Large road bridges in northern NSW: 19th century evolution from timber to iron and back again

Abstract

This paper describes the evolution of large road bridges in NSW, citing examples of various timber and iron genres in northern NSW. In particular it highlights the high proportion of iron bridges constructed in northern NSW over approximately a 25-year period from around 1870. Various postulates are canvassed as to why that might have been so. Financial astringency forced the engineering profession to account for deteriorating economic conditions and political imperatives. Typical of such major changes was a dramatic swing from substantive and expensive iron road bridges to more slender, astutely-designed and economical timber truss bridges. These colonially-designed "lean and mean" timber truss bridges were a far cry from the earlier, stockier, high maintenance versions that were inherited from British/European designs. In some respects such innovative local design was a symbolic way of releasing the restraining shackles of the colonial past and the spawning of a new nation. For over 40 years these new-style timber bridges, of successively improved forms, dominated timber truss bridge construction in NSW, to the extent that NSW was euphemistically known as the "timber bridge state". It was not until innovations and improvements were made in steel production, steel-fixing and concrete technology in the early 1930s that the newer materials started to replace timber.