The Hidden Power of Residual Stress in Structural Steel

Watch what happens when this hot-rolled H-section is cut longitudinally into two T-sections. At the very end, the steel suddenly springs apart!

No external load. No hydraulic force. So where does that energy come from?

Residual Stress and Stored Elastic Strain Energy.

Structural steel can develop residual stresses during hot rolling, welding, cold forming, flame cutting and straightening, primarily due to non-uniform thermal contraction or plastic deformation.

Even without external loading, these self-equilibrating internal stresses can store considerable elastic strain energy:

u = σ² / 2E

When the steel is cut, its internal stress equilibrium is disturbed. Some of that stored energy can be released as kinetic energy, causing sudden movement.

In this video, residual stress release is a likely contributor, alongside thermal stresses introduced by flame cutting.

This is not merely a fabrication issue. Residual stresses influence member buckling, structural stability, distortion and fatigue behaviour — important considerations in steel design, including AS 4100.

No external load does not mean no internal stress. And no visible deformation does not mean no stored energy.

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