Grasshopper Development

In the development of the Grasshopper plugin, key considerations are taken to create a quick and effective interface that allows engineers and architects to communicate while designing. Knowing that this tool needs to be implemented at an early stage in design to effectively encourage BIM project results, considerations are made as to the scope of the wrapper and the tools it required. The goal of this wrapper is to create a robust parametric and genetically optimized design for study at an early stage in the design process. It is not, however, seen as a final analysis tool. Knowing this, the breadth of the wrapper was limited to allow seamless integration of architectural and structural disciplines without requiring time-consuming post production analyses such as connection design or

construction sequencing. Specifically, the wrapper created may be used to design any type of frame-based structure, be it a truss, moment frame, or some hybrid of the two. For the context of this thesis, a truss structure was used for simplicity in analysis and ease of examination. The wrapper also focuses on linear analysis, sacrificing a degree of accuracy for the greater benefit of saving time. Time that would be spent on non-linear analysis may now be allocated to the amount of design iterations the program framework can perform, increasing the amount of possible solutions.

The Grasshopper element needed to be robust enough to accommodate different drawing and development styles so that only minor changes would be needed to run the analysis tools. Due to the large quantity of illustration methods available in Rhino3D, the

Grasshopper element needed to be able to transform any structure created into the same data required for parametric study and optimization. Thus, the wrapper moves through design space in a similar way that a finite element package would, building a stiffness matrix and mapping members to the constructed design space. When using the wrapper, the first step is to define the model geometry. The primary reason Grasshopper was chosen for development is its ability to seamlessly integrate with Rhino3D. Thus, the architect and engineer have the opportunity to sit with one another and create a model that is both

architectural and analytical in nature. As current software stands, there is no user interface that allows for both architectural design and engineering input to be used with

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independent packages such as SAP2000 and Rhino3D. There are small, Grasshopper-based analysis tools such as the SOM tool mentioned in Chapter 2 and Kangaroo (Kangaroo Physics, 2013) that allow a user to create structures for specific studies, but the depth and breadth of analysis is limited in comparison to a full finite element package such as

SAP2000. The integration of major design platforms for both professions to use

simultaneously will save precious time in the back-and-forth interplay of traditional design development.

Once the model is done, the designers then move into the Grasshopper element itself. The second step is defining the materials and section geometry. All material values required to perform a linear analysis are available for selection. The wrapper also allows the user to define the names of the materials and sections for ease of use in the SAP2000 program. An input for initial cross section is given, which for this study was a circular, solid member. The section can easily be changed to represent any arbitration of shape supported by the SAP2000 shape libraries and configures.

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Once the material definitions are developed, the designer simply selects the model for analysis and inputs the frames into the tool in the “Members of Model” object. In the current development, there is an option to release members to create axially loaded objects or fix them for moment resistance across the structure. The designers then are free to select nodes on the structure for loading and restraining. The load input takes the form of a traditional global interface, calling out forces in the x, y and z directions, as well as moments about each of these axes. Once the corresponding load values are input, and corresponding load cases are defined, the model is ready to be output for its multiphase analysis. The users are free to simply copy and paste the existing framework for both the selection of loaded and restrained objects as well as load case definitions to create

additional restraint and load types. The last step involves directing the output to a

directory that is convenient for the users. The module creates a series of text files which it uses to send information to the parametric analysis and genetic algorithm C# programs. These text files are submitted when a Boolean toggle is switched to “True.”

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Figure 14: Output Station in Wrapper with Text File Location Input

It is important to note that the intent of the wrapper is to create a dialogue between the architect and the engineer. From the very beginning, the two practices must decide what an appropriate model entails, knowing how it will be analyzed through the wrapper. The two practices must then use their relative expertise to give insight and input to the constraints and restraints the wrapper requires.