The development of transparent space grid roofs made of steel glass modules can be described by the systematic replacement of elements in the compression layer of a traditional space structure by
glass panes. The transition of steel space grid structures into innovative transparent space grid structures assembled of steel-glass-modules is demonstrated at the example of a plain double layer
grid. For the prototype, the geometry of both the upper and lower layer both consists of square grids. The upper layer is diagonally displaced to the lower grid, so that the knots of one layer align with the
panel centroids of the other layer. The connection of the upper and lower grid is achieved by diagonal bars that interlink the knots in both layers.
The prototype is a complete modular construction of a half-octahedron geometry. Each module consists of a glass pane, four quarters of a knot at each end, four tension rods in the joints, four
diagonal bars and one knot in the lower layer. The dimensions of the glass panes are 1.25 m by 1.25m. The panes consist of laminated glass made of two layers of 10 mm heat-strengthened glass. The dimensions of each knot are about 10 cm by 10 cm.
There are different methods to erect space grid structures and more than one method is often used at one single structure. The first tested principle can be described as free-cantilevering method. The
second construction method that was tested was a on the ground preassembled roof structure which was then lifted up to its final position. The roof mock-up with the largest span comprised an eightmodule-
strip with an overall dimension of 10 m x 1.25 m.
In the roof structure described above, the glazing is part of the load bearing system and transfers axial forces. Glass structures designed to transfer axial loads are not defined in the German code regulations. Load bearing test as part of the necessary individual approval by the building authorities are required to build such a roof structure. The reaction forces and deflections recorded during the tests were in accordance with the results obtained from FE-calculations.
Tests for walk on access and post breakage robustness tests primarily define the suitability of the glass element for roof applications. The positive result of these tests encourages the authors to
continue their research in this field. The continuous process of improving the construction has to be supported by extended test series.