Stephen Gilbert

The Use of FRP Composites in Enhancing the Structural Behavior of Timber Beams

This paper describes aspects within an experimental and theoretical programme aimed generally at improving the structural performance of laminated beams fabricated from Irish-grown Sitka spruce. Such timber is characterised by low density and small dimensions, is likely to distort when dried and tends to fail in tension due to the presence of knots. The well-established technique of laminating timber overcomes some of these disadvantages and the improvements are most marked with low quality donor material. It has been found that the addition of modest ratios of FRP composite reinforcement can suppress tension failure in beams. The study of failure modes, particularly in tension-reinforced beams, is the main focus of this paper. It establishes that the ultimate load capacity depends on the behavior of the timber in compression, resulting in much more consistent behavior as well as a considerable increase in flexural stiffness.

Development of a technique to measure the residual strength of woodworm infested timber

Abstract This paper presents a study of the residual strength of Pinus sylvestris , which has been subject to attack by the furniture beetle ( Anobium punctatum ). It is relatively easy to stop the infestation, but difficult to assess the structural soundness of the remaining timber. Removal and replacement of affected structural elements is usually difficult and expensive, particularly in buildings of historic interest. Current on-site assessment procedures are limited. The main object of the study was to develop an on-site test of timber quality: a test which can be carried out on the surface and also at varying depths into the timber. It is based on a probe pull-out technique using a portable load-measuring device. Pull-out force values have been correlated with both strength and energy absorbed as measured by compression testing on laboratory samples of both sound and infested timber. These two relationships are significant and could be used to assess whether remedial work is needed. In addition, work on the use of artificial borings to simulate the natural worming of timber is presented and the findings discussed.

The strength and performance of cold formed steel purlins

Abstract An experimental and computer based investigation was carried out on a range of locally manufactured cold formed steel purlin sections to assess their behaviour at both serviceability and ultimate load levels. The test programme and test facility are described and a selection of typical results presented and discussed.

The 'Belfast' roof truss - worth conserving?

Abstract Timber trusses have been used in many forms since ancient times. The ‘Belfast’ timber truss was developed around the mid-nineteenth century to meet the demand for efficient, lightweight, and longer span roofs, brought about by the Industrial Revolution. It is a very efficient structural form with a curved top member that behaves essentially as an arch in combination with a horizontal tie member. Several thousand still exist, many in buildings of historic interest. This paper outlines the development of this truss type, explains why it is an efficient structure, and demonstrates that trusses can be replicated in historic buildings almost exactly as the original. This is supported by comparisons of the actual and theoretical load-carrying behaviour, based on the results obtained from new trusses, tested in laboratory conditions, and on trusses tested in existing buildings. In addition, the findings in a report of load tests on prototype trusses in 1906 have been included in the comparative study. All the work on the analysis, design, fabrication, and testing of ‘Belfast’ trusses has resulted in a better understanding of their behaviour, which is not only of historic interest, but also fundamental to the repair and restoration of existing trusses. As well as their significance in historic building conservation, the paper proposes that ‘Belfast’ trusses are an attractive alternative to other structural roof types.