The structural engineering of the Downland gridshell

The Downland Gridshell, at the Weald and Downland Museum in Sussex, England, forms the roof of the new Archive Store and Workshop building.

The prime benefit of the timber gridshell is the simplicity of the construction sequence: aregular grid of slender timber laths is laid out flat; at each intersection point the members are connected by a special connector; finally the grid is shaped so that it takes up a doublycurved form. It is able to do this because of the flexibility of the laths and the rotational freedom at the gridshell intersections. After erection of the lattice, bracing is introduced which triangulates the square grid, providing shear strength.

The complete form of the Downland Gridshell structure is a triple hourglass, 12–15 metres wide and 50 metres long, 7m to 10m high. It is the double curvature of the shell that generates the geometric stiffness and is fundamental to its structural action in resisting asymmetric loads. Extensive structural analysis is necessary to find the shape that can be formed from the original flat pattern. Issues addressed in this paper include the formfinding, specification of the timber laths, the development of an appropriate formation technique and methods to monitor and assist the formation process.

The gridshell construction was completed in August 2001. The building was completed in April 2002.

• INTRODUCTION

• THE BUILDING

• STRUCTURAL MODELLING AND ANALYSIS

• TIMBER

• STRUCTURAL DETAILS

• CONSTRUCTION

• CONCLUSIONS

• REFERENCES