LIGHTWEIGHT STRUCTURES IN CIVIL ENGINEERING DEVELOPMENT OF JOINTING SYSTEMS FOR MODULAR PREFABRICATED STEEL SPACE STRUCTURES

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1 LIGHTWEIGHT STRUCTURES IN CIVIL ENGINEERING PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM Warsaw, Poland, June, 2002 G E N E R A L L E C T U R E S DEVELOPMENT OF JOINTING SYSTEMS FOR MODULAR PREFABRICATED STEEL SPACE STRUCTURES Z.S.MAKOWSKI 1 1 Professor, F. Eng., Ph.D., D.I.C., F.C.G.I., D.Sc. Hon., London, UNITED KINGDOM ABSTRACT: The steel industry witnessed within the last decades a remarkable acceptance of space structures for many structural applications. The popularity of three-dimensional structures has been growing steadily, but their present acceptance all over the world is truly phenomenal. Nowadays, space structures are willingly used by architects and engineers for sport halls, gymnasia, leisure centres, industrial buildings and hangars. References 1,2,3 describe in detail the recent developments in many countries. The large number of space frames built shows clearly that, through prefabrication and industrialisation, these systems often compete very successfully with more conventional structures, at the same time providing architects with more impressive forms. As a rule, space frames are built with simple prefabricated units which are often of standard size and shape. Such modular units, mass produced in the workshop, can be easily and rapidly assembled on site by semi-skilled labour. Key words: Joint, system, modular, prefabricated, steel, space structures 1. INTRODUCTION In the past, the chief barriers towards the general use of these systems, were the complexity of analysis of space structures and the difficulty of joining several members in space at different angles. The introduction of electronic computers solved the first difficulty. The type of joint depends primarily on the connection technique (bolting, welding or use of special mechanical connectors). It is also affected by the shape of the members usually this involves a different connection technique depending on whether the connecting members are hollow section, structural tee, angle or wide flange (see Fig 1,2,3). This paper looks at the problem of connecting members in space. It is obvious that a connector is an extremely important part of any prefabricated system and the final commercial success relies directly on its effectiveness and simplicity. Fig.2. The famous Eiffel tower, erected in Paris for the 1889 exhibition by the French engineer Alexandre Gustave Eiffel is a typical example of a three-dimensional structure. It also illustrates the complexity of a three-dimensional joint in the age of gusset plates and riveting. Fig.1. An early example of prefabrication of cast iron three-dimensional structures. The details of joint and strut described by a French architect Violet-le Duc in 1863 as an example of prefabrication of space structures which, according to him, will open l ere d une structure nouvelle. Many different types of connector have been proposed for space structures the author of this note has details of over 250 different types of connectors suggested or actually used in practice. Some designers have made the mistake of trying to produce a universal connector suitable for all types of structures. The early work of Konrad Wachsmann (see Fig 4) belongs to this period and though his universal connector proved to be rather complicated and not used in any practical applications, it paved the way for further improvements that led eventually to some very ingenious solutions. OPENING SESSION 17

2 One can refer to Mr Alexander Graham Bell, as the father of prefabricated space strctures. He was responsible for the development of multi-layered space structures based on tetrahedron. His early experiments in were carried out on prefabricated skeleton structures using tubes and a specially designed connector. Fig.3. Early examples of the German system Oktaplatte used for tubular space structures. It consists of tubular elements arranged to form octahedra, which in turn are welded to steel hollow spheres which constitute the nodes of the framework. Two hemispherical parts of the joint are reinforced at the juncture with a steel diaphragm. As a rule, the attempts to produce a universal connector resulted in unnecessarily complex solutions, too sophisticated, consisting of too many parts and ultimately too expensive. However elegant such a universal joint may be, commercially it is doomed to failure. The performance of structural connections of all types have been the subject of intensive research during the last decade. Tests show that butt welded joints in steel can develop 100% efficiency for tensile strength, but welding aluminium structural alloys leads, as a rule, to unavoidable annealing which can reduce efficiency to the order of only 50%. The efficiency of riveted and bolted joints is usually assumed to be around 75% in both aluminium and steel construction. A critical item in the fabrication for any space structure consisting of large number of interconnected parts is the dimensional tolerance that can be achieved during the erection. The tolerance of individual parts depends mainly on the method used to join individual members. Some Jointing systems are much better in this respect than others the SDC system (see Fig 13) is an outstanding example, in which the connector allows an easy adjustment of the length and angular inclination of members meeting at a joint. Welded connections give the maximum strength in steel space structures and as a rule, are used for large spans. On the other hand, site welding extends considerably the erection time and requires highly skilled welders. In jobs where prefabricated structures have to be erected by semi-skilled labour, bolted connections are preferred and this is one of the reasons why within the last few years large span space frames erected in the Middle East have used almost exclusively prefabricated systems relying on bolted connectors or specially designed mechanical connectors like the British NODUS system (see Fig 19 - in chapter 8 Illustrations ). One must also realise that the often over-emphasised disadvantage of bolted connections in that they are wasteful in the use of material as the holes reduce drastically the useful load-carrying cross-sectional area of the members, can be remedied through the use of specially designed end pieces, which allow the utilization of the full cross-sectional areas of the members. The survey of the connectors which have been used in practical applications shows that preference of the designer for a particular type of connector depends greatly on his own experience and his connection with a particular firm of civil engineering contractors. The cost of the production of joints is one of the most important factors affecting the final economy of the finished structure. A successful prefabricated system requires joints which must be repetitive, mass produced, simple to prefabricate and able to transmit all the forces in the members interconnected at the nodes. The French engineer, Robert le Ricolais, realised the advantages of space structures some 50 years ago however, his early models constructed in timber used rather complicated connectors and probably this is a reason why his ideas did not find a general acceptance at that time. The famous American comprehensive designer of geodesic domes, Buckminster Fuller, proved to be more successful in spreading his ideas as his first geodesic domes used very simple disc-type bolted connectors. All connectors can be divided into two main categories: (i) the purpose made joint and (ii) the proprietary joint used in industrialized systems of construction. The proliferation of numerous purpose made joints for one-off projects is partly due to the unwillingness of the consultants to use a well-tried proprietary system as it involves the payment of royalties. On the other hand, there is an obvious paradox. As a rule the purpose-made joints are either used for modest span structures or for very large-span structures, when the limitations of most of the standard proprietary joints are realised by the designer. In the first case, the designer does not worry about the strength of his joints, which normally are overdesigned. In the second case, the large loads to be carried by his structure would not be resisted by the commercially available systems, which cater only for average loads and as a rule are not suitable for very large spans. The design of the hangars at London Airport could be used as a typical example of the second case. For small spans bolted connections are preferred at there are numerous examples of such applications. The introduction of hollow sections into structural engineering produced an impact on the development of joints suitable for tubular structures. The German Oktaplatte system illustrates this point (see Fig 3). This system originally used joints consisting of two hollow hemispheres and a dividing diaphragm. This enabled a fully welded tube connection to be made to the spherical node, and latticed panels to be fabricated before fixing together, at works or on-site, using the spacing washer as a tolerance piece. The advantage claimed is that the individual tubular members are straight cut at their extremities and welded without any edge preparation to be hollow sphere. The same reason has been mentioned by several Spanish and Romanian designers who stated that the sphere junctions have had the great advantage that the tube ends do not need any processing since the cutting of the tubes is straight. Such a welded joint had an additional advantage of producing structures of greater rigidity and hence smaller deflections. The rigidly connected tubular member had also an increased capacity to resist buckling load. However, it is interesting to mention that Mannesmann firm, which introduced the Octaplatte system, in fact decided to modify their original system and introduced the Okta-S grid system, which is a bolted version of the welded Oktaplatte system. In their modified system, the tubular members are jointed on site to the hollow steel spheres by a screwed socket connection (see Ref 4). The reason for the modification was that site welding required for the original Oktaplatte extended considerably the erection time and presumably increased its cost. Many designers of tubular structures (see Ref 5) that it is essential to OPENING SESSION 18

