Arup. FinnforestMerk. Plaza Mayor in Seville with the Metropol Parasol

Transcription

1 Arup FinnforestMerk Plaza Mayor in Seville with the Metropol Parasol

2 Metropol Parasol Digital Timber Design The redevelopment of the Plaza de la Encarnación and the design of the unique free formed timber mega structure Metropol Parasol (Fig. 1.1) started with a design competition in The aim was to provide a new underground museum for the newly excavated roman mosaics, space for shops and the original market stands at ground floor level and a public plaza at 5 m above ground, including bars and a restaurant. The Berlin architect Jürgen Mayer H. together with the engineers of Arup submitted the winning scheme. Most visible is the huge timber structure resembling six merging mushrooms of up to 28 m in height and 150 m in total length, which provide the shading for the new centre point of urban live. Meandering walkways on top of the parasols and a restaurant at 21,5 m above ground invite tourists to enjoy the view on the old town. The geometry for the structure is based on a free-form, outlining the tree-shaped shading structures. The individual laminated wood plates (LVL) are generated by cutting vertically in an orthogonal 1.5x1.5 meter pattern through the free-form. Outline of the Parasols Rhino-Model of the wooden structure for the Metropol Parasol

3 Jan-Peter Koppitz, Gregory Quinn, Volker Schmid, Anja Thurik Section profiles for a selection of the wooden elements Different materials are employed in the structure depending on the various architectural and structural demands. The foundation and the cylindrical elevator shafts below the platform restaurant are made of concrete. The museum area was spanned with composite trusses of steel and reinforced concrete held together beneath by tie rods. A composite steel structure bears the weight of the restaurant and is supported by various slanted struts made of hollow steel sections, which follow the path of the outside stairs and are connected to two concrete cores. The timber plates are 1.5 to 16.5 meters long; the width of the Kerto-Q LVLplates varies from 68 to 311 millimeters. The parasol elements reach a maximum height of about 3 meters, while the largest construction piece, in the trunk, measures 16.5 x 3.5 x 0.14 meters. Overall, there are about 3,400 elements, with a total volume of about 3,500 cubic meters of laminated veneer lumber. Cross section of the hybrid structure for the Metropol Parasol

4 Metropol Parasol Digital Timber Design FE-model showing the steel diagonals and the observation walkways Since the shading structure does not have a closed, stiffening roof, but rather one that is open at the top and exposed to the elements, additional steel diagonals were necessary to stabilize the wooden structure so that it could bear weight. A clever, well-defined arrangement of the diagonals made it possible to achieve bidirectional shell action in the wooden grillage. The parasols wooden structure is at the mercy of the elements. In order to protect the wood, the laminated veneer lumber was sprayed with a two to three millimeter thick layer of 2K polyurethane (Fig. 4.1). Thanks to its outstanding flexibility and its excellent adherence to wood surfaces, this layer can help to prevent possible fissures in the wood. At the same time, the 3mm thick PUR layer is sufficiently vapor permeable. Together with the light ivory-colored topcoat of paint that serves as UV protection, the polyurethane coating lends the wood an entirely new surface quality. This new combination of PUR and wood provides the engineers and architects completely new ways to treat wooden structures. 2-3mm thick 2K polyurethane coating sprayed onto Kerto-Q with glued-in threaded rods

5 Jan-Peter Koppitz, Gregory Quinn, Volker Schmid, Anja Thurik In accordance with the original cutting pattern of the structure, all of the joints in the ground plan are at right angles. In elevation, however, all of the 2700 joints are at different angles. The wooden joints have to bear forces of up to 1.3 MN. Because the foundations load-bearing capacity is limited, the lightest possible connecting detail is required. Since each joint is different, a flexible, modular system has to be developed. The connection has to accommodate tolerances on site and be easy to assemble. Since every connection is visible, their dimensions have to be as minimal as possible. The answer to these requirements is connections that use bonded rods: a modern concept featuring great load-bearing capacity, but relatively lightweight. For the moment connections on the top and bottom sides of the elements, a special, standardized clevis connector was developed; it can be rotated and quickly bolted on at the construction site, as in steel construction. The two steel plates are interlocked via a saw-toothed connection and connected by pre-stressed, high-tension bolts to the flange. The high forces are transferred between the steel and wood via the threaded rods glued into the wood. a b Principle of moment connections using glued-in threaded rods (a) and pre-stressed bolts (b) FF

