If you are working in the AEC industry then you know how crucial it is to start off any building design with a proper grid system. “Off the Grid” is a generative tool designed to facilitate the discussion and decisions related to selecting the perfect grid system that meets the need of the architects, structural engineers, and construction managers involved in the project. The tool utilizes the Revit Generative Tool plugin, which can be download from the Autodesk website.

From Revit, you can create a generative study that will allow you to quickly design numerous building shell composed of PT-slabs and RC columns. From the generative tool interface, you have the option of selecting which input values you would like to consider. These include (1) the number of columns in both the X and Y direction (2) the concrete strength (3) the building floor-to-floor height (4) the total number of floors in the building, and (5) the number of floors that will repeat each type of design column. After selecting which inputs you would like to use, the generative tool runs through different combinations of these inputs and outputs the representative building shells for each of these trials. With each output, the user is able to evaluate the building based on several quantifiers (1) the slab thickness code satisfaction (2-4) the open space between column grids [X, Y, and combined] (5) the difference in spans (6) the column to room ratio (7) the cost of construction, and (8) the largest force in a column. From these outputs, you will have the option to compare numerous building shells and their evaluation performance to make an informed design decision.

This tool helps integrate the desires of the architect, the engineer, and the CM to create the best building as a product based off the grid in the early stages of the project. Whether it’s the desire of the architect to have large open spaces for interior flexibility, the engineer’s desire for creating a design with reduce column demands, or even the construction manager’s desire for reduced costs, “Off the Grid can be a helpful tool for you to initiate design discussions with your fellow AEC professionals.

Below we have the list of inputs that are both changeable (Figure 3) through the generative design tool and constant (Figures 4-6), which can be altered by the user if desired (Note: These should remain as constant when running the actual generative study).

Before we can begin modeling, some of the input values need to be used to create useful values that will be utilized later on in the script. In Figure 7, we have computed three different floor level related lists, whose descriptions can be seen through the comments below. Next, the distributed load value needs to be modified to create a list of design loads for the design columns that will be created. For example, if the bottom three floors of the building will have the same column type, the design distributed load value will be based on the bottom level, which has the highest load demand. This can be see in Figure 8.

Now beginning with the model creation, the footprint of the building is created first, as seen in Figure 9. This is then used to create both the room geometry, which is used to determine the useable volume of each building, and the concrete slabs for the building (Figure 10).

Next, the script performs calculations related to the columns. First the placement of the columns based on the building dimensions and the number of columns to be placed in each direction is computed. Then the spans between each column is calculated for both the x and y directions. These two initial column related calculations are seen in Figure 11.

With these initial calculations completed, the actual column geometry can be created. In Figure 12, we have the dynamo logic that is used to place the columns based on the computed grid. The actual height of the column depend on the floor-to-floor height and the slab thickness. The width and length of the column (designed as a square column) is computed based on the load of the column and the strength of the concrete used. The logic relating to the column sizing calculations can be seen in Figure 13.

Once all the geometry has been created, we can colorize the dynamo geometry to represent the columns and slabs in the design (Figure 14).

Once we have a model created, we can compute the values associated with the evaluation outputs:

The first one is the evaluator for slab thickness code satisfaction (Figure 15). This is based on the Post-Tensioning Institute that states that a span/depth ratio of 45 must be satisfied in a design to assure code compliant slab deflections and sufficient shear strength to avoid punching shear.

Next, we have the evaluators relating to grid spacing. Figure 16 shows the open space evaluator that determines how much open space we have between the columns. Figure 17 shows the grid uniformity evaluator that determines the difference between the X and Y span. To create a more uniform architectural space and constructibility, you will want to minimize this value.

Next, we have the evaluator that determines the column to room ratio (Figure 18). To decrease column interference with open space, you will want to minimize this value.

To determine cost of construction, we have to take into account the amount of concrete used in the columns and slabs and the construction costs of each floor based on its elevation. These considerations can be seen in the cost of construction evaluator (Figure 19). The cost of the concrete is scaled based on the type of concrete used, with high strength concrete being more expensive. Additionally, a multiplier has been computed to increase the cost of column construction depending on how many design columns are used. The more types of columns used in a building lead to increased costs. This multiplier logic can be found in Figure 20.

Lastly, the structural redundancy of the system is determined based on the column force evaluator. This takes the list of design loads for all the columns and pulls out the maximum value, which would be the most critical value for a structural engineer (Figure 21).

Once we have finished the computation of the evaluators, the dynamo script outputs these values to the generative design tool (Figure 22). These evaluation outputs can be used by the designer to evaluate the trade-offs between different designs.

Using the generative design tool interface built into Dynamo, you can quickly utilize the dynamo logic described above to explore various design options by simply selecting which inputs you want to manipulate and which outputs you want to optimize. The study results will provide you multiple building shell options and their respective inputs and outputs (Figure 23). Using this plot you identify the trade-offs between specific input or output values that can help you target the design that best fits your needs.

For a quick demo of how to use “Off the Grid” please reference the video posted below. (The video is slightly over 2 mins)