Cast and wrought iron (heritage structures)

Assessment of iron structures does not follow a single current material code, because the Eurocodes cover steel, not historic cast and wrought iron. Instead we work from established guidance for historic ironwork, period design practice and, where the value or risk of the building justifies it, testing of samples to establish tensile and compressive strengths. We survey the members and connections, look for the defects these materials are prone to, casting flaws, blowholes and cracks in cast iron, corrosion and lamination in wrought iron, and assess the real loads against a realistic capacity rather than a textbook one.

The behaviour drives the checks. For cast iron beams the brittle tension side governs, and we apply the caution that a sudden failure mode demands, checking whether the historic member still has the capacity for its current use or whether load has increased since it was installed. Connections in these structures, cotters, gibs, riveted joints and simple bearings, are assessed on their own terms, and we look at how the whole assembly behaves rather than any one member in isolation, since these frames often rely on details modern analysis would not assume.

Where an iron structure needs help, the aim is to keep as much original fabric as possible and to intervene reversibly and sympathetically, which matters both for listed building consent and for good conservation. Options range from relieving the load by introducing a discreet new support, to strengthening a member with added steel or plating, to careful repair of cast iron cracks by specialist methods. On a listed or historic building the repair strategy is developed with the conservation officer and, where relevant, the heritage adviser, so the structural fix respects the building's significance.

Corrosion is the slow threat, particularly where iron is built into damp masonry, because rusting iron expands and can crack the surrounding stone or brick, a problem often seen with embedded cramps and beam ends. We identify these hidden points, plan the removal of trapped moisture and, where needed, the replacement of failed embedded iron with a compatible material. The output is an assessment and a repair strategy that keep the historic structure in safe use, whether the building is being conserved, altered or brought back into service, across the UK.