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Thread: reversal of concrete pressure calc.

  1. #1
    Associate Engineer
    Join Date
    Jun 2019

    reversal of concrete pressure calc.

    hi I'm trying to reverse a pressure calc for concrete.

    I can calculate the pressure easily and have set up an excel document to do this.

    I would know like to use all the same variables except I know the pressure, and know want to know the rise rate.
    basically allowing me to change the temp co efficient and get an output of different rise rates.

    formuale is

    P = D[C1√R+C2K√(H- (C1√R)])

    so want to make R the value to be found.

    Walls = where width or breadth > 2.0m, Columns were Width and Breadth <2.0m
    C_Struc = Column Unitless (Wall = 1, Column = 1.5) , Concrete Stucture Type
    C1 = 1.5
    Coeffcient dependant on size & shape of formwork
    C_Type= Retarded unitless (Normal = 0.3, Retarded = 0.45, Heavily Retarded=0.6) Cement Type
    C2 = 0.45
    Coefficent dependant on the constituent of Concrete
    D 25 kN/m Weight Density of Concrete
    h 9.05 m Vertical Pour Height
    H 9.05 m Vertical Form Height
    R 1 m/hr rate at which the concrete rises vertically up the form
    T 12.5 C Concrete Temperature ( Not Ambient Temp)
    K 1.60 Unitless (36/T+16), Temp Coeffcient
    Cira 108 Provisions
    -When C1 R > H, the fluid pressure (Dh) Should be taken as the design pressure
    P1 = 1.5 m
    H = 9.05 m Vertical Form Height
    Pd1 = Pressure is, D[C1√R+C2K√(H- (C1√R)]) Design Pressure = 86.82 kN/m
    Pd1 = 86.82 kN/m Calculated Pressure - The Design Pressure is the smallest between the two calculated values
    Pd2 = 226.25 kN/m Dh, Pressure
    Hz= 3.47 m Height of Hydrostatic Zone

  2. #2
    Lead Engineer
    Join Date
    Aug 2013
    Houston TX USA
    If you have M***cel, one way to solve equations like this is to set up a sheet where you have inputs for all know data including a cells for P and R, then place the equation for P in a cell and use Excel's "Goal Seeking Function" and have it seek the desired (known) value for P by changing R. Note: Before starting the Goal Seeking enter an arbirary positive value in the R cell to give Goal Seeking a starting point.

    If you are not familiar with the "Goal Seeking" function, you can find it under the "Data" tab, by picking the scroll down arrow on "What If Analysis" and you find the "Goal Seeking" function there.

    See the below sample excel sheet with the goal seeking function selected:

    Goal Seeking Sample.JPG

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