3 keep the amount of workmanship on the tube itself to a minimum. The easiest solution is to cut the ends off square and then to weld them to the end piece or directly to the connector; however, there are many other techniques, such as saddling, crimping, flattening, reducing, slotting, etc., but as they are the second operation in fabrication, they add to the final cost. a) An advantage of tubular structure is that the outside diameter can be constant, simplifying the construction and sometimes enabling the designer to use only one size of the connector for his whole structure. Differing wall thickness of the tubes can often take account of the variation of forces in the structure without changing the outside diameter of the tube. The ideal solution is to obtain a member able to take the same force in tension and compression however, this is specially difficult to achieve in pin-connected structures because of the increase of the slenderness ratio introduced by the hinged ends of the members. Some systems, e.g. the Nodus joint (see Fig 19 - in chapter 8 Illustrations ), enable the engineer to design the member as a fixed ended strut and provide in his connector the ends fixed capable of developing full restraint. The hollow sphere concept has been developed into hemispherical forms, though it has obvious limitations regarding the number of members which can be connected, e.g. Segmo system (see Fig 31 - in chapter 8 Illustrations ). One of the most advanced connectors developed for single- and double-layer grids is the Japanese NS system (see Fig 37 - in chapter 8 Illustrations ), only very recently put on the market. Very many steel space structures have been constructed within the last 5 years in the NS system. From the category of the proprietary joints one has to describe briefly: (1) the MERO connector (2) the Unistrut (Moduspan) system (3) Space Deck (4) Triodetic system (5) Unibat system (6) Nodus system b) 2. THE MERO CONNECTOR Introduced in 1942, by Dr. Mengeringhausen, proved to be extremely popular and has been used for numerous industrial buildings, churches, assembly halls and domes. In this form of construction tubular members with threaded ends are connected to a steel sphere node drilled and tapped to accept up eighteen members. A main feature of this system is that the axes of all members pass through the centre of the connector, eliminating eccentricity of loading at the joint, though originally the MERO joint (see Fig 5) was developed for the pin-connected structures, recently a modification of the shape of the end pieces welded to the tubular members allow the members to resist fixity moments in addition to axial forces. The versatility of the bolted MERO spherical joint is already well known to all designers of steel space structures. One has to report, however, that in an attempt to reduce the cist of MERO structures, and as a result of an extensive programme and development in their Würzburg research centre, the MERO firm some 5 years ago started to use four new versions of a connector for some of their recently constructed space frames. They are known as: (1) the cylindrical joint (type ZK) (2) the plate-disc joint (type TK) (3) the hollowsemi-spherical joint (type NK) and (4) the block joint (type BK). These extremely efficient newly developed joints quickly proved to be specially useful for single-layer shell-type structures. Their use results in considerable cost benefit. They are described in detail in Ref 6. c) Fig.4. Many designers have made the mistake of trying to produce a universal connector suitable for all types of structures, As a rule, such an attempt will produce an unnecessarily complex, too sophisticated connector consisting of too many parts. Konrad Wachsmann in 1944 produced his famous connector consisting of 13 parts for prefabricated hangars. Fig 4a illustrates the component parts of the connector, Fig 4b shows the assembled node and Fig 4c gives the interior view of a giant hangar designed as a double-layer grid using this joint. OPENING SESSION 19

4 Fig.5. The MERO system, introduced in 1942, consists of modular bars and connectors. The spherical joint is cast in steel, drilled, tapped and threaded to receive high tensile bolts. The tensile forces carried along the longitudinal axis of the bolts are taken over through the coneshaped end pieces welded to the ends of the tube. An excellent, widely used system. Thousends of buildins using this system are constructed all over the world. OPENING SESSION 20

5 Fig.6. The MODUSPAN system (previously known as the UNISTRUT system) is used exclusively for double-layer grids. The structures consist of framing struts, all of the same length, the same for top and bottom layers and the diagonals. The struts are connected at the joints by one bolt only to the specially shaped pressed-steel plate. OPENING SESSION 21

6 Fig.7. The SPACE DECK system, the first British system pyramidal units which are erected apex downwards with the angle frames butting against each other and inter-connected with bolts. The bottom layer is formed by tie-members of high-tensile steel which are fitted with turnbuckles. OPENING SESSION 22

7 3. THE UNISTRUT SYSTEM It was developed in 1955 by Charles W. Attwood with the help of the Engineering Research Institute of the University of Michigan. The UNISTRUT connector (see Fig 6) consists of pressed steel plate produced automatic in a special tooling machine, ensuring an extremely high precision in manufacture and very low cost through massproduction (see Ref 7). A sized steel blank is automatically fed into the machine by a feeder. It is transferred through two draw stations and three pierce stations (two of which pierce holes and form lugs). The connectors for the top and bottom layers are identical and therefore the UNISTRUT double-layer grids consist of only four components: - the plate connector - the strut - the high tensile bolt and - the nut. As all units are manufactured on a special jig, a very high degree of tolerance is obtained so that the individual pieces are always very easy to install. The UNISTRUT system is thus self-aligning and self-levelling. 4. THE SPACE DECK SYSTEM It was introduced in the United Kingdom some 40 years ago as a fully industrialised space frame system based upon the repetitive use of factory made components, which when assembled on site, produce a double-layer square-on-offset square configuration (see Fig 7). The basic unit is an inverted square based pyramid consisting of an angle top tray and four diagonal or bracing members. The units are interconnected by bolting their top layer members and interconnecting the lower chord node points by means of high tensile steel tie bars. Opposite ends of each tie are threaded left- and right-hand, thus providing a trunbuckle facility to adjust the centre camber of the structure. The idea of using prefabricated pyramidal units has been further developed by many other designers, though the details of the connections differ. The PYRAMITEC structures of S. du Château are a good example of such systems in France (see Figs 15,16). Whereas the Space Deck is using only the square-based pyramids, the PYRAMITEC system employed also triangle based pyramids (tetrahedral) as well as hexagonal based pyramids. There are now many similar systems developed in other countries. Fig.9. The details of a joint used for a three-way latticed grid construction over an amphitheatre in Fez, Marocco. A very similar solution to that used by Du Château for his French structures. 5. THE TRIODETIC SAYSTEM It relies on ingenious method of joining materials replacing welding, bolting or riveting, developed by a Canadian firm of F.Fentiman and Sons Ltd. The connection involves the use of an extruded aluminium hub, into which may be inserted members of any cross-section following the application of a deforming process to their ends. The TRIODETIC connector can be used for any type of three-dimensional skeleton structure (see Fig 10). The aluminium extension hub contains slot or keyways and the connecting members have their ends pressed or coined to match the slot. Normally the members are inserted into the hub using automatic hammers. Fig.8. The TRIDAMATEC joint for three-way grids. Du Château used this system for many structures built from modular latticed units. Originally only aluminium structures were built in this system, but nowadays TRIODETIC space structures are being erected using steel tubes and aluminium hubs since practical tests showed that the use of two different materials did not involve any electrolytic difficulties. OPENING SESSION 23

