Modeling Process

This topic describes a general process for creating a model using ETABS. The intent is to demonstrate the interaction of the various commands available in ETABS.

  1. Click the File menu > New Model command to display the Modal Initialization form. Initializing the model determines the units to be used and the default definitions of all properties, loads, and the like—everything except the grids, objects, and assignments to the objects.   

TIP:  To review  the specific parameters associated with these settings, click the Options menu > Display Units command and the Design menu > {Design Type} > View/Revise Preferences command after  the next step.

Note: The User Default Settings are saved using the Options menu > Save User Default Settings command. Thus, if this is the first time the program is being used, no saved user default settings are available; therefore, in such a case, it is recommended that the Use Built-In Settings With option be used.

  1. Click the OK button on the Model Initialization form to access the New Model Quick Templates form. Use the form to set up grid lines and define story levels. Click a template button to start a model (Steel Deck,Staggered Truss,Flat Slab, Flat Slab with Perimeter Beams,Waffle Slab,Two Way or Ribbed Slab). In all cases except Grid Only,  this adds structural objects (e.g., beams, deck/floor, braces and so on), which is the recommended approach to be used  whenever possible. The Blank button opens windows, but does not load objects or grid lines regardless of what is specified for grid or story dimensions on the New Model Quick Templates form.

  2. After clicking a template button (with the exception of the Blank and Grid Only buttons), use the Structural Geometry and Properties for {Structure Type} form to specify any deck overhangs, initial dead and live loads, initial object section properties, restraints, diaphragm rigidity and other structure-specific parameters. Click the OK button on  the Structural Geometry and Properties for {Structure Type} form and  the New Model Quick Templates form to close both forms and generate the model based on the settings and data provided.

TIP:  By default, ETABS displays two windows and the Model Explorer.  Close the windows or the Model Explorer by clicking in the right-hand corner of the tab. Add a window by clicking the Window List down arrow in the far right upper corner of the window/Explorer. If the Model Explorer is hidden, display it using the Windows List arrow or the Options menu > Show Model Explorer command. The Model Explorer window displays in hierarchical (tree) format using multiple tabs. The tabs have nodes. Depending on the tab and the node, right clicking on a node may display an action or a menu of actions. The nodes also may have subnodes that when right clicked provide shortcuts to the various program commands used in the following steps.

Note:  By default, the model will display with grid-paper-type grid lines indicating the working plane. Uncheck the Working Plane check box in the Other Special Items list to turn off those grid lines.

  1. Various commands and buttons are available to set the view, including 3D, Plan, and Elevation. With those settings applied, views can be set and display options can be applied.  When view limits  are set, only objects that fall entirely inside of the view limits are displayed. Setting  display options allow the user to choose which object types, object labels, and certain assignments to the objects are shown in the active window, or in all windows if that feature is enabled. Zoom and Pan commands can be used to focus in on portions of the model. Commands that work in conjunction are available to show only selected objects, invert the visibility of selected objects (i.e., if objects are selected to be shown, inverting that means the selected objects become invisible and the previously invisible objects become visible), make selected objects invisible, restore the visibility of previously selected objects, and show all objects.

  2. Review or define the material properties used for steel, concrete, aluminum, cold formed, rebar and other structural components,  including where appropriate, material property design data, material property mechanical data, nonlinear material data, material damping properties, and time dependent properties.

  3. Review or define frame section properties,  slab, deck and wall section properties, rebar, link/support properties,  nonlinear hinges, and panel zones as required. These definitions include material properties and geometry of the components used to build the model.

  4. If needed, define rigid or semi-rigid diaphragms or spring properties (point, line, area). Also define groups -- collections of objects that are assigned names. After a group has been named and objects have been assigned to it, named groups can be used to select objects, design steel frame objects by group, and define section cuts.

  5. Use the Define menu > Load Patterns command to define  load patterns.  Loads represent actions upon the structures, such as force, pressure, support settlement, thermal effects, ground acceleration, and others. A spatial distribution of loads upon the structure is called a load pattern. An unlimited number of load patterns can be defined in ETABS. Typically, separate load patterns would be defined for dead load, live load, wind load, snow load, and so on.  Loads that need to vary independently, for design purposes or because of how they are applied to the structure, should be defined as a separate load pattern. ETABS uses the type of load pattern to create automatic design load combinations (see step 10).

  6.  Load patterns by themselves do not create any response (deflections, stresses, and so forth). Therefore, a load case must be defined to apply the load patterns using the Define menu > Load Cases command.

  7.  Design load combinations are used to determine the various combinations of the load cases for which the structure needs to be designed/checked. The load combination factors to be used vary with the selected design code. The load combination factors are applied to the forces and moments obtained from the associated load cases and are then summed to obtain the factored design forces and moments for the load combination. The Define menu > Load Combinations command can be used to create  user-defined load combinations.

