Vertical span Introduction In Europe, after a strong overcomeof the concrete in the 20th century as the primary construction material,combined by the movements of Modernism and Postmodernism, the traditionalconstruction materials, such as stone, wood or brick were held back by thespeed of building process during the last century. Before this period, some regionsfrom all over Europe, had a significant connection with their own land, andthis was shown also by their architecture. There wasn’t a universal buildingtechnology, which everybody can acces it, neither the preparation of the localmasterbuilders was not enough for a wider use of material. It is well known, thatthe vernacular architeture (architecture without an architect) uses the possibilitiesoffered by its own land and forms its own people. If we look at the olderbuildings, the historic centres of the settlements or at the wider landscape,by studying them, we can have a really precise knowledge about how the landforms its own habitants and how they do habit their space.
This observation, ifwe apply all over the continent, dividing in time during the centuries, we caneasily classify smaller or bigger communities, regions, or even states, whichshare a common building technology, material or technique given by itsterritory. As examples, we can mention the stone architecture of Ticino, in France,the wood architecture from Norway, Switzerland, Austria, Transylvania or the brickconstructions of the Romans and Greeks. Universally, all these heritage ofthe past was put away in the last century, giving place of the era of theconcrete.
Interestingly, some local regions, still remained in contact withtheir own architectural heritage, without needed to deny their local inspiration.In Switzerland, one of the most significant area where the local architecturehad a continous history and evolution was the canton of Grisons. This area ofSwtizerland, was always characterized by wood constructions, which we cantranslate with the landscape of forests through the whole area.
There is asignificant heritage of log constructions, called “Strickbau” or”Mischbauweise”. This region, in the 20th century, when the concreteas material was having his paradise, gave birth to some significant specialistsin the field of construction, or was the place where they performed in theirhighest level. The canton of Grisons became a pilgrimage land for architectsand specialists, interested in wood constructions. There is a rational andpragmatic world which appears in the front of the visitor, helped by strongengineering condition, which gave birth of significant projects. Also, thisattiude has its positive and negative aspects.
Thinking of the fastly growninfrastructure, highways, bridges, office buildings, without any substantialpreoocupation to the details, the projects you can find in Grisons, are a deepknowledge about the place, the people, the material itself, and this results ina simplest architectural structures, solved even the very last detail in aunique level, which as Peter Zumthor once confirmed: “I think you havebigger chance to find beauty, if you are not working directly on this. Thebeauty in architecture is held by its expedience. This is, what we can learnfrom the city- and villagescapes built by the Swiss farmers. If you do what youneed to, then in the end will result in something, which maybe you cannotexplain, but if you are lucky, it is linked directly to the life.
” As having this as starting point, itwas interesting to study how in contemporary architecture form Grisons is thewood still applied. Luckily, during the last period, some significantarchitects and engineers did work with this material and they did contribute tothe evolution of the building technology of the region. Among other, less wellknown professionals, the works of Peter Zumthor, Bearth & Deplazes, GionCaminada or Hans Jörg Ruch are the most important to mention.
For this work, were selected fourprojects, each of them from a different architect, but by the same engineer,Jürg Conzett. All the works are built in Grisons, all by local architects andall of them treat the theme of the span, of an opening over a wider empty space,with a careful and unique architectural and static design, all made in wood. Allof the studied situations, treat the same problem in a different way, thefunctions of the buldings is also diverse. The selected works are: · School Gymnasium in Flerden byHans Marugg· Multipurpose Hall in Alvaschagn byBearth & Deplazes· Verweilbrücke in Trutg dil Flem byJürg Conzett· Community Hall in Vrin by GionCaminada The purpose of this confrontation isto have a deeper image in the understanding of how a simple question, of aspan, can be solved in different ways, having the same cultural basis. SchoolGymnasium, Hans Marugg, Flerden, 1992 One of the first project on whichthe newly established office of Conzett started to work, was the School buildingin Flerden, designed by Hans Marugg, an architect form Engadin.
Being a schoolbuilding, the opening to cover with the roof was about c. 12m in its width. Theused material was glulam timber.
The starting structural principle ofthe roof of the gymnasium was abstract, to use the laminated timber astwo-dimensional elements, in order to apply as a concrete based wall-slabsystem. The initial idea was to have a single ridge beam structure with acentral purlin, as is well suited for the simple shape of the roof. Due to itsopening, in this case the beams would have act as simple beams, having too bigbending moments.
