Author: J. Miller (CTP Consulting Engineers)
1 May 2016
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J. Miller (CTP Consulting Engineers)
The term “filler joist” is a generic one used for certain types of building floors dating in particular from the late Victorian era to World War II. These may commonly have embedded iron or steel joists. Those of earlier date, from the 19th century, can have wrought iron sections, or even cast iron tees in early floors. They span one way between beams or bearings, and are encased in concrete made with coke-breeze, clinker, broken brick or conventional aggregates.
The filler-joist floor was – at the time – a very important structural development, now long superseded by other systems, such as flat slabs and composite decks. It grew out of an enthusiastic age of Victorian invention that had created a wide range of proprietary, patented make-ups that all worked in a roughly similar way. Filler joists are encountered frequently in the alteration and remodelling of large office and institutional buildings.
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.
This article focuses on the phenomenon of 'bond timbers', which were commonly built into masonry walls from the late 17th to the early 19th century. Guidance is offered to engineers who may encounter these when working on an existing building.
Replacement of stone on historic buildings may be required for numerous reasons. These include age-related decay and weathering, poor workmanship in terms of material choice or setting, defective fixings, and structural failure. The main aim, in assessment, will be to retain the historic fabric where practical. However, the decision to replace will depend to a great extent on having a clear understanding of the significance of the stone, both individually and within the context of the element that it is part of, its predicted life or durability and its cost.