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Architecture has the purpose of creating and enriching space for human activities. Structure is the means by which space is spanned and enclosed. Structure, then, is an integral and inevitable part of architecture, its form, its function, its economy, and its spirit. Today this simple relationship is often lost, since, for smaller buildings, contemporary structural technology can support almost any chosen form. For large spans structural form is still important, for tensile solutions it is critical. Yet this is not always obvious to architectural designers at a time when new technologies are evolving rapidly and design tools are not yet user friendly.
218 ENGINEERING AN INTEGRATED ARCHITECTURE FOR WIDE SPAN ENCLOSURES Horst Berger Light Structures Design Consultants, White Plains, N Y, USA Professor, School of Architecture and Environmental Studies The City College of the City University of New York ABSTRACT This paper deals predominantly with tensile architecture whose application for permanent buildings has occupied this writer for the more than 30 years. In tensile architecture the historic unity of structure and architecture is maintained and many building functions are integrated. The fabric membrane acts as structure and enclosure; reflector and transmitter of light, heat, and sound; generator of the interior space and the exterior sculpture. Using the Denver Airport terminal and other structures in whose design and engineering the writer played a critical role, this paper mainly presents principal tensile structure forms and their impact on function and construction of the building. The examples include the Hajj Terminal of the Jeddah Airport, Riyadh Stadium, Canada Place in Vancouver, and the San Diego Convention Center. Their dramatic forms and spaces consist primarily of minimal surfaces deriving from their structural tensile order. Weight of construction material is drastically reduced, construction time shortened, energy saved, maintenance simplified, and life cycle cost improved. Raising technology to an art form lets tensile architecture add a softer tone to a new vocabulary of architectural design. The paper ends with the new UniDome roof structure, which replaced the 25 year old air-supported roof with a combination of an opaque grid- dome and a translucent fabric structure in its center. INTRODUCTION: STRUCTURAL FORM IN ARCHITECTURE Architecture has the purpose of creating and enriching space for human activities. Structure is the means by which space is spanned and enclosed. Structure, then, is an integral and inevitable part of architecture, its form, its function, its economy, and its spirit. Today this simple relationship is often lost, since, for smaller buildings, contemporary structural technology can support almost any chosen form. For large spans structural form is still important, for tensile solutions it is critical. Yet this is not always obvious to architectural designers at a time when new technologies are evolving rapidly and design tools are not yet user friendly. We live in a period of transition from the relatively settled world of the Middle Ages to a New Age whose outlines are only beginning to become apparent.The last two centuries were marked by a huge population growth (six times world wide, three times in my own life time) and by drastic changes in the way people live as a result of the innovations of the industrial age and the electronic age. The evolving built environment is a critical part of this changing world in which human activity puts a burden on the resources of our planet and exerts pressure on the delicate balance which maintains an environment friendly to human existence. The consequences could be Fig 1 The Jeppeson Terminal, Denver International Airport Fig 2 American Indian Wigwam Frame disastrous. Therefore, to survive on this planet may make it necessary to select order systems in which visual form and structural form are congruent and which respect the natural balance of the natural environment. It is my belief that our ideas and images of what constitutes architecture were first formed long before the tiny fraction of the human evolution which we call 'history'. There is evidence that human dwellings of substantial size and grouped in community settings date back over 400 000 years. More significantly, the form and structure of these dwellings was most likely similar to village houses found in Africa and Asia reaching into the last century and to the American Indian wigwams encountered by the European settlers. Their shape derived from the process of building the shelters using available natural means. Flexible saplings, would be set in the ground in a circular or oblong floor pattern. Bending opposite members inward, lacing them together, and adding horizontal rings, domes were formed. Two principle patterns emerged: radial and orthogonal grids. They are identical with the two principal engineered dome forms we have today. Thatched with grass, leaves, or reed, they provided protection against rain and wind, produced ventilation and modified temperature. These enclosures were minimal surface lightweight structures forming comfortable interior spaces and gracious exterior building forms. The similarity of their geometric order (Fig.2) to recent air-supported fabric domes (Fig.3) and the most recent grid domes is amazing. FABRIC TENSILE