The temporary roof canopy for open-air theater (OLT) De Doolhof in Tegelen, Netherlands, ensures a dry stage all summer long. The canopy is a tensioned membrane structure that is assembled and disassembled each year for peak season from April to October. This project was built by Polyned. Summum Engineering provided form finding and structural engineering services. The canopy covers a podium of 12 by 8 meters, creating a so-called anti-clastic, or negatively curved surface. The membrane is tensioned via edge cables from eight corners, supported by circular hollow section H-frames in the front and steel masts and tie rods at the rear. The structure is designed to avoid rigid supports and connections, resulting in a lightweight structural system. The shape of the membrane structure was determined using a process called form finding, which involved finding the shape of the membrane that distributes the loads evenly, has minimal stress concentrations, and maximizes structural efficiency. Geometrically nonlinear calculations were necessary for accurate engineering of the structure. A parametric workflow coupling form-finding and structural analysis allowed for efficient exploration of different design options and optimization of the structure. The membrane structure was designed to account for seasonal load conditions and material properties to avoid unnecessary material use.

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