Category Archives: Civil Engineering

the application of mathematics, science, and engineering to the design, maintenance, and analysis of the build environment

Useful Soil Coefficients

Previously we discussed mechanical analysis and the method of sieve analysis. This allowed us to develop the particle size distribution curve. With this curve we can find some useful parameters. They are:

  • The Uniformity Coefficient
  • The Coefficient of Gradation

Both of these parameters are used in soil classification. The Uniformity Coefficient is defined as:

The Coefficient of Gradation is defined as:

where

These diameters are obtained from the particle size distribution curve by going across from the percent finer, coming to the curve, and turning 90 degrees down to the abscissa to locate the diameter as seen below.

Related Posts:

Sieve Analysis

Soil Moisture Content

Specific Gravity of Soil

Sieve Analysis

The first method of mechanical analysis is sieve analysis. It is pretty straight forward and involves straining a soil sample through a series of sieves. Generally the sieves are stacked as seen in the above diagram with a US Standard Sieve No. 4 at the top (This sieve size has a 4.75 mm opening) and a Sieve No. 200 at the bottom (with a 0.075 mm opening). The stack usually consists of 5 to 7 sieves and has a pan at the bottom. As you can see, the opening in the sieve gets smaller as you go down. Therefore larger particles will be captured while smaller particles will pass through. This allows us to measure how much soil of each size was in the original soil sample.

A few important steps:

  • the soil sample needs to be oven-dried and all clumps broke.
  • the weight of the empty sieves needs to be obtained.

Once this is done, the soil sample is placed into the top sieve, the lid is placed on the stack and the stack is placed in a mechanical shaker. The stack will then be shaken vigorously for approximately 5 minutes to ensure proper distribution of the particles.

The next step is to calculate what is called the percent passing or the percent finer. This is simply the percentage of the entire soil sample that passed through a particular sieve. For example, the percent passing the No. 200 sieve would be the mass of the soil in the bottom pan (since that is the soil that passed through the No. 200 sieve) divided by the total mass of the original soil sample. So in general we can write:

where

  • %P is the percent passing
  • i represents the ith sieve
  • n represents the number of sieves
  • m is the mass

Once the percent passing is determined for each sieve, a plot is made of sieve or particle size versus percent passing as seen below. The percent passing is on the ordinate and the sieve or particle size is on the abscissa. Also notice the abscissa is reverse logarithmic.

In future posts we will look more carefully at what information this distribution curve can provide, but for now we are highlighting the process. If you have any questions, please let me know in the comments.

Related Posts:

Specific Gravity of Soil

Soil Moisture Content

Structural Finite Element Analysis Software Installation

My engineering capstone design team and I recently completed our design and implementation of a structural finite element analysis (SFEA) tool. It allows a user to analyze any two-dimensional structure (beam, frame, truss). The user provides the geometry of the structure along with element parameters (cross-sectional area, modulus of elasticity, etc.) and the loads applied. The program will then calculate the nodal displacements, the reactions at the supports, and the forces acting on each element. The tool is built on the free, open-source platform called Scilab. My desire here is to make the code available to everyone for use or for further modification and development, and to provide instructions on its installation.

In order to run the application it will of course be necessary to have Scilab. Click here and you will be directed to the Scilab site where you can download and install the program. Once you have done this, open Scilab. This will bring up the main console. In the top menu, select ‘Applications->Scinotes’.

This will open the Scinotes editor in a new window. In this window you should paste the SFEA code from the end of this post (sorry for the length)

Once you have pasted the code into the Scinotes editor, save it as ‘SFEA.sci’ in the ‘C:\Program_Files\scilabx.x.x\modules\scinotes\macros’ folder and execute the code from the execute menu or the control button.

Now return to the main console and at the command prompt enter the function name, ‘–>SFEA’ , in all caps. When you hit enter, the program will run and open up two new windows. The left window will provide the controls for user entry while the right window will be used to plot the structure graphically.

To learn how to utilize the program, I have written a user’s guide.

If you have any questions or problems, please let me know in the comments section.

————————————————————————————————————————————————————————–

function SFEA()
//=======================================================================================
//DECLARATIONS OF GLOBAL VARIABLES AND CONSTANTS
//=======================================================================================
    clearglobal();

    global main_window_x;   //constants
    global main_window_y;
    global main_window_w;
    global main_window_h;
    global plot_window_x;
    global plot_window_y;
    global plot_window_w;
    global plot_window_h;
    global margin_x;
    global margin_y;
    global spacing_x;
    global spacing_y;
    global text_w;
    global text_h;
    global button_w;

    global Truss_Switch;   //variables
    global Beam_Switch;
    global Node_Entry_Switch;
    global Member_Entry_Switch;
    global Reactions_Entry_Switch;
    global Num_Nodes;
    global Node_Coord;
    global Axes_Size;
    global Node_Type;
    global Num_Members;
    global Connect_Mat;
    global Num_Load_Types;
    global Loads;
    global Num_Load_Combos;
    global Load_Factors;
    global Ultimate_Loads;
    global Local_k;
    global Transf_Mat;
    global Displacements;
    global Structure_Forces;

//==============================================================================================
//GLOBAL CONSTANT DEFINITIONS
//==============================================================================================    

    main_window_x      =0;
    main_window_y      =0;
    main_window_w      =335; //width
    main_window_h      =600; //height

    plot_window_x      =main_window_x+main_window_w+18;
    plot_window_y      =main_window_y;
    plot_window_w      =640;
    plot_window_h      =main_window_h;

    margin_x           =10;
    margin_y           =15;

    spacing_x          =10;
    spacing_y          =10;

    text_w             =145;
    text_h             =25;
    button_w           =120;

//==================================================================================================
//CREATE THE PRIMARY WINDOWS AND MENUS
//==================================================================================================
    //create the figure 'Main_Window'
    Main_Window=figure(1);
    Main_Window.Figure_name = "Structural Finite Element Analysis";
    Main_Window.Position = [main_window_x,main_window_y,main_window_w,main_window_h];
    Main_Window.Background = 8; //white

    //create the figure 'Plot_Window'
    Plot_Window=figure(2);
    Plot_Window.Figure_name = "Structure Plot"
    Plot_Window.Position = [plot_window_x,plot_window_y,plot_window_w,plot_window_h];
    Plot_Window.Background = 8; //white

