Tucked away in the mountains near Schiers, Switzerland, the Salginatobel Bridge is widely considered a masterpiece of 20th-century structural art. Designed by Swiss engineer Robert Maillart, the bridge spans 90 meters across a sheer, 90-meter-deep gorge. At the time of its design, traditional concrete bridges were heavy, solid structures that copied stone masonry traditions, consuming massive quantities of cement and requiring immense falsework supports.
Maillart broke away from tradition by treating reinforced concrete as a unique, plastic material that could perform best when structural elements were integrated into a unified shape. The core breakthrough of the Salginatobel Bridge is its three-hinged hollow box arch. Instead of a solid concrete arch ring, Maillart designed a thin-walled hollow concrete box girder whose cross-sectional depth varies dynamically along the span.
The arch is thickest at the quarters where bending moments are highest, tapering down to elegant points at the dynamic crown and abutment hinges. By making the arch hollow, Maillart drastically reduced dead weight while maintaining extraordinary torsional rigidity against mountain crosswinds. Furthermore, Maillart merged the arch, vertical support walls, and upper roadway deck into a single monolithic box structure.
Load from vehicles traveling across the deck is immediately transferred into the arch walls and down to the granite bedrock. The three steel pin hinges located at the crown and base footings allow the rigid concrete structure to flex slightly, safely relieving stresses caused by seasonal temperature fluctuations and concrete shrinkage. Maillart’s efficient use of materials meant his design won the original construction competition simply by being the cheapest option, proving that structural elegance and economic efficiency can be identical.