8 Fig.10. The TRIODETIC system has been developed in Canada now used all over the world. The connection involves the use of an extruded aluminium hub containing slots and the connecting members have their ends pressed to match the slots. The members are inserted into the hub using automatic hammers. Fig.13. The SDC joint developed by a French designer Stéphane du Château. The node is made up of two cast shells which when welded together provide six circular apertures to allow the connection by welding of six tubular units at the same nodal point. The tubular components can slide into the node which allows a certain amount of angular adjustment, permitting a gradual change of the curvature of the surface of the structure. Used for domes and double-layer grids. Fig.11. An early example of an American system for aluminium cast connector for geodesic domes. The tubular aluminium members slip into the pockets provided by the connector and are fixed to it by bolts. a) b) Fig.14. The SPHEROBAT node consists of a hollow spherical forged steel node with a detachable cap that is secured to the main part of the node with a through bolt. Tubular members are tapered and the tubes ends are drilled and threaded to allow for concealed bolted connections. Fig.12. Examples of a recently introduced Yugoslav system for doublelayer grids. Fig 12a gives details of the TORUS joint, Fig 12b of the second version known as the TORUS-GUSTO. 6. THE UNIBAT SYSTEM It was introduced some 25 years ago by S. du Château and at the time was popular in France. It uses modular pyramidal skeletal units which are bolted only at their corners to the adjacent units using high tensile bolts and have their lower layer provided by tubular members which are flattened at the nodes and jointed to the pyramids by only one vertical bolt. Strictly speaking, the UNIBAT had no prefabricated standard joint and therefore was not limited by usual restrictions imposed by the connector as to plan form or architectural layout. It used any type of structural section, hollow sections or rolled sections, separately or combined. The clear spans OPENING SESSION 24

9 possible for UNIBAT system are not limited as it usually is in other systems, by the node connector, but simply by the maximum size of structural section available. Theoretically, UNIBAT can be used for double- or multilayer structures. This system is rarely used now in France being replaced by another system based on SPHEROBAT connector (see Fig 14). 7. THE NODUS SYSTEM It was introduced in 1972 by the Tubes Division of the British Steel Corporation. The development of the NODUS joint (see Fig 19 - in chapter 8 Illustrations ) has been an outcome of several years of research and extensive testing carried out at the research centre of the British Steel Corporation the Tubes Division at Corby. The NODUS joint is a typical example of a mechanical connector. It comprises a body divided into two half casings which are clamped together by means of a high strength friction grip bolt. The bolt head is accommodated in a hexagonal recess in one half casing, thus leaving the exterior of the joint flush with the outside of the chord member so that cladding can be fixed directly onto the chords. The mating half casting has four protruding lugs drilled for connecting to the bracing members, either in line with or at 45 degrees to the chords, by use of the appropriate half casings. The horizontal chord members are butt welded to connectors having circumferential rings which lock into corresponding grooves in the half casings. The bracing members have steel forked connectors welded to their ends. These members connect to the casings lugs by means of headed pins, secured with split cotter pins. A sealing gasket is inserted between the half casings and is clamped with the central bolt, which is tightened to a specific torque value. at the Building Research Institute in Bucharest, (Ref 10, in Poland, (Refs 11 and 12) and in Italy on the Permit system developed at the University of Bari, (Ref 13). It is very difficult to prepare a reliable cost comparison of different connectors developed in different countries for different local markets. Improvement in welding techniques and recent development of computer controlled tube flame cutting machines now makes the use of welded joints a more economical proposition in some countries. In Denmark, according to Mr. Thomsen (Ref 14), experience shows that on a cost basis, system built up from individual members with bolted connections cannot compete with systems built up from bigger shop-made components with welded nodes. On the other hand, the experience of MERO, NODUS and some Japanese firms shows that firms specialising in prefabricated space structures often receive orders not because their prices are lower (sometimes they are) but simply because their products are known to be very reliable, tested and because they can guarantee the delivery and erection within a specified time. One should draw attention to an extremely interesting article (Ref 15) which discusses the conceptual design of spherical joints in space structures. It contains a formal topology of spherical joints in the context of innovative design. 9. ILLUSTRATIONS Although the NODUS system has been used principally in the construction of horizontal double-layer grids, it can be adapted to a variety of other applications including vertical, inclined or multi-layer grids. These applications are particularly effective in the covering of exhibition halls, shopping centres, museums or similar buildings where the structure is exposed or viewed through glasing. Numerous buildings have been erected in this system during the last nine years in the U.K., Middle East, and many other countries. Altogether some 500,000 square meters have been covered with the NODUS space frames. In the early stage of the development of the NODUS joint, prototypes were rigorously tested in a specially designed rig at the BSC s Tube Division s Research Centre at Corby. These tests applied loads to the joint in all directions simultaneously and account was taken of varying bracing angles which induced an eccentric moment. These tests enabled the yield strength of the joint and the maximum working load to be determined. Due to the construction of the joint, it was found that compression loads resisted by members meeting at the NODUS joints would be 15% higher than those for tension loads. The design of this connector makes it suitable for automatic welding process (see Ref 8). 8. THE REVIEW OF RECENT DEVELOPMENTS It clearly shows that the search for an economical connector for various types of space structures did not lose momentum. An interest in this field is probably best illustrated by the competition organised in 1964 by the French Chambre Syndicale des Fabricants de Tubes d Acier for the development of efficient connectors for tubular space structures. Over 40 entries were received. Reference 9 gives details of the various proposals submitted during this competition. Several articles and even books have been published to discuss the relative advantages and disadvantages of numerous connectors. It is also known that some commercial concerns have tested their own and their competitors connectors. However, as a rule, the results of these comparative tests are not available to the general public. In addition to extensive tests on various connectors carried out during the period of by Stewarts and Lloyds Co. Ltd., the Mannesmannröhre Werke A.G. have produced results of their tests on the strength of the OKTAPLATTE (see Fig 3) and OKTAPLATTE-S systems. Their tests were carried out at the Technical University of Karlsruhe. There are also publications giving details of tests on joints for space structures carried out Fig.15. Details of a double-layer grid system known in France as the PYRAMITEC. The system consists of modular prefabricated pyramids with triangular, square or hexagonal bases which can be assembled by bolting. OPENING SESSION 25

10 Fig.16. The three basic configurations used in the Pyramitec system consisting of pyramids having triangular, hexagonal and square bases. The top layer is constructed by bolting the flanges of the adjacent bases of the inverted pyramids using horizontal bolts. The bottom layer consists of long tubular members flattened at nodal points and connected together by means of vertical bolts passing through the apices of the pyramidal modules. Fig.17. The details of connection used during the construction of the dome over the Fort Regent leisure centre at Jersey. The dome is a singlelayer grid structure consisting of almost square trays made of hollow sections which are joined together at their corners by site bolts and finally site-welded. OPENING SESSION 26

11 Fig.18. The French system known as the NEWBAT consists of members with flattened ends which fit into a cast node. The structure is assembled by bolting and pinning only, no welding is required neither in workshop or on the work site. OPENING SESSION 27