    //modify the menus of 'Main_Window'
    delmenu(Main_Window.figure_id, gettext("&File"));
    delmenu(Main_Window.figure_id, gettext("&Tools"));
    delmenu(Main_Window.figure_id, gettext("&Edit"));
    delmenu(Main_Window.figure_id, gettext("&?"));
    toolbar(Main_Window.figure_id, "off");
    // create the "File" menu on the menu bar
    file_menu = uimenu(Main_Window,'label', '&File');
    //create two submenus in the "File" menu
    new_submenu=uimenu(file_menu,'label', '&New');
    close_submenu=uimenu(file_menu,'label', '&Close', 'callback', "Close_Program()");
    //create submenus of "New"
    new_select1=uimenu(new_submenu,'label', '&Beam','callback',"Beam_Analysis()");
    new_select2=uimenu(new_submenu,'label', '&Frame','callback',"Frame_Analysis()");
    new_select3=uimenu(new_submenu,'label', '&Truss','callback',"Truss_Analysis()");

endfunction
//========================================================================================================================
//MENU-ROUTINES
//========================================================================================================================
function Close_Program()
    scf(2);
    close(); //close the plot window
    scf(1);
    close(); //close the main window
endfunction
//========================================================================================================================
function Beam_Analysis()
    global Truss_Switch;
    global Beam_Switch;
    global Node_Entry_Switch;
    global Member_Entry_Switch;
    global Reactions_Entry_Switch;
    Truss_Switch = 0;
    Beam_Switch = 1;
    Node_Entry_Switch = 0;
    Member_Entry_Switch = 0;
    Reactions_Entry_Switch = 0;
    Clear_Figures();
    Load_Controls();
endfunction
//========================================================================================================================
function Frame_Analysis()
    global Truss_Switch;
    global Beam_Switch;
    global Node_Entry_Switch;
    global Member_Entry_Switch;
    global Reactions_Entry_Switch;
    Truss_Switch = 0;
    Beam_Switch = 0;
    Node_Entry_Switch = 0;
    Member_Entry_Switch = 0;
    Reactions_Entry_Switch = 0;
    Clear_Figures();
    Load_Controls();
endfunction
//========================================================================================================================
function Truss_Analysis()
    global Truss_Switch;
    global Beam_Switch;
    global Node_Entry_Switch;
    global Member_Entry_Switch;
    global Reactions_Entry_Switch;
    Truss_Switch = 1;
    Beam_Switch = 0;
    Node_Entry_Switch = 0;
    Member_Entry_Switch = 0;
    Reactions_Entry_Switch = 0;
    Clear_Figures();
    Load_Controls();
endfunction
//========================================================================================================================
//SUB-ROUTINES
//========================================================================================================================
function Clear_Figures()
    scf(2);
    clf();
    scf(1);
    f=gcf();
    C=f.children;
    for i=1:length(C)
        c=C(i);
        if c.type~="uimenu"
            delete(c);
        end
    end
endfunction
//========================================================================================================================
//========================================================================================================================
function Load_Controls()
    global main_window_x;
    global main_window_y;
    global main_window_w;
    global main_window_h;
    global plot_window_x;
    global plot_window_y;
    global plot_window_w;
    global plot_window_h;
    global margin_x;
    global margin_y;
    global spacing_x;
    global spacing_y;
    global text_w;
    global text_h;
    global button_w;

    //================================================================================================
    scf(1); //set current figure to 'Main_Window'
    //================================================================================================
    //frames:
    //inputs frame
    Frame1=uicontrol(gcf(),"style","frame");
    Frame1.Position = [(margin_x/2),435,320,185];
    Frame1.HorizontalAlignment = "center";
    Frame1.BackgroundColor = [1,1,1]; //white

    //results frame
    Frame2=uicontrol(gcf(),"style","frame");
    Frame2.Position = [(margin_x/2),300,320,130];
    Frame2.HorizontalAlignment = "center";
    Frame2.BackgroundColor = [1,1,1]; //white
    //==================================================================================================
    //1st Line: number of nodes and their coordinates
    //creates text in the main window
    Node_Text=uicontrol(gcf(),"style","text");
    Node_Text.Position = [margin_x,main_window_h-margin_y,text_w,text_h];
    Node_Text.BackgroundColor = [1,1,1]; //white
    Node_Text.String = "Number of Nodes";

    //creates edit box for entering data in the main window
    Num_Node_Box=uicontrol(gcf(),"style","edit");
    Num_Node_Box.Position = [margin_x+text_w+spacing_x,main_window_h-margin_y,text_h,text_h];
    Num_Node_Box.String = "0";
    Num_Node_Box.Tag = "NNB"

    //create a pushbutton in the main window
    Node_Button=uicontrol(gcf(),"style","pushbutton");
    Node_Button.Position = [margin_x+text_w+2*spacing_x+text_h,main_window_h-margin_y,button_w,text_h];
    Node_Button.String = "Node Coordinates";
    Node_Button.Callback = "Get_Node_Coord()";
    //====================================================================================================
    //2nd Line: node reactions
    //creates text in the main window
    Reactions_Text=uicontrol(gcf(),"style","text");
    Reactions_Text.Position = [margin_x,main_window_h-margin_y-text_h-spacing_y,text_w,text_h];
    Reactions_Text.BackgroundColor = [1,1,1]; //white
    Reactions_Text.String = "Node Reactions";

    //create a pushbutton in the main window
    Reactions_Button=uicontrol(gcf(),"style","pushbutton");
    Reactions_Button.Position = [margin_x+text_w+2*spacing_x+text_h,main_window_h-margin_y-text_h-spacing_y,button_w,text_h];
    Reactions_Button.String = "Select Reactions";
    Reactions_Button.Callback = "Get_Node_Reactions()";
    //====================================================================================================
    //3rd Line: number of members and their connectivity
    //creates text in the main window
    Member_Text=uicontrol(gcf(),"style","text");
    Member_Text.Position = [margin_x,main_window_h-margin_y-2*text_h-2*spacing_y,text_w,text_h];
    Member_Text.BackgroundColor = [1,1,1]; //white
    Member_Text.String = "Number of Members";

    //creates edit box for entering data in the main window
    Num_Member_Box=uicontrol(gcf(),"style","edit");
    Num_Member_Box.Position = [margin_x+text_w+spacing_x,main_window_h-margin_y-2*text_h-2*spacing_y,text_h,text_h];
    Num_Member_Box.String = "0";
    Num_Member_Box.Tag = "NMB"

    //create a pushbutton in the main window
    Member_Button=uicontrol(gcf(),"style","pushbutton");
    Member_Button.Position = [margin_x+text_w+2*spacing_x+text_h,main_window_h-margin_y-2*text_h-2*spacing_y,button_w,text_h];
    Member_Button.String = "Member Data";
    Member_Button.Callback = "Get_Member_Data()";
    //====================================================================================================================
    //4th Line: applied loads
    //creates text in the main window
    Loads_Text=uicontrol(gcf(),"style","text");
    Loads_Text.Position = [margin_x,main_window_h-margin_y-3*text_h-3*spacing_y,text_w,text_h];
    Loads_Text.BackgroundColor = [1,1,1]; //white
    Loads_Text.String = "Number of Load Types"

    //creates edit box for entering data in the main window
    Num_Loads_Box=uicontrol(gcf(),"style","edit");
    Num_Loads_Box.Position = [margin_x+text_w+spacing_x,main_window_h-margin_y-3*text_h-3*spacing_y,text_h,text_h];
    Num_Loads_Box.String = "0";
    Num_Loads_Box.Tag = "NLTB"

    //create a pushbutton in the main window
    Loads_Button=uicontrol(gcf(),"style","pushbutton");
    Loads_Button.Position = [margin_x+text_w+2*spacing_x+text_h,main_window_h-margin_y-3*text_h-3*spacing_y,button_w,text_h];
    Loads_Button.String = "Loads";
    Loads_Button.Callback = "Get_Loads()";
    //=========================================================================================================================
    //5th Line: load factors and load combinations
    //creates text in the main window
    Combos_Text=uicontrol(gcf(),"style","text");
    Combos_Text.Position = [margin_x,main_window_h-margin_y-4*text_h-4*spacing_y,text_w,text_h];
    Combos_Text.BackgroundColor = [1,1,1]; //white
    Combos_Text.String = "Number of Load Combinations"

