Rogier Houtman, Harmen Werkman

Transcription

1 Rogier Houtman, Harmen Werkman The castings are determined aesthetically by a fluid arm following the curvature of the edge cables, and a disk representing the possible range of rotations. Although in this design step important functions of the corner plate are fulfilled, the membrane still needs to be secured and some fine-tuning of the corner plate design remains necessary. Fig By using two identical castings and by mirroring as well as the use of mutual rotation of the corner plates, a system able to meet different geometrical conditions could be made. During this fine-tuning process the exact type of cast alloy was chosen and the minimum dimensions determined. This resulted in the use of a durable and reasonably processable stainless steel, and also in doubling the arms of the casting for direct load transmission (to avoid eccentricities). Upward sliding along the edge cables of the membrane can be prevented by clamping the membrane. Because of the geometry of each corner point, the clamping plates had to be different from one another, and the elements could not easily be standardized. This was because the project was so close to the erection deadline that a further feedback loop could not be accommodated. Fig Sketch of the corner plate, including membrane securing system. TensiNet I 169 I

2 Detailing and Connections Fig Shop drawing of the final mould. The overall dimensions of the casting were determined by the necessary tolerances and dimensions of the cable terminals, as well as by the clearances needed for assembly. The final shop drawings of the mould were made (see Figure 5.38) defining the three dimensional shape of the casting. The geometry and dimensions of the castings made it impossible to meet all the ideal geometrical conditions. In a tight corner, such as Figure 5.38, there is not enough space for the connection of the cable. Because adapting the casting design was not possible at this stage, a special and separate solution had to be found. Shop drawings were made for assembling the casting, the clamping system, the position and dimensions of holes and other follow-up treatments (Figure 5.39). Whether the chosen solutions are still satisfying will become clear during erection and life-time of the membrane structure. Once installed an evaluation will give insights into the functioning of the structure and its connections. I 170 I European Design Guide for Tensile Surface Structures

3 Rogier Houtman, Harmen Werkman Fig Shop drawing for follow-up treatments for putting together two castings to form one corner plate. TensiNet I 171 I

4 Detailing and Connections BLUE MOON, GRONINGEN (NETHERLANDS) A temporary roof for a theatre was needed for an Architectural manifestation in Groningen (Netherlands). The membrane structure, shown in Figure 5.40, was designed with Foreign Office Architects and differs in size and shape from the previous example. Normally a structure s size is proportional to the dimensions of its elements, e.g. large spans result in large cable diameters. Thick cables and in particular the accompanying terminations are disproportionately expensive. This approach implies another attitude towards connection detailing. Fig The Blue Moon theater covering (Tentech). The corner base plates form the connection between the membrane, cable structure and the foundation. In this particular case, as well as the edge cables there are also valley and ridge cables that are connected to these plates, therefore the corner base plates will be more complex. A careful determination of rotations and transformations in all connections was necessary. Fig The corner plates during erection. The corner plate itself is pulled using chain hoists. After the corner plate is brought into position the membrane is pulled downwards. Each low point consists of a single hinged foot connection, screw thread and corner plate, which receives the various cables. In this design it should be noted that the corner base plates are part of the total low point system, comprising the load transmitting connection to the foundation as well as the tensioning facility. The distance between the foundation points and corner plates is among other things determined by the required length for tensioning. In the form finding and analysis models this situation needed to be explicitly modelled and developed. In fact, a process of dividing one single point into a spatial configuration of cables and connection elements I 172 I European Design Guide for Tensile Surface Structures

