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We also applied our scheme in the form-finding of the 3D-Hybgrid (Fig. 9). The plane grid is composed of 18 composite beams. Each composite beam has a structure that is similar to the 2D Hybgrid in the last example. In plain view, two crossing beams have a 60-degree included angle. Two types of constraint are applied: the surface constraint and the curve constraint.

For the surface constraint, the upper chord nodes that will be subsequently connected with struts after form-finding are constrained by the upper surface. Similarly, the lower chord nodes that will be subsequently connected with struts are constrained by the lower surface. The two surfaces are equivalent with an interval of 0.375m between the surfaces. The surface is defined as a surface of revolution that is generated by an arch of radius of 2.9m with a revolution of radius of 22.9 m.

For the curve constraint, we constrain four nodes, which are located on the top layer around the central crossing point, by two curves that are produced by projecting two straight crossing lines, which have a 60-degree included angle, on the upper constraint surface. This constraint helps grids to maintain the included angles in general.