Assessment Procedures for Structural Wrought Iron

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Abstract

The main objective of this research project was to develop a new methodology for the assessment of wrought iron structures using a more informed knowledge of the material.A database of tensile test data for wrought iron across the range of all types of structural elements was compiled and analysed to establish the characteristic yield strength for comparison with the value of 220N/mm2 quoted by the UK Highway Standard BD21. It was found that the characteristic yield strength of bar iron is 151N/mm2 and that of plate iron is 187N/mm2.Bending tests of wrought iron beams were conducted to investigate the potential for brittle fracture under static loads, which was observed, and further investigated by conducting Charpy impact tests, where it was found the that ductile to brittle transition temperature of the metal lies in the range 20 to 80oC, whereas that of mild steel, is typically in the range -30 to 10 oC.A new assessment method was proposed that incorporates a 'quality factor' and a 'component significance factor' into the definition of design yield strength. Comparative studies using the proposed method and the existing method were conducted on a trussed highway bridge, a long span iron roof to a railway station and the Clifton Suspension Bridge. The newly obtained lower values of characteristic yield strength tend to dominate the final design strength value of a component, but this may be improved by the expansion of the database. Furthermore, the inclusion of the quality and significance factors offset this effect and their inclusion was validated by proving that a safe yet not overly conservative design yield strength may be established by application of the proposed method.

Keyword(s)

Assessment; Structural Wrought Iron

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