A computational and experimental study of Irish orientated strand board in bending active gridshells

Timber gridshells are structures that involve sophisticated analysis, design and construction processes. Like shells generally, they can achieve large span to thickness ratios. However, in addition to the analysis, design and construction processes their material requirements (low material and section stiffness, high strength and few defects) often result in high selection and processing costs associated with solid timber. Engineered timber may be a viable alternative that avoids these costs. This study examines the suitability of an Irish engineered timber product, orientated strand board (OSB) for use in bending active gridshells.

A precedent study identified the desirable material properties for bending active gridshells. The bending, torsion and compression strength and stiffness of an Irish OSB product was measured. A modified test approach was adopted to obtain the relevant material properties. Significant variations in both material properties and product thickness were observed and measured. The test results indicated that Irish OSB has good potential as a structural material for the proposed application.

In order to verify the provisional conclusion of the material testing program a number of bending active OSB gridshells were designed, constructed and tested. The moment-rotation and load-deformation behaviour of two joint types used in the physical models were measured and the associated equivalent elastic constants determined. A computational model, MattGrid, was developed to predict the non-linear load-deformation behaviour and strength of the proposed designs. This model uses Dynamic Relaxation and is capable of modelling behaviour during both the form finding and subsequent in-service stages of the structure’s design life. It includes provision for a piecewise-linear material model, elastic boundary supports, bending active bracing and double layer construction. MattGrid was validated using numerical and analytical benchmarks and its predictions compared against experimental measurements.

A series of single and double layer gridshells were designed and constructed using Irish OSB. The measured deformations under a series of load cases showed good agreement with the deformations predicted by MattGrid using the mean material properties.