Considerations for the design of bending active timber gridshells

Bending active gridshells are generated by deforming a flat timber grid towards a curved shell-like target shape. As a result of this deformation bending pre-stresses are developed during the forming of the structure. This is a condition virtually unique to this structural form. Additionally the forming process generates combined bending, torsion and axial stresses in curved members. Design rules for this complex condition are not yet included in current design standards. Various researchers have proposed limit state criteria for individual combined stress pairs. These are discussed in the light of EN 1995-1-1:2005 and a possible integrated approach is suggested. Some outstanding testing needs are identified. The impact of the construction process on the design and modelling process is also discussed.