218. Modular space frame structures

F. ESCRIG, Seville School of Architecture, Spain, and J. V ALCARCEL,La Coruna School of Architecture, Spain

SYNOPSIS. The construction of space frames with prefabricated bars and jointshas resulted in a successful method of building roofs and walls, primarily due tothe simplicity of connections, the lightness of the structure, the attractiveappearance coupled with economy in designo The generalised use of these systemconfmns their advantages, but there are sorne restrictions and inconveniences thatmay make the system inadequate. Modular systems are formed from groups ofbars which are easier to assemble compared with single members andconsequently can offer an altemative means of constructing space grids. Sorneconstrueted struetures offering clear advantages are shown to illustrate this aspeet.

MODULAR SYSTEMS OF SPACE BAR STRUCTURES1. One oí the greatest advantages in the conslruction of skeletal pace structures

is lhat they can be formed by using members of only a few different lengths.2. Using bars with Iengths which are easy to handle and standard joints, great

struetures can be constructed, which are light in weight, very rigid with regulargeometry and also urprisingly attractive.

3. Spatial structures made out of bar have been successfully developed becauseof their versatility. economy and rapid erection. The initial difficulty associatedwith the complex and large analysis of the structures has been overcome withcomput.er techniques that are now used in the automation of the manufacturingprocess, allowing the conslrucúon of structures wiLh very complex geometry' .

4. The advantages of using skeletal space structures. outlined previously, aregreatly influenced by the type of joint used in the structure. From earlierproposals where members were welded directly to each other requiring thecomplex cutting oí me rnember end ; to mOre sophisticated nod - ,[orrned in highquality steel, forming almo t impercepúble poinLc; where many bars meet together;mere are nurnerous different patented node types exhibiting different levels ofingenuity.

5. Quality, strength, appearance, economy and marketing of each patented nodehave prioritised sorne nodes in preference to others and indicate why only a fewtypes have become popular.

Space structures 4. Thomas Telford, London, 1993 1997

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6. The advantages of skeletal space slructures can be summarised as follows:a) economlcal in material use resulting in light structures;b) construeted using relatively few different member types;c) adaptable to any perimeter and topography;d) aesthetieally pleasing allowing the structures to remain uncovered and visible;e) easy access for services allowing pipes and tubes unrestricted routing;f) used to construct roofs and walls and if desired, the whole building;g) easy transportation of component members because they occupy very littlespace, when eorrectly packed.7: Nevertheless Lhey have sorne disadvantages too that limit their use, namely:a) the economy in weight does not necessarily correspond with financialsavings;b) the structures are difficult to analyse and require sophisticated numericaltreatment usually undertaken in conjunction with assumptions on loading andSUPP0rl conditions;c) single layer and foldable structures may be very flexible with largedisplacements placing limitation on imposed loads;d) the structures may be highly statically indeterminate but nevertheless stabilityof the whole strueture depends of the stiffness of only few bars, with risk offailure attached to a small number of sections;e) the simplicity of geometry in practice is complicated by architecturalrequirements. Por instance a flat structure needs sorne slope for drainage andthis means that the depth of the structure rnay be variable, resulting in differentlength bars;f) usually these structures need a complementary structure to support the roofc1adding;g) they may cause access difficulties in their final position when constructingthe surrounding structure;h) nodes are individual elements, usually patented and therefore controlled byspecialised builders;i) nodes are subjected to severe concentration of stresses.8. This indicares that although these kind of structures may provide the best

possible architectural solutions they may not be the panacea desired for and betteraltematives may be available.

9. One of these alternatives are "modular systems of bar structures". Spaceframe structures are not always built from individual bars and nodes. This formof construction eases transportation bUl eornplicales the assernbly. To bulldpiecemeal requires seaffolding or alternalively building lhe structure on theground and lifting it into position, is expensive.

10. However, the modular alternalive has serious drawbacks wiLh respect tolransportation, prirnarily due to the large volume, but nevertheless this iseompensated by a higher stiffness and simplicity of joints. Both aspeets thatdirectly affect the overall economy and aesthetics of the structure.

11. ParadoxicaUy while lhere ex.isl a wide bibliography on space structures, it isdifficult lo find publications on SLruclures built from modules. In part, this is due

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to the large versatility of solutions but also because it is not a usual technique ofstructural designo

Fig. 1. Fig.2.

12. Because the difficulty of beginning from zero and establishing a guide ofpossible logical pattems, the authors prefer to explain particular applicationsdesigned for construction.

13. The Crystal Palace constructed in London for the Intemational Exhibition of1851, is usually quoted as the first example of rigorous prefabrication. Althoughmost of the components were planar, the complexity of the whole structure madeit desirable to record the behaviour of the rigid modular covered surface. TheCrystal Palace was a surprising structure, considering the level of technology atthe time of construction (Fig. 1).