The sections of the elements, would need to be overly large. For economical reasons, a variant ofthe above design was applied, having two central purlins. The bending momentsof these are reduced, complemented by small cantilevers at their end. All the pieces are the samethickness, 100mm, and are designed as walls or slabs, so in section, they looklike shallow rectangles.
The orientation of them are decided by the structuralroles they have, as: the lowest tension piece of the frame is orientatedhorizontally in his plane, in order to overcome the orizontal forces generatedby the hung sports equipment. This piece is in the middle is almost two timeswider than its ends, where also is a one and a hal meter long cut, for thelinking purlins. These purlins are orientated upwards, as the diagonal strutsto take over the bending forces. The purlins have a specific geometry, whilethe struts have the same principle as the flat piece, two times wider one endthan the other. These struts, are linked together by a short, approximately 2mlong horizontal compression beam, also orientated upwards. Between the struts,we can find two diagonal joists, also increasing in size upwards, where theyconnect the struts. These elements are not completely vertical, they have aninclination of 9 degrees, this angle being the bisector of the inclination ofthe two type of struts. These struts, while are sandwiched by the compressionstruts, at their side, they also hold the bigger part of the roof.
For this areprovided two 25cm wide “moustaches” on the pieces, on which arestanding the beams of the roof, orintated perpendicular to the orientation ofthe fall of the water. As the struts overtake the forces, they transfer them tothe horizontal tension piece, which transfers them at its base. At the both of the basis, arebirch-ply pieces, having a unique designed shape, which resist the shearstresses. Through the whole roof system, beside glueing, there are visibleconstruction screws for a better connection between the elements. By this system, for the whole roofstructure over the gym, were used just 40 elements. Six pieces by each pair of span,and other 10 for the longitudinal roof beams.
MultipurposeHall, Bearth & Deplazes, Alvaschagn, 1990-91 Theprinciple of overlayed structural systems were often used in the preindustrialera. Maybe the most famous example for this is the bridge of Hans UlrichGrubenmann form Schaffhausen from 1758. The advantage of the structural overlayconsists in principle of solidarity: while one system stop working, thenanother system comes into the scene, helps, and all together resolves theproblem. This is thecase of the village hall from Alvaschagn, designed by the architecture officeBearth & Deplazes. The function of the building is a multipurpose hall,deserving as space for cultural and community events, but also for sportactivities. The use of the space needed and adaptable structure, so there youcan store the sport equipment away during the concerts or plays. The mainload fo the roof structure comes form the snow. As the biggest shear forcesappear in the horizontal pieces, before they are transferred to the sides; thesides, as being the smallest part in section of the roof, due to the roofgeometry, need the bigger number of noggins.
The wholesystem can be divided in three portions. All three portions are enclosed bylaminated timer profiles, shaping the silhouette of the frames. The middlepiece is 220mm wide and and inside the frame, There is a stiffened arch of thinlaminated timber.
This arch is taking over most of the vertical forces of theroof. On the side of this frame, there are attached 27mm thick plywood platesin order to take over the forces form the snow. The combiantion of this systemprovides a thin construction. In addition, against the shearing forces, areadded two more frames on both sides, creating a box construction together withthe plywood plates. Through all the construction, the horizontal pieces aremuch thicker than the vertical ones.
The explanation of this means that themoments on the corners are smaller under the vertical loads, the horizontal wecan be considered as simple beams, and verticals are acting when horizontal areapplied, against the lateral bending moments. In theconstruction technology, this meant that the corner pieces are simply the fixedstarting elements, and to this were stiffened the other pieces by gauge bolts. Asthe arch is inside the “sandwich” construction, just the bolts on theplywood plates hint its existence.