    //creates edit box for entering data in the main window
    Num_Combos_Box=uicontrol(gcf(),"style","edit");
    Num_Combos_Box.Position = [margin_x+text_w+spacing_x,main_window_h-margin_y-4*text_h-4*spacing_y,text_h,text_h];
    Num_Combos_Box.String = "0";
    Num_Combos_Box.Tag = "NLCB"

    //create a pushbutton in the main window
    Combos_Button=uicontrol(gcf(),"style","pushbutton");
    Combos_Button.Position = [margin_x+text_w+2*spacing_x+text_h,main_window_h-margin_y-4*text_h-4*spacing_y,button_w,text_h];
    Combos_Button.String = "Load Factors";
    Combos_Button.Callback = "Get_Load_Combos()";
    //=========================================================================================================================
    //6th Line: find displacements
    //create a pushbutton in the main window
    Displacements_Button=uicontrol(gcf(),"style","pushbutton");
    Displacements_Button.Position = [margin_x+10*spacing_x,main_window_h-margin_y-5.5*text_h-5.5*spacing_y,button_w,text_h];
    Displacements_Button.String = "Find Displacements";
    Displacements_Button.Callback = "Find_Displacements()";
    //=========================================================================================================================
    //7th Line: find reactions
    //create a pushbutton in the main window
    Reactions_Button=uicontrol(gcf(),"style","pushbutton");
    Reactions_Button.Position = [margin_x+10*spacing_x,main_window_h-margin_y-6.5*text_h-6.5*spacing_y,button_w,text_h];
    Reactions_Button.String = "Find Reactions";
    Reactions_Button.Callback = "Find_Reactions()";
    //=========================================================================================================================
    //8th Line: find member forces
    //create a pushbutton in the main window
    Reactions_Button=uicontrol(gcf(),"style","pushbutton");
    Reactions_Button.Position = [margin_x+10*spacing_x,main_window_h-margin_y-7.5*text_h-7.5*spacing_y,button_w,text_h];
    Reactions_Button.String = "Find Member Forces";
    Reactions_Button.Callback = "Find_Forces()";
endfunction
//=============================================================================================================================
//Data Entry and Callback Functions
//=============================================================================================================================
function Get_Node_Coord()
    //Extracts the number of nodes submitted by the user, obtains the node coordinates, and plots the nodes in the plot window
    global Num_Nodes;
    global Node_Entry_Switch;
    global Node_Coord;
    global Axes_Size;

    //Extract Num_Nodes from Edit Box in Main_Window
    Num_Nodes = evstr(get(findobj("Tag","NNB"), "String"));

    //Used to initialize the node coordinate matrix to zero during the first iteration
    //but maintain the inputted node coordinate entries during future callbacks
    if Node_Entry_Switch == 0 then
        Node_Coord=zeros(Num_Nodes,2);
        Node_Entry_Switch = 1;
    end

    //Let the user select the Node Coordinate data entry method
    Menu = list('',1,['Singularly','By Sets','From File']);
    Node_Entry_Method = x_choices('Select Entry Method',list(Menu));

    //execute the users selection
    select Node_Entry_Method
    case 1 then //======================================================================================================
        //Enter Nodes Singularly:

        //initializes dynamically sized matrix for coordinate labels
        Row_Labels=zeros(Num_Nodes,1);
        for i=1:Num_Nodes
            Row_Labels(i,1) = i;
        end

        //displays a matrix dialog box for user inputs and saves the coordinates to the matrix 'Node_Coord'
        Node_Coord=evstr(x_mdialog('Enter the Coordinates of the Nodes',string(Row_Labels),['X','Y'],string(Node_Coord)));

    case 2 then //===========================================================================================================
        //Enter Nodes via Sets:

        //Obtain the number of sets to be entered from the user
        Num_Sets = evstr(x_dialog('How many sets do you want to enter?','0'));

        //initializes dynamically sized matrix for set labels
        Row_Labels=zeros(Num_Sets);
        for i=1:Num_Sets
            Row_Labels(i) = i;
        end

        Set_Data = zeros(Num_Sets,7); //initialize the Set_Data matrix

        //displays a matrix dialog box for user inputs of the set data
        Set_Data=evstr(x_mdialog('Enter the Set Data',string(Row_Labels),['Node Number Start','Node Number Increment','X Start','Y Start','X Increment','Y Increment','Number of Nodes in Set'],string(Set_Data)));

        //take the data entered into the 'Set_Data' matrix and determine the coordinate matrix it produces
        for i=1:Num_Sets //for each set
            for j=0:(Set_Data(i,7)-1) //for each node in the set
                Node_Coord(Set_Data(i,1)+j*Set_Data(i,2),1)=Set_Data(i,3)+j*Set_Data(i,5);
                Node_Coord(Set_Data(i,1)+j*Set_Data(i,2),2)=Set_Data(i,4)+j*Set_Data(i,6);
            end
        end

    case 3 then //================================================================================================================
        //Enter Nodes from a File:

        File_Directory = uigetfile(["*.txt"],"SCI/modules/scinotes/macros/","Choose a file");
        fi=mopen(File_Directory,'r');
        Node_Coord=evstr(mgetl(fi,Num_Nodes));
        mclose(fi);
    end //========================================================================================================================

    //plots the nodes in the plot window
    Axes_Size = zeros(4);
    X=Node_Coord;
    Y=Node_Coord;
    X(:,2)=[];
    Y(:,1)=[];
    scf(2);
    clf(2);

    //determine the axes size for plotting
    //initial estimates
    Axes_Size(1)=min(Node_Coord(:,1))-((max(Node_Coord(:,1))-min(Node_Coord(:,1)))/10);
    Axes_Size(2)=min(Node_Coord(:,2))-((max(Node_Coord(:,2))-min(Node_Coord(:,2)))/10);
    Axes_Size(3)=max(Node_Coord(:,1))+((max(Node_Coord(:,1))-min(Node_Coord(:,1)))/10);
    Axes_Size(4)=max(Node_Coord(:,2))+((max(Node_Coord(:,2))-min(Node_Coord(:,2)))/10);

    //check for good proportionality
    width=Axes_Size(3)-Axes_Size(1);
    height=Axes_Size(4)-Axes_Size(2);
    if height==0 then
        aspect_ratio=3;
    else
        aspect_ratio=width/height;
    end

    //if not then adjust
    if aspect_ratio<0.5 then
        new_width=height/2;
        Axes_Size(1)=Axes_Size(1)-((new_width-width)/2);
        Axes_Size(3)=Axes_Size(3)+((new_width-width)/2);
    elseif aspect_ratio>2 then
        new_height=width/2;
        Axes_Size(2)=Axes_Size(2)-((new_height-height)/2);
        Axes_Size(4)=Axes_Size(4)+((new_height-height)/2);
    end

    //plot points
    plot2d(X,Y,style=-4,rect=Axes_Size);

    //print out the node coordinate matrix
    print(6,Node_Coord);
endfunction
//===========================================================================================================
//===========================================================================================================
function Get_Node_Reactions()
    //Presents a toggle dialog box for the user to select a type for each node and then
    //re-plots the nodes in the plot window with representative symbols
    global Reactions_Entry_Switch;
    global Num_Nodes;
    global Node_Type;
    global Node_Coord;
    global Axes_Size;