5 Rogier Houtman, Harmen Werkman had to be embarked upon. The cables, which have different orientations, are singly hinged at their connections to the corner plates. In addition, rotational possibilities are provided by the adjustable swinging links and the hinged masts. Thus the whole system has sufficient rotational and translational freedom making movements possible in all directions. In this project fixed cable lengths were used, and to avoid expensive cable fittings the prestressing and adjustment facilities were to be separate from the cables at the corner plates. This is a cheaper solution but demands precision in the determination of cable lengths. The elongation of the long cables needs to be accounted for very carefully since it directly influences the required tensioning length of the system. In this particular case the membrane is also connected to the corner plate with small belts to prevent upward sliding of the membrane away from the system point MULTI-PURPOSE TENT IN HAMINA In Hamina, Finland, a temporary multi-purpose tent was built for the celebrations marking the completion of the restoration of the city s fortifications. The membrane structure, covering an area of around 4800 m2, consists of undulating surfaces, which arise from alternating valley and ridge cables (Figure 5.42). The membrane structure is supported by four Vshaped trussed pylons and several border masts. Pre-tensioning the membrane was planned by using the perimeter masts. By pulling these outwards the membrane can take up its final prestressed shape. The tensioning facilities are part of the supporting structure and all cable lengths are fixed. In this structure the membrane is adjustable locally in relation to the corner plates and also the back stay anchors are adjustable in length. Due to relatively limited adjustment possibilities a very precise design, production and execution process was required. Fig Temporary multi-purpose membrane structure of Tensotec Consulting for the city of Hamina (outside and inside). The undulating membrane is supported by large V-shaped columns and peripheral masts. At the corner plates the edge, ridge/valley, stay and safety cables are connected. Adjustments are provided to prevent the membrane from sliding away from the corner plates. Safety cables connect all mast tops and provide stability in case of failure of the membrane. Degrees of freedom were needed at each cable connection during erection and service-life thereafter. Each cable connection has one degree of freedom, an axis of rotation, but consideration of the total system reveals that the low points of the membrane contain more degrees of freedom. TensiNet I 173 I

6 Detailing and Connections Oversize holes in connections can provide enough space for small rotations at right angles to their axes. These movements can then be compared with the figure of equilibrium of the structure under extreme loading. In this case a good understanding of the movements and rotations of the complete structure and all its discrete structural elements has resulted in an apparently simple but well functioning system. Fig Single and double guyed border masts. In the base connections of the guy cables, movements perpendicular to the axes are possible. 5.9 References (1) Bubner, Ewald (1997). Membrane Construction Connection Details, Druckerei Wellmann Gmbh, Essen ISBN BIBLIOGRAPHY FOR DETAILING Schock, Hans-Joachim (1997). Segel, Folien und Membranen, Birkhäuser Verlag, Basel ISBN Huntington, C.G., (2000-1). Connections and Detailing part 1. Fabric Architecture Huntington, C.G. (2004). The tensioned fabric roof ASCE. Detail, numbers , , , , , see Deutsche Bauzeitschrift Blum, R. (2001). Detailing in textile architecture. Labor Blum, Stuttgart. Werkman, H.A. (2003). Een podiumoverkapping voor het openluchttheater in Soest; H.A. TU Delft, Delft. Llorens, J.I. (2002). Details and Connection Design; J.I.; School of Architecture; Barcelona View into the world of textile architecture; Ceno Tec, Greven, 2001 I 174 I European Design Guide for Tensile Surface Structures

7 Rogier Houtman, Harmen Werkman 5.9.2ANCHORAGES Llorens, J. I. (2002). Details and Connection Design ; School of Architecture; Barcelona Das, B.M. (1990): Earth Anchors, Elsevier Science Publishing Habib, P. (1989). Recommendations for the design, calculation, construction and monitoring of ground anchorages, A. A. Balkema, Brookfield Hanna, T.H. (1982). Foundations in Tension. Ground anchors, McGRaw Hill & Transtech Publications Llorens, J. I. (1985). Passive anchors for tensile structures, Proceedings of IASS symposium Milan: Spatial structures: heritage, present and future, G.C. Giuliani ed. SGEditoriali, Padova, p Widmann, R. (1995). Anchors in theory and practice, Balkema Rotterdam Xanthakos, P. (1991). Ground anchors and anchored structures, John Wiley & Sons, New York TensiNet I 175 I

8 Detailing and Connections I 176 I European Design Guide for Tensile Surface Structures