OPENING SESSION 17

LIGHTWEIGHT STRUCTURES IN CIVIL ENGINEERINGPROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM

Warsaw, Poland, 24-28 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.MAKOWSKI1

1Professor, 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.

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.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”.

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).

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.

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 18

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.

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 1906-7 were carried out on prefabricated skeleton

structures using tubes and a specially designed connector.

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 19

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.

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

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.

a)

b)

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 20

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 cone-

shaped 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 21

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 22

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 23

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 mass-

production (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.

Fig.8. The TRIDAMATEC joint for three-way grids. Du Château used

this system for many structures built from modular latticed units.

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.

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 24

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.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.12. Examples of a recently introduced Yugoslav system for double-

layer grids. Fig 12a gives details of the TORUS joint, Fig 12b of

the second version known as the TORUS-GUSTO.

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.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.

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 25

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 multi-

layer 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.

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 1969-70 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

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

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 26

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 single-

layer 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 27

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 28

Fig.19. The NODUS joint has been developed in 1972 by the British Steel Corporation Tubes Division for prefabricated steel tubular double-

layer 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 29

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 30

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 31

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 32

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 33

Fig.26.

OPENING SESSION 34

Fig.27. A very economical system developed in France and known as the TRIDI 2000. 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 35

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 36

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 37

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 38

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 39

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 40

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 41

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 double-

layer grids. Applied Science Publishers/Halsted Press, London and

New York, 1981.

2. Z.S.Makowski (editor): Analysis, design and construction of braced

domes. Granada Publishing Ltd., London and Nocholls Publishing

Company, New York 1984.

3. Z.S.Makowski (editor): Analysis, design and construction of braced

barrel vaults. Elsevier Applied Science Publishers Ltd., London, 1985.

4. V.Hauk: The Mannesmann Okta-S joint for tubular space structures.

Proc. of the 2nd

International Conference on Space Structures,

University of Surrey, 1975, pp.432-6.

5. (a) G.M.Rose: A comparative examination of a wide variety of joints

for space structures. Space Structures Conference, British Steel

Corporation, London 1970.

(b) S.Boar, M.Raskin: Noeuds de structures tubulaires spatiales. Sm80

St6, Liege, 1970.

6. 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. 21-43.

7. S.C. Hsiao, G.C. Dygert: The Moduspan space-frame system. Proc. of

the 2nd

Intern. Conf. on Space Structures. University of Surrey, 1975,

pp.296-299.

8. 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, 1966.

10. Toader et al.: Aspecte privind calculul si realizarea unor invelitori

reticulate, Bul. Stiint., Institutul de constructii Bucuresti, T.21, No.3-4,

1978, pp.77-93.

11. Z.Kowal: Przestrzenne struktury pr towe z w z ami t oczonymi.

PNIB P.Wr. Wroc aw, 1975.

12.Raport Instytutu Budownictwa. Nr.1-2/R-131/75. Badanie w z ów.

Wroc aw, 1975.

13. D.Mitaritonna, G.Prete: Proposta e sperimentazione di un nuovo

sistema di connessione nodale per grigliati spaziali in acciaio.

Construzioni Metalliche, No. 4, 1977.

14. K.Thomsen: Trends in the design of double-layer space grids. Proc.

of the 2nd

Intern. Conf. on Space Structures, University of Surrey,

1975, pp. 382-398.

15. T.Arciszewski, Udmak: Shaping of spherical joints in space

structures. International Journal of Space Structures, vol.3, No.3,

1988, pp. 171-183.

16. G.S.Ramaswamy, M.Eekhout, G.R.Suresh: Steel space frames,

analysys, design and constrution. Produced by Thomas Felford

Publishing, London, 2002

1) 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 42

LIGHTWEIGHT STRUCTURES IN CIVIL ENGINEERINGPROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM

Warsaw, Poland, 24-28 June , 2002

G E N E R A L L E C T U R E S

OPENING SESSION 43

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 1970.

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

Fig. 2: Plan of the main floor

OPENING SESSION 44

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. 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

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.

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 45

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

Fig. 7: Interior view of the main reading/stack area and the sky

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

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 100th 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 #92-080534 ISBN#0-918941-04-0.

2. 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 1998. A description of the Mount Angel Library is given on

pp 288-291.

3. Uniform Building Code 1967, vol. 1 and 2, International

Conference of Building Officials, Whittier, California, 1967.

OPENING SESSION 46

Fig. 8: View of the Library from the North

Fig. 9: Interior view of the main area and skylight

Fig. 10: Interior view of the main area and skylight

Fig. 11: Interior view of the main area and skylight

OPENING SESSION 47

Fig. 12: Auditorium ceiling and fixtures

Fig. 13: Door from the Auditorium as seen from outside

Fig. 14: Detail of the base of a porte-cochere column

Fig. 15: Detail of Aalto-designed desk lamp

OPENING SESSION 48

Fig. 16: Detail of an exterior window wood screen

Fig. 17: Interior view of the main area stacks

Fig. 18: Interior view during construction

Fig. 19: Interior view of the main area

OPENING SESSION 49

Fig. 20: View from the roof

Fig. 21: Detail of exterior

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.