12 Fig.19. The NODUS joint has been developed in 1972 by the British Steel Corporation Tubes Division for prefabricated steel tubular doublelayer grids. The joint consists of two castings, the chord connectors and the fork connectors for the disagonals. The main casings are held together by means of a centre bolt. Four basic layouts of the grid can be obtained using the NODUS joint: a) square on square offset b) square on large square offset c) square on diagonal d) diagonal on square. OPENING SESSION 28

13 Fig.20. The plan and elevations of a three-way double-layer grid supported at four points only over a square in Kuweit. The structure supports sun shades designed by a French firm of Space Engineering. OPENING SESSION 29

14 a) b) c) Fig.21. The details of the three-way double-layer grid for the Kuweit roof. The structure consists of tetrahedral modular units made in tubular stee The cast end pieces are welded to the tubular members which are bolted together at the joints. OPENING SESSION 30

15 Fig.22. The K.T. Space Frame system developed in Denmark for double-layer grids. The tubular bars are fitted with internally fixed bolts which are screwed into the spherical connectors. Fig.23. The joints used in an American system developed by Pearce. The diagrams illustrate three basic space frame geometries square, isosceles triangle. The bars have sets of hinge elements welded to both ends. Paired hinge elements join strut ends together with a simple bolted connection. OPENING SESSION 31

16 Fig.24. An American system known as the POWER-STRUT. Suitable for double-layer grids. There are only two types of basic components web members (for diagonals) and chord members. They are connected to the module connector by means of bolts and nuts. a) b) c) Fig.25. The connectors developed by an American firm of Space Structures Corporation of New York. Fig 25a illustrates the OCTA HUB connector, Fig 25b the ORBA HUB connector and Fig 25c shows the joint used for aluminium triangulated shell structures. OPENING SESSION 32

17 Fig.26. OPENING SESSION 33

18 Fig.27. A very economical system developed in France and known as the TRIDI The node consists of an assembly of plates welded together. Members of any shape can be connected to the gusset plates by means of high tensile friction bolts. Many industrial buildings, sport halls and assembly halls covered with this system. OPENING SESSION 34

19 Fig.28. An Italian PREMIT system developed for prefabricated double-layer grid industrial buildings. It consists of two standard structural components: a) the diagonal member, b) the chord member. Both elements have special end pieces. The connection is ensured without eccentricity be means of four high strength friction bolts. Fig.29. The Spanish ORONA system developed for double-layer grids and domes. The tubular members have specially formed ends with high tensile bolts which are screwed into a spherical connector. Used with great success over a number of large span buildings. OPENING SESSION 35

20 Fig.30. The COSMOS joint developed recently in South allowing variable angle adjustments from flexible knuckle joint. Tubular members are fitted in the workshop with an end piece. No welding on site. Fig.31. A French system SEGMO developed specifically for double-layer grids. The joint consists of two casings to which the tubular members are welded. Fig.32. A French system Villeroy, consisting of two casings. Tubular membe connected by means of high tensile bolts. A neat connection, able to appreciable loads. Fig.33. A simple joint used for small span single-layer shell structures or do layer grids. In France this system is referred to as the SARTON system tubes are flattened at the joint and connected by a single bolt. Suitab moderate loads. OPENING SESSION 36

21 Fig.34. A French system developed by Delcroix rarely used in practice. Fig.35. A French system developed by Raccord H based on spherical node with tubular member with end pieces which are screwed and later we the joint. Rarely used in practice. Fig.36. A Polish joint developed for steel tubular three-way single-layer grid domes. Three bars are bolted to the gusset plate, and the other three bars specially shaped end pieces welded to the gusset plate. OPENING SESSION 37

22 Fig.37. This the NS Truss system U-type developed a few years ago by the Japanese Nippon Steel Corporation for tubular members. The node is a steel sphere with threaded holes for the connection bolts. Used for numerous double-layer grids. The tubular members have cones welded to both ends. The bolts are fitted into the end cones before welding. The fastening tool is inserted through the node opening into the square hole at the end of the bolt. A spring at the head of the bolt presses the bolt to engage with the thread of the node. OPENING SESSION 38

23 Fig.38. Stressed skin space grids introduced in the 1960 s take advantage of the roof covering becoming an integral part of the load carrying structure. They consists of thin sheet pyramidal modular units made in aluminium, glass fibre reinforced plastics sheets which are interconnected in space systems. The drawing shows several examples of such structures designed by the author with the details of aluminium cast connectors. OPENING SESSION 39

24 Fig.39. The connector used for the aluminium stressed skin space grid designed by the author for International Union of Architects Congress Headquarters building erected in 1961 in London. Fig.40. Type of connection used for timber double-layer grids. OPENING SESSION 40

25 Fig.41. Nodes of braced domes built with laminated timber components. Very simple gusset plates are required to interconnect six members meeting at a joint. Further details are given in an excellent book on timber construction (Holzbau Atlas published by Institut für Internationale Architektur Dokumentation, München, 1978). 10. REFERENCES 1. Z.S.Makowski (editor): Analysis, design and construction of doublelayer grids. Applied Science Publishers/Halsted Press, London and New York, Z.S.Makowski (editor): Analysis, design and construction of braced domes. Granada Publishing Ltd., London and Nocholls Publishing Company, New York Z.S.Makowski (editor): Analysis, design and construction of braced barrel vaults. Elsevier Applied Science Publishers Ltd., London, V.Hauk: The Mannesmann Okta-S joint for tubular space structures. Proc. of the 2 nd International Conference on Space Structures, University of Surrey, 1975, pp (a) G.M.Rose: A comparative examination of a wide variety of joints for space structures. Space Structures Conference, British Steel Corporation, London (b) S.Boar, M.Raskin: Noeuds de structures tubulaires spatiales. Sm80 St6, Liege, Z.S.Makowski (editor): New trends in spatial structures. Bulletin of the International Association for Shell and Spatial Structures. April 1986, No. 90, vol XXVII, pp S.C. Hsiao, G.C. Dygert: The Moduspan space-frame system. Proc. of the 2 nd Intern. Conf. on Space Structures. University of Surrey, 1975, pp Design Manual: Space Frame Grids, 3rd Edition, 1976, British Steel Corporation, Tubes Division. 9. Chambre Syndicale. Le Tybe d acier dans la construction metallique noeuds et assemblages. CSFA, Paris, Toader et al.: Aspecte privind calculul si realizarea unor invelitori reticulate, Bul. Stiint., Institutul de constructii Bucuresti, T.21, No.3-4, 1978, pp Z.Kowal: Przestrzenne struktury pr towe z w z ami t oczonymi. PNIB P.Wr. Wroc aw, Raport Instytutu Budownictwa. Nr.1-2/R-131/75. Badanie w z ów. Wroc aw, D.Mitaritonna, G.Prete: Proposta e sperimentazione di un nuovo sistema di connessione nodale per grigliati spaziali in acciaio. Construzioni Metalliche, No. 4, K.Thomsen: Trends in the design of double-layer space grids. Proc. of the 2 nd Intern. Conf. on Space Structures, University of Surrey, 1975, pp T.Arciszewski, Udmak: Shaping of spherical joints in space structures. International Journal of Space Structures, vol.3, No.3, 1988, pp G.S.Ramaswamy, M.Eekhout, G.R.Suresh: Steel space frames, analysys, design and constrution. Produced by Thomas Felford Publishing, London, ) Z.S. Makowski, Co-editor with H. Nooshin of International Journal of Space Structures, Space Structures Research Centre, Department of Civil Engineering, University of Surrey, Guildford, Surrey GU2 7XH, United Kingdom. OPENING SESSION 41

