Material substitution and the expansion of operative capacities: the Iron Bridge and the Hennebique system

This article examines material substitution as a technical phenomenon in which a new material is employed according to the constructive grammar conventionally associated with another. The study focuses on two episodes situated in the early implementation of new structural materials: the Iron Bridge (1779), where cast iron engages with masonry and timber logics, and the Hennebique reinforced concrete system (1892), whose timber-derived structural organization later became the object of critical reformulation by Robert Maillart and Pier Luigi Nervi. The analysis combines historiographical interpretation, examination of mechanical behaviour, and comparative finite-element models in order to study how constructive transfer operates at different levels of structural organization. In the Iron Bridge, the transfer remains concentrated in joints and assembly techniques derived from timber construction. In the Hennebique case, finite-element models clarify the transition from hierarchical beam grids toward more continuous and bidirectional force transmission in the work of Maillart and Nervi. The study argues that inherited constructive grammars may generate processes of technical reconsideration capable of expanding the operative capacities of structural materials within architectural technique.