Author: J. Miller (Ramboll)
1 December 2015
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J. Miller (Ramboll)
The greatest threats to the structural integrity of timber are from attack by rot and insect; therefore, in the damp British Isles, those working in conservation will often need to reach for the sketchpad to record and re-detail areas damaged by the effects of moisture.
Interventions to historic timberwork are also necessary when a building is converted. This happens, for example, when floor joists are reframed or loading is assessed for a new use. While philosophically this is different to a simple repair, it nevertheless requires similar skillsets to achieve the best, most sensitive results.
This article looks briefly at these matters, first from the aspect of conservation philosophy and material choice to establish some ground rules, and then by showing some of the details typically in use in the UK today. In order to focus on these, it does not consider survey and diagnosis.
The Timber Engineering Notebook series concludes by examining the use of glued-in rods for timber connections. The increased use of manufactured timber, such as glued laminated timber (glulam) and laminated veneer lumber (LVL), with improved mechanical properties and the ability to produce cross-sections of almost unlimited size,has driven the timber engineering industry to come up with improved connection systems. Glued-in rods and plates have been used in the UK as a method of connecting timber since the 1970s. They offer the possibility of creating concealed connections that are capable of transferring large forces and moments with minimal slip due to their high stiffness.
Historic buildings and structures, like any other, move to some degree, whether due to thermal effects, changes in moisture levels in the structural fabric, influences on the founding subsoil, or environmental forces. The key question for the conservation engineer is to determine whether the movement is progressive and presents a risk to the structure. This article introduces engineers to the various techniques available to monitor movement in historic structures, from simple manual techniques which are less commonly used today, to sophisticated electronic systems. The form of monitoring will depend on the nature of the assumed movement, the funds available, and the possible consequences if the movement is progressive.
This article looks at some aspects of floor loading and how its application has changed for the better. It encourages a careful consideration of loadings to avoid unnecessary and irreversible loss of fabric through the application of significant strengthening schemes, cutting away existing historic framing.