26 LIGHTWEIGHT STRUCTURES IN CIVIL ENGINEERING PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM Warsaw, Poland, June, 2002 G E N E R A L OPENING SESSION L E C T U R E S 42

27 Fig. 2: Plan of the main floor work - preliminary design, final design, and supervision of construction - be undertaken by an architect closer to the site: the firm of DeMars and Wells of Berkeley, California. The control of design remained, however, with Aalto. This arrangement was accepted by Father Barnabus and by the Abbey. ORGANIZATION OF WORK It may be of interest to describe briefly the manner in which the task of design, and eventually also of supervision of construction of the library building was organized. As noted, the concept of the library was developed entirely by Alvar Aalto in Helsinki. Working on it in Aalto s office at that time was Eric Vartiainen, a young American architect, who graduated from the University of California at Berkeley where, in fact, Vernon DeMars was one of his instructors. When the project was moved to the DeMars and Wells office in Berkeley, Vartiainen came with it. An important part of his duties was to maintain liaison with the Aalto office in Helsinki. Working with Vernon DeMars and John Wells, Vartiainen developed the necessary details of the project in a manner which, he felt, carried out Aalto s concepts. These details were then discussed with Alto by telephone and through the mails. Eventually, with Aalto s approval, these details were incorporated into the design. The procedure was not simple, particularly in view of the large - 10 hours - time difference between Berkeley and Helsinki. It should be noted that, at the time, telephone and mail were the only practical means of communication - the fax, let alone the internet, did not exist! Fortunately, Vernon DeMars, a famous architect in his own right, was a long-time personal friend of Aalto s, and the partner-in-charge, John Wells, was that rarity among architects, a man with a keen design sense, combined with a complete command of the technology of construction. These factors made it possible to complete the project seamlessly after the untimely passing away of Alvar Aalto. Our office was retained to supply the structural engineering services when the project moved from Helsinki to Berkeley, and we saw it through the completion of construction. All those involved had a clear sense of the historical importance of the project, one of only two Aalto designs in North America. The project was completed in ARCHITECTURE OF THE LIBRARY The Abbey at Mount Angel consists of a number of buildings located at the periphery of a flat-topped hill. The library is one of these buildings, with the main entry at the top floor level, and with additional floors below, following the slope of the hill. The plan of the main floor is shown in Fig. 2. A porte-cochere defines the entry on the south side of the building. The essentially rectangular south, single-story side contains various offices and service areas. Adjacent to it is the north side, which contains the stacks and reading areas. In plan, it has the form of a fan, so characteristic of many Aalto libraries (and the subject of many anecdotes). Located at the center of the fan-like area is the control desk. Seated behind it, the librarian can see all of the main floor reading/stack area, as well as the area of the entry hall. A very large appropriately shaped opening in the main floor permits the librarian, sitting at the control desk, to see also the reading/stack areas on the floor below. Some comments about the fan shape may be appropriate. The simplest shape affording the librarian visual control is a segment of a circle; however, the circular form is somewhat static. Instead, Alto chose a more dynamic fan shape. It makes both the north side exterior and the interior Fig. 3: North - South section through the Library OPENING SESSION 43

28 main space more exciting and challenging. The line of the fan shape itself was developed by Aalto as a free-hand sketch on tracing paper. If memory serves, the scale of this sketch was approximately 1:200. It was necessary to translate this sketch into a dimensioned working drawing. Aalto s free-hand sketch proved remarkably close to a spiral curve defined by a mathematical equation. Instead, Vartiainen carefully measured and scaled-up Aalto s original shape; this, properly dimensioned, became a part of the project drawings. This is illustrative of the care that Eric Vartiainen took to make sure that the project followed Aalto s concepts. Above, in the roof, there is a strongly articulated skylight, which provides indirect, diffused light. In plan, the skylight corresponds in shape to the shape of the floor opening below, and is also centered on the center of the fan area. However, both the sky and the floor opening are defined by segments of circles. The seminar room, which can accommodate an audience of more than 100 persons, is located off the entry hall. Mechanical rooms are located on the floors below the main floor, convenient to their function, but out of the way of the essential operations of the library. Fig. 5: A view of the Library from the outside preferred shape for a column, because of its poor buckling characteristics. However, in this case, the loads are insignificant. The columns were designed by Eric Vartiainen, who added to the steel surfaces a facing of teak wood, thus making them look wonderfully soft and mellow. The very simple detailing of the base and top connections assists in creating this feeling, and Eric s design, accepted by Aalto, proved most successful. THE STRUCTURE OF THE LIBRARY In developing the structural system for the Library building it was necessary to consider the usual factors: 1. The general layout developed by Aalto in the course of conceptual design, 2. Project location, including the governing codes, 3. Short term (cost of construction) and long term (cost of maintenance) economics. Fig. 4: View of the Library from the north DETAILING In general, the structure is not exposed. This made the detailing of structural connections somewhat easier, particularly the detailing of steel connections. Nevertheless, every effort was made to keep the connections simple, with a direct path of forces, easy to install and to maintain. The detailing of the columns that support the roof of the porte-cochere at the main entrance may be of interest. The columns are welded of structural steel plate, and their shape in cross-section is a cross, the sides of which varies with the height - smallest at base, largest at the top. Strictly from the point of view of structural behavior, a cross is not the Of course, very much in the forefront was the desire to develop a structure which would match, and enhance, the concepts developed by the architect. As noted in a preceding paragraph, the building was to be located at the edge of a flat-topped hill. Thus, at the main entry level, the building is one story high, while at the bottom of the slope it is three stories high. Local load conditions, based on the Uniform Building Code (Ref. 3), require that the building structure be designed for very large seismic accelerations. For these reasons, the structure from the foundations all the way up to the underside of the roof is poured-in-place reinforced concrete. The structure of the roof is framed in structural steel. OPENING SESSION 44

