Steel truss bridges—common across roads and railways and often over a century old—have long posed a puzzle. Some collapse after a single component fails; others stay upright. A study by the Polytechnic University of Valencia and the University of Vigo finally cracked that mystery, tells Tech Xplore.
Researchers built a scaled-down model of a Pratt-type railway truss bridge and deliberately damaged key elements, such as cutting a critical beam, while applying loads similar to a passing train. They instrumented the model with strain gauges and displacement sensors and then fed the data into a validated computational model to run over 200 virtual failure scenarios. Finally, they pushed one damaged test to collapse by increasing the load.
They found that when a main component fails, the bridge almost magically activates six secondary resistance mechanisms, i.e., behaviors not part of its original design, that reroute loads and stabilize the structure. These include:
- In-plane flexural distortion: bending around the damaged area
- Transverse distortion: shifting loads across the bridge’s width
- Global torsion: the whole structure twists to redistribute forces
- In-plane hinged rotation: acting like a hinge around the failure
- Out-of-plane bending: tilting across its section to relieve stress
- Uniaxial bending of nearby members: neighbors flex to bridge the gap.
Even after damage, these bridges still held between 1.8 and 3 times their regular loads before collapse, showing surprising robustness.
This insight matters. It allows engineers to design future bridges that lean into these natural resistances and retrofit older ones to be more resilient. The safety of transport networks and lives could benefit significantly.