Grid lines (reference grids or simply grids) are the glue that ties all of the engineering and architectural drawings together. They provide reference points which helps the reader identify the same locations on each disciplines drawing set. They are equally important for your analysis model to assist in providing snapping points. It also assists in coordinating your analysis model with the design drawings. So lets take a look at how to set up grids in ETABS…

In the simplest way possible, to set up grids in ETABS, you need to navigate to the following location…

1. Edit
2. Edit Stories and Grid Systems
3. The Edit Story and Grid System Data dialog box will then display
4. Click on “Add new Grid System”
5. Then to change the grids within that grid system, navigate to that grid in the previous dialog box and press “Modify/Show Grid System”

But there are more options available to set up grids in ETABS. There is also a neat (best practice) way to set up grids in ETABS to ensure your model is efficient and easy to analyse as well as check. So lets dig a little bit deeper…

(Do you enjoy using ETBAS? Would you like to learn more? Take a look at THIS article which explains a step-by-step process to modelling cracked shear wall behaviour in your ETABS model).

The “Old School” Way of Setting up Grids in ETABS

ETABS has been around for quite a number of years. It has progressed from a data entry software to a slick 3D interface FEA modelling juggernaut.

In the 16+ years I have been practicing as a Structural Engineer the software has changed considerably. Most of the old ways of doing things in ETABS are still available to the user, however there are also new and quicker ways of doing certain tasks in ETABS. Setting up your grid system is one of those such tasks. Lets first take a look at the “old school” way of setting up grids in ETABS. As indicated in the introduction of this article, the navigation for grids in ETABS is…

Edit >> Edit Stories and Grid Systems >> Add new Grid System…

The following dialog box then displays…

This dialog box is pretty self explanatory with flexibility for the user to add a number of self-explanatory parameters for the grid system…

• Grid System Name: It is handy to name the grid system something descriptive logical which follows a system (my best practice approach to setting up grids will be covered later on in this article)
• Grid System Type: You can chose cartesian (x, y coordinates) or Cylindrical (circular grids). I must admit I’ve never had the need to use the circular grid function, yet!
• X Grid Labelling: Here the user can specify whether the x grids are lettered or numbered in ETABS
• Y Grid Labelling: Here the user can specify whether the y grids are lettered or numbered in ETABS
• Grid System Origin and Orientation (Plan): This section allows the user to set an origin point and angle for the grids. To save confusion I often don’t use this feature but rather specify my grid coordinates accordingly.
• Grid Dimensions (Plan): Here you can pre-populate the x and y grids using this section (number and spacing of grids). I have never come across a building yet in my career which has regular grids in both directions, you will most likely need to modify this in detail in the following dialog box…

Clicking OK takes you back to the previous dialog box. You can now jump into your newly created grid system and modify, add, or delete any number of grids you like within that system. Here is what that dialog box looks like (it can be reached by pressing “modify/show grid system” in the “Edit Stores and Grid System” dialog box)…

This data represents a very simple grid system with 4 grids in the x and y direction all spaced at 6m (19.7 ft). Here is what that resultant grid looks in the ETABS user interface…

What about an angled or inclined grid? Angled grids can be very common in buildings, lets take a look how to set these up…

How to Draw Inclined Grids in ETABS

Lets use the previous grid system example and draw a diagonal inclined grid line straight across the entire grid system. This may not represent a practical grid system for a building however it shows you the method on how to generate an inclined grid for your own project.

Lets go back to the modify/show grid system dialog box for the previous example grid. The easiest way I’ve found to input inclined grids is to use the “General Grids” portion of the modify/show grid system dialog box. Here is what that looks like for this specific example (I’ve chosen to call this diagonal grid, grid “Z”)…

Using this approach, you input the start x,y coordinate of your gird line then your end x,y coordinate. ETABS then draws a straight line between these points and that is your inclined grid set up in ETABS. Here is what our example grid system now looks like…

How to Supercharge Grid Input in ETABS

My Favourite way to set up grids in ETABS is to take the Old School method and supercharge it by adding an element of automation.

For this approach, I use the API for AutoCAD…

API is an acronym for Application Programming Interface. The interface basically allows two applications to talk to each other. In this instance I use Microsoft Excel to “control AutoCAD” using AutoCAD’s API. This allows me to “farm” the grid line coordinates directly out of a CAD drawing for the project.

The workflow for this is simply as follows:

1. Open the Excel Tool (which controls AutoCAD using its API through the VBA coding within Microsoft Excel)
2. Open the CAD plan which you would like to “farm” the grid coordinates from.
3. Press the macro button associated with the X grid coordinates then simply click on all the X grids on the CAD plan consecutively. All mouse click coordinates for these grids are then directly recorded by the Excel tool.
4. Repeat the same process for the Y grid coordinates on the CAD plan.
5. Cut and paste all of this data from Excel into the Modify/Show Grid System dialog box in ETABS.