29 challenge. The problem of providing a structure, which would enhance the space definition achieved by the architect, was more complex. In this regard, of particular interest was the space of the reading area and stacks on the main floor. Conceptual design envisaged four fin-like rectangular columns extending the full height of the building, and supporting the floors and the roof. We proposed instead that the columns be circular, and placed in pairs. Aalto approved, and that is how these columns were built, adding a measure of dramatic rhythm to the interior space definition. REFLECTIONS Fig. 6: View of the Library from the south Lateral loads resulting from seismic excitation or wind are transferred by a system consisting of vertical reinforced concrete walls, and horizontal diaphragms. At the floor levels, these were the poured-in-place reinforced concrete floors - slabs and beams. At the roof, it was a welded metal deck, suitably braced. Foundations are a combination of spread and continuous footings, and caissons. During construction, the contractor suggested excavating the area, building the caissons as formed columns, and then placing engineered fill; this was done. The poured-in-place concrete was also well suited to supporting the brick masonry veneer, which faced all exterior walls. From the description above it is clear that the problems of structural strength, stiffness and stability presented only a fairly common Viewed from the outside, the Mount Angel Library building is quite modest in scale. This is true whether it is observed from the south at the level of the campus above, or from the north at the base level of the building. In each case, it blends well with its neighbors, with which it shares the brick veneer facing. At the south side, the building is only one story high, and at the north side only three. Thus it is quite unobtrusive - no grandiose statement here. What may attract attention is the curved shape of the façade, behind which the fan-shaped reading/stack rooms are located, but this form, too, is quite restrained. It appears that Aalto accepted the exterior space definition provided by the existing buildings of the Abbey. The spaces inside are treated differently. The offices and service areas are quite simple, no different, really, from any that have been designed by a competent architect. The main reading/stack areas are treated quite differently. The fan shape area, the roof skylight, the large floor opening, and the interior column design were already mentioned. Their very rich forms are accentuated by the fact that all surfaces are plain, and painted off-white. Thus the form reigns supreme, and what a rich and dramatic form it is! The interior space is strongly defined, but in a very restrained way, so that it does not overwhelm the user of the Library. The overall mood is enhanced by the fact that many of the interior furnishings of the building were designed by Aalto. This includes reading lamps, desks and chairs, etc., as well as some fixtures such as door handles. In fulfillment of the intentions of the Abbey, the Aalto Library has been, since it completion in 1970, a focal point for many wider community activities. As an example, a seminar was held there in 1998, memorializing the 100 th anniversary of Aalto s birth. And this was just one event out of many. One cannot help but feel that all those involved in the project should be well pleased with the results of their efforts. ACKNOWLEDGMENTS The photograph shown in Fig. 1 was taken by John Wells, and his permission to use it here has been much appreciated. All other photographs were taken by the author. The important assistance of John Wells in gathering materials necessary for the preparation of this paper is gratefully acknowledged. Above all, the assistance, advice, insights and patience of Betty Medwadowski have been truly beyond measure. REFERENCES 1. Canty, Donald, Lasting Aalto Masterwork, The Library at Mount Angel Abbey, published by the Mount Angel Abbey, 1992, Library of Congress # ISBN# Reed, Peter, Alvar Alto, Between Humanism and Materialism, with essays by Kenneth Frampton, Pekka Korvenmaa, Juliani Pallasmaa, Peter Reed, and Marc Treib, The Museum of Modern Art, New York A description of the Mount Angel Library is given on pp Uniform Building Code 1967, vol. 1 and 2, International Conference of Building Officials, Whittier, California, Fig. 7: Interior view of the main reading/stack area and the sky OPENING SESSION 45

30 Fig. 8: View of the Library from the North Fig. 10: Interior view of the main area and skylight Fig. 9: Interior view of the main area and skylight Fig. 11: Interior view of the main area and skylight OPENING SESSION 46

31 Fig. 12: Auditorium ceiling and fixtures Fig. 14: Detail of the base of a porte-cochere column Fig. 13: Door from the Auditorium as seen from outside Fig. 15: Detail of Aalto-designed desk lamp OPENING SESSION 47

32 Fig. 16: Detail of an exterior window wood screen Fig. 18: Interior view during construction Fig. 17: Interior view of the main area stacks Fig. 19: Interior view of the main area OPENING SESSION 48

33 Fig. 20: View from the roof Fig. 22: Detail of exterior Fig. 23: Panel discussion during the opening ceremonies. Seated in the Auditorium (l. to r.) are Vernon DeMars, Ada Louise Huxtable, and Eric Vartiainen. Fig. 21: Detail of exterior OPENING SESSION 49

34 LIGHTWEIGHT STRUCTURES IN CIVIL ENGINEERING PROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM Warsaw, Poland, June, 2002 G E N E R A L L E C T U R E S ON SOME CHARACTERISTICS OF PANTADOME SYSTEM M. KAWAGUCHI 1 and M. ABE 2 1 Professor, Dept. of Architecture, Hosei University, Koganei, Tokyo 184, Japan 2 Lecturer, Dept. of Architecture, Hosei University, Koganei, Tokyo 184, Japan ABSTRACT: Some important structural features of Pantadome System are described. A structural system developed and named Pantadome System by the principal author has successfully been applied to seven major spatial structures of various shapes and dimensions in different corners of the world. Pantadome is a structural system (not a construction method) incorporating a temporary kinematic mechanism in it during construction for a rational erection of domical structures. One of its important structural features is that the system does not need any such provisions as guys or braces against possible lateral forces due to winds or earthquakes during the erection of a spatial structure. Thanks to this special feature a Pantadome structure can be lifted even in an inclined direction as is shown in erection of Namihaya Dome. A Pantadome changes its shape very largely during its erection, and the reactions in pushing posts change the magnitudes accordingly. In some special cases the reactions in the pushing posts become negative, and a kind of unstable phenomenon becomes prone to occur. This was foreseen in construction of a recently built coal storage, and a shock-absorbing device was developed to realize a safe construction. 1. INTRODUCTION It is well known that a spatial structure, or a structure of three-dimensional characteristics, is one of the most efficient structures capable of covering a very wide area, once it has been completed. The spatial structure is not always efficient, however, in the process of construction, because it requires big amount of scaffoldings, labor and time and often encounters difficulties in terms of accuracy, reliability and safety of work during its erection. Modern erecting methods such as lifting systems which are very often adopted in erection of roofs of flat, plate type can not equally be applied to a spatial structure. Buckminster Fuller once tried to solve this kind of problems in a few ways when he encountered them in building some of his geodesic domes. For construction of one of his domes in Honolulu in 1957 he adopted a system in which a temporary tower was erected at the center of the dome from top of which concentrically assembled part of the dome was hung by means of wire ropes. As assembly of the dome proceeded the dome was gradually lifted, enabling the assembling work to be done along the periphery of the dome always on the ground. He also adopted another method when he built a huge dome of 117m in diameter at Wood River, U.S.A., in 1959, where the assembled part of the dome was raised on a balloon-like enclosure. Some other cases have also been reported where different lifting methods have been applied by several engineers to different domes. However, none of the above attempts for lifting domes have become popular unlike those lifting methods which became widely used to raise plate-type roofs. A patented structural system called Pantadome System which had been developed by the author for a rational construction of spatial structures was first successfully applied to the structure of World Memorial Hall completed in Kobe in Pantadome System has since been applied to the Sant Jordi Sports Palace in Barcelona, the National Indoor Stadium of Singapore and some important structures of wide spans realized in Japan. Seven major spatial structures have so far been realized by this system in various corners of the world (Table 1). 2. PRINCIPLE OF PANTADOME SYSTEM The principle of Pantadome System is to make a dome or a domical structure geometrically unstable for a period in construction so that it is foldable during its erection. This can be done by temporarily taking out the members which lie on a hoop circle. Then the dome is given a kinematic mechanism, that is, a controlled movement, like a 3-D version of a parallel crank or a pantagraph which is popularly applied to drawing instruments or a power collector of an electric car (hence the name, Pantadome ). (Fig.1, Fig.2) By folding the dome in this way, the constituent members of the dome can be assembled on a lower level. The assembly work is thus done safely, quickly and economically, since it can be carried out near the ground level.since the movement of a Pantadome during erection is a controlled one with only one freedom of movement in the vertical direction, guying cables or bracing members which are indispensable in conventional structures to assure their lateral stability against wind or seismic forces are not necessary in erection of a Pantadome structure. The movement and deformation of the whole shape of the Pantadome during erection are three dimensional and may look spectacular and rather complicated, but they are all kinematically determinate and easily controlled. Three kinds of hinges are incorporated in the Pantadome System which rotate during the erection. Their rotations are all uni-axial ones, and of the most simple kind. Therefore, all these hinges are fabricated in the same way as normal hinges in usual steel frames. In Pantadome System a dome is assembled in a folded shape near the ground level. As the entire height of the dome during assembling work is very low compared with that after completion, the assembly work can be done safely and economically, and the quality of work can be assured more easily than in conventional erection systems since inspection by structural supervisors is much easier. Not only the structural frame but also the exterior and interior finishings, electricity and mechanical facilities are fixed and installed at this stage. The dome is then lifted up. Lifting can be achieved either by blowing air inside the dome to raise the internal air pressure, or by pushing up the periphery of the upper dome by means of hydraulic jacks. When the OPENING SESSION 50