6 Metropol Parasol Digital Timber Design In Seville temperatures can reach well over 40 C in the shade. This causes problems to the epoxy resin used to glue in the threaded rods, because the resin is only approved for up to 60 C. Arup s thermal simulations showed that temperatures of at least 60 C or more could be reached inside the wooden structure. For this reason Arup s suggested to raise the glass transition temperature of the epoxy resin by tempering it: Working with WEVO Chemicals, Finnforest Merk developed a controlled process for heating the timber elements, including the bond lines of the rods, to about 55 C, making it possible to increase the glass transition temperature, to well over 80 C. Temperature simulation performed on 68mm thick Kerto-Q boards 7.1 Continuous Electronic Data Transfer The Metropol Parasol project was only conceivable by means of an integrated design development among all team members; architect, structural, services and fire engineers as well as the timber contractor. A prerequisite for such a design process is the seamless transfer of electronic data between all team members including the general contractor both in Germany and Spain. Collaboration in the team begins at the very first design phase. Virtual 3D models from the architects provide geometry that is directly modified or optimised by the engineers according to analysis results. 7.2 Generating Input Values for Structural Calculations The structural analysis of the Metropol Parasol requires highly complex three dimensional calculations. The starting point for the analysis is the architect s 3D model which provides the height and profile of the wooden elements as well as their orientation in space. With the help of a custom made computer program, the structural engineers automatically import the relevant geometric data from the model and generate an analysis model. The analysis model assigns a mass to each

7 Jan-Peter Koppitz, Gregory Quinn, Volker Schmid, Anja Thurik individual wooden element and steel connector in the system depending on the element s width. A key issue with the structural analysis of the Metropol Parasol is the sheer number of structural elements which results in a serious computational challenge, i.e. how do I obtain results if my input values are constantly changing? The final geometry of the structure depends on the forces acting at each node in the structure and these forces depend on the width and subsequent weight of the structural elements as well as the necessary connector sizes. This cycle of interdependence can only be broken if the whole structure is solved iteratively. For each iterative step the input values are extracted from the results of the previous step. Convergence of the iteration is reached when all geometric and load bearing criteria have been met. Due to the complexity of the geometry, this convergence can take up to several days to compute. 7.3 Automated Iteration Routines The structural engineers at Arup developed a software routine in order to automate the iteration. This takes into account the thickness and weight of the wooden elements and of the connection details at each node in the structure. The thickness and subsequent weight of the wooden elements are redefined at each step of the iteration process depending on the loads in the system. Similarly, the weight of the connectors is redefined at each step of the iteration. The various connector types which differ in weight and load-bearing capacity are defined according to the thickness, height and geometric orientation of fibres in the wooden elements with the help of a large custom-made data matrix.

8 Metropol Parasol Digital Timber Design Screenshot from the matrix that assigns connector types according to size and loading categories of the wooden elements. Once the iteration process is complete, the results are collected and forwarded electronically to the wood contractor and the architects. This same data is then used directly for the fabrication and detail checks. After completion of detail design, the real weight of the timber structure including the connection details was compared with results from the last iteration of the FE model. Various widths of LVL, matched to the given forces in the timber beams 7.4 Computer Aided Manufacture Data from the architectural model (JMH) is combined with data from the structural engineers (Arup) in order to generate a virtual object model for the timber

9 Jan-Peter Koppitz, Gregory Quinn, Volker Schmid, Anja Thurik contractor (FFM) to which further production-specific data is added. The output from this is information that can be used for remaining detail checks by specialist engineers (IB Harrer) and to produce final working drawings. Isometric view including connections, 3D-construction model by FFM The vacuum treated raw panels, 24 and 33 millimeters thick, were bonded together into large panels, from 68 to 311 millimeters thick, in a vacuum process. A CAD team using macro programming constructed semi-automatic processes for the approximately 3,400 individual wood elements and connections. After being approved, timber elements of the same thickness were optimally nested in the slabs taking into account the grain direction in a process similar to cutting cookies out of dough. The elements were precisely cut down to the millimeter by a CNC-controlled trimming robot, and were milled and notched at the same time. The 35,000 longitudinal bores (65 70 cm deep) for the glued-in threaded rods were drilled manually.

10 Metropol Parasol Digital Timber Design Cutting pattern of the individual Kerto panels FFM The fundamental idea behind the montage of the parasol structures was to keep element assembly as flexible as possible and to use simple, steel connection details to transfer the axial forces and bending moments, and also accommodate the construction tolerances. The assembly was carried out with the help of a complex scaffolding system, which was coordinated with the geometry of the parasol and its corresponding loads. In addition, assembly baskets were specially made to fit one person, matching the dimensions of the parasol grillage. Views of the platform and scaffolding, carpenters in custom built baskets