    //Used to initialize the node type matrix to 1s during the first iteration
    //but maintain the inputted node type entries during future iterations
    if Reactions_Entry_Switch == 0 then
        for j=1:Num_Nodes
            Node_Type(j) = 1;
        end
        Reactions_Entry_Switch = 1;

    end

    //generates a toggle selection dialog box for node type selection
    //current options are: Free, X-Roller, Y-Roller, Pin, Fixed, X-Spring, or Y-String
    //Free is the default value
    L=list();
    for i=1:Num_Nodes
        s='Node'+string(i);
        l  = list(s,Node_Type(i),['Free','X-Roller','Y-Roller','Pin','Fixed']);
        L(i)=l;
    end
    Node_Type = x_choices('Select Node Type',L);

    //re-plot the nodes as their respective node types
    X=Node_Coord;
    Y=Node_Coord;
    X(:,2)=[];
    Y(:,1)=[];
    scf(2);
    clf(2);
    for i=1:Num_Nodes
        select Node_Type(i)
        case 1 then
            s=-4; //Free
        case 2 then
            s=-3; //X-Roller
        case 3 then
            s=-9; //Y-Roller
        case 4 then
            s=-6; //Pin
        case 5 then
            s=-11; //Fixed
        end
        plot2d(X(i),Y(i),style=s,rect=Axes_Size);
    end

    //print out the node type matrix
    print(6,Node_Type);

endfunction
//==============================================================================================================
//==============================================================================================================
function Get_Member_Data()
    //Extracts the number of members from the user input, presents an x_mdialog box for the
    //user to input the starting and ending nodes of each member as well as the cross-secional
    //area, modulus of elasticity and moment of inertia, and plots the members
    //connecting the nodes in the plot window
    global Num_Members;
    global Member_Entry_Switch;
    global Connect_Mat;
    global Node_Coord;
    global Axes_Size;

    //Extract Num_Members from Edit Box in Main_Window
    Num_Members = evstr(get(findobj("Tag","NMB"), "String"));

    //Used to initialize the member data matrix to zero during the first iteration
    //but maintain the inputted member data entries during future iterations
    if Member_Entry_Switch == 0 then
        Connect_Mat=zeros(Num_Members,5);
        Member_Entry_Switch = 1;
    end

    //Let the user select the Member data entry method
    Menu = list('',1,['Singularly','By Sets','From File']);
    Member_Entry_Method = x_choices('Select Entry Method',list(Menu));

    //execute the users selection
    select Member_Entry_Method
    case 1 then //======================================================================================================
        //enter Member Data Singularly

        //initializes dynamically sized matrix for member labels
        Row_Labels=zeros(Num_Members);
        for i=1:Num_Members
            Row_Labels(i) = i;
        end

        //displays a matrix dialog box for user inputs and saves the member connections to the matrix 'Connect_Mat'
        Connect_Mat=evstr(x_mdialog('Enter the Members Information',string(Row_Labels),['Starting Node','Ending Node','Cross-Sectional Area (A)','Modulus of Elasticity (E)','Moment of Inertia (I)'],string(Connect_Mat)));
    case 2 then //=========================================================================================================
        //enter Member Data by sets

        //Obtain the number of sets to be entered from the user
        Num_Sets = evstr(x_dialog('How many sets do you want to enter?','0'));

        //initializes dynamically sized matrix for set labels
        Row_Labels=zeros(Num_Sets);
        for i=1:Num_Sets
            Row_Labels(i) = i;
        end

        Set_Data = zeros(Num_Sets,9); //initialize the Set_Data matrix

        //displays a matrix dialog box for user inputs of the set data
        Set_Data=evstr(x_mdialog('Enter the Set Data',string(Row_Labels),['Member Number Start','Member Number Increment','First Start Node','First End Node','Node Increment','Number of Members in Set','A','E','I'],string(Set_Data)));

        //take the data entered into the 'Set_Data' matrix and determine the connectivity matrix it produces
        for i=1:Num_Sets //for each set
            for j=0:(Set_Data(i,6)-1) //for each member in the set
                Connect_Mat(Set_Data(i,1)+j*Set_Data(i,2),1)=Set_Data(i,3)+j*Set_Data(i,5); //extracts member starting nodes
                Connect_Mat(Set_Data(i,1)+j*Set_Data(i,2),2)=Set_Data(i,4)+j*Set_Data(i,5); //extracts member ending nodes
                Connect_Mat(Set_Data(i,1)+j*Set_Data(i,2),3)=Set_Data(i,7); //extracts member cross-sectional area
                Connect_Mat(Set_Data(i,1)+j*Set_Data(i,2),4)=Set_Data(i,8); //extracts member modulus of elasticity
                Connect_Mat(Set_Data(i,1)+j*Set_Data(i,2),5)=Set_Data(i,9); //extracts member moment of inertia
            end
        end
    case 3 then //=========================================================================================================
        //enter Member Data from a file

        File_Directory = uigetfile(["*.txt"],"SCI/modules/scinotes/macros/","Choose a file");
        fi=mopen(File_Directory,'r');
        Connect_Mat=evstr(mgetl(fi,Num_Members));
        mclose(fi);
    end //=================================================================================================================

    //Draws the members between the nodes with a line
    for i=1:Num_Members
        for j=1:2
            X(j)=Node_Coord(Connect_Mat(i,j),1);
            Y(j)=Node_Coord(Connect_Mat(i,j),2);
        end
    plot2d(X,Y,style=1,rect=Axes_Size);
    end

    //print out the connectivity matrix
    print(6,Connect_Mat);

endfunction
//============================================================================================================================
//============================================================================================================================
function Get_Loads()
    //obtains the number of load types (i.e. dead, live, seismic, etc.) and presents the user
    //with an x_mdialog box to enter the horizontal and vertical loads as well as applied
    //moments at each node for each load type
    global Num_Load_Types;
    global Loads;
    global Num_Nodes;

    //Extract Num_Load_Types from Edit Box in Main_Window
    Num_Load_Types = evstr(get(findobj("Tag","NLTB"),"String"));

    Loads = zeros(3*Num_Nodes,Num_Load_Types);

    for k=1:Num_Load_Types
        //initializes dynamically sized matrix for loads entry and associated
        //labels
        Row_Labels=zeros(Num_Nodes);
        Loads_Entry=zeros(Num_Nodes,3);
        for i=1:Num_Nodes
            Row_Labels(i) = i;
        end

        //displays a matrix dialog box for user inputs
        Loads_Entry =evstr(x_mdialog('Enter the Loads Applied to each Node for Load Type '+string(k),string(Row_Labels),['Horizontal Load','Vertical Load','Applied Moment'],string(Loads_Entry)));

        for i=1:Num_Nodes //for each node
            for j=1:3 //for each applied load
                Loads(3*(i-1)+j,k)=Loads_Entry(i,j);
            end
        end
    end

    //print out the loads matrix
    print(6,Loads);

endfunction
//=====================================================================================================================
//=====================================================================================================================
function Get_Load_Combos()
    //obtains the number of load combinations from the user and provides an x_mdialog
    //box for the user to input the load factors for each load type for each load
    //combination
    global Num_Load_Combos;
    global Load_Factors;
    global Num_Load_Types;
    global Loads;
    global Num_Nodes;
    global Axes_Size;
    global Node_Coord;
    global Ultimate_Loads;
    global Num_Members;
    global Connect_Mat;

    //Extract Num_Load_Combos from Edit Box in Main_Window
    Num_Load_Combos = evstr(get(findobj("Tag","NLCB"),"String"));

