Wave Canopy 2009

Introduction

The Emergent Technologies and Design (EmTech) Masters programme at the Architectural Association includes an experimental construction each year, this year located on the upper terrace of N.36 Bedford Square. ‘EmTech’ constructions are undertaken in collaboration with a team of young engineers from Buro Happold, led by Wolf Mangelsdorf. The ‘Wave’ canopy has two principal subsidiary systems – wave-like strips of a thin timber composite and upright timber fins that provided local stiffening to the strips and the connection to the existing steel columns that are a permanent feature of the upper terrace. The upper terrace is one of the schools most public areas, used throughout the year by all staff and students, and so the multiple constraints of this situation determined the initial brief – the canopy has to provide partial shelter from the rain, shading from the sun and modulate the wind. The fabrication method was constrained by the size of the CNC bed and the standard size of timber veneer and plywood panels. Finally, the fabrication by students had to take place within the school and the assembly conducted in a very small space with limited access brought further constraints on the scale, weight and assembly logic.

Design: Material, Structure and Fabrication

The 5 metre long wave strips were fabricated by the students in studio from two layers of 1.5mm plywood with an interlayer of glass fibres and resin, and the fins were fabricated from three rather thicker layers. The two outer layers were 12mm thick plywood and the central inner layers were 18mm thick. The fins were assembled from two separate parts, joined together by a steel flitch plate. A 20mm diameter steel pin connected each fin to the plate at the top of each column. The lower part of the fin was positioned on the outer side of the balustrade, and was connected to the columns by a two part steel ring clamped around the base of each column and extended through the balustrade to the bottom of the fin.

The canopy project brings together two of the principal research paths of the ‘Emech’ programme – the mathematics of evolutionary development processes and physical experiments whose geometry is developed in relation to material behaviour. The iterative process of design and fabrication involved advanced computational tools whose input parameters were derived from physical models together with manufacturing and assembly logics. The design of the strips and fins were co-evolved together with the assembly sequence to make the best use of the limited space and time available on the upper terrace, and to ensure that the assembly all took place safely ‘inboard’ of the balustrade at the edge of the terrace.

The overlapping wooden wavelike strips were explored and developed in a series of physical models that began with the initial component and concluded with full size joinery prototypes. The structural capacity of the assembled strip morphology was developed by testing various degrees of overlap between the layers of strips, and differing patterns of simple bolted connections between them. Exploratory physical models gave a close but still approximate structural configuration that was refined by digital analysis of deforma-tions under self-weight and wind load. The spatial arrangement and the environmental conditions of the terrace were transformed into data inputs for the optimization algorithms and 20 successive iterations developed the initial surface to minimize wind load, and direct the rain to the drainage points. Computational Fluid Dynamics (CFD) simulations were used to assess the consequences of each geometric modification on the environmental conditions, and the successive iterations of the associative digital model progressively reduced the turbulence under the canopy, increased the laminar airflows, increased the porosity to prevent the canopy from acting as a sail, and enhanced the structural capacity.

Digital Design and Evaluation

Parametric modelling, developed using Generative Components software, underlined the entire design process by facilitating a seamless interdisciplinary exchange between the architects and engineers, enhancing the integrity of the design. The associate modelling software enabled a significant level of control over an intensely complex structure through a hierarchical build-up of parametric relationships in tandem with certain control mechanisms. The model was continually updated using interpolated data from the engineering analyses regarding global geometric strategy, local and global population densities, force vector paths and structural depths. For example, in cases where the engineers indicated, after structural analysis, that a certain part of the structure exhibited an excessive magnitude of stresses, the architecture was seamlessly adjusted in multiple ways to better accommodate the stress distribution along the surface: [i] by increasing the sectional dimensions of the local compression elements, [ii] by altering the overall form to reduce the extent of the cantilever, [iii] by maximising local component density and thus creating less surface exposure, [iv] by increasing structural depth caused by an increase in the height of vertical elements or [v] by altering the orientation of the compression elements streamlined to match the stress trajectories, thus better encompassing the stress flow.

The chosen material assembly along with the geometric behaviour, structural requirements and manufacturing restrictions became the variables of the associative model, leading to a variation of possible solutions, all of which complied with the set range of constraints. The final form therefore was derived not from a formalistic exploration but from the negotiation of different design criteria that allowed for the generation of a robust and multi-performative system. Iterative analyses through different software, along with a series of physical tests drove the ‘fitness ranking’ of each phenotypic result and helped for the identification of the most coherent solution in terms of the design objectives and assembly logic. CFD analysis, in feedback with environmental simulation analysis, demonstrated the system’s interaction with environmental inputs and aided in its development and calibration.

Construction – Manufacturing – Assembly

The physical experiments also generated the information on the curvature radii that could be achieved by bending thin strips of veneer. The selected material gave the desired curvature but was insufficiently stiff, and so two layers of wood were laminated together with glass fibres and resin to create a much stiffer composite. Prior to lamination the strips were laid up on the jig, curved and clamped in order to check the precise dimension of each curve against the digital geometry that had been evolved with an ‘attractor’ script that incremental¬ly increased the dimensions of the openings that are formed by the overlapping ‘waves’ of the strips, and so reduced the wind load in the most critical areas. The lamination process required a jig that to be constructed that accurately set out the overall curvature of the finished canopy. The strips were laminated together and then directly curved and bolted in place. Each strip was held in position by clamps until the resin was dry, and then the next strip strips was then fabricated on top of the previous, securing the relative position of the two strips with bolts.

Once all the pieces were fabricated, the three fins were laid out on the terrace, and the first three layers of the wave strips were fitted to them. The partial assembly was then lifted and bolted to the top of the columns, so that the ‘foot’ of each fin was pointing up to the sky. The remaining 11 layers of strips were fitted to complete the material system, and once fully assembled the whole system was rotated on the pins that hold the fins to the column. The rotation brought the ‘foot’ of each fin outboard and down to position so that the ring clamps could be fixed.

Students

Selim Bayer, Stephanie Chaltiel, Kunkun Chen, Shuai Feng, Ittai Frank, Utssav Gupta, Konstantinos Karatzas, Mohamad Khabazi, Tamara Lavrovskaya, Mohammed Makki, Maria Mingallon, Michel Moukarzel, Sara Pezeshk, Sakthivel Ramaswamy, Jheny Nieto Ropero, Revano Satria, Kyle Schertzing, Pavlos Schizas, Xia Su, Ioanna Symeonidou

Acknowledgements

This project would not have been possible without the generosity of Buro Happold who worked alongside us in studio throughout the project.’ Unto This Last’ trusted us to use their CNC equipment outside of normal working hours. We also thank Alec Tiranti Ltd for sponsoring 50% of the resin and glass fibre strands used for the lamination of the wood.