NZASM Steel bridge superstructures
The Dutch came to the NZASM: Nederlandsche Zuid-Afrikaansche Spoorweg-Maatschappij endeavor in the ZAR [Zuid-Afrikaansche Republiek] with their experiences of railway construction both at home and in Indonesia. By this time empirical knowledge and understanding had been systematized into a kit-of-parts. Contracts could be awarded in both sections of lines as well as their various categories of construction – earthworks, stone-masonry, ballast and rail-line placement and engineered steel works.
All steel was imported from either the Netherlands, Germany or Great Britain in prefabricated sections to the design supplied by the NZASM engineers, inspected there then landed in one of the harbours – either Lorenço Marques (Maputo), Durban or East London and brought in by ox-wagon, later on the railway wagons along newly completed lines.
All drawing were supplied in metric measure and supplied to metric tollerances. All bridge spans were designed in increments of five metres. Any variations in span widths were resolved in combinations of these span distances. While much of the NZASM steelwork no longer remains, all structures and tracks being re-laid for heavier rolling-stock and freight, much of the replaced steel followed the same design as the original NZASM, although with heavier steel sections.
The shortest spans of five meters were flat plate girder steel.
The next span of ten metres was also of plate girder.
Spans of twenty metres were of plate fish-belly girders.
Twenty-five meter spans were bridged by-bow-string trusses.
Thirty meter spans were of truss-girders, either upright or inverted.
There was a longer thirty-five meter span, also of a girder truss design, for bridging a section of the Vaal River at Standerton.
Much of the steelwork was deliberately damaged by Dutch explosive engineers serving the Boer forces as they retreated in the Anglo-Boer War, the IMPERIAL MILITARY RAILWAYS (IMR) effecting repairs or replacement as these positions and infrastructure were captured, occupied and put to their own use.
After the War the railway infrastructure was eventually unified into a single and centrally managed railway system, and, in time, all steel was replaced, so that little by way of original NZASM steel is still in place.