  8. To apply mass in a model, use the Define menu > Mass Source command to specify the source of the mass. The mass definition is applied in Step 14.

  9. Use the commands available on the Draw menu to draw additional shell, frame and joint objects as needed. We recommend using the Properties of Object form to assign properties to the objects as they are drawn, including structural properties, loads and masses. Also the frame objects might be used as guidelines for snapping (see Snap Options), guidelines for extending or trimming other frames (see Trim  Frame Object or Extend Frame Object options on the Align Joints/Frames/Edges form), and divide slab type shell objects that lie in the model datum plane into smaller objects (see Divide Shells).

  10. Use the Edit menu > Edit Story and Grid System Data command to modify and in some cases tweak the geometry of a model as needed (e.g., add or delete a story, add a new grid system or modify an existing one).

TIP:  Some of the Edit commands and virtually all of the Assign menu commands (see next step) require objects to be selected before the command can be used. While objects can be selected directly by clicking on them in the active window, various commands are available on the Select menu to aid in selecting (or deselecting or inverting the selection of) all objects sharing a common characteristic. For example,  objects can be selected by Object Type or Properties (e.g., Material Properties, Frame Sections) as well as a Story.

  1. Use the Assign menu commands to revise properties in a template model where necessary and to make additional assignments to template members as well as to any other members that were added to the model using the Draw menu commands. See the topics in the Assign book of this Help for more information about those commands. The types of assignments that can be made include the section properties  (springs, diaphragms),  panel zones restraints,  frame sections, end length offsets, output stations, insertion points, tension/compression limits , loads (force, ground displacement, temperature to point objects; distributed, point, temperature and open structure wind parameters to line objects; and surface, temperature and wind pressure coefficients to shell objects) , masses, moment releases and partial fixity, and several more. To make an assignment to an object, select the object then click the appropriate Assign menu command.

    Note that mass is required if you are doing a modal analysis to determine mode shapes (see Additional Point Mass, Additional Line Mass and Additional Area Mass). It is also required for the non-iterative method of considering P-Delta (see P-Delta Analysis Options). It is also required to convert static nonlinear force-deformation results into the capacity spectrum ADRS format.

  2. Various methods can be used to review the status of the model, including the Display menu > Load Assigns command,  the Display menu > Show Tables command, and the Model Explorer . Alternatively, to review loads and other assignments on an object-by-object basis, right click on any object to access the {Object} Information form, which shows the geometry, all loads, the design procedure, and the assignments made to the object (see Joint Object Information form, {Frame, Beam, Column, Brace} Information form, or  {}Slab, Deck, Wall} Information form). In addition, the View menu > Set Building View Options command, or the Set Building View Options button, , can be used to toggle on/off the display of various input items, such as section properties, member end releases, nonlinear hinges, diaphragm extent, and the like.

  3. If desired, use the File menu > Create Report command to print input data to a file or to the printer. Model Explorer > Reports also can be used to prepare printed output.

  4. Use the Analyze menu > Set Active Degrees of Freedom command to specify  the building degrees of freedom.

  5. If the model has floors, walls or ramps that require manual meshing, use the manual meshing options available through the Analyze menu > Automatic Rectangular Mesh Settings for Floors  or Analyze menu > Automatic Rectangular Mesh Settings for Walls commands to mesh these objects. Note that ETABS can automatically mesh floors that have membrane properties only. All other floors and all walls and ramps must be manually meshed. We recommend waiting to perform manual meshing until just before running the analysis.

  6. Use the Analyze menu > Set Load Cases to Run command to check the analysis status of the cases, delete results for cases that have already been run, set which cases are to be run, and run the analysis or just save the settings. After these settings have been set, subsequent analyses can be run using the  Analyze menu > Run Analysis command. When the analysis is complete, scroll through the text in the Analysis Window to check for any warnings or errors that might invalidate the analysis.

  7. Use the display features available on the Display menu, or the Display node on the Model Explorer, to display analysis results directly on the model or on the screen in a tabular format. See the topics in the Display book of this Help for more information about displaying results. See the topics in the Output Conventions book of this Help for more information about model output.

  8. If desired, use the File menu > Create Report command to print output to a file or to the printer. Alternatively, the  File menu > Export > Save Tables to Access command can be used to save the analysis output data in a database file that can be reviewed, modified and printed using Microsoft Access.

  9. If desired, use the commands available on the Design menu to run the model through one or more of the ETABS design postprocessors (Composite Beam Design Procedure, Concrete Frame Design Procedure, Shear Wall Design Procedure, .Steel Frame Design Procedure, Steel Joist Design Procedure).

  10. After the design has been run, save the model before exiting ETABS or the design will not be saved.

TIP:  Save your models often!