STRUCTURES FOR PERMANENT BUILDINGS Tensile structures satisfy at least part of this challenge. The terminal building of the new Denver International Airport, completed in 1994, illustrates most of the significant features of a fabric tensile structure. It took less time to build than a conventional roof system and provided protection during construction of the spaces below. It weighs one tenth of any conventional roof system. Using Teflon coated fiberglass, it cost more than a conventional opaque roof, but less than any roof with similar translucency. It reduced the cost of supports and Fig 3 UniDome air-supported roof structure, 1975 foundations, required less mechanical equipment and simplified the drainage. It saves energy because of the use of daylight, the reflection of heat from the sun, and the outward night radiation. And there is less general maintenance. Therefore, its life cycle cost is lower than that of any comparable roof system. Above all, the bright interior (Fig.4 ), with its sweeping tensile shapes offers a great space for the traveler. And the exterior sculpture is powerful and distinctive (Fig.l). Architectural form is identical with structural form. And the structural form I kept as pure and direct as possible. It is one of a number of significant public buildings using tensile structure as the dominating architectural feature. The roofs of the San Diego Convention Center and of Canada Place in Vancouver have become landmarks for these two cities. The roof structure for the King Fadh Stadium in Riadh is still the largest stadium cover(despite its large central opening). The Haj Terminal of the Jeddah International Airport, now almost 20 years old, is still by far the world's largest roof cover. Amphitheaters, indoor sports facilities, malls, stores, and industrial structures are among the other frequent areas of application. These and many structures by other designers indicate the successful entrance of fabric tensile technology into the world of permanent architecture and the potential of a larger role in the future when fabric properties will advance and their cost will reduce, and when architects Fig 4 Jeppeson Terminal, Denver International Airport, Interior View 220 and engineers will be more familiar with their design, and when this technology and its forms become more acceptable to both design professionals and the general public. PRINCIPAL CONSIDERATIONS: THE DENVER EXAMPLE As a structural category fabric tensile structures are a special form of lightweight surface structures which include shells, grid-domes and cable nets. In each of these the continuous spatially curved surface is a critical and integral structural element. In tensile structures the surface elements, consisting of structural fabric and high strength cables, can carry load in tension only. The primary advantage of tensile members over compression members is that they can be as thin and as light as their tensile strength permits. Consequently the weight of tensile structures is almost . The weight of the Denver roof, for instance, is 10 kg/m2, which is one tenth the weight of a light steel truss roof, one thirtieth the weight of the most intense snow accumulation which this roof is designed to carry. The fabric skin is not only part of the structure but also the building's enclosure, requiring no additional dead load for cladding. A further advantage of thin, lightweight tensile components is that they are easy to ship and erect. Their flexibility allows them to be coiled, rolled or folded into small packages. Cables can be a few hundred meters long, requiring no splices or internal connections. They can be raised and connected to their end supports by* cranes, winches or helicopters, requiring no scaffolds. In fact, the erection time for a fabric structure is much shorter than that for a conventional structure. Form and prestress, rather than gravity and rigidity, are the basic means of providing the stability and the strength to carry load. Structural form becomes a critical determinant of architectural form. To make a tensile surface structure work, requires a minimum of four support points, one more than needed for a rigid structural system. The most basic form, therefore, is a four point structure. (Fig.5). If an orthogonal grid is used, this is the basic module. One of the four points has to be Fig 5 Four Point Structure outside the plane defined by the other three to achieve the double curved surface which gives the structure its stability and its capacity to carry load. The alternative geometry is a radial tent. As long as these surfaces are in tension the structure is stable. Under external loads part of the surface can be permitted to go slack in one direction as long as the stability of the support system is not lost in this state. The pattern of surface stresses which is required for the stability and load carrying capacity of the structure results in horizontal forces at the anchors in addition to the customary vertical forces. This is the price to be paid for the advantages of a tensile structure. The skill and efficiency with which these horizontal forces are A A U-Cl—E2U Fig 6 Denver Section, showing ridge and valley cables, and the building's horizontal anchor elements anchored or balanced has a large impact on the economy of the structural system. The Denver roof, for instance, is anchored to the conventional sub-structure by supplementing the existing structural frame with diagonals to balance the horizontal forces along the shortest possible path.