American Society of Civil Engineers

Evaluation of Wrought Iron for Continued Service in Historic Bridges

by Robert Gordon, (Prof., Dept. of Geophysics and Appl. Mech., Yale Univ., P.O. Box 208109, New Haven, CT 06520) and Robert Knopf, (Res. Affiliate, Dept. of Geology and Geophysics, Yale Univ., P.O. Box 208109, New Haven, CT 06520)

Journal of Materials in Civil Engineering, Vol. 17, No. 4, July/August 2005, pp. 393-399, (doi:

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Document type: Journal Paper
Abstract: Doubts about the strength of wrought iron used in historic structures can be resolved with appropriate methods of evaluation. Since wrought iron is a composite material of metal and slag fibers, its performance in structures cannot be adequately evaluated by the techniques routinely used for testing structural steel. Both historic and modern test data show that wrought irons from different sources vary little in strength but greatly in ductility. Since adequate sampling for mechanical ductility tests is often difficult, alternatives based on metallurgical analysis can assist evaluation of the metal in historic structures. Test data show that more than 0.3% phosphorus in solid solution embrittles wrought iron. This level of phosphorus can be detected by optical microscope techniques. Excessive or poorly distributed slag fiber is the other principal source of inadequate ductility, and can be evaluated by metallographic examination either in place or on samples much smaller than those required for mechanical testing.

ASCE Subject Headings:
Bridge inspection
Iron (material)
Service life