    //initializes dynamically sized matrix for members and associated
    //labels
    Load_Factors = zeros(Num_Load_Types,Num_Load_Combos);

    for i=1:Num_Load_Types
        Row_Labels(i)= 'Load Type '+string(i);
    end
    for i=1:Num_Load_Combos
        Column_Labels(i) = 'Combination '+string(i);
    end

    //displays a matrix dialog box for user inputs and saves the member connections to the matrix 'Connect_Mat'
    Load_Factors =evstr(x_mdialog('Enter the Load Factors',string(Row_Labels),string(Column_Labels),string(Load_Factors)));

    //Apply the load combinations to the loads and find the ultimate load at each node
    Combined_Loads = Loads*Load_Factors;
    Ultimate_Loads = zeros(3*Num_Nodes,1);
    for i=1:(3*Num_Nodes)
        if max(Combined_Loads(i,:))==max(abs(Combined_Loads(i,:))) then
            Ultimate_Loads(i,1) = max(Combined_Loads(i,:));
        else
            Ultimate_Loads(i,1) = -max(abs(Combined_Loads(i,:)));
        end
    end

    //define a unit length for graphing the forces
    L=zeros(Num_Members,1);
    for i=1:Num_Members
        Start_Node=Connect_Mat(i,1); //starting node number
        End_Node=Connect_Mat(i,2); //ending node number
        X1=Node_Coord(Start_Node,1); //starting node coordinates
        Y1=Node_Coord(Start_Node,2);
        X2=Node_Coord(End_Node,1); //ending node coordinates
        Y2=Node_Coord(End_Node,2);
        L(i)=(((Y2-Y1)^2)+((X2-X1)^2))^(1/2); //length of the member
     end
     unit_size=min(L)/8;

    //graph the ultimate applied forces
    for i=1:Num_Nodes
        for j=1:3
            if Ultimate_Loads(3*(i-1)+j,1)~=0 then
                select j
                case 1 then //horizontal forces
                    X(1)=Node_Coord(i,1);
                    Y(1)=Node_Coord(i,2);
                    X(2)=Node_Coord(i,1)+unit_size*(Ultimate_Loads(3*(i-1)+j,1)/abs(Ultimate_Loads(3*(i-1)+j,1)));
                    Y(2)=Node_Coord(i,2);
                case 2 then //vertical forces
                    X(1)=Node_Coord(i,1);
                    Y(1)=Node_Coord(i,2);
                    X(2)=Node_Coord(i,1);
                    Y(2)=Node_Coord(i,2)+unit_size*(Ultimate_Loads(3*(i-1)+j,1)/abs(Ultimate_Loads(3*(i-1)+j,1)));
                case 3 then //moments
                    x = Node_Coord(i,1)-unit_size/2;
                    y = Node_Coord(i,2)+unit_size/2;
                    w = unit_size;
                    h = unit_size;
                    if Ultimate_Loads(3*(i-1)+j,1)<0 then
                        a1 = -80*64;
                        a2 = 160*64;
                    elseif Ultimate_Loads(3*(i-1)+j,1)>0 then
                        a1 = 100*64;
                        a2 = 160*64;
                    end
                    //plot moment arcs
                    xarcs([x;y;w;h;a1;a2],[5]); //5 - red
                end
            //plot force lines
            plot2d(X,Y,style=5,rect=Axes_Size); //5 - red
            end
        end
    end

    //print out the load factors matrix and final ultimate loads vector
    print(6,Load_Factors);
    print(6,Ultimate_Loads);
endfunction
//=====================================================================================================================
//Find Results Subroutines
//=====================================================================================================================
function Find_Displacements()
    //this function calculates the local and global stiffness matrices as well as
    //the transformation matrices for converting between the two. Finally, it finds
    //the node displacements and plots the deformed structure
    global Num_Nodes;
    global Num_Members;
    global Connect_Mat;
    global Node_Coord;
    global Local_k;
    global Transf_Mat;
    global Truss_Switch;
    global Beam_Switch;
    global Node_Type;
    global Ultimate_Loads;
    global Displacements;
    global Num_Load_Types;
    global Axes_Size;
    global Structure_Forces;

    //global structure stiffness matrix
    K=zeros(3*Num_Nodes,3*Num_Nodes);

    for i=1:Num_Members
        //obtain the parameters for the member stiffness matrices
        Start_Node=Connect_Mat(i,1); //starting node number
        End_Node=Connect_Mat(i,2); //ending node number
        AE=Connect_Mat(i,3)*Connect_Mat(i,4); //the product of A and E
        EI=Connect_Mat(i,4)*Connect_Mat(i,5); //the product of E and I
        X1=Node_Coord(Start_Node,1); //starting node coordinates
        Y1=Node_Coord(Start_Node,2);
        X2=Node_Coord(End_Node,1); //ending node coordinates
        Y2=Node_Coord(End_Node,2);
        L=(((Y2-Y1)^2)+((X2-X1)^2))^(1/2); //length of the member

        //find the member directional sines and cosines
        if X2==X1 then //the member is vertical
            if Y1<Y2 then //the member points up
                phi = (%pi/2); //angle of the member with the horizontal
            elseif Y1>Y2 then //the member points down
                phi = ((3*%pi)/2);
            end
        elseif Y2==Y1 then //the member is horizontal
            if X1<X2 then //the member points to the right
                phi = 0;
            elseif X1>X2 then //the member points to the left
                phi = %pi;
            end
        else //the member is at some intermediate angle
            phi=atan((Y2-Y1)/(X2-X1));
        end
        C=cos(phi);
        S=sin(phi);
//===================================================================================================
//STIFFNESS MATRIX
//===================================================================================================
        //compute the stiffness matrix for each member in terms of the local
        //coordinate axis
        Local_k(1:3,1:6,i)=[(AE/L),0,0,(-AE/L),0,0;0,(12*EI/L^3),(6*EI/L^2),0,(-12*EI/L^3),(6*EI/L^2);0,(6*EI/L^2),(4*EI/L),0,(-6*EI/L^2),(2*EI/L);];
        Local_k(4:6,1:6,i)=[(-AE/L),0,0,(AE/L),0,0;0,(-12*EI/L^3),(-6*EI/L^2),0,(12*EI/L^3),(-6*EI/L^2);0,(6*EI/L^2),(2*EI/L),0,(-6*EI/L^2),(4*EI/L);];

        //compute the transformation matrix for converting forces and displacements
        //from the local coordinate axis to the global structure coordinate system
        Transf_Mat(1:3,1:6,i)=[C,S,0,0,0,0;-S,C,0,0,0,0;0,0,1,0,0,0;];
        Transf_Mat(4:6,1:6,i)=[0,0,0,C,S,0;0,0,0,-S,C,0;0,0,0,0,0,1;];

        //stiffness matrix for each member in terms of global coordinate system
        Global_k(:,:,i)=Transf_Mat(:,:,i)'*Local_k(:,:,i)*Transf_Mat(:,:,i); //k*=T'kT

