Enter the Panda – linking geometry to structural analysis

My team designs big stuff, with complex geometry. For a while now (since well before my time with the team; I’ve been here for a year and a half) we’ve been using Grasshopper 3D to define our geometry – beams, columns, trusses, struts, etc – with some pretty cool results.

Geometry definition of the Al Wakrah stadium roof, Qatar, produced in Grasshopper by AECOM Sports in London.

Alright, it’s all well and good to parametrically define some funky geometry – and maybe impress some architects along the way – but that’s just the first step. Let’s look at structural engineering in terms of The Three D’s: Define, Design, Draw. What we’ve done so far is just step 1, Define.

The second D, Design, requires the use of a three dimensional finite element analysis package, in our case Nemetschek’s Scia Engineer. Previously, we did one of two things to go from Define to Design: we either used Scia’s spreadsheet input by outputting our parametric members and nodes from Grasshopper into an xls document, opening Excel, copying the whole lot and pasting it into Scia; or we baked our geometry from Grasshopper into Rhino, output a dwg from Rhino, then imported it into Scia.

Both of these methods can be rather clumsy, lead to rounding errors, have some major drawbacks (e.g. the spreadsheet method can’t import curved members at all), and, most importantly, are long-winded. Thus whenever you make a change to the geometry it takes a long time (by parametric design standards) to rebuild the geometry in your analysis model. You then need to redefine all of the member and node parameters, such as element releases, supports, cross-section information, and loads.

Enter Panda, our in-house Grasshopper tool which takes geometry of any kind and converts it into Scia’s native XML format, ready for import directly into Scia. When set up properly, we can import an entire model, open it up in Scia, and press Run, without having to set up any additional parameters from within the Scia interface. The model will already include everything we need to analyse the structure and run Scia’s automatic steel design functionality.

Below are some screenshots of the Grasshopper script, including a zoom-in of our Model Creator component. As you can see, everything from cross section, load cases & combinations, applied forces, hinges, supports and design parameters (buckling lengths and restraints) are already defined before we even open Scia. The “Pandarator” – the component to the right of the Model Creator – is the final step; it writes out the complete XML file, ready for import into Scia.

So how do you do this yourself? Well, it’s all about learning about Scia’s native XML format and how to generate the files, and then automating the process. You can start by exporting an XML file from Scia, looking at how it works, and adapting the code for your own scripts.

Or if you just want to get a quick geometry model into Scia, as part of this blog post we’re releasing Panda Lite – a free Grasshopper component we’ve created to generate a Scia XML file from a set of lines and arcs. Simply plug the curves into it, set an xml filename, start a new model in Scia, and go to File->Update->XML. It’s that easy!

Get it here and try for yourself: PandaLiteHere! *

And what about the third D, Draw? Well, that’s the second part of the Panda suite: our link from Grasshopper to Revit, with Autodesk’s Dynamo as an intermediary. But that’s the topic of a future Blog entry to be posted by my esteemed colleague, MBMB (a.k.a. Matt Byrton).

End User Agreement*

Pandametrics (The Zen Art of Parametrics) – Episode I

Defining Pandametrics:

Parametric design – defining a series of design processes by a set of adjustable parameters

Zen – enlightenment through meditation, self contemplation and intuition

Not a panda...but pretty Zen

In structural engineering when we talk about parametrics we are traditionally talking about our modelling and design workflows, where the input parameters are a series of geometric definitions such as intersecting circles, variable frame settings, definable surface forms etc.

However, we often meet many definitions of parametric throughout the construction industry, just as we meet many definitions of BIM (an argument for another day)!

The zen art of parametrics, or Pandametrics as we like to call it (in true naming workflows and software after animals fashion), is using our experience and intuition to pick the right parameters for the most holistically efficient design workflow. 

A brief aside,  As I'm writing this at this years Autodesk University 2015 I'll take this opportunity to point out that architects and engineers who have been using parametric design, you're the choir and this is piece is going to come across as me preaching what you already know, although hopefully with a few talking points or bits you've not considered. Primarily this is written from the point of view of talking to those who haven't used parametric design but are considering making the plunge. Anyway, I digress, back to the content...

Why Panda? –  Some Chinese philosophers believe that the black and white of the Panda represents the opposing forces of Yin and Yang and in the time honoured tradition of using animal names for workflows and plugins we have focused on the Panda. Is there an animal more zen that representing the balanced peace and harmony of parametric design? 

Zen Panda

Let's expand that…

When I am asked to create a parametric model my first task is to work out what the key adjustable inputs are that can optimise our solution and most importantly what constitutes ‘optimised’.

We should talk about what we mean by optimised as it forms the foundation of the parametric process. In my experience, optimised in terms of building structures could be any number of things, for example:

• A found form which produces pure structures such as a pure tension structure, or a pure arch.

• a form which is confined by specific criteria such as avoiding ponding, or minimum curvature. 

• a structure which can be mapped to a specific aesthetic but adjusted for material performance.

• workflows which improve interoperability speeds to allow rapid prototyping and analysis. 

• a structure which is optimised for alternative key performance indicators such as cost, or additive material tonnage, or reductive material tonnage, or aesthetic, or energy performance, or user comfort…..the list goes on ad infinitum.

Benefits of Parametric Design

The largest benefit of producing a parametric model should come from an understanding of

1. the specific outcome you are looking to achieve; and
2. which small group of inputs with best help you achieve this.

One thing I can say for certain is that creating a parametric design process without fully understanding both of these will end in something too unwieldy to be practical or so inflexible it finds itself on the scrap heap the second your input requirements change. 

The basic benefit of all parametric design (sweeping statement coming) should be to make your design processes more efficient and anything that has to be binned off at the first hurdle because it's too inflexible fails even this simple test.

And I’m gonna stop right there… right before launching into the do’s and don’ts of parametric modelling, mainly because this blog is getting a bit on the long side, but also because it means when we return for the thrilling conclusion there will also be a hint of the workflows we’ve developed and a lead in to the free bit of software for download that Ricky has been pioneering….watch this space