Rendered bird’s eye view of structural model before construction documentation; Rationalization and regular appearance was an important objective in the design. 

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... paper describes innovative aspects in the parametric structural design process of an automotive flagship store from competition to construction documentation. Novel approaches in design workflow and tight integration of architecture and engineering from the earliest phases on enable a strong correlation of design intent and realized artifact. Parametric structural analysis, cross section sizing, and multi-goal optimization are part of an adaptive procedural model managing a growing body of information throughout all planning phases. Intuitive representation enhances the interface of design engineer to model resulting in amplified adaption of changes in design conditions and requirements. Software interoperability and custom drafting pipelines form a building information system to finally document and deliver complex architectural engineering within a seamless digital chain. Keywords : Digital workflow, building information system, continuative procedural model, detail design, structural optimization, parametric engineering, karamba, multi-objective optimization, octopus, cross section optimization A distinctly ‘shaped sky of steel’ opposes the concrete exhibition landscape in the design for an automotive flagship store by Delugan Meissl Associated Architects (Fig. 1), re-articulating the ancient desire for flying structures in architecture. The roof achieves his incisive appearance particularly on account of lacking perceptible columns (Fig. 2). The horizontal continuity is only partially intercepted by four concrete cores. All further supports are organized in clusters of five to seven single pillars; each of these is accordingly small in diameter and therewith extremely slender. Interpretations of a forest are trying to blur the structural connection of the two parts and integrate in the architectural context not only visually, but respond to different functions and usages. Although with the architectural program the geometry was subject to profound change several times during the schematic design phases, the design of a hierarchical structural system came about early on. The four cores are the main elements stabilizing the shaped sky vertically and horizontally, see the detail for the connection in Figure 4. The vertically supporting column clusters are built just as pinned rods for the sake of their slenderness, not taking any bending moments or horizontal forces. Spanning in between and cantilevering out from the cores, the main trusses form the primary load bearing system in the roof. They use the entire height of the roof, which is up to 9 meters, to bridge the gaps of up to 40 meters, respectively cantilever up to 26 meters. Arrays of I-beams form a secondary system with distances of less than 3 meters to easily produce closed surfaces by application of simple trapezoidal metal sheets. Regularity hereby is an important objective for economic fabrication (Fig. 3). The column clusters are arranged after several conflicting criteria, and support both the primary and secondary system. The final steel structure of the shaped sky weighs around 3000 tons with 6500 modeled elements. The design happened after Korean Building Code 2009 such that 38 governing load combinations were modeled in karamba. The maximum displacements in the ultimate limit state were bounded by 25 cm, under live load it was 5 cm. A beam to hang the entire glass façade from is placed on the underside of the roof, set in from the perimeter between 5 and 20 meters. The maximum vertical displacements for the façade beam were bounded to 10 cm (see Figure 4). Dimensions of 160 x 75 meters in plan, irregularity as ubiquitous condition, an inherently complex structure, and a dynamic design process from competition to design documentation require advanced algorithmic parameterization- and optimization technology to conclude with efficiency of workflow and designed structure in the given time frame. The project is developed in different phases throughout about a year. Though the architectural idea remains the same, profound changes still happen in late phases. This way, a number of different approaches in fitting structures into the design had to be developed and tested to facilitate feedback quick enough to inform the design process again. The establishment of a feedback loop between the design teams involved is of great importance to the development of a synergetic, well negotiated solution. On each design iteration, the time needed to incorporate changes and new requirements is critical to supply quantitative feedback as a basis for decisions. Procedural modeling is used to set up different building blocks which can be recombined and adjusted upon each new design adaptation. Generation of the axe geometries in early phases, a search process for the placement of column positions, dynamic application of load scenarios, assignment of ambience-aware cross-sections, or many different custom result analysis modules are so being grown alongside the project. Collaborative modeling is possible to a certain extent. In the first place the work on subjects which were to remain divided on the long run is split up to different engineers. The difficulty in apportioned work on the actual parametric structural model is that dependencies between tasks sometimes are unforeseeable and dynamic, and therefore are challenging to be done separately. Visual procedural modeling bears advantages to traditional programming in the development of a model like this. The visual data flow makes it easier to learn, use, and debug, such that also non- programmers can become professional users. Speaking of modular collaborative modeling, though it can become hard to re-use the building blocks after a software update of the platform or the plug-ins used, which does not happen to code as easy (Park, 2010). Further for a large scale project the bare handling of big data becomes a challenge, as Grasshopper3d (Rutten, 2015) being the tool used is geared towards user-friendliness and for this sake produces a lot of overhead computational load. Software faults and debugging show to be a major factor, especially when exploring new applications with software packages still in development. Nevertheless the very same procedural model is refined over the course of over 6 months, where the focus firstly lies in the fast adaption of changed architectural design, and later becomes the incorporation of additional detail information. Feedback from a . dstv file based interface to a secondary engineering program used to perform the official checks and non-linear dynamic analysis is broken down to simple conditions and idealizations to be fed into the generative pipeline again. The result is a process distinguished by its flexibility in design changes, its efficiency in producing detailed output, but also by its dependency on software compatibility and a few persons operating the master models. Still the approach proved to be very successful as the lever achieved by the emergent complexity and its optimization capabilities by far outbalanced the efforts needed to produce and maintain the model. Karamba3d (Preisinger, 2013) is used as a structural modeling tool which provides high-performance feedback and seamless integration with flexible geometric modeling. The parametric model in Grasshopper3d is acting complementary to the model drawn in Rhino, where the axes of beams are drawn and fed into the scripting environment (see Figure 5, top row). They are converted to beams with automatically assigned parameters differentiated on a per-element basis. Those properties (see Figure 5) include a possible allocation to a smoothing set (middle left), an application of different joint conditions (middle right), maximum profile dimensions defined by offset surfaces (bottom left), and loads to be applied for various scenarios and combinations. Most of this ...