There are three modes for obtaining and visualizing analysis results for structures in Ftool. These are the Diagram, Influence Line, and Load-Train Envelope modes of operation. Select the desired mode of operation using the buttons on the results toolbars, as described below.
In Diagram and Load-Train Envelope modes, Ftool automatically analyzes the structure using the stiffness method to construct the requested diagrams. Just clicking on the appropriate button switches the display to show the desired result. In Influence Line mode, the program prompts the user to indicate a cross-section on a member to display the desired influence line.
If the Result Values display option is active (see The Display Menu), the diagrams will be plotted with printed nodal values. Local maxima and minima will also be printed if present. If the Step Values display option is active, values will be printed along the diagram according to the defined result step size.
Diagram result mode considers the visualization of internal force diagrams (axial forces, shear forces, bending moments) and deformed configuration under static loads.
For the deformed configuration diagram, the user must select which of the deflection components to print with the diagram: the rotation, horizontal or vertical displacement or none at all. The plotted diagram itself is the same regardless of the selected value.
To get numerical results of a diagram, move the mouse cursor to a position on a member and click the left mouse button. The desired values will be displayed on the top line message. Additional results may be consulted clicking the right mouse button. These results will be displayed on the lateral area of the screen (see Numerical Display of Results).
In this mode the user may apply transformations that do not alter the structure’s topology (see Transformations). To do so, the user must open the transformations window, select the desired objects and then apply the transformations. The results are automatically updated, maintaining their scale.
In Influence Line mode, first click on a button for the desired type of influence line (e.g., shear force or bending moment). Then place the mouse cursor at some point along a member and click the left mouse button. Ftool imposes the required unit displacement or rotation discontinuity to create the desired influence line, which is displayed on the structural model. To display an influence line, the program ignores the applied loads on the structure. An influence line represents the effect of a unitary vertical force that traverses the members of the structure. The unitary force has always a vertical downward orientation, no matter the orientation of a member on which the force passes.
In case there is a currently selected load-train (vehicle live load for bridges), the critical positions of this load-train are displayed above and below the displayed influence line. These critical positions are the ones that cause the minimum (negative) and the maximum (positive) target result values on the desired cross-section. In this case, the influence line is displayed only along the members of the structure that belong to the load-train path.
When it is not possible to automatically define a load-train path of members along the structure, the program prompts the user to go selection mode and to select a group of members that form a continuous and smooth path for the load-train. When the user provides a valid load-train path, the program stores the corresponding group of members and the user will be prompt again to specify a load-train path only in case the model is modified.
As long as the button to select a cross-section (rightmost button of the toolbar) is active, Ftool displays a new influence line for each selected section. To avoid the selection of another section, deactivate this button. When this button is not active, point results along the influence line may be consulted by just selecting a target position using the left mouse button. The desired value will be displayed on the top message bar. Additional member results may be consulted using the right mouse button (see Numerical Display of Results).
In this mode, the user may apply transformations which do not alter the structure’s topology (see Editing - Transformations). To do so, the user must define an influence line for some point and then open the transformations window, select the desired objects and apply the transformations. The influence lines are automatically updated, maintaining their scale. Should one wish to then check another influence line, one should simply select the desired result (or the button to select a new section) from the menu once again. Should one wish to then apply new transformations (with the transformation window already open), one must press the Select button so as to allow for the selection of objects prior to their transformation.
The Load-train Envelope mode is used to display envelopes of limiting internal force values along a structure under moving loads. Envelopes are diagrams of minimum and maximum values of an internal force (axial, shear or bending moment) for the current load-train (vehicle live load for bridges). If there is no current load-train, or if no load-train path is defined, the program does not activate the Load-train Envelope mode. The load-train path, if not automatically defined, has to be defined by the user selecting a continuous and smooth chain of members prior to getting an envelope result.
Envelopes of internal forces can be calculated adding the effects of static loads to the current load-train (vehicle live load) effects. The diagram of static internal forces due to static loads are displayed as dashed lines on the envelope image. In the Options menu (see Configurations - Superposition of static load and load-train results), there is an item to activate and deactivate the superposition of static and vehicle live load effects in the envelope calculation. By default, this superposition is activated. This option is reset when a new model is created or when a model is opened from a file.
The construction of the load-train envelopes interpolates minimum and maximum results calculated at cross-sections automatically selected along the members of the structure. For each selected section, Ftool builds the corresponding influence line and finds the critical positions of the current load-train that cause the minimum and maximum vales at that section. Envelopes are diagrams that linearly interpolate the minimum and maximum values calculated at the selected cross-sections. The same step used to build internal force diagrams, deformed configuration, or influence lines is adopted to select the cross-sections for the construction of the load-train envelopes. Should the relevant option be active (see above), the envelopes are then superimposed on the static load diagram.
Point results of load-train envelopes may be obtained by just selecting a target position using the left mouse button. The minimum and maximum values at that point are shown in the top message bar.
In this mode it is not possible to perform object transformations.
The sign convention for internal forces and moments can be displayed in the program by selecting the option Sign Convention on the File menu. A window appears on the screen which shows the sign convention. The user may alter the sign convention for resulting diagrams and influence lines.
Top and Bottom Fibers
The sign convention for internal forces and moments depends on the definition of the "lower" and "upper" fibers of the members. In horizontal and inclined members, the lower fibers are in the bottom when looking at the screen with the vertical axis in its natural position (up). In vertical members, the lower fibers are on the right. The figure at the top of the sign convention display indicates lower fibers of a structure that contains members with all possible directions.
The internal force diagrams, deformed configuration, influence lines, and envelopes have a default initial scale on the screen to create a reasonable image. This scale can be modified using the slider bar at the left of buttons of the Results toolbars. Use the slider bar to modify the scaling of displayed diagrams as desired.
The scaling of the results may also be adjusted by the user editing its value on a text box in the top toolbar, between the load attribute buttons and the result scale slide. In Diagram and Load-train Envelope modes, the result scale factor is defined in terms of units of the corresponding internal force per unit of length. In the deformed configuration, the scale factor is a displacement amplification factor (Deformed Factor). In influence lines, the scale factor is an adimensional parameter that controls the influence line display scale in relation to the model.
The images on the following sections highlight the text box on the graphics interface that is used to edit the result scale factor and the buttons that are used to obtain the desired result visualization.
Deformed configuration Axial force diagram Shear force diagram Bending moment diagram Axial force influence line Shear force influence line Bending moment influence line Axial force load-train envelopes Shear force load-train envelopes Bending moment load-train envelopes
In Diagram mode, clicking a point on a member with the mouse left button displays the value of the corresponding diagram for that point in the top message bar above the drawing area. In this mode, clicking a node with the mouse right button displays result information, such as displacements, rotation, or reaction forces, related to the selected node in the right-most area of the screen.
In Influence Line mode, if the option to select a new cross-section is NOT active, clicking a point on a member with the mouse left button displays the value of the corresponding influence line in the top message bar.
In Load-train Envelope mode, the minimum and maximum envelope values at the selected point are display in the top message bar.
In all the modes, if the right button of mouse is used, additional information related to the selected member results appears in the right-most area of the screen. If a step for the displayed result is defined through the Step Values option in the Display menu (see Visualization Controls - The Display Menu), the step results of the diagram for the selected member will be shown in this area.
The image below shows an example of the visualization of a bending moment diagram with step values indicated in the display and in the lateral area for the selected member.