35 (a) (air pressure j hydraulic jacks (b) No.1 Hinge No.2 Hinge No.3 Hinge (c) removed temporarily No.1 Hinge Line No.2 Hinge Line No.3 Hinge Line No.1 Hinge No.2 Hinge No.3 Hinge No.4 Hinge No.5 Hinge (d) Fig.1. Principle of Pantadome System Fig. 2. Model Study of Pantadome Principle dome has taken the final shape, the hoop members which have been temporarily taken off during the erection are fixed to their proper positions to complete the dome structure. The lifting means such as air pressure or hydraulic jacks can be then removed, and the dome is completed. When the dome is very big, it can be doubly folded as shown in Fig.1 (d), so that assembling works can be done at a level that is very close to the ground level. The Pantadome System is sometimes misunderstood as a construction OPENING SESSION method, but it is not. It is a structural system in which a kinematic mechanism is incorporated so that it can largely change its shapes for a rational construction. After completion the hinges installed in the structure at three different levels are very often left as they have been during the erection, and the hinges at the two lower levels act as structural hinges even after completion of the structure so that it can breath freely according to temperature changes to avoid the thermal stresses in it. 51

36 NAME WORLD SINGAPORE ST.JORDI FUKUI NAMIHAYA SHAPE AND DIMENSION SMALL CIRCLES IN PLANS INDICATE PUSH-UP POSTS 110 m 200 m 128 m 116 m 127 m BUILT COVERD AREA 7,700 m 2 14,000 m 2 12,000 m 2 10,500 m 2 11,000 m 2 TOTAL WEIGHT 1,680 t 2,600 t 3,000 t 5,430 t 4,690 t STEEL WEIGHT 760 t 1,250 t 950 t 2,770 t 1,160 t LIFTING HEIGHT 20 m 20 m 32 m 28 m 29 m LIFTING POINTS SPECIAL FEATURES OVAL PLAN RHOMBIC PLAN UNFINISHED SHAPE PURE CIRCLE INCLINED ROOF FIRST ATTEMPT ABROAD ABROAD HEAVY SNOW QUICK LIFT Table 1. Realized Pantadome Structures NARA HALL 127 m ,500 m 2 4,660 t 14 m 32 PRESTRESSED CONCRETE UNITS COAL STORAGE 251 m ,000 m 2 7,500 t 6,500 t 30 m 14 BIG COVERED AREA LIGHT WEIGHT OPENING SESSION 52

37 3.IMPORTANTCHARACTERISTICS OF A PANTADOME 3.1 Lateral Stability of A Pantadome One the structural features of a Pantdome is that the system does not need any such provisions as guys or braces against possible lateral forces due to winds or earthquakes during its erection. This feature will be best understood by looking at Figure 3. A horizontal force H may occur at the top part of a Pantadome at an instant of erection of the dome due to wind, earthquake or any other reasons. The force is transmitted successively through No. 1, 2, 3 joints to the adjacent lower panels in the form of shear forces h1, h2 and h3. Provided that the vertical supports are rigid enough to provide any necessary vertical forces at No. 1 hinges, it may be easy to understand that the whole system is capable of transmitting the horizontal force to the ground at any phase of erection. The magnitude of the horizontal shears h is different from a panel to another on the same level according to their rigidities in the direction of the force H. The panels which are parallel to H normally take the maximum shares. Fig.4 Erection of Namihaya Dome Fig. 3 Lateral Shear Transmission 3.2 Application of Lateral Stability Namihaya Dome Lateral stability of a Pantadome explained above can not only be utilized for resistance to the lateral forces such as due to wind and earthquake, but it can also be applied to a more interesting attempt lifting of a dome in a non-vertical direction. This was most typically realized in the construction of Namihaya Dome, whose erection will be described below (Figs. 4 and 5). The Namihaya Dome was constructed as one of the main venues for the National Athletic Meet held in Osaka in The dome was designed by Showa Sekkei Co., and it has an oval plan of 127m and 111m in major and minor diameters, respectively. The main function of this building is swimming pools, having a racing and a diving pools of international standards. In other seasons than summer it is used for athletic games and exhibitions, and for ice skating in winter. One of the special features of the dome was that its equator was not horizontal, but inclined 5 degrees. The Pantadome structure was designed accordingly, and it was erected in the direction inclined 5 degrees from the vertical. OPENING SESSION Fig. 5 Non-Vertical Lifting of Namihaya 53

38 3.3 Folding of Walls In earlier built examples of Pantadome System the positions of hinges were such that No.1 hinges were put on the top part of the dome and No.3 hinges along the bottom periphery. No.2 hinges were located between No.1 and No.3 hinges, mostly on top of the columns or similar locations in the dome. The positions of No.2 hinges are somewhat arbitrary, however, as long as the folding mechanism of the Pantadome system is possible during construction. As an example of such application the construction of Nara Centennial Hall will be explained below (Figs. 6 to 9). Phase 1 Assembly of Roof Structure Phase 2 Assembly of Wall Structure 3.3 Nara Centennial Hall Nara Convention Hall designed by A. Isozaki is a building to accommodate two music halls of high standard. It has an elliptic plan of 138m and 42m in major and minor diameters, respectively. The height of the roof is 24.8m. The vertical section of the wall has a single configuration everywhere, in the shape of a clothoid having a very little curvature at the bottom and bigger ones upward. Phase 3 Lifting For a better acoustic insulation every part of the envelope (roof as well as wall) was designed heavier than in ordinary buildings. The roof is covered by a structural steel plate of 6mm in thickness on top of which are put precast light-weight concrete panels (100mm) and in-situ concrete (80mm) with insulating layers in between. 23,850 1FL B1FL The interior of the wall is constituted by exposed precast concrete panels of 120mm in average thickness reinforced by steel sections, while its exterior is covered by 33mm thick roof tiles which are lined by concrete precast panels of 50mm. The overall stability of this domical structure is assured by a curved skin (or thin shell) structure of the wall which is stiffened by the roof diaphragm at the top. Phase 4 Works on Interior Structures Since the dome has a long and narrow elliptic plan, the wall resists effectively lateral forces in the longitudinal direction, but its resistance is not sufficient in the transverse direction. To increase the lateral resistance of the building in the transverse direction, the double wall which separates the two music halls from each other is utilized in design as a pair of shear walls in that direction (Fig.7). The peripheral wall was divided into the top and bottom halves and into 120 sections along the periphery, and each of the 240 wall panels was prefabricated in a factory, and Fig. 6 Erection Process of Nara Centennial Hall Pantawalls Fig. 7 Pantawalls to Take Transverse Shear Forces During and After Erection OPENING SESSION 54

