☰ Workshops

Structures in Building Culture

Steel Skeleton (2013)

During the first days of the Steel Workshop in Spain the students made 1:10 scale models using iron wire. Almost every shape can be made as a scale model, because iron wire is flexible and can ‘hang’ in the air easily. However, that changes when ideas are scaled up to their full size, because self-weight then comes into play. A length of steel enlarged in diameter ten times is increased in weight a thousand times, so scaling up is when designing with a material really starts. The weight of the material lets you feel gravity at work. Steel bars can withstand tension, especially longitudinally. Scaling up therefore seems easier when tensile force is exerted on steel. Compressive forces cause the bar to bend or deform. In all objects constructed at full scale, the weight of the steel initially turned out to be an important ‘spoilsport’. Two of the objects, the Iglo and the Tent, defeated gravity by making use of two opposing structural principles.

The students imagined the Iglo as a domed structure made up of numerous circles that together create the form. Initially the students wanted to stiffen this structure by making use of the friction between the circles, but no matter what the students did the weight of the steel hoops caused the structure to sag all the time. In addition, the hoops seldom remained in position. So the group reluctantly concluded that the circles had to be connected to one another firmly at the points where they overlapped, and the ‘triangles’ created by these fixed connections stiffened the structure.

The members of these triangles are short, which means that they don’t bend. Even though force is exerted on the object, the dome retains its shape. No longer do the circles determine the strength of the structure, for they are now subordinate to the ‘sturdy’ triangles.

The Tent was suspended between the ground and a wallhead. Securing the structure firmly to both the ground and the wall is essential, for this is where the tensile forces are transferred. This connection was solved with adhesive tape in the scale model, but at full scale, as the students discovered, serious forces come into play. The net structure is strong and can span a great distance, provided the forces are transferred towards the connection points and the structure is secured firmly at the edges. Taking these structural lines seriously excludes lots of forms and determines the building blocks of the net. After a number of tests, one module was chosen.

The weight of the steel causes the net to sag, and it is impossible to pull the whole structure back into shape. Several points of connection distribute the tensile forces over a number of locations and as a result, the structure could be stretched to its maximum within these constraints.

Contending with the weight of the steel made all workshop participants aware of the interplay of forces. When you try to pull the steel tautly or try to counter its tendency to sag, you physically become part of the structure. The forces in the steel are then taken up or absorbed by the makers.

The two forms are based on opposing structural principles. All the steel members of the Igloo are under compression, but all the structural members of Tent are subject to tension. Experimentation gradually reveals the structural principle of both objects, and the eventual form is determined during the construction process with the material.

In the last century the architects Frei Otto and Buckminster Fuller conducted extensive research into steel structures, both of them with a tremendous passion for experimentation. They tested and explored models, mock-ups and full scale constructs. Frei Otto worked chiefly with tensile roof structures, motivated by a desire to create the greatest possible span. He studied the performance of the material and its structural behaviour through experimentation, and he used scale models made of fabric, steel and rope to gain an understanding of the possible shapes of tensile structures.

Buckminster Fuller, in contrast, was obsessed for much of his life by Geodesic domes, which are structures composed of numerous identically shaped elements. All structural members of the Geodesic dome are under compression. Buckminster Fuller spoke fondly of the many experiments he carried out during his quest to discover the smartest structural member and the most efficient method of assembly. He frequently experimented with help from students during workshops all over the world.

Making models teaches you about the distribution of forces and helps you to understand form in relation to structure. But ‘construction’ really only starts when you build at full scale, since working with a material at full scale confronts you with its self-weight and with gravity. That is the moment when you determine the sequence of assembly, discover the performance characteristics of the connections, and shape the appearance of details. The struggle with gravity can lead directly to success. Built structures collapse, sag or break, but experimentation ultimately leads to discoveries. As Buckminster Fuller’s stated: “You succeed only when you stop failing.”

Machiel Spaan
Academy of Architecture, Amsterdam