        //add the global stiffness matrix for each member into the global structure stiffness matrix,K
        K((3*Start_Node-2):(3*Start_Node),(3*Start_Node-2):(3*Start_Node))= K((3*Start_Node-2):(3*Start_Node),(3*Start_Node-2):(3*Start_Node))+Global_k(1:3,1:3,i); //adds submatrix global_k11 into K
        K((3*Start_Node-2):(3*Start_Node),(3*End_Node-2):(3*End_Node))= K((3*Start_Node-2):(3*Start_Node),(3*End_Node-2):(3*End_Node))+Global_k(1:3,4:6,i); //adds submatrix global_k12 into K
        K((3*End_Node-2):(3*End_Node),(3*Start_Node-2):(3*Start_Node))= K((3*End_Node-2):(3*End_Node),(3*Start_Node-2):(3*Start_Node))+Global_k(4:6,1:3,i); //adds submatrix global_k21 into K
        K((3*End_Node-2):(3*End_Node),(3*End_Node-2):(3*End_Node))= K((3*End_Node-2):(3*End_Node),(3*End_Node-2):(3*End_Node))+Global_k(4:6,4:6,i); //adds submatrix global_k22 into K
//======================================================================================================
    end

    //create an index matrix to keep up with what index of rows are left after deletion due to
    //boundary conditions
    Index=zeros(3*Num_Nodes,1);
    for i=1:(3*Num_Nodes)
        Index(i,1) = i;
    end

    Eliminate = [];
    Counter = 1;
    //if the structure is a truss there are no moments
    if Truss_Switch == 1 then
        for i = 1:Num_Nodes
            Eliminate(Counter)=3*i;
            Counter = Counter+1;
        end
    end

    //if the structure is a beam there are no axial forces
    if Beam_Switch == 1 then
        for i = 1:Num_Nodes
            Eliminate(Counter)=3*i-2;
            Counter = Counter+1;
        end
    end

    //extract boundary conditions from the Node_Type selections
    for i=1:Num_Nodes
        select Node_Type(i)
            case 1 then
                u=1;//Free
                v=1;
                theta=1;
            case 2 then
                u=0; //X-Roller
                v=1;
                theta=1;
            case 3 then
                u=1; //Y-Roller
                v=0;
                theta=1;
            case 4 then
                u=0; //Pin
                v=0;
                theta=1;
            case 5 then
                u=0; //Fixed
                v=0;
                theta=0;
        end

        //Determine where the boundary conditions give zero displacement
        //these rows/cols will be deleted to generate the final
        //invertible matrix
        if u==0 then
            Eliminate(Counter)=3*i-2;
            Counter=Counter+1;
        end
        if v==0 then
            Eliminate(Counter)=3*i-1;
            Counter=Counter+1;
        end
        if theta==0 then
            Eliminate(Counter)=3*i;
            Counter=Counter+1;
        end
    end

    //before removing rows and columns, preserve the full vectors and matrices
    k = K;
    ultimate_loads = Ultimate_Loads;

    //delete rows and columns corresponding to given parameters and boundary conditions
    k(Eliminate,:)=[];
    k(:,Eliminate)=[];
    Index(Eliminate,:)=[];
    ultimate_loads(Eliminate,:)=[];

    //calculate the unknown displacements
    Unknown_Displacements=inv(k)*ultimate_loads;

    //Develop the full displacement matrix
    Displacements = zeros(3*Num_Nodes,1);
    for i=1:size(Index,"r") //for each element in the index
            //copy the rows from the calculated Unknown_Displacements matrix into the correct rows
            //of the full Displacements matrix
            Displacements(Index(i,1),:) = Unknown_Displacements(i,:);
    end

    //plot the deflected shape
    Def_Node_Coord = zeros(Num_Nodes,2);
    for i=1:Num_Nodes
        Def_Node_Coord(i,1) = Node_Coord(i,1)+Displacements(3*(i-1)+1,1); //x-coordinates
        Def_Node_Coord(i,2) = Node_Coord(i,2)+Displacements(3*(i-1)+2,1); //y-coordinates
    end
    for i=1:Num_Members
        for j=1:2
            X(j)=Def_Node_Coord(Connect_Mat(i,j),1);
            Y(j)=Def_Node_Coord(Connect_Mat(i,j),2);
        end
    plot2d(X,Y,style=2,rect=Axes_Size);
    end

    //Calculate the global force vector for finding the reactions
    Structure_Forces = K*Displacements;

    //print out the global structure displacements vector
    print(6,Displacements);

endfunction
//=====================================================================================================
//=====================================================================================================
function Find_Reactions()
    //this function determines the reactions at the structure supports
    global Num_Nodes;
    global Node_Type;
    global Structure_Forces;

    //Extract the reactions from the Structure_Forces matrix
    Reactions = zeros(3*Num_Nodes,1);
    for i=1:Num_Nodes
        if Node_Type(i)==1 then
            Reactions((3*i-2:3*i),1)=0;
        else
            Reactions((3*i-2:3*i),1)=Structure_Forces((3*i-2:3*i),1);
        end
    end

    //print out the reactions vector
    print(6,Reactions);
endfunction
//=====================================================================================================
//=====================================================================================================
function Find_Forces()
    //this function uses the global displacements to determine the forces on each
    //member of the structure in terms of that member's local coordinate axis
    global Num_Members;
    global Connect_Mat;
    global Displacements;
    global Local_k;
    global Transf_Mat;

    //Adjust the forces to local coordinates
     Local_Member_Forces = zeros(6,Num_Members); //the i-th column vector represents the forces on the i-th member
                                                 //in terms of the local coordinate axis
     Member_Displacements=zeros(6,1); //for extracted each member's displacements in terms of global coordinates

     for i=1:Num_Members
        Start_Node=Connect_Mat(i,1); //starting node number
        End_Node=Connect_Mat(i,2); //ending node number

        //extract the member's displacements from the structure displacements matrix
        Member_Displacements(1:3,1)=Displacements(3*Start_Node-2:3*Start_Node);
        Member_Displacements(4:6,1)=Displacements(3*End_Node-2:3*End_Node);

        Local_Member_Forces(:,i)=Local_k(:,:,i)*Transf_Mat(:,:,i)*Member_Displacements(:,1); //f=kTD        

    end

    //print out the local member forces matrix
    print(6,Local_Member_Forces);
endfunction

Structural Finite Element Analysis User’s Guide

Now that you have downloaded and installed Scilab, the Structural Finite Element Analysis (SFEA) program, and got it up and running, how do you use it. Well that’s what we want to go through at this point. What you should see on your desktop are two blank screens. The one on the left will provide the user input controls while the one of the right will graphically depict the structure being analyzed. If this is not the case then you should read here first.

Getting Started: The File Menu

In the left screen there is a ‘File’ menu. If you click it you will see that you can select ‘New’ or ‘Close’. ‘Close’ is pretty obvious. ‘New’ will give you a sub-menu of three choices: Beam, Frame, or Truss. To make clear the difference, in this program an element of a beam supports transverse and moment forces, a frame supports axial, transverse and moment forces, and a truss element supports axial and transverse forces.

To give an example of why this might be important, consider a simple cantilever beam with a non-orthogonal loading. (In other words, the load does not meet the beam’s longitudinal axis at 90 degrees) Now although it is a ‘beam’ due to its form and positioning, since the load will produce an axial force in the structure, it is not a ‘beam’ with regard to the methodology of this program. If you were to analyze this structure, you would select ‘Frame’.

Once you make this selection, the left window will populate the controls. You will notice that there are two frames. The top frame walks the user through the step-by-step acquisition of the necessary data. The bottom frame contains the controls for obtaining the results of node displacements, support reactions, and elemental or member forces.