(Fig.6). Because of the lack of structural weight, there need to be elements which resist upward loads from wind suction in addition to the elements which carry downward loads. In order to generate the structural surface grid which satisfies all these requirements there have to be supports at the high points of the surface, others at the low points, and still others located around all sides of the periphery. The choice of these support points defines the shape of the structure. Their geometry combined with the stress pattern assigned to the surface leads to the form of the structural surface. New forms can be explored with the help of stretch fabric models which simulate the actual shape rather well and are easy to make. The final shape is determined with the help of a formfinding computer program. It puts all the tensile forces in all the elements in equilibrium. For one given configuration of supports and one internal stress pattern there is only one equilibrium shape. Form clearly follows structural function. Since the surface which is generated in this way is also the enclosure, the structural form defines the sculptural shape of the building on the outside and the form of the space on the inside. There is no longer any distinction between engineering and architecture. The shape of the Denver roof consists of fabric spanning between alternating ridge and valley cables, with the periphery defined by edge catenaries. Fig. 7 shows the entire form of the 320 m long roof. This image is based on thee writer's iterative geodesic formfinding system. Fig 7 Denver membrane grid The photo of Fig.9 shows the completed structure. My initial proposal for the shape was to keep all interior fabric units identical . The concern was the simplicity and economy of the structure. The visual impact would be naturally enriched by the deep perspective caused by the large scale, an effect seen in medieval cathedrals. The architects' desire to emphasize the two main entrance points which also divide the terminal into three functional sections, led to the use of four larger units with higher masts.( See Fig.l, Fig.7, and Fig.9). This resulted, of course, in a tremendous variation of shapes due to the continuity of the stress pattern. The impact on cost was considerable but probably worth it. Fabric as the surface element in a tensile structure is critical in maintaining the hierarchy of materials which makes the system compatible. Fabric stretches more than cables, they stretch more than rigid structural elements. Rigid surface elements instead of fabric cause compatibility problems unless frequent expansion joints are provided or the surface is regarded a rigid shell and included as such in the analysis. There is no expansion joint in the 320m length of the Denver roof. Fig 8 Clerestory with inflated tube closure. 221 Fig 9 Aerial View of Denver terminal roof Translucent fabrics further define the character of the spaces they enclose by bringing in daylight. High reflectivity and low absorption of heat greatly moderate the interior climate. And the surface geometry, together with characteristics of the fabric or of an inner liner control the acoustics in the space. The sound dissipating geometry of tent shapes combined with the sound absorbing surface of the inner liner acts as a "black hole" for internal sound. Users of the Denver airport, which has an acoustic inner liner, comment on the quiet atmosphere inside this busy terminal. A feature of critical importance in a permanent building .with a fabric structure roof is the treatment of the connection between the flexible membrane and the rigid periphery wall. Clamping the components of the roof structure directly to the top of the wall requires the wall to be designed for substantial horizontal forces. If the membrane forces are anchored separately, a connection has to be found which allows for the substantial differential movement between fabric and roof membrane. In the case of the Denver roof with its high, cable supported cantilevering glass walls and the big fabric roof overhangs, a workable solution was the introduction of an inflated fabric tube which allows roof movements in the order of 0.65 m at the clerestory windows (Fig.8). and around 1 m at the south and north walls. Simple spring operated valves let the air escape and the tube flatten out or elongate. A small pump keeps the tube inflated. The inner fabric liner, connected directly to the top of the periphery glass walls, hides the tubes from the inside. Fig.8 shows the tube before installing the inner liner. 