39 transported to the building site. The whole structural scheme of this building was designed as a Pantadome. Three hinge lines necessary for Pantadome kinematic mechanism were put at the top, bottom and the middle of the wall panel. The construction of the dome was proceeded with in the following sequences: The roof trusses are assembled on temporary supports. When the trusses are completed, they are made simply supported at the two ends, the secondary structural members are fixed to them and the top finishing is continued (Phase 1 in Fig 6). The lower panels of the wall are brought into the positions, and they are secured to the concrete lower structure by means of the bottom hinges (hinges No.3). Then the upper wall panels are brought to the positions, and connected to the roof and the lower panels by the top (hinges No.1) and the middle (hinges No.2) hinges (phase 2 in Fig. 5). By this stage the roof is finished to the maximum possible extent, both exterior and interior. It is not necessary to finish the interior surface of the peripheral wall, because it is of precast exposed concrete. When the assembling work is completed, the whole dome structure is lifted by means of hydraulic jacks and temporary posts (phase 3). 64 hydraulic jacks are employed, and each pair of them are set on top of one of the 32 lifting units. The lifting forces of all the jacks, the lifting speeds at all the lifting units and the stresses at a few important points of the dome structure are measured and controlled in the central control room with the aid of computers. The steel skeletons of the transverse double wall at the middle of the dome are provided with hinges to make Pantawalls, so that they can resist the possible lateral forces in the transverse direction due to wind or earthquake during the lifting work (Fig. 7). When the roof has reached the specified height, the lifting work is finished, and adjacent wall panels are put together with each other by bolting and welding. Then the dome structure is completed (phase 4). All the secondary structures and finishings inside this huge envelop are then worked out without being disturbed by the weather. Lifting work of the Nara Convention Hall started on December 1, The dome was lifted only in the morning, everyday, to receive the visits of the citizens, many of whom wanted to see the dome largely change its shape everyday. Thousands of people visited the dome during the lifting work. On December 6 the dome reached its final height. The dome was completed in October, Fig. 8 Shape of the Structure at an Earlier Erection Fig. 9 Aerial Views of Erection of Nara Centennial Hall OPENING SESSION 55

40 4. Instability Possible to Occur in Erection Process When one tries to apply Pantadome System to various types of spatial structures, it should be noted that in some special cases the structures may become unstable during erection processes. This phenomenon may be best exemplified in conjunction with construction of a coal storage This facility was designed and constructed in an industrial area near Tokuyama City to store some 300,000 tons of coal. It has a huge hexagonal doughnut-like shape in plan. The section of the doughnut roof is a triangle having a span of 90m and a height of 45m. The diameter of the overall plan is some 250m (Figs. 10 and 11). The area covered by the roof is approximately 40,000 m 2. The roof is a steel spatial structure covered by a fabric membrane (PVC coated polyester fabric).the erection process of the roof is shown in Fig. 12. When the erection method of the roof was planned in the design stage, a kind of unstable situation was foreseen in the final stage of lifting. This can be most conveniently explained in terms of reaction in pushing hydraulic jacks during the lifting work. The roof was pushed up by means of 14 hydraulic jacks and pushing posts as shown in Fig. 10 (black circles) and Fig. 12. Total reaction in the jacks is plotted in Fig. 13 against height. The right end of the graph implies the location of the roof 0.2 m below its final position. It is clearly seen that the reaction in the jacks reduces rapidly as the roof approaches its final shape (Phase C to D in Fig. 12). This is due to the fact that in the final shape the joints No. 1, 2 and 3 align almost in a straight line. Theoretically the reaction tends to become minus infinity, as the roof comes close to its final position. The movement of the roof in this process is so quick and dynamic that a kind of impact effect is anticipated. To avoid this phenomenon, a set of simple shock absorber was provided to every upper chord member at the No. 2 hinge (Fig. 14). The shock absorber consists of a pair of EPP (Expanded Polypropylene) blocks, each of which is provided at the end of the upper chord member at the No. 2 hinge. When the pushing work proceeds, and the shape of the roof comes closer to its final one (Phase ( C ) in Fig. 12), the two bocks of a shock absorber touch each other, and come to push against each other. Then the roof structure changes its manner of force transmission from axial force system to bending one softly and smoothly without producing any impact phenomenon. This method was followed in the building site, and the structure was completed safely, economically and well in time. Fig. 10 Plan and Section of the Coal Storage 5 COMCLUSIVE REMARKS In previous presentations of Pantadome System various examples realized with this system have been described, but the general characteristics underlying those examples have not been explained. In the present paper some characteristics of Pantadome System which should be in mind when one tries to apply the system to various spatial structures are described. After explaining the principle of this system, the horizontal resistance of the structure inherent to this system has been noted. With this resistance a pantadome can be erected without worrying about its lateral instability due to wind, earthquake or other reasons. This resistance assures the structure to be safely lifted even in non-vertical directions, as in the case of Namihaya Dome. It was then shown that the No. 2 hinges can be located even in external walls as in the example of Nara Centennial Hall. In that example the Pantadome principle was applied to the internal walls as well to provide horizontal resistance to the structure in transverse direction. In some special case an unstable transition from axial to flexural systems of the structure should be investigated. This phenomenon occurs when the three Pantadome hinges align in a straight line in erection process of the dome. This can be very dangerous, since the movement of the frame in this phenomenon is very quick, and it may bring about an impact effect to the structure. This phenomenon was foreseen in the design stage of a huge coal station recently built in an industrial area near Tokuyama, and a simple shock-absorbing device was provided to the structure during the erection. With this device the structure was completed successfully, in terms of safety, economy and construction time. Fig. 11 Aerial View of the Coal Storage OPENING SESSION 56

41 6. REFERENCES Fig. 13 Change of Reaction in Jacks Fig. 14 Location of Shock Absorber 1. Kawaguchi, M. et al A Domical Space Frame Foldable During Erection Proc. Third Int. Conf. On Space Structures, Moeschler, E. Die Hubmontage des Daches eines Hallenstadions in Barcelona Stahlbau, 1989, Heft 9 3. Moeschler, E. The Lifting of a Roof for An Indoor Stadium Proc. FIP XIth Int. Cong. on Prestressed Concrete, June, Kawaguchi, M. et al Design and Construction of Sant Jordi Sports Palace Journal of the Int. Assoc. for Shell & Spatial Structures., vol.33, No.2, Abe, M. et al Design and Construction of Singapore Indoor Stadium IASS-MSU Int. Symp. Istanbul, Kawaguchi, M. Possibilities and problems of Latticed Structures Proc. IASS-ASCE Int. Symp. Atlanta, Kawaguchi, M. Sports Arena, Kadoma, Japan Journal of IABSE, SEI vol.6, No.3, Kawaguchi, M. Ein Pantadome für die Convention Hall Bauwelt, vol.89, No.4, Kawaguchi, M. et al. A Structural System Suitable for Rational Construction, IASS Symp. Sydney, Une, H. et al. Design and Realization of A Large-Scale Coal Storage Facility, IASS Symp. Nagoya, 2001 (D) (C) (B) (A) Fig. 12 Erection Process of the Coal Storage OPENING SESSION 57