/Ry

    Factors of Safety
    Factor of safety against sliding, FSs
    FSs=μRy/Rx>1.0

    Factor of safety against overturning, FSo


    FSo=RM/OM>1.0

    Where μ = coefficient of friction between the base of the dam and the foundation.

    Foundation Pressure
    Eccentricity, e
    For e < B/6
    From Combined axial and bending stress formula:

    q=−Ry ± (Rye)(B/2)
    q=−Ry (1 ±6e) , where e< B/6
    B1 B³/12
    B B
    q=−Ry ± 6Rye
    B B²

    Prepared By: Engr. Chezanie Miya S. Asuncion


    1st Semester, S.Y. 2021-2022
    ISABELA STATE UNIVERSITY: ILAGAN CITY CAMPUS
    CE 76B: COURSE CORRELATION II
    (GEOTECHNICAL ENGINEERING, FLUIDS AND MECHANICS AND STRUCTURAL ENGINEERING)

    For the sign of 6e/B6e/B, use (+) at point where Ry is nearest. From the diagram above, use (+)
    for qT and (-) for qH. A negative q indicates compressive stress and a positive q indicates tensile stress. A
    positive q will occur when e>B/6e>B/6. In foundation design, soil is not allowed to carry tensi le stress,
    thus, any +q will be neglected in the analysis.

    If e>B/6, Ry is outside the middle third and the foundation pressure is triangular.
    Soil cannot carry any tensile stress, the result of Combined axial and bending stress formula is invalid if
    the stress is positive. Tus will happen if e>B/6, should third happen the equation to be used is,

    When e> B/6


    Xbar= a/3
    A= 3 x bar
    Ry = ½ aqe1
    Ry = ½ (3 x bar) qe

    qe=2Ry/3x¯

    Source:

    Mathalino.com

    Fluid Mechanucs & Hydrau;ics 4th Edition by Gillesania

    Prepared By: Engr. Chezanie Miya S. Asuncion


    1st Semester, S.Y. 2021-2022
    ISABELA STATE UNIVERSITY: ILAGAN CITY CAMPUS
    CE 76B: COURSE CORRELATION II
    (GEOTECHNICAL ENGINEERING, FLUIDS AND MECHANICS AND STRUCTURAL ENGINEERING)

    Prepared By: Engr. Chezanie Miya S. Asuncion


    1st Semester, S.Y. 2021-2022

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