Real Lab – Experimental construction: Pavilion as roof batten construction

Elective subject experimental construction: pavilion as roof batten construction | Bachelor and Master programme in Architecture| summer semester 2022

Starting with a large pile of roof battens, softwood C24 with dimensions 24x48 mm, the only building material to be used, we asked ourselves:

What can be done with these roof battens? What supporting structures can be realized with them? How can this material be intelligently converted into a building structure? What spans and loads are possible? How can or must these elements be joined to form a load-bearing structure?

In a workshop at the end of the last summer semester, we, Prof. Benno Bauer and Prof. Stefan Zimmermann, together with a group of 28 students from the Faculty of Architecture and Design, dealt with the diverse constructive possibilities of rod-shaped load-bearing structures. In order to achieve the realization of a small pavilion within one week, we sharpened the boundary conditions as follows: All bars from said roof battens should be no longer than 1 meter and nearly identical. A barrel-shaped lattice shell with a radius of 3 meters was to be created and only one joining principle or connecting means was to be used in each case. The bicycle parking spaces in front of Building 8 were intended as the location.

Various ideas were initially pursued in small groups, resulting in three different structures.

First, a barrel shell was created as a lever support structure. The principle is known from Leonardo da Vinci's famous sketch. It is based on the superposition and canting of bar elements by exploiting their bending stiffness. The single-layer design did not achieve the required dimensions due to the low bending stiffness of the roof batten, but careful fabrication resulted in a precise barrel shell.

Square meshes with face bolted connections of four intersecting bars each characterized the second structure. The lengthy fiddling with the complex geometry of the intersection in the end only allowed the realization of a small sculpture. The design principle and the load-bearing effect, however, were very well understood.

The third load-bearing structure took into account from the outset that a barrel shell with a circular cross-section is only dimensionally stable due to the netting of the beam elements, and that it must have a certain bending stiffness for eccentrically applied loads. Following the Zollinger or lamellar design, only identical components should be used, which are joined with bolts as fasteners. However, since - in contrast to Zollinger - no upright boards were available, the structure had to be designed in two layers.

The difficulty with all structures lay in the fact that the circular arc was to be created in a poligon-like manner from the straight roof battens, i.e. the curvature had to be generated at the joining point. This required the three-dimensional imagination of all those involved, especially in the case of the two-layer lattice structure. There was a real competition between individual small groups to find the right solution, and a large number of knot models were built. It was interesting to note that even the attempt to solve this knot in 3D with the help of the computer could not be mastered without the spatial imagination of the draftsman.

In scorching heat, the three described structures could then be erected at the bicycle parking spaces in front of Building 8 by the end of the week. An experiment, the "methodically designed investigation for the empirical acquisition of information" (quote Wikipedia) explicitly includes the error. In this way, we were able to see from all the models what was not necessarily wrong, but what could have been done better. And these insights are the most valuable in the end.

The success of this workshop consisted primarily in the doing, in the experimental process, characterized by sketches, experiments, model building, discussions, then in the "serial production", the sawing, drilling and assembling of the battens and in the end with the completion of the pavilions. The sense of achievement of a manual process in a team, in contrast to the mostly theoretical doing of the architecture studies.

Special thanks go to our workshop foreman Phillip Spoun, who helped us with the sawing and drilling.

The student research project was supervised by Prof. Benno Bauer and Prof. Stefan Zimmermann.

Text: Prof. Stefan Zimmermann