The wholeconstruction is fixed together with bolts on horizontal, and later on were putin place all together. As the frame is getting shallowers as going downwards tothe ground, the section at its very lowest point arrives to approx. 200x500mmmassive timber. Thecombination of the conctruction system, arch and boxes, underlines theefficiency of the combination, as each system takes over the loads of which wasoriginally intended to be: the thin boxes as load-distributor, while the archas good stifness under a uniform load. Community Hall, Gion Caminada, Vrin, 1995 Thisbuilding is one of the most significant among Gion Caminada’s career and it wasimportant for the architect’s fame in his own region and village. The theme ofa community hall was nothing expectional in the canton of Grisons, some of therenoowned local architects had the chance to complete one. Villagessuch as Vrin has very few communal spaces, beside the school, just the churchcould be considered that. In addition to these was commisioned Gion Caminada bythe local authorities, to complement the coherent appearance of the church andthe school built in 1857.
As most of these community halls, the space alsoneeded to serve as a gym for the neighbouring school. Given the theme, were twoimportant factors in his design, which we cannot find in the above twoexamples. The village of Vrin is on a big slope, and such a big footprinthardly can find its place flat. The second was an incredible connection of thearchitect with the building material and the conservation of the Alpineterritories; he is saying that the goverment should protect the farmers, asthey are the guardians of the Swiss Alpine landscape. Conformethese two aspects, the bulding is a wooden roof on a concrete plinth.Positioned dramatically on the edge of the village, where the slope starts tohead down, there was buitl a solid concrete plinth, half in the ground (facingupwards the hill).
The timber also refelcts the richness in pine of thecommunity, but also the local architectural tradition. Using local timber, cutat the nearby sawmill, there was a possibility to obtain large cross sectionedwood pieces. The opening to cover was about 11m wide, and for this, it waspossible to use these huge pieces of wood as non-spliced tension members. Theorientation and arrangment of the fibers was also a help, so like this, the imaginedstructure was like a very simple open girder construction, the single challengebeing in the connection of the ends of the beams. Other contemporary strcutres,for which glulam timber was used, supposed to be cut and assembled in theworkshop, providing a big precision and accuracy of the result. Not in thiscase, where the frames were built on the site, and the connections were addedlater. The massive timber elements are useful in traction, and the idea was tobe joined with flexible nodes. During thedesign process, Conzett used as a reference the Magazzini Generali SA buildingin Chiasso designed by the renowned Swiss engineer, Robert Maillart.
Thisreference was considered during the process, as the the initial two beams structurehad a strctural problem for which Maillart provided a solution. Thedifference between Maillart’s and Conzett’s design, was that in Chiasso, theroof is tensioned just by a think skin of snow, while in Vrin, this wood roofstructure needs to resist to heavy snow loads and strong open winds, as ispositioned on an open edge of a slope in a valley. This also means that inChiasso, the snow is mostly uniformly distributed, but in Vrin is significantlyassymetrical. At this point, other refernces were considered by Conzett, theBridge near Donath and the one near Tamins, both made by Maillart. The centraljoint between the two beams was tempted to move upwards as the compressionforces act in their end, so there was no need for a central vertical support. In contrast, the ends of the beams are tempted to actoutwards, so a bottom chord was introduced. This chord is made out of five 25mmthich timber planks, going through the whole space creating an almost constantcurve under the roof beams.
The interesting part of the structure is the jointbetween all these elements. Needed to be found a system which allows to connecteach plank individually to the beams so they can act as a chord. For this, wereused thin steel plates. Every of these plates were holed in the middle, withthe thickness of the beams, folded in two, slunged around horizontally over a24mm diameter dowel botls. The two ends of the steel plates were holed eachwith 4.5mm holes, each of them having 84 holes.
It was necessary to have astrong connection spread in as much screws as possible, cinsidering the smallthickness of the planks. These plates are clearly using the principle of a tensionmember. A delicatepart of the structure is the laterial connections. Based on the principle ofthe bridges by Maillart, as the loads from the beams are directioned downwards,bigger and bigger compression forces are appearing. As the middle could beopen, considering the pushing upwards, the other ends needed to be anchored, toreduce the moment variants.
There were introduced 12 pieces of verticalelements. Each of them is growing in its transversal section as it goes more tothe lower end of the roof. The short distance between these elements also preventsthe planks from buckling. The designof the roof is interesting as it stoods out of its predecessors made byMaillart, converting them into a high-performance hybrid system, but still donot deny neither the local architectural traditions, nor the experience ofcreating something new. Verweilbrücke, Jürg Conzett, Trutg dil Flem, 2010 99. Conclusion 100. Bibliography 101.
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