|
Spreading its wings – a network for tensile structures
Tensile structures are becoming more common, with soaring panels of lightweight material twisted into fantastic geometric forms above our heads in airports, sports arenas and commercial buildings. However, most of us pass right under them without giving a thought to the complex design and engineering principles that go into their construction. EU funding for the TENSINET project has helped tensile-structure engineers and other enthusiasts to band together to share knowledge and promote the technology across Europe.
 Though architecture as a concrete reality dates back to the earliest beginnings of human culture, the study of architecture is relatively young. The principles of construction elaborated by the Greeks and Romans 2 500 years ago for building with stone, concrete and brick are largely unchanged today. The modern era's addition to the discipline dates back only to the late 19th century with the rise of skyscrapers and their novel design of glass walls hung from steel skins, a technique that demanded a new understanding of architectonic stress and strain. More recently, computer technology has enabled architecture to break out of its rectilinear modernist box into weird and wonderful shapes that use unorthodox materials.
Few better examples of this new architectural freedom are found than tensile structures whose functioning depends on a multi-directional redistribution of load via sophisticated cabling or structural fabric. Such tension-membrane structures have been around for longer than you think – strictly speaking, an ordinary tent is a tensile structure – but it is only in the last 50 years that they have begun to make a visible impact on the world of architecture and on our daily lives and living environments.
The use of structural membranes has attracted much attention in recent years and there are some spectacular examples of tensile structures to be found in public buildings such as sports stadia. While this market is still in its infancy, and the volumes of technical coated woven fabrics used so far are relatively small, overall textile use in the construction industry is growing steadily. Tensile structures contribute to solving modern issues in urban planning. Due to their flexibility, use of minimum means and capability of easy removal they have enormous potential and are waiting to find more applications.
Tensile constructions come in every shape and size, from stadium-scale structures to umbrella-sized ones. London's Millennium Dome is one example. So are those festive but protective fabric roofs you stand under at garden parties or outdoor wedding receptions. But stretching an open-air canopy across a garden is one thing; designing parabolic tensile panels to arc acoustically across a concert hall or to span a main railway station concourse is quite another.
Where does the engineer or architect find the critical know-how to design and build such structures? Moreover, how are the installations of these structures certified as sound and safe for public use?
TensiNet – building stressed-out know-how
The potential shapes and uses of tensile structures are virtually endless but their application as a branch of architecture is still young. Indeed, the principles of tensile structure engineering and the materials used are relatively unknown, though this is changing fast.
TensiNet is a network for all parties interested in this form of construction and is devoted to spreading the word about tensile structures. It is the first network in the world devoted to tensile structures. TensiNet grew out of a three-year EU-funded project of the same name, which ended in March 2004. As a thematic network funded by the Fifth Framework Research Programme, the original project comprised 22 participating organisations from nine EU member states. Participants were a multi-disciplinary cross-section drawn from industries involved in tensile construction such as coaters and weavers, manufacturers, engineering companies and architectural firms, as well as universities and other research organisations.
The project's primary goal was to make participants' knowledge in their particular area of tensile expertise available to all, and thus promote the exchange and share of know-how between different sub-disciplines. That these exchanges have now been formalised in the guise of the TensiNet Association and website is a testament to the project's success. There is also a regular newsletter and an annual workshop to disseminate the progress and results of ongoing research in the field.
Pulling a network together
Only a limited number of high-tech engineering offices have developed appropriate know-how to design and construct membrane buildings. Just a few specialists understand the full potential of this construction technique. Most engineers (structural, acoustics, building physics, lighting . . . ) do not know how to model and simulate the behaviour of the doubly curved translucent flexible forms of tensile structures. Through Tensinet they are now getting this information and making contacts with the multidisciplinary partners needed in the field.
Through its website and databases TensiNet makes updated state-of-the-art knowledge on structural membranes available to external interested parties and promotes the wider use of lightweight materials in the building industry. Especially in this field, where materials and tools are continuously evolving, a ‘life-long-learning' support is of great importance.
Coordinated by Marijke Mollaert, a civil engineer at the Brussels VUB (Vrije Universiteit Brussel), the TensiNet Association now has 120 members, mainly from Europe, who range from architecture and engineering firms to manufacturers and students.
“People do not network enough in this discipline,” says Mollaert. “We need to promote many more contacts and interaction between engineers, architects and manufacturers. Among the group's first tasks, she recalls, was to convince people that design rules and standards need to be established and “to spread the word that tensile structures offer enormous design flexibility, and are efficient and economical to build. Tensile structures' mixture of glass and membranes can regulate heat and light in fantastic ways. These are big advantages over traditional building techniques.”
But the group faced a number of challenges in promoting that message, starting with its own enthusiasts. As TensiNet's website itself notes: ‘There is insufficient transfer of multi-disciplinary know-how between architects, engineers, the construction industry and research institutes.'
Moreover, it adds, common reference data is still scarce – meaning that uniform guidelines are still developing for the design and construction of these structures in Europe – while new research is needed to investigate tensile structures' materials and behaviour under varying wind and other climatic conditions.
On the horizon . . .
To tackle these problems, TensiNet has already issued a first reference book for the sector, “European Design Guide for Tensile Surface Structures”, and is collecting new technical information for a second guide in a few years. “We need better descriptions of materials and their performance criteria, new research into load variables and a better understanding of the effects of wind, heat and precipitation on the structural integrity of tensile constructions,” says Mollaert.
Ultimately, the group would like to see common Europe-wide certification standards for tensile structures, and may set up a new expert working group to tackle the subject.
“Currently, we have attained the level of ‘rules of good practice' for the discipline. But to get from there to bona fide building-and-certification codes such as the steel-and-concrete construction industry enjoys . . . well, there is still a distance we have to travel,” Mollaert observes. “But in the meantime we are building up confidence in the sector.” | 
