Structural Rationalism. In the advent of industrialization which is marked by the affordability and mass production of construction of materials like iron steel and glass, an architectural school of thought emerged known as structural rationalism which emphasized the important and distinctive role of structural efficiency in the form of buildings including space requirements and architectural design.

This philosophy was promoted by French architect Eugène Viollet-le-Duc whose theories were specifically written in his book, Discourses on Architecture (Frampton).   Viollet-le-Duc adhered to the restoration to the localized style of building vis a vis the ‘abstract’ international style conspicuous during his time.

Belgian architect Victor Horta is one of the pioneering advocates of this architectural philosophy which he exemplified in the design of the Tassel Hotel in Brussels in 1892.
The design featured exposed decorative iron balustrades shaped as a plant filament combined with local axial plans that resulted to a simple yet striking decorative work of art. Interior architecture involved rooms with irregular shapes blended with decorative painting and furniture.
The masterpiece of Horta marked the commencement of the Art Nouveau movement which was perpetuated and advanced by Hector Guimard, a French architect and furniture designer.  (Pile) While maintaining highly decorative curved line that usually follows a floral pattern, Guimard highlighted indigenousness of design that conformed to function and climate and even patriotism.
Guimard’s most famous designs are the entrances of the metro subway stations in Paris that featured metal cast in curvilinear flowerlike lines meticulously designed in detail.
By the early 20th century, Dutch architect Hendrik Petrus Berlage adhered to a return to the conservative objectives of true constructive rationalism that stressed simplicity of form and clarity of structure.
He underscored the notion that the structure itself functions in the creation of space which reduce the need for decorative structures.  This idea was embodied in the design of the Amsterdam Stock Exchange of 1903 and initiated the emergence for modernism.
Frampton, Kenneth. Modern Architecture: A Critical History. Oxford University Press, 1980
Pile, John F. A history of interior design. Laurence King Publishing, 2005

Structural Rationalism