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Wednesday23 July 2014

Super structures

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Which building best marries architecture and engineering? In their own words and sketches, six architects make their case

Bill Taylor on Sagrada Familia, Barcelona

I never “got” Antoni Gaudi until I visited his buildings. But beneath the neo-gothic rhetoric and overloaded decorative style lies a structural experiment of awesome modernist rigour — the significance of which lies as much in the method as in the making.

The Sagrada Familia was the father of all form finding exercises. The design was executed as “tension in reverse” — a concept we are familiar with today, but which, to my knowledge, was without precedent 120 years ago.

Initially, a net of suspended strings was weighted with sand bags and gravity did the rest. The strings, under tension, revealed the natural path of gravity. The shape was captured, by dripping wax over the net and when inverted, a pure compression structure was created.

Having found the natural form, it seems that Gaudi was almost compelled to make it tree-like. The waxed strings become spiralling trunks, branches and twigs, which are masoned from stone, shaped and profiled in a way that almost “feels” the loads as the structure is pulled up to heaven.

But chains and strings in a studio do not model horizontal loads, particularly wind, which is a dominant load case for tall buildings, or settlement, thermal expansion, shrinkage or the myriad conditions we now can understand analytically. Yet still it stood, fine and slender — and not a “risk register” in sight.

Bill Taylor is a director at Hopkins Architects.

Penny Richards on World Expo 2000, Hannover

This structure by architect Thomas Herzog and structural engineer Julius Natterer was designed to provide cover to a series of freestanding stalls at the Expo 2000 in Hanniover.

The canopy comprises 10 modular elements, each one measuring 40m x 40m, at a height of 20m above ground level. The elements are timber double-curved lattice shells, each supported on a central structure.

The roof shells cantilever out on all sides looking like giant whale tails. The shells are covered by a pre-stressed translucent membrane and the rainwater is collected and brought to the ground through each of the central structural supports. These supports are each cut from a single tree trunk, from the classic Silver Fir, of the Black Forest. Seventy trees 50m tall were selected. The bark was stripped with high-pressure water jets and the trunks were cut in half lengthwise, to form each of the four corner columns.

This elegant but robust canopy is a demonstration of a tree reborn from the forest to the structure. The columns represent the simple vertical structure of the tree, and the filigree lattice shells represent the tree canopy. The timber lattice allows daylight to penetrate below, just as it does in the forest.

Penny Richards is a director at Pringle Richards Sharratt.

Graham Haworth on Arango House, Acapulco

In his 1973 Arango House, architect John Lautner refined innovations in siting, material and structure that he had been experimenting with in earlier projects.

The structure of the house is the architecture — it flows in sculptural in-situ concrete curves to form the three main surfaces of the vast 2,300sq m dwelling. The three surfaces — a retaining structure to negotiate the steeply sloping site, a living floor open to the elements with a continuous perimeter moat, and a soaring curved sloping roof supported on three monumental raking concrete pillars — all uniquely adjust to the site-specific requirements.

The shell roof structure slopes at 16 degrees spanning between the main piers and forms a continuous soffit on the underside. When viewed from above, the rib beams and inverted vaults are expressed. The roof is 15m wide and its lower section contains a mass concrete counterweight and heavy earth-filled planter to balance the 9m cantilever. The massiveness of the cave-like structure is however breathtakingly light, framing the pan-oramic views of Acapulco Bay.

The structure is held off the cliff face so that light penetrates the back of the site bouncing indirect light off reflective surfaces into the habitable spaces.

Graham Haworth is a director of Haworth Tompkins Architects.

Roger Hawkins on Fallingwater, Bear Run, Pennsylvania

Frank Lloyd Wright’s Fallingwater is perhaps the most famous modern house in the world. The reinforced concrete cantilevered balconies are breathtaking in their daring, played against solid stone walls and the waterfall below. The myth remains that the contractor did not believe in the structure and refused to remove temporary supports. Frank Lloyd Wright himself had to take a sledgehammer to the scaffolding.

Fallingwater has little of the “boxiness” of other contemporary modern movement buildings. In his 1943 autobiography Wright identifies that “an entire building might grow up out of conditions as a plant grows up out of soil…”

To me, this building offers a complete statement of the organic simplicity, continuity and plasticity that Wright sought in his architecture. The floor slabs are stiffened and extended to form cantilevers like branches of a tree with the fireplace providing necessary central support. Wright describes this as a waiter’s tray resting upon his upturned fingers. Following Fallingwater, the cantilever became a new feature of design in architecture.

Roger Hawkins is a director of Hawkins Brown Architects.

David Marks on The Palm House, Kew Gardens

The result of a collaboration between architect Decimus Burton and ironfounder Richard Turner, the Palm House (1844-48) is one of the most radical structures of its time.

It was once the largest glasshouse structure ever built, but it is so delicate it continues to delight, and to my mind is a perfect combination of the creative and innovative skills of engineer and architect.

Its use of wrought iron allows it to be light, airy and slender in a way that wouldn’t have been possible using only cast iron. And its aerodynamic shape reduces wind load, thereby reducing structural member sizes.

The 20m-high structure has no cross bracing and its arched elements have no ties. It has few columns and great widths of unsupported space. Undesirable deformations of the structure are controlled by a 1.2m-wide whaling beam (doubling up as a visitor walkway) which is cantilevered off the tops of the cast iron columns and restrained by curvilinear wrought-iron ribs originally used in shipbuilding. The hollow columns support the tops of the lower ribs, the upper ribs and the cantilevered walkway and beam and double up as down pipes to collect rainwater for irrigation.

Finally, unique post-tensioned hollow purlins (using a Turner-patented internally wedged rod system) brace the wrought iron ribs and provide intermediary support for the minimal glazing bars and also contribute to structural stability.

The Palm House heralded in the age of glass and steel, one hundred years before Mies, with a great flourish.

David Marks is a director of Marks Barfield Architects.

John Jenner on Snowdon Aviary, Regents Park Zoo

Cedric Price’s 1962 aviary project was influenced by Buckminster Fuller’s work on tensegrity. In collaboration with structural engineer Frank Newby, he calculated that certain cables would have to be pre-tensioned to carry compression forces effectively in the structural design.

The most striking structural feature is the two 16m-high, V-shaped, 610mm-diameter welded aluminium columns at each end of the aviary.

They are like giant outward leaning arms raised aloft, gripping at cables in an incredible effort to maintain a structural equilibrium in partnership with the four corner polyhedral frames anchored into the ground.

The structural elements and the welded aluminium mesh enclosure were high technology for the time and answered Price’s design requirements providing the maximum free-flight volume combined with perching positions for the birds at each end.

The aviary was a perfect project for Newby and Price to push design and engineering to its limits. The project is a tribute to their special working relationship that I was able to observe when I worked for Price. It has resulted in a structure of great beauty and delight.

John Jenner is a director of Greenhill Jenner Architects.

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