1 December 2015
First published: 1 December 2015
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Timber and stone are the oldest known building materials. Our most ancient buildings are characterised by their use. So it is no surprise that an engineer looking after historic fabric will regularly encounter the need to repair timberwork.
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.
Alfriston School is a secondary day and boarding school for girls in Buckinghamshire, UK. The project involved the construction of a new 750m2 swimming pool and sports department. The building has a floating timber roof, which houses a four-lane swimming pool and changing areas.
The structural challenges included realising the complex geometries in the roof while maintaining an open soffit. A system of panels was developed using cross-laminated timber boarding fixed to glued laminated beams. The roof panels act as the structural elements spanning the swimming pool and provide stability.
Small-diameter steel columns were designed to act as cantilevers from the reinforced-concrete retaining walls, transferring the vertical and horizontal loads from the roof structure. This method eliminates any cross-bracing and minimises the visual structure, giving the appearance of a floating roof.
Letters this month focus on CE marking, particularly CE marking of steel and whether it is possible to CE mark a swing bridge.