Air Inflation Method

7/30/2019 Air Inflation Method

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1 . s i tuat ion

covering "Les Arenes de Nim.es' wi tban ai r - inf la ted P a ~ r i c s t ruc tureDipl. lnq. RUdolf BerqarmannDr.lnq. Werner Sobek

In 1986, the municipal authority of Nimes considered to hui lda new t.own hal l in the center of the "v i l l e romaine". Thesein tent ions f ina l ly could not be rea l ized because of problemswith sui table s i tes . Besides there was no need for a townha l l during summer t ime: The ancient arena, bui l t nearly 2000years ago, s t i l l i s the center o f the cul tura l l i fe withinth i s period. Within the l a s t years it even became more a tt ract ive because of a number of events and ac t iv i t ies .Together with a team of archi tects , we therefore started todevelop and to design a s t ructure which should cover the cen-t r a l par t of the arena.

2. s t ructureThe ancient arena i s class if ied as a h i s to r i ca l monument.Therefore a l l modifications of the exist ing structure havebeen prohibited. In addi t ion, the designers have been askedto develop a s t ructure which was not able to be seen from th e


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surrounding s t ree t s , and, which has to be removed to ta l lyfrom the arena during summertime.The s t ruc ture therefore has been designed under the imperat ive of a quick annual erect ion and dismantling procedure. Reduct ion of deadload became a necessi ty. The design yielded toa l ightweight s t ruc ture which i s able to be insta l led within21 days, designed to withstand a windspeed of 200 km/h andable to carry a snow load of 360 to - more than twice thedeadweight of th e new building.The ( loadbearing) s t ructure is composed out of 3 par t s : 30columns with a height of 9.80 m have been placed along theperimeter of an e l l ipse . They carry an e l l ip t i c s tee l - r ingwhich i s f ixed excentr ical ly onto the top of the columns. Ana i r inf la ted cushion with a span of 60 x 90 m has been arranged within the e l l ipse defined by the r ing. Fig . l .The a i r in f la ted cushion consis t s out of PVc-coated PETPfabr ic membranes. Several single membranes may be dis t inguis hed : The upper membrane, the lower membrane (layed onto are inforc ing cable ne t ) , the seal ing membrane and the h i g h t rans lucent covering membrane. Fig.2.The upper as wel l as the lower membrane are edged by 30 garland cables . These cables t ransfe r the forces from the mem-


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brane to the columns resp. the s tee l - r ing . Therefore thes t ee l - r ing ac t s as a compression element. Although the r ingi s loaded with compression forces in the range of more than400 tons , it could be real ized as a hollow box beam with across-sect ion of only 300 x 500 rom: Global s tabi l i ty is ensured by th e cushion.The upper and the lower membrane are connected by a so cal led"seal ing membrane". This membrane completes the cushion. I ti s f ixed onto the upper as well as onto the lower membrane.I t may be opened along i t s equator using a loop-fastener ,and, to ensure proper a i r - t igh tness , an addi t ional zip .Because the cushion i s f ixed onto the r ing a t only 30 points ,a t ranslucent "covering membrane" has been spanned from th eupper membrane to the s tee l - r ing , in order to close the eyeshaped openings.An incl ined facade spans from the upper s tee l - r ing to a lowerfacade-ring. It completes the building. The facade had to bet ransparent because we wanted to use the ancient masonry outs ide the new Duilding as a scenery. Therefore we developed afacade which consis ts out of about 450 hollow box beams. These beams show a rhombus-shaped cross-sect ion , real ized by3 mm Polycarbonate-plates . An internal aluminium web re infor ces the t ransparent beam. The beams have to carry the samesevere wind and snow loading as the main s t ruc ture . Therefore


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deta i led analysis and loading t es t s have been carr ied out.They showed t ha t the deformations of the elements s t i l l re -main within the l imi t s defined by the french building codes.The beams can be rotated by 90 degrees around the i r axis . Because of t he i r rhombus-shaped cross-section, the ent i re facade can be opened th i s way, crnating a natural venti la t ion.The loadbearing capacity of the cushion is guaranteed by thein ternal pressure . The level of the in ternal pressure hasbeen defined in order to carry fu l l snow loading resp. toavoid f l a t t e r ing of the fabric , even under heavy wind loading.While the f i r s t type of loads had been defined by the Frenchbuilding codes, detai led wind tunnel t es t s have been carr iedout in order to obtain the most rea l i s t i c wind load dis t r ibu-t ion. s tudies of posi t ive /negat ive pressure si tuat ions withinthe auditorium, caused by dif feren t opened/closed door arrangements, have completed the table of windloads f inal ly .Nonlinear f in i te element analysis has been applied to evaluat e the loadbearing behaviour of the s t ructure in deta i l andto confirm the choice of the levels of the air-pressure within the cushion.