Entering Node Data

Now that the controls are up, the user simply starts at the top left and goes across and down just like reading text. Start by entering the number of nodes in the text box at the top and then click the ‘Node Coordinates’ button. This brings up a dialog box that asks the user if they want to enter the nodes ‘Singularly’, ‘By Sets’, or ‘From File’. ‘Singularly’ means manually enter the node coordinates one at a time. ‘By Sets’ means the user will enter some criteria about the nodes that is repetitive and the computer will determine the nodes for you. This is a helpful function when you are entering a large number of nodes that follow some consistent pattern with regard to their geometric arrangement. ‘From File’ means the user can open and import the coordinates from a user created text file that contains all the node coordinates.

Singularly

If the user selects this method, a new dialog box will open to let the user input the node coordinates.

The number of rows in the dialog box will dynamically correspond to the number of nodes the user entered would be in the structure.

By Sets

If the user selects this method, another dialog will appear to ask the user how many sets they have to enter. This is a simple integer input.

After entering the number of sets, another dialog box will be displayed to obtain the set data from the user.

The rows in the dialog box correspond to the number of sets. For each set the user must enter the node number to start with, how the node     number for each subsequent node should increment from the beginning node, the beginning x-y coordinate for the first node, the x and y distance each subsequent node will increment from the previous one, and how many nodes in the set.

For example if I was analyzing a simple cantilever beam and I wanted to divide the beam into 20 separate elements, then I would have 21 nodes. Since I would space the nodes out evenly along the length of the beam, I could enter those nodes by sets without having to enter them one at a time. If the length of the entire beam is 120 inches (10 feet), then I would have 20 elements each 6 inches long. So in entering the data by sets in the dialog above I would input: node number start = 1, node number increment = 1, x start = 0, y start = 0, x increment = 6, y increment 0, number of nodes in set = 21. The program would generate 21 nodes starting at the x-y coordinate (0,0) and at every 6 inches horizontally for the full length of the beam.

From File

If the user selects this method, a standard Windows dialog box will open where you can search in the file tree structure to find the text file containing the node coordinates data. The text file should be formatted with one node coordinate per line starting with the x-coordinate followed by a space followed by the y-coordinate.

Which ever method the user selects, once the data has been provided to the program, it will output the node coordinate matrix to the Scilab console. The user can verify the correct coordinates numerically there. Additionally, the nodes will be plotted graphically in the second SFEA window. This allows the user to verify the nodes visually.

Entering Support Reactions Data

Once the nodes have been entered, the user can set the boundary conditions for the structure by pushing the ‘Select Reactions’ button. A dialog box will then open and allow the user to select the support type at each node.

Notice the default node type is free, so the user only has to define those nodes which are supports. An ‘X-Roller’ allows rotation and movement in the y-direction but no movement in the x-direction. Likewise a ‘Y-Roller’ allows rotation and movement in the x-direction but no movement in the y-direction. A pin allows rotations but no x or y movement. Finally a fixed support allows no movement at all.

Once the user defines the node types, the node type matrix will be displayed in the Scilab console and the structure plot will be modified with different symbology for different node types as seen below. The symbols are from left to right, free, x-roller, y-roller, pin, and fixed.

Entering Member or Element Data

Once the nodes and reactions are defined the user can input the members that run between the nodes. In much the same way as the entry of the nodes, the user will enter the number of members in the textbox in the SFEA first window and then push the ‘Member Data’ button. As with the nodes, a dialog box will permit the user to input the data ‘Singularly’, ‘By Sets’, or ‘From File’.

Singularly

If the user selects this method, a dialog box will appear to allow the user to input the data for each member. The data required are the start node number, the end node number, the member’s cross-sectional area (A), the member’s modulus of elasticity (E), and the member’s moment of inertia (I).

By Sets

In the same way as with node entry, the ‘By Sets’ method of member entry allows the user to systematically enter a large number of members with repetitive characteristics. With regard to member entry, each member of a set must have the same A, E, and I.

From File

As before, this allows the user to load the member data from a text file on the computer. The format of the file should be one member per line with each line having: start node number-space-end node number-space-A-space-E-space-I

Once the member data is entered, this data is output to the Scilab console as the connectivity matrix. Also the members will be plotted in the SFEA plot window.

Entering Applied Loads

There are two aspects to the entry of the loads that affect the structure. To understand this fully, let’s define some of the terminology. The first piece of information to enter in the SFEA first window control is the ‘Number of Load Types’. A load type is typically something like dead loads, live loads, wind loads, seismic loads, etc. These are each different load types. If a structure was going to have each of these load types listed then it would have 4 load types. Another term in the program is ‘Number of Load Combinations’. A load combination is a linear combination of the form:

Where each ‘x’ is a load type and each ‘A’ is a load factor. A load factor is something that is typically used in Load and Resistance Factor Design (LRFD) as a form of scaling factor or safety factor. So for example we might have:

Where D stands for dead load and L stands for live load. In many structural applications and building codes there are sets of multiple load combinations and corresponding load factors. Each of these combinations must be calculated and the worst case scenario is then selected for design. The SFEA program provides the capacity for this type of analysis.

Load Types and Loads

Once the user enters the number of load types and pushes the ‘Loads’ button,  a dialog box that allows the entry of the different loads for each type will appear.

Each row in the dialog box corresponds to each node in the structure. Consequently you can enter a horizontal, vertical, and moment load at each node. After pressing ‘OK’ another identical dialog box will appear for the next load type.

The loads matrix will be displayed in the Scilab console after entry. Each column of the matrix is a different load type. The rows follow the following pattern. Each node has 3 potential loads therefore the first 3 rows correspond to the 3 loads on node 1. The next 3 rows correspond to node 2 and so on. Therefore there should be 3N rows where N is the number of nodes. Additionally, the order of the loads in each set of 3 rows is the same as it is entered in the dialog box: horizontal, vertical, moment.

Load Combinations and Factors

As discussed above, the number of load combinations and load factors are often listed in manuals or code books. Once the number of combinations is entered and the user pushes the ‘Load Factors’ button, the following dialog box appears.

Here the user enters the load factors that correspond to each load type for each combination.

Once this data is entered the load factors will be displayed to the Scilab console as well as the ultimate loads. The ultimate loads are the maximum loads at each node calculated from all the given loads, load combinations, and load factors. Also, the ultimate loads will be depicted in the plot window on the structure with red lines or curves. The line goes from the node in the direction of the force. A semicircular curve around the left side of a node is a positive moment according to the right-hand rule while a curve around the right side of a node is negative.

Find Displacements

At this point the structure is fully defined and graphically displayed in the plot window. Now when the user pushes the ‘Find Displacements’ button, the displacements vector will be displayed in the Scilab console and the new displaced shape of the structure will be plotted in blue. The displacements vector follows the same convention as discussed above with the loads matrix. The first 3 rows correspond to the horizontal, vertical, and angular displacements of node 1. The second 3 for node 2 and so on.

Find Reactions

When the user presses this button next, the reactions vector is displayed in the Scilab console. Again, as with the loads and displacements you have the horizontal, vertical, and moment reactions for each node starting with node 1 and going down.

Find Member Forces

Finally when the user pushes this button, the local member forces matrix is displayed in the Scilab console. Each column corresponds to a member. Column 1 for member 1 and so on. The first 3 rows are the horizontal, vertical, and moment forces on the member at the starting node while rows 4,5, and 6 are the forces on the member at the ending node. It is important to understand that these forces are with reference to the member’s local axis. The local axis for each member has its origin at the starting node with the horizontal or x-axis directed toward the ending node. The vertical or y-axis is then appropriately orthogonal to the local x-axis.

