Keywords: computation of a doubly curved grid shell, paper laminates, novel material for numerous recyclings, material properties, experimental studies, structural devices for a civil engineering structure made of cardboard and paper.

So far little is known about light-weight civil engineering structures made of paper laminates. Starting in the late eighties of the 20th century the famous Japanese architect Shigeru Ban used this new material first for temporary and then for permanent structures. One of his decisive ideas was to rapidly provide houses or shelters for the people in earthquake-struck regions at low cost. Furthermore offered this quite unusual composite material many new ideas to create novel architecture not known until then. Another major aspect was the effort to recycle buildings to a yet unknown extent. His so far most outstanding structure was the Japanese exhibition pavilion at the EXPO 2000 in Hannover, Germany. The dimensions of this doubly curved roof made of paper laminates were: length 72 m, width 30 to 35 m and maximum height above ground 15.40 m. The load carrying grid 33m chosen for the final structure incorporated a grid of the paper tubes 11m.

Since the supporting paper tubes of 68 m length had to be strong enough to bring the load of the roof to the foundations; however, on the other hand had to be extremely flexible to gain the desired doubly curved roof shape, model testing took place in Japanese laboratories. At this stage two versions were under consideration of the architect: A lattice shell made of two layers of paper tubes crossing one another fixed by loop connections between the paper tubes or a latice shell which had to be stiffened by wooden arches. Because of the necessary flexibility of the paper tubes small diameters had to be chosen which on the other hand resulted into large vertical deflections of 1m and more which could not be tolerated since the cover of the grid had to be a paper laminate.

Finally the composite structure of paper tubes and wooden arches spanned above them was further examined. The foundation had to be recycled, too, thus steel frames with wooden shoring and sand filling met these requirements. Two strengthened arches at the gable ends, wooden templets and a space-enclosing paper-synthetic laminate sheeting with partially PVC sheeting had to be further examined.

The paper tubes had a length of 68 m, a diameter of 120 mm and a wall thickness of 22 mm. These tubes 120/22 consisted of 30 layers of paper rolled unidirectionally with an interia layer of sandwich paper incorporating a polyethylene (PE) film. The thirty layers of Durolene paper glued together with a PVA sticker were secured at the outer surface with another layer of sandwich paper with an acryll-FEIG 2768/5 coating.

One of the decisive tests was to determine the dominating influence of the moisture in the paper tubes in order to find out which largest diameter could be chosen to make sure that the tubes under construction would be able to bend (without force) into the mathematically determined final roof shape without cracking. Further tests were carried out mainly by Dr. K. Block, Institut für Banforschung, Universität Dortmund, to find the characteristic features of this novel materials.

The computation for the roof that was finally built was based on a lattice shell of paper tubes with Trevira loops, on top with wooden arches and steel stringers spanned beneath them with wooden templets (m) and with 2 steel braces at each of the 2 end arches of wood. With these assumptions a calculation was carried out to get a safe structure for the duration of the EXPO 2000. The deflection of the roof was about 2-4 cm when the supporting steel structure that had ensured the doubly curved surface during the lifting process had been removed. Nevertheless it remains unknown to which extent the paper tubes took part in the load carrying of the roof.

Based on all these novel data the structural designer Happold Ingenieurbüro GmbH Berlin, the proof engineer being the author, the company carrying out the building work Takenaka Europe, Düsseldorf, and many unnamed individuals were able to complete a unique space structure of the outstanding architect Shigeru Ban, Tokio.

The choice of new composite materials and their development for sustainability and recycabiltiy is quite a challenge. The paper laminates as well as the paper tubes had a be recycable on the one hand and fire- and waterproof on the other hand, not talking about the necessary material strength to sustain all given loads. Our knowledge about this building material is still only a little bit above the stone age level.

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