Vebjørn Sand is a contemporary Norwegian artist, who divides his time between the United States and Norway. In 1996, in viewing a special exhibition of drawings and replicas of Leonardo’s inventions, Mr. Sand became transfixed by the shear beauty and modernity of a bridge the Renaissance master had sketched in a notebook — a bridge he proposed building in Istanbul 500 years earlier. On his return to Oslo, he approached the Norwegian Public Roads Administration offering a partnership in building a variation of Leonardo’s bridge in Norway. Rare among public utility works anywhere, the Norwegian Public Roads Administration is known to operate with a policy of promoting art in public spaces. Nonetheless, finding receptive officials willing to resurrect a half-millennium old design planned for Turkey and implement it in Scandinavia had to be a pleasant surprise for Mr. Sand. Soon an ideal partnership would develop between the resourceful artist and the enlightened Public Roads Administration.
Leonardo’s original design for a single-arch bridge made of stone and long enough to span the 240 m (800-ft) width of the Golden Horn in Istanbul, called for a “pressed bow structure.” This is the mathematical shape described as an “inverted parabola” or “a parabola that spills water.” The parabolic structure supports the weight of the roadway draped over it by pressing down and outward against the bridge’s abutments that are anchored in terra firma. More generally, the silhouette of the bridge in Leonardo’s drawing suggests that a pair of parabolas with different steepness is superposed. The area between the wider parabola, located above, and the steeper parabola (below) creates an elegantly tapered parabola, resembling the upper reaches of the Gateway Arch in St. Louis (built between 1963-65). The roadway in Leonardo’s drawing is draped over the supporting parabolic structure.
THE BRIDGE IN ÅS
Mr. Sand and the Norwegian Public Roads Administration agreed that Leonardo’s design could be adapted for a pedestrian/bicycle bridge over Highway E-18, connecting Oslo and Bergen and about 20 km southwest of Oslo. Leonardo’s original specs for the Golden Horn would be scaled down to roughly 1/3 for the Ås site. The roadway would measure 360 feet in length.
Between 1996 and 2001, the Leonardo Bridge Project team performed systematic design and structural load tests in close collaboration with architects and engineers. Both a Leondardesque stone bridge and a laminated-wood version were developed and tested. In the end, the bridge in Ås would be created as a steel-reinforced structure, comprised of laminated wood. It was fortuitous that the technology to build massive structures out of laminated Norwegian Spruce had already been developed in forest-rich Norway. For the 1994 Winter Olympics in Lillehammer, laminated wood had been employed in the construction of a cavernous arena. In the creation of the Leonardo Bridge precisely shaped components could be prefabricated, then assembled with the use of cranes. A set of three parabolic supports were created for the bridge, a central component supporting the roadway, and two others stabilizing the central parabola. The roadway would rest on metal pillars of varying lengths (visible in the photos below).
BRIDGES BUILT OF ICE
After spearheading the building of the Leonardo Bridge in Ås, Mr. Sand and the Leonardo Bridge Team launched a program to build bridges on each of the earth’s continents. Several Leonardo Bridges already have been created of ice.
During the first decade of the 21st century, the Leonardo Bridge Project Team built a series of four ice bridges. At any level, they are works of art, far more aesthetic than utilitarian, and far more fleeting than permanent, but they all resonate with strong symbolism. They represent bridging space and time, ethnic and cultural differences, or in Sand’s words, “…touch something eternal.” The four ice bridges seen in the array above were intended to promote the “LIVE ICE” Project, calling attention to the fragility of the Earth’s ice cover. • Ice Bridge in Copenhagen created for the Climate Conference in late 2009. The spire in the background belongs to the Copenhagen Contemporary Art Center (formerly the Church of St. Nikolaj) • Ice Bridge at the UN Plaza, New York, 2007 • Ice Bridge in Greenland in early 2009 • Ice Bridge in Antarctica 2005. An amalgam of water and crushed ice hacked at the site is poured into prefabricated metal forms and allowed to freeze. When the forms are removed, left behind is an ice bridge with the graceful design inspired by Leonardo’s original drawing.