222 Fig 10 Construction of Denver roof MAST SUPPORTED STRUCTURES The example of the Denver terminal building shows the principle structural features of a mast supported tensile structure. The upper support points are formed by pairs of masts which are spaced 46 m apart. Ridge cables are draped over these masts and anchored to the adjacent lower roofs similar to the main cables of a suspension bridge. They occur every 18.3 m along the length of the building and are designed to carry the downward loads, Fig 11 Denver, main fabric, stressed. mainly snow in the case of Denver. Valley cables are placed between any two ridge cables and run parallel, taking on the form of an arch. They carry the upward load from wind suction and are tied to lower roof anchors. The edges of the roof are formed by edge catenaries outside the window walls which are anchored against the building. Construction progressed linear (Fig. 10), a bay at a time, starting at the north end , and ending at the south, where external anchors complete the structure. The exterior fabric was stressed by pulling down on the main connectors right outside the clerestory walls. (Visible in Fig. 11 at the far end of each valley cable). This photo shows the main fabric, stressed and before installation of the inner liner. The cables running parallel to the fabric seams are redundancy cables which act as rip stops and as replacement of fabric stresses in case of a rip or during replacement. An interesting and integrated part of the Denver enclosure are the cable supported glass walls around the entire periphery of the terminal space. The south wall itself is one of the largest glass walls built, being up to 20 m high and 67m long. The upper edge anchors the inner liner. The deflection of the top of this wall under wind load is only 8 cm. Fig 12 Shoreline Amphitheater, during constrution A few notes on a number of other mast supported structures, pointing out features of special interest: The roof of the Shoreline Amphitheater shows a mast supported structure in its simplest form and largest scale. The two masts are 45 m high, spaced 61 m apart, supporting a roof with 8,000 m 2 of plan area. The front edge catenary spans 140 m between two pile supported abutments. The fabric spans between ridge cables and edge catenaries with only a few internal cables placed within the fabric surface for sectionalizing the membrane and reinforcing it along a few critical lines. The fabric was stressed by jacking the masts at the ground level. In the roof design for Canada Place (Fig. 13) in Vancouver the masts are placed at the ends and are anchored back with external tie-down cables. The tent units have a 45o skew in plan, orienting them parallel to the city streets. This arrangement made the patterning .1- Fig 13 Canada Place 223 complex. But it gives the building the sail-like character for which it has become known. The large external moments created by the position of the high masts at the ends was balanced by engaging two floor levels of the building and utilizing the building's structural components. Pairs of cables are used for the external anchorage to provide for redundancy and to make it possible to replace them. In the earlier design for the Haj Terminal of the Jeddah Airport, completed in 1982, central mast supports were avoided by suspending the 46 m span square tent units at their peaks. Eight suspension cables carry the load of each unit up to the top of the 46 m high pylons, which consist of single masts in the interior and of rigid frame double pylon structures along the periphery of each module as well as between modules. The roof covers a total of 420,000 m2 or 105 acres of plan area, by far the largest roof cover in the world. The roof's purpose is to moderate the climate by simulating the functions of a forest in the desert. The translucent roof provides shade and reduces the effect of the heat and light from the sun to about 10%. It avoids the heat storage in the ground and its subsequent radiating back into the space. It allows warm air to rise up and escape through the center ring openings. The construction of this very large project made use of its repetitive design, which becomes visible in Fig. 14. The 210 tent units are arranged in 10 modules, each three units wide and seven units long. The 21 units of one module were assembled close to the ground. The support ring in the center of each ring was split in a top and bottom section. The top ring, hanging from the main support cables, contained winches and jacks, which could be operated from one central control space on the site. The winches lifted all 21 units simultaneously within about one meter of the top ring. Four screw jacks each were then installed. Again, simultaneously jacking all 21 units the rings were docked, the structure fully stressed and the rings bolted to each other. In the photo the five modules of one side of the structure (Modules A to E) are completed. The first module of the other side Fig 14 Jeddah Airport Roof: Construction (Module F) has been raised and is being stressed. Module G, next to it, is being installed near the ground, soon to be raised. It should be noted that this process was tested on two full scale test modules which were also instrumented with stress sensors to check the accuracy of the computer analysis. The test results deviated from the analysis output by less than 5%, giving us confidence in the reliability of our analysis process. Because of the tremendous scale of this nearly 20 year old structure it is becoming a test for the reliability of fabric tensile construction. The Riyadh Stadium extends the concept of mast supported tent units to create the largest span roof structure to date. (The design could have been adjusted without difficulty to cover the area formed by the central opening which is only one quarter of the total plan area. Functionally this was not desired). This 247 m diameter Fig 15 Riyadh Stadium Roof span is achieved by arranging 24 units in a circle with an outer diameter of 290 m, covering an area of 49,000 m2. In each unit a main vertical mast and a smaller sloping mast combine with