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The pressure within the cushion i s provided by four bloweruni t s . Two of them, equipped with a sound absorbing system,are powered by e lec t r i c engines. The remaining two blowersare diesel-powered. one engine i s sUff ic ien t to guarantee the. .proper air-pressure within the cushion. An a i r -pressure mea-surements device manages the speed of the ac t ive b ~ o w e r . Dur ing the blowing up of the cushion (end of . e rec t ion) , a l l 4blowers are running para l le l . Caused by t he i r huge capacityof 75 000 m3/hour , they are able to i n f l a t e th e cushion within 25 minutes.

3. The MembranesAll membranes are composed out of PVC-coated PETP-fabrics.This material has been chosen because of i t s good ab i l i ty tobe folded and stored each year , i t s high loadbearing capacityand because of the qood behaviour of the materia l and i t s jo in t s under the influence of environmental e f fec t s .Different qual i t ies of materials have been chosen, dependingon the forces they have to carry as a s t ruc tu ra l element:The upper membrane i s a quali ty type GUWA IV. Yarn i s 1670dtex, weave i s P 3/3 . The greycloth-weight i s about 490gr/sqm, t o t a l weight i s about 1300 gr/sqm. The t ens i l es t rength i s 149/128 kN/m (short term loading, 23 degrees) .


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The s t r ip s of the cu t material have been joined using an80 rom HF-welding and, in addit ion, four backst i tch sewings.The ent i re upper membrane has a surface of about 4000 sqrn.Material t e s t s have been carried out in order to achieve aguaranteed high level of strength of the jo ints . For the upper membrane, t e s t s have been done for a l l types of jo ints a t23 and 70 degrees.The lower membrane i s a qual i ty type GUWA I I . Yarn i s 1100dtex, weave is P 2/2. The greycloth-weight i s 275 gr/sqm, to t a l weight i s 900 gr/sqm. The t ens i le strength i s 104/116kN/m. The single s t r ip s have been joined using an 60 mm HFweld. The st rength of the lower membrane i s less then thes trength of the upper one: The lower membrane i s l a id onto acable net . Therefore the span of the membrane i s in the rangeof 7 by 7 m only. The ent i re lower membrane with about 4000sqm, as well as the upper one, has been delivered as one pie-ceo

The sea l ing membrane also i s a qual i ty type GUWA I I . I t hasbeen fixed onto the upper resp. the lower membrane using an60 mm HF-weld.The t rans lucent covering-membrane i s a grid-fabr ic (widemeshed fabr ic) . Weave i s LIl l , to ta l weight i s 700 gr/sqm.


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Tensi le s t rength is 40/36 kN/m. The s ingle s t r ip s have beenjoined using a 40 mm HF-weld.

4. cut t ing pat ternIn order to rea l ize the shape of the cushion as precise aspossible , the evaluat ion of the cutt ing pat tern has been doneusing computer-based methods.For these procedures, the ent i re surface of the cushion( incl . seal ing membrane) has been t ransfered in to a d ig i t a lsurface model. Based on th i s model, the s ingle s t r ip s of themembrane have been designed under th e aspec ts of t h e i r maximum width and under the aspect of an optimum seam-layout.For the upper as well as for the lower membrane, a so called"mixed-pattern" has been chosen. This means t ha t there i s arad ia l s t r ip arrangement a t the edges and a para l l e l arrangement of s t r ips in the center area o f the surfaces .Total ly, the upper membrane consis ts out of 144 s t r ip s with amaximum length of 84 m and a maximum width of 2.50 m. The lo -wer membrane consists out of 140 s t r ips , the seal ing membranei s composed out of 92 s t r ips and the t rans lucent covering ,"membrane consis ts out of 124 s t r ips .


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5. Lis t o f persons and firms involved:Maitr ise d'ouvrageDesign, analysis and detai l ingby archi tec ts and engineers

s t ee l contractor

Membranes

Mater ial by

Facade

Material by

Conception of the Montage

: Ville de Nimes

: LAB F AC F. Geipel,N. Michelin, Paris ands tu t tgar tSchlaich Bergermann undPartner, s tu t tgar t

: Baudin Chateauneuf,Chateauneuf sur Loire,Groupement des Metall iersdu Gard, Nimes

: Stromeyer Ingenieurbau,Konstanz

: Verseidag, KrefeldHammersteiner, Huckelhoven

: Merlo, TorinoGeneral Electr ic France,Paris

: IF, l


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Fig . 1: The main par t s o f the s t r u c tu r e


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Sealing Membrane

Ring-beam

Column

Fig . 2: Deta i l ing of the cushion a t its edge.

Air Inflation Method

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