Ultimately, Leonardo’s bridge exhibits the “pressed bow design,” or an “inverted parabola” (in the language of calculus, a “parabola that spills water”). Its shape is described by a simple quadratic equation, including a leading negative sign to insure that the parabola “spills water,” and a coefficient employed as a “Dilation Factor”, that determines the steepness.
“Let no man who is not a mathematician read the elements of my work.” — Leonardo
Leonardo did not know very much formal mathematics, but he had abiding respect and love for mathematics. He would have had no understanding of the analytic geometry and calculus, areas of mathematics that would be formulated during the 17th century by Descartes, Newton and Leibnitz, and used in describing curves, and calculating optimal shapes. Yet he demonstrated an intuitive feel for mathematical shapes and patterns. The hyperbolic spiral appears in the curls of his subjects’ hair, and in the eddies in flowing water. He knew the parabola well, having recognized a century before Galileo that the trajectory of a projectile is a parabola. This is seen in his drawings. He illustrated the book de Divina Proportione (“The Divine Proportion”) for his mathematician friend, Luca Pacioli, demonstrating again that mathematical intuition.
The more one studies Leonardo, the more one realizes that he was in the business, not of predicting the future, but of inventing the future. It would not be until the Industrial Revolution that the materials and the mechanical power would become available for Leonardo’s mental inventions, his dreams, to be fully realized. By the late 19th century the use of steam and electrical power, of new materials and techniques, of steel girders, high tensile strength cables made his idea more practical. But, Leonardo had realized four hundred years earlier that the parabolic arch would be the key to distributing the weight, especially with the widening footholds. One of the most celebrated bridges of the 20th century, built in the 1930s, is the Sydney Harbor Bridge, spanning a waterway of 503 m (1650 ft). A pair of parabolic structures, one above the other, is used in suspending a flat roadway, rather than supporting it from below. A truss-system of cross-arms in a saw-tooth pattern gives it a more slender overall silhouette, and minimizes the steel required.
Daniel Levy had written in a 1999 edition of Time Magazine, “A bridge that Leonardo designed in 1502…is scheduled for construction outside Oslo and there is talk of building similar bridges in Des Moines, Iowa and Istanbul itself.” The bridge in Norway was built, and indeed opened with pomp and circumstance by no other than Queen Sonja in 2001. An array of ice bridges have been built across the world. And Leonardo is one step closer to getting his bridge built in Istanbul. The bridge in Iowa, unhappily, fell through, deemed, “…too modern for our times.”
For informative discussions and for photos of the Leonardo Bridge Project I am deeply grateful to my friends Vebjørn Sand and Melinda Iverson.
Vebjørn is the visionary artist who spearheaded the building of Leonardo’s Bridge in Ås, and subsequently the ice bridges in other parts of the world.
Melinda is the International Projects Producer for the Leonardo Bridge Project, Inc., charged with developing the group’s projects around the world and writing, designing and curating events related to the Leonardo Bridge Project/LIVE ICE and Vebjørn’s other public art projects. See the website, http://www.leonardobridgeproject.org/
Finally, I am grateful to my friend, Murray Lines, who shared the photo of Sydney Harbor for this article.
So far in this series:
Still to come: Part 4. “Hakan Kiran and Variations on a theme by Leonardo”
In October 2012 the Turkish Government announced through the public media plans to build Leonardo’s Bridge over the Golden Horn (Haliç). The Istanbul based Architectural Firm of Hakan Kiran, that has been garnering an impressive international reputation for its bold works in Turkey and Europe, was awarded the commission that Leonardo sought in 1502. Hakan Kiran, his wife Tülin Kiran, along with Chief Architect A. Ulvi Altan, have been working on variations of Leonardo’s Bridge. The timing is auspicious with Mr. Altan currently serving as the President of the Mediterranean Society of Engineers and Architects (SEAMED). The group operates under the auspices of the scientific organization Réseau Méditerranéen des Ecoles d’Ingénieurs (RMEI). Under Mr. Altan’s leadership, SEAMED itself is rapidly growing into a unique institution in its collaborative efforts on the Leonardo da Vinci Bridge Project (LDV Bridge). The group’s motto, “Bridging Cultures and Sharing Heart,” would have pleased Leonardo. The bridge for the Golden Horn is still in design stage, but it is in decidedly good hands!