triangulated peripheral tie downs to provide the rigid supports which hold the structure out and up. On the interior the horizontal forces are balanced by a large ring cable with 130 m. diameter. Again, ridge 1 ' : * : Fig 16 Riyadh Stadium : start of fabric erection 224 and valley cables form the main elements to which the fabric membrane is attached with the valleys forming the downward anchors. The ring cable, suspension and stabilizing cables provide redundancy and make a simple erection feasible. Fig. 16 shows one step in the erection process. The entire cable system is in place. Fabric is laid out on the ground, ready to slide into position. Note in both photos that only two fabric panel shapes were required to make up the entire roof and give it its dramatic shape. Fig 17 San Diego Convention Center, exterior The roof of the San Diego Convention Center provides a 91.5 m clear span by suspending the masts. They rest on the main suspension cables placed 18.3 m apart, which carry the load to triangular concrete buttresses whose dominant forms give the building its character. The roof structure is again formed by stretching the fabric between ridge cables, valley cables, and edge catenaries. A special feature of this roof design is a horizontal flying pole with forked ends which has the purpose of resisting the tensile forces of the two open ends. (Fig. 18) This makes it possible to keep the end openings totally free of supports, giving the roof its sense of floating weightlessness. A visually delightful feature is the so- called rain-fly, a closure structure on top of the main roof which covers the ventilation openings of the main roof. In 1997, Light Structures!Horst Berger were engaged to provide an enclosure design for for the area under this roof. The schematic design proposed a convertible enclosure to include a free standing, cable supported glass wall at the 91.5 m long open end similar to the south wall at the Denver airport. Movable wall panels were to convert the space from naturally ventilated to fully air-conditioned, curtains and fabric baffles from bright daylight to a shading level permitting video presentations to 6,500 people. A different scheme by a design/construct team is presently under construction. Fig 19 Mitchell Amphitheater, near Houston A-FRAME SUPPORTED STRUCTURES Tent shapes require a support at the peak of each tent unit. Architectural spaces most often need to be free of interior supports. Of the examples above, at Canada Place this was resolved by moving the supports to the edge. The result is a space which is high at the ends and low in the center, and a structure which is not very efficient. At Jeddah the masts were placed at the corners and extended upward to be able to suspend the tent units from them, again a structurally inefficient solution. At San Diego the masts ride on support cable which transfer the load to the perimeter requiring heavy anchors there. One way to resolve this problem is to replace the mast by an A-frame. One of several such structures is the roof of the Cynthia Woods Mitchell Center of the Performing Arts at the Woodlands outside of Houston, Texas. It covers 3000 fixed seats. Three A-frames form the support system together with the stage house structure. Horizontal anchors are avoided by introducing compression struts which link the support columns and edge cable anchors to the stage house, thereby balancing the horizontal components of the membrane forces. The supports of the A-frames form low points of the membrane which function as drainage locations for the rain water. The trussed columns supporting the A-frames contain the rain leaders and support platforms for the follow spot lighting of the theater. Fig 18 San Diego Convention Center, interior 225 Fig 20 Mc Clain Practice Facility ARCH-SUPPORTED STRUCTURES For spans of rectilinear structures of up to 100 m arch supported fabric roof systems can be highly efficient. For domes with circular, elliptic or super-elliptic edge shapes spans of more than 200 m can be an efficient solution, as long as the arch components remain within dimensions which are shippable by trucks. A number of structures have been built using prefabricated steel sections, often with a triangular cross section. The largest one using such prefabricated steel arches is the McClain Indoor Practice Facility of the University of Wisconsin in Madison. This building covers a football practice field. Arches of 67 m length, spaced 18.3 m apart, span the the full width between rigid concrete abutments. They are 2.1 m deep. Shop fabricated in 12 m long sections they were bolted together in the field to form half-arches. These were lifted by cranes, pinned in the center and braced against the adjacent arch, requiring no temporary support elements. It took 10 days to assemble the entire arch system. The outer quarters of the roof are covered by standing seam, stainless steel roofing. Only the middle half is covered by fabric membrane which spans between the arches and is held down by valley cables. This arrangement provides excellent natural lighting conditions for sports by concentrating vertical light in the center. Also the combination of the insulated opaque roof sections with the translucent, reflective fabric roof help reduce thermal energy consumption. Up-lighting against the reflective underside of the roof make for good lighting conditions in the night. One of the