The multi-purpose hall built for the Federal Garden Show in Mannheim in 1975 is regarded as the world's largest wooden lattice shell construction. One of the most important facts about the Multihalle is the generation process of the pavilion, based on a Gridshell.
Otto developed a Gridshell form finding process that involved hundreds of scale models of Gridshells. He developed a catalog with several forms and shapes that the Gridshells can generate when hanged. Just like Gaudi, Otto worked on scale models to see the behavior of the grid he was working on. The studies he did were about form and shape but also involved architectural basic needs, as space and light.
The Gridshell is a structure which derives its strength from a double curvature surface. The most important thing about this kind of membrane is the perimeter, which has to be rigid enough to support the deadweight of the structure and most importantly, all the loads sitting above it. Otto worked on models with a rigid perimeter from which to hang the Gridshells he fabricated. After that he hung small loads on the Gridshell that would represent actual and real weights of the materials used to build the structure and the membrane.
When the form finding process was over, and Otto just had in mind what he wanted to build, the construction process begun. Not forgetting that in that time computers where not as accessible as they are now, so all the calculations where done by hand.
The Gridshell was assembled on the ground and very carefully it was put in to place. Due its dimensions, this process was quite long and a lot of scaffolding was needed. The other important fact about its size was the stiffness of the entire structure, Otto's team designed it composed by hundreds of small triangular cells to give the whole structure the required strength. There were parts that then needed extra structural reinforcement.
The resulting building that Otto designed turn out to be an amazing construction, from the inner space to the smallest details of structure. Finally the building served as exhibition space and hosted the restaurant of the RuralCity exhibition.
Reconstruction or Demolition
Today, over 40 years later, the future of multi-hall is uncertain. Originally planned as a temporary structure, it was never demolished due to its architectural importance and was put under monument protection in 1998. Although already several times rehabilitated, the construction is in a regrettable condition. A total of 12 million euro is estimated for a general renovation. In spite of its status as a "cultural monument of particular importance", the city council of Mannheim decided in June 2016 by a large majority the demolition of the multi-hall, if it should not be possible to collect a significant amount by end of 2017.