Issue 17

Success in achieving durability of timber structures lies in fulfilling a suitable design brief. The early discussion of appropriate detailing and specifications, accounting for the materials, fabrication facilities and quality of construction workmanship, enables clients to balance the cost of alternatives against the later inconvenience of excessive maintenance or premature replacements. The construction process and the establishment of the building’s in-service performance environment are both part of what can be termed the ‘building chain’. This chain represents a process, through which durability can be addressed. At each stage of the process, different demands and values are sought from construction products by each party. A greater common ground needs to be created. There is potential for a more systematic approach, which would better equip timber designers to tackle durability issues. However, appropriate IT-based tools are needed in order to facilitate this. A variety of numeric, and non-numeric techniques are becoming available, which could assist in addressing all of the hard-to-soft topic aspects concerned, in achieving overall improvements. R. J. Bainbridge, BEng, MSc, CMIWSc Principal Engineer, TRADA Technology C. J. Mettem, MSc, CEng, MIMechE, FIWSc Chief Research Engineer, TRADA Technology M. W. Milner, BSc, MSc, CEng, MIStructE, MICE Managing Director, Chiltern Clarke Bond

The first double layer timber gridshell in the UK has recently been constructed as part of a new building for the Weald and Downland Open Air Museum in West Sussex. Despite their many advantages, double layer timber gridshells are uncommon; the Downland Gridshell is only the fifth of its kind ever to be built. The reluctance to adopt this type of structure may stem from the difficulties associated with its construction, which entails the formation of the doubly-curved final shape from an initial flat mat of laths. The challenges presented by the formation process had to be overcome during the Downland Gridshell project. Issues that had to be addressed included the development of an appropriate formation technique and methods to monitor and assist the formation process. This paper describes the challenges presented in erecting the double layer gridshell and the solutions and techniques that led to the successful completion of the project. O. J. Kelly, BE, MEngSc R. J. L. Harris, BSc, CEng, MIStructE, MICE M. G. T. Dickson, FREng, BA, MS, CEng, FIStructE, FICE J. A. Rowe, MA, MIStructE, MICE All the contributors work at Buro Happold

This paper by R. Hankin was presented at a meeting of the Institution of Structural Engineers on 19 October 2000 with John Hill (President) in the chair and published in The Structural Engineer Vol 78 No. 19, 3 October 2000.