OPENING SESSION 50

LIGHTWEIGHT STRUCTURES IN CIVIL ENGINEERINGPROCEEDINGS OF THE INTERNATIONAL SYMPOSIUM

Warsaw, Poland, 24-28 June , 2002

G E N E R A L L E C T U R E S

ON SOME CHARACTERISTICS OF PANTADOME SYSTEM

M. KAWAGUCHI1 and M. ABE

2

1Professor, Dept. of Architecture, Hosei University, Koganei, Tokyo 184, Japan 2Lecturer, 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 1984. 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 51

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

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.

Fig.1. Principle of Pantadome System

No.1 Hinge No.2 Hinge

No.3 Hinge

No.1 Hinge No.1 Hinge

(a)

(b)

(c)

(d)

No.1 Hinge No.2 Hinge

No.3 Hinge

No.4 Hinge

No.5 Hinge

removed temporarily No.1 Hinge Line

No.2 Hinge Line

No.3 Hinge Line

No.1 Hinge

No.1 Hinge

No.2 HingeNo.3 Hinge

(air pressure j

hydraulic jacks

Fig. 2. Model Study of Pantadome

Principle

OPENING SESSION 52

Ta

ble

1.

R

eali

zed

Pa

nta

do

me

Str

uct

ure

s

251 m

40,000 m2

7,500 t

6,500 t

30 m

14

2001

6,500 m2

4,660 t

14 m

32

1998

127 m

PRESTRESSED CONCRETE

UNITS

BIG COVERED AREA

LIGHT WEIGHT

COVERD

AREA

TOTAL

WEIGHT

STEEL

WEIGHT

LIFTING

HEIGHT

LIFTING

POINTS

7,700 m2

14,000 m2

12,000 m2

10,500 m2

11,000 m2

1,680 t

2,600 t

3,000 t

5,430 t

4,690 t

760 t

1,250 t

950 t

2,770 t

1,160 t

20 m

20 m

32 m

28 m

29 m

18

12

12

816

BUILT

1984

1989

1990

1995

1996

SPECIAL

FEATURES

OVAL PLAN

RHOMBIC PLAN

UNFINISHED SHAPE

PURE CIRCLE

INCLINED ROOF

WORLD

SINGAPORE

ST.JORDI

FUKUI

NAMIHAYA

FIRST ATTEMPT

ABROAD

ABROAD

HEAVY SNOW

QUICK LIFT

NAME

SHAPE

AND

DIMENSION

PLANS INDICATE

SMALL CIRCLES IN

PUSH-UP POSTS

NARA HALL

COAL STORAGE

110 m

200 m

128 m

116 m

127 m

OPENING SESSION 53

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.

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 1997.

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.

Fig. 3 Lateral Shear Transmission

Fig.4 Erection of Namihaya Dome

Fig. 5 Non-Vertical Lifting of Namihaya

OPENING SESSION 54

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).

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.

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.

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.

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

Pantawalls

Fig. 7 “Pantawalls” to Take Transverse Shear Forces During and After Erection

23,8

50

1FL

B1FL

Assembly ofRoof Structure

Assembly ofWall Structure

Lifting

Works onInteriorStructures

Phase 1

Phase 2

Phase 3

Phase 4

Fig. 6 Erection Process of Nara Centennial Hall

OPENING SESSION 55

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, 1997.

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, 1998.

Fig. 8 Shape of the Structure at an Earlier Erection

Fig. 9 Aerial Views of Erection of Nara Centennial Hall

OPENING SESSION 56

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 m2. 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.

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. 10 Plan and Section of the Coal Storage

Fig. 11 Aerial View of the Coal Storage

OPENING SESSION 57

Fig. 13 Change of Reaction in Jacks

Fig. 14 Location of Shock Absorber

6. REFERENCES

1. Kawaguchi, M. et al “A Domical Space Frame Foldable During

Erection” Proc. Third Int. Conf. On Space Structures, 1984

2. 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, 1990

4. 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, 1992

5. Abe, M. et al “Design and Construction of Singapore Indoor

Stadium” IASS-MSU Int. Symp. Istanbul, 1993

6. Kawaguchi, M. “Possibilities and problems of Latticed Structures”

Proc. IASS-ASCE Int. Symp. Atlanta, 1994

7. Kawaguchi, M. “Sports Arena, Kadoma, Japan” Journal of

IABSE, SEI vol.6, No.3,1996

8. Kawaguchi, M. “Ein Pantadome für die Convention Hall”

Bauwelt, vol.89, No.4,1998

9. Kawaguchi, M. et al. “A Structural System Suitable for Rational

Construction”, IASS Symp. Sydney, 1998

10. Une, H. et al. “Design and Realization of A Large-Scale Coal

Storage Facility”, IASS Symp. Nagoya, 2001

Fig. 12 Erection Process of the Coal Storage

(B)

(D)

(C)

(A)