Parametric Structural Design and beyond Anke Rolvink, Roel van de Straat and Jeroen Coenders international journal of architectural computing issue 03, volume 08 319 Parametric Structural Design and beyond Anke Rolvink, Roel van de Straat and Jeroen Coenders Abstract In order to directly make insightful which implications follow from structural design changes and to be able to adapt a structural design quickly to geometrical design changes made by the architect, the structural engineer may embed a parametric and associative design approach in the structural design process.This approach focuses on parametric modelling and the development of parametric tools which serve specific needs in the structural design process, allowing designers for instance to quickly communicate and discuss alternatives or to inform design team members of structural results of changing design parameters. The paper presents multiple projects within these categories of parametric approaches.They are concentrated on design and analysis with the goal of presenting practical examples of these approaches in structural design which were integrated in the full design process in order to benefit from the qualities of a multi-disciplinary parametric and associative design process. 320 1. Introduction Design of the built environment requires the collaboration of a team of different roles and disciplines:The client, the architect, the structural engineer, the MEP consultant, etc. However, most parametric and associative design systems and research do not focus on a multi-disciplinary approach, but mainly part of the architectural domain: the geometry. However a parametric approach from the architectural perspective alone does not serve the collaborative possibilities of a parametric and associative design process.Working within a multi-disciplinary design team, the project can benefit if the structural engineer adopts a structural parametric and associative design approach that follows the general design intentions of the project and that provides insight, shows possibilities and presents boundary conditions which have to be taken into account by other members of the design team. This paper presents a number of research and development projects as well as case studies of real buildings and structures, within Arup around the globe which all exemplify the influence of structural parameters in the design process.The experiences by the engineers and computational designers will be discussed alongside some of the technical details of the approaches. The paper will be subdivided in two main components: design projects which are based on parametric modelling and research and development projects that employ and enhance the possibilities of parametric technology. All projects made use of Bentley’s GenerativeComponents [1] and/or McNeel’s Grasshopper plug-in for Rhinoceros [2] as parametric and associative modelling system or as a base for custom tool development. 2. Structural Parametric Modelling Over the past years,Arup has more and more experienced the need to have full control over the complete design to improve the behaviour and performance of the design by design variations and optimisation. Especially in the case of adaptation of the structural design to the geometric architectural design (usually with a complex geometry) the project and designers can greatly benefit from parametric control. If construction models and analysis model have to be remodelled manually, especially in early stages of the design where the architectural design is usually liable to many influential design changes, the parametric approach delivers further benefits of easier change and exploration.The projects below show how parametric modelling approaches are embedded in the structural design process to quickly set up structural alternatives, generate construction models and to reanalyse the structure. Parametric Structural Design and beyond 321 2.1. Competition entry for the Austrian Pavilion of the EXPO2010 Viennese architects, SPAN and Zeytinoglu Architects designed a geometrically complex surface model for the competition entry of the Austrian Pavilion for the EXPO2010 in Shanghai, China. For the structural engineers of Arup the main challenge was, next to proving a sound structural concept, to convince the jury of the buildability of the project within a limited timeframe and within a tight budget. Based on initial hand sketches, the structural design was set up parametrically in GenerativeComponents in a way that a number of key structural elements could be analysed individually, but also were associated into an overall parametric model that could be communicated with the architects, Figure 1. The parametric model proofed its value in allowing for quick design ᭡ Figure 1. Left:The parametric model updates when the geometric surface model was edited by the architects or of the structural elements. Middle:The rendered structural model including when structural alternatives had to be examined. For example for the the profile sections. Right:The design of a cantilevering truss, a parametric setup was essential in generating architectural image render of the quick construction and analysis models.The truss, with a height of 10m competition entry. Image (c) SPAN and arranged for the 18m long cantilever at the south-west side of the building. Zeytinoglu Architects. The complexity in the design of the truss was related to the bad soil conditions, urging the designers to avoid tensile forces in the foundation.As a result, the tuning of the downward counter loads from the first floor and roof structure with the upward loading from the rotational moment of the cantilever was matter of constantly changing the number and location of the floor beams as well as their support locations which determined the floor loads that were transferred to the backside of the truss. Employing this parametric approach to model and analyse structural elements based on structural parameters allowed for a quick setup of the structural design and a proposed building sequence, Figure 2.The main benefit however was that the parametric model could easily demonstrate that a complex architectural model could be simplified to a fairly straightforward structure, consisting of mainly standard elements which could be easily assembled, convincing the jury of the buildability of the project within the given boundary conditions. 322 Anke Rolvink, Roel van de Straat and Jeroen Coenders ᭡ Figure 2.The proposed building 2.2. Scheme Design for Coastal Canopies sequence of the main structural elements of the Austrian Pavilion The second project aimed to design a series of coastal canopies with a complex geometry. Having considered typical structural systems for a series of freeform canopies, the limitations (long spans, material constraints, tight budget, ease of construction and specific architectural details) gave rise to a single acceptable solution: a steel structure following a rationalised approximation of the original geometry.Together with the architect a system was set out in Grasshopper to interpret the architectural geometry using simple geometrical surfaces, such as spheres and cones and settled upon a system of interconnected tori, Figure 3. Four patches of four tori would be connected tangentially together, all meeting at a single point, forming the basis of the geometry of each canopy. These tori were generated parametrically so that their base radii, their ᭤ Figure 3. Geometry logic based on four tori Parametric Structural Design and beyond 323 inclinations and translations relative to global coordinates could all be controlled based on parameters.The idea being that the engineer would define the rule-set and the architect would determine which geometry they preferred based on the rules was agreed upon. The base geometry permitted the development of a parametrically defined structural grid upon the surfaces of the tori, so that the maximum length of any element could be fixed.This created structural elements based on arc geometry, with much repetition in the structural nodes and elements, with only a handful of different node types per canopy, creating a cost-effective solution, Figure 4. Considering that there were upwards of 2000 elements per canopy, this would facilitate prefabrication of the steel arc members. Additionally, the base geometry has been used to generate the cladding panelisation system, which inherits the repetitious quality of the toroidal geometry.This creates a set of panel types that only vary where drainage is ᭢ Figure 4.Arc based structural grid system for one of the canopies required.These panels also vary at the perimeter of the surfaces where the thickness between the top of bottom cladding surfaces taper to give the illusion of a very slender volume. The final geometry is that of the tori with the original architectural perimeter (in plan) slicing through the base geometry giving the edges a fluid “random” flow, thus presenting to the naked eye what appears to be a freeform surface, but is in fact a highly rationalised surface. 324 Anke Rolvink, Roel van de Straat and Jeroen Coenders 2.3. NSP Arnhem transfer hall The NSP Arnhem transfer hall project, designed by UNStudio includes a large freeform concrete shell with a complex geometry, Figure 5.The geometry of the shell has been defined by the architect in Rhinoceros as two free form surfaces, consisting of NURBS surfaces. However, the architectural geometry was not directly usable for structural analysis , since it only comprised geometrical