14. ~odular construction is not only an established method of construction foriron oc steel. Reinforced concrete has been used in very complex buildings. Nerviin the Exhibition Palace of Turin (Fig. 2) shows a clever use of repetitivemodules, to cover a span of 80 m.

15. Nevertheless, it is in relatively light structures where the use of steelmodules is more frequent. Polyhedrical f0110S are more adequate than other fonnsto be used repetitively and there are many structural designers using proposals ofthis kind. For example Candela (Fig. 3), Richter (Fig. 4), or Perez Pinero, the

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Spanish architect who built structures, so light, that they could be assembled byhand (Fig. 5).

16. When professional commitments have allowed, the authors have tried toadvance proposals with the same aims and goals. The structures constructed arenot large projects but they are conceived with vocation of scale.

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CANTILEVER ROOF FOR TIIE AUDITORIO OF LA RABIDA, HUELVA.17. The authors have used triangular modules like those shown in Figs 6 and 7

assembled together to forro the structure as shown in Figs 8 and 9. After theinitial assembly a diagonal strut has been introduced into the structure to stiffenthe hexagonal units so that they could be used to support the roof material.

Fig. 10.

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Fig. 11. Fig. 12.

ESCRIG AND VALCARCEL

18. As the structure was spanning only a short distance the elements used in thestructure are aH the same weight, facilitating easy eonstruction, enabling thestructure to be erected in two days with the minimum of scaffolding (Fig. 10).

PAVILION üF EXTREMADURA AT EXPü'92 - SEVILLA.19. A similar system was used to support the glass floor of a building

eonstrueted using one basie module (Fig. 11). The modular units were joinedtogether by means of two bolts in the upper layer and a tie in the lower layer.Seaffolding was not used during the assembly of the strueture. Eaeh new unitwas joined to the previous one, finalIy forming the entire surfaee as shown inFigs 12-14. /'

Fig. 13.

Fig. 14.

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SUSPENDED GARDENS FOR EXPO'92 SEVILLA.20. The aim of this project was to cover 50,000 m2. of open spaces at

EXPO'92 with a repetitive, industrialised, portable structure, capable ofsupporting very large flowerpots and plants. Economy was another of severa!conditions necessary to comply with to win the public competition.

21. Fig. 15, shows a scheme of the proposal and Fig. 16 the solution used toachieve it. The authors chose rectangles 12 x 6 m2 supported on four corners by acollection of four tubes. On each support it was possible to connect between oneto four modules at different levels (Fig. 17).

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Fig. 15. ~

Fig. 16.

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Fig. 17.

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22. Each one of the modules was built in four parts joined together in its finalposition with bolts (Fig. 18).

23. To reduce the construction costs, joints were formed from bent tubes insuch a way that lhe diagonal web members were made fram one length of steel.This meLhod produced problems with the concurrence of the axes of the bars

(Fig. 19). Because the radius of curvature must be at least 2·5 times the bardiameter, solution "a" (Fig. 19) was not possible neither solution "b". Solution"c" was chosen giving edges not aligned to one point. The load test showed thatthe influence of eccentricities was negligible.

24. The connection between the space frames and supports was by a weldedelement used as a guide introduced ínlo Lhe tubes.

25. To ease the construction, iL was not possible to anchor the supports to theground buL illSLead heavy concrete blocks were used to preveot up lift of thewhole structure.

26. Once the structures were assembled it was not possible to erect themdirectly into their final place because it was first necessary to wait fOI" shrubs andplants placed in containers inside the structures to grow. At lhe correct time thecomplete frames together with plants and shrubs were lifted ooto a platform,transported and erected on site (Fig. 21).

LOS TUBOS IRAN SOlDADOS A UNA BASE DE:CHAPA QUE SE ANClARA. A LA CII.lENTACIOHWEDlANTE ESPERAs A.TOR}HU~AS DE OIAlolE;T'RO20 mID•

CAHAUZACJOH DE LAS INS·U.UC10HES POREL TUBO CENTRAL ESTE TUBO ESTAAAA1l1ER1'O POR EL EX'I'RDlO SUPERIOR yQUEDARA A <tO em. DEL SUELO POR rtEXTREMO INFERIOR PARA CONEXION DECOIIDUCCIONE:S

SOPORTE rORMAOO POR CUh1RO TUBOS DEDIAME'llW 90 mm Y ESPEsan VAItIAIILF. yUN rUBo INTERIOR DE DIAUETRO gQ mmy ESPESOR 3 mm. QUE CONECTA A !"oSDEMAS Y SIRVE DE CAXAUZACION DE LASrNST~CIONES

INSERCION DE LA CELQS[A SOBRE EL SOPORTEPOR lLtDlO DE UN W.CHON TRONCOCOHICOQUE SE rHTRODUCE EN EL TUBO SOPORTE YQUEDA ESTABIUZADO POR El. PROPIO PESODE LA.. ESTRUCTURA

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