I hope this user’s guide has been helpful and provided sufficient information or answers to your questions. However if you are still stuck or want further information just let me know in the comments.

Measuring the pH of a Solution

Another frequently used measure of water quality along with electrical conductivity and turbidity is the pH. pH is a measure of the hydrogen ion activity in a solution. Solutions with high hydrogen (H+) or hydronium ion (H3O+) activity are called acids and solutions with low hydrogen ion activity are called bases. Another way of looking at it is by looking at the reciprocal quantity of hydroxyl ions (OH-). The more hydroxyl ions, the more basic a solution is and so on. pH is a mathematical way of quantifying these concentrations and placing them on a relative scale. It is defined as:

In a parallel fashion the quantity pOH is defined as:

Conversely, to determine the activity or concentrations given the pH or pOH, we have:

The relationship between pH and pOH at standard temperature conditions (25 degrees Celsius) is:

pH + pOH = 14

From here, we can see that the relative scale used is from a pH of 0 to a pH of 14 with 0 being very acidic, 14 being very basic, and 7 being neutral.

There are 2 basic types of techniques for measuring pH. The first type is called colorimetric measurement. The use of litmus paper is a colorimetric technique. The second type is called electrometric and is done using an electrical instrument. The instrument is calibrated with 3 standard solutions at known pHs of 4, 7, and 10. Then the instrument can be used to measure unknown solutions. The typical range for drinking water is ideally around 6 – 8.5.

Specific Gravity of Soil

The specific gravity of soil is an important weight-volume property that is helpful in classifying soils and in finding other weight-volume properties like void ratio, porosity, and unit weight. In this lab we first weighed an empty 1000 mL graduated cylinder. Then we filled it to 500 mL with distilled water and weighed it again. This allowed us to find the density or unit weight of the water. Secondly we filled another graduated cylinder with a mixture of soil and water. This mixture was heated on a stove to remove air from the mixture. Then it was filled to the 500 mL mark with additional distilled water and weighed. Finally an oven-safe container was weighed empty and then the soil/water mixture was poured into the container and dried in the oven for a 24-hour period. This enabled us to find the weight of the dry soil solids. Once this procedure was completed and the data collected, the specific gravity could be obtained via the following computations.

The specific gravity is defined as the ratio of the unit weight of the soil solids to the unit weight of water.

The unit weight of the soil solids is given by:

Where Ws is the weight of the soil solids and Vs is the volume of the soil solids. Likewise the unit weight of water is given by:

Consequently we can substitute these expressions into the first equation and obtain:

To obtain the weight of the soil we subtracted the weight of a dish container from the weight of the dish container with the oven-dried soil.

The volume of water we used was known at 500 mL.

The weight of the water corresponding to this volume was simply obtained by subtracting the weight of the flask or graduated cylinder from the weight of the flask with the volume of water.

Determining the volume of the soil was more difficult. We used the mixture that consists of the flask, soil, and water. Here the volume of the soil will be the total volume minus the volume of the water. (The volume of air is negligible)

In order to evaluate this we make the assumption that the unit weight of the water is constant.

We know all the values in this last expression except Ww2. This is the weight of the water in the water-soil-flask mixture. It can be found by:

This is all the information we needed. Simply substitute the solution from this last equation into the equation for the second volume of water, the solution from that into the equation for volume of soil, and all the known and determined values into the substituted equation for specific gravity to obtain the specific gravity. Here are the values and calculations we obtained in our experiment.

This was a reasonable finding since the specific gravity of soils typically falls in the range of 2.6 to 2.9.

 

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Turbidity and Suspended Solids

Another method of analyzing water quality is through the measurement of turbidity and its correlation with total solids.  Turbidity is a relative measure of the clarity of a water sample by measuring the scatter of light as it passes through a sample. A sample with high turbidity will appear unclear while a sample with low turbidity will appear more clear because light passes through it with less scatter and absorption. It is relative in that it is measured against a standardized sample of stabilized formazin or gelex. The preferred units used in turbidity measurements are nephelometric turbidity units or NTUs. It is usually measured with a nephelometric turbidimeter or spectrophotometer. A key point here is that the turbidity can be measured in just a few minutes including calibration.

Total solids can be categorized into 4 categories: suspended solids, dissolved solids, settable solids, and volatile solids. They include all the solid materials that are contained in the water matrix. They can be measured as a concentration of the sample volume using gravimetric measurement techniques. This requires that we use an Imhoff cone to measure settlable solids, a filter to measure suspended solids, and the filtrate to measure dissolved solids. Usually suspended solids is the primary concern. These constituents are what typically affect the clarity of the water. However since it is time consuming and not necessarily practical to collect a sample, put it in an evaporating dish, evaporate the water in an oven over the course of 24 hours or more, and weight the solids remaining, we attempt to find a correlation between suspended solids and turbidity. Turbidity cannot by itself be used to quantify the concentration of suspended solids in a body of water. However by analyzing a few samples we can find and plot the correlation between concentration of suspended solids and turbidity. This gives us a relationship (valid only for a particular location and time) so that we can determine the amount of suspended solids in a body of water by simply measuring the turbidity.

The primary reasons that suspended solids are a concern is first, simple aesthetics and second, the harboring of pathogens or pathogen supporting envirnoments. The EPA has set primary drinking water quality standards at less than 1 NTU. Prior to 2002, less than 5 NTU was acceptable.

Electrical Conductivity and Water Purity

Our first environmental engineering lab was concerning one method of water quality assessment called electrical conductivity. The theory behind this technique is based on the fact that pure water is not a good conductor of electricity. As the amount of inorganic, ionic elements or compounds in the water increases, the conductivity also increases. Conductivity also increases with temperature, therefore most results are standardized at 25 degrees Celsius. With this understanding we can make comparative analysis of conductivity values to assess the purity of the water. Conductivity in this context is usually in units of microsiemens per centimeter. In the lab we utilized a handheld electrical conductivity meter like the one above. Below is a table we were given of the typical value range found in different types of water.

The reason for the high conductivity in seawater is the high salt content and thus a high number of sodium and chloride ions in this aqueous solution. If you are interested in additional information, I found a good EPA website concerning water quality monitoring and electrical conductivity.

Dirt or Mud – A Scientific Question?

My first soil mechanics lab was an exercise in analyzing the moisture content of a soil mixture. Soil is an aggregate consisting of what are called “phases”. The 3 phases are solids (tiny rocks and minerals), water, and air. The water and air make up what is called the void space. In evaluating moisture content (w), we are only interested in the water and solids portion. In fact, the moisture content is defined as the ratio of the weight of the water content (Ww) to the weight of the solid content (Ws). The weight of the air is considered negligible.

The procedure we followed to obtain values for these calculations was to use 3 small metal tins or canisters. First we used a digital scale to measure the weight of each canister. This weight we called W1. Next we partially filled each canister with a small sample of soil. Next we measured the canister and the soil. This weight we called W2. Finally we placed the canisters in a soil drying oven to dry out the soil and remove the water from the samples. After 24 hours we returned to the lab and used the digital scale to measure the dried soil samples in the canisters. This weight we called W3. To find the weight of the water (Ww) we used:

To find the weight of the solids (Ws) we used:

Here is a tabulation of the results we obtained:

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