This method is very useful if you have a large number of grids and saves a whole bunch of data entry time (you just need to be careful of your mouse clicks). Here is a quick GIF animation of how this all works…

ETABS also has its own API capability. The tools you can create to streamline your design process is restricted only by your imagination. Take a look at THIS very useful article which shows you how to make your own VBA tool within Excel to control ETABS functionality through API. It gives you a step-by-step guide on how to code in VBA and gives you the tools you need to make your own automation apps.

The principles for harnessing the API within AutoCAD is very similar with the methodology used in the article linked above. Using the reference article above with the code hints below should give you all the tools you need to also play around with both AutoCAD and ETABS API functionality (the code below only works with full AutoCAD v18 or above, not AutoCAD lite)…

CAD Background in ETABS to use as Grids

On recent versions of ETABS, the user can import a CAD background straight into the model. Originally this only worked with DXF files however you can now use either a DXF or a DWG file.

This allows you to bring a grid system across straight from the drawing into ETABS. You can also use this functionality to import slab edges, columns and walls.

There are a few things you need to keep in mind when preparing your CAD file for this exercise…

1. Full version of AutoCAD needs to be used, this won’t work with files generated using AutoCAD lite.
2. All elements in the CAD drawing need to be exploded prior to importing. If any blocks exist in the file an error message will be presented in ETABS.
3. It is best practice to remove any lines, text or layers which are not required for the import.
4. Elements in layer “0” or “Defpoints” will not be imported in ETABS
5. ETABS will only recognise arcs, lines and closed polys from a DXF or DWG file. Therefore if any other blocks are used they will need to be converted to one of these elements.
6. In order for ETABS to recognise columns and floors, these need to be set up as closed polygons.
7. In order for ETABS to recognise beams and walls, you will need the centreline defined in the CAD file (either as a straight line or arc)

Once you are happy with your cleaned up CAD file you are ready to import the file into ETABS as a background (grids and all). You simply need to navigate to the following location within ETABS…

File >> Import >> DXF/DWG File of Architectural Plan…

The following dialog box will then appear…

This dialog box allows you to allocate the CAD file to specific storeys as well as set a coordinate point where you would like the original point inserted into ETABS

With the grid system now included in the CAD file you have imported as a background you can use the grids as a snapping point within ETABS. The functionality of this is very similar if you had the grids located within ETABS itself.

Once the CAD background grids have been imported into ETABS you can view the different layers of your CAD plan by navigating to the following location in the model explorer…

Display >> Architectural Layers…

Here you can turn layers on and off which are within the CAD file. This approach has some great advantages but also some disadvantages. The main advantage is that you can get the initial grid system set up pretty quickly in ETABS. The downside is that if the grid system changes (which it often will on most projects) you need to re-modify the original CAD file then import it back into ETABS.

Part of me prefers to have all the grid data stored directly in the ETABS file rather than have information supplemented with a CAD background, but that’s just my personal preference. Having the grid information set up directly in ETABS does allow you to them modify the visibility of the grid systems and have more control over how they appear in your model (which we will now cover in the next section how this can be used to your advantage)…

Best Practice Approach to Setting up Grids in ETABS

Analysis models are best set up in a logical and neat manner. This not only makes it easier to complete your modelling and analysis, it also makes it easier for those who will be checking your work!

I like to use a very methodical approach to setting up my grids in ETABS. The grids are a powerful tool to help you set up the rest of your model. Here are some tricks I’ve learned along the way through trial and error and also borrowing approaches that I’ve seen other Structural Engineers use:

1. Set up your grids as one of the first tasks you perform in your model. This creates snapping points for you in future
2. The base architectural grid system should always be placed into the model. This is irrespective of whether a specific grid actually has a structural element on it or not. Often Architectural grids sometimes don’t correspond with any structural elements. Providing the project grid system in your model gives perspective for comparison of your models geometry against the project documentation (both the Architectural and Structural drawings).
3. Set up several different grid systems so that you can turn grid systems on and off as required in your views. This is especially handy when you have a lot of grids on your building and a very complex model. Here is how I generally set up my different grid systems:
   – Base project (or architectural) grid system
   – User added grids for additional column locations for columns which don’t fall on the architectural grid
   – Slab edge grid system (slab edge locations which do not lie on the the base architectural grid)
   – A full separate grid system for a core structure and separate grid systems for individual shear walls. Wall elevations are an important view to check in your modelling and analysis. To make navigating your model easier and cleaner, a separate grid system for all sperate cores and shear walls makes it easier to navigate your model and review the results.
4. Ideally all structural elements should have a grid to snap to, whether it be as part of the project grid system or user added grids. Snapping assists in meshing which helps in reducing errors in your model that you will need to track down and fix when you run your model. For an in-depth article on how to check if your model is correct and the results it is outputting are logical, take a look at THIS article.