John Fleetwood Baker

Plastic Theory

John Baker demonstrated the difference between elastic and plastic behaviour of steel beams by simple experiments.

By working to the point of plastic collapse, designers were asked to think differently about structures.

Baker - elastic behaviour
Baker - plastic behaviour

Video: Baker demonstrating elastic behaviour

Video: Baker demonstrating plastic behaviour

Very simplistically, instead of working out what the loads on a structure are likely to be and then making that structure twice as strong (elastic design) designers worked out what load would make them collapse, and then make them able to withstand twice that load.

Elastic theory does not accurately model the stresses in real buildings because the equations are very sensitive to small anomalies in a real structure. Thus a small settling of the foundations or a slight error in the manufacture of the length of a steel girder can give very different stresses to those calculated. That is why Baker considered elastic solutions not to be a proper design tool for structural frames.