many other arch supported designs was for the tennis practice facilities of the AELTC in Wimbledon. It uses exterior, exposed precast concrete arches from which the fabric is suspended. This provides a neutral geometry of the translucent ceiling which is essential for playing tennis. It was completed in 1988. Fig 21 Bayamon Baseball Stadium Roof Design STADIUM DOMES A single arch spanning 168 m was proposed to support the cover for an existing baseball stadium in Puerto Rico. This dramatic design illustrates one of many ways of spanning a full size stadium facility. The arch, rising over the middle of the field, supports two cable reinforced fabric membranes, one anchored to a horizontal edge beam behind the outfield, one connected to two cable stayed masts located in front of the stadium. Fabric structures entered the world of permanent buildings with large and super-large spans. Geiger Berger's low profile air-supported roof design for the US Pavilion at the 1970 World's Fair in Osaka led to eight stadium-size roofs built in the United States and Japan between 1973 and 1985. All followed David Geiger's special geometry, consisting of a superelliptic ring and a cable net with cable lines parallel to the diagonals of the superscribed rectangle. The economy and speed of erection of these domes together with the attraction of high levels of daylight of the new Teflon coated fiberglass fabric made them win out over conventional structural systems. They became the engine that drove the new train of fabric structure technology. Problems with snow melting and removal, the cost and inconvenience of operating mechanical devices to maintain the stability of the roof structures, and the limitation and expense of a highly pressurized building led owners to return to static structural systems. This writer's first opportunity to respond to this development with a fabric tensile roof came in 1983 with his initial design for the St. Petersburg Sundome, for which he was the partner in charge. He called the system cable dome. The main principle of this patented system came from the idea of spanning suspension cables from opposite points of the ring beam and supporting sets of Fig 22 Original Cable Dome system developed by author for Sundome, 1983 Fig 24 Hybrid Cable Dome system with arches as top chord members, author, 1985 flying poles on them, similar to the basic arrangement of the San Diego roof. Integrating these elements leads to this simplest of all cable dome systems, where each cable carries two poles, each pole is supported by two intersecting cables. Again, one, two, or several layers can be used, whereby each layer is added like a cantilever. Erection needs no temporary supports. Fig 23 Cable Dome for Sundome by David Geiger, built 1986 In the final design, carried out by David Geiger (after the dissolution of Geiger Berger Assoc. in 1983), the configuration was changed to a system consisting of concentric rings and radial cables. ( Fig. 23). There fabrication and erection is difficult. A number of other cable dome structures have been executed, most prominently the roof of the Georgia dome in Atlanta, designed by Weidlinger Associates, using a triangulated configuration. Cable domes of this type are not efficient in heavy snow areas because of the multiplying effect which this geometry has in transferring loads from the center to the periphery. This leads to very high cable quantities accompanied by very large deflections. To avoid these problems this writer's cable dome patent includes a version with arch-shaped compression members at the top. These carry gravity loads in the most direct way to a peripheral ring. The cable system below the arches becomes very light as its function is reduced to carrying part of the unbalanced roof loads, stabilizing the arches and allowing the roof to be erected without a scaffold and a minimum of interference with the space below. In studying the replacement of the air-supported UniDome roof at the University of Northern Iowa, a cable-dome proved to be impractical. It was not possible to adapt its radial configuration to the existing orthogonal geometry and the first row of flying struts interfered with the sight lines from the upper seats which is a common shortcoming of all cable dome structures. It was also not economical for Iowa's heavy snow loads. The answer evolved from taking advantage of the special nature of the existing geometry in which the horizontal forces from the cable grid are in perfect funicular balance with the shape of the ring beam. The initial concept was a grid of compression elements following the same plan configuration as the existing cable net but located above it. The compression members were assembled from shop fabricated, three dimensional truss sections which were connected by vertical ties to the old cable net re-installed below. This combination offered the most direct force flow for downward or upward loads for the 15 000 m2 Fig 25 New UniDome, Arch and cable grid. The cable net is that of the former air structure Fig 26 New UniDome Hybrid roof, computer image superimposed on photograph dome spanning 140 m across the diagonal. The cable net stabilizes the grid dome and provides sufficient bending capacity to accommodate eccentric load cases for snow and wind. In the final version of the design the center section was replaced by an arch-supported fabric tensile roof which reduced the dead load where it is most critical and provided translucency where it is most desired. The rest of the roof surface is enclosed with a stainless steel standing seam roofing on metal deck and bar joists. Fig.26 shows the roof design in a computer generated image superimposed on an existing aerial photograph. The concrete ring beam which on this structure was made of rather thin precast sections was prestressed with tendons rapped around its exterior face to give it the capacity to become a tension ring. Fig 27 Prestressing tendons applied to the out side of the existing ring beam The construction began with the prestressing process in the winter of 1997/98, while the stadium was in full use. (The air-supported roof had failed in a sudden snow fall two winters before and had been repaired with PVC coated polyester fabric, a process which took Birdair only weeks to complete). Parallel to prestressing, shop fabrication of structural components took place.The stadium remained in use until the middle of March 1998. The new roof was completed and the first football game took place in the stadium in October of 1998. Fig 28 Erection of steel grid dome members. Fig 29 Beginning of steel erection Though a support free erection was studied, the use of four construction masts under the intersection points of the four continuous arches proved most practical and economical. (See Figs. 28 and 29). The arch sections (1.2m X 1.8m ) were shop fabricated in up to 17m straight lengths, bolted on site into sections ready for installation. The four long arch sections were strengthened by tie cables. Bar joists, spanning between arch ribs, and metal deck, spanning between joists, followed. Insulation and stainless steel roofing was installed parallel to the center fabric structure and the cable net below. Fig 30 The UniDome with its new roof [...]... new engineering advances and ideas towards a new architecture And, finally, an attempt to set up a broad scope of objectives for architecture and of the built environment in general can be found in the new issue of American Building LITERATURE Light Structures - Structures of Light The Art and Engineering of Tensile Architecture by Horst Berger, Birkhauser, 1996 Engineering a New Architecture by Tony... light, heat, and sound Construction is regarded an integral aspect of the structure While a substantial number of fabric tensile structures have been built world wide, this art and technology is still on the fringes of architecture and building construction And as the example of the UniDome roof replacement demonstrates, even for substantial spans (the span is of the size of Madison Square Garden) conventional... led by an architect, sometimes assisted by other engineers This short paper covers too many projects for comprehensive credits They can be found in the the writers book (Horst Berger: Light Structures - Structures of Light), which also covers additional information on the subjects above Tony Robbin's book, Engineering a New Architecture, tries to give an overview of the potential offered by new engineering. .. fabric which is easier to handle; simpler, less labor intensive detailing and construction; and more use of prefabrication • a broader acceptance of these new forms by the general public The Denver airport terminal, one of the very few tensile enclosures of a regular 24-hour public building has had a very positive reaction The Millennia Dome can be expected to have an important impact Further, by measuring... structures and a large hybrid grid dome as examples of surface structures which each form the dominating architectural feature of a permanent building They are major projects out of over 40 designs built over the last 25 years Emphasis is on the integrating impact, which does not only extend to the unity of structure and enclosure, but also to the building's main functions as control of light, heat, and sound... qualities by standards beyond visual excellence, fabric structures will be able to prove themselves as highly desirable, when looked at by the slightly adjust ancient standards of usefulness, stability, economy, environmental desirability and visual delight The buildings shown in this paper are, hopefully, part of a development in this direction It should be mentioned at this point that for each of these... more cost- effective than a pure tensile fabric structure Several things need to happen to make the art and technology of fabric structures a common component of the new built environment: • design tools need to become more user friendly so that architects and engineers will be willing to use them • the cost of construction needs to be reduced This requires a cheaper, more translucent, longer lasting... and Engineering of Tensile Architecture by Horst Berger, Birkhauser, 1996 Engineering a New Architecture by Tony Robbin, Yale University Press 1996 American Building The environment forces that shape it by James Marston Fitch and William Bobenhausen Oxford University Press, 1999 ... the natural light level remains approximately the same as in the air roof Over sixty percent of the roof surface is insulated Air pressure is no longer required The resulting energy and operating savings are sufficient to finance the difference in cost of the new roof as compared with simply replacing the fabric in the existing air supported system